New crankset sizing issue
 

My bike was in a small accident and the crankarm was bent. So, I need a new crankset. The bike is a hybrid Cannondale Quick. It has a Shimano 48/38/28 chain rings and 170 arms. I asked my LBS if there were any cranksets that didn't cost a huge amount with 165 crank arms. I favor the shorter length. Also, my bottom bracket is grinding so I figured I would change that at the same time.

Anyway, they sold me a Sora crankset and and new kind of bottom bracket, not the square taper that I am used to, and the tool to put on and take off the new BB. My issue is the crankset. It turns out that it is has 50 teeth on the big ring and 30 on the smallest. Did they sell me something that is not going to work well with my front derailleur? Does this mean a lot of adjustment on the front? I am wondering if I made a bad purchase. As everything is still in boxes I trust I can return them.

It should work if you can move the FD up a couple of mm to clear the 50. Probably will shift as well or better than what you had.

Yeah, but it has 170 arms. Actually, this is the crankset that I put on my relatives crap bikes. :) Good price, eh?

As long as they're both triples you'll be fine.

As noted above, you'll probably need to raise the FD a bit.

But before you remove the old crank set, use a ruler and measure the distance from the outer ring to the down tube (or seat tube). When you install the new set, it'll have spacers which allow you to adjust the chainline. Use the combination of spacers which gets it closet to the original, to ensure that you're in the FDs travel range.

Thanks.

I'll see if anyone has any other comments and if the consensus is that this will work great I'll keep the set. I think I can handle moving up the front derailleur, I had to adjust it on my husband's bike as it had slipped down over the years.

Good tip! I would not have though of this.

That is standard chainring set , packaged for OEM assembly by the millions.
[low price follows]

want different sized chainrings?. buy them , just match the bolt circle.

you would have paid as much for just the crankarms..

They sold you a road triple to replace a MTB triple (48/38/28 was a standard size to match freewheels, freehubs are often paired with 44/32/22 chainrings). Whether you'll have problems depends on what FD you have and if you can get the chainline worked out. 48/38/28 cranksets are still readily available so I wouldn't want the trouble of dealing with a road crankset.

Yes, they are readily available, but with 165 arms? Or where the crank arms can be separated from the chain rings?

(The bike is an 8 speed with a cassette, not a free wheel)

goldfinch, The shop probably offered that crankset primarily because of the crankarm length. Other than moving the FD to clear the big chainring and adjusting the chain line I don't think there'll be any problems with function. You may find yourself in a lower ratio gear at the cassette than previously.

Brad

I have never been sensitive to crank length riding 170 and 175 mm etc. and would have to look to even know what one I was on. I do understand some people are more sensitive.

I like to tell people the 5 mm is the thickness of 3 penny’s stacked up or something like a 3% change in length.

If you know that difference will be a factor in your riding then by all means go for the 165 arms.

Well heck, the price was right for the crankset and I really do prefer 165 arms, so I am going to give it a go. If I have trouble adjusting the chain line I'll take it in to the LBS. I want to get this done because it is my rain bike.

OK, it wasn't so bad. Had to raise the derailleur a smidge and adjust the limit screws to bring it in a bit. Now I just have to go for a ride!

Wow. I am glad I used the Sora crankset. This bike has never pedaled or shifted so smoothly. Very nice. And the funny click that I used to have when I pedaled is now gone. :) Maybe it is psychological but I find the smaller diameter crank arms so much more comfortable to pedal.

Actually you changed two things other than the gearing; the tread width and the crankarm length. If you reset the FD limit screws to deal with chainrings closer to the seatpost, you reduced the treadwidth. Pleased it all worked out.

Brad

Yes, I had to reset the FD limit crews quite a bit as the chainrings are much closer to the seatpost. I didn't realize that was called "treadwidth."