Bicycle Mechanics - Max teeth for a Dura Ace 8-speed RD

I recently got a mid-1990s Specialized Epic Pro road bike and am looking forward to getting back into modern cycling after twenty five years or so off. It's a carbon frame with aluminum (?) lugs and fork, and a full Dura-Ace 8-speed groupo. Since I'm not in shape yet :), and since it's pretty hilly around here, I need to get a little lower gear ratio on the lowest gear(s). I believe that it currently has a 12-24 cassette. I'd love to be able to get two gears lower than the current 24, if possible.

My question is, what is the max number of teeth that my Dura Ace RD can manage? Sheldon's site seems to indicate 27 in some places and 30 in others.

At this point I'm not really interested in converting to 10 speed or replacing the crank; I don't want to get into that kind of cost until I have a few more miles on the saddle.

Thanks in advance for any help!

I run a 13>26 8 spd D/A on my winter bike with no issues.

Be careful about cross chaining though.

'Rasher

It is probably rated for a 26 or 27, like the 9 & 10-speed D-A RD. If you can't find what you want in an 8-speed cassette you can probably build a custom 8-speed cassette. Just be careful to get the cog spacing correct, or at least very close. I would suggest that you try for a 13-26, 13-27, or 13-28. You may need to adjust or replace the "B" screw to get it to clear the largest cog.
In case you don't already know, The 8-speed Dura-Ace right shifter and rear derailleur have a proprietary cable pull and throw ratio and are not normally compatible with other groups. When the shifters wear out you can upgrade to 9 or 10-speed by replacing the shifters, cassette, rear derailleur, and chain.

Al

Thanks for the responses!

So, how will I know if I should get a 27 or 28? Also, when do you know your shifters are worn out, and not just the cables?

Thanks.

I got a 28 on mine, but it was VERY close as the pulley was almost touching the cog. Make sure you don't exceed the recommended chainwrap. I did that on mine (50/34 front, 12-28 back) and destroyed the rear derailleur mid ride.

You know the shifters are worn out when they start sticking. You will click the shifter but nothing will happen. Mine were starting to do that before I had the incident mentioned above. A good dose of WD40 got them working on borrowed time, though.

Thanks for the responses!

So, how will I know if I should get a 27 or 28? Also, when do you know your shifters are worn out, and not just the cables?

Thanks.

Cables and cable housings are cheap and easy to install. Replacing these can sometimes make a big improvement to shifting performance. Hosing out the insides of the shifters can help clean them and soften old hard grease. When these two tricks don't help it's probably time for new shifters. The shifters are the most expensive part of a drivetrain upgrade and are a benchmark for timing the upgrade.

Thanks again! Lots of great information, but it raises even more questions for me. I currently have either a 52/39 or a 53/42 Dura-Ace crankset (I'll have to count it when I get home), so how will I know if I've exceeded the recommended chain wrap? Oh, and I'd better ask, what exactly is 'chain wrap'?

You're addressing two different things in this thread. First is maximum rear cog size, the second is the amount of slack that can be handled by the RD - usually called "capacity".

For cog size, Shimano generally specs 27T as the max for its road RDs, but experience has shown that they can usually handle 30T. That's why you see the two different numbers. As per urbanknight, you may want to assume that 28T is the max. The 7400 group is an odd duck and may behave differently than the "norm" for Shimano.

For capacity, it's the difference between the biggest cog pair (front+rear) and the smallest, in tooth count. I don't know what the 7400 spec is, but you shouldn't have a problem with those two cranksets.

I have a Dura-Ace 6-speed RD (7400) which is very similar to 7-speed (7401) and 8-speed (7402). I think the specs are the same for all three and are 28T big cog and 29T capacity. I've run 13-30 with no problems and have also run up to 33T capacity requirement (50x34 with the 13-30) with very careful chain length setting. YMMV.

Hi all,

Thanks for all of your answers; I ordered the 12-28 from Nashbar yesterday, so hopefully that'll help me get up the hills. I checked and I've got a 39T chainring, so the cassette is really my only answer aside from a compact crank or getting stronger :)

Thanks again everybody.

Hi all,

Thanks for all of your answers; I ordered the 12-28 from Nashbar yesterday, so hopefully that'll help me get up the hills. I checked and I've got a 39T chainring, so the cassette is really my only answer aside from a compact crank or getting stronger :)

Thanks again everybody.

You could replace the 39t chainring with a 38 for a very slightly lower gear combination.