So if the minimum chanstay length that Shimano recommends for all of their road 10 speed components is 405mm then why are most tri bikes made with shorter chainstays? Most triathlon bikes are around 390 or 380mm. Is shielding the rear wheel more important than chainline and shifting efficiency? Would this be a good reason to only run 9-speed shimano on triathlon bikes. I think 9 speed shimano minumum chainstay length is 390mm.
Stay away from crossover gears and you won’t have a problem.
True enough but even without crossover on the ends of the shifting spectrum isn’t anyone here concerned about losing watts to bad chainline on the too short chainstay length? Did that make sense?
One can minimize drivetrain losses by avoiding bad chain lines in the crossover gears. Instead of only avoiding the largest and smallest cassette cogs in the largest and smallest chain ring, avoid 2, maybe 3 if you’re on an XS size.
If you’re that concerned, do the trig, find out which cogs you would need to exclude to make equivalent angles, and then make an informed decision on whether or not 9-speed is the way to go for you.
Any BTR-types out there who can quantify drivetrain losses based on chain angle?
I appreciate the wisdom and insight of what your saying but on a hilly course (like Lake Placid) one needs all options in gearing and avoiding certain combinations isn’t practical. Doing that might lead to a bad cadence and a power spike when the terrain changes. Besides… isn’t the point of having a 10 speed actually giving more options?
Thinking in terms of triangles. As the hypotenuse angle increases near the cogset, the center to center spacing of the cassette causes the problem. Maybe a triple would be a solution.
Any BTR-types out there who can quantify drivetrain losses based on chain angle?Im pretty sure that I read over at BTR that the drivetrain losses are minimal even at high chain angles provided the chain tension is high.
I believe you may be thinking way too much about this.
If you are riding in your 39x27 and you are worried about chain line and shifting performance you are missing the major point.
If you are riding your 53x11 and worried about chain line you are probably riding a gear too hard for as you may be missing the major point.
If you are truly concerned ride a 12x27 with a 55x42 front ride the 55x15 for a nice straight chainline and the 42x23 for a relatively straight chainline. If these gears sound too hard for you, hire a coach.
Wait. What is the “major point” of a 39x27 gear selection that I am missing? One, two, three, I don’t get it.
the major point is that it is obvious that you are unsure about gearing and pacing and rolling hills and your major concern is worrying about surviving. And worrying about chain line and chain stay length should probably be the least of your concerns.
like I said, I think you may be thinking too much.
I don’t understand his post either but I do agree this is a non issue. As the number of gears has gone up chains appear to have got much more laterally flexible and I doubt you’d get significant losses even in a completely crossed gear. Also, shorter chain stays help with weight distribution so fairing the rear wheel is not the only advantage.
If that’s true (and I’m not saying it’s not) then still the question remains. Why is the minimum Shimano chainstay length ~2cm longer than many triathlon bikes?
So if the minimum chanstay length that Shimano recommends for all of their road 10 speed components is 405mm then why are most tri bikes made with shorter chainstays?
A better question would be “Why are triathlon bicycle manufacturers including Shimano in their OEM spec?”.
Shimano or not, it doesn’t matter. Sram 10 speed, Campagnolo 10 speed & Campagnolo 11 speed minimum chainstay lengths are all listed at 40.5mm.
probably worth mentioning the brands you are talking about.
Guys heavily into tri geo frames like QR may use 385mm, but other brands with tri-specific bikes like BLUE remain at 405.
Both use seat tubes with rear wheel recesses. It isn’t either/or.
Right SuperDave. Talking about triathlon/time trial models, in recent 700c frames, Felt, Kestrel, Look, Blue, Scott and others are all mostly within the spec for minimum chainstay length. Other companies such as Cervelo, QR, Kuota, Specialized, mostly fall well below with lengths in with 38-39cm being typical. Still others such as Trek, Fuji and Cannondale are only a hair short at 40cm.
I think it’s a worthwhile question. I don’t feel bothered by the chainline losses personally but I have found that it can be nearly impossible to avoid front derailleur rubbing due to the increased angle. I find that gears that SHOULD be usable (the 18 gear combinations you theoretically should be able to use) end up having enough of a chain angle that the chain will either touch the inside edge or the outside edge of the front derailleur cage despite all efforts to trim it…and this is NOT while using a click-shift front shifter, but rather my bar-end friction shifter.
It’s a little annoying, but doesn’t keep me up at night.
Anyone else have a comment on this topic?
Hi NYSLIM,
Most of the issues have been mentioned:
Very little power loss at even high chain angles, so that’s not a reason to worry about short chainstaysWeight distribution is improved with short chainstays (which was the main reason old tri bikes had dual 650C wheels - even shorter chainstays were possible then.)Shimano’s (and other brands’) minimum spec is fairly recent, maybe within the last 5 or ten years I think. So newly designed bikes may have slightly longer chainstays, even if they aren’t fully up to the minimum.Chain rub on the front derailleur: some customers understand the benefits of short chainstays and are willing to avoid one more gear at each end. But many don’t, and complain of rub. “My road bike doesn’t do that!” Wheel cutout was more of an issue with welded frames. With molded frames it’s less.For thoughtful designers, the actual length chosen is typically a balance of these factors. With good engineering, all those chain stay lengths can be good. With bad engineering, they can all be bad. In nearly all cases, factors other than chain stay length make different bikes truly faster or slower.
Cheers,
Thanks, Damon.
When you say: “Very little power loss at even high chain angles, so that’s not a reason to worry about short chainstays” is there a study on that? Specifically with a bike that has a 38cm chainstay (like my Cervelo P3) are you talking about less than 1 watt, 1-2 watts, 2-4 or more? Do you think there cause for concern for an average age grouper fighting to produce 180 watts at Ironman Lake Placid - a course that requires a lot of shifting and high chain angles? I just say this because with a season of training one works so hard to gain a precious few watts that the thought of loss of even a few watts makes me wonder if I should switch bikes.
Finally do you have any thoughts on the best chain (most flexible) and/or appropriate gearing for a 20mph bike split and a candance of 80-85 that would cut down on the chain angles?
Sorry for all the questions. I just thought I should pounce now that I might have an expert ear.
Cheers!
Pete
Damon, thanks for stating this. Weight balance is one drum I keep beating, and USAT, the industry, and riders seem to be deaf to it. Chainstays can only get so short, regardless of the “recommended minimums” from the component manufacturers. That makes front-centers maxing out the legal limits before good weight balance is even approached…