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-   -   changing cranks (http://www.bikeforums.net/general-cycling-discussion/367430-changing-cranks.html)

maltess 12-03-07 04:39 AM

changing cranks
 
Hello, I have a trek 7.3, yhis bike comes with a 49/39/ something, crank. It is possible to change the crank to a 50 or 52 crank in order to get more speed? is this makes sense or is stupid thing to do? I mean, are bicycles designed in a way you canīt do these kind of things and the bike can be damaged?

best regads

biknbrian 12-03-07 04:57 AM

Once you figure out what BCD you need, you can just get a new chainring. Search for BCD here and try a search of sheldonbrown.com for BCD, there should be a way to measure the hole spacing. I have a guide that came with a bash guard which lets you easily determine the spacing. Then just order a new chainring and adjust your front derailer up a bit. The whole process is quite easily done by anyone who works on bikes.

Velo Dog 12-03-07 11:08 AM

Easy to do and very common. As the other post said, you may have to readjust the front derailleur--if it's set up properly now, there may not be enough clearance for a larger ring. You might have to install a longer chain, too (there's probably enough slack in the old one, taken up by the rear derailleur, but it's a possibility). Any bike repair book can tell you how to do it, or check www.parktool.com.
A gain of one to three teeth, from 49 to 50 or 52, isn't a lot, though. You might think about swapping the cassette instead, from a 13-26 or whatever you have now to something like a 12-24 or 11-23 (I'm guessing at the specific numbers because I've never, EVER needed higher gears--I've been engaged in a 10-year quest for lower ones). That would be essentially a bolt-on, and cassettes are available everywhere.

Retro Grouch 12-03-07 11:20 AM

Quote:

Originally Posted by maltess (Post 5735436)
It is possible to change the crank to a 50 or 52 crank in order to get more speed?

First answer this? Do you frequently find yourself "spun out" in your highest gear combination? Unless your answer is "Yes", changing cranks or chainrings isn't going to do what you want. Honestly, 49/11 is a pretty fast gear.

Putting a Ferrari transmission into a Yugo won't give you a 150 MPH Yugo. Changing gears on your bike won't make you faster unless you've got the legs to turn it.

bbattle 12-03-07 08:35 PM

Quote:

Originally Posted by maltess (Post 5735436)
Hello, I have a trek 7.3, yhis bike comes with a 49/39/ something, crank. It is possible to change the crank to a 50 or 52 crank in order to get more speed? is this makes sense or is stupid thing to do? I mean, are bicycles designed in a way you canīt do these kind of things and the bike can be damaged?

best regads

The 7.3 comes with a 48/38/28 triple with 11-30 8spd. cassette. Going to a 50T or 52T chainring won't give you that much extra speed, 3 mph @ 100 rpm going from 48-11 to 52-11.

maltess 12-05-07 11:14 AM

Thanks very much for the answers, I am noy very familiar with this yet. I guess is not worthit to do this, Is probably better to sell this bike and uograde to a faster bike in the near future. Sirrus comp or Jamis Allegro 1 look like a very nice options.


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