Aluminum Vs. Chromoly Chassis suspension setups

[Shawn_Mc]

This has been buggin me since the MEC race.

Dungey's bike looked like shit in those rollers. The rebound was spastic..really really fast from fully bottomed until about 3 or 4" to fully extended and then its was super super slow. It was flippin wierd. Like it only packed in the last 30% of the stroke. Prior it looked way too fast!

The fact that he was able to go as fast as he did on the thing I think shows more talent than he normally shows.

Knowing that he knows what he likes, Im curious to the nature of the difference from the aluminum chassis vs. the Chromoly chassis the KTM runs.

Ive never tuned at steel framed bike. Ridden lots but I hadnt messed with the suspensions. Seems the Chomoly bikes would be more lively in the chassis. Where the aluminum ones would be deader..not as springy. And how that acts on the suspension itself is what Im curious about. Fore/Aft etc.

[Spocko]

rigidity to weight ratio would be a factor in what they decide to run i think. While the two different materials would differ in how they flex and store energy which one is better or worse I'm not sure. Good topic tho, interested to see what people think of the two.

[bigbludo]

Personally having ridden both ktms for years and yz's for a year, I can say the chromo frames have a more deadened feel to them as If they act as part of the suspension to a point with greater flex characteristics. Its harder to make aluminum as compliant and my yz shows it especially in the rocks, where you have to pay more attention as the bike reacts quicker to things on the ground, especially hard pack. Its a livelier bike per say, meaning the suspension is working harder as the chassis flexes less. The am-pro yam team were altering their frames to add in some flex last thing I heard.

[grayracer513]

At least in the case of the YZF's, there is more to the question than which material is used. The overall mass in the first generation aluminum frames was more centralized than in the steel bikes, and this is even more true of the latest version. While this makes the bike easy to maneuver, it also creates problems for suspension tuners, because the same characteristic that let's the rider change the yaw in the air more easily allows a bump striking either end to change the pitch more easily.

The problem then becomes how to keep the suspension robust enough to deal with the full weight of the bike when it is flat landed, for example, while allowing it to be compliant enough to keep the chassis from being pitched around its CG when hitting an obstacle with one end.

It would be far easier to tune the suspension if the weight were divided into two equal masses, each perched squarely over one wheel with minimal weigh in between, like a barbell, but you'd have a much tougher time steering it.

[mog]

sounds like too much free bleed to me

[djcr]

sounds like too much free bleed to me

are you refering to the op mog?

[Shawn_Mc]

are you refering to the op mog?

I was thinking they hadn't worked out the rising rate in the linkage just yet. But at that level, I dont know why they wouldn't just copy the Suzuki stuff to a tee and duplicate the shock as much as possible and at that point the Chromoly Chassis would be the wild card.

The way aluminum work hardens it seems like building flex into the chassis would be kind of an ethereal thing. Like you'd have it nailed down, then 5 hours later on the same bike under a pro that chassis would be junk because the aluminum work hardened and stopped flexing as much in the same situations. Where the Chromoly would seem to remain more consistent for a longer period.

ahhhh, its just me thinkin out loud again

[mikerides33]

I was under the impression the linkage/ rising rate mimics yamaha.

[highmarker]

here we go again, let's all go back to steel swingarms and handlebars too, LOL

[grayracer513]

Anyone who thinks aluminum won't flex and stay flexible for a long time has no experience with the earlier aluminum road racing bicycle frames such as the Alan and Vitus. They flexed to a fault, and in the larger sizes, were unusable by stronger riders.

IMO, as someone who has built a few frames in the past, I think the whole concept of chassis flex as a good thing, something that contributes to a bike's handling in a positive way, is massively exaggerated as to the effect it really has on things in many people's minds.

[GDI70]

very good thread here. let me just say, i loved my 96 cr 250! the subsequent honda 1st gen alum. gave too much feedback, but by using the rubber top clamp isolater bushings, they helped a bunch. even foam in the bars was an improvement. i really like the ergos of the new suzuki chasis. to me it just works well. the rmz's just have that "feel" to me.

[mikerides33]

I ride an aluminum framed Cervelo Soloist road bike. Some roadies squawk at the idea but it is very comfortable for aluminum even with tire pressure at 110psi. That being said mx frames are much bigger and for a guy who goes from a KX450 to a 350SXF the difference is major. I like to feel the track and run a firm suspension setup in my bikes and feel that somehow with the chromoly frame I fel more connected to the ground. It's a different feel like I am pushing the bike more into the dirt while braking. Perhaps it's my imagination.?@#$$

[Piney Woods]

very good thread here. let me just say, i loved my 96 cr 250! the subsequent honda 1st gen alum. gave too much feedback, but by using the rubber top clamp isolater bushings, they helped a bunch. even foam in the bars was an improvement. i really like the ergos of the new suzuki chasis. to me it just works well. the rmz's just have that "feel" to me.

WOW!!! Everything I am searching for suspensionwise was in my Jeff Slavens tuned '95 CR250. Steel. My '01 aluminum is driving me crazy, to the poor house and beating me up. Steel/aluminum, I don't know but I have my suspicion. Thanks again GD170.

[grayracer513]

Comparing aluminum road bike frames can be illustrative. The Alan and Vitus were limp and only useful by strong riders in the smaller sizes. They were favorites for long rides on rough roads because of the smooth ride they had as a result of that same flex.

The other side of that was the original Cannondale frames. These were also all aluminum, but built from large diameter tubes to increase rigidity. No one was ever strong enough to flex one in a climb much at all, but they quickly fell from grace because of the excessively harsh ride.

So, yes, frame flex yielded a more pleasant ride, but at the expense of performance. The point I'm trying to make is that both frames, one rigid, one springy, were aluminum. That to me indicates that the material itself is not to blame for the harsh feel the old CR's had, only the construction. What really happens is that a very rigid frame highlights all of the shortcomings in the suspension, which is where the ride quality should come from, not the frame.

[kawamaha]

My '01 aluminum is driving me crazy, to the poor house and beating me up..

funny, at this time my 01 CR250 was the best handling and cornering bike I have ridden. also I valved it a lot stiffer than my previous bikes (but considerably softer than stock) and loved the suspension too.

[Piney Woods]

funny, at this time my 01 CR250 was the best handling and cornering bike I have ridden. also I valved it a lot stiffer than my previous bikes (but considerably softer than stock) and loved the suspension too.

I understand but have lost the humor. My 01 was very close with just a lower oil level, then i went for great suspension. Now either overly stiff or overly soft, no middle ground. Yes, I was much better off and had a lot more money in my pocket. Lot of very nice, knowledgeable guys have offered help though. Thats the silver lining. I do love the motor and handling so will give it another shot.

[mgorman]

I see we have a few roadies in here too. I recently bought a BMC SL01 and that thing rides so bad it will be on EBay in a few weeks. I'm going back to a more compliant frame like my half breed Six/13 or a steel CX bike.

Frame flex definitely made a difference for me but it was between 2 different model years of Hondas of the same size. (95 XR250 vs 99 XR250) The 95 flexed so bad you could see the bike warp in the rough. AT one point I thought the frame was broke.

I just rode a CRF250 back to back with my 250XCF and honestly, the suspension on the CRF was so bad, I couldn't do a fair comparison unless what I was feeling was the aluminum but those forks killed my wrists and the rear felt to be sagging in comparison to the fork.

I'm hoping I can help him get that thing set up better and see how the 2 compare for real.

[Bushmechanic]

IMO, as someone who has built a few frames in the past, I think the whole concept of chassis flex as a good thing, something that contributes to a bike's handling in a positive way, is massively exaggerated as to the effect it really has on things in many people's minds.

So, yes, frame flex yielded a more pleasant ride, but at the expense of performance. The point I'm trying to make is that both frames, one rigid, one springy, were aluminum. That to me indicates that the material itself is not to blame for the harsh feel the old CR's had, only the construction. What really happens is that a very rigid frame highlights all of the shortcomings in the suspension, which is where the ride quality should come from, not the frame.

my thoughts exactly, you hit the nail right in the nads there :busted:?

[Shawn_Mc]

What really happens is that a very rigid frame highlights all of the shortcomings in the suspension, which is where the ride quality should come from, not the frame.

If the connection between the bars, seat and pegs is happy, who the hell cares?

If the package in the end works, and I'm talking about a motorcycle, not a bicycle here, why would it matter?

My thought was more towards the suspension set up if the two different materials were similar in flexibility.

[mog]

well many respected tuners say valving is only 30% of suspension and just as much tuning can be done by engineers building in the right amount of flex