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My road bike has a Campagnolo Veloce gearset. It's running 53 and 39 tooth chainrings. I have a 13-25 10sp cassette.

I find that a lot of the time when I'm cruising, I'm on the big chainring and in the 3rd or 4th largest gears on the back. There is a fairly significant chain angle. Because of this, the chain is a bit noisy and I'm sure it's stressing the drivetrain a little. Also, when I need to drop down a gear I quickly need to drop onto the small chainring which necessitates significant adjustments on the rear.

I'm thinking of changing the 53 chainring to a 50t. I am happy to lose a little top end speed.

According to my theory, dropping a 53t to a 50t will reduce my gear ratio by 1.06 (53/50). Which would be the equivalent of switching from a 17t on the back to an 18t. Assuming this is correct, it's not going to have a very big impact, but it might be enough to make it worthwhile.

I know there is an option of using a 3 chainring crankset, but I think that will be a bit too expensive and still won't solve the core issue of getting the right sized large chainring.

The other option is to change the cassette but I can't see many that would really make much of a difference. If I could get a 15-25 that'd probably be about right.

My questions are:

  1. Will the change mean I need to change or adjust the front derailler, the rear derailler or the chain?
  2. Will there be any other impacts I haven't thought of?
  3. Any other ideas to solve the problem?

EDIT: I can't seem to find a 135mm BCD 50t chainring. I asked my LBS and they said no go. ChainreactionCycles don't have the combination I want. Can I get a 50t 135mm BCD campag chainring? If not, what can I use as an alternative?

EDIT: I've found that BBB make a campag compatible chainring that looks like a good option

EDIT: As indicated here the BBB chainring doesn't fit. Looks like a proper compact crankset is my only option now.

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Added the [gears] tag. –  Neil Fein Jul 19 '11 at 19:46
    
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3 Answers

up vote 5 down vote accepted

I would consider changing your crankset to a true compact, 50t/34t, and running an 11/25 rear cassette.

Campy actually made a specific derailleur for running a compact front, because they said that the 50t doesn't work well with the standard front derailleur (that may be a function of the tooth differential, so it may not apply if you leave the 39t in place).

(Edit: It does appear that my data on the campy front derailleur may be outdated. Their 10 speed Chorus and Record had an individualized front derailleur, but current product appears more universal.)

The 50t x 11t combo is a 119.6in gear, compared to 107.2inches for the 53t x 13t you're running now.

It will give you a slightly faster gear than current, a better climbing range, and slightly crisper shifting. Downside is you have to buy the crank set and cassette, not just a chain ring.

Check out UBI gearcalculator for more info on how gearing changes will affect you.

Hope that helps.

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That's an interesting idea. According to my interpretation of the campag page, my existing derailleur should work on both normal and compact cranks campagnolo.com/jsp/en/groupsetdetail/item_derVE_catid_1.jsp. –  Mac Jul 18 '11 at 23:24
    
A new crankset would be $170 (evanscycles.com/products/campagnolo/…) instead of $70 for just a chainring. But then I'd get the two new chainrings and a new crank. –  Mac Jul 18 '11 at 23:24
    
and I'd also need to get a new cassette. The prices seem to be getting pretty high when the alternative of just changing the big chainring to a smaller one might achieve most of what I'm after. –  Mac Jul 19 '11 at 6:15
    
I know it's more expensive. I would say the benefit is there. But it's a personal balance of budget and benefit. Maybe for you it's not the way. –  zenbike Jul 19 '11 at 9:10
    
That link is blocked from my location. :( –  zenbike Jul 19 '11 at 9:12
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Since you may need a big gear to power down big hills, let's look at the effect in gear inches of changing from 53 to 50.

53/13*27=110

50/13*27=104

(27 is arbitrary figure for comparison)

So you will be losing 6 'gear inches' at the top end.

Your next sprocket is presumably a 14 tooth, 53/14*27=102

If you went for a 49 then 49/13*27=102

Therefore, you could go smaller still, with 49, to effectively lose only one big gear.

The amount of teeth on the chain rings and sprockets is always going to be a compromise of weight, reliability and range. Going smaller saves weight, which we like.

When your rear cassette is due for replacement you could get the 14-28 one (with a new chain). This will drop your big gear down to 49/14*27 94.5 - some mountain bikes can manage that. If you lack top-end gears then you could put your 53T back on.

Hopefully you have got a good cadence already, and, unless you have huge hills to power down, loss of some of the big gears should not be a problem.

As noted by @Daniel R Hicks you will need to adjust the front derailleur to be 1-3mm above the outer chain ring teeth, outer cage parallel with the chain-ring and cable adjusted accordingly.

Although it is very 'macho' to have big chain ring and miniscule sprockets, realism is helpful, think whether you really need to have the biggest gear and go for it.

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There are no 135 BCD 49t sprockets available (that I can find.) Please let me know if you do. But it might be better to address the gear range problem by swapping the whole crank to a Compact, i.e. 50t-34t, and running a 11-25 cassette in the rear. The GI difference actually improves your top speed with a 50tx11 when compared to the Standard 53tx12,or the 53x13 here, and you get a better climbing range as well. Downside is a wider differential percentage between gears. –  zenbike Jul 18 '11 at 9:25
    
@zenbike - check out this page. 135BCD in many different tooth counts. bbbparts.com.au/products/category/KJUURSYI –  Mac Jul 18 '11 at 23:26
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If you reduced the size of the large ring substantially it would probably be "recommended" that you to adjust the front derailer and shorten the chain (though from a mechanical limits/clearance point of view adjustment wouldn't be required). However, reducing by only 3 teeth is not likely to affect derailer adjustment, and at most you'd remove one double link from the chain -- not really worth bothering with.

If you were to go the other way -- put on a larger ring -- then you'd more likely have to make adjustments.

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It would require a derailleur height adjustment, which would require adjusting the mechanical stops as well. But with most frames, it is no problem to make that adjustment. There are a few Frames, Like the Felt AR0 which do not accept a Compact crank (or a 50t chain ring size in this case), because the derailleur can't be lowered enough to compensate correctly. –  zenbike Jul 18 '11 at 9:00
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