Topic: is pressurizing fork tubes effective?

[chippyfive50]

I have read multiple posts about installing schrader valves running 10psi or so in the forks, how effective is this?? 
I am putting the dual 750 disks on my 550, and have some concern about the dive i will encounter.

[MRieck]

 I've found it increases stiction as the fork seals grab the tubes more. If you're worried about dive get some aftermarket springs like Progressive, Works Performance, Hyperpro etc.

[KB02]

...Or a higher weight oil.

[crazypj]

Don't use a lot thicker oil unless you like your suspension packing down. Lots of people came into shop 'back in the day' and wanted 20 weight fitted (monkey see monkey do) Its fine as long as you don't hit a series of bumps, forks keep compressing but cannot return (unless you enlarge damping holes, kind of defeats the purpose then) Use  a higher oil level, try 6" from top of tubes and work from there (springs out fork compressed) Its already been mentioned about increased stiction with air pressure (on MX bikes the schrader valves are usually to let air out, not put it in) Progressive springs are probably the safest option with oil level adjustments. The oil height in fork tubes is probably more important than the quantity (and easier to measure)
PJ

[HondaMan]

Use teflon-coated fork seals, widely available. With dual brakes, add washers inside the top of the fork tube (about 1/2" worth or 3/4" worth, depending on age of springs) to raise up the height and forces.

The 500/550 forks were too soft to begin with: dual brakes make this worse. We routinely added cut-off pieces of tubing or washers or air forks to the 500/550/750 family to improve trail, braking and cornering. My 750 has 5/8" pipe pieces inside plus air forks and modified rebound damping holes. MUCH better....

[crazypj]

I fitted 750 fork tubes and springs to 550 to improve the oversoft front end. Worked really well and the increase in ground clearance was  welcome (fitted 750 rear shocks as well, heavier springs and about 3/4" longer) Still ground chunks out of stuff though.
PJ

[chippyfive50]

thanks for the tips fellas..... I will persue the teflon seals and preload me springs   yarrrrr...

[Terry in Australia]

I like the old S&W air kits with the cool handlebar mounted gauge, it's almost hypnotic watching that little needle bounce around the gauge on a bumpy country road, so I'm unsure how badly the "stiction" problem really is, but I'd rather fit an air kit than pack my forks full of washers and crap. Cheers, Terry.

[crazypj]

HI Terry,
 Know what you mean, back in the 80's I almost crashed a customers Gold Wing watching the S&W gauges bouncing around (had air rear shocks as well) fascinating but stupid
PJ

[Terry in Australia]

I bought a 1975 Kawasaki Z900 (a notoriously bad handler) in the early 1980's and fitted Marzocchi Strada shocks on the back, progressive fork springs, a steering damper, Pirelli Phantom tires, and an S&W air kit for the forks, and I'd put 10 psi in them.

Interestingly, at 60+ Mph the gauge would read 0 psi, then return to 10 psi when I'd slowed back down to commuting speeds. I realized that in the normal upright riding position I was actually acting as a "sail" and making the front end go light, which probably accounted for the notorious squirrely handling?

There have been many and varied theories on why the early Kawasaki 4's handled so poorly, but I'd never heard this one before, so I reckon I learned something with that little S&W air kit that the "boffins" couldn't figure out with all the fancy test equipment at their disposal! Cheers, Terry.

[crazypj]

My sister had a 74 Z1b ( ex husbands)With the frame brace kit and lower bars  usual Marazocchi's,and fork mods it was suprisingly good handling up to 135mph ( on clock) She only sold it about 2yrs ago , got fed up with the overextended rebuild ( 12 yrs at last count!)
PJ