Super Mini Sized Trials Bike Build

[denisesewa]

 I started a winter project , purchased a roached 93 GG GT 160 frame, subframe and swingarm , a Paoli USD Beta fork and 96 JT shock, the doner bike is a 2003 TTR 125, while waiting for the parts to arrive I rebuilt the engine with BBR 150cc kit, performance clutch and have a stock flywheel as well as a lightened one and a CRF 150 carb and will be converting to hydro clutch as well a fabricating carbon bodywork , airbox and tank.

 The idea is to have a little thumper with trials geo ( I hate the TTR geo) and I needed a long term project. So far I have cut the frame up to accommodate the engine fabbed up new engine mounts and tack welded it back together ( 1st pic), after assembling enough parts to "see what I have" I realized the fork angle doesnt seem/look right( about 74 degrees) and the wheel base is longer than expected ( 1346 mm), (2nd pic) , after lifting the rear wheel 2 inches off the ground and compressing the forks 1 inch the fork angle looks better, ( 3rd pic) .searching the web hasnt provided much info on modern trials head tube angle, the present rear wheel is 16 inch and that will get relaced with a 17 inch rim so it may help a bit, I will also extend the slots for the rear axle forward to help shorten the wheel base.

If I have to remove and reinstall the headtube I would like to have actual specs for angle so  I would appreciate any specs from a late model bike, thoughts, insight and constructive criticism are welcome. ( Yes I know I could have just bought a bike but this is as much a project as anything else.

 

 

Edited November 23, 2015 by denisesewa

[suzuki250]

The bikes looking good, but the workshop wiring's shocking (literally)

[taffe]

Hi, Interesting project, but the workshop caught my eye before the bike. I could not work in that space . Anyway, I cant help with spec's but would measuring a trials frame help? What is the bikes intended use?

Good luck with it.

Taff

[denisesewa]

Well, I dont have a nice shop, just a little 100 year old shed , it is what it is.  just thought someone might offer some useful info * about the bike* .

O-well 

[htrdoug]

USD forks might not have the proper triple clamp offset for trials head angle,rear motor mount needs to attach to swingarm pivot and be sturdy enough to help hold frame together,which means some sort of head stay needs to be fabbed too. Get rid of Knobbies,trials tires use sidewall flex to provide traction(think drag slicks or 4wd trucks)

[taffe]

Hi, if using the bike in rocky trials type country l would be thinking about those upsidedown forks too, might be a bit too easy to damage the sliders.

Taff

[denisesewa]

 Thank you for the replies , the forks are trials forks with offset triple clamps, both gas gas and Beta used these Paoli forks in the 90's, they will have slider guards, I had to move the brake caliper to the rear to accommodate the KX wheel and caliper which makes it look like an MX fork. I do have trials tires, just waiting for spokes to arrive so I can lace the rear wheel to a new rim and then mount the tires. motor mounts are engaging the swingarm pivot bolt and the front stays are as original to this frame just moved forward, this frame did not have stays attached to the headstock.

original 93 gas gas gt-

 

 I do have trials experience and have owned several from twinshocks to a Fantic Section as the latest model on which I got hurt bad enough to have to step out of trials comps, the intended purpose of this bike is to have a challenging winter project and something fun and different to ride while observing or minding .

 

 out of my crappy little workspace I have built some decent items including an electric trials bicycle which is fun but power delivery is a bit harsh.

 

Video of maiden ride - 

 

 And a little board track racer

 

 So I do intend to build this into a viable trials bike which functions and looks decent, with a little advise such as headtube angle and observations and opinions It'll happen. Seems odd that geometry of modern bikes is so closely guarded by manufacturers . 

Again, Thank You for your replies.

[oz thumper]

According to the manual Montesa 4RT caster angle 24deg 34', and trail length is 63mm with a wheelbase of 1,320mm.

if I recall correctly the TLR 250 has similar angle of 24 degrees.

 

 

[monty_jon]

Maybe you could do with a longer swing arm?  

Edited November 7, 2015 by monty_jon

[slicktop]

I think your garage has class, the Husqvarna box is an indicator. 

I like your Board Racer, Whats your nearest velodrome? I have only seen one, Indianapolis.

[lineaway]

You have come a long way in a short time! Interesting project. Keep us posted.

[scot taco]

I read about converting Hodaka trail bikes into trials bikes.They had done a few different builds and found out that anything less than 24 degrees on the head angle was not good and I think 24 is what they said seemed to work best.Don,t know if that helps,but maybe a starting point?

 I would maybe try it like it is and then go from there.Cool project.

Edited November 7, 2015 by scot taco

[denisesewa]

 Thanks for all the helpful info ! Looks like I will shoot for about 24 degrees and somewhere around 60 mm trail. going to internally shorten the forks a bit to gain some on the head angle, since it has a 19" front wheel I can get away with less travel.

 

No board tracks around here , it was just a project and kinda a cool townie bike.

 

Lineaway - Hopefully I will give a new life to your old frame, we'll see.

[tony27]

What is the reason for the odd sized wheels, are the wheels off a big wheel 80? If you lace in trials sized 21" & 18" rims you'll actually be able to get tyres that work & it may solve some of the geometry problems

I don't know if I'd want to go shorter on the wheelbase, trials bike steer quick anyway & get nervous if trail ridden at speed

[denisesewa]

What is the reason for the odd sized wheels, are the wheels off a big wheel 80? If you lace in trials sized 21" and 18" rims you'll actually be able to get tyres that work and it may solve some of the geometry problems

I don't know if I'd want to go shorter on the wheelbase, trials bike steer quick anyway and get nervous if trail ridden at speed

Sorry for the late response, notifications dont seem to be working .

 

There is no real reason other than I am using the wheels that were on the TTR , I had installed a KX 100 fork and front wheel on the TTR so am using the front wheel on this bike ( 19 inch), The rear hub from the TTR will be used with a 17 inch rim, these are the same size wheels and tires the GAS GAS Rookie / Cadet/ and 2015 TXT pro 80 use , I have the tires on hand just not mounted yet.

 As an update, I got a few more things done the past couple days, fabricated/ reconfigured a brake pedal, that was a bigger job than expected due to having to clear the kicker and since for now I am using the drum brake from the TTR I didnt want to change anything on the frame so I have the option of going to Hydro's later when I find a decent deal on a rear hub/brake setup, turned out decent if not goofy looking.

 Adapted the Beta fork to the Frame, had to shorten the headstock and remachine bearing race pockets, this offered an opportunity to offset the pockets ( same effect as eccentric bearing sets) and induce a change in the rake so the geo is getting close. ( just getting the forks "properly" mounted helped the geo a bit)

 Made a plug( mold shape) for the airbox and lower half of the gastank , took a mold casting for the top half of the gas tank in preparation for making the carbon parts. machined a spigot for the carb along with a bunch spacers and bushings for the wheels.

From one of these couplers -

Machined to a carb spigot -