I written this up and added to it as I've built up my bikes. I'm not saying it's gospel but it has worked for me. Perhaps it can save someone else some time and drama.
XT/TT500
Front end. A couple of years ago I ended up with a front end from an IT465
Yamaha as well as the PE175 Suzuki front end I was using. I switched the
entire IT front end onto my bike and found no real difference in handling
apart from differences in springs and damping.
I had both front ends off the bike so clamped each one to the table on a
milling machine and did some measuring. Both front ends have a total offset,
from axle to steering tube, of 60mm. The Yamaha has 25mm in the triple
clamps and 35mm in the fork legs. Th Suzuki has 30 in the clamps and 30mm in the fork legs.
Both the PE and IT triple clamps use the same size bearings. The steering
tubes are different lengths. I started out by using spacers to fit either
the PE or IT front end but have now re-machined the longer PE steering tube
to fit.
XT/TT 500's use ball bearings in the steering head. There are a few kits
available to convert them to tapered rollers. This mod is very worthwhile
as it firms up the feel of the front end a great deal.
I've also de-raked the frame on mine to achieve a decent fork rake. An angle
of 27-28 degrees seems to work fine. You can reduce the steering head angle
by fitting longer shocks but this raises the bike and makes it awkward to
kick-start.
The rear of the bike can be raised but there seems to be an ideal swingarm angle.
I've found this to be about 16-17 degrees from horizontal, or have the swingarm pivot about 140mm higher than the back axle (this applies to a swingarm 540mm long, PE400).
The chain will rub on the swingarm buffer at full extension.
If you set the bike on a box and aim for a fork angle of 27-28 degrees with a
swingarm angle of 16-17 degrees this will give a nice balance between stability and good turning.
At the time I was doing all this I was asked to repair what was supposed to
be a 490 Maico frame. Long involved story but basically it never happened,
BUT, while I was trying to find frame details and specs to do the job I
found the rake and trail figures for the best handling MX bike ever,
thank you Lex. See where this is going??
On the Internet I found TONY FOALE's site. Well worth a look. I down loaded
a rake and trail calculator and put in the figures for the big Maico with an
assumption on front tyre size.
This gave me the approximate total offset for the Maico (although I have not
been able to measure one). By using the PE forklegs and IT triple clamps I
got very close to the same front end geometry, ie rake and trail.
The difference was incredible, I now had a TT that followed the front wheel
no matter what the back was doing. Suddenly you could change lines when half way through a corner and no more need to steer it around from the back,
although you can still do this if you feel like it.
The front end set-up does not make the bike faster all by it's self but it
allows you to take corners a lot faster and your confidence increases from
there.
To fit the front end together I did the following.
The IT/YZ triple clamps are about 5mm wider than the PE clamps so a longer
axle spacer was needed. I used an IT/YZ front wheel as the brakes are better.
To get the brake anchor lug on the baking plate to engage the lug on the PE
fork-leg I had to machine about 3mm off the axle mounting lug on the inside
of the fork-leg. Remove just enough to get the lug to engage the backing
plate but not enough to let the brake arm touch the fork-leg. I allowed the
wheel to sit offset to the left then offset the spokes to move it back to
the centre.
XT/TT 500 back end
When I fitted the Suzuki PE 250/400 swingarm to my TT it was done on a weekend using what parts were available. The swingarm I used had no bearings so I made Phosphor Bronze bushes to suit. Now I have a complete PE swingarm and to fit this I need to make some stepped washers to locate the swingarm bolt. The PE swingarm bolt is about 2mm smaller than the TT bolt.
The PE swingarm is very slightly wider than the TT swingarm but should fit if the shims are removed from under the dust covers. The other option is to use a car jack and spread the frame rails about 1mm in the swingarm area.
The PE swingarm fouls on the TT brake pedal, it’s probably easier to cut the inner lever off and weld it to the brake pedal outside the frame. This also removes the cumbersome linkage and rod that the TT’s use.
I’ve used Yamaha wheels as they are light, plentiful and have great brakes.
If you use a backing plate with an arm type anchor the anchor arm can be bolted to the lower flange on the PE swingarm. I’ve used a hub with the slot type anchor and welded a tab to the swingarm.
The PE swingarm will take a 20mm axle so a wheel off a larger Yamaha (IT/YZ465, 490 or TT600) will suit. This is probably a plus as a TT can be fairly heavy. I use a 20mm axle and snail cam type axle adjusters.
You will need to make new spacers for the rear wheel. I clamped a straight piece of steel RHS (about ½” square) to the outside of the front sprocket and layed it over the swingarm pivot and down to the rear wheel. I carefully moved the rear wheel across until it just touched the RHS. I then made spacers to suit the wheel in this position.
TT’s have a long distance from the front sprocket to the swingarm pivot. This makes for large changes in chain tension during suspension travel and it gets worse with longer swingarms or modified suspension. I have installed a roller below the swingarm pivot to maintain steady tension on the chain. The roller is fixed to the frame and it’s position is set as follows. Remove the rear shocks or strap the bike so the front sprocket, swingarm pivot and rear sprocket are all in line. Set your chain tension in this position. Refit the shocks or unstrap the bike and allow it to sit at full extension. Place the roller under the chain, below the swingarm pivot and push the roller up to get the same chain tension as before. Drill the frame flange and mount the roller in this position. A roller from a late model bike works fine. I do not use a spring loaded chain tensioner but do use a chain guide from a late model bike. I also suggest making a case saver to protect the crankcase from an errant chain if it comes off. I lost one engine case before I worked this one out.
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.
With the Yamaha triple clamps and Suzuki forks the bike turns much better than the all Suzuki or all Yamaha set-up.
With the Honda triples it turns much better again! The Honda triples do take more work to fit though.
My bike feels different to a normal TT500 to ride. It feels a lot lighter than it’s 126kg (that's full of fuel)and is very responsive to steering input. The suspension is supple and currently a good balance between trail riding and natural terrain MX.
For gearing I run 15 or 16 teeth on the front sprocket and 51 on the back for trail riding. Bigger sprockets help keep the chain off the chain runner over the swingarm.
For racing I’m running 17 up front and 48 on the back but will soon be trying 46 and maybe 44 teeth. The current race gearing means second gear is still a little low for slow corners and third gives enough speed for the usual tracks I ride. Overall this means changing up or down only one gear!
YZ125C tank to an XT/TT500
Early models with inline front axles have the tank mounted fairly well forward. The front of the seat/back of the tank lines up with the front edge of the side cover.
Later models had leading axle forks and less offset in the triple clamps. These models have the seat and tank mounted about 50mm further back than the early models to clear the fork tubes on full lock. There is a noticeable difference in the seat, tank side panel area.
When you fit leading axle forks to an early model you need to move the seat and tank back or dent the tank to clear the fork legs.
When you fit a YZ125C tank you need to move it back to clear the oil filler, dipstick hole.
Doing this actually moves the tank to pretty much an ideal position with regards to using leading axle forks. The steering stops may need to be altered to suit.
There is some denting required in the underside of the tank and the top frame tube.
I think it's an idea to have your forks before you fit the tank.
