gear compatability advice reqd plz

The original PhilthyPhil

Hi all,1st post from me
im trying to restore a subway2 and have bought various parts from the auction site,before i found this site.
The problem is,my bars came fitted with shimano rapid-fire type shifters,which go up2 8 gears,but the wheels i bought came with a 7speed block (not even sure its shimano tbh)
i dont yet have a rear mech,and i have been told that an 8 speed mech will need a narrower chain?
does this mean that the 7sp sprockets are thicker than 8 or 9 speed ones?
i need a chain also so the big question is,should i see about changing the sprockets and chain at the same time or is there anyway that i can use the existing shifters with a 7speed set up? are there any rear mechs out there that can handle 7or8speed use,as they all seem to be 9speed now??sorry so many questions
.bikes have changed a bit since my mis-spent youth.
Thanks in advance for all help & advice.
Phil.

nicklouse

first things first. measure the rear hub width and then measure the rear frame spacing.

they need to be the same.

6/7/8spd have the same spacing and the same chain.

8/9spd have the same hub width but different cassette spacing and chain width.

any mech will work.

the chain needs to match the cassette and the cassette match the shifter. (7spd cassette can be used with a 8spd shifter you just do not use one click).

keep brands together.

shimano with shimano and sram with sram.

The original PhilthyPhil

Thank you very much for the informative reply.
Can i just ask,could i fit an 8speed cassette to the 7speed body (have now checked and its shimano) if the sprocket spacings are closer would i get 8 in the space for 7??
The wheel fits the frame ok. Ta.

whyamihere

The original PhilthyPhil wrote:

Thank you very much for the informative reply.
Can i just ask,could i fit an 8speed cassette to the 7speed body (have now checked and its shimano) if the sprocket spacings are closer would i get 8 in the space for 7??
The wheel fits the frame ok. Ta.

The sprocket spacings for 8 speed are the same as for 7 speed, so unless the 7 speed cassette is fitted using a spacer (unlikely) then it won't take an 8 speed.

The original PhilthyPhil

Ok, my mistake.
Need to get new wheels now in order to make good use of 8speed shifters....ho hum

whyamihere

The original PhilthyPhil wrote:

Ok, my mistake.
Need to get new wheels now in order to make good use of 8speed shifters....ho hum

You can still use the 8 speed shifters with the 7 speed cassette...

nicklouse

(7spd cassette can be used with a 8spd shifter you just do not use one click).

as already said.