San Rensho 

I suspect what is also going on is that the gears that people claim are equivalent, are not. For example, a 46/14 is 88.71 inches. A 49/15 is 88.2 inches. Now many people would say that both of these gears are 88 inches. They are not, one is 1/2 inch bigger than the other.

A very experienced track racer could probably feel a 1/2 gear inch difference, and therefore he or she would say that they can tell the difference between different chainrings, but reall what they are feeing is the small difference in gear size.

But I don't buy that a track rcer can feel the difference in rotational momentum between a 48 and 52 tooth chain ring.

Yoshi

I've said it before and I'll say it again - there are dozens of variables and gear inches is just one of them. It happens to be the most important, but ignoring the others is foolish. You will definitely feel the difference between different ring/cog set ups that give you the EXACT same gear inches. The performance difference is probably negligible for most people and I don't even know how the sizes would effect performance anyway. But you will still feel different.

Six jours

I could never feel a half inch difference, or even an inch difference. Two inches, minimum.

As a slight aside, at some point in my coaching career I noticed riders starting to obsess about very small differences in development. You'd hear people talking about an 88.2 vs. an 88.6 or whatever. I always thought it was silly but was soundly poo-pooed by all my riders. Finally I had everyone put on the exact same combination and rolled out all the bikes. There was a three inch difference from shortest to longest rollout. Tires, rims, and phases of the moon apparently wash away any slight differences we think we're making with gearing. I'd like to say that ended the silliness, but of course it didn't. It certainly did make up my mind for me, though.

I doubt I could define "rotational momentum" on a bet. But big differences in how you get the devolopment can be felt. I can't explain it, but I can't explain how my computer works either. My ignorance doesn't mean things don't work the way they do.

CafeRacer

After talking to some old euro guys who know their stuff (Or myths) I still say it has nothing to do with flex, a more direct torque path, leverage, weight or any of that stuff. The key is in the noise. In long race you want the most efficent drive line you can get. A 49x15 runs quieter because the load is spread over more teeth (4 to be exact) compared to a 46x14.

The other good point I heard might be negated by modern parts but seldom does a sproket or chain ring run 100% concentric. A smaller set up will have less of a tight / loose spot differance than a bigger set up witch would require more chain slack and possibly a chain coming off. I have a vintage 60's track bike in my basement that has top end (for its day) parts on it. Compared to my Dura-Ace stuff this theroy would make sence.

genericbikedude

This thread has not yet answered WHY. The efficiency argument for larger/larger combinations makes some sense, but the converse argument is that smaller/smaller combinations are less efficient. Why would lower efficiency mean that sprinters find them to be faster?

Maybe there are leprechauns that like little track cogs?

Yoshi

I think we'll need a phsycist to weigh in. My guess would be things like: chain vibration, chain angle, chain length, teeth engaged, chain velocity, etc. All of which probably only have a slight effect on efficiency/feel but altogether would be somewhat noticeable (especially to a pro).