Replaced cassette lose - but why?

So........a few weeks ago I get hit - my carbon rear wheel is mashed......

Now I have taken the 10 speed cassette from it and put it onto a shimano R500, very simple eh??

No.

the cassesttes are both shimano - the R500 had a 9 speed cassette on it before but with the 10 speed cassette it's catching on the spokes and there is at about 7/10mm play and the whole sodding thing is lose - I can't figure out why.

in theory it should be a straight swap?!

The rear mech on the carbon is ultegra where as the bike the R500 was on at first is tiagra - have a just answered my own question?

Any help of course will be much apperciated.

You need a (1mm I think) spacer when fitting 10spd cassette to 9spd freehub.

I see - I am still confused because the cassette is recessed at the back - just an amateur you see..........

The spacer usually comes in the box/bag with the cassette when you buy it. Getting one shouldn't be difficult from an lbs. It's a pretty common part.

Thanks both - I might just have to leave it tonight - too much of the same thing this time of night isn't good - well unless it's something better...........