Looking for some advise here, though I may ask on the maintenance forum as well.
I need to replace the chain, cassette and chain rings on my 20 year old Trek 750. Currently has a 7 speed 12-28 cassette and the big ring is the original 48T. On flat terrain I normally ride with the gears set at 3-6 or 3-7, which means that I have nowhere to shift for a downhill. Only option to go faster is to pedal faster.
Since I have the opportunity, I figure that I might as well tweak the gearing. I could go with a 11-28 or 11-30 cassette, but I'm leaning towards putting in a bigger ring, maybe a 52T. Anyone have any experience with gear upgrades? Will what I have in mind do what I want? Will increasing the gear differential make shifting rougher?
I'll probably be ordering the parts next week, so any help would be appreciated.
I totally replaced the drivetrain on my 7.5FX. The original chainrings were 26/36/48 and I changed them to more of a "road" triple -- 30/39/52. The cassette was 11-26 9 spd and I changed it to a 12-23 10-speed.
The thing you need to watch out for is the compatibility with your derailleurs and shifters. Regarding the front, the FD will usually be capable of a certain range, you need to make sure that your new chain rings are within that capacity. For the RD, the cage length represents "capacity", so if you make major changes to the chain rings then you might have to change the RD (for example, going from a double to a triple usually means a short cage RD wouldn't work any more. Also, if you have a 7 speed and you want to upgrade to something other than a 7 speed, your shifters may not be compatible (depending on what kind of shifters you have).
All that said, if you keep with a 7 speed and make only the changes to gearing that you suggest above, my guess is that your derailleurs will likely be compatible. The point is that you need to check and be really certain, or you will own some parts that don't work!
I have ordered a 50T big ring and 11-28 7speed. I'll stay the same on the climbing end, but my top G.I. will go from 105 to 123. Then I can normally run in 2-7, 3-5 or 3-6 and will still have a better gear to shift into for downhills.
It is only costing me parts. I've been taking bike maintenance workshops put on by a LBS, and drive train upgrade using my bike as the demo subject will be the topic in two weeks.