is it possible to Use 7 speed shifter with 8 speed Cassette?

[the_abhiG]

If I tweak RD to make the range from second biggest sprocket to smallest sprocket (that is 7 usable sprocket) and don't use one (biggest) sprocket at all, in this way can I use the 7 speed shifter to work with 8 speed cassette?

 

[Hugh Manatee]

You won't know until you try! Rubbish answer I know! Back when I got my first mountain bike, top of the range was Deore XT II 7 speed. Not long after everything went to 8 at the back. The XT II thumbshifter had a hidden click that in theory let you use an 8 speed cassette. I am fairly sure the cable pull is almost exactly the same. It worked pretty well on my MTB until the rear mech started to wear. Of course, the joy of thumbshifters is that you can convert to friction shift.
Try it on a work stand. Make note of how much you adjust the limit screw by so you can easily return to what it was.

What bike is it?

 

[Ajax Bay]

A 7sp shifter will shift the chain to most sprockets of an 8sp cassette but the guide wheel will become increasing misaligned at the extremes of the cassette. Get the alignment correct for the middle two sprockets and you can put up with it. Or get a 7sp cassette (and spacer ?4.5mm worth).
The dimension between adjacent sprocket is different (8sp v 7sp) by 0.2mm. May not seem much but easy to piss you off.
I tried to make this work on one bike for a few months before just getting a 7sp cassette.
Sheldon

 

[fossyant]

Just remove a sprocket, and add a spare spacer on the freehub first (next to spokes). I've done this on two bikes. Old cassette will have some spare spacers. As 7 speed cassette's are not available, I buy an 8 speed, remove a sprocket I don't want (here is where you buy a cassette with the teeth you want). Pop a spacer or two on before the 7 speed cassette. The number of spacers will vary with the hub manufacturer. On my Mavic MTB wheels, I use 2 spacers, then the 7 sprockets and spacers off my 8 speed cassette.

7 speed sprockets use a 3.1mm spacer, 8 speed 3mm. This difference is small enough not to worry about it with a 7 speed shifter and works fine.

Saves weight as well not having an unused sprocket.

 

[Ajax Bay]

As 7 speed cassettes are not available,

https://www.tweekscycles.com/shimano-cs-hg20-7-speed-cassette-796422/

 

[fossyant]

https://www.tweekscycles.com/shimano-cs-hg20-7-speed-cassette-796422/

Gah, that's horrid. HG20, erm no chance. Got to be nice plated sprockets, hence HG50 or above, or SRAM for lighter weight !

 

[Ajax Bay]

'Shiny'!
? https://www.wiggle.co.uk/hope-7-speed-dh-cassette/
HG50: https://www.ebay.co.uk/itm/HG50-7-s...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

 

[the_abhiG]

It is working but not to perfection, it took very fine RD adjustment to make it work but still sometime it skip cogs but very rearly. I will buy buy 8 speed shifter ASAP for best performance.