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Suspension components of "new technology" bikes?

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Guys:

Given that I prefer the reliability and power band of the XR over that of the CRFnnnx or the WRFnnn bikes, I see no reason to purchase one of the newer technology bikes except for their suspension components.

(And I don't need electric start: If the jetting is correct and the air filter is clean my XR starts up on the first couple of kicks hot or cold. If its a hot start after dumping the bike I am still able to start the XR with a couple of kicks after clearing out the carb with the decompressor engaged. Yeah, electric start would be nice for the potential stalling on the side of a hill, but I don't consider that worth $1,000 let alone the price of a new bike ($5,500 to 6,500+).)

I've briefly ridden the CRF250X: The steering was easy and precise compared to my XR250. I didn't like the vibration from the aluminum frame being transmitted through the thin seat padding.

What specifically about the suspension components of the newer bikes makes them perform better? I am including the bike's frame as a suspension component.

Is it the width of the forks or the valving or the spring rates that allow the rider to aggresively attack the whoops and perform the other gymnastics that we put these bikes through? Is it the design and composition of the frame? Is it the valving and spring rates of the shock? The rake?

Need some help in understanding this from some of the TT faithful.

Thanks,

Joe

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I'm no expert, but I think the rake or angle of the forks on the 250X is a main contributor to it's steering feeling better than the XRs. Also, the 250X is slightly longer (longer wheelbase) than the XRs, and that too makes it handle better I think. :)

Also, combine these aspects with a bike that weighs slightly less, has a slightly lower CG than the XR, and you have a bike that handles very well. It's the overall design and the way they put it all together. :)

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First off, one should compare the XR250 to the CRF and not bring the XR4 into the picture. The XR4 is almost 30 pounds heavier than the CRF. The XR250, on the other hand, is within four pounds of the CRF in weight. (242 for CRF and 246 for XR).

I have ridden an XR250R with "good forks" and few others here probably have, so I can tell you that from my experience it is a difference in fork rigidity, suspension valving, and frame geometry. Some will say the frame itself is "flexy" on the XR. But, my experience is that the frame design and frame rigidity on the XR250R is more than adequate for the purpose. An aluminum frame is not stronger or necessarily lighter than a chrome moly steel frame - it takes alot more aluminum to equal the strength of steel.

I had one XR250R with WP 4054s in the front (upside down forks ala Scott Summers) - and another with a '96 43mm kyb fork off of a CR125. The fork rigidity issue is a first order effect. After the forks are taken care of it steers much more confidently. But it is also a short wheelbase machine, so it will be twitchy at speed - this is not due to frame flex as some might say, the wheelbase is 2 inches shorter and the front end has 1 degree tighter steering angle than the CRF-X. This is a deliberate design decision to have the bike steer tightly in low speed situations at the cost of high speed stability.

The XR is designed to perform in tight woods - this is done at the cost of high speed stability. But, it is then also targeted toward the low cost/beginner market so certain cost tradeoffs are made in terms of suspension component selection.

  • Small diameter conventional cartridge fork
  • Soft Suspension settings
  • Small cast triple clamp.
  • Low cost fork internals.

The stock steering lacks precision due to the smallish size of the fork and the weak front triple clamp. The suspension settings are oriented towards a slow to medium speed beginner rider and the front fork lacks the internal valving to provide good performance at both ends of the spectrum (low speed compliance and high speed stability). The valving issue can be remedied by a Race-Tech base valve - cost is about $150.00

The quality of the rear suspension on the XR250 is quite adequate. In order to shorten the wheelbase on the XR250R, the size of the linkage is compact. This results in the linkage ratio being nearly twice that of the CRF. The spring rate on the XR might be in the 9-10 kg range whereas the CRF (or another motocrosser) will run a 5.6 kg spring. An XR will also have a broader ratio - e.g. it firms up faster as it goes through the stroke.

The XR250R has a shock with a 44mm diameter shock piston, The CRF250 has a 46mm shock piston. The 44mm piston is more suited to the high leverage rear shock linkage and is very adequate for the task. In this case you need a smaller piston, and smaller piston shims, to control the rear wheel with more dampening force.

At high speeds, the stock suspension on the XR250R is not very confidence inspiring. Okay, it's downright scary. :)

I am building another XR250 now. The main difference will be in an updated front fork. If you combine the torque advantage of the XR250R with the tight steering - properly suspended or even in stock form, it can and will walk away from anything in tight woods. And just to put things into proper perspective, my definition of tight woods doesn't exist in california - I am riding in an oregon or washington rainforest!!! :)

- jeff

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Jeff:

Thanks for your time in explaining the above. I appreciate the excellent information.

Based on your experience what is the impact of changing the triple clamp? What manufacturer do you recommend?

Also, do you think a stablizer to reduce the fork flex is worth the investment?

Thanks again,

Joe

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I don't have any experience with a fork brace or changing out the top clamp for a stronger one. Only a top clamp is available, not a full set - this is so that you can swap out the top clamp and run a protaper bar.

For triple clamps, BRP is the best. They make them for everyone else - including scotts.

I have always jumped from stock wimpy forks & triple clamp to big beefy billet triple clamps & an upside down fork. Night and day difference.

If you want to stick with the stock fork - The SRC triple clamp is $200, the race-tech base valves are around $150. For me, I would rather put this money towards a new set of "real" forks. But, my best friend used to be a machinist and he has a lathe and a mill in his shop - if you don't have a friend with a machine shop - cost of having a few custom parts fabricated can be prohibitive.

If you do want to go with new forks or a set off of e-bay. Be careful. Buying a set from a CR may not be a bolt-on operation. The steering head is shorter on the XR - to get a set of '96 CR KYB upside down forks to go on my '95 XR250 the steering head had to be lengthened to accomodate this fork. The fork has an area where you can clamp it - you have to be "in that range".

I have seen some recommend a 89-90 CR Honda forks as a set of forks that will bolt on - the problem is that it is the worst fork ever made and by a wide margin.

I have a set of marzocchi shivers off of a cannondale that I purchased, new, off of e-bay for $189. They look like they will "go" - the clamping surfaces on this fork will work with the existing steering head length. A set of BRP triple clamps off of a CRF look like they will work. Probably have to machine a wheel spacer and axle. Then find a caliper holder that will line up with my existing front rotor. Machine a small spacer to allow the XR steering stem to be pressed into the CRF triple clamp (from BRP).

I talked to my friend about rounding up some leftover cannondale forks and coming up with a kit - he doesn't think we could sell enough of them to justify it. At this point - the masses would rather put their money towards a new shiny aluminum frame instead of fixing up their old XR...

- jeff

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I put 91 CR125 upside downs onto my 91 XR250. Straight swap.

Huge improvement. Shock modified to balance it out.

The newer bikes only seem to have an advantage in the open, when they can use there top end power. I love chasing and passing WR250F's

thru the trees, but they blow me away when it opens out

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