Author Topic: A Trials bike from a Trail bike  (Read 1321 times)

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TT

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A Trials bike from a Trail bike
« on: June 28, 2010, 06:29:22 PM »
Time and money are at a premium right now, but all this talk of building a trials bike out of something that wasn't meant to be, has got me thinking.............
I've got a good SP370 engine and frame without any use in mind and I've got plenty of forks and wheels to fit.  So after Harrow, I thought I might throw a few parts together to build a kind of trials bike.
Apart from losing weight, (both me and the bike) what should I do to it?
Grind off the steering stops? Lower gearing? Small seat & tank?
I working on the thought that the SP enine should weight too much more than a TL250 engine............. should it?
Does anyone know what a TL engine weighs?
Maybe a dumb idea, but I like the idea of building another bike essentially for free.  ;D

Offline Mike52

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Re: A Trials bike from a Trail bike
« Reply #1 on: June 28, 2010, 06:31:13 PM »
The Tl,s have really big flywheels don,t they. :)
85/400WR,86/240WR,72/DKW125,Pe250c,TC90,TS100,XT250,86/SRX250,XR400r
Friend  struggling up a hill on a old bike at MTMee .http://www.youtube.com/watch?v=cjj6E2MP9xU.

TT

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Re: A Trials bike from a Trail bike
« Reply #2 on: June 28, 2010, 06:36:38 PM »
That's a point, but it's not exactly going to be a serious machine, so maybe I can ignore that bit.  ;)
If anyone's got a really cheap trials type tank and seat, I'd be interested.

Offline sudman

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Re: A Trials bike from a Trail bike
« Reply #3 on: June 28, 2010, 06:59:13 PM »
In fact the TL has the lightest flywheel of all the honda four valve motors it is 1/2 the weight of a XL350 flywheel, steering head angle is the the big one but this is easy done with short forks & long rear shocks, I have a TL250 pay bike & they are lots of fun & so will your project be.
PE175T,RM175T,C & J XL350 73,C&J XL350 75

TT

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Re: A Trials bike from a Trail bike
« Reply #4 on: June 28, 2010, 07:15:38 PM »
Thanks for the encouragement, sudman.  ;D
Shortening the forks is easy. So maybe I'm not completely mad after all.  :D

Offline David Lahey

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Re: A Trials bike from a Trail bike
« Reply #5 on: June 28, 2010, 08:51:17 PM »
Tony thats a great dream. With that motor it will be pretty entertaining.
See if you can find a swingarm that gets the tyre right up against the swingarm pivot. That should get the wheelbase into the ballpark. You should aim for 51 to 52 inches.
Move the pegs back to the front edge of the rear tyre in its new location.
Yes get the steering steeper - aim for head angle of about 27-28 degrees.
Reduce the trail. Triple clamps with lots of offset are the go here and will help you get more left right  steering angle. You could probably find some 1970s trials bike triple clamps and machine them out to 36mm for the SP forks.
Use soft suspension. Standard SP370 forks will be close to right. I was thinking of experimenting with a set of mine on a trials bike but havent yet but I remember what my SP370 was like when they were on it.
On the rear probably 50 lb/in springs and get rid of almost all the damping both directions.
Get as much clearance under your bum as you can. You may need to raise the pegs a bit to get enough without cutting the frame down.

Things working against that motor are the lack of flywheel effect and the overall height of the motor, but no matter what you do it will be great fun.
previous pseudonym feetupfun

TT

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Re: A Trials bike from a Trail bike
« Reply #6 on: June 28, 2010, 09:09:33 PM »
Great info, David. Thank you!
There's no plans to start winning trials events on it, but just something I can play around on almost anywhere without offending the neighbours etc and without spending much (any?) money.  :D

Thanks for not making fun of me, fellas.  ;D
« Last Edit: June 28, 2010, 09:15:52 PM by Tony T »