southern rider

I am in need for a lower gear. I notice when climbing my buddies are able to climb with higher rpm and seated while I am grinding it out of the saddle. my front chain ring is a double 42t and 53t campy and my cassette is a dura ace 12-21 8 speed.

What is the easiest way to make a change? Change the 42t chain ring to a 39t or go with a 12-25 or 13-26? Would changing the rear cassette require a change in the chain where as the chain ring would not?

Crank57

If you go with a smaller ring up front you might have to shorten the chain; depends on range of the rear DR arm. Going to bigger cogs in the rear is just the opposite; may have to lengthen chain. If I was a gram junkie I would go smaller ring, maybe shorter chain, for lower weight.

sunburst

You could play around with Sheldon's gear calculator to see which will have the bigger effect. A 3-tooth difference in the cassette is more meaningful than 3 teeth on a chainring. And you're proposing 4 or 5 in the back - even better!
https://i27.photobucket.com/albums/c1...0sale/spd3.jpg

I would make both changes, if you can afford it. The front shouldn't cost much. The back may require a new RD, if you've got a short cage one. And maybe a new chain.

My old Trek already had a 28 tooth rear freewheel, and I put a compact crank on last year, 50/34. I have not regretted it for a second.

Jynx

Do both. The gearing you have is typical old school road gearing. Get a 39 tooth ring (or even a 38) and a 12-27 cassette and while you are at it a new chain.

joeprim

42 sounds big for the small ring. Nashbar has an 8 speed rear cluster 13 - 32. If you need your 12 I'll bet you can find 12 - 32 or at least 12-28. Stick with the same nuber of gears or you have to make too many changes.

Good climbing
Joe

zacster

I just changed my 2nd bike from 42/52 fr with 12-25 rear to 39/53. This made a bigger difference than I thought it would. Give a smaller chainring a chance before you go through the trouble of changing the cassette. You shouldn't need to change the rear derailleur for that, but maybe change the chain at the same time.

Steev

How old is the bike? Didn't Campy use a non-standard bolt pattern? It may be tricky to find an appropriate chain ring.

Gonzo Bob

Depends on how much lower you need. A Campy 135mm BCD crank is limited to a 39 small ring and 39/21 is only about 7% lower than 42/21. If you need a bigger change than that (or if your Campy crank is 144mm BCD which is limited to a 41 small ring), you will need to do it with the cassette. A 42/25 is 19% lower than a 42/21 and a 42/26 is 24% lower. If you don't need the 53/12 top gear, I recommend the 13-26.

southern rider

this is the best forum I have ever experienced, thanks for the INTELLIGENT replies. My bike is circa 95 it is a Klien Quantum II, aluminum 56cm, with dura ace shifters, cassette, rear derailer, and campy chain rings, front derailer and brakes. I was told the brakes are "blue dot", is that good vintage stuff? The frame is in mint condition and the rear cassette is showing some wear (probably from over changing the gears). I am also looking at changing the front fork to carbon. I understand that I will need to find different bearings to use a 1 1/8tube. Or I am sure there are 1" ones to be had. also where I live there are a lot of rollers and usually a couple of good hills on a ride. I am getting back into group rides and have done a couple of tri's already this year.

badmother

1" is 1" and 1 1/8" is 1 1/8" . Buy what is already on the bike.

southern rider

thanks Gonzo Bob looks like the BCD is 135 so I can do a 39 which is certainly the easiest change to make, but only a 7% reduction does not look as good on paper as your suggestion for 19% - 24% reduction. I am going to calculate a 39/25 to see how that looks otherwise I think a 42/26 is enticing. How does a 39/25 compare to a bike properly set-up for a novice or Tri bike?

southern rider

Thanks badmother rather obvious answer at the time but now I know there are plenty of 1" forks to be had. any idea what type of rake or is most geometry pretty standard unless otherwise specified?

oldbobcat

Distance per revolution = large ring / small ring x wheel diameter x pi. Find out what your buddies are using and follow their example.