Let's design the ideal suspension

Over the past year, I've learned quite a bit form TT and Race Tech's Suspension Bible about how our suspensions work. In that time, I've revalved a number of bikes for my son and I to set them up for hare scrambles.

I can't help but to think there's a better design out there than what we have to work with now. BTW, I'm a mechanical engineer and I design machinery for a living.

It seems like the current state of the art still involves too many variables that overlap in their effect (for example mid and base valve).

It's also a pain in the neck that you have to completely disassemble things to make any meaningful changes.

These are the idease that are bouncing around in my head:

In my design, the piston would be connected to the wheel like in current dual chamber forks in order to keep the unsprung mass low. We don't want to move the dead weight of the oil up and down.

How about using a double rod cylinder. There would be a rod coming out each end of the piston and out of each end of the chamber (cylinder). The advantage to this is that you can get away from cavitation problems since the oil simply moves from one side of the piston to the other and none of it has to leave the chamber. This would allow you to do all valving on the piston or what is now called the mid valve. The disadvantage is that the assembly has to be three times the length of the travel. We may have room in the forks, but probably not in the rear shock unless something else changed.

For valving, I'm thinking that the piston would have a series of holes in it. Each hole would have a plate covering it, preloaded with a spring and preload screw. These springs would have different preloads, so that they would lift off at different pressures. These lift off pressures would be adjusted with the screws. I'm thinking that the rod would be of larger diameter and hollow so that long screws or long holes would give access to these screws from outside the suspension. Ideally, you would be able to change the springs from outside the suspension so you could easily make drastic changes in the performance.

I'm thinking there might be four or five of these springs and screws, allowing you to shape the damping curve.

I haven't yet figured out just how to get from the center of the rod to the valves on the piston. Some seals will no doubt be involved.

Anybody have any ideas?

check this: http://www.thumpertalk.com/forum/showthread.php?t=973128&highlight=the+most+interesting

i may be missing something about your double rod idea. It seems you would still have the possibility of cavitation, because the non compression side would still have decreasing pressure because even if you backfill it with the compression side it has to be at a lower rate than the compressed side otherwise you would have no damping force. I admit I only spent 2 seconds thinking about it and maybe this is not the idea you were presenting.

I do agree that the ability to tune externally (over the entire range) as a general goal would be a huge advance.

Hmm... I'm not an expert at this. Yes, you have different pressures... that's what slows the piston down. But, I'm thinking that the pressures in both sides would be higher than a conventional shock (same pressure difference, but both higher.) I don't know if this would eliminate cavitation, but I would think it would help.

it sounds like you ate describing the ohlins ttx and the norst valves on forks

Thanks for the info.

The TTX performs a similar function by routing the oil that is displaced by the rod back into the expanding side of the cylinder. I had originally thought of doing something like this, but I thought there may be too many side effects from moving all that oil around. That's why I wanted the double rod and to have all of the oil flow through the piston.

I haven't been able to determine exactly how the Nost works, but it looks like some fancy valving to replace the current mid and base valves. I can't tell if their base valve is externally adjustable, but I'm assuming their mid valve isn't.

Dont they use this technology currently in some formula 1 applications?

Penske sells a shock to anyone who wants it (and has the funds) that is similar to the JRI shock Joe Gibbs Racing was running.

It uses a secondary shim stack that can be adjusted externally for preload (on that shim stack) that then preloads the primary shim stack for a huge range of adjustments.

Gonna put us out of business some day..

Naw! We will still have to tune it.

The shock I was thinking about is used in formula one and it has a rod that passes thru the top of it , I think it is called a non displacement shock . Because the rod, is the same diameter on both sides of the shock, does not displace any fluid.

...Because the rod, is the same diameter on both sides of the shock, does not displace any fluid.

do you guys expect it to work much better because of that design (less cavitation problems)?

some people dont like the feel of less cavitation.

hey pete "through rod damper"

pics on the ohlins site show the automotive TTX is like this too

Squidless make it lighter please :thumbsup:

Good info, gents.

What would people dislike about less cavitation?

ask ktm riders about that!

a few people dont like the feel of the ttx due to less cavitation, i wish i could ride one myself to see.

I love em! best forks ever IMHO

they do the same thing every time no matter what, just priceless....

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