Gearing

[kaiser]

Trying to work out what gearing to run on a new build. Really want to fit a dura ace mech I have. The 8 speed one also have a 42 big ring and a 24 small and looking to fit a 12-25 or 13-25 block. Any way of knowing if this will work before hand? Anyone using a dura ace rear mech? Cheers

 

[utahdog2003]

Dura Ace vintage stuff (RD-7402, et al)is not happy with other Shimano goodies. You'll need Dura Ace shifters of the same vintage. :cry:

 

[kaiser]

Dura Ace vintage stuff (RD-7402, et al)is not happy with other Shimano goodies. You'll need Dura Ace shifters of the same vintage. :cry:

Doh, I thought this was a mod BITD and I've seen someone on here recently with one.

 

[Iwasgoodonce]

I certainly remember seeing 105 and Ultegra around BiTD. Did Dura Ace have one ore ratio though?

 

[hamster]

The thing to check is the amount of chain the mech can wrap. For road mechs it's usually about 29 teeth. Add the differences in the front and the back. The data is on the Shimano site.

So: 12-23 back with 22-32-42 front is 11+20=31. For MTB use you may well need a 29-42 or similar double.

Usually manufacturers play a bit on the safe side so breaking the rules slightly is worth a try. I run a 12-23 with a 30-39-48 on my road bike with a Campag Chorus short cage mech.

 

[Xesh]

Bitd I used an Ultegra r/mech on a 12-28 7spd cassette with 26/36/46 triple and it worked fine as long as you used the gears correctly.

 

[hamster]

Yes, you can usually get away with the whole lot going slack on the small-small combination. Insufficient chain to do big-big usually stuffs the rear mech into the wheel at the most inopportune moment. If you are really keen you might also be able to rip the dropout off.

 

[kaiser]

:shock: Must get a break away bolt then. I'll give it a go anyway nothing to loose.

BTW how do folks find having a low gear around the 1:1 ratio?

 

[hamster]

No, no, don't! Just don't run the chain too short. Usually the whole drive train locks solid first which equals a crash. A long and baggy chain looks horrible on small-small but is safe. The difference is usually about 3 links extra.

I can't emphasise this point enough. Don't Don't DON'T

I know that you say you'll be careful but the reality is that it happens when you are otherwise distracted - like that bus turning left across you or whatever.

On the second point, my lowest is 29T front, 28 back on a 7s setup. OK for anything here (New Forest) but would probably kill me if I lived in the Peaks! But BITD we all survived with 28T front and a 13-30 cassette.

 

[Xesh]

...small-small combination....big-big

I've never used those combos because it's unnecessary. You can get the same, or similar, gears with other combinations. It also accelerates wear on the drivetrain due to the extreme angle of the chain (much more of a problem than it used to be).

On the granny gear at the front I only ever use the larger sprockets and never go further than halfway down the block. On the large ring I only ever use the smallest sprockets, again never going beyond the halfway point. Obviously on the middle ring I use the whole range of the cassette.