Interesting rear suspension setup

[DeleriousZ]

Randomly googling stuff a few days ago I ran across this setup. I think it looks pretty cool, but I'm really unsure of the function. I've only seen this type of setup on mountain bike rear suspension and forms of it on race bred cars.

 

Anyway check it out and discuss.

 

http://www.fatcatfabrication.com/id3.html

 

[Drax240z]

Pretty neat. A-arm transfers motion through a pushrod, through the stock strut hole, to the bellcrank. The bell crank transfers the motion to the shock/spring. Interesting little idea they've got there.

[AkumaNoZeta]

From my point of view, that's just done to look cool and doesn't actually improve anything. The reason I see it being done to open-wheel race cars is to get the shocks and springs out of the air to reduce aerodynamic drag. But it does look cool.

[JMortensen]

From my point of view, that's just done to look cool and doesn't actually improve anything. The reason I see it being done to open-wheel race cars is to get the shocks and springs out of the air to reduce aerodynamic drag. But it does look cool.

Agreed. Not certain that the mount is all that wonderful either. I suppose it does look cool until you start to analyze it though...

[bart628]

 

fc3spro.com "A cantilever suspension suspension system removes the damper and springs away from the wheel hubs and runs them remotely via a bell-crank system. By moving the damper and springs, unsprung weight is greatly reduced - the wheels and tires react a lot quicker to changing road conditions."

 

I could see the benefit of such a system, but less unsprung weight with a higher center of gravity. Additionally, the rear suspension of 240sx is already independent, so there's less of a gain to say doing the same for the Z's Chapman strut or the FC's semi-trailing arm setup.

 

That's beside the point considering, that as you've all said, the quality looks debatable; Interesting no less.

[dan5138]

If this is actually designed properly...the main benefit I see is being able to run any tire / wheel combo you like. The push rod is going to be much thinner than any coil over set up, allowing more backspacing. You could also achieve much more drastic drops (imagine a 4" drop) and bolt everything up so you don't have too much camber. Just my 2 cents, If were going to build something like this I would make the brackets / cantilevers a little more beefy.

 

 

Edit: Thanks for the additional info on benefits of this set up Bart. Looking at the pic you posted, I like that much better as it connects to the chasis at 3 points, rather than just the strut towers.

[JMortensen]

If this is actually designed properly...the main benefit I see is being able to run any tire / wheel combo you like. The push rod is going to be much thinner than any coil over set up, allowing more backspacing. You could also achieve much more drastic drops (imagine a 4" drop) and bolt everything up so you don't have too much camber. Just my 2 cents, If were going to build something like this I would make the brackets / cantilevers a little more beefy.

 

 

Edit: Thanks for the additional info on benefits of this set up Bart. Looking at the pic you posted, I like that much better as it connects to the chasis at 3 points, rather than just the strut towers.

Tires run into fenderwells before they run into 2.5" coilovers in my experience. It would be a lot more useful on a car that had underbody aero that the struts were interfering with, I think.

 

bart628, I think the info you have there is wrong. Cary aka tube80z was talking about this unsprung weight issue on another thread, and there is a logical argument that says that when the wheel travels, the spring and shock still have to be moved. Since the weight is moved when the suspension is moved it doesn't become part of the sprung weight and remains unsprung.

 

Here's one discussion of the same topic: http://www.eng-tips.com/viewthread.cfm?qid=159112&page=11

[bart628]

My bad; reading your thread and such that totally makes sense. Just copy and pasted without much thought. But I do agree with dan5138 that wheel fitment would be much cooler with a cantilever rear suspension.

[eec564]

I suppose one could have it in place so the passenger could adjust ride settings while the car is in a race. Or get the shocks out of the way when converting a vehicle to be amphibious. I know all too well what salt water does to, well, most anything.

 

Still cool though. One advantage I could see is having shocks which are not compressed at a 1:1 ratio to wheel movement. There may be some slight advantage with that, in setting high and low-speed dampening. Even so, I think an amphibious Z (or even 240SX) would be cooler.

[jerryb]

Funny, I came across this site a few days ago while searching for S13 suspension set-up specs for the track. All I could think was...cool:bling:..why wouldnt it be traingulated to something? And then bart628 comes up with his pic.

 

Im confused, jmortenson says...Since the weight is moved when the suspension is moved it doesn't become part of the sprung weight and remains unsprung.

 

Are you trying to say the opposite? ..become part of the unsprung weight and remains sprung.

 

As I see it the unsprung weigh is reduced....your not moving the entire spring, strut housing, strut...etc. Just compressing the spring and moving the piston off a rod and cam. ...yes?

[Dan Juday]

I think there is more than bling here.

 

For a street/track car this makes rear supension adjustments much easier: ride height, spring rates, shock rates. With some modifications to the basic design you could also adjust camber and caster (caster in the rear?).

 

I would also argue that the structural design is adequate since the loads are parallel to the main bar. I don't see any need to triangulate unless you are also using the device to reinforce the body structure.

 

Just my observations. There are much more qualified suspension guys here than me.

[johnc]

Interesting idea that any moving suspension component is by definition part of the unsprung mass - basically any suspension component that sees compression or rebound from the road surface or springs. I'm going to have to think about that.

 

As for the above suspension setup, the shocks need to be painted red.

Edited May 28, 2009 by johnc

[tube80z]

As I see it the unsprung weigh is reduced....your not moving the entire spring, strut housing, strut...etc. Just compressing the spring and moving the piston off a rod and cam. ...yes?

 

I think you can argue unsprung weight is reduced from the classical definition. But if you look at the suspensions interia it is often greater and you really need to look at the dynamic rather than static case. You also have to look at suspension friction being increased too and ff the rocker and push/pull rod are all not in the same plane you'll introduce some bending that can cause additional friction effects.

 

On a closed car (GT) the aero advantages are often not really there. But you do get increased motion ratios and the ability to change them and if done right you can reduce spring-to-spring chassis length (meaning the car will be torsionally stiffer). And you cannot discount the bling factor. Think of the chicks you could pick up showing them your cool rocker arm suspension

 

Cary

[jerryb]

As for the above suspension setup, the shocks need to be painted red.

 

[AkumaNoZeta]

What's spring-to-spring chassis length?

[TheNick]

There are a few other advantages that others haven't mentioned

 

3rd spring/damper that is only active in pitch/dive - this explains it better than I can:

http://optimumg.com/OptimumGWebSite/Documents/TechTips/Springs&Dampers_Tech_Tip_3.pdf

 

and

 

http://optimumg.com/OptimumGWebSite/Documents/TechTips/Springs&Dampers_Tech_Tip_6.pdf

 

 

 

You can also make your sway bar much much smaller/lighter. Also have the ability of using rising rate rocker arms. There is also the ability to change the motion ratio of the suspension very quickly if you use multiple holes in the rocker arms, this will give you a very easy change in wheel rates - you don't have to worry about taking multiple sets of springs with you to the track.

[tube80z]

What's spring-to-spring chassis length?

 

It's a BS term that I made up. But what I mean is where the suspension loads are put into the chassis. That distance from front to rear is part of the torsion spring we call the chassis. The closer together these get the shorter the spring and potentially the higher the rate. Longer cars (wheelbase) are often less stiff than a shorter model.

 

Hope that helps,

 

Cary

[AkumaNoZeta]

I think I get it. Like if you run the cantilever set up parallel to the chassis instead of perpendicular like they did on that 240, then the mounting points of the springs will be closer to each other and therefore have less of the chassis itself being affected?

[jerryb]

Im going to make one out of wood and mount it in my car

 

Ya baby!

 

Whittle away!

[AkumaNoZeta]

Here's one discussion of the same topic: http://www.eng-tips.com/viewthread.cfm?qid=159112&page=11

 

You know what? I thought I had a good grasp on suspension designs before I started looking at the other posts there, now I realize how far behind I really am. I love it though, I have so much more reading to do...I wish I had the money to buy this book http://www.amazon.com/Race-Car-Vehicle-Dynamics-R146/dp/1560915269/ref=pd_sim_b_6