Med!c

So I'm looking to buy a new derailleur for the rear and I was hoping someone could help me out before I spend the money.

I have an 8 speed bike and i was told on the forums that i could use a 9 speed derailleur. I want to get something good that will last, so I figured 'd get the shimano saint.

this is the exact product.
https://www.amazon.com/Shimano-RD-M81...ear+derailleur

From other derailleurs I've looked at usually it says the long cage has a max capacity of for example a 44T front crank, and the short cage one has a 32T capacity. I dont really see that for this product and some of the info in there is a bit confusing for me. So I was hoping if someone could just flat out tell me if this will fit my bike or not. And if not if you could recommend a product I'd appreciate it.

DCB0

THe 'capacity' is the difference between the big and small chainrings plus the difference between the biggest and smallest cogs. Since you did not specify what gears or components you have on your bike you are hte only one who can say if the derailleur will work.

Med!c

I have a 11-32 cog in the rear and the front is 42/32/22. I was under the impression this was sort of the standard, but it looks like this range is out side what the derailleur supports?

brian669

you can cross reference the rd with the manufacturer about compatibility with 8/9/10 but with that cassette you're going to need a medium or long cage dérailleur to clear the cogs above 28t. you shouldn't have issues with the chainrings. my guess is the one you are looking at has a 32t cog limit.

Delmarva

Check the Shimano website for specs on the derailleur but I suspect the total capacity is 45 for a Shimano longcage. I would suggest that you think through what you will gain by going to a 9 speed cassette. To help you in that process the Sheldon Brown website https://www.sheldonbrown.com/gears/ has a great online calculator that will display the gear inches for all combinations chainwheel and cassette. Just plug in the existing and proposed configuration and see if that extra cog will make a difference. To be honest I'm not convinced.

One easy way to find out if a 9 speed will work is to just take your bike to a good local bike shop. Ask whether it can be done and what the price is. And if it is an easy swap that you think makes sense, then consider having an expert do the work.

Unless my math is wrong your current configuration has a 41 spread which is within the 45 capacity of a longcage.

DCB0

https://techdocs.shimano.com/media/te...9830647022.pdf

^ the tech doc from Shimano

It says, if you use the 'mode converter' the capacity is 37t. You need (32-11) + (42-22) = 41t capacity.

Is this for a dirt-jump or DH bike? Because that is the primar use intended for the Saint group.

You are likely better off with a Deore or SLX derailleur... Designed for use with triple chainrings and wide spread cogs.. and likely much cheaper.

DCB0

I think the OP is intending on keeping his 8 speed cassette and shifters, but switching to a 9 speed derailleur, which is 100% compatible with 8 speed Shaimno spacing (except for Dura Ace).

HillRider

A 9-speed rear derailleur will work fine with your 8-speed drivetrain. Do not buy one of the new Shimano Dyna-Sys 10-speed MTB rear derailleurs but any 9-speed version will be fine. You will require an MTB rear derailleur to clear the 32T big cog and you need a "total wrap capacity" of 41 teeth or more as your current gearing has 41 "total teeth" ((42-22)+(32-11)=41)

Med!c

The thing is that I want an indestructible derailleur and I dont want mind spending the money if I will be getting quality. As far as riding goes, I guess I mostly do XC since thats a lot of whats around here.

The other thing is that I never use that 3rd gear on the front. I'm 99% in 2nd which is the 32T. I guess with that concidered the saint will work. But I think I will take the advice and get an SLX. Maybe get new brakes with the money saved.