Here's some more ramblings. These are my collection of thoughts based on a lot of reading and lot more mistakes over the last few years.
XT/TT, thoughts of a victim.
I started out writing this about XT/TT500’s but it really applies to any hybrid.
When setting up an XT/TT500 with “other” parts I think it pays to look at what you want overall and select the parts to achieve this.
I’m not saying I’m an expert but over the last five or six years I’ve learned a lot and made a lot of mistakes.
To look at the overall package you need to look at.
What do you want the bike for? Will it be a trail/play bike or are you building a race bike? Do you want to race in a certain class? Remember to build your bike to suit the rules, don’t expect the rules to change to suit you.
Forks. What sort of forks will you use? Do you want to qualify for a certain class i.e. Pre 78? EVO? Will travel be a consideration?
Fork angle. XT/TT500’s have a fairly shallow steering head angle. This gives stability in a straight line but is not the best for turning corners. Later models do have a steeper steering head angle.
What spring rates will you need? Most available forks will be off a two stroke that was a lot lighter then the XT/TT so the springs will be way too soft (spring rate too low). Easy you say, just preload the springs a bit more. Sitting still this is fine but you end up with a harsh ride at low speeds and it bottoms on any sort of jump.
And what about damping? The forks you’ve picked up were probably underdamped to start with and now they are having to cope with quite a few more kilos, (both the bike and us!) YSS PD fork valves or Race-Tech cartridge emulators are the go here. They will give both a better ride and much better control.
Remember, most of us cannot ride anywhere as well as we remember we could all those years ago. Give your self an advantage, in comfort, safety and enjoyment.
Triple clamps. Most people will use the clamps that are on the forks. This is the easy way but how will they affect the handling. The offset from the steering tube to the axle in concert with the steering head angle and front tyre diameter determine the trail of the bike. Trail will affect how the bike will turn, how it will track, how stable it will be, how it will self correct and how the back will follow the front.
Will you need to move the tank back or dent the front of it to clear the fork tubes if you change to leading axle forks.
You may also need to modify the steering stops.
Swingarm and shocks.
What length swingarm will you use? For an XT/TT I suggest going longer by 3-4 inches. XT/TT’s were quite rear heavy, made for great wheelies. A longer swingarm puts more weight on the front and improves stability. Most swingarms you are likely to fit will also be a lot more rigid than the standard one, this gives a big improvement in ride and control.
What length shock will you use? This will determine the swingarm angle. Too steep and the bike will rise under power. This is good for holding a tight line coming out of a corner under power but will cause the rear to kick on sharp edged bumps under acceleration.
Too shallow an angle and the bike will squat under acceleration, this will cause the bike to run wide accelerating out of a corner as the fork angle flattens.
Get the swingarm angle just right and the bike will remain neutral. It will hold a nice line out of a corner and won’t preload the rear suspension.
What is the ideal angle, it depends on how your bike is set up.
Springs and dampers. A lot of bikes seem to get set up with a set of shocks from the wreckers that were about the right length. A set of shocks which have been tuned to the bike and rider with spring rates to suit will make the world of difference.
Keep in mind that a set of shocks for a standard XT/TT will be wrong if you have changed the swingarm length or angle or if you’ve changed the weight of the bike.
When properly set up your front and rear suspension must be balanced and work together both in relation to both spring rates and damping.
I cheated a certain amount and let someone else do the hard work. I found the chassis figures for an 81 MAICO. Generally regarded as the best handling MX ever built. If you get the chance ride one and you will know why. My TT runs fork legs from a SUZUKI PE 175 with triple clamps from a HONDA XR250. I did de-rake my frame to steepen the steering head angle. I use a swingarm from a SUZUKI PE400 and run my swingarm angle at 16-17 degrees fully extended.
You can reduce the steering head angle by using longer shocks but this will steepen the swingarm angle and can lead to other undesirable traits.
The chassis figures for my XT500 are
Wheelbase 1500-1530mm
Swingarm length 540mm
Rake 28 degrees
Trail 126mm
Swingarm angle 16-17 degrees
Weight 126kg full of fuel and oil.
Weight balance F 47% R53%
Rear spring rate 115lb/in
Front spring rate 23lb/in (XR250 Honda plus Kayaba top out spring) with
YSS PD fork valves or RACE-TECH cartridge emulators.
I measure fork angle and swingarm angle with a stand under the balance point of the bike, the suspension fully extended and both wheels touching the ground.
It may not be the “right” way to measure it but it is consistent.
The above figures are as close to the MAICO as I could get by using parts I could find at the wreckers. Most parts required some degree of modification.
I think you need to sit the bike on blocks and decide what you want before you start. This saves having to redo things when other parts won’t fit due to previous mods.
Sit the bike on a box at the height you want, fit forks and wheels, swingarm etc.
Set your swingarm angle. Check your fork angle and move the front of the frame up or down as required. Recheck your swingarm angle and change if required.
This is where you decide if you want to de-rake the frame or not. I try to keep the seat base parallel to the ground. When you’ve got the bike sitting with the measurements you want, now measure the shock length. I can’t recommend a shock length at present as my top mounts are in a different spot to standard.
