# Need Bigger Chainring, Spinning out on flats.



## LOUISSSSS (Dec 14, 2009)

think i'm becoming a stronger ride. i'm currently on a 42t chainring in the front of my ss/track beater/commuter bike.

Whats a decent sized jump in chainring? If this question is too vague, what other info can i give you guys to help me get the best sized ring for me.


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## wim (Feb 28, 2005)

For starters, tell us your cog size.

If you have any idea what your cadence limit is, use this calculator to see what you need to keep from "spinning out". If you spin out around 100 rpm, also consider training yourself to spin faster. 
http://www.machars.net/bikecalc.htm

I'm doing fine with two rings and four cogs, which I mix and match depending on what I want to do: 42 and 48 ring, 14,15,16 and 18 cog. Once it becomes routine and you have a pre-cut and master-linked chain at the ready, it just takes a few minutes to change rings or cogs.


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## 11.4 (Mar 2, 2008)

We train all winter long for track racing on a 42x18, riding 35-40 miles a day three times a week, all at about 120-130 average cadence. On downhills and with tailwinds we do 150-180. That's a 63 inch gear. For most of the season we warm up for about 15 miles on the track in a 46x16, which is a 77 inch gear, starting at 20 mph and finishing at 32 mph. You can go up in gears a bit if you want, but it depends on what you're actually riding now, any hills, and what you're trying to do. If you're on a 42x14 or 42x15, you really shouldn't have to change gearing. 

A lot of fixie riders start lugging big gears, but they simply hurt your knees and don't make you a better rider. The only reason at all for a big gear is if you are going brakeless and can't manage a smaller gear on a fast downhill -- but a big gear won't really stop you and is just an alternate prescription for a bad accident.


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## PdxMark (Feb 3, 2004)

the size of the cog matters too... a 70 inch gear is a fairly common gear for a fairly wide range of conditions. I can spin it out on a long tailwind-assisted flat, but not in normal considitions... Anything you can not spin-out with a bit of descending help you will have to climb up a hill. 70 inches is nice.


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## LOUISSSSS (Dec 14, 2009)

The bike has an 18t cog...

the link above tells me that 42x18 is ~62 gear inches. and that @ 100rpm i'm only going 18mph... i wanna be able to go 20 and up at least...


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## wim (Feb 28, 2005)

LOUISSSSS said:


> The bike has an 18t cog...
> 
> the link above tells me that 42x18 is ~62 gear inches. and that @ 100rpm i'm only going 18mph... i wanna be able to go 20 and up at least...


You don't need a bigger chainring. Just change your rear cog to a 16 or 15:
42 x 16 (70" gear) @ 100 rpm = 21 mph 
42 x 15 (74" gear) @ 100 rpm = 22 mph

If you insist on the larger chainring, a 48 paired with your existing 18 or a new 17 rear cog would yield almost the same numbers as above. But chainring changes cost more, take longer to make and often require a different-length chain. And as 11.4 said, getting comfortable with high cadences is really the key to becoming very fast, not just plain fast. High-cadence riding _with power _ is not easy though—you need to train up for it.


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## mtnbikecrazy55 (Apr 9, 2009)

i would also swap that 18 cog out for a 16....

around 70 gear inches seems to work best all around for me


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