I put a Maxton rear spring on mine and it made it loads better.
As for the performance, I find that while the bike feels plenty quick enough (for me) on the road, on the track it feels slow. At Cadwell the DD 600's weren't all that much slower on the straights, if I only used 7000 rpm it was about the same and although revving it to 8500/9000 it would go past fairly easy , the 99* bikes still flew past. Also while is steers and handles well, it is much harder work that the newer bikes. If I were you and doing lots of TD's I'd get a 99* (which is just what I'm thinking of doing - or an S4R)
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