hi i want to convert to 9 speed what do i need. i have got the 9 speed rear cassette i know i need a 9 speed shifter but not sure what else i need.

are you going from 7 speed to 9 speed, or 8 speed to 9 speed?

8 speed my bike is 8 on back 3 on front

Cassette, chain, and rear shifter.

do i not need a new crank so there is only one cog at the front instead of 3. also will my 9speed cassette fit on my existing hub.

You can keep all three rings up front with the same crank. Yes, the cassette will fit your existing hub.

ok but i would like to convert to the single cog on the front so i only need the one shifter but dont no what i need to do to convert to one cog

I think you mean chainring on the front but if you do do the one cog up front you only need the one shifter for the rear derailler. If your doing jumping or something it might be good to have one of those chain tensioner whatever you call them things to prevent the chain from jumping off the teeth. If you have a triple crankset you could just leave it on whichever ring you prefer. Or you could have one chainring with a bashguard and the tensioner thing.

yeah thats right. i want the one cog one with the chain thing. can you fit a bmx chain ring to a mountain bike?

What you're talking about is called a 1x9 setup. A 9 speed cassette will work in place of an 8 speed. All you'll need is the narrower chain for 9 speed and a new rear shifter. For the front, ditch the granny gear, replace the big ring with a bash guard/rock ring. You might also want to ad an n-gear jump stop chain guide to make sure the chain can't jump off to the inside (the bash guard keeps it from jumping off to the outside).

No, you can't use a bmx chain with a 9 speed cassette. It is too wide.

Just curious, why change to 9 speed? 8 speed can cover the same range and is more robust, since the chain is wider... I usually run a 1x8 (or even 1x7) for my projects. Have fun.

-Joe

magic thank you.
to answer the question i heard that 8 speed is harder to set up the gearing and the gears slip a lot which is what is happening in my bike now the gears always slip and i cant get it quite right. i was told it is easier to stop that using 9 speed

Hmmm... never heard that about 8-speed. Maybe others will chime in also. I suspect you've just got some worn components causing slipping. The same thing will happen to 9-speed as they wear. If you want to describe the slipping in detail, I'm sure the group can troubleshoot it for you (and maybe save you some money).

-Joe

all components are fairly new sram stuff dont no if thats very good tho it came with bike. well i will select my gear and all will be fine for flat riding then as soon as i come to a climb and have to stand up to pedal the gears slip and it hurts mite be my grip shift gears though they have a bit of play between each click selection. i plan on changing them to shimano shifters.

You might want to figure out why your 8 speed set up is slipping or between gears before you lay down money on a new 9 speed set up. Sort of sounds like a bent derailluer or something.

Check your chain links also.

Actually, if your 8 speed chain is still good use it on your new 9 speed cassette. Tolerances are not that tight on the 9 speed. I'm running SRAM 8 speed chains on both my 9 speed mountain and touring bikes. Of course, once these chains need replacing Ill replace them 9 speed specific chains.

Depending on chain wear, he may also need new chainrings as well.