GT250/ GT380 Forks modification

water cooled · Post by **water cooled** » Thu Nov 05, 2009 3:26 pm

I need to have a set of forks cut down about 2.5 - 3 inches. The top end configuration is a groove with keeper.

Can anyone advise who could cut these for me.

tz375 · Post by **tz375** » Thu Nov 05, 2009 3:36 pm

Kevin,

Almost any machine shop should be able to do that for you.

Do you need to shorten the tubes or can you get away with a spacer around the damper rod to restrict travel and a shorter spring?

water cooled · Post by **water cooled** » Thu Nov 05, 2009 3:53 pm

No, I need the outer tubes shortened. The forks are GT250/380 and do need to be stiffer. Ideally, I would like to have 1/2" - 1" max travel beyond the compression of the forks from the weight of the bike. But the immediate challenge is to shorten them be cutting the top of the tube and re-machining the groove for the keeper.

I don't know if the spring needs to be cut or if I can just compress it which might help by giving a pre-load and higher initial spring force. That spring is awfully light compared to the GT550 forks on there now.

Barry S. · Post by **Barry S.** » Thu Nov 05, 2009 6:00 pm

If you cut 3" off the forks and the spring, the spring will be much stiffer since it has been cut shorter.

krwalsh · Post by **krwalsh** » Thu Nov 05, 2009 10:13 pm

In general...

K2 = ( L1 / L2 ) * K1

Where:
K2 = spring constant of new spring
K1 = spring constant of old spring
L1 = free length of old spring
L2 = free length of new spring

Suzukidave · Post by **Suzukidave** » Fri Nov 06, 2009 5:04 am

Kevin , if a local shop cannot help you contact Franks http://www.frankmain.qpg.com/

rngdng · Post by **rngdng** » Fri Nov 06, 2009 6:33 am

Frank's can (and will) make anything you want, but any decent machine shop should be able to cut yours down. I have no idea which would be cheaper. Frank's usually charges about 200 bucks for a set of tubes.

And yes, if you shorten the springs, they will be much stiffer.

Lane