Rake and trail for dummies

[Billy Golightly]

This is one area admittedly I've always had a little trouble fully grasping.

I know that there are several different components that account for this obviously. Fork length, tire size, steering neck angle, leading or trailing axle, amount of offset distance between the centerline of the forks and the centerline of the steering stem, etc.

I've Googled and read a lot about this over the years, and have made some changes and adjustments by shortening forks, changing tire sizes, making new triple trees that have less rake built into them, etc. But I've never actually set a front end up from scratch. I'm considering a new project with the Rotax motor, and this would be a necessity.

I know Jason Hall, Louis, Swinehart, a few others have already been down this road with their builds. You guys or anyone else, what kind of range of #s am I looking for if I was to do this from scratch essentially?

[jeswinehart]

My method most likely will be of little help to you Billy. I too looked/studied all the information you mentioned and even applied it.
Since my front end was designed to be a bolt on set up I was able to adjust the rake sevral times (and I did haft to) to find what I felt was the best for me. My biggest concern that I way over thought was to get the goose neck centered. It really is much easier then it sounds using 2 know center points on frame and rear axle. I marked those 2 area on garage floor and then I drew a straight line on concrete floor under gooseneck area.
Using a plumb bob hung from center of goose neck I adjusted until it matched up.
Like I mentioned about the rake, it took me several times using spacer v blocks to get what I wanted. Being able to ride it was key for deterring what suited me best.
I now have my trike up to a weld shop to permanently attach front end. After a year and a half of riding, the front end had loosened up so knowing what worked I decided to make it solid.

[Red Rider]

Billy, If you recall, when I made the welded-up tripleclamps for my 250R, I kept the factory rake built into the tripleclamps, and went from trailing-axle to leading-axle, which was a big mistake. I never measured the resulting trail, but it was much less than factory, if not zero, which made for twitchy handling.

When I drew up the designs for the billet tripleclamps, I wasn't concerned with the rake/trail measurements, and therefore never measured it. I just needed a design that would hold the forks in a leading-axle configuration, with the front wheel back in the same location, as it was with the stock tripleclamps & trailing-axle forks. Based on my rake/trail research, as long as the front wheel was in the same location, with respect to the frame, then it would have the same factory handling traits. (This assumes that there were no changes to the steering head angle or height, fork length, or tire diameter.)

I don't know if the manufacturers published rake/trail specs on trikes, but you might do some research and see if you can find that info. Or, if you have access to other good-handling trikes, I would try measuring the rake/trail on them and see if a pattern emerges. If you do see a pattern, there might be a corresponding sweet spot to shoot for with your build.

[barnett468]

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I don't understand your question or what you are trying to achieve . . If you want your bike to steer a certain way, I suggest you try a few different bikes as Red Rider suggested and copy the geometry from the one you like the best . . Most, if not all of the steering geometry numbers for the Honda are available, and I do have them stored on my other computer, but you can just measure the geometry of any bike that you like the steering characteristics of and start with those as a baseline.

Steering geometry is incredibly complicated, and I can assure you from first hand experience that what looks good on paper does not always work exactly as planned in actual use, which is why every manufacturer has an R and D facility . . One of our engineers named Randy Hall took a 1983 KX 250 and made his own 3 wheeler which had a trailing axle, and we actually compared that against the Tecate prototype, and imo, it was noticeably better overall, lol.

Since both the Tecate and the Honda won several Championships, one really can't say that one steers better than the other, they just steer a little differently.

One of the most complicated aspects of steering geometry is offset triple clamps . . In this case, I am referring to triple clamps where the lower clamp is a little forward of the upper one . . Systems that do not use offset clamps like these are many times easier to understand and deal with.

[El Camexican]

From my extremely limited experience I think that determining rake and trail is easy if you have a jig and a bit of a pita if you don’t. A spare set of hands is very helpful.
The problem is what to do with the numbers. Everything listed below changes the rake and trail:

- Putting on tires, or wheels with a different diameter
- Chain adjustment
- Moving the forks up or down in the tree
- Suspension pre-load

Like Barnett said, you’d be best served to start by measuring the chassis of something you like riding. It might get you close, but the location of the swing-arm pivot (height and distance from front axle), length of the swing-arm, location of the engine and the center of gravity, seat and handlebar location can all make huge differences to how it will feel when you get it up to speed and start trying to turn.

When looking for happy medium numbers to build around I believe you also need to consider what the numbers will be when the suspension is compressed.
Fortunately all my rakes have been for the purpose of straight line stability, which is a no brainer; just pull out your front end till you either get to 36 degrees, or until you have only 2” of ground clearance.

If you are planning to build something that needs to be steered with dignity over 20mph you may want to build a set of adjustable trees. Sandy Kosman designed one for his Gucci frames. I can’t find an image of it, but it was very trick, perfect for fine tuning.

[barnett468]

If you are planning to build something that needs to be steered with dignity over 20mph you may want to build a set of adjustable trees. Sandy Kosman designed one for his Gucci frames. I can’t find an image of it, but it was very trick, perfect for fine tuning.

. . . . http://www.mustang.org.au/forum/Smileys/smilies/thumbsup.gif


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[El Camexican]

The one I saw on the Gucci frame had a helm joint looking thing on an adjustable threaded rod. Cool as the ones you posted, this was MEGA cool:lol: I think Kosman is shut down.:( All the website links take me to Harley sites.

[Billy Golightly]

Thanks for the all the feedback and replies gentlemen. What I'm assuming is that I would be building and setting a front end up from scratch essentially. I'm currently exploring this little fantasy I have that I may be able to take a 250R frame and make a front and rear end that could bolt onto it to make a 2 wheeler cafe racer type machine, but then go back to trike parts also if desired. So my challenge is to figure out some front end rake and trail #s that I can work with, without having to reangle the steering neck on the frame itself. 2 wheelers in general have a much much different type of rake and trail from what I've observed, so this might not be really feasible, but that's what I'm working on trying to get a "range" of measurements basically I can work within the confines of. As far as trikes, I love how the 3rd gen 250Rs handle, and even better with a smaller front tire (I'd prefer a slightly twitchier/quicker turner than not for my style on a trike) but I have my doubts that if I just bolted on a new front end with similar dimensions and a street bike front wheel and tire it would behave in a way I'd like on the road.


Sounds like some good old fashioned trial and error will be on the agenda :)

[Jason Hall]

Billy here are some of the things I have learned over the years. First is a 350X is leading axle with 0 rake in the clamps. A 250r is trailing axle with 6° of rake built into the clamps. If you think about 3 wheeler front axle working like Caster in a normal front spindle. It will help you see the difference in the 2 front ends. When you turn the front end the side of the axle that you are turning towards is actually getting closer to the ground. That is what makes the handlebars want to return to the center position like the angle of a spindle of a car or quad. More rake in the front end of a 3 wheeler will change how close the axle gets to the ground when you turn. So, more rake will turn harder, and will want to return to center faster. Now there is leading and trailing axle. If you think about that, it affects the way the front end puts weight on the axle. So I explain that like this. With a leading axle, there is more tire in front of the axle. Imagine picking the front end up by the way the weight is pushing down on the front tire. If you were picking up a leading axle the way it pushes against the ground, you would pick up the front wheel. If you picked up a trailing axle front end by the way it was pushing against the ground you would pick up the forks. This gets confusing, but it all ends up changing the way the handlebars feel in your arms. The trailing axle actually has a harder time turning because the forks are sitting on the axle, so the front end will want to return to center faster because of the way the forks are pushing down on the center line of the axle. With the trailing axle the forks are on more of a angle in order to have the correct amount of trail because of the built in rake in the clamps. With a leading axle the axle center line is in front of the forks, and there is more tire in the front of the forks, so the axle is being pulled up by the weight of the bike. With 0 rake this gives you an easier feel at the bars because of the way the weight is pulling up against the forks. With a leading axle you can have less rake, which means less fork angle, and less caster angle which will make the bars turn easier. Man, I hope I didn't confuse you by talking around in circles lol.. It would be easier to explain this in person with a 350x, and 250r to look at so you can get what I'm saying :)

[Billy Golightly]

Jason,

Could I summarize - that if the rake angles and everything else being the same, I would in a 2 wheeler application prefer something probably with a TRAILING axle design, so as to offer more straight line stability?

[Jason Hall]

Every motorcycle built for the last 20 years is leading axle. Also
from my experience with the Missle 250r that Kasey built and I rode in the dunes I would stay as far away from trailing axle as you can!! Lol.. Leading axle is the way to go IMO for anything! Adjust your rake angle to give yourself hi speed stability. You can always slide your forks up or down in your clamps to change the rake angle. You can also adjust rake by adjusting your rear ride height.

[83ATC185]

Sorry to hijack your thread but i just have a few questions that i hope make a little bit of sense. Say if you took a 200x and flipped the forks around to make it a lead axle bike, what effect would that have on handling? Would you be able to adjust for the difference by moving the tubes down in the tree? Would you even want the same rake with the lead axle? If a 350x has no rake built into the clamps, what differences are there in the angle of the frame neck, compared to the 250R with 6 degrees of rake in the tree? Also how does changing the height in the rear to get more or less rake affect handling compared to just changing the rake on the front? Just trying to wrap my head around all of this information :wondering

[Jason Hall]

I have ran 250r's with the axle flipped leading for drag racing at the dunes. The front end will push and not want to carve and turn. Trail is measured like in the pics I posted below. With rake built into the clamps, the forks are on more of an angle than the steering head. By flipping the axle leading with rake you would make the trail measurement to long. The first pic shows the difference in the steering head angle and the fork rake angle. So imagine what a leading axle with rake would do to your trail measurement. Not only would the trail be to long, but it would lengthen the wheelbase and make a 3 wheeler more tippy.

[Jason Hall]

Raising and lowering the rear suspension will change the angle of the steering head/forks.

[Jason Hall]

One thing I keep forgetting about with a motorcycle is a lot of turning a 2 wheeled motorcycle is done by Leaning the bike, so that would probably change quite a bit of my thinking as I seem to concentrate more on 3 wheelers. Lol..

[barnett468]

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TRAIL

Jason and others have posted a lot of good info and I just wanted to mention that the images Jason posted depict the measurement for "false" trail . . This is a simplified way of measuring trail and is one that some custom bike builders use, however, measuring it this way can lead to slightly different results in other measurements . . Motorcycle and bicycle mfg's etc measure what is referred to as "true trail", and the difference between the two is depicted in the image below.

The long angled solid lines represent the angle of the fork tubes . . The broken lines that run somewhat parallel to those solid lines represent a line drawn thru the center of the steering stem.

Although the tripple trees have a slightly different stagger in both examples, the image still shows a reasonable example of how the elevation of the steering head will change when the steering head angle is changed if the length of the forks and the amount of axle offset remains the same.

The greater the steering head angle is, the more trail it will cause.

The greater the tripple tree stagger is in the positive direction [the lower tree being positioned further forward of the steering stem than the upper one], the less trail it will cause.

Changing the amount of trail the front wheel has also changes the amount of trail the rear wheel has.

http://www.gearheadcollege.org/articles/Figure%203.jpg

[Billy Golightly]

Great info gentlemen...thank you. From my continued research it appears that 3-6 inches of trail is "normal" on 2 wheeler applications, and how you arrive at those numbers (fork length, rake angle, triple tree offset, front tires size, etc) is not particularly important although they all have effects on it.

[Yamada]

What about the old dirtbike where the axle was at the end of the fork tube, they are not trailing or leading?

[oldskool83]

I'd think neither.

[barnett468]

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Below are specs from the owners manuals . . One of your dilemmas is that the steering head angle will be fixed, therefore, you need to pick one that will work decent in both tc and cafe mode . . once this is decided, adjusting the trail becomes much easier and is manly a matter of fork and tripple tree selection to achieve the amount of trail you like . . Since falling off on the street will hurt a bit more than falling off on the dirt, you might consider setting the steering head so it will be more stable at high speed if you plan to corner it hard in street mode or go 80ph plus on it.

I agree with Jason in the regard that I would not use a trailing axle, especially on the street . . Honda has proven that it "works" in the dirt, but to make it handle like the 250R, you need the same geometry which is a 21 degree steering head and 31 degree forks and 48 mm of trail, so therein lies the main problem of trying to use 250R steering geometry for the dirt, and street type steering geometry for the street.

I really suggest you ride an '86 Tecate for a few hours and see how you like it because it's steering geometry is a little closer to a dual purpose one than the Honda's, plus it does not use a trailing axle . . Using a 26 degree rake will slow the Tecate steering down a little but you could speed it back up a little by lowering your forks or raising your back end or by doing a little of both which will help maintain overall ride height and center of gravity, however, the center of gravity would actually change very little even if you only lowered one end anyway.

This being said, I have not seen anything other than a center axle on a street bike for maybe 40 years . . Every one I am aware of all use center axles . . Kawasaki used center axles on their Championship winning 165 mph road race bikes, so I don't see any reason to vary from a well established norm for street mode.

Dual purpose bikes have leading axles but they are not getting ridden hard in turns on the street.

Another of the problems is that you like a "twitchy" bike in the dirt, however that is the last thing you want in a turn or even a straight line at 80 mph, especially on the asphalt.

Below, is one option to look at for street mode . . The rake is the same as the NINJA 250R which turns like a race bike which is NOT exactly what I think is best for your app because it turns pretty quick, however, the trail is slightly more than the NINJA which will slow the steering down a hair...kinda sorta.


WEIGHT BIAS VS WEIGHT ON FRONT WHEEL

Don't forget to consider the weight bias.


TIRE PROFILE

This has a noticeable affect on how a street bike corners . . The more crown it has, the easier t will be to lean over and with the steering specs below, I would try a tire with a uniform crown meaning one that is not higher in the center than the rest of the tire.


VEHICLE SPECS

PROPOSED FOR STREET
Rake ............................ 26 . . 27 would be better imo, but it would hurt the dirt mode.
True trail approx .............. 4.0 in
Axle location ................. center
Tripple tree .................... non staggered


NINJA 250R
rake ............................. 26 deg
trail .............................. 82 mm . 3.23 in
w/b .......................... 1400 mm . 55.12 in
dry weight ................ 335 lbs
wet weight ................ 373 lbs
wet bias .................... ft 181 . rr 192 lbs
bias percentage ........ ft 48.5 . rr 51.5
axle position ............. center
tripple trees .............. non staggered


1984 ATC250R
rake ............................ 69 mm . This is measured from horizontal instead of vertical so using current methods, the rake is actually 31 degrees but it is unknown if this is the forks or the steering head.
rake forks ....................... ?
trail ............................. 45 mm . . 1.8 in
w.b .......................... 1197 mm . 47.1 in
dry weight ......... ..... 302 lbs
dry bias ..................... ft 117 . rr 185 lbs
bias percentage ........ ft 38.7 . rr 61.3
axle position ............. trailing
tripple trees .............. unknown but look staggered which would make sense


1985 ATC250R
rake .............................. 21 deg
rake forks ........................ ?
trail ............................... 37 mm . . 1.45 in
w/b ........................... 1295 mm . 51.00 in
dry weight .................. 291 lbs
dry bias ...................... ft 117 . rr 174 lbs
bias percentage ......... ft 51.3 . rr 48.7
axle position .............. trailing
triple trees ................. unknown but im guessing they are staggered the same as the 86'


1986 ATC250R
rake .............................. 21 deg
rake forks ..................... 30 deg ? . . if this is the fork rake then these tripple trees are staggered 9 mm
trail ............................... 38 mm . 1.5 in
w/b ........................... 1905 mm . 75 in
dry weight .................. 289 lbs
dry bias .................... ft 116 . rr 173
bias percentage ......... ft 50.9 . rr 49.1
axle position ............... leading
tripple trees ................ staggered 9 mm?


1984 and 1985 TECATE
rake ............................. 24 deg
trail .............................. 40 mm . 1.57 in
w/b .......................... 1280 . 50.4 in
dry weight .................. 286.6 lbs
wet weight ................. 312
wet bias ..................... ft130 . rr 181
bias percentage ....... . ft 42 . rr 58
axle position ............... leading
tripple trees ................ non staggered


1986 TECATE
rake ............................. 24 deg
trail .............................. 48 mm . 1.57 in
w/b .......................... 1280 mm . 50.4 in
dry weight ................. 280 lbs
wet weight ................ 299 lbs
wet bias .................... 121 . 178 lbs
bias percentage ........ ft 40.5 . rr 59.5
axle position .............. leading
tripple trees ............... non staggered


1974 CB 250
caster .......................... 63 deg . This is measured from horizontal instead of vertical so using current methods, the rake is actually 37 degrees.
trail ............................. 85 mm . 3.35 in
w/b .......................... 1320 mm 52.00 in
curb weight ............... 353 lbs
wet weight ................ 489 lbs
wet bias ................... ft 212 rr 273 lbs
bias percentage ........ ft 43.4 . rr 56.6
axle position ............. center
tripple trees .............. non staggered


This is a high crown type tire which I would not use.

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQCcwSI73Fj25lPPX3ib1e9hHaNuQgxV obYLADLFQdFkqvGiGFj


This crown is more uniform and doesn't have much of a peak in the center . . I would us one more like this.

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSs930Vz4eVeUWp7iOe475WngYmo802B TZBHpakVp__BLmgc7PS

[barnett468]

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POST CORRECTION because I have no edit button.

For 1986 ATC250R

w/b ........................... 1905 mm . 75 in

should be

w/b ........................... 1305 mm . 51.4 in

[barnett468]

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To test different amounts of trail on the cafe style, you may be able to use a set of old Kawi F5 350 big horn tubes . . The drum brake would work for the test and is designed to be switched from one position to the other . . With this setup, the lower tube can also be rotated 180 degrees to make it a leading axle....and for those that are hoping, unfortunately no, there are no old Tecate pipes laying around on the shelves. :)

.................................... Photo shamelessly plagiarized from Harry Klemm.

.......................... http://www.klemmvintage.com/fp%20brake%20g.jpg

[barnett468]

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Billy, hopefully some of this will be useful.

Rake and trail calculator

https://www.rbracing-rsr.com/rakeandtrail.html


Expanded rake and trail calculator

https://www.rbracing-rsr.com/advchoppercalc.html


If you like to use the long method, here's some free online math calculators including ones for cosines and tangents etc.

http://www.math.com/students/calculators/calculators.html


Here's a very good percentage calculator.

http://www.percentagecalculator.net/


You need to change trail by at least 20% to notice a difference.

You need to change rake by at least 2 degrees to notice a difference.

You can also buy "raked steering head cups" . . These are just bearings with offset races that allow you to change the effective rake of the steering head, so If you want to modify your steering head, you can run a different set of steering stem races for each setup, unfortunately, the most rake they have is 3 degrees, so if you left your geometry stock, this would leave you 2 degrees of the minimum amount of rake I think you should run in street mode.

If you modified your steering head angle to 24 degrees, you could run these bearings reversed to get the stock 250R steering head angle of 21 degrees, then simply remove them and rotate them 180 degrees to get a steering head angle of 27 degrees for street mode which is the angle I preferred in my post above . . If you use these offset cups and you like how the 250R works in the stock configuration, the only thing to test would be different amounts of trail in the street configuration after you reversed the cups from the ATC position.

If you didn't need to run the raked cups but wanted a little more adjustability with the offset, you could run offset steering cups, however, since the most offset you would get from them is around 6mm, it wouldn't be noticeable unless you're someone like Wayne Rainey and therefore they wouldn't be worth the effort.

.................................................. .. http://thumbs3.ebaystatic.com/d/l225/m/mqXnuUmC-BLH8IRq8KfEUYw.jpg

..................................... https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcQypB7SfIV7iAYcus_KWVIe0NzlEnMas Yy59_t6RPFpM8AUdda7LQ

[Billy Golightly]

Holy trailprotrailprotrailprotrailpro - those offset bearing race cups are BRILLIANT! I didn't have any idea such a thing even existed.

[barnett468]

Holy trailprotrailprotrailprotrailpro - those offset bearing race cups are BRILLIANT! I didn't have any idea such a thing even existed.

LOL, yes, they are quite cool aren't they . . I didn't think of them earlier but I have actually been contemplating your idea since you started the thread and now that I thin I have a reasonably good idea of what you want to achieve, I thought...hey, these might be absolutely perfect.

They were actually invented by the harley chopper guys to help with their steering issues on the bikes with heavily raked forks . . this is an alternative to the raked/staggered tripple clamps or can be used in conjunction with them to increase the trail.

[OZQUAD44]

Re the raked steering head cups, could these item be used in a dirt bike to trike conversion as a simple method to reduce trail without having to reposition the goose neck? Or is it a moot point if most of the YZF and CRF conversions have the reduction in trail designed into the triple clamps? Your always going to need manufactured triple clamps.


Sent from my iPad using Tapatalk

[barnett468]

Re the raked steering head cups, could these item be used in a dirt bike to trike conversion as a simple method to reduce trail without having to reposition the goose neck?

In general yes however they obviously change the rake also.



Or is it a moot point if most of the YZF and CRF conversions have the reduction in trail designed into the triple clamps? Your always going to need manufactured triple clamps.

Rake affects trail but rake is also an independent function . . In other words you cant use rake for the sole purpose of changing trail because changing the rake will also affect handling and the length of the bike which will also affect handling.

[barnett468]

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TIRE AND RIM MADNESS

This is might be a bit early to talk very much about tires and wheel types, but since I stated thinking about them I thought you might be interested to see what is out there anyway . . The two tire models I posted "should" still be available in a couple years.


WHEELS

The easiest type of wheel to find is a spoke type and that will require inner tubes, however, many of the bikes came with aluminum or stamped steel rims and all of those use tubeless tires . . Ebay has many different types . . If you look on Googe at old bikes you can see some of the different types.


TIRES

The easiest type of wheel to find is a spoke type and that will require inner tubes, however, many of the bikes came with aluminum or stamped steel rims and all of those use tubeless tires . . Ebay has many different types . . If you look on Googe at old bikes you can see some of the different types.
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The tire and rim sizes on the old bikes were 18" or 19" front and 18" rear, unfortunately, most of the new super street tires are 17" or are too wide for your app, therefore unless you run 17" rims, you are stuck using older technology tires . . These older tires are bias ply and the newer ones are radials . . This being said, unless you are going to be pushing the bike extremely hard, the old style bias ply performance tires will be more than you need, and many people with vintage road race bikes use them and they run over 100 mph in these races . . I posted some of the better ones that are still reasonably priced.

You don't want really wide tires for your app because they make it more difficult to corner, especially on tight twisty mountain roads, although I don't remember seeing any of those the last time I was in Florida, plus your bike won't weigh 500 lbs or more and the narrower tires I posted will stick extremely well.

The first number in the tire size is width in mm . . The second number is aspect ratio [sidewall height] . . 90 is fairly tall by current standards, but is still far better than the old school tires that came stock on these early bikes . . 80 is the lowest you can get in the sizes you need.


NOTE - Spoke rims require a tube . . You can use inner tubes that are designed for tube type bias ply tires in tubeless bias ply tires although some mfg's frown on this idea . .


I would consider any of the tires and sizes below,

AVON AM26 - These are the tires and sizes I would prefer to use.

http://www.bikebandit.com/tires-tubes/motorcycle-tires/avon-am26-roadrider-motorcycle-tire?b=1483110&utm_source=feed&utm_medium=merchantfeed&utm_campaign=pla&gclid=CNOdptDgjskCFRKRfgodruUD5g

Front --- 3.25-19 w 2.15 wide rim V rated --- $86.00 . . Use with 4.00 tire below.
Rear ---- 4.00-18 w 2.50 wide rim V rated - $105.00

Front -- 90/90-18 w 2.15 wide rim V rated --- $78.00
Front -- 90/90-19 w 2.15 wide rim V rated --- $89.00
Rear - 110/90-18 w 2.50 wide rim V rated -- $102.00
Rear - 110/80-18 w 2.50 - 2.75 wide rim V rated -.-$101.00


MICHELIN PILOT ACTIV

http://www.bikebandit.com/tires-tubes/motorcycle-tires/michelin-pilot-activ-motorcycle-tire

Front --- 3.25-19 w 2.15 wide rim H rated -- $86.00
Rear ---. 4.00-18 w 2.50 wide rim H rared - $106.00


.................................................. ...... AVON AM26

...................................http://ecx.images-amazon.com/images/I/51Zmlme4toL._SY300_.jpg


................................................. MICHELIN PILOT ACTIV
........................http://motorcycle.michelinman.com/var/ezflow_site/storage/images/motorcycle-website/pneus/michelin-pilot-activ/143892-3-fre-FR/michelin-pilot-activ_tyre_large.png

[barnett468]

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ADDITIONAL TIRE INFO

Forgot to mention . . You need to find dead center between the swing arm mounts, then mark the back of the engine for reference . . Then measure from that point to the inside of the chain . . Then subtract 6 mm from that number . . Then multiply that number by 2 . . This will be the maximum width the rear tire can be . . Then you need to exact width of the tire mounted on the rim you plan to use so you can see if it will clear the chain or not . . Unfortunately you can not go by the advertised widths of the tires.

If you determine that a 110/80 and 110/90 tire is too big, but one that is a total of 10 mm narrower which will be 5 mm narrower per side will fit, you can use a 100 mm series or 4" wide tire . . Neither will be to small for your app . . The 11o mm tires I posted are the biggest I would use on the rear.


TIRE BALANCING

Not everybody does it but I would . . Static balancing is better than nothing but dynamic balancing on a machine that does not use the clamps on the outside of the tire to spin is better.
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[barnett468]

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WHEELBASE

I figured I would mention this in case you hadn't thought about . . If it's too short, it will turn too quick and possibly be a little unstable at high speeds with the proposed steering geometry . . If its too long, it will turn like a pig . . In your case, I would make a swing arm that would have at least 1 1/2" of adjustment and 2" if possible and so the wheelbase can be adjusted from 54" to 55 1/2" or 54" to 56".

Although you would need to calculate how long the swing arm needs to be to achieve this length, without having more dimensions and doing a bunch of math, I would guess that with the street front end on with around 4 - 4.5 inches of trail and a steering head angle of 27 degrees, the front axle location would be within around an inch of its current location . . If this is the case, you would need a swing arm that is only a few inches longer than the stock 250R one.


SUSPENSION

There is not much point in putting a lot of money into different valving etc until you see how it handles in street mode when ridden casually, but I would at least run it a little on the firm side for initial testing which is how Cafe and road race bikes are set up anyway . . This can easily be done on the front end by using a heavy oil like 20 wt and preloading the fork springs by maybe 1 1/2" with a piece of pcv pipe.


FORK TUBE DIAMETER

33 minimum, 42 maximum . . 33 mm is the same size as a 1980's Honda CB450 and the earlier Honda 350 and 400 twins . . I think it is also the same size as the stock Hatta forks on the F5 350 big horn that Harry Klemm won every AHRMA road race with including the Championship and his bike went over 100 mph.

The 2,000 lb 1500 cc Honda Gold Wing and the 166 mph 1988 1000 cc Kawasaki Ninja ZX 10 had 41's . . The 86 250R tubes are a fairly stout 39 mm and the Tecate's are a stupifying 41.


FORK BRACE

I would definitely use one and any tube smaller than 35 mm . . The first photo is the typical old school on you can find for maybe $20.00 that only fits certain forks . . The one below that is one that I think Harry Klemm's brother made . . They had to machine a perfectly round spot on the fork legs so it would clamp properly.

.......................................http://automotoclassicsale.com/sites/default/files/ebay_251867783217_1.jpg

.......................................http://www.klemmvintage.com/fork%20brace%20f9r.jpg
.

[barnett468]

.
Billy, hope you have a happy Thanksgiving and here's a couple of the movies I mentioned to you.

1985 AMA 500 cc road race with Kenny Roberts, Randy Mamola and Mike Baldwin doing wheelies all the way down the front straight at over 100 mph after about the 4th lap.

https://www.youtube.com/watch?v=J7_WAeCe8oE


This is the Isle Of Man road race which is the fastest road race in the world thru city streets and country highways and reaching speeds of 200 mph . . A box stock Kawasaki H2R recently broke the track top speed record there during an exhibition lap at 206 mph.

https://www.youtube.com/watch?v=iRWp9rhfS_0

[El Camexican]

By no means am I claiming to know anything about this topic, but a few things have come up while trying to do the math on my KTM conversion that I thought were worth sharing on this old thread.

In no particular order...

- The "race" trikes from the 80's that used leading axle forks are the Tigers, Tecates, 350X and the Cagivas. The 250R & Tri Z used trailing axles

- According to RB Racing that provide a sweet trail calculator on their website https://www.rbracing-rsr.com/rakeandtrail.html a leading axle needs to be considered in determining your rake. In other words, if you have a 0 degree rake in your forks and a steering head that is 25 degrees when parked, then the distance of the center of the axle from the centerline of the fork tubes should be considered as additional rake. In the case of my KTM frame it adds about 1.5 degrees to the rake.

- A leading axle makes your front wheel look smaller to a trail calculation as it moves the contact patch away from the centerline of the steering head. In the case of a 22" tire with a 36" long fork it reduces the value by .558" (if I understand them correctly)

So, the stock trail for my KTM bike is 4.40" If I shorten the leading axle forks 1", use a 22" tire, 2.5" offset triple clamps with zero rake built into them and don't modify the stock 25 degree steering head I will end up with 2.29" of trail. Considering that all the stock trikes Barns listed earlier in this thread were under 1.8" (Tiger 250 specs say 1.7" of trail) I guess that's not bad for something meant for sand and it can always be altered with rear end height and fork length.

I should also post this up https://www.customtripletrees.com/MAIN%20PAGES/tech.html

"A growing number of motorcycles, domestic and imported, are being converted into a 3 wheel chassis or are installing a side car to the frame. These motorcycles are similar in style and looks, but create a whole new challenge in steering. Adding the third wheel changes the standard trail measurements. Trail reduction is needed to offset handling irregularities created by using a third wheel. A growing number of trike and side car riders are calling on us to solve their handling problems. In most stock frame applications, a 4 to 7 degree raked tree set solves the majority of handling complaints, including steering wobble and slow speed wheel flop. With the wide variety of rake angles offered in our triple trees, a set can be built to solve any of your steering problems."

Disclaimer: I know NOTHING about this topic, but I thought I should share my confusion on this topic with others :)


.
1984 ATC250R
rake ............................ 69 mm . This is measured from horizontal instead of vertical so using current methods, the rake is actually 31 degrees but it is unknown if this is the forks or the steering head.
rake forks ....................... ?
trail ............................. 45 mm . . 1.8 in
w.b .......................... 1197 mm . 47.1 in
dry weight ......... ..... 302 lbs
dry bias ..................... ft 117 . rr 185 lbs
bias percentage ........ ft 38.7 . rr 61.3
axle position ............. trailing
tripple trees .............. unknown but look staggered which would make sense


1985 ATC250R
rake .............................. 21 deg
rake forks ........................ ?
trail ............................... 37 mm . . 1.45 in
w/b ........................... 1295 mm . 51.00 in
dry weight .................. 291 lbs
dry bias ...................... ft 117 . rr 174 lbs
bias percentage ......... ft 51.3 . rr 48.7
axle position .............. trailing
triple trees ................. unknown but im guessing they are staggered the same as the 86'


1986 ATC250R
rake .............................. 21 deg
rake forks ..................... 30 deg ? . . if this is the fork rake then these tripple trees are staggered 9 mm
trail ............................... 38 mm . 1.5 in
w/b ........................... 1905 mm . 75 in
dry weight .................. 289 lbs
dry bias .................... ft 116 . rr 173
bias percentage ......... ft 50.9 . rr 49.1
axle position ............... leading This might not be correct. Oh wait, the edit button thing.
tripple trees ................ staggered 9 mm?


1984 and 1985 TECATE
rake ............................. 24 deg
trail .............................. 40 mm . 1.57 in
w/b .......................... 1280 . 50.4 in
dry weight .................. 286.6 lbs
wet weight ................. 312
wet bias ..................... ft130 . rr 181
bias percentage ....... . ft 42 . rr 58
axle position ............... leading
tripple trees ................ non staggered


1986 TECATE
rake ............................. 24 deg
trail .............................. 48 mm . 1.57 in
w/b .......................... 1280 mm . 50.4 in
dry weight ................. 280 lbs
wet weight ................ 299 lbs
wet bias .................... 121 . 178 lbs
bias percentage ........ ft 40.5 . rr 59.5
axle position .............. leading
tripple trees ............... non staggered

[BOB MARLIN]

I'm still not getting how a leading axle would change the rake. Rake is a frame measurement so how does the leading axle change the rake in the frame ?. Are they saying that leading axle changes the trail so they have to change the rake to bring it back in to spec ?. I'm not trying to contradict, just trying to understand more about steering geometry. Adding "Rake" to the triples is a way of adjusting trial but the rake on the frame remains unchanged, other than the position of the front tire would move forward or backward changing the height of the of the frame neck, which would in effect ,change the rake of the neck as it relates to the ground. Do you think that's what they are getting at ?.

[El Camexican]

I'm still not getting how a leading axle would change the rake. Rake is a frame measurement so how does the leading axle change the rake in the frame ?. Are they saying that leading axle changes the trail so they have to change the rake to bring it back in to spec ?. I'm not trying to contradict, just trying to understand more about steering geometry. Adding "Rake" to the triples is a way of adjusting trial but the rake on the frame remains unchanged, other than the position of the front tire would move forward or backward changing the height of the of the frame neck, which would in effect ,change the rake of the neck as it relates to the ground. Do you think that's what they are getting at ?.

I agree with you that the rake on the frame is just that, but I think what they are trying to say is that it doesn’t matter what the frame rake is unless the trees have a zero rake and the axle is positioned at the bottom of the forks. In that scenario the frame rake is suitable for use in calculating theoretical trail.

However, my understanding of how a leading axle adds to the rake is that true rake for the purpose of calculation is the angle of the center of the top of the triple tree stem hole to the center of the axle. So while one may have a 25 degree angle on their steering head, the true rake for the purpose of calculating theoretical trail depends on whether or not they have a rake built into their clamps, as well as where the axle is located.

At the end of it all the final word is the physical measurement of the distance between a straight line through the center of the steering head to the ground and a vertical line from the center of the axle.

I’m going to speculate that when a factory like Honda, or Yamaha uses triple trees with an angle build into them its because they wanted to change the handling characteristics of the vehicle after the tooling for the frames was completed, rather than any sort of advantage that would come from having a few degrees built into the clamps.

[BOB MARLIN]

I agree with you that the rake on the frame is just that, but I think what they are trying to say is that it doesn’t matter what the frame rake is unless the trees have a zero rake and the axle is positioned at the bottom of the forks. In that scenario the frame rake is suitable for use in calculating theoretical trail.

However, my understanding of how a leading axle adds to the rake is that true rake for the purpose of calculation is the angle of the center of the top of the triple tree stem hole to the center of the axle. So while one may have a 25 degree angle on their steering head, the true rake for the purpose of calculating theoretical trail depends on whether or not they have a rake built into their clamps, as well as where the axle is located.

At the end of it all the final word is the physical measurement of the distance between a straight line through the center of the steering head to the ground and a vertical line from the center of the axle.

I’m going to speculate that when a factory like Honda, or Yamaha uses triple trees with an angle build into them its because they wanted to change the handling characteristics of the vehicle after the tooling for the frames was completed, rather than any sort of advantage that would come from having a few degrees built into the clamps.


Got it.
So they have you adding in a factor for leading (or I assume trailing also) because their formula is based on the axle being on centerline of the fork leg, because that would be the only constant for the calculation. After the bike was all together you can measure the actual rake (at the frame) and the actual trail at the centerline of the axle. At that point it doesn't matter if it is leading or trailing- it is what it is. So they are adding a variable for the leading axle only because their formula is based on a centered axle, not because it actually changes the physical rake. Does that sound logical or am I confusing everyone including myself ?.

I believe when Honda added the so called "Rake" to the 250r triples it was to shorten the trail to correct some steering issue after the frames were already set.

[ironchop]

Nevermind... Was just repeating what someone else said already

This is a good article. It's how I figured out that I was measuring trail wrong back in the day.... Check the diagrams

https://www.streetchopperweb.com/rake-and-trail#page-3

Sent from my Z958 using Tapatalk

[ironchop]

In my opinion, raked trees are to correct excessive muscle movement needed in order to turn the handlebars with the rake and trail being set at optimal locations

If you think about it, since our forks aren't straight up and down, the wheel and tire technically kind of flops from side to side when you turn the forks and it's especially notable when you have alot of rake. Long bike chopper guys have to keep ahold of those handlebars or the front end "flops" over to the side when you turn the bars as a natural tendency with that kind of geometry.

I'm pretty sure that the force required to turn the handlebars left and right are also figured into the rake and trail and that's why I think you have raked trees is to try to affect the amount of force or leverage needed to turn the bars left or right at a specific and optimal rake/trail setting

That's just my guess. I'm probably way off base but that's my best guess

Sent from my Z958 using Tapatalk

[El Camexican]

Got it.
So they have you adding in a factor for leading (or I assume trailing also) because their formula is based on the axle being on centerline of the fork leg, because that would be the only constant for the calculation. After the bike was all together you can measure the actual rake (at the frame) and the actual trail at the centerline of the axle. At that point it doesn't matter if it is leading or trailing- it is what it is. So they are adding a variable for the leading axle only because their formula is based on a centered axle, not because it actually changes the physical rake. Does that sound logical or am I confusing everyone including myself ?.

I believe when Honda added the so called "Rake" to the 250r triples it was to shorten the trail to correct some steering issue after the frames were already set.

I think I agree with everything you just wrote

[El Camexican]

In my opinion, raked trees are to correct excessive muscle movement needed in order to turn the handlebars with the rake and trail being set at optimal locations

If you think about it, since our forks aren't straight up and down, the wheel and tire technically kind of flops from side to side when you turn the forks and it's especially notable when you have alot of rake. Long bike chopper guys have to keep ahold of those handlebars or the front end "flops" over to the side when you turn the bars as a natural tendency with that kind of geometry.

I'm pretty sure that the force required to turn the handlebars left and right are also figured into the rake and trail and that's why I think you have raked trees is to try to affect the amount of force or leverage needed to turn the bars left or right at a specific and optimal rake/trail setting

That's just my guess. I'm probably way off base but that's my best guess

Sent from my Z958 using Tapatalk


Earlier on in this thread I think there was mention of a leading axle being easier to turn. I've also read that its better for sucking up bumps, hence all modern dirt bikes having leading axles.

As far as ease of steering I wouldn't be surprised if a raked triple tree provided some sort of change to the amount of force needed to move a wheel.

I do know that the front end combination I have on my stretched Suzuki is terrible for everything but straight line stability. I need to go back to it and determine if I messed up on the front end, or if it all relates back to the 8" over swing-arm. I want to say my trail came in around 6"+ and that the rake is about 37 degrees. Never looked at the off-set during the build. Sure would be nice if it steered a little lighter.