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Old 09-26-09, 01:44 PM   #1
J-rides
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Drivetrain advice

I currently ride an older Specialized Allez (year unknown) with RSX. I recently moved to very flat SE New Mexico and find my self using only the highest 4 of my 27 gears combos. My front triple is 46-36-26, and the rear is 28-24-21-18-15-13-11. I do local races and group rides and would like a more appropriate set up. I can't afford a better bike right now and will need to change rings soon anyway. Any advice on what is possible/sensible.

Thanks a ton
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Old 09-26-09, 02:52 PM   #2
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With 46-36-26, I assume your cranks are 110 BCD so won't work with standard 52t or 53t road rings. You might consider a more standard road set up in front with a new double cranskset with 53-39 rings (130bcd). You could also go with a more aggressive rear cassette -- say 11 or 12-25.
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Old 09-26-09, 02:58 PM   #3
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Are you looking for taller and tighter gearing, just taller, or just tighter? A 46/11 with 700C wheels seems tall enough for flat terrain to me, even for the final sprint of a race. 46/11 is just a smidge taller than a 50/12 and @ 120rpm is ~39mph. But if you need more top end, get a 48T or even a 50T ring. BCD is very likely 110mm since 130mm can't go below 38T.

I can certainly understand wanting tighter gearing. Your options there depend on whether the rear hub is freewheel or cassette. It it's freewheel, you are pretty much SOL as that is probably the tightest HyperGlide 7-speed FW that Shimano makes (OK, they do make a 13-28 but then you'd lose the top end).

If it's a HyperGlide cassette hub, you could try to find an 11-21 or 11-24 7-speed cassette but you may not have much luck. However, you may be able to use some 8-speed cogs. The thickness of Shimano HG 7-speed and 8-speed cogs is almost identical (1.85mm vs 1.8mm) and you can put a few 8-speed cogs in place of 7-speed cogs without degradation to indexed shifting. For example: you might be able to find a 12-21 or 12-23 8-speed cassette and build an 11,12,13,14,15,17,19. One important note is that some HG cassettes that start with an 11 have a wider built-in spacer on the 11 and a depression cut into the 2nd cog for the 11 to seat into. You cannot put a "flat" cog in the 2nd position if this is what you have.

Last edited by Gonzo Bob; 09-26-09 at 03:01 PM.
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Old 09-26-09, 03:19 PM   #4
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You can get larger chainrings for 110 BCD. http://www.loosescrews.com/index.cgi...id=15816715181
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Old 09-27-09, 09:40 AM   #5
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THANKS GONZO BOB!

Forgive my ignorance but what would be the benefit of tighter gearing on my hyperglide cassette?

You are right about my set up being 110mm, so I think the first step might be to bump the front up to 50-39-??

Thanks for your time and expertise
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Old 09-27-09, 09:45 AM   #6
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Thanks Dos!

If I was able to spring for the new double cranks, is it possible to adjust my RSX shifters to work with a double chainring set up? I assume most of that adjustment would come from the limit screws, do they have that much range?

Thanks a ton
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Old 09-27-09, 03:24 PM   #7
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Or find some donor chain rings off another bike. I have gone from 52/42 to 47/36 that way, with a 110 bcd crankset.

With the larger big ring, you just need to raise your FD. There is good info on doing that pretty simple job on the web.

Going from a triple to a double will probably mean getting a new bb as well. So getting a used 110 bcd crankset with larger rings will be your cheapest option. I am usually going the other way as I live in the mountains. In fact, my newest addition to the fleet has the gearing of your bike.
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Old 09-27-09, 03:36 PM   #8
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Benefit of close ratio cassette - your top 4 cogs span 11-18. An 11-21 or 11-23 will give you 6 or 5 cogs in that same range, and more specifically, it'll give you about a 10% jump per gear at the top end (1 tooth increments). This allows you to adjust your cadence to stay within a closer range, which makes it easier to ride.

Flat roads usually means wind, and a tailwind ride could get pretty fast. Likewise a headwind ride could really slow you down. It's important to be low in headwinds, more so for someone on flat terrain because the wind just never stops. So try getting low. It also helps recruit more muscles so you get more power.

You can get a 53T big ring - Ritchey has been selling a road crank with 53/39 110 BCD forever, and similar rings have been on the market as long as I can remember. You can go a bit smaller, maybe a 52 or 51, and pair it with a 36. You could get rid of the third ring and get a shorter cage rear derailleur.

The shorter cage rear derailleur, combined with a 52/36 and 11-23, should allow you to keep the same chain, give you less chain slop when you're in the (now) small ring when hitting bumps, and give you a very nice usable range of gears. You should be okay even if you visit some hillier terrain.

cdr
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Old 09-27-09, 05:07 PM   #9
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Originally Posted by carpediemracing View Post
The shorter cage rear derailleur, combined with a 52/36 and 11-23, should allow you to keep the same chain,
The length of the rear derailleur cage has no effect on how long a chain is required. That's controlled by the sizes of the biggest cog, the biggest chainring and the chainstay length.

It only affects how much chain can be "wraped" so it defines how much difference between chainring sizes and the big and small cogs can be used.
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Old 09-27-09, 06:21 PM   #10
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Thanks carpediemracing,

Insightful and dead-on thoughts regarding the wind around here. A couple questions;

Will switching to a 52-36 rings up front require a new front derailluer (I have a RSX FD now)?

Did I understand you correctly when I heard you say I could simply replace the front two rings and blow off the inside ring? Should I be able to adjust my current shifter to work with that set up? Replacing the front crank and possibly the bottom bracket is not in my budget right now.

Will I definitely need a new rear derailluer? I have to replace the chain anyway.

Thanks all
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Old 09-27-09, 06:52 PM   #11
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Originally Posted by J-rides View Post
Thanks carpediemracing,

Insightful and dead-on thoughts regarding the wind around here. A couple questions;

Will switching to a 52-36 rings up front require a new front derailluer (I have a RSX FD now)?

Did I understand you correctly when I heard you say I could simply replace the front two rings and blow off the inside ring? Should I be able to adjust my current shifter to work with that set up? Replacing the front crank and possibly the bottom bracket is not in my budget right now.

Will I definitely need a new rear derailluer? I have to replace the chain anyway.

Thanks all
1. Just raise your front derailleur. The Sheldon Brown site will give details.

2. OK to dump the small ring if you want, and adjust your derailleur stop accordingly.

3. Assuming your RD is working now, it should work fine after the switch.

4. Might need longer chain, but you are replacing it anyway. Sheldon has a great guide on chain length.
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