Upgrade my crank size from a 50 39 34 to something bigger.



Just Bob

New Member
Jul 17, 2007
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I have a 2007 Trek Pilot 5.0 with a 105 crank 50 39 34. (Ultegra 10 cassette)

I would like a bigger chainring because I am running out of speed (topping-out).

I also rarely use the smallest chainring, so I might (might) change to a double.

How do I know what type of BB I have, and what is comparable if I do decide to change the entire crank? ( am very mechanically inclined, but ignorant to what is comparable to what). Any good bike mechanics books to look for that cover a lot of this stuff?

I am not a racer, and ride about 1500 miles a year. Most of the terain is rolling hills, and most of my rides are 20-25 miles.

Any suggestions on types of cranks to look at would be greatly appreciated.

Thanks in advance,
Bob
 
From looking at a pic on the trek website it appears that the 105 cranks on that bike are Octalink so not only will you need new cranks such as a standard double of 53/39, but a 109.5 Octalink bottom bracket (5500/6500 models). Once you do that you'll have to raise your front derailler to accomodate the larger chainring. If it turns out that you have the newer external bottom bracket style cranks (ie; the website pic is outdated) then all you need is the cranks as the BB doesn't care whether it's a double or a triple poking throuigh the hole.
 
Thanks for the reply.

The site photo is not accurate to what is on the bike. The crank on the bike looks completly different. The crank is a Shimano 105.

As far as the BB, how do I know what type I have? Are there certain sizes, or configurations that are critical to changing an entire crank?

Thanks for the info so far.

Bob
 
Just Bob said:
Thanks for the reply.

The site photo is not accurate to what is on the bike. The crank on the bike looks completly different. The crank is a Shimano 105.

As far as the BB, how do I know what type I have? Are there certain sizes, or configurations that are critical to changing an entire crank?

Thanks for the info so far.

Bob
Unless you are really hooked on going double, you can just put biggger rings on your triple as well... Depending on your long term and short term objectives, this saves bucks, and then you can save the $ until you upgrade the bike at some point in the future.

Unless you NEVER use the small ring, don't jump too quickly without realizing that you will be giving up some low gearing that you do occasionally use. Perhaps you can do without it, but you may want to go with a slightly wider cluster if you do occasionally need the 34... or count on standing to grind it out in the 39 a little more often.

You could perhaps also get the higher speed you are looking for by increasing your capabilities at higher cadence.... How fast do you go before spinning out now? The riders in le Tour would have to be going pretty fast before they really needed anything bigger than a 50. :D I'm just sayin'
 
It is cheaper and easier to change the cassette at the rear. Buy one with an 11 tooth cog. ;)

Also, an increase in cadence will produce an increase in speed! :eek:

If you must play with the crankset, just buy a new big ring, a 53 tooth 130pcd, make sure it is matched to a 39 middle. Shimano sell these.
 
Just Bob said:
Thanks for the reply.

The site photo is not accurate to what is on the bike. The crank on the bike looks completly different. The crank is a Shimano 105.

As far as the BB, how do I know what type I have? Are there certain sizes, or configurations that are critical to changing an entire crank?

Thanks for the info so far.

Bob

If your crank looks like this, it is non-Octalink:

http://tinyurl.com/yvwot5
 
Thanks for the replies everyone.

dgregory57, I notice you live in Wilkes Barre, I grew-up in Mt Cobb (10 miles east of Scranton), and my brother currently lives on New Alexander street in Wilkes Barre. I currently live in upstate NY at the foothills of the Adirondacks.

capwater, the link you posted looks just like the crank on my bike.

I am not "topping-out" on the flats, but these nice long hills just beg to fly down, and I am "topping-out" peddling at about 35 mph, and could get coasting to about 42-45 mph going down them.

I would just love that extra ooomph!

As far as the smallest ring, after a thousand miles, I think I used it once, so I am leaning towards going with a double.

I don't mind spending the money for a new crank if need be.

Any recommendations on brands/types, if I go that route?

Thanks so much for all of the help so far.

Peace,
Bob
 
Just Bob said:
Any recommendations on brands/types, if I go that route?

Why not go with a 105 double? Great value, quality and performance. EBay has some NIB ones for about $130, though I have seen them go for about $70.
 
Shimano do DA Pairs of Triathlon Chainrings in 130mm PCD:
ISMDAGEARTR1 FC-7800 CHAINRINGS 56-44 10-SPEED TRIATHLON SET $
ISMDAGEARTR2 FC-7800 CHAINRINGS 55-42 10-SPEED TRIATHLON SET $
ISMDAGEARTR3 FC-7800 CHAINRINGS 54-42 10-SPEED TRIATHLON SET $