I’m looking at what spare parts I have kicking around, and trying to shoehorn 6 sprockets from a 7 speed cassette into the back of my 120mm singlespeed frame using a Suntour XCD hub.

I have an old Veloce derailleur, and Charlie the Bike Monger sells 9 speed Sunrace bar end shifters, SRAM do a nice 7 speed cassette with the ratios I want (once I’ve removed the biggest cog).

It’s been so long since I’ve run 7/8/9 speed that I can’t remember the compatibilities…

1) I want to run a 7 speed chain

2) 9 speed indexing is the same as 7 and 8 speed?

3) Shimano/Campag incompatibility is in the cassette spacing, not the derailleur? i.e. if the shifter is indexed for Shimano, will the mech work?

Anything I’ve missed?

Ta

9 speed indexing is the same as 7 and 8 speed?

Same cable pull ratio, i.e pull 1mm of cable a 7/8/9 speed mech will move 1.7mm sideways, but its different increments for each shifter, more gear mean closer sprockets and smaller steps.

So 7spd pulls more cable per click than 8, 8spd pulls more cable per click than 9… make sense?

This is a useful resource:

https://en.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/Gear-changing_Dimensions

It does also discuss mixing and matching Campag and Shimano…

Same cable pull ratio, i.e pull 1mm of cable a 7/8/9 speed mech will move 1.7mm sideways, but its different increments for each shifter, more gear mean closer sprockets and smaller steps.

So 7spd pulls more cable per click than 8, 8spd pulls more cable per click than 9… make sense?

Oh wow, really? I’ve forgotten more than I realised, I always thought the increments were the same, but that there were just more of them! Better read up, sounds like I might end up struggling to find an appropriate (non-friction) shifter at this rate…

Edit: excellent link, thanks!

Also…

3) Shimano/Campag incompatibility is in the cassette spacing, not the derailleur? i.e. if the shifter is indexed for Shimano, will the mech work?

No, Shimano 7/8/9/(and road 10 but not Tiagra 4700!) speed mech ratio is 1.7, Campag 9 speed is either 1.4 (old Campag 9sp) or 1.5 (new Campag 9 speed), so you need to factor that in as well.

Assuming your Veloce mech is ‘new’ 9 speed with a shift ratio of 1.5, and you’re going to run a ‘normal’ 7 speed cassette with cog pitch of 5mm (but with one sprocket removed) then you need a shifter that pulls about 3.3mm of cable per shift, of which sadly there are none!

No Shimano index shifters since 6 speed have pulled more than 3mm of cable per click except newer MTB 10 and 11speed. A Shimano 6 speed shifter will pull 3.2mm of cable which is close, but not close enough, but…

3.2 x 1.5 = 4.8

And 4.8 is Shimano 8 speed cassette cog pithc, so if you cna find a Shimano 6 speed indexed  shifter, and use an 8 speed cassette with one (or two) cogs removed you could make it work, but finding a decent 6 speed indexed shifter is going to be a ball-ache.

Campagnolo 8 speed shifters pull 3.5mm though, and mated with an ‘old’ Veloce 9 speed mech will index to 5mm cog pitch (Shimano 7speed, Campag 8 speed) so that could be an option if your mech is ‘old’ 9 speed.

Beyond that you’re now into the realms of either custom spacers in the cassette, or using a different mech, there are a lot more options available if you’re willing to use a normal 1.7 ratio Shimano mech instead…

There’s also potential options with alternate cable clamping/routing if the mech allows it, ie: Shiamno ‘Hubub’ style or the Alternate route/clamp methods used on the old 8speed Dura Ace.

The easiest solution might just be a friction shifter, which I think SA/Sunrace do sell

^ or that 😉

Yeah, or an 8spd Ultegra bar end shifter which exists but unfortunately seems to come as a pair, and I have no need for the front one.

Haven’t searched very hard yet, sure I can find a suitable bar end shifter, if it means using a butchered 8 spd cassette rather than 7 speed then that’s not the end of the world.

Good advice gents, thanks.

Edit: although that would rule out the use of the Campag rear mech of course… hmm. Could be a J-Tech shift-mate solution coming on!

Does a SR LH barend Friction shifter (intended for operating a front mech) pull enough cable to move that campag mech across 8 sprockets? if so there’s nothing really stopping you fitting it to the RH barend other than aesthetic sensibilities…

Failing all of that (and this is getting a bit involved now perhaps) could you re-space the sprockets to suit?

if you look at table 4 on the page I linked before it suggests (extrapolated) cassette spacings to get campag mechs working with 1.7 ratio pull shimano shifters if you could produce 5.26mm sprocket spacings it could work apparently, but then again how long is your Freehub body?

The late Chris Bell’s website was a good resource for this kinda stuff as he’d also make custom spacers – this is what I’ve done previously in a similar situation

Sheldon Brown has a nice chart with all the viable options displayed. You may just make it work anyway. Old Campag is very forgiving. A bit of play in the jockey wheels and a bit of chain wear and it will possibly work happily. I have done all sorts of strange combinations. Some work.