10sp cassette to 9sp cassette

[dudi]

Evening all.
I am in the process of building myself a new bike (once all the parts arrive), this one is going to have gears!!

I have a shimano 105 groupset, it's a 9sp double, so 18 gears in all... don't know what i'm going to do with them all!

I also have a 10sp cassette, can I just take off one of the sprockets from the 10sp cassette and use it with the 9sp shifters? or is it, as I suspect, a bit more complex than that?

I presume that the 9sp shifters move the deraillieur (sp?) a larger distance on each shift than the 10sp one would, so as to cover fewer cogs in the same distance.

Would this mean I need to get some different size spacers? or should I just be done with it and buy myself a 9sp cassette and stop faffing about?. Thanks

 

[John the Monkey]

You can't just remove a sprocket, as far as I know - the spacing will be wrong.

You're right in the presumption that the key is how far the shifters pull the cable to the derailleur.

You could respace the cassette, but I'm *fairly* sure that the bottom part of it won't come apart (check anyway). I do have some 9 speed spacers somewhere that you'd be welcome to. Last thing if you do go for this option is that the sprockets will be slightly too narrow for the chain - that might accelerate wear as the chain could (I suppose) move from side to side more than it might on a 9sp cassette.

Ribble had decent prices on 9sp Tiagra cassettes last time I needed one.

 

[dudi]

I just had a look, there's a section of the larger sprocets that are all held together...

Better get a new cassette I reckon.

 

[RedBike]

No sorry, you'll need a new cassette.

Hard to believe but the overall width of a 10speed cassette, despite the extra sprocket, is actually slightly less than that off a 9 speed. the spacing is quite different.

 

[andrew_s]

Would this mean I need to get some different size spacers? or should I just be done with it and buy myself a 9sp cassette and stop faffing about?. Thanks

Get a 9 speed cassette
a) the larger sprockets are commonly grouped on carriers that can't be respaced (as you've found).
sprocket pitch is determined by sprocket thickness plus spacer thickness. Unless 10-speed sprockets are the same thickness as 9-speed sprockets, borrowing the spacers from another cassette won't work. If they aren't the same you would have to get custom made spacers (eg from Eggrings), which would likely cost more than a 9-speed cassette.