As much as we seem to talk about forks on this bike I'm surprised I couldn't find too much on actual fork swaps beside the yz. I brought my TR650 to a local guy here in Vegas to have him look at the forks to see what he can do as far as getting a more compliant spring and damper rate as well as to see what can be done to quell the bottoming that I get with any speed. We looked at spring rates and he was going to revalve the forks dampening. In the end we both came to the conclusion it would be a waste of time and money. They are what they are and can't be much else. What we did find was a set of forks that was a close match to the TR650 triples. The 2000-2002 WP 43mm forks. These were mostly on the husabergs and KTMs. The uppers clamp is a perfect fit and the lower is very close requiring a small shim to make it a perfect fit. The travel needs to be taken down from 12 to 10" with the droop setting back down to about stock. Heavier springs and a revalve should round it out. Braking should swap right over. Conversion is in the process currently, and when it gets closer I'll have impressions of actual fit. Really looking foreword to seeing how a real front suspension will feel on this bike and how it will make the back feel.
I understand this. I am doing this in conjunction with a man who builds and tunes dual sports for a living. This is his suggestion. I am taking it. These forks are almost as available and every bit as good. The triples will be at their stock clamping diameter.
Agreed, that is how I got here. I started by looking to make the stock forks rideable in my terrain. We came to the conclusion they just are not capable of what I need.
I'm looking forward to hear how it works out for you. I am going to have to do something with my forks and shock at some point.
just an FYI saw a post on my FB it seems TBT has come up with a way to get KYB SSS guts into WP 4CS forks word is its a sweet ride
Well a little progress has been made as far as planning. The forks have been switched from the 43mm to the 48mm from an 03 KTM EXC 525. This was just due to what parts I had in front of me. The top clamp is still the same size but the bottom will be reemed for the larger diameter. The valving will be done by John, my suspension guru. The spring will be a 4.7-5.4 progressive. Should take all the rocks and junk on our trails decently and still not bottom except on hard hits. Right not I'm bottoming it on every ride at about 225lbs all geared up.
Good! Now you can get on Shawn Johnson's YZ Forks thread and compare the two. He like competing ideas on his thread. Did you ever just try increasing the fork oil weight? BMW's were notoriously light weight fork oil from the factory - 7.5 wt.
Actually the fork oil was like motor oil in mine. I have never changed it in my 7000 miles. We are unable to measure the stock spring rate but from what John can find it is a 7.0 which is insanely stiff. This makes us believe that the valving is absolute crap. Almost no compression dampening leaving the job to the heavy spring. That's the only way I'm bottoming it at my weight. As far as comparison on the YZ forks it will be like apples and oranges I'm afraid. I'll be running a progressive rate spring with custom valving. I'm trading labor for the work otherwise I don't think I'd be doing such a custom setup on this bike. I would like to see how one rides though if anyone is in the Las Vegas area. Anything has to be better than stock once you start hitting rocks and washes.
I'm interested in how you go about enlarging the bore on the lower triple. I spend some time looking for a way to simply ream to the correct diameter, but couldn't find a proper tool. I know a machine shop could set up and bore, but that's expensive! I just don't like the idea of spreading the lowers as it seems to me that a lot of stress would be induced into the already-thin aluminum.
This is another reason we were going with the 43mm forks to begin with. They will just drop in with a small shim. Spring, valve and bam- custom forks with stock geometry. In this case my suspension guy has a mill with the proper bit. He has done this kind of modification before. I don't know for sure but you probably have the same type of riding I do with lots of long poweline roads and technical rocky trails. Easily finds the limits of the TR650.
Oh yeah, it's fairly similar here vs. Vegas. Let me know how it goes; I might want to take a spin to LV to get my bike done as well. I wish I'd taken the rear shock off when doing the air box mod. Has to all come apart again to get to the top shock bolt.
Ahhhhh, I need to look at that! As many time as I've been in there I guess I never looked hard enough. That hole has to be there for a reason!
Yes you are able to measure the spring rate, it is a simple equation and there are a number of spring rate calculators on line, I put one on my web site for GS owners The spring rate on the Terra/Strada is more likely to be far lower that the 7.0 stated above, any suspension tuner would normally be expected to calculate it quickly
FWIW, Racetech at one point was quoting the stock fork springs at 7.0..Alex Martin at Konflict Motorsportzs had a set custom made for me that are 8.0. I weigh in at 235 and am running 5wt oil.They don't bottom anymore except on really hard hits
I'm pretty sure that's where he got his number from. That's is so ridiculously stiff though. Really makes me wonder if there is compression dampening at all!
