Size Matters???

[Luke Pinneo]

Hi Folks,

I have 26', 21 speed mountain bike, and need to replace the 7-speed rear cassette cluster. I found a few online, but do I need to confirm that they are "compatible" with my bike/hub, and if so how do I do that? What do I measure? Anyone have any idea? Or is it pretty straight forward as long as it is a 7-speed cassette?

Best and Thanks!

Luke

[Bill]

Snapshot a picture of the cassette cluster if you could and also what kind of Mountain Bike is it?

[Joe_W]

Any 7 speed cassette by SRAM or Shimano is compatible to SRAM and Shimano 7 speed hubs and drivetrains. Just make sure you don't have a freewheel but rather a cassette / freehub.

[Luke Pinneo]

Hi Bill - sorry to have been so long replying ... Here are some pics of the cassette, as best I could. http://tiny.cc/n98ra

You'll notice the surface rust on the chain from not having used the bike in a few weeks

Here's more info on the bike itself, a cheapo starter. http://tiny.cc/h974d

I don't do a alot of crazy downhills or serious mb'ing, and don't need a super-strong body, but I usually take it off trail and up hill most often. ALOT of shifting and cranking. I've been modifying my technique, as not to rip through the gears when cranking .. but still ... I burnt through that stock cassette REALLY fast.

There are some great vids on replacing the rear cassette, and I can get the tools fairly cheap.

I don't know anything about fixing bikes, but am committed to learning one thing at a time. After all, once I've done something the first time, I'll know how to do it better and quicker next time.

Any insight you could offer on helping me get the right cassette would be great.

Many thanks,
Luke

[Joe_W]

Only thing you have to think of is what gearing do you need. Are you ok with the gearing (highest - lowest gear) you have at the moment? If so: count teeth on largest and smallest sprocket and get a cassette with the same setup. If you don't like it, think about what you want to change: higher gears -> smaller sprockets, lower gears -> larger sprockets.
Other than that: any Shimano or SRAM 7 speed cassette should do. Just don't go for the cheapest model. Oh, and replace the chain, too!

[Bill]

I could not have said it any better then Joe just said. He is right if you want serious performance in that area and something to stand up to the rugged abuse you are going to need a high end drive train. Wish there was a cheap way around that but there isn't.

[Joe_W]

Well, mid-range is perfect. I don't trust the extreme lightweight stuff to hold up against abuse better, after all it was designed for being lightweight and the pros swap out their stuff quite often -> no problem there. Look at the price progression, somewhere there will appear a "kink" in the graph, that is the price difference to the next better model will be much larger than the differences before. That said: there are no really high end components for seven speed. This has been abandoned for quite a while (I think).

[Luke Pinneo]

Thanks for the great info guys. It really helps. Another quick Q: I looked up the difference between a freewheel and freehub, and am pretty sure mine is actually a freewheel. Here's a closer look with the wheel off. http://www.flickr.com/photos/lukepinneo/4723052110/ Is this right? Freewheel?

[cyclerUK]

(06-21-2010, 09:26 PM)lukepinneo Wrote:  Thanks for the great info guys. It really helps. Another quick Q: I looked up the difference between a freewheel and freehub, and am pretty sure mine is actually a freewheel. Here's a closer look with the wheel off. http://www.flickr.com/photos/lukepinneo/4723052110/ Is this right? Freewheel?

I'm fairly certain that is a freewheel.
You will have to determine which tool to buy if you want to do the job yourself.
There are a number of different tools for various makes and design of freewheels.

You have to make the choice of whether it's economical to the job yourself (ie the job may require doing again if you intend to keep the bike for a long time) or let your LBS do it?
You will also have to source the correct tool and purchase a similar freewheel.
You could get a new freewheel that has the same sprocket ratios but requires a different tool to remove in future.??

ALL FREEWHEELS ARE NOT THE SAME!

[Bill]

(06-21-2010, 09:26 PM)lukepinneo Wrote:  Thanks for the great info guys. It really helps. Another quick Q: I looked up the difference between a freewheel and freehub, and am pretty sure mine is actually a freewheel. Here's a closer look with the wheel off. http://www.flickr.com/photos/lukepinneo/4723052110/ Is this right? Freewheel?

I think I read the lettering on it which is backwards printed on the photo but does one of them say "freewheel"? I attached your pic edited with a red arrow pointed to the word I mean.

[Luke Pinneo]

Bill - it does. That, and comparing cassettes online, is what got me thinking it was freewheel.

Cycler UK - "Not all the same" ... So it seems.

So - I tried taking the hub out of the wheel last night, to get a better look at the center of the cassette, to better determine for myself if it was a freewheel or freehub - and all the bearings fell out of the center of the wheel. I want to get new lighter rims with quick release anyway - so now I have an excuse.

It's kind of a can of worms tho, I don't know anything about bikes. I go to fix or adjust one thing, and something else gets jacked up. But - I really don't mind using a $200 Walmart bike as a sacrificial sheep.

I'm pretty confident that on the long term, I can learn to do my own maintenance. I've already learned a lot about cassettes and hubs this week! Thanks again guys.

[JonB]

Erm, if bearings are flying everywhere I suggest you watch Alex's tutorial again as you shouldn't need to touch the bearings to get the freewheel off.

[Bill]

I think I know what you are saying. This type has loose bearings and when you took out the axle they fell out. This is not a total loss. Count the splines (ridges) and take a ruler with Millimeters and measure from spline to spline. I have attached a picture to show ya what I mean. Red arrow shows what a spline is and those should be counted. The blue is where you need to measure from spline directly straight across to another one as shown. Let me know this and I can look up the freewheel remover you need.

[Luke Pinneo]

I will measure it out, and let you know what I find. Thanks! Also, Is is possible to just replace the axle, to make it quick release? (provided I find one that is compact)

[Bill]

Yes I have heard of many conversions like that. Measure your axle length and diameter to find what you are looking for.