An Uneven Number of Teeth ?

Does anyone out there consistently use either a sprocket, chainwheel or both with an uneven number of teeth ? I've ridden a fixed gear for around 50 years, both for touring and racing, and always favoured:
47x17, 47x18 or 47x19 for general use. I've had a sneaking feeling that an even number of teeth on both sprocket and chainwheel doesn't ride quite as smoothly. In addition, it may be possible for the chain to always turn in the same relative position with an even number of teeth on both.
Your thoughts please.

There is probably a thread about this but it might be talking about skid patches and as I use brakes it of marginal interest to me. However, my favoured ratio is 48X18 and have no problem about sommithness of ride.

A prime number for either or both chainring and sprocket increases the skid patches so saves on tyre wear.

Matching the number of chainring teeth to the number of links in your chain will mean the same teeth always meet either inner or outer links and this supposedly makes for better wear/smoother running but I've only read this, never experienced it myself.

In all gear design one of the gears should always be a prime number.

It means that the gears will wear evenly and that all teeth will have an equal distribution of contact with the other gear (or chain, or belt, etc).

This applies to everything: watches, cars, trains, heavy machinery, drills, etc.

If something has a gear, then one of the gears should have a prime number of teeth.

In bicycle drivetrains the gears should be co-prime, which means relatively prime. There's a wikipedia page on it: http://en.wikipedia.org/wiki/Coprime_integers

With a bicycle this is easily achieved by having one sprocket be a prime number, but can be achieved otherwise by using two non-primes that result in a co-prime.

The goal is to avoid an intersection of the numbers when plotted, which is demonstrated by this image from WIkipedia:

So yes... an odd number of teeth help, but much better is to achieve co-prime at minimum, and much simpler is just to make the rear sprocket have a prime number of teeth.

Do you even derailleur?

You'd have a problem on a derailleur if you never changed gear and put it in a pair of evens. Such pairings are fairly unavoidable when the cassette teeth vary by so little.

Which is why most derailleur set-ups will put a prime number on the most used chainring to solve the problem.

53 big ring was not chosen by accident, it's a prime number.

It's only ever going to be a problem if you sit in one gear the whole time though... and everyone changes gear some time.

It's only ever going to be a problem if you sit in one gear the whole time though... and everyone changes gear some time.

Do you even fixie?

Well now you're just trolling, clearly the entire context of that post was in response to a derailleur question.

Thanks for the post Velocio, that explains my puzzle, it's a pleasure to hear from someone so well informed.
Regards, John.

On the question of derailleur gears, my most used c/w is a 47x 14 to 28, the granny gear is 36 c/w, which agrees again with Velocio.

47:19... Ratio of teh Godz...

I'm using a 19t sprocket. Luck or kismet?

Thanks TS agreed, did the end to end on that one, plus full touring kit.

This idea has been around for many years, and I believe that in a series of gear pinions the odd tooth is known as a 'hunting tooth'.

I've been using 50 x 20 fixed for some time now (just because I happen to have a 50 tooth eighth of a inch ring). I did worry a bit at first that this might cause uneven wear, but I can't honestly say I've noticed any more wear than with any other combination of teeth.

So far as bike chains go, a more significant factor, certainly so far as chain ring wear is concerned, is uneven wear caused by pressure from the cranks (e.g between the 2 and 3 o'clock position on the right hand side, and 10 to 9 on the left). So the life of the chain ring can be extended simply by changing its position on the crank.

47:19... Ratio of teh elderly...

ftfy.

With a bicycle this is easily achieved by having one sprocket be a prime number, ...

/pedant
that condition is insufficient, as it could be met by ratios such as 13:52, 17:51, 17:34, 19:57... i.e. where the larger sprocket has the smaller prime sprocket for a factor. Coprime is the right answer, and two integers are coprime if they share no prime factors. Prime guarantees coprime only if it's the larger that is prime or the ratio is closer than 2:1.

Although possibly you want each of your sprockets to be coprime with your chain length too.

Sheldon had a theory that even numbers of teeth would be good because chains have a natural period 2 variation between inner links and outer links, and having different sprocket teeth assigned to match the different wear patterns of each might be better.

You'd have a problem on a derailleur if you never changed gear

Do you even derailler?

Now you're just trolling.

Do you even troll?

#fixieskidda4lyf

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An Uneven Number of Teeth?

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Thanks Ian, my worn out chainrings don't look as bad as that !