JMak00

Have a 2008 Trek Portland. Having shifting issues in the rear with the my current 105 group set-up. So, I've decided to use some extra cash and buy some 105 5700 pieces. So far, I have the chain, rear derailleur and cassette. Now I am looking at crankset, bottom bracket, and front derailleur.

Questions:

How do I figure what length crank arms I should get?

Should I replace the bottom bracket since I will replace all other drive train parts?

How can I tell if the front derailleur shoul be replaced or should I replace since I'm replacing all other parts?

Thank you in advance for any tips, hints, or suggestions.

J

zukahn1 

Not the way I would go I would try and Id isolate the problem which could likley be pretty basic, worn cassette chain, adjustment cabling, rear dr alignment all pretty cheap easey to fix. Before I started mix a and mach upgrade approach.

JMak00

Appreciate the insight. I bought the bike used and don't know the history of the components or how well they were maintained. Hence, I feel more comfortable replacing the set, well, all except the shifters. As well, there are some great deals I am taking advantage of right now for the 105 pieces.

This is my first time buying components. I am getting the Shimano 105 FC-5700 Crankset - 53/39. Will the Shimano 105 SM-5700 bottom bracket work with this crankset?

Here are the bike's specs - 2008 Portland - Bike Archive - Trek Bicycle

Edit - will the 5700s work on my 2008 Portland??

Thanks, again.

cny-bikeman

You need to do the research to answer that question, specifically their respective spindle lengths and chainline. Sheldon Brown's Bottom Bracket Size Database

headloss 

So, you like to spend money? In my opinion, you just replaced a bunch of perfectly good parts... I wouldn't even be surprised if your crank "upgrade" ends up being a downgrade but I'd have to look up the individual cranksets to verify the quality of the chain rings. Never mind my snark, though, it's your money and your peace of mind...

I wouldn't worry all that much about crank length, the ballpark estimates that usually are based on frame size are good enough and you are unlikely to go more than one size up or down from that for a more ideal fit. I don't personally believe that there is a *correct size* based on physiology alone, there are multiple factors to consider in selecting a crank size: leg&foot length are a big part of that, but so is pedalling style (longer arms more leverage vs shorter arms for spinning). A third consideration is the geometry of the frame itself, the saddle height, how you are balanced on the bike... keep in mind that when you use a shorter crank your saddle height will likely go up and when you use a longer crank, the saddle height will most definitely go down in order to reach the new lower pedal at bottom-dead-center. These related changes in saddle position due to crank change will change where your knee goes relative to the top tube as you pedal.

surreal

Actually, he's going 5603 to 5700. These are both HT2; simple swap, same BB is going to work with both.

OP: it's your bike and your money; do whatever you want with it! Just make sure you either sell or donate the used bits. My gut is telling me that the original group just needs a tune-up and some of the consumables replaced (chain, cassette, cables)-- the co-op guys can decide that and hopefully put the functional stuff to good use!

cny-bikeman

Yes, but the next time he runs into such an issue, and more importantly the next time someone reading my post runs into it they will be able to answer the question themselves (Give a fish vs. teach how to fish).

surreal

If everyone knew how to fish, there'd be no traffic at the Fishermen Forum.

fietsbob

Stimulate the local economy .. if you dont do it who will?


Hire out the work, then whip out the bank card when they are done.

JMak00

Thanks for the replies, snarky and otherwise. They may very well be good parts that need minor maintenance. But this is my commuter bike and I dont have a car available so I can leave the bike at a shop for two or three days so that they can diagnose something that they likely wont reproduce.

Through deliberate savings and a surprise bonus at work, I'm gonna buy the rd, cassette, fd, crankset, bb, and new chain and end up spending less than $250.

Seems like a sweet deal to me for brand new parts and piece of mind.

Meanwhile, I'll sell the old parts and make some money back.

Appears to be a win-win and needed some help to get going.

I think my last consideration is whether my current sti shifters will work with these 105 5700 components. I think they will...

cny-bikeman

As for crank arm length, it's my opinion that it does not make a great deal of difference. If you're inseam is in the 30-34 range 170mm, which is still the most common, is fine.