Framebuilders - How to quantify the effect of chain-stay length on handling

Three frames, each with the same front to center(600mm) but with 3 different chainstay lengths.

Frame 1 410mm
Frame 2 440mm
Frame 3 460mm

How would placing a set amount of weight on the back effect the handling.. say 15% of the rider's mass.

Is there even a way to describe this?

"How would placing a set amount of weight on the back effect the handling?"

are you talking about baggage here, as with touring bikes? I don't think there is much difference in handling, obviously not much compared to changes in the front end. The main reason I build longer rear ends is heel interference, ride, and greater room to actually get stuff on the rack. Most touting bikes, even so called long stay models are not long enough in the trunk to properly support tents bags or mats. Overhang isn't a big problem just kinda messy looking. You can build a bike using the full chainstay length, trimmed only enough to cope it in, and it will make if anything a better bike. It just doesn't handle as well in the pack for racers, or climb as well I am told, but for most kinds of every day riding it might be superior.

"How would placing a set amount of weight on the back effect the handling?"

are you talking about baggage here, as with touring bikes? I don't think there is much difference in handling, obviously not much compared to changes in the front end. The main reason I build longer rear ends is heel interference, ride, and greater room to actually get stuff on the rack. Most touting bikes, even so called long stay models are not long enough in the trunk to properly support tents bags or mats. Overhang isn't a big problem just kinda messy looking. You can build a bike using the full chainstay length, trimmed only enough to cope it in, and it will make if anything a better bike. It just doesn't handle as well in the pack for racers, or climb as well I am told, but for most kinds of every day riding it might be superior.

Yeah, basically. Many people tell me the handling of a touring bicycle improves with weight in the rear, i am wondering how one figures how much weight and at which length of chainstay gives the optimal distribution for smooth cornering for such a design. How would shortening the chainstay 20mm affect things, 40mm? Likewise would some negative effects be noticed on the shorter chainstay bicycle.

I regard them as two somewhat separate issues, one being the handling of the bike generally, and the other being how the bike is loaded. Way back when the low-riders were first coming out, and the previous average set-up was rear panniers and a front handlebar bag, they had to sell us on the idea of all that weight on the front wheels. At that point it was suggested that ideal handling occurred when the front carried 60% of the weight. This has become gospel these days, but there are as many individual approaches as riders, and it can be difficult to split the weight that way depending on a range of factors, like how much weight one is really carrying, bulk, and on an on. I mostly don't worry about it too much. These days we see a return to rear panniers only, particularly given the popularity of super lightweight gear. We also have some riders who put all the weight on the front with a sleeping bag to the rear; all the pannier weight in the front and a trailer, and so on.

As far as the rear axle position is concerned, the too short position is not recommended for practical reasons like you can't get wheels in there, mudguards, etc... As far as going long is concerned It just smooths out the ride. I don't find any real handling difference, since the bike is mostly used for straight running. I like to be able to ride the white line which gives less resistance where present. Jobst Brandt who is well known for his technical writings on cycling, and seems to do training runs and credit card touring, apparently uses a frame with the longest stays he could get added on them, just because it's all upside even for his riding style. Short wheelbase seems to be a racing type thing, whether offroad or road. If one where to tour on a Rans one could have a wheelbase as much as 20 inches longer than on a standard touring bike, so I don't think 20mm is something to expect dramatic results from. Longer wheelbases were commonplace on older bikes, but today most bikes are sold on some reflection of racing results more than practical uses.

I regard them as two somewhat separate issues, one being the handling of the bike generally, and the other being how the bike is loaded. Way back when the low-riders were first coming out, and the previous average set-up was rear panniers and a front handlebar bag, they had to sell us on the idea of all that weight on the front wheels. At that point it was suggested that ideal handling occurred when the front carried 60% of the weight. This has become gospel these days, but there are as many individual approaches as riders, and it can be difficult to split the weight that way depending on a range of factors, like how much weight one is really carrying, bulk, and on an on. I mostly don't worry about it too much. These days we see a return to rear panniers only, particularly given the popularity of super lightweight gear. We also have some riders who put all the weight on the front with a sleeping bag to the rear; all the pannier weight in the front and a trailer, and so on.

As far as the rear axle position is concerned, the too short position is not recommended for practical reasons like you can't get wheels in there, mudguards, etc... As far as going long is concerned It just smooths out the ride. I don't find any real handling difference, since the bike is mostly used for straight running. I like to be able to ride the white line which gives less resistance where present. Jobst Brandt who is well known for his technical writings on cycling, and seems to do training runs and credit card touring, apparently uses a frame with the longest stays he could get added on them, just because it's all upside even for his riding style. Short wheelbase seems to be a racing type thing, whether offroad or road. If one where to tour on a Rans one could have a wheelbase as much as 20 inches longer than on a standard touring bike, so I don't think 20mm is something to expect dramatic results from. Longer wheelbases were commonplace on older bikes, but today most bikes are sold on some reflection of racing results more than practical uses.

Excellent info... thanks for taking the time to write it out. I had heard about the "Great chain-stay shortening" via one of Brandt's archived newgroup postings. I figured 20mm wasn't so drastic but there are people out there raving about how it changes everything. While I haven't heard any discussion on the 60/40 weight distribution I suppose 60% is something to shoot for.

Anyway, I am off to sort through more marketing claims.. Up next do disc brakes mounted on chain-stays allow for thinner seat-stays for a more supple ride... :)

The reason racers like the shorter chainstays is because it is easier to get the bike underneath you when you stand up to sprint or climb. It is somewhat easier to stand up and lean down on the pedals if you can get the bike underneath you, and the shorter chainstays help that. Other than that, the longer chainstays seem to do almost everything else better. The ride is better and there is more weight on the front wheel, helping handling in corners (almost 2/3 of the weight of a bike is on the rear wheeel, not quite the optimum 50/50 balance the motorcycle guys strive for).

Yes and also I suppose shorter CSs are a bit stiffer, something racers would favour.

But yes generally speaking longer stays mean a bit more weight up front, perhaps more comfort over large bumps, and perhaps a longer turn radius? It's hard to know specifically, especially if a load is in the picture. From one day to the other you might have different weights in your panniers, and that may just counter balance or exacerbate the effect of longer stays. And for handling I would agree that balancing the load is important, assuming a given front-end geo. For example having all the weight at the back makes pedaling out of the saddle very awkward. But putting weight up front with a bike that has lots of wheel flop will make the bike fall badly into turns.

I'd say 20mm more is not that big in any case. Older horizontal drops had that amount of travel. For a touring bike with fenders, big tires, rear rack and say 72deg ST I'd stay you'd probably need a mini of 43-44cm. So take it up from there!

I think short chainstays for racers were a quest for stiffness and possibly low weight. Back in the day when all chainstays were the same size, shorter=stiffer.
Now that you can pick and chose wider ones, you can get stiffness without shortness.

I wonder how chainstay length is (should be) related to the size of a rider. With a constant seat-tube angle, bigger riders are placed further back. With larger frames having shallower angles, this throws the rider even further back. This seems to call for a rear axle futher back to ensure good weight distrubution.

My own feeling is that big riders need big chainstays to give the same weight distribution and "rider feel" as a medium rider on med bike. Also the seat-angle is really an attempt to fit the rider to the crank length rather than other way around.

Similarly with small riders, small wheels at the rear permit shorter chainstays and a similar weight distribution to the medium case.

Just to clarify, the 60 40 I referred to relative to low riders/racks/bags is the weight distribution of the panniers, not the weight at the axles. The arbitrariness of this can be seen in the fact that it gets used regardless of the actual weight of the panniers...

Just to clarify, the 60 40 I referred to relative to low riders/racks/bags is the weight distribution of the panniers, not the weight at the axles. The arbitrariness of this can be seen in the fact that it gets used regardless of the actual weight of the panniers...

Ah, alright... what would ideal distribution over axles be? even?

I've seen the guideline 55% rear/45% front not loaded with rider. Calculating for some of my bikes, I need a real long CS and that's with a lot of upper-body weight. But, the interpretation always seems ambiguous.