Mountain Biking - 9-speed chainrings on an 8-speed?

Well, my center chainring is screwed, and my nice cheap stock Shimano chainrings refuse to be able to be replaced so I am going to get a new crankset...I think. Since I have a dumb square taper bb I suppose I will more than likely have to get a new bb, also. Most of the cranksets I have looked at say that they work with 9-speed setups, but I have an 8sp and am pretty intent on sticking with it as I just bought a new chain and cassette. Yes I rode with a worn out chain and wish I had known to check it, before it was too late... So will a 9-sp crankset work with a SRAM PC-58 chain? It is an 8-7-6 speed specific chain so I don't know if it will jive with the narrower 9-sp setup? I also do not want to spend over $100 on the crankset. Is the 9 speed set okay? or am I just oblivious to a way to replace my chainring without replacing all 3?

Keep your BB and shop away......http://www.jensonusa.com/store/sub/131-Cranksets.aspx?s=1260

a 9 speed crankset will work with 8 speed.
Why won't your rings come off?

Keep your BB and shop away......http://www.jensonusa.com/store/sub/131-Cranksets.aspx?s=1260

he could get a LX crankset for $93

i use an xtr 970 crank with an xtr 8 speed cassette

Oh hell, totally forgot that Jenson has a far superior search/categorizing function than PP or Cambria, which are the only two I've used so far. As far as the 9 speed compatibility though? I see a few that are 6,7,8 compatible but most say they are only 9 speed chain compatible.

pack o' lies! It will work

haha, thanks zecanon... just wasn't sure because I know the 9 speed chains are thinner than the 8 speed ones. Does anyone have recomendations as to whether I should just get a new square taper crankset, or should I get a new bb, say an isis or octalink, and then match the crankset to that? I would think one of the later two would have more strength than the square taper? Oh, and zecanon, my chainrings will come off, but only in one piece (all 3) and the 4-bolt pattern wont fit any of the chainrings I looked at. Also, I cannot for the life of me get the bolts to come out of the backing-thread thingy since there is no set of slots for a chainring-bolt tool to slip into.

9 speed chains are thinner than 8 speed chains, true. However, you are running 8 speed, so putting a 9 speed (theoretically thinner) chainring on will, if anything, just make the chain fit a bit looser. But this isn't actually the case, because in reality the chainrings will be the same width regardless.

As far as a new crankset, I always recommend the Shimano LX external BB crankset for those on a budget. It can be found very cheap, the BB is sturdy, and the weight penalty isn't massive.

Thank you very much ZeCanon! You cleared a lot of stuff up for me. I will look into the lx also. Thanks again.

I replaced my stock crankset on my 2001 Gary Fisher Marlin. I bought an LX Mega 9 speed. I have it with Sram 9.0's Grip Shifts and an Alivio Front deraileur and a 9.0 rear deraileur. It has an XTR 8 speed cassette. Top it off with a Sram 8 speed chain and it shifts better than most systems out there.

Well, my center chainring is screwed, and my nice cheap stock Shimano chainrings refuse to be able to be replaced so I am going to get a new crankset...I think. Since I have a dumb square taper bb I suppose I will more than likely have to get a new bb, also. Most of the cranksets I have looked at say that they work with 9-speed setups, but I have an 8sp and am pretty intent on sticking with it as I just bought a new chain and cassette. Yes I rode with a worn out chain and wish I had known to check it, before it was too late... So will a 9-sp crankset work with a SRAM PC-58 chain? It is an 8-7-6 speed specific chain so I don't know if it will jive with the narrower 9-sp setup? I also do not want to spend over $100 on the crankset. Is the 9 speed set okay? or am I just oblivious to a way to replace my chainring without replacing all 3?

don't do it - the world will end:rolleyes:.

I have 9-speed LX cranks/chainrings on my 8 speed drivetrain. Works like a charm, no problems whatsoever.

Great, thanks for all the help. I think I can see how the 9speed would work with an 8 chain. Now I have to decipher the stupid bottom bracket code. The one I have on now is a 113/68 with one spacer on the drive side. Do bb's say whether they need a spacer or not, or should I just judge that by the chain line? The truvative xr I have now gives a list of spacer vs no spacer with respect to the bb shell, I guess? something with 113/68E doesn't need one... Do I need to look for 113/68mm exactly?

I'd ask my LBS to be for sure. Are you using a square taper bottom bracket cause the old ones don't have spacers. The new cranks have to spacers for chain line.

For the BB, take it to a shop. It will depend on the crank you get, especially with square taper (some cranks fit farther onto the BB than others).

But like I said before, take a look at some of the crank/bb combo options out there, with external BBs. They are not too expensive at all.

Just ordered a truvativ firex sl (or some other combo of two letters...) and a howitzer bb. The firex info directly said it needed a 113mm bb length, since that is what I used, bingo! Now I just have to wait 7-10 days because damn near EVERY bb that I looked at was backordered. Jenson, cambria, pricepoint, all backordered on 113mm.