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Old 05-20-12, 10:26 PM   #1
discord
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Can I replace my chainring to one with less teeth? Will it be easier to pedal uphill?

Hi,

I don't know too much about bike mechanics. I have a bike I bought last year with a Shimano FC-6400 crankset. There are 2 gears on the front, one which is marked 52T, and another that is marked 42T. There are 7 gears in the back. Is it proper to call the front gears the chainring, and the rear gears a casette? I would then refer to the bike as a 14 speed, correct?

I live on an island with really steep hills, and sometimes I need to get off the bike and walk it uphill. It also does not feel nice on my knees when I push myself up these hills. I was wondering if I replaced the smaller front gear to one with less teeth, and possibly smaller, would it be easier to pedal uphill? What are my options are for the smaller gear.

This is what my crankset looks like: http://velobase.com/ViewComponent.as...2-65f92ecdfcbe

Here is another post that mentions Shimano 600, but refers to 8sp : http://www.bikeforums.net/archive/in.../t-783006.html

Finally, will can I replace the 42T chainring with this 28T? : http://www.ebay.com/itm/Shimano-Biop...item19d01d400f
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Old 05-20-12, 11:18 PM   #2
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Your crankset has a 130 mm bolt circle diameter (BCD) so I think the smallest you could put on would be 39, not much of a difference..... about the same as 1 gear change in back. You could replace the entire crankset to a compact with a 34 tooth small chainring. You'd need to get a "square taper" type like you have now.

If you have 7 in the back, it's likely you have an older style freewheel, not a cassette. You may also be able to get larger cogs in the back for easier gearing. Depending on how much bigger you go in the back, you may need a long cage rear derailleur and longer chain.

Can you provide actual close-up pictures of your bike ?
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Old 05-21-12, 12:06 AM   #3
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Thanks for the help Homebrew! I will take some pictures of the bike tomorrow.

After more searching I found a post which suggests I can put a 38T on: http://www.bikeforums.net/showthread...-600-yes-or-no
In that same post one claims that with 39teeth it felt much easier than 42T.
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Old 05-21-12, 03:26 AM   #4
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Read some chainring info here.

You can get cheaper rings but they may not shift as smoothly or last as long as better rings.
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Old 05-21-12, 08:49 AM   #5
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The effect of the change is a direct calculation; 38/42 = 0.9, so the change will make pedaling 10% easier. If you think that's enough help then go for it. Otherwise a cassette or freewheel, which ever you really have, with A larger large cog will also help.
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Old 05-21-12, 08:55 AM   #6
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Shimano 600 tri-color 7-speed = cassette freehub unless the rear wheel is not original. Depending on what you have for a cassette, you could possibly get a cassette with a 28T with your current RD, or put on a MTB RD and a new chain and go up to a 32 or 34T rear, but then the gaps get a lot bigger between gears.

Going from a 42T to 39T ring is a relatively small change, but may be a worthwhile start as you don't have to change anything else to make the swap.
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Old 05-21-12, 09:07 AM   #7
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I switched from 42 to 39T up front and it is a noticeable and pleasant improvement.
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Old 05-21-12, 09:09 AM   #8
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The change may help some, but it won't be huge. I went up one tooth from a 39 to a 40 when i replaced a warped chainring recently. Can't perceive any difference.
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Old 05-21-12, 09:15 AM   #9
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You may need to change deraillers, but I think you'd be happiest moving to a triple in the front. 26-36-48 would seem like it would suit you well.
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Old 05-21-12, 09:24 AM   #10
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Originally Posted by jon c. View Post
You may need to change deraillers, but I think you'd be happiest moving to a triple in the front. 26-36-48 would seem like it would suit you well.
+1

Going from a 42t to a 39t will help marginally, but not all that much. It's roughly comparable to a change by 2 teeth in the back. Going o a larger freewheel (you didn't mention the size) would also help, possibly more depending on what you have there now. However there's a limit to what you can do by changing a chainring or freewheel alone.

Trying to broaden the range of gearing with your 7s will mean reducing your mid range gear selection. Going to a triple will allow you to maintain decently close gearing in the mid range where you do most of the riding, yet allow for an ultra low set of gears for climbing walls.

This is a more expensive option, but from your OP, I suspect something you'll end up doing anyway, so you're better off biting the bullet now rather than spending dough for a 39t chainring that won't solve the problem.
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Old 05-21-12, 10:31 AM   #11
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The best starting point is to go to online gear calculator : http://home.earthlink.net/~mike.sherman/shift.html to see where you are and simulate where you want to be.

For example: assuming your wheel size 700c - it appears that even if you move to 39t chainring and use 34t granny gear in the back - you'll be at 30 gear inches - which might be ok, but still, some prefer 25 gear inches for steep ascends. It seems the best route for you would be to switch to mtb crankset with smallest of the chainrings @ 28t or less.
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Old 05-21-12, 10:55 AM   #12
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If it was my bike I'd get a 50/34 compact crankset.

In fact, I've done that before and I thought at the time that it was the best change that I'd ever made on a bicycle. It was a major transformation. In my case I bought a compact crank that matched my existing bottom bracket. I swapped out cranksets, shortened the chain, lowered the front derailleur and I was good-to-go. The only thing that I had to buy was the crankset.

The trick is finding a compact crrankset that matches your existing bottom bracket.
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Old 05-21-12, 11:26 AM   #13
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Or rebuild the back wheel with a Hybrid IGH, freehub combo.

the Internal reduction-gear Low is 1:0.75
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Old 05-21-12, 11:42 AM   #14
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It's simple math to know how much easier one gear is than another, especially when considering only front or rear. A 39 tooth front is 7% easier than a 42 tooth, a 34 is 20% easier. Considering price and complexity of various options I would agree with changing the front to 50/34. You won't miss 2 teeth on the high end and the 20% jump should help a lot. You would probably be in the small ring only when starting up and going up hills and in the large chainring most of the time.
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Old 05-21-12, 11:48 AM   #15
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Depends upon what the OP needs. "Easier" must be quantified with numbers:

1. what grade is the hill?

2. what RPM are they struggling at when going up this hill in his lowest gear?

3 what mph is this?

4. what is their heartrate at AT when going up this hill at this mph and RPM?

THEN we would know what's most appropriate. If they're going up the hill at 70rpms, then going down to 38t inner-ring might be enough (gives equivalent of one lower gear on rear cluster). If they're struggling to push 50-60rpms, then going to a 50/34t compact crank may be most appropriate as that gives the equivalent of two lower gears on the rear cluster.
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Old 05-21-12, 12:06 PM   #16
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I think it safe to assume that when the OP's knees are hurting, he is actually dismounting to walk up hills, and they are "really steep" that he needs a significant downward adjustment. I doubt we are going to be supplied with heart rate and rpm's, so the 34 tooth is most likely the best option, other than selling the bike and buying a lower gear one. There are just too many possible problems and expenses when one gets into changing freewheel/cassette.
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Old 05-21-12, 12:14 PM   #17
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Knowing the existing cog range on the rear wheel would help too. Switching to a compact (50-34) , with a larger freewheel is pretty cheap, simple to do and might be enough.
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Old 05-21-12, 12:16 PM   #18
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There are just too many possible problems and expenses when one gets into changing freewheel/cassette.
Wait, what? There are exactly three things the OP would need to put a 34T cog on the back:

- Cassette/freewheel with that cog
- New longer chain
- Shimano MTB rear derailer

What's so hard about that? Changing the front to a triple (while probably the best solution) is more complicated and almost certainly more expensive because besides the crank a new BB may be needed, and possibly a new FD.
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Old 05-21-12, 01:17 PM   #19
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Wait, what? There are exactly three things the OP would need to put a 34T cog on the back:

- Cassette/freewheel with that cog
- New longer chain
- Shimano MTB rear derailer

What's so hard about that? Changing the front to a triple (while probably the best solution) is more complicated and almost certainly more expensive because besides the crank a new BB may be needed, and possibly a new FD.
There's always the possibility that the new chain won't mate well with the old chainrings, and then you're looking at replacing chainrings / cranksets along with everything else.
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Old 05-21-12, 02:18 PM   #20
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Old 05-21-12, 03:02 PM   #21
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Compact crankset and possibly a change to a slightly wider range cassette. The good news is that your shifters will be fine with the change. The bad news is that you will probably need a different (medium or long cage) rear derailleur and possibly a different front derailleur to handle the extra range.
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Old 05-21-12, 03:43 PM   #22
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Mmm, tricolor...

Looking at that saddle, it doesn't seem like the bike is set up properly. The saddle should not be nose-down like that, and as a rule of thumb, should be set high enough so that your legs straighten completely if you try pedalling with your heels on the pedals. A too-low saddle robs power and can cause knee pain.
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Old 05-21-12, 06:57 PM   #23
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Probably an old 7 speed Uniglide cassette. 24 or 25 tooth ?
If you go compact, and maybe swap to a 28 tooth, you might get away with the same chain & rear derailleur ... maybe.
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Old 05-21-12, 07:13 PM   #24
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You may need to change deraillers, but I think you'd be happiest moving to a triple in the front. 26-36-48 would seem like it would suit you well.
N.B. -- this option would require replacing both the cranks and the bottom bracket, and a wider range rear derailleur.
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Old 05-21-12, 10:32 PM   #25
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Nice horse! Find a cheap 38t front ring and try that with a 28t cog in the back. If it's not low enough then a triple with a 24t small ring is the way to go.
You can use this chart to get a rough idea of your needs. http://www.jbarrm.com/cycal/cycal.html
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