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I have several questions that arise from the fact that the current drivetrain on my old Peugeot road bike is pretty tough to ride when climbing up some steep hills: so I've got a 42/52 up front and 6 speeds (largest: 24) on the back.

So my first question: will changing the front to e.g. 39/52 setup make a noticable difference.

If so, can it be exchanged to e.g. some older/used crakset such as this Campa http://apro.bikemag.hu/files/4/2/listing_photo159024_555485241366650384.jpg

It has the same tapered square connection as the current one.

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It may be efficacious to replace your freewheel as well. You could probably fit a 14-28 freewheel without having to replace your derailleur and freewheels are super cheap. A 42 t ring x 24 t cog would yield a low gear of 3.5 gain ratios; a 39 t x 24 t would yield a low of 3.3 gain ratios; a 39 t x 28 t would yield a low of 2.8 gain ratios...so on and so on. –  WTHarper Jul 11 '13 at 20:49
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sheldonbrown.com/gears –  WTHarper Jul 11 '13 at 20:49
    
Is the rest of the drivetrain Campy also? –  mikes Jul 11 '13 at 20:55
    
great tips, and link, I'll look into these –  whitezo Jul 11 '13 at 21:54
    
the drivetrain is of various standard Peugeot parts I think: Atom freewheel, Sedis chain, not sure about the crankset –  whitezo Jul 11 '13 at 21:55
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4 Answers 4

You asked: will changing the front to e.g. 39/52 setup make a noticable difference? My answer is an unequivocal 'yes'. If you can however, consider 34 or 36-tooth inner and 50T outer, if you can find chainrings that fit your spider. TA make a large range of chainrings, however new ones will probably cost more than the monetary value of your bike.

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You will definitely notice the changes. I have found this online calculator to be the best of a kind: http://gear-calculator.com/

Just enter your gear combinations (for cogs use custom and drag 6 of them in rigth places) and wheel size. For cadence use values 60-120 (these are "comfortable" values for short periods, "normal" would be around 90) to see the speed you can get with each gear combo.

There is also an option to compare two configurations, use your current config as a reference

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Usually easier to change rear cassette (or wheel) than the crank. If you are really cheap, a fleamarket wheel might be the ticket, just check tor trueness and tight spokes.

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Gearing is a function of the ratio between the chain rings on the front and your cassette on the rear wheel. Check out WTHarper's link to Sheldon Brown's gear calculator.

FWIW, I have an old Motobecane with similar gearing. Trying bikes with a slightly different gear ratio didn't seem to make enough of a difference on extreme hills (like in San Francisco) to significantly improve my ride.

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