Bicycle Mechanics - Can I replace HG20-7spd with M580-9spd without changing hubs?

I've been off the saddle for years, and just a few days ago, decided to buy a Cannondale trail MTB.
It only comes with a 7-speed ALTUS shifters and drivetrain and I plan to use my old 9-spd DEORE from an older bike on this MTB.

Can I swap the 7speed cogs(HG20-7) with my M580-9spd without replacing the hubs??

Thanks.

No. However, you can use 8 cogs of a 9 speed cassette on your 7 speed hub and shift with your 9 speed shifters. Google "8 of 9 on 7."

Why don't you try the bike as-is for a while and see what you do and don't like about it? Going from 7 to 8 or 9 speeds won't do a whole lot more than add additional redundant gear ratios and create a more finicky drive train. IMO, the manufacturers' piling on more and more gears is little more than a marketing gimmick; there's not a lot of advantage for an ordinary rider.

No. However, you can use 8 cogs of a 9 speed cassette on your 7 speed hub and shift with your 9 speed shifters. Google "8 of 9 on 7."

Thank you.. Well, I guess I'll be needing a new hub..



Why don't you try the bike as-is for a while and see what you do and don't like about it? Going from 7 to 8 or 9 speeds won't do a whole lot more than add additional redundant gear ratios and create a more finicky drive train. IMO, the manufacturers' piling on more and more gears is little more than a marketing gimmick; there's not a lot of advantage for an ordinary rider.

I guess I'm just so used to 10-speed road drivetrains, but I'll take your advice and try it out..
I have not been on a 7-speed since the 90's.. I was actually surprised that they still make 7 speeds now.
Thanks.

IF it's a new bike with 135MM spacing, you might want to check a bit more closely.
At least some more recent 7 speeds use a 8/9 speed free hub body with a 4.5MM spacer added to take up the extra space.
Look for an "extra wide" gap on the spoke side of the largest cog.

Hi Bill,
It is under Cannondale's 2012 line-up. I'll check it out.
Thanks a lot.

Dex

Can't the OP simply replace the 7-speed freehub body with an 8/9/10-speed compatible one? It might require re-dishing the wheel slightly, but that'll be a damn sight easier than rebuilding it with a different hub.

Can't the OP simply replace the 7-speed freehub body with an 8/9/10-speed compatible one? It might require re-dishing the wheel slightly, but that'll be a damn sight easier than rebuilding it with a different hub.

Yes. I've done it several times. It's easy and not very expensive. Much simpler and cheaper than rebuilding the wheel with a new hub.

Can't the OP simply replace the 7-speed freehub body with an 8/9/10-speed compatible one? It might require re-dishing the wheel slightly, but that'll be a damn sight easier than rebuilding it with a different hub.

It's a new bike so possible that the OP's freehub is already 8+ compatible and has the spacer that, Bill, alluded to.

Brad

It's a new bike so possible that the OP's freehub is already 8+ compatible and has the spacer that, Bill, alluded to.

Brad

Hopefully it will be, but if not, will the 8+ speed freehub body off the Deore hub fit it? I can never remember what the compatibility is between Shimano freehubs, IIRC there are two types of hub/body interface...

Can I swap the 7speed cogs(HG20-7) with my M580-9spd without replacing the hubs??

Probably.

The first thing to measure is the distance between your rear dropouts. Unless the bike is really old it'll be 135mm. If that's the case, you can modify your existing hub and rear wheel to accept a 9-speed cassette.

You'll need an 8/9/10-speed freehub body. New ones cost around $30.00 or so. I generally find a trashed rear wheel with a Shimano hub and salvage the freehub body off of that. After replacing the freehub body you'll need to remove a 5mm spacer from the non-drive side and redish the rim. If you go around the rim loosening each non-drive spoke 1/2 turn and tightening the drive side spokes 1/2 turn, you won't have to retrue the wheel.

Why don't you try the bike as-is for a while and see what you do and don't like about it? Going from 7 to 8 or 9 speeds won't do a whole lot more than add additional redundant gear ratios and create a more finicky drive train. IMO, the manufacturers' piling on more and more gears is little more than a marketing gimmick; there's not a lot of advantage for an ordinary rider.

I agree that this is the best advice so far... falls in the category of "if it ain't really broke, don't fix it" and "KISS". If one has been off the saddle for a while, best thing is to get out there and put some miles on the bike and on the rider. All offered imho, of course.