8 and 9 speed indexing compatibility

I would like to run a certain gearing combo, and cannot get consensus on whether this would work or not. Basically I would like to use 8 speeds of 9 within this set up, what I'd like to achieve is an old school bike which has a lightweight large gear range, which can be set up to either use the top 8 or the bottom 8 depending if I'm in the hills or racing in flatter country.

Dura ace 7400 8sp STI shifters
Dura ace 7403 8sp rear mech
Dura ace 7410 52/40 chainset
Dura ace 7700 9sp 12-27 cassette
KMC X9SL chain

Will the 8sp indexing work over a 9 speed cassette even though a 9 speed cassette has inter cog spacing of 2.7mm as opposed to 3mm for the 8sp?

Cheers,

yes, with a bit of fiddling.
Try and get it dead right in the middle of the cassette.
I have got away with this OK, and amazingly you can set it to get all 9 gears too, there is a sort of dead spot above the lowest gear, if the shifters are OK it will stick there, but when they are worn it drops back down again.

I'd personally just run a wider range block, but it's up to you.

amazingly you can set it to get all 9 gears too, there is a sort of dead spot above the lowest gear, if the shifters are OK it will stick there, but when they are worn it drops back down again.

thats what I was hoping to try - any more info? the shifters are in good nick, is that dead spot below the highest gear as well?

I'd personally just run a wider range block, but it's up to you.

It's also really hard to get a hold of a lightweight 8 speed cassette, and I'd prefer dura ace. the 8 speed dura ace ones didnt have the titanium lower cogs, and weren't as ramped and profiled as the 7700 one. 9 speed chains are also much lighter and apparently shift much more readily due to the space avialble for the outer link plate profiling

Sheldon Brown talks about alternative cable runs at the derailleur anchor bolt to adjust the amount the derailleur travels per click.

Go here: http://sheldonbrown.com/derailer-adjustment.html and scroll down to "Alternate Cable Routings" towards the end of the page. You can increase or decrease the travel per click. Never tried it myself - if Sheldon sez it, consider it gospel. Not that I'm endorsing the Gospels as Truth, but you get the meaning.

12-25 Tiagra cassette here... http://www.chainreactioncycles.com/Models.aspx?ModelID=1864

Weight penalty over Dura Ace is 58 grams. Compensate this by removing the excess of seatpost in your frame or by not wearing two thin socks or one thick one.

I am new here. My bikes are all heavy, as am I. My shifting, however, is perfect.

I think you'll find the weight difference is over 200g, which on a wheel is a lot. I'm trying to keep the bike under 9Kg which for a 62cm steel frame is not easy!

9 speed DA 12 25 is about 175 gms
9 speed Tiagra 12 25 is about 230 gms so the actual difference is 55 gms.

I'd personally just run a wider range block, but it's up to you.

Or change the chainring for a smaller one.

you're correct that a Dura ace 7700 is around 180g for the range I want, 12-27, but show me a 9 speed Tiagra cassette that weighs 230g and I'll buy it! Wiggle has a published weight I can see for a 9 speed Tiagra of 270g and thats for a 12-23 block...easily 100g in the difference.
@ Scoble I'm running 39-53 up front for the widest possible gear range

I was quoting weight weenies
http://weightweenies.starbike.com/listings/components.php?type=cassettes
perhaps I should actually weigh them, as shimano don't seem to list the weights on their website
I have always assumed weight weenies stuff to be pretty accurate

thanks for the link - looks like tiagra and ultegra are very similar in weight and materials, the price difference is huge though, how can they justify it?

magnets

I would like to run a certain gearing combo, and cannot get consensus on whether this would work or not. Basically I would like to use 8 speeds of 9 within this set up, what I'd like to achieve is an old school bike which has a lightweight large gear range, which can be set up to either use the top 8 or the bottom 8 depending if I'm in the hills or racing in flatter country.

Dura ace 7400 8sp STI shifters
Dura ace 7403 8sp rear mech
Dura ace 7410 52/40 chainset
Dura ace 7700 9sp 12-27 cassette
KMC X9SL chain

Will the 8sp indexing work over a 9 speed cassette even though a 9 speed cassette has inter cog spacing of 2.7mm as opposed to 3mm for the 8sp?

Cheers,

It's also really hard to get a hold of a lightweight 8 speed cassette, and I'd prefer dura ace. the 8 speed dura ace ones didnt have the titanium lower cogs, and weren't as ramped and profiled as the 7700 one. 9 speed chains are also much lighter and apparently shift much more readily due to the space avialble for the outer link plate profiling

Moans about a cassette not having titanium lower cogs but it willing to carry 9 cogs (of whatever material) everywhere but only ever use 8 of them.

Go figure.

Edit: To run a 9 speed cassette and alternate between using the top 8 and bottom 8 with an 8 speed shifter you will need to adjust cable tension and high/low limt screws everytime you change the gearing. You will need to entirely reindex the gears to go from 'mountain gearing' to 'racing gearing'. And remember that you'll be re-indexing gears that won't index properly anyway because of the different cog spacing between 8 and 9 speed.

Will the 9 speed chain work ok with the jockey wheels in the 8 speed mech?

I still want the lightest 9 speed cassette, I just want to try it if possible - changing the high/low limit screws is a lot easier than changing the cassette, I think I'm going to be able to use all 9 anyway, I just have to change the cable routing on the rear mech to compensate for the spacing between the cogs according to sheldon.

I have an 8 speed cog anyway, just wanted to try using a 9 speed cog, as far I as i can tell they're a fair bit lighter than the old 7410 8 speed ones, and I might get the use of 9 gears. If not, I'll take 8 of 9, I won't be switching it around that often, if I'm riding in Greece I'll take the low 8, in the Netherlands the high 8.

Not sure about the jockey wheels yet - I'd like to find out before I buy the chain - Sheldon seems to imply that most of Shimano can be pretty much compatbile with a bit of tinkering..