Bicycle Mechanics - Compact Crank Conversion ?

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SSRI
11-20-05, 07:24 PM
I am considering converting my 53/39 shimano ultegra cranks( 6400 seris) to compact gearing (ie 50/34).
what is the smallest chaining I can get? or is 39 the smallest I can go.

thanks for any input.

sydney
11-20-05, 08:04 PM
Generally a 38 but, there use to be an obscure source for a 37.
HillRider
11-20-05, 08:40 PM
"Compact" cranks have a 110 mm bolt circle diameter (BCD) that permits using a 34T chainring. You have a 130 MM BCD crank that, as Sydney said, takes a 38T ring as the smallest (I've never seen a 37 offered). Don't pay for a 38T for your current crank as the improvement over your 39 will be minimal.

jhs
11-21-05, 05:10 AM
Just curious...

But why do you want to change to a compact crank. Weight savings, or better gear ratios or are there another reason?
SSRI
11-21-05, 06:13 PM
I want to swap it out mainly for better gear ratios, since I hardly find myself pushing the 53 (for city riding anyway). The main factor was the compact crank I install on my bro's bike a 50/34.
I find the 34 kinda wimpy but I can accelerate with the 50 with out too much effort.
after that I am pretty much sold.
Al1943
11-21-05, 08:57 PM
I want to swap it out mainly for better gear ratios, since I hardly find myself pushing the 53 (for city riding anyway). The main factor was the compact crank I install on my bro's bike a 50/34.
I find the 34 kinda wimpy but I can accelerate with the 50 with out too much effort.
after that I am pretty much sold.

You might consider a 50/36 compact. If I were looking to buy a compact that's what I'd want. It really depends on your needs, get what you need.

Al
toomanybikes
11-23-05, 03:59 PM
You might consider a 50/36 compact. If I were looking to buy a compact that's what I'd want. It really depends on your needs, get what you need.

Al

I've yet to find a 50/36 being sold anywhere. They are normally, it seems, being sold as 50/34 but you can buy a 36 ring to replace the 34. You may be able to get it done at point of purchase if you buy at LBS as opposed to Internet purchase.
Rev.Chuck
11-23-05, 04:09 PM
We have lots of guys liking the compact road setup. Some of them are running the outboard bearing two-piece crank setup and switch back and forth, quickly, depending on the type of riding or race. Lots of guys using it for cyclocross as well.