Sprocket and Groupset Compatibility

It will be fine with a spacer behind the cassette.

Get the 10 speed deores, it'll work.

The difference is just the recent 10 speed derailleur, not the cassette.

Brilliant! Thanks Picard and I'll make it so:)

Thanks Ed. New Deore derailer will be at the shop tomorrow, so will give it a go.

Yeap the 9sp works perfectly, all is good.

Good to know.

to narrow it down, the road 8/9/10 speed have the same cable pull (with the exception of the new Tiagra 4700 which in theory have the same pull as the 11 speeds one).

MTB 8/9 (and old 10 speed) have the same cable pull as the road, the exception is the modern 10 speed which required a different pull.

The 7/8/9/10/11 cassette spacing remain the same.

I have a Shimano 600 groupset on my 80's Cyclocross bike (frame shifters) which runs a 7-speed cassette. Is it possible to run an 8-speed cassette? I have a seller with a lovely wheel set who is wondering why I just don't take the 8-speed cassette the set comes with. Calling Cpt. Picard or other knowledgeable mechanics?

You can, spacing between 7 and 8 is near identical, just with one extra cog.

If it's friction shift, just set the rear derailleur limiter.

Also you can fit 7 speed cassette on it with spacers

Thanks for the reply. I would be importing a new wheel with the 8-speed cassette already installed so no problem. I had been asking if it was 7-speed compatible but if the 8 speed works then Bob's your uncle. Appreciate the help :)

Friction shifting solves all the cable pull compatability problems that you get with indexing.

Using a customer's bike for references, he had an old 7 speed Shimano indexed set-up that was in great condition (the kinda guys who replaced the chain twice a years preserving the cassette and chainring), but his downtube shifters broked.

He was getting old and wanted a more accessible shifters, instead of using the inferior Shimano Tourney that have a tiny thumb shifters, I was able to set up a new 8 speed Claris shifters set which worked perfectly well throughout the gears.

Technically, the Shimano 7 speed have a 5mm gap between each cog, and the 8 speed is 4.8mm, the 0.2mm difference is too small to make any noticeable incompatibility.

The 8-speed cassette already installed so no problem.

Just realised this, what the range of that 8 speed cassette? (like 11-23, 12-25), and what range is your current 7 speed cassette is?

You might want to change your chain if it haven't been touched in years.

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you make 7 speed work with 8 speed shifters you have to set the indexing from the 4th cog otherwise over the other 7 cogs that 0.2mm difference adds up to 1.4mm which means a noisey low gear.

If I can't source a short-cage DA 7800 rear derailler, what current DA spec. RD will be able to take its place?

IIRC it's normally the levers that control the cable pull so could I fit a DA9000 11spd RD with no ill effects or is there some other geometry trickery going on?

@hippy, my understanding (which would need to be confirmed) is that the derailleurs had the same pull ratio from 6 to 10 speed (with the exception of DA up to and including 7400), meaning the shifter was the only thing determining the movement.

But that changed between ten and eleven speed (with the other exception: 10 speed tiagra, which went to "11 speed" pull ratio), so 11 speed rds respond differently to the shifter.

That might explain why you're having trouble sourcing the last of the lineage, they're expensive to upgrade from and people want to replace them. You could go back to 7700 (to maintain a fairly consistent appearance), I have a short cage one of you're interested. Or get a ten speed Ultegra Rd.

Summary: I don't think you can use any current gen DA derailleur, sorry.

I had a feeling something like that was the case. I think similar happened with 7900 brakes and cable pull ratio. Since it's now an insurance job I'm just going to leave it with Evans to see what they can do. Thanks for the info.

If I can't source a short-cage DA 7800 rear derailler, what current DA spec. RD will be able to take its place?

5700, 6700, 5600, and Sora (inc. current version).

@edscoble all viable, but I thought he meant "current DA".

Would be interested in your thoughts on how time and trickle down relate though - what kind of model or dura ace would you equate with current sora?
Does the higher level of effort put in to old top-of-the-line stuff count for anything in longevity etc vs modern entry level made with less effort but modern tooling?

It's DA spec. though, I'm not putting something cheaper on it. I'm not sure how the insurance shit works but I shouldn't end up with lower spec. parts because someone else fucked my bike up.

In my case I don't even care about new vs. old function, I'm just not putting something like Sora on an S-Works/DA spec. bike.

It's a 15 years old groupset, hopefully, the branch of the fallen Evans you've chosen will quote a new groupset.

All the "specs" (like real specs, weight, strength, tolerances) move down the range over time though. Current sora is probably better engineered than 90s DA, and certainly Ultegra. I know that's not how we see it, but insurance may well want to argue something like that.

Whenever I have an insurance claim I always argue for the cash so I can control the tradeoffs. Had real problems getting equivalent spec laptop replacements in the past. I'm a software engineer, so I have specific requirements, insurance were only willing to provide something which cost similar to the old ones heavily depreciated RRP rather than something which actually performed similarly...

That was generic home insurance after burglary. Specialist insurance might be a bit better. But if you have requirements, make them known, because otherwise the insurers definition of "repaired" might not suit you at all.

Yeah, like Ed says, push Evans to specify what you want to see out of it.