braintree39

I currently have an old derailleur that I'm using with friction shifters on a SRAM 8-speed cassette PG-850. I have a 105 front derailleur. I'm thinking about buying a 105 rear derailleur to match the front. Ultimately, I want to buy a 10-speed cassette to replace the 8-speed (index my rear derailleur, etc. etc.).

Will a 10-speed cassette fit on my hub or will I have to replace the whole hub? Could I just swap out the cassette and chain and be good to go?

Wilfred Laurier

10 sp cassette should fit on your hub no problem, but the wheel with 10sp cassette might be a tight squeeze in your frame.

HillRider

Why? If the wheel fits now why should changing from an 8-speed to a 10-speed cassette on the same freehub body change the overall width?

CyclingFool95 

Presuming your frame has 130mm spacing you should be fine. Even if not you should be fine. I had a 1989 Fuji (6 speed) that I converted to 10 speed Tiagra a couple of years ago. The rear axle had to be jammed in since it was a 126mm frame, and I had to lock out (via limit screw) the smallest cog, but that was because the derailleur hanger had been stripped and repaired, and the insert had a flange that protruded into the space

Shimano hubs are 8/9/10 compatible

braintree39

I have 130mm spacing - so I think I'm all set! Thanks!

braintree39

Would it be a bad idea to put the derailleur on now or should I wait I until I upgrade the cassette? Does it matter if it's an 8-speed chain? I'm using friction shifters.

CyclingFool95 

I'd suggest leaving it as is and upgrade derailleur, cassette, chain, and levers (presumably you are going to STI) all at once. You might see some issues with the wider 8 speed chain on parts meant to run with 10. I know it's not an issue with cranksets but I'm not so sure about the detailed, and a ten speed cassette would probably have issue with an 8 speed chain.

braintree39

Yeah, you're probably right. I was definitely planning on doing the cassette and chain at the same time. I think I'm actually going to skip the sti levers. They are really expensive and I'm pretty used to downtube shifters.

I know it's ideal to do it all at once, but would it mess up a 10-speed derailleur to use it with an 8-speed chain?

Ironfish653

As long as it fits between the cage plates, an 8-sp chain should go through a 10-sp RD without a problem, especially since you're using friction shifters.

I run a 9-sp chain and cassette with a 10-sp RD, with 9-sp STi's with no problem, you should be OK.

Iride01 

I'd also agree with doing the entire upgrade at once. Shifters will be the big expense. DR's, cassettes, chain and even brakes are relatively inexpensive. If for some reason you can't use the existing wheel, then that might be somewhat large expense depending on how much elitism you want to pay for.

ART_K

shouldn't be a problem

bakerjw

Our road tandem came with a Claris 3x8 shifters and some cheapo rear derailleur. One of the first things that I did was to swap out the low end rear derailleur with a Deore SGS derailleur. IIRC, the main difference between an 8 and 10 speed chain is the outer width. The inner is the same.