Chainstay length

[saab2000]

Can any of the builders here comment on the effects of a longer or shorter chainstay length. I am quite pleased with my new/used Serotta CIII. It has (well, I haven't measured them, but the chart says it has) 41.5 cm chainstays. I have not yet hammered down a mountain or anything like that, but the bike feels nice and balanced, fore/aft I mean.

There seems to be a pretty big gap between the tire and the chainstay. Some so-called pure racing bikes have a much smaller gap and presumably shorter chainstays. But I also know this bike, in contrast to many other pure racing bikes, has 8cm of BB drop.

I don't know much about design and the effect of changing these dimensions. That is one reason I was so happy to get a stock Serotta. I guess they have it figured out up there in New York. I like racing bikes and this one seems 'raceable' by most standards.

Would having shorter chainstays possibly ruin the fore/aft balance? Any thoughts on this? Obviously getting too short and you have tire clearance problems.

[saab2000]

I know the 'gap' here is already small and I am not wondering about aesthetics. I am wondering why a builder will choose one type of length over another. I assume that there is a compromise between balance/handling/stiffness, etc. when this is all done.

[Smiley]

Saab , what you have here is more of a road bike then a shorter wheelbase higher BB crit bike. The longer wheel base will smooth out the bumps better . Think more compliant rear end .

[Rapid Tourist]

Touring bikes use longer chainstays so that you don't kick the panniers with the back of your heel...

[saab2000]

Smiley,

I am confused. The longer seat stays should not be more compliant. That would imply compression or flexing of the seatstays. That is not possible on this bike. But it is very smooth riding. Of that there is no question.

Comfort is, I suppose, not a bad thing in and of itself if it does not come with performance compromises. But comfort and smoothness are not as important to me as they are to some. Handling and responsiveness are very important. Race-worthy.

I am wondering what effect shorter stays, by say 7 or 8 mm here, would have on this bike. Would the fore/aft balance be negatively effected?

These are things I think about when I am not riding..... I am stuck in Richmond, VA and won't be able to ride 'til Sunday, if the weather holds out in Minneapolis. Way too much time on my mind in the hotel in Richmond.

[Ken Robb]

I think a designer can adjust other dimensions to compensate for any reasonable length chainstay and keep the bike balanced. All things being equal though a bike with longer stays can ride smoother because your butt is not so close to being right over the rear axle. It's like the difference in ride when you ride in the front or back seat of a short wheelbase car like a jeep.
I think longer chainstays also help triples shift well due to less acute chainline angle.

[Ray]

I'm no builder, fitter, or otherwise knowledgeable, but I've ridden a lot of bikes with stays that are long, short, and every gradation in between. In addition to Smiley and RT's points about a smoother ride and heel clearance for panniers, I find that longer stays make a bike feel more stable, all other things being equal (which of course they never are). They can also make a bike feel pretty sluggish if they're long enough. The longer they are, the less the bike seems to move back and forth in response to hard pedalling - its more locked into a straight line and harder to knock askew. Sometimes I think that locked in stable feeling makes the bike FEEL less responsive - not that it necessarily is, but the lack of immediate feedback to your pedal stroke just makes the whole thing seem more planted and less movable. But I think that's mostly an illusion. It may stop being an illusion if the lack of responsive feeling changes the way you ride - bikes like that don't feel like they reward hard efforts so sometimes you stop making hard efforts. But to me, really short stays feel worse, making a bike feel really herky jerky (no offense the Jerk). As with most things, there's probably a sweet spot for any given bike where the length of the stays combined with the front center creates just the right weight distribution for the rider.

-Ray

[Smiley]

Ray , your correct assuming the longer stays are used for carrying a set of weighted panniers. If I ride my tandem solo the bike feels like Cr*p , but once my wife sits in the stoker position all feels well again. My new uniscasi has a 42.5 cm stays BUT this is also in response to a 72 STA and the need to carry a wider tire and fender too .

[Ti Designs]

This subject has been on my mind a lot as the one thing I'm not in love with on my own Serotta is the chainstay length. Picking the right chainstay length for a bike is tricky, there are a lot of factors. Bottom bracket drop increases the angle of the chainstay, thus the need for longer stays. Seat angle also plays a role, steeper seat angles allow the wheel to be pulled in closer. Tire clearance, chain line, heel clearance in some cases... Then there's how the bike rides and reacts - that may be the toughest of all.

The up side of shorter chainstays is hard to explain. I'll use the example of using a shovel. If you grab a shovel with both hands at the top, you're not gonna get much work done (back me up on this one Dirt...). If you hold the shovel with one hand at the top and one in the center, you find that you can move some dirt. When you hit that big rock, and you need to lift it, one hand goes near the top, the other hand goes way down near the other end. It's all about mechanical advantage. The hand at the top is at the end of a lever, the other hand acts as a fulcrum, even though it's doing at least half the work. The force at the spade end of the shovel is multiplied by the ratio of the two distances. Hey, we've invented the lever!!! OK, now look at the bike. You have hands on the bars, you have feet on the pedals (we'll call the bottom bracket the fulcrum 'cause it's a center point between the two pedals) and you have a point of force which is the contact patch of the rear wheel. This example works best when the rider isn't in the saddle, so let's say there's a hill and it's steep, so you're out of the saddle. Pulling up on one side of the bar while pushing down on the pedal of the same side does set up the same mechaincal advantage relationship as using a shovel. The distance from the bars to the pedals is set by the fit of the bike, the distance from the bottom bracket to the wheel is up to the frame designer. The differences may seem small, but the change to the ratio of those two distances can be noticable.

There are down sides to super short chainstays. My Peter Mooney race bikes were 1cm shorter than my Serotta in chainstay length, which is what I point to when I try to explain why they sprint and climb so well for bikes that tip the scale on the wrong side of 20 pounds. They were also dangerous when it first started to rain and the roads became slick. I would have to crawl around corners or the back end would come out from under me. The weight balance also made the bike less than stable, something I never realized until I rode the Ottrott.

It's hard to get companies to make a frame with short chainstays. When I asked Peter Mooney for the shortest chainstays, he wound up shortening my horizontal dropouts (it was a while ago) so I could get the wheel in there without letting the air out of the tire. I asked for same of Serotta and I think I can fit a cross tire in there. Independent Fabrications often points to Shimano as their reason for not going any shorter, the swing across the cassette is beyond what the chain wants to see for bend. Yet a number of bigger companies are fine with putting on chainstays so short that they need to indent the seat tube to keep the wheel from rubbing. Nobody bothers to spell out the pros or cons of shorter vs. longer chainstays, but they do make a difference.

[e-RICHIE]

Originally Posted by Ti Designs

Nobody bothers to spell out the pros or cons of shorter vs. longer chainstays, but they do make a difference.

for as long as you're using a bicycle that is
not direct-drive, there is no upside to short
chainstays - none. and the difference in 1cm
between two choices will not be noticeable to
the rider, but it certainly will rear its head with
respect to the friction and rapid wear of moving
parts, especially in the gear selections that are
not in-plane choices.

[Ray]

Originally Posted by Ti Designs

Nobody bothers to spell out the pros or cons of shorter vs. longer chainstays, but they do make a difference.

Check out Rivendell's marketing material. Grant's a strong proponent of longer stays. Both because of generally increased stability and also because he recommends a very butt-back, upright position which shifts the weight back to the point that you just about need the longer stays and shorter front center to get the riders weight back to center (or 55-45 or whatever it is you're going for). As with other of his ideas, I think this is a good one that he sometimes takes too far for my tastes. I don't ride in a full-upright Riv position but I'm not in a real flat racer position either and mid-length chainstays seem to work great for me, about 42 or 42.5 on the bikes I've liked best. Longer than that and the bike starts feeling like a truck that you CAN'T knock off line, or turn - shorter and it starts feeling like a unicycle, going every which way in response to pedal feedback.

I think other folks market super short chainstays as "stiffer" or more direct, but obviously aren't going to talk about the downside.

-Ray

[palincss]

Originally Posted by saab2000

I am wondering what effect shorter stays, by say 7 or 8 mm here, would have on this bike. Would the fore/aft balance be negatively effected?

Judging from the picture you posted, I'd think removing 8mm of clearance would have the effect of putting the tire right in contact with the seat tube, thereby stopping you dead in your tracks.

And I'd certainly call that "negative".

"Long" chainstays would give you enough room to fit a pump vertically between the seat tube and the tire, or clearance for a tire as large as 35-38 mm with a fender... which would also move panniers far enough aft so as to get them out of the way of your heels.

You don't have long chainstays on that bike. If that tire's a 23, you barely have room for a 25mm, ATMO.

[chrisroph]

TK made my latest spectrum with 42cm chainstays. We talked about it a lot. He can explain things much better than I of course. His primary reason for the stay length was that, since I use a 72deg ST because of really long femurs and sit way back in the saddle, it was all about putting my center of mass in the correct relationship between the wheels. The longer chainstays effectively move my center of mass forward and put more weight on the front wheel than if the stays were shorter. Of course the front center length also factors in.

After riding the bike for a year, I have to say that TK nailed it again. The bike is everything I wanted. Its smooth and comfortable, has great directional stability, so taking off and putting on jackets or vests is easy, its responsive, and it descends like a demon.

I think you are really going to like your new bike. I know you sit back in the saddle like I do. The longer chainstays, coupled with the 8cm bb drop, and 59mm of trail as usually spec'd on standard serottas in the 57-58 size range, make for a beautifully stable and responsive bike when the rider is positioned back and low in front. Please post your impressions when you have a chance to get to know her better.

[e-RICHIE]

[QUOTE=chrisroph]TK made my latest spectrum with 42cm chainstays. <cut> since I use a 72deg ST QUOTE]


with shallow seat angles, longer (as compared
with shorter) chainstays are even more necessary.
otherwise, the seat tube will be too near the tire.

[ergott]

Originally Posted by e-RICHIE

for as long as you're using a bicycle that is
not direct-drive, there is no upside to short
chainstays - none. and the difference in 1cm
between two choices will not be noticeable to
the rider, but it certainly will rear its head with
respect to the friction and rapid wear of moving
parts, especially in the gear selections that are
not in-plane choices.

I would think that CS length cannot be looked at without looking at the rider weight distrubution. SA and setback will have a great impact on what the CS length will "feel" like. What would shoving the wheel 1cm foward do the weight dist assuming the current is 55/45 and there is enought room to do so?