Running modern crankset on 8 speed

[mike-L]

I have an 8 speed shimano cassette and STIs and I'm happy with it - see no need for more gears. However, the cranks are mid nineties 105 with 39 so 39-52, the BB is on its way out, and I'd like to go compact - 34-52.

Cranksets have moved on a lot, as have BBs - they are a lot lighter these days. All the new sets seem to be designed for 10-11 speed, except Sora, which isn't much lighter than old 105.

Question is: can I run a modern light crankset/BB with my 8 speed cass and chain? What would work? anyone experience of doing this? I'd guess at least that I'd have to add spacers between the rings to get the chain happily changing?

cheers!

 

[gbb]

Hiya Mike.
I cant speak on some aspects, but what i do know is i run a Tiagra 9 speed double crankset on an 8 speed setup.
Compact ? I gather some front derailleurs may face problems with the reduced diameter of the 50T on a compact, the arc is different and the FD will need lowering on the downtube.. Ive read you may get away with using a standard FD, but no personal experience.

 

[Zoof]

I have an 8 speed shimano cassette and STIs and I'm happy with it - see no need for more gears. However, the cranks are mid nineties 105 with 39 so 39-52, the BB is on its way out, and I'd like to go compact - 34-52.

Cranksets have moved on a lot, as have BBs - they are a lot lighter these days. All the new sets seem to be designed for 10-11 speed, except Sora, which isn't much lighter than old 105.

Question is: can I run a modern light crankset/BB with my 8 speed cass and chain? What would work? anyone experience of doing this? I'd guess at least that I'd have to add spacers between the rings to get the chain happily changing?

cheers!

Hi from experience you are moving into an engineering nightmare.

It's best just to dig deep, and change the lot.

Try http://www.spacycles.co.uk/ for a strong-light to fit rear cass.

or http://www.sheldonbrown.com/home.htm

This is the best web-site for technical advice




Good luck Zoof

 

[boydj]

I upgraded the cranks on my old 8-speed Mercian with a bargain-basement Campag Centaur 10-speed triple crankset, retaining the original Campag front shifter. The front shifter later gave up the ghost and was replaced with a Shimano 105 triple unit. Both setups with the 8-speed rear and 10-speed chainset worked fine. The only real difference is that the chain is slightly wider than the chainset is designed for. It probably helped that the Campag front shifter has multiple positions to allow trimming of the mech position to avoid chain rub.

As for going compact - I've got compact on my newest bike, and triple on my commuter and the bike I did most of my miles on last year. I have to say I prefer the triple as the jumps between gears when changing chainrings are much smaller and it's a lot easier to stay in a comfortable gear and maintain a relatively straight chainline. I'll be changing from 34 - 50 to 36 - 48 on the good bike to try to make it more user-friendly, and I'll swap cogs depending on the routes that I'll be doing this year.

Note that you may well have to swap your front mech if you switch from a standard to a compact double - as has already been pointed out - but I'd give it a try with the original as it may work ok.

 

[Zoof]

Hi boydj I had the opposite problem to you on F/chain-ring.

I upgraded to a 9 deore Cass, this uses a supper narrow chain.

So, first I had to skim the strong-light F/rings.

The next problem was a thick stem, leaving the F/Dr proud.

Which left not enough clearance, to allow the F/Dr to kick-down to low-ring.

I ended up using a 1970s F/Dr that dropped flush with the stem.

The profile also fitted my 52t chain-ring much better.

(To solve this problem, Shimano move out the C/ring by 4 mm.

This stops you using low cog in mid ring, not always convenient.)

My changes now are sweet and clean, and I am well chuffed with the result.

But I must point out that, my steed is a Cherished bike, and some parts now are unavailable.




Changing from standard: it can be an engineering nightmare!!!!!




Good cycling Zoof