Why doesn't chainstay length change with frame size.

My point is you can’t compensate with body position to effectively change front to rear weight distribution

I reckon that’s true, as your feet are always on the pedals. Obviously you can change the fore-aft weight distribution from that neutral point but only by as much as you physically can without your feet actually leaving the pedals. On an XC bike I always feel like I’m hanging right off the back of the bike on descents where I would hardly need to move on my Enduro bike. They are not the same for sure.

JCL – Member
Funny enough he went from 420 to 440 rear centre to try and get that bike to work.

For him. Funny enough, Brosnan and Ropelato left the geometry unchanged, and Brosnan was only a few points behind Gwin. So what does that mean?

Great photo’s of the DH guys in chutes etc but I’m talking cornering.
Look again, most of them are cornering.

Brosnan rides a small (possibly medium this year) so a bit less FC/RC differential. Plus he’s been on the bike since a junior so he’s had a long time to compensate?

Gwin came off a more neutral, balanced bike and was a mess on the Demo. You could see it was weight distribution related, especially in that early Redbull promo video. I honestly knew then that he was going to have a mare on that bike.

If a guy like him can’t ride around it how important does that make rear centre length for guys like us?

That said I’m not really arguing this point based on DH bikes, they’re very specific use bikes. Which is why I kept saying trail/AM bikes. Bikes that go up and down and should be as balanced, neutral, handling as possible.

JCL
Gwin came off a more neutral, balanced bike and was a mess on the Demo.

He also said he didn’t ride any proper dh tracks, any world cup grade tracks to train. Just his local dh trails.

We’ll probably never really know, Gwin might not know why he had a mare switching to the demo. If there’s any truth in what you’re saying though, it’s that the cs length can make a massive difference. I personally doubt that’s what his issue was, to me it seems like an excuse, but it could prove that cs length is noticeable anyway.

That geometry didn’t slow Hill or Brosnan down.

Demo. You could see it was weight distribution related, especially in that early Redbull promo video. I honestly knew then that he was going to have a mare on that bike.

This video? Reeaally? You knew he was going to have a bad season based on this? JCL is the STW forum name for Sam Hill and I claim me free can of Monster.

JCL Which is why I kept saying trail/AM bikes. Bikes that go up and down and should be as balanced, neutral, handling as possible

If you mean handling, well yeah that would be nice. But I doubt that can be got without bias/compromise. I’ll happily take a bike that can climb okay, but is a dh weapon, over something thats a great climber but a twitchy descender.

To be fair Hill crashed his brains out on the bike a number of times as has Bronson but yeah it’s not the best example as those guys can usually ride around anything.

I could tell from that vid because he looked so different to his riding style on the Trek. Dont forget, 30mm rear centre difference between the Demo and Session. Huge. Look at the 90’s huck to rear wheel landing he does. You think he meant to do that? I reckon he was wondering what the hell was going on.

That bike was the worst example of what I’m talking about. It was a nightmare working out rear spring rate. Weight is so rear biased that the rear has to be oversprung to compensate. You end up hanging over the back to make sure you don’t get bucked. Run softer rear spring rate and it choppers out massively on flatter corners and the front washes out.

I simply don’t believe you can compensate for it with a forward weight shift and even if you can it doesn’t feel natural and you’ll be on a much finer line of eating shit.

If you mean handling, well yeah that would be nice. But I doubt that can be got without bias/compromise. I’ll happily take a bike that can climb okay, but is a dh weapon, over something thats a great climber but a twitchy descender.

I agree 100%. The only compromise is slow speed tight turns but I’m happy to take that trade off as I can be precise at slow speeds and get my lines sorted far easier than at high speed. I’ll take that trade off for a bike that is stable/balanced on the grip limit. It’s marketing that has led to the perception that bikes with longer than “as short as possible chainstays” are not agile etc. I used to believe it too but it’s BS, like every other measurement, there’s an optimum.

JCL

I agree 100%. The only compromise is slow speed tight turns

Personal preference etc etc but I notice a lot more positives than just slow speed cornering. The things I notice short chain stays contributing to would be easier to lift the front end, easier to manual for those who can, easier to pump terrain, easier for me to jump with and better low and high speed cornering.

I find that bikes with longer stays can sometimes have an unpredictable weight shift mid corner or on corner entry which is unsettling. I’ve not personally noticed this twitch with shorter cs bikes. Rather, I find if they do get unsettled mid corner it’s more manageable.

I also feel that shorter chainstays contribute to a more direct pedal feel and have more snap or response under power. Could be me.

I like a long wheel base up to a point, but i personally think the best compromise is to have a long tt, and short cs, not just a limousine of a thing, because as I see it, the only downside of short chainstays is a loss of climbing traction, especially out of the saddle, which I can easily circumvent by staying in the saddle. Long stays for stability yes, but not for handling, same as vehicle wheelbase in general.

Funny you should post a hill climbing mx bike JJ. Gwin’s preference for a longer cs may be due to his two-wheeled background, motocross.

Look at the 90’s huck to rear wheel landing he does. You think he meant to do that?

When this vid was first released, someone also mentioned that jump (may have been you JCL). I think it’s obvious he meant to land back wheel first as just after landing there’s another kicker. I don’t know about you but i’d not be landing flat just before a lip of another jump – especially at that speed.

Did someone say ultra short chainstays?

Claud Butler Ultra-Shortbase Tandem by Ben Cooper[/url], on Flickr

😀

You’re not wrong Jim, for a stylish skillful rider short stays are simply more fun to ride. JCL sounds like a racer so fun is perhaps lower on his agenda. 😉

Yep those hill climb bikes are obviously forward biased but do you know what a normal dirk bike F/R weigh distribution with rider is? 45/55. What’s a short RC modern medium mountain bike? 30/70+.

But those guys who are 40 years ahead of mountain bikes and with 10X the R&D don’t know what they’re doing right…

Dirt bikes can afford to wheelspin a bit if it gives them better front wheel traction. MTBs not so much. I don’t think you can directly compare the two.

Anyhow, 70/30 sounds extreme, 60/40 is more normal for bikes.

Dirt bikes can afford to wheelspin a bit if it gives them better front wheel traction. MTBs not so much. I don’t think you can directly compare the two.

No they don’t set dirt bikes up like that. Not from everything I’ve read. They want 100% stable, neutral handling. Go sit on a well set up dirt bike and compress the suspension. They’re very even in their response. Half the 420mm RC mountain bikes don’t compress the fork 1mm when you jump on the pedals.

For some bikes 30/70 is conservative. Especially a bike like a large size Kona Process or 26″ SJ Evo.

Yes, and if bicycles magically propelled themselves along the trails, a 55/45 split would be pretty much perfect. But they don’t, the rear wheel is driven by a motor system that tends to fall off if the rear wheel loses traction for more than a fraction of a second.

So perfect weight distribution is sacrificed for increased rear wheel traction. A 2WD bike could well get closer to 55/45, I don’t know if the companies who have built 2WD bikes like Christini et al have considered that.

Interesting debate this. Be interesting to see if Specialized choose to shorten the chainstays on the next evolution of the Stumpy 29 as a lot of people have predicted following the success of the Enduro 29.

The Enduro sure feels nimble for a big hitting 29er and it’s actually easier to get the front wheel off the ground than my old short wheelbase 26″ bike. It does feel like I’m sat well back on the bike, but very much “in” rather than “on” the bike. I like it so far, but haven’t had chance to push it hard up or downhill yet.

Yes, and if bicycles magically propelled themselves along the trails, a 55/45 split would be pretty much perfect. But they don’t, the rear wheel is driven by a motor system that tends to fall off if the rear wheel loses traction for more than a fraction of a second.

Give me a rear wheel that looses traction before a front wheel all day long.

What I recommend some people try is a unicycling while holding a bar/stem/fork/wheel out in front. Zero length chainstays. Totally wicked fast in the corners dude.

JCL brought up Hill when describing his own lack of skill in 2 wheel drifting. Hill and is indeed king of thus skill in DH racing and has always ridden short stay set ups. Becoming confidently stable while drifting does not require long stays. It requires practice.

Odd that he used Sam as a referance at all, Sam was credited with having adifferent riding style on the flat pedals, leaning right forewards in the corners to weight the front wheel and allow the bike to drift!