Bicycle Mechanics - what exactly is trimming in regards to STI?

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bluenote157
10-14-07, 07:27 PM
Whats the purpose of trimming? If my bike was tuned right, shouldn't i just be able to go from small to large chainring in one shift? Why is the trimming there? To overshift and drop back down? Or is it for use when you are in extreme gear combinations like large chainring and largest cog?

dtrain
10-14-07, 07:31 PM
Or is it for use when you are in extreme gear combinations like large chainring and largest cog?

Getting warmer...

As you are in the small ring and heading into smaller cogs, you can give the FD a little bump to the outside an minimize the chain rub. Oh, and you don't have to trim on your way to the large ring. You can pass right through it with a full sweep.
vpiuva
10-14-07, 07:31 PM
Trim is only to keep your chain from rubbing on your FD - extreme or even less than extreme combinations. Middle of the cassette/small ring the chain is in a different position than the large cog/small ring. If yours never rubs, you don't need to trim. But there are cyclists that must like to listen to chain rub because they don't trim.

bluenote157
10-14-07, 07:38 PM
good deal..thanks!
rodrigaj
10-15-07, 04:07 AM
It's has not been explicitly stated yet: Trimming is probably more of a factor if you have a triple crankset.

Campy FD is much better than shimano for this reason.
Sammyboy
10-15-07, 04:44 AM
Trim is the major manufacturers subtle way of letting you know that friction shifting was always a better idea really.