[c101aviojet]

Hi,

My bike runs on 3x7 speed (something like 22-32-40) and I'd like to throw the big and middle rings and put a 36t or 38t chainring + bashguard.

Keeping in mind that finding anything for 7s now is almost a challenge - the only real drawback I see to this "obsolete" transmission, BTW- and that I'd like to pay as little as possible, I was wondering if a 9s chainring would do the trick.

In theory, the 7s chain is wider and longer than a 9s one, so I'm afraid it wouldn't grab on the ring as deep as required, and might have some side play too. However, I've read quite a couple of comments here and there saying it's doable and works well (perhaps the difference between chains isn't that noticeable)...

Similarly, I'd like to know if I could use a modern derailleur when I break the current one. A 9s cassette is wider than a 7s one, so I have some hopes that the spacing between each shift is the same (only varies the amount of travel from lowest to highest sprocket).

Have fun!

 

[samnation]

it sounds like you'll be fine a 9 spd derailleur can be setup and work with a 7 speed cassette and shifter. you just need to keep your cassette and shifter at the same number. 10spd mechs are where things get funny but it doesn't sound like your price range puts you in that realm.

Chainrings don't matter in your case.

 

[HAB]

I assume you're running Shimano stuff? Any of their 9s derailleurs will be fine. The spacing between cogs isn't the same but that doesn't matter. The shifter dictates how much cable is pulled and thus how far the derailleur moves. So long as the derailleur moves the same amount per amount of cable pull, which has been the case with Shimano's mountain stuff for a long time until the advent of 10s you're good.


Also, 8s has the same spacing between gears as 7s so you can use an 8s shifter if your 7s one craps out. There'll be an extra click that doesn't do anything but if you have the derailleur set up right you won't be able to access it anyway.

 

[c101aviojet]

samnation, chainrings don't matter? Should I expect the new ones to be a direct replacement then, (i.e. unscrew old bolts, remove old rings, put new ones, screw again)?
Well, nice to know the derailleur idea can work. No, definetely not looking at 10s anywhere soon. For my riding 7s is enough and strong, if I switch to 9v it's because of "market pressure".

HAB, I currently use shimano derailleurs (modern LX for the rings and old Slx for the sprockets) with sram gripshift shifters.
The difference in cable pull between brands means my setup causes a certain mess with the rear sprockets, but it's rideable. The rings don't suffer the problem (they shift great) because of the freedom the gripshift allows.
When something breaks out I'll probably look at sram stuff (I am a bit tired of adjusting derailleurs often).