Front Suspension.. Suggestions.

[pearson*]

Potentially looking at upgrading the front end to something USD based, a set of 748r forks have come up for sale quite cheap so im tempted by those so far.

Anyone have any other recommendations or know of any good known mods.

Also worth noting im one of those ocd guys that hates bits of forks sticking out the top and that hence writing off the r6 forks i've previously seen. Secondly, i fancy a challenge.

[Evilchicken0]

I was going to say - measure the new forks first the headstock on the 3TJ is quite low / the top yoke is cranked down.

I'm not sure of the length but maybe consider the YZF750 - the later forks were fully adjustable and you can put blue spot calipers on ... the only thing is the 320mm disks will leave the bike a bit over braked.

Remember your're going to need a full front end for USD forks, that's wheel, brakes, clip-ons, and yokes it could get expensive.

[pearson*]

I've managed to get some money left over from when they fucked up my current set of wheels last time and its also getting to the point where the disks and pads need changing over, the headstock bearings are on their way out too, the right clip-on is quite scratched anyway and the forks definitely need looking at.

To me its going to cost quite a bit to sort out the current problems so im thinking it might just be worth putting a bit extra in and making it nice. that and the bikes going to be off the road for a good 6/7 months aswell.

[thunderace]

R6 front end should be about the right length, or ZX6R

[pearson*]

the zx6r has passed my mind, they fit into the rgv 250 triples and they are apparently a strait bolt on fit.. or near enough anyway

[Maelstrom]

I do not know if the RGV250 offset is the same as a 400. That being said the thing that has the greatest effect on your handling is trail. If you change the offset between the steering stem centre and the centreline of the forks then you are changing the trail and by much more than the difference in offset. Please consider this before using different triple clamps.
cheers

[Evilchicken0]

Alex used the RGV tripples and ZXR stanchions - pm him, I think he made up some spacers so he might be able to give you some dimensions.
He didn't mention any ill effects to the handling but Maelstrom's right check the rake and trail figures for the RGV first.

[Alex.]

Do you mean this minor mod, EC?



The RGV VJ22 (or GSX-R4 GK76a) yokes bolt directly onto the 3TJ headstock, the bearings are right as is the length of stem. Then all you need is the ZX6R forks (03-06), clip-ons (or RGV or GSX-R4) and brake calipers, GSX-R4 GK76a front wheel (GSX-R is 3.5", RGV is only 3"), axle, brake discs and speedo drive. I also used the ZX6R front mudguard.
As the ZX6R forks are longer than the 3TJ, they do not poke up above the yokes on my bike.

Then all you need is a bunch of spacers, one in each fork leg (the ZX6R axle is much larger in diameter), one on the opposite side of the wheel to the speedo drive, spacers for the calipers and spacers to move the discs out a couple of mil. 03-04 ZX6R uses brake discs that are 20mm smaller than the RGV, so need 10mm spacers under the calipers, the 05-06 ZX6R uses the same size discs as the RGV, so does not need these spacers. I can provide drawings for these spacers, or they are available over on the RGV forum. One mod I did make to the spacers is to allow the speedo drive to be retained, which needs a dimension change for one fork leg spacer. If the speedo drive is used, one of the spacers on the outside of the pic below is not needed.



The trickiest part is to modify the yokes, the lock stops are in the wrong place so need to be taken off. I attacked the bottom yoke with an angle grinder to remove them and then welded some new ones on. Also the ignition switch is in a different place between the two bikes, so the steering lock is lost and the switch needs to be fitted further away from the top yoke. I now have an aftermarket top yoke with no key switch, just a toggle switch somewhere inconspicuous...

I did not take any geometry measurements before I started, but if someone was to tell me what to measure I can get the figures.
There was a marked improvement in handling after the conversion, but the forks I had were weeping at the seals so it could be that was more a problem than I thought.

Alex.

[Alex.]

Just a couple of pics to illustrate the ignition switch issue.

RGV yoke with switch spaced out:-



Aftermarket top yoke, no switch:-



Any excuse for some pics...

Alex.

[Maelstrom]

A good diagram of rake and trail at
http://www.motorcyclistonline.com/howto ... to_05.html
Once the change in offset is known, the new value for trail can be calculated. It involves a bit of trigonometry, based on the original values for rake and trail. Assuming that all things, fork length, front and rear wheel radius etc, being equal, which of course they never are. The point is not to arrive at some magic number but rather to have a reference to the original factory setting. As an example, a friend asked me to help him set up his Suzuki GSXR750 that he raced. The track in question included a quite steep downhill section that flattened out as it turned onto the straight. Most bikes suffer on that turn because their steering became too twitchy, and the change in camber was also a problem. He had raised the ride height at the back and lowered the front (doesn't everyone). I measured the bike and calculated his current rake and trail. The trail being the most relevant factor. I then altered the setup so the trail was back at the same value as a standard road bike. The net result was that he could push the bike through that difficult corner and get onto the straight at a much higher entry speed. He got the first podium of his life. If he raced at a different track then I would be looking for something else. The point being that you can manage what you can measure. In those days I used a programmable calculator at the track. Now you could use your phone. This is all based on my own experience and is not the gospel according to St Peter.
cheers