mstateglfr 

I ride old steel- a handful of road and touring bikes 1980 thru 90, so all traditional tubing. Also have a modern steel gravel frame thats OS tubing.

I am going to build a frame this winter(under the watch of someone who builds and teaches) and want to build a road bike.

So 415mm compared to 435mm chainstays on a modern OS steel frame- will there be a lot more noticable deflection/twisting of the BB and chainstays, or is 2cm not significant?


I would guess the chainstays will be 420mm or so, but just curious to hear from those who build how much difference there is.

Canaboo

Unless you build one of each you'll never notice.

dsaul

I built my Road frame with 407mm chainstays and my Gravel frame with 435mm stays and I can't tell a difference in terms of flex. Both were built with 3/4" round .035" tubing for chainstays, so the stays are pretty stiff to begin with.

Andrew R Stewart 

Humans' perception is only exceeded by their willingness to be led/influenced by others.


I have snubbed short stays for years as I see no bennies and a lot of short comings (bad pun). Go long and ride well. Andy

bikemig 

Looking forward to checking out the bike once you're done!

unterhausen

I'm really horrible at telling bike characteristics apart. I have 2 bikes with about 2 cm different stays, the longer stays are thinner, and I can't really tell the bikes apart at all. I just wish the one with the shorter stays had at least another cm longer stays so I could fit bigger tires. I have always wondered if the people that think one bike is a lot different from another bike have scrupulously transferred their position from one to another. That's a mistake I have made many times.

mstateglfr 

Appreciate all the responses.

I can tell a riding difference between my 450mm touring bime stays and my road bikes that are arpund 415mm, but that is overall so taking into account the rest of the geometry.
Wasnt sure if idolating 1 thing like chainstay length would mean much or not.

This bike is going to be completely overthought prior to starting and ultimately the guy teaching the class is going to know best and all the thinking will have been unnecessary.

fietsbob

just a swing arm sticking straight out, or the base of a Triangle?

If the seat stay is bent, like a fork blade J, lt will have some flexibility..

TiHabanero

Two weeks ago I replaced my road frame with 40cm stays with one using 43cm stays, and moved all of the parts from the former to the latter, including wheels and tires, I feel absolutely no difference in stiffness whatsoever, but have noticed cornering at high speed requires a larger arc through the turn. The tubing is exactly the same tubing throughout the frame.

fietsbob

it is a rear Triangle after all , triangles are strong structures..

FamilyMan007

My latest bike design included longer chain stays (435mm, I am down to about 185cm tall and shrinking slowly).
Just loving my new bike (completed my first double classic - 200 mile - one-day ride this summer).

My comments include:
~ no difference in flex I can detect vs Synapse with shorter chainstay;
~ wonderful feeling going downhill (added nearly 10kph to my comfort zone);
~ doubt I will get another bike, but if I do I think I would regard a shorter chain stay as a negative;

waterlaz

Well... that is rather easy to estimate. A 435mm chainstay will be (435/415)^3 = 1.15 times more (15% more) flexible than a 415mm one.

Andrew R Stewart 

Is this with the stay as a part of a frame or just the stay itself? I suspect this is with the stay as a separate part, not as it's is in a frame. If so then this 115& more flex might not transfer over to a built frame's measurement. Andy.

waterlaz

That's just the stay itself of course. But I believe that only chain stays make any real contribution to the lateral stiffness of the rear triangle. So at least that's what we can predict. I have no idea as to how much does the rear triangle flex contribute to the overall feel of the frame.

unterhausen

I don't see how you can model a chain stay as a cantilever beam. And the chain stay is a part of a complex structure resisting pedaling forces. Imagine only changing the chainstay length and seeing what effect that would have reacting to a side load at the bottom bracket. The seat tube, down tube, and seat stays all resist a force like that, and I think the rear hub also plays a significant role. And in use, the real stiffness of the frame to a side force is dominated by the headset. I don't think we could even agree on a loading condition.

waterlaz

Because it is one. It does suffer some compression/tension loads but those cause no measurable deflection.

The seatstays are so thin and so long that they provide no stiffness to the rear triangle. (except for being incompressible, that is not changing their length).

Either I misunderstood this statement or this is horribly wrong.

unterhausen

you can't ignore the hinge in the middle of the system when talking about stiffness. Some not-inconsequential amount of lateral stiffness is supplied by the rider. I know I'm a lonely voice in the wilderness on this point.

But ignoring that, my main point was that, in the system as ridden, modeling the chainstay length change as a cantilever L/L^3 is going to overstate the difference in stiffness significantly. For the factors I cited and you dismissed because treating it as a cantilever in isolation is so much easier.

ksisler

Ditto Andrew ... also never saw much value to short ones. Likewise for very big bike for very big riders (like both 6'8" and 275 lbs) needing lots of tire clearance, fenders, etc.; Attached is technically doable and not difficult to achieve 50cm stays, assuming well executed brazing and pinning. Starting with materials such as "NOVA CRMO TANDEM CHAINSTAY OVAL 1.0 WALL (XCS214OV)" works well and they are inexpensive.

duanedr 

If all other dimensions are the same, you'd notice perhaps increased stability and perhaps slightly less tight turning capability. Designers should attempt to mitigate these traits with different fork offset or BB drop (or other dimensions) to achieve neutral handling with the longer stays. It sort of depend on what you ask for.

As for flex, I doubt you will notice.

Damon Rinard did this test across a broad selection of frames and found that that stiffest (big tubed Alu track bike) and noodliest (Columbus Air) exhibit deflection ranging between 0.26" and 0.86" under a 47.5lb load at 90 degrees.

The Rinard Frame Deflection Test

I remember, back when I worked in a shop, guys would come in and ask how stiff a frame was. I would always cringe when they would put the pedal down at 6 o'clock and push on it sideways to feel how stiff it was - it would move 2-3 inches! The tire would nearly roll off the rim, the spokes on one side of the wheel would go slack, the pedal and crank arm would flex, the front suspension would compress! !!??

Well, the point is the tires and wheels and other parts flex potentially in 'inches' so, the increased flex in a frame from 2cm longer stays will be un-noticeable. IMO

mstateglfr 

Interesting posts, i really appreciate the discussion. Its nice to get away from marketing hype and hear experienced views.

CliffordK

My driveway goes through a short section of about a 16% slope. It gives a good place to observe traction characteristics of a couple of different bikes. I also don't drive enough to get the needles knocked aside, and the moss cleaned off.

I have one folding bike that gives me an upright seated position on the bike, and I believe short chainstays. It is really hard to keep the front wheel on the ground while climbing.

On the other hand, on most of my road bikes, I like to climb the section standing, and that tends to throw my weight forward enough that I tend to have troubles with traction, especially when wet.

I think longer chainstays also negatively impacts my traction. It is pretty sensitive.

I have one bike with a curved seattube, and effectively short chainstays. It seems to climb like a champ, although my entire body position is pushed a bit forward on that bike. However, it has other issues with the front derailleur. In particular, derailleur clearance over the chainring depends on the seat tube coming out of the bottom bracket in a straight line, and front derailleur capacity is determined by the angle of the seat tube. Anyway, the curved seat tube messes up both adjustments.

I do tend to carry cargo, and heel clearance is a pain.

Anyway, for carrying cargo, I'd choose longer stays for better heel clearance (also depending on trailer attachments).

For road riding without cargo, I might be tempted to use a shorter stays for better climbing traction, and don't really see any downsides of it other than big tire and fender clearance, and clearances around stuff like derailleurs and water bottle cage brackets which are now obsolete.

Sorry, no "perfect numbers" yet.