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Old 06-15-12, 12:40 PM   #1
clerkofkirk
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Upgrading a Shimano Exage LX500 Chainring

Hello everyone, this is my first post. I have a 1992 Cannondale M500 MTB like this

http://66.147.244.179/~vintagm8/year/1992/1992.pdf

This is a multi-use bike; commuting, trails, and most recently a Sprint triathlon (50-59yr age group). I would like to upgrade the Shimano Exage LX500 chainset with a larger large chainring to get a little more top end speed. What are your suggestions for a 50T or greater chainring for this setup that would be compatible with my current bike. Chain is a Shimano Hyperglide and the front derailleur is a Shimano LX400. Thanks!
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Old 06-15-12, 01:23 PM   #2
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This question gets asked a lot here. THere are three possible solutions:
1. Train your legs to spin at a higher cadence... according to Sheldon Brown's Online Gear Calculator, if you have 26 X 1.25" tires (very narrow road tires on a MTB), you will be going 43 km/h if you spin your legs at 100RPM, and 52 km/h if you spin at 120 RPM. If you can maintain that speed you shouldn't be doing an age group sprint tri, you should be qualifying for the olympics. Spinning faster is the preferred solution - it makes you more efficient and will result in less muscle fatigue so you will be fresher for the run.
2. Get a new cassette with a 12 tooth small cog. This is an easier change and actually makes a bigger difference than changing from 48 to 50 tooth chainring.
3. Modern 'compact road' chainrings fit on onld MTB cranks as they both have a 110mm bolt circle. You can easily put a 50 tooth chainring designed for 9 or 10 speed on your bike and it will work perfectly.
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Old 06-15-12, 01:27 PM   #3
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You can conceivably go up to a 54T, but the expense get's a bit absurd for ONE chain ring. (assuming you have bolted -not riveted- rings)
Changing the crank will likely also require a different BB.
A larger ring will require a longer (new?) chain.

Why not change the cassette to a 11 or 12-28?

MUCH SIMPLER! MUCH CHEAPER!
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Old 06-15-12, 01:57 PM   #4
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Additional information: The chainring under consideration is Shimano SG D-48 "For Narrow Chain Only". The rear cassette is a Shimano Hyperglide 7-speed cassette 13-30.
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Old 06-15-12, 02:09 PM   #5
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Bill, sorry for the newbie questions but what exactly do I look for and where if I go the cassette route? If I go to an 8-speed cassette would I have to change my indexed shifters as well? This looks like it would work "plug-and-play":
http://www.ebay.com/itm/SHIMANO-7-SP...#ht_500wt_1054
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Old 06-15-12, 02:33 PM   #6
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Just crunched the numbers on Sheldon Brown's Gear Calculator and it it obvious that a new cassette is the way to go. Still confused about whether changing to an 8-speed or greater cassette will require new shifters.
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Old 06-15-12, 04:17 PM   #7
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Quote:
Originally Posted by clerkofkirk View Post
Just crunched the numbers on Sheldon Brown's Gear Calculator and it it obvious that a new cassette is the way to go. Still confused about whether changing to an 8-speed or greater cassette will require new shifters.
Here's a Sheldon Brown article that might help: http://www.sheldonbrown.com/k7-7.shtml
Your 7 speed shifters only have enough indexes ("clicks") for 7 speeds. Therefore, yes, you'll need new shifters if you put an 8 speed cassette on there. I think you might have wheel dish issues.

I don't know if, in the current way you're using the bike, you really need the 30t sprocket. If not, you can get a seven speed 12-28 which would help you a lot for the on-the-road speed.

If you sometimes need low gearing and sometimes high gearing, but usually either will work, you can get two cassettes and just swap them at the occasional times you need to. Once you get the tools (about $25 for a chain whip and a cassette tool), you can swap cassettes in about 5 minutes or less. I'm sure you can get a chain length that would work with both your current cassette and a new 12-28, so it would be a pretty quick/easy swap.

Although, it's not what you're asking, you can use 8 speed shifters with a 7 speed cassette (you just won't be using one "click" - the derailleur will come to the stop before you get to that click).

Last edited by Camilo; 06-15-12 at 05:48 PM.
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Old 06-15-12, 04:24 PM   #8
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Thanks, Camilo. So would this cassette be a good fit for $18.70 shipped? I have a friend with the tools to do the swap.

http://www.ebay.com/itm/SHIMANO-7-SPEED-HYPERGLIDE-HG-CASSETTE-CS-HG41-11-28-/110892433021?pt=Cycling_Parts_Accessories&hash=item19d1b43e7d#ht_500wt_1054
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Old 06-15-12, 04:30 PM   #9
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Yes, that cassette would be what you need. An 8-speed "upgrade" will require a lot of changes including a new rear wheel (8-speed cassettes are wider and won't fit on 7-speed hubs) and new shifters. For the bike you have it's not worth the cost.
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Old 06-15-12, 04:57 PM   #10
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Quote:
Originally Posted by clerkofkirk View Post
Thanks, Camilo. So would this cassette be a good fit for $18.70 shipped? I have a friend with the tools to do the swap.

http://www.ebay.com/itm/SHIMANO-7-SPEED-HYPERGLIDE-HG-CASSETTE-CS-HG41-11-28-/110892433021?pt=Cycling_Parts_Accessories&hash=item19d1b43e7d#ht_500wt_1054
Are you sure you want an 11T top cog? That's a pretty major jump from 13T. Something like 17%!
Your 2T chain ring increase was only about 4%.

Often when "spinning out", you really aren't spinning out as much as you think.
If you pick a gear "too steep", it becomes unusable.
A 12T cog will give you about an 8% increase, which really is quite a bit. (4T more on the big ring equivalent)
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Old 06-15-12, 05:23 PM   #11
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http://www.jensonusa.com/Bicycle-Cas...Speed-Cassette
http://www.jensonusa.com/Bicycle-Cas...-HG50-Cassette

The above are links to 7-speed cassettes, which can be dropped in place without modification.

An 8 speed cassette will not fit on your 7 speed wheel.
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Old 06-15-12, 05:55 PM   #12
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Clerkofkirk: As for the 11-28 or 12-28, really it's a judgement call as some have said. I have a bike with a 50X11 (cassette is 11-28) and I do use it downhill even though I'm not a super strong rider (age 58, ~100 mile a week rider, no racing... but steep up and downhills here, and I love to go fast downhill!)

I'm sure I could get away with a 50X12, but a friend with similar strength and love for downhill speed is unsatisfied with his 50X12 and will change to an 11-28 as soon as his cassette wears out.

We like to go 40-50 down hill though on racing type road bikes, 45 being pretty common. If you're anticipating top speeds in the 30-40mph range or less, I'm pretty sure a 12 would be fine with your 48t big ring. I doubt you'll need a 48X11 on a mountain bike riding on flat or rolling roads.

On the other hand, at the amount of money you're spending, I would just give one or the other a try, say the 12. If you're unhappy after a few rides, buy the other one. A pretty cheap experiment at $18.

Last edited by Camilo; 06-15-12 at 06:04 PM.
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Old 06-18-12, 11:38 AM   #13
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Hyperglide C Body

Turns out, according to Sheldon Brown, I would need a Hyperglide C body to use an 11 tooth cassette. I'm not sure what I have so I guess I'll just stick to what I have for now. It doesn't seem worth the hassle just to go from a 13T to a 12T cassette. So we can close this thread unless someone can convince me that it is worth the trouble.
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Old 06-18-12, 02:34 PM   #14
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Changing from a 13 to a 12 small cog is the same as changing from a 48 tooth chainring to a 52 tooth chainring.

48/12 = 52/13

However, I do not think you should make this change. I think the limiting factor now is the motor. Train your legs to spin at higher RPM (aim for 90 rpm or more) and your gears will no longer seem too small.
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Old 06-25-12, 05:29 AM   #15
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Quote:
Originally Posted by DCB0 View Post
Changing from a 13 to a 12 small cog is the same as changing from a 48 tooth chainring to a 52 tooth chainring.

48/12 = 52/13

However, I do not think you should make this change. I think the limiting factor now is the motor. Train your legs to spin at higher RPM (aim for 90 rpm or more) and your gears will no longer seem too small.
That's the conclusion I came to as well. Thanks for your reply.
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