In explaining to someone the difference between compact and standard cranksets, I mentioned that you can’t just slap compact rings on a 130 BCD crankset. Some companies, however, do manufacture standard-size chainrings (53t, etc.) for 110 BCD cranksets. See, e.g., http://www.vueltausa.com/components/corsa-comp-crankset-1.html. I’m sure there are other examples.
If it’s feasible to make a 53t chainring with a 110 BCD, why bother with the 130 BCD cranksets at all? It would seem only to limit your options. I can imagine two answers: (1) Aesthetics; and (2) Something to do with mechanical advantage (perhaps the wrong term) from having wider spider arms. Still, I’d appreciate an answer from someone who’s not just pulling speculation out of his a**, as I’m doing. Any thoughts?
One reason is stiffness. Crank spiders are much stiffer than chainrings, so having more spider and less chainring is better. Campy cranks are 135 BCD and track cranks are usually 144 BCD.
overall crank stiffness, which has a direct effect on shifting performance, (ignoring the contribution of the BB/frame) relies on spider stiffness and chainring stiffness.
once the chainrings get beyond ~52T size 110BCD chainrings have too much lateral flex and can affect shifting performance especially for larger cyclists. Yes there are companies that produce 53T 110BCD chainrings but this is not an optimal design, and often these chainrings have to be beefed up weight-wise to compensate.
Furthermore, you have to bear in mind that in the “real” world of road cycling, 53/39 is the smallest ratio that is used, with the exception of the hilliest of the hilliest mountain stages in the grand tours.
putting a 54T or 55T chainring on a 110BCD crank would make for quite the noodle, especially in prologues and TTs.
Thanks for this - I always wondered why there was a limit on 110 BCD cranks. So what determines the step-down width from the big ring to small ring (ie how come the smallest you can have with 53 is a 39?).
well actually the smallest a 130BCD spider can accommodate is 38T. This is governed by the diameter of the spider. get below 38T and the bolt holes get too close to the teeth.
In fact Shimano did spec 52/38 and 52/39 combinations on their entry level sora/tiagra/105 groups. Don’t know if this is still the case.
the other consideration is the difference between the big and small chainrings. Modern FDs are more tolerant and can shift 50/34 quite well (16T difference) but the larger the difference the more apparent the drop-off in shifting performance.
I used to run a 50/38 on 130BCD for a short while and i could confidently go from 38>50 while out of the saddle midway through a climb but i would be more hesitant to do that with 34>50.
I recently bought a used SRM that’s a 110/130BCD hybrid. I’m growing to appreciate how flexible this combination is. You can run basically any combination of chainrings you could imagine on this thing. To my knowledge, nobody else makes such a crank. I think the better question is- why isn’t every crank a 110/130 hybrid? Aside from the need for a second set of chainring bolts, I can’t think of a drawback.
I recently bought a used SRM that’s a 110/130BCD hybrid. I’m growing to appreciate how flexible this combination is. You can run basically any combination of chainrings you could imagine on this thing. To my knowledge, nobody else makes such a crank. I think the better question is- why isn’t every crank a 110/130 hybrid? Aside from the need for a second set of chainring bolts, I can’t think of a drawback.
I love this combo and wished more people would develop cranksets like this. I think LOOK uses it also. A crankset like the new Shimano design that has the chainrings bolted on from the backside could accomodate this. I’ve been asking for 52/36t cranksets for a few years now. We are finally getting some options available. Several of the Felt TT/Tri models use a 5238t combo on a 110mm BCD in 2011. Vision/FSA made an aero crankset with this option.