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changing the small chainring..

Old 02-08-11, 11:45 PM
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changing the small chainring..

Has anyone changed the small chainring of a compact gearing to say.. a 36 or 38? Is that even possible without having to change the 50 tooth chainring as well? Reason for asking is that I find shifting from the big chainring to the small one a bit too drastic, or too steep of a drop. I could be pedaling at a decent cadance then, when the need arrives to shift down, I find myself spining the cranks like crazy. Perhaps its because i started riding on a triple and only recently bought a bike with a 50/34 setup? Anyway, the cranks are FSA, and I was wondering if they do in fact sell a 36 or a 38 small chainrings? And, yes, I do know that I'll be giving up some low gearing but I'm OK with that. Thank you for your patience.
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Old 02-09-11, 12:37 AM
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When you shift down from the big chainring to the small chainring,
Shift up one or two gears (from a larger cog to a smaller cog) on the cassette.

Read Sheldon Brown on Gear ratios. https://sheldonbrown.com/gearing/index.html
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Old 02-09-11, 12:45 AM
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Yeah - its pretty straight forward

And if FSA doesn`t make what you want then a number of other companies do. You`ll just have to locate something with the same bolt pattern and and spacing.

I replaced a FSA 48/39 combo with a Schimano 52/42.Fit perfectly and nothing obliged me to change both rings.
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Old 02-09-11, 11:54 PM
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52/42? Wow, thats some fairly tall gearing. Anyway, thank you for the reply.
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Old 02-10-11, 12:00 AM
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Believe me I've tried everything..just short of cross running the gears. Thank you for the reply.
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Old 02-10-11, 12:05 AM
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I run 53/42 x 13-28 works pretty well around here.
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Old 02-10-11, 02:40 AM
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What is the Bolt circle Diameter of the crank? 110 you have choices , 144 you don't.
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Old 02-10-11, 03:00 AM
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The current setup is 50/34. I think we can rule out 144 BCD.
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Old 02-10-11, 07:21 AM
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Originally Posted by skilsaw
When you shift down from the big chainring to the small chainring,
Shift up one or two gears (from a larger cog to a smaller cog) on the cassette.[/URL]
Yes. What he said. Of course. This is completely normal. The FD should be thought of as changing ranges. The jump between rings is about equal to three cogs. To get to the next gear, shift the front up or down, then the rear down 2 or up 2 to compensate. Check out this gear calculator to see what's going on:

https://home.earthlink.net/~mike.sherman/shift.html
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Old 02-10-11, 10:32 AM
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I guess gearing is relative

Originally Posted by nubike
52/42? Wow, thats some fairly tall gearing. Anyway, thank you for the reply.
Yeah - that could be considered tall gearing for some bikes but it really depends on the rear casette and the intent of the bike as well.

That crankset started off on a Kona Jake The Snake cyclocross bike with a 12 - 25 casette. The original chainring combo made sense for that dicipline where 50 /36 ringset combos are also pretty classic.

But the BB and crankset ended up on a triathlon machine with a 12 - 22 rear cassette. On the road the higher gearing makes a lot more sense - particularly since the smaller chainring is what I use almost exclusevely. The 50 tooth is reserved exclusevely for `overdrive`.
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Old 02-10-11, 01:03 PM
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Originally Posted by LesterOfPuppets
The current setup is 50/34. I think we can rule out 144 BCD.
Rules out 130 mm too.
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Old 02-10-11, 01:43 PM
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Time to bring up half-step, I see!
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Old 02-10-11, 04:09 PM
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Several compacts were equipped with 50-36 chainrings, that's what I'd do.
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Old 02-10-11, 05:50 PM
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Originally Posted by Looigi
Yes. What he said. Of course. This is completely normal. The FD should be thought of as changing ranges. The jump between rings is about equal to three cogs.
Unless you have both a 50-34 compact and tight cassette which make it six cogs for the same ratio and a five cog change to get the next gear.

Ex: 50-34 x 13-14-15-16-17-18-19-21-23

50x21 and 34x14 are the same.

Mike's gear calculator is good.
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Old 02-11-11, 08:19 AM
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If you don't have hills or can handle them, for a standard double I like the 50/39 combo, for a compact 50/38 combo, if you need a little oomph for the hills, consider a 26 cassette or even a 28 cassette.
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Old 02-11-11, 11:30 AM
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The 110 bolt centers were the most common in the 1980's and you should have an almost infinite choice of inner ring diameters. 38 and 40 tooth rings were quite common.
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