XR 650 with inverted forks



16 replies to this topic
  • Big_Junior

Posted November 28, 2003 - 10:32 AM

#1

I am interested in hearing from anybody who has converted a stock XR 650 front end to inverted forks

  • cat0020

Posted November 28, 2003 - 10:42 AM

#2

I've tossed the same question back in September..
there seems to be no need for USD forks for the XR650R..
I've got a set of Ohlins 48mm USD forklegs that I would like to put on my XR650R to try them out.. so far I've not tried to see if the triple clamp from a Cannondale would fir onto the steering tube of a XR650R, if it does, I'm certainly putting the Ohlins on..

  • CISCO

Posted November 28, 2003 - 03:01 PM

#3

Im doing it to my DRZ kicker. It weighs 265lbs.
Ive never seen a BRP with USD though. The type of riding these bikes are built for, doesnt necesarily mean you need USD forks. Plus the weight of the bikeVS frame stresses that will increase with such a rigid fork could mean a cracked frame. Ive heard most people object to this mod on the BRP.
I may see some adverse effects on my DRZ from rigidity and my tendency to hit everything in the course at high speed :)
My thoughts: Team suzuki DRZ = USD forks
Team honda BRP = Conventional.
Although built for different races, Id look at that as...probably shouldnt if they didnt?

  • Carlisle1972

Posted November 28, 2003 - 05:51 PM

#4

USD's are great for tracks not trails. There is a reason soo many off road racers stick to conventional forks. Your better off with new valves and heavier springs

  • CISCO

Posted November 29, 2003 - 06:00 PM

#5

USD's are great for tracks not trails. There is a reason soo many off road racers stick to conventional forks. Your better off with new valves and heavier springs


Who??? So many people say this...and I have yet to see KX250 or equivelant GNCC bikes being modded to accept conventional forks. Thats old hat IMO.

  • Carlisle1972

Posted November 29, 2003 - 09:24 PM

#6

Conventional works better in large abrupt rocks roots and obsticles. My point was only not to spend huge amounts of money on usd's because conventional forks will perform great if set up correctly. Have you ever ridden an xr through solid rocks? Most all trials bikes use them for a reason, they work in rocks

  • cat0020

Posted November 30, 2003 - 04:44 AM

#7

Suspension performance is not depended on the type of fork that you use when you go through the same valve job on them.
USD forklegs are stiffer torsionally, more material on the top of the top end of forklegs where the tripple clamps are located.
Given the same amount of weight, USD forks will always be stronger structurly than the telescopic forks.
USD forks are less prone to seal failure, gravity pulls the lubrication to the location of the seals.
USD forklegs just looks much better than telescopic forks, without the boots that's covering up the inner legs.
It's a project, I'll put my Ohlins on the XR650R someday.

  • Big_Junior

Posted November 30, 2003 - 08:52 AM

#8

Is there a particular reason for choosing the Ohlins ?
I am looking into using a set of Showas off a CR.
So far I have learned that the bottom bearing (steering stem) is the same as the XR and I am still researching the rest of the crossover parts.

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  • XR250rdr

Posted December 01, 2003 - 02:34 AM

#9

cat, I'm going to play devil's advocate here for a second. If USD forks are less prone to seal leakage why do I see a lot of USD forks leaking and almost never see a bike with leaky convention forks?

  • XR500R

Posted December 01, 2003 - 05:23 AM

#10

I've got a bike with leaky conventional forks...but then again it is 20 years old :)

  • cat0020

Posted December 01, 2003 - 05:40 AM

#11

I spoke of seal failure, not leaks.. :D
It is less likely to have dirt, sand getting inside of USD forklegs due to seal failure, than that of a telescopic forks, hence less fork maintenance, less frequent change of fork oil. I have not have my USD forklegs leak on any of my KTM's. Only the telescopic forks from my older bike have leaked in the past. I guess each person's experience can be different. :)
I chose Ohlins because they are valved to my weight and riding style.. and just happen to have a set laying around in my garage from a parted Cannondale. :D nothing like a free pair of Ohlins.. now if only I can figure out a use for that Ohlins rear shock.. :D

cat, I'm going to play devil's advocate here for a second. If USD forks are less prone to seal leakage why do I see a lot of USD forks leaking and almost never see a bike with leaky convention forks?



  • steve_f

Posted December 01, 2003 - 02:45 PM

#12

I am interested in hearing from anybody who has converted a stock XR 650 front end to inverted forks


I haven't but Steve Drew has. He rides an XR650 in Supermoto Unlimited. Read this article:

page down for Drew

  • JR650

Posted December 01, 2003 - 09:11 PM

#13

ya, i was toying with the idea of putting some cr250 forks on mine, but then i remembered, oh yeah, i ride with 3 bikes that have blown the seals in their usd forks. I do mean BLOWN too. 2001 rm250, 2003 yz125, 2003 ktm 450mxc. all blew the seals, leaving the entire oily contents of the forks in the garage shortly after the ride, all on different occasions, so dont tell me that usd forks dont blow seals as much. but, i like the thought of more precise steering and maybe lose some weight too. Like anything else, advantages and disadvantages. JR

  • motart

Posted December 02, 2003 - 06:45 AM

#14

steve drew runs usd forks, but has also broken a few frames. the frames on these bikes are not made for usd forks or honda would have engineered it that way. although usd forks are much better looking, the conv ones flex enough to compensate for the frame. i run a summers fork brace on mine and am very happy with the results.

  • Big_Junior

Posted December 02, 2003 - 07:40 AM

#15

steve drew runs usd forks, but has also broken a few frames. the frames on these bikes are not made for usd forks or honda would have engineered it that way. although usd forks are much better looking, the conv ones flex enough to compensate for the frame. i run a summers fork brace on mine and am very happy with the results.


Who or what was your source of this info?

Do you know details of the frame problems : where they were breaking and why? And more importantly - how did they solve this problem?

I would think that the frame could possibly be strengthened to compensate for insufficient OEM engineering to handle the stiffness of the USD forks.

  • cat0020

Posted December 02, 2003 - 08:14 AM

#16

USD forks does cause more stress to the headtube of the frame, dues to the stiffer forklegs.
But in my application of USD forklegs, I'm not getting big air, no 80+ mph in the desert and hitting huge rocks. Very little likelihood of myself breaking the frame with USD forks. :)

  • qadsan

Posted December 02, 2003 - 09:58 AM

#17

I can't say for certain, but strengthening the frame might be more complicated than simply adding more material. Aluminum does not handle cyclic loads as well and fatigues much quicker than steel or titanium which is what would concern me for the long term with the more rigid USD forks on this frame. Don’t get me wrong because I like the idea of USD forks and the frame might hold up just fine for many years of riding given the average rider, but the frame will likely fail sooner with USD forks than with conventional forks. How much shorter the life would be is difficult to guess without enough real world testing in a controlled manner, but there have been a few guys that have done the conversion and were quite happy with the results. Spotting a fatigue problem in aluminum is much more difficult and you generally don’t find the problem until it’s too late unlike steel which commonly propagates noticeable cracks unlike aluminum. The stress peak in aluminum increases as it’s flexed unlike some steels and it’s just a matter of time before you have a failure when you combine higher stress peaks with enough cycles. The aluminum frame on the XR650R is also stiff on purpose by its design and many things are taken into account such as materials and component choices, processes, wall thickness, butted sections, tube diameter, weld type, frame geometry, etc, all of which play a purpose to minimize flexing so that the frame does not fatigue for it’s given life whatever that may be. You can bet that Honda has done their homework on this frame and that they have plenty of documentation on the variables for failure, but the chances of getting their specific data is almost non-existent. Team Honda’s Bruce Ogilvie ‘supposedly’ came down hard on Dirt Bike Magazine when they featured a XR650R project bike with USD forks back in the March 2000 issue and ‘supposedly’ warned them against using USD forks on the XR650R because of potential frame failures if people were to convert their bikes, but I don’t know how much truth there is in this. If Bruce Ogilvie really did make comments along those lines, then perhaps Honda may have had some real liability concerns.

When you take a look at some of the top XR650R pro’s such as Johnny Campbell, Steve Hengeveld, Andy Grider, Chris Blais, etc, it’s interesting to note that they’re all still use conventional forks and just won another Baja victory last week. Even Scott Summers had been racing a XR650R with conventional forks earlier this year and was actually seen racing his CRF450 with conventional forks installed from his XR650R instead of the USD forks that came on his bike! I heard he only did this because he hadn’t yet nailed down a good enough setup on his CRF USD forks, but it was still interesting that he went to that much trouble for a race.

The average rider may never have a problem with USD forks and perhaps only a few if any would ever have frame problems with USD forks, but I’ve been quite happy with my conventional forks once they were revalved for my simple riding needs. I’ll be anxious to hear more about any USD conversions, so if anyone here goes forward with this, please feel free to share your short & long term experiences.





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