Drivetrain Compatibility
 

I have a 3x8 drivetrain on my mountain bike. Shimano hubs, Shimano cassette, and a 3 ring Sachs crank from circa 1995. I use Rapid Fire shifters.

I wish to install a new crank with the hollow bottom bracket spindle that will work with the rest of the drive train. Will the current Shimano 10 speed triple MTB XT cranks work with my current front derailleur setup and 8 speed chain? Are the chain wheels on the crank spaced the same as on an old triple crank that was made for a wider chain?

Any help would be appreciated.

You might have rub problems using smaller cogs and rings together unless you shim the big and small rings back to 8 speed spacing.

When I tried combining an alleged "9 and 10 speed compatible" FSA Carbon Pro compact crankset with a Campagnolo C9 chain I had rub in the big ring on the last few gears which produced no usable overlap between rings until I spaced it back to 9 speed dimensions.

You can get 0.6mm spacers from letour made specifically for that problem and 1mm are not uncommon.

Might or might not work. Chain ring spacing could be an issue. Amazon has spacers, search for round shims, you need 10mm ID, 12mm OD, stainless steel; or any industrial supply house - much less expensive than bike specific parts, which are just repackage industrial parts.

Why do you want to make the change?

If you insist on the change, I would strongly recommend a new cassette at the same time, along with a new 9 speed chain, which is more likely to play nice with the 10 speed crank set.

The spacing for a 2015 triple MTB crank is the same as for a 1995 crank. The 8 speed chain should work fine 10 speed crankset and 8 speed drivetrain compatibility

Hope your running Rapidfire Plus not Rapidfire, Rapidfire shifters were discontinued around 1990.

Lose the Indexing and Friction shifting makes all combinations compatible

You dont have to be a Marketing Victim, 8 speed is Fine , just replace worn cassettes and get a new Chain.
all that happesn with the latest Chainrings is the teeth have to be Thinner so the narrower chain slips over them.

they may be closer together , but thin shim washers can cure that.

8 cog cassettes are a bit longer wearing and the chains Cheap enough.

Gear Ratios matter more than "speeds"

8 speed may be just fine, but running it back in the 90's, as soon as 9 speed came out, the supply of XT cassettes dried up, almost forcing you to go 9 speed, today isn't as bad when speeds are changed, being able to source parts from anywhere on-line, add to that Shimano has changed the hierarchy format for parts like Cassettes and BB's so they cross over levels and are much more available.

Looking at 8 speed cassettes available today, you are limited not by ratios, but weight/component level, SRAM's highest offering is the PG850, Shimano HG51/Alivio

To be fair, the HG51 was Deore before it became Alivio. Classic "trickle down" Shimano. It didn't become a worse cassette when they decided to put it at a lower level.

Agree with they didn't become worse in a shifting sense, but if you are running a mid-high level setup, say LX/XT in mid 90's terms, changing to an Alivio level cassette today will be very noticeable in weight.

Its a consumable .. steel in the cogs is the same, just the plating to look pretty when clean, separates the models .
go by tooth count

I'm not sure that's true is it? Weight losses for cassettes have trickled down as well as technology. A HG51 in 11-30 configuration weighs about 300 grams. A mid 90s XT is going to be in that range also.

Looking at Weightweenies, an XT 8 speed (11-28 or 11-30) come in around the 250g-255g range, not a lot, but you would notice this vs the 300g for the HG51

Getting back on topic, I've used 8 speed chain on Shimano 9-speed MTB triples without issue. I've also used it on Shimano 10-speed road doubles without issue, but haven't tried a 10S MTB triple yet.

You can still find new HollowTech 9-speed MTB triples. I'd go for one of those.

I double checked and the latest HG51 in that range of gears is 283g apparently. I'm not going to pretend that I can tell the difference of 30g in a cassette when riding, but fair enough, it is heavier.