47x14 vs 50x15



kula2000

kula2000

New Member
Dec 3, 2004
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I'm new to track racing and I'm slowly adding to my gear collection. I currently have 48 & 49 rings and 15 & 16 cogs, but I want to add a new gear ratio. Either a 50 ring or a 47x14 to get me into the 90+ range.

I primarily would be racing mass start events like Scratch, Points, etc, but also events like Sprint, Keirin, and chariot.

I'm just wondering what other experienced trackies out there would recommend between a 47x14 and a 50x15 (if you could only purchase one combo) and why.

The other issue that comes up is going to the smaller rings gives me too much chain slack to deal with.

Advice please :)
 
In my experience (10 years of racing on the track), the 50x15 just feels faster than a 47x14. It's totally subjective and based on nothing scientific, but hey, your psychological state has an impact on your performance ;). Actually, there was a study done by a university engineering class about just this question. They found that larger chainrings created less friction in the drivetrain. I think I read it in Velo News, but it was several years ago.

Also, your chain length and rear dropout length can be a factor. If either or both are on the short side you'll have to go with the smaller combo, and the opposite if they are longer. Unless of course you want to start with a new chain and cut it to length.

One last thing to consider: Cogs are a lot cheaper than chainrings. If you already have a 48 and 49, all you need is a 14t cog and you're set. I rode a 48x14 for 2 or 3 years and had good results before I could afford to buy 50 and 51t rings, you'll do fine with the same.
 
Using larger combinations IS more efficient as the study quoted by RSD suggests. More friction is generated by pulling the chain around smaller sprockets and relates far more to the sprocket than the chainring. (chain deflection is much higher as it goes around the smaller sprocket).

I'd go 50x15 even though it's a wee bit lower than 47x14. (gives you a bit shorter wheel base as well) If your chain gets too short and is still in good condition just add a link. That's the beauty of chains.

Kind Regards Jay.
(Six years track racing as a kid, just started up again as a veteran - 30+ years in manufacturing and automotive engineering)
 
RSD said:
<snip> Actually, there was a study done by a university engineering class about just this question. They found that larger chainrings created less friction in the drivetrain. I think I read it in Velo News, but it was several years ago. <snip>
Click to expand...

I recall, if it was the same study (MIT?), the conclusion was drawn from rear cogs not chainrings.

Something like a 1% increment between cogs with the 12t being 92% efficient and the 18t being 98% efficient.

About a 60x18 would be your optimum choice :)
 
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