bottoming out

[chuck]

Raced my 73 125 six days for the first time last weekend and had a blast. The track wasn't very vintage friendly with many large jumps, doubles and two sections of whoops. The front forks were bottoming out on just about every jump. I'm using 10wt fork oil and am going to switch to 20wt. Has anyone had the same problem? What has worked for you? Has anyone tried different forks?

Thanks for the help.

chuck

[Lew Mayer]

You can try increasing the oil level in your forks to help resist bottoming. It takes time, do it gradually. Put a pull tie around your fork legs before testing each time to tell how far down your forks go under hard compression.I read an article on this procedure but I can't remember where it was. If I find it I'll let you know.

Lew Mayer

[behindbars]

I would try stiffer springs, heavier oil, and more oil. Especially if you are a bit heavier than the bike is set up for..... I would imagine that there must be someone on this page who can point you to a stiffer set of springs. If not, send me the dimensions and I may be able to find something. The springs will help stiffen the forks in a way that oil alone can't. You usually will need to run heavier oil to compensate for the extra rebound from the heavier spring rate. Anyone have a source for stiffer springs out there?

[socalmx]

I had the same problem with my '72 forks. I replaced the 10 weight with 20 weight (standard quantity) which turned out to be too stiff. I would suggest starting with 15 weight at standard quantity and increase as needed.

[Big Mac]

Got my stiffer springs for 35MM Ceriani's (Harescrambler) from Dave Boydstun at AMS. Mac

[chuck]

Thanks for the help. I think I'll try the 15 weight and a little more oil. If that doesn't work, I'll give the stiffer springs a try.

Chuck

[TGTech]

Chuck:

   You definitely don't want to rely on just the oil volume and weight to keep the forks from bottoming. In order to keep the forks working as responsively as possible, you want to use as light an oil as possible. This of course affects the rebound dampening, and you don't want to make that too fast or slow.

   The force that keeps the forks from bottoming, will be the air cushion above the oil and the spring rate itself. The if you make the air cushion too small (raise the oil capacity too much), you'll get harsh action on small bumps.

Dane