Upgrading from 7spd to 8spd

[benseddon]

hi folk,

maybe this topic has been discussed before but I recently discovered that my Shimano 105 rear der. is a 1056 model. as I understand it the 1056 is an 8spd der, an upgrade from the 7spd 1055.

I have also acquired some 8spd shifters. do I just simply need an 8 cog freewheel and im good to go? is there anything else that ive not considered??

 

[mattsccm]

It will be a cassette in all likely hood. Now a 7 speed cassette had a different free hub to an 8. The later won't fit the former. Might be an 8 fitted. Look at Sheldon Brown for guidance.
Chain will be different as well.

 

[glpinxit]

I did this with 7sp RX100 (same as 105 but alloy rather than painted finish) and found the mech had the range with 8sp shifters. Main issue is the 7sp cassette to 8sp where you need to enable this by changing from ultraglide to hyperglide freewheel (or is it the other way round). Sheldon explains what you need to do this as it is an easy parts upgrade using your existing hub.

 

[bigfatron]

Re:

Be careful going to 8 speed.
Try to do this with a screw on freewheel and you have a broken axle.
Dear old Sheldon Brown suggests an 8 speed screw on freewheel needs a 10mm axle, disaster otherwise!
Richie

 

[Pionir]

Re:

The big question is what hub do you have?

As has been said, its probably a cassette and not a freewheel. In fact I'm pretty sure there are/were no 8 speed freewheels or if they are they are pretty hairy - the extra width means there is more stress on the bearings (which are located close to the spokes) due to the long cantilever.

Assuming you have a cassette hub, the next question is whether it's uniglide or hyperglide.

I believe that 7speed hubs were only ever available in uniglide so you need a hyperglide cassette. However hyperglide won't fit on uniglide freehub due to an extra wide spline. As mentioned previously Sheldon has all the information you'll need.

There will also be the question over rear spacing - 7speed were generally 126mm spacing but 8speed and up were mostly (if not all) 130mm. Alot of people just spread the dropouts as 2mm either side isn't much for a steel frame, but if you've got a carbon frame then that's a bad idea. I'm not sure about aluminium, but judging by the amount old Alan frames used to flex I'm sure it won't be a problem

You have several options if you have a 7sp hyperglide cassette.

Get a new freehub. SJS have a few for old shimano hubs at around £20 a pop.

Use the 8or9 or even 9of10 trick. As the 8,9 and 10 speed cassettes have the same overall cassette width you can remove one cog and one spacer to bring them down to the overall width of a 7speed cassette and therefore fit them on a 7 speed freehub. However this would require matching shifters to make sure they index with the right spacing properly (the last click is then redundant) and you'll end up paying more for the shifters than saving on a new freehub.

You could also just buy a new 8sp rear wheel on ebay.

Also worth noting is all shimano rear derailleurs work with all speeds except 740x Dura Ace so your 8sp rear mech is the same as a 7sp. The difference is purely in the shifters which have an extra click and shorter pull for each gear (because the spacing of the cogs in the cassette is smaller)

My advice would be to check which rear hub you have and go from there.