8 speed wheel/cassette in place of a 7 speed.

[widowmaker]

Probably another daft question, mine usually are (I have searched)

I am replacing a wheel with a 7 speed cassette for one with a 8 speed, am I right in assuming i shall be able to select 7 of the 8 gears or am I way off.

I haven't got the bike with me so cant check and amassing parts for when the bike gets here.

 

[marc two tone]

Seems logical to me.
Another option would be to get an 8 sp shifter. Or just use 7 , of the 8.
Anticipate whether or not you prefer 1 to 7 or, 2 to 8.
One you have adjusted the the mech limit screws, itll just work the same.

 

[curzons246]

I concur the 7 speed shifter will work fine on your 7 chosen gears. Have you respaced the dropouts for the wider hub?

 

[mynchiboy]

I concur the 7 speed shifter will work fine on your 7 chosen gears. Have you respaced the dropouts for the wider hub?

Respacing shouldn't be necessary if you're switching the entire wheel .The O.L.D for the hub should be the same, whether 7 or 8 speed.

As for the shifting, I guess that depends on what you have shifter and rear mech wise. If you have a thumb shifter with friction mode or the 'hidden click' along with a long cage mech, there's nothing to stop you tweaking the mech limit screws to make use of the full 8 speeds. You'll still probably still need to tweak a bit for making 7 speeds work, but I can't see why that wouldn't work either

 

[widowmaker]

I am building a MTB into a tourer and have some XT 7/8 speed thumbshifters lined up, but am going touring in less than 2 weeks so wont have enough time to fit them with work etc. So I was hoping to put the 8 speed on for a the time being.

 

[Tootyred]

Yes they will work, but they wont work too well....the probem is the indent spacing on the shifters will move the derailleur the amount for a 7 speed spacing.

Standard 7 hg cassette uses 5.0mm c to c sprockets with a 1.85 sprocket width.

Standard 8 hg cassette uses 4.8mm c to c sprockets with a 1.8mm sprocket width.

It dont sound like much, but add those differences up and you would start to notice the top / bottom cogs just wont sit right and could be rattly and jumpy as your over moving 0.25mm per shift.

Ive done it in the past, it will run, but dont expect the indexing to be perfect t at the top or bottom.

Hope the trip goes well.

 

[widowmaker]

How do you guys know so much in details too

I'll just have to make time to fit the 7/8 speed thumbies before the trip, save any issues.

Thanks for the info chaps!!!

 

[Tootyred]

We are sad and have far too much time on our hands

 

[gtturbo]

The nice thing with thumb shifters of course is you have friction mode if indexing goes tits up so probably worthwhile to fit them before you go touring anyway. Only takes a bent hanger and you will be glad you have that option.

 

[was8v]

There's no 7/8 thumbies, the 7 will shift 8, but badly as above. Just match the shifter to the cassette for clean shifts