i have an 02 dt125r and a work friend of mine has an 07 dt125sm, i was wondering if his rear shock and mine are both the same as his feels a lot firmer when you push the seat up and down, we have looked underneath and the preload/adjustment nuts are virtually in the same position but there is definately a difference as his feels firmer and mine feels as though it has a more smoother through action. both the rear shock springs are red

Different shock on the SM versions. Made by Sachs

ok thanks for that, as i only use my dt on the road for commuting i may go along that route and see if i can get hold of one and fit it if the fiiting are all the same 

It's a straight swap but good luck getting hold of one. I ended up fitting a shock from a R when I rebuilt my bike. 

You might be better off going aftermarket, YSS do one for the DT.