Maybe this has been covered, but I didn't find it-Since the fork springs are waaay light, as in 140 lb rider (and I'm 185), I've been thinking about what to do to stiffen the front end. I've had this problem with a couple of other bikes, years ago, and the solution was drilling the fork cap and tapping it for a threaded tire stem, then putting a few lbs of air pressure in it. Good fork seals would hold the air for weeks, and stiffen the fork without losing travel! It really didn't take much to make a big difference either. Some guys used to use a short stiff spring, like a V-8 valve spring, and put it over the fork spring to stiffen it. Anybody tried either of these? I realize option 2 would likely cost a little travel, but the airspring option wouldn't. Makes them a little adjustable too.
doc

 

The manual states that the forks will build up pressure if you ride for any amount of time over rough terrain and at the end of the day/ride whatever you should open the bleeder caps and let the pressure equalize. So to me it sounds like they would hold low pressures just fine.

 

Ah, not sure on that one.

I'm not a suspension guru by any means, but having pressure in your forks seems like a really bad idea. A lot of people are fanatical about making sure they have no pressure in there forks and fit bleeders etc. I bleed my forks regularly through the screws and my suspension guys said it's a good thing to do.

In effect though, what yu are saying is correct (wait while I put on my engineering hat...)

The amount of force required to compress a spring is a linear function, as in it increases at a steady rate the further the srpoing is compresses. The rate at which it increase is determine by the spring coefficient (in this case .38 kg/mm)

Air, in a constant diameter cylinder (fork), if we assume for our purposes is an ideal gas (don't ask), will also have an linear increase in compression force.

I think the problem will arise though when you actually start to compress that gas even further. The pressure in the forks when you do a big bottom out etc will probably exceed the limit of the fork seals and I'd say you'll end up doing damage and loosing fork oil.

I've just got my forks resprung and will be going for a good ride tomorrow (I'm also around 185lbs). I'll let you
know how it goes!

Drof

 

Yeah I had a (road) bike with air valves on the forks and the recommened pressure was 10 psi, I played a little with it and as little as 1 psi difference would have a marked difference on the handling, funny now they have valves to bleed the air out lol

 

It's an interesting theory, as there are air sprung forks used in mountain biking. But the difference is they're designed as air sprung forks-there is no coil spring.

 

Neuro, try a heavier weight oil. Just changing the fluid made my suspension stiffer.

 

Not a guru, but I've learned some things on suspensions.

Heavier oil will stiffen the suspension as it dampens movement. However it will NOT support any additional weight.

By adding a spacer - which is what you are adding with the valve spring (a piece of schedule 80 PVC works just as well!) is putting some pre-load into the suspension. As with many other things in life, some is good, too much is bad!

There is really just one way to make the suspension on your motorcycle support your combined body weight properly - change out the fork springs and the rear shock spring to those specifically set for your combined body weight.

Anything else is nothing more than a bandaid!

FYI, many early editions of sportbikes were air adjustable suspensions in front and rear. A prime example of this is the Kawasaki Concours. They built a crossover tube that equalizes the air pressure in the front suspension. The rear shock is also air adjustable. A 22 year old design that still works.

 

Well, guys, some good thoughts being shared here. Thanks! Part of what I'm thinking is the value of having some way of adjusting preload in the forks. For example, when I ride to work, I carry about 20-25 lbs of stuff with me-patient charts, notebook pc, etc. When I go trail riding I'm effectively 25 lbs lighter. If I bring my wife, the bike is carrying about 135 lbs more. Yet, no way to adjust the preload on the front even a little! even with stiffer springs it would be nice to have a little adjustability, though stiffer springs would be an overall improvement as it's never too stiff with the stock springs. I think the reason for bleeding the air out of the forks is to keep the fork springs effectively at the same pressure; ie if you bike is set up just right, and then your forks get pumped up, now things are too stiff and your whole handling characteristics won't be as good. I wonder how hard it is to replace a blown fork seal....may have to try this.
doc

 

Tony-what I'm trying to adjust is the sag, not the damping. For the type of riding I do, the stock damping rate isn't too far off. It's just how much it sags from me sitting on it. And, even though I could stand to lose about 10 lbs, I'd like to have more spring up front so the suspension can be set up right for me. From what I've read, the springs are right for a 140 lb rider, so they're not close for 175 or 185. I probably will put thicker oil in them also, when I change out the fork oil, as I'm sure it too would be an improvement!
doc

 

Very true, check out this site for explination and maybe some help. I had them rebuild my forks and rear, added proper springs the works, just like getting brand new olins forks and shock for 1/2 the cost. http://www.racetech.com/SubMenu.asp?...&showPage=dirt