Is this suspension better?

JOSEPH · 05-20-05, 10:08 PM

How about you experts make some comments on this suspension. What is it called and is it similar to the new formula 1 cars? Looks interesting to me. [img]/ubbthreads/images/graemlins/confused.gif[/img]
Joseph

JOSEPH · 05-20-05, 10:10 PM

# 2

Clay · 05-20-05, 11:49 PM

That is a push rod inboard suspension, there are several benefits to this. Mounting the coilovers horizontally on top of the gear box removes the coilovers from the unsprung mass, and essentially makes it sprung mass. You can tilt the coil overs any which way as long as the lever arm is situated in such a way that it will input forces directly into the coil over. This way of mounting the coilovers is convenient considering the ammount of space you're working with.

Another feature of this suspension setup is that everything is mounted directly to the gearbox, there is no additional frame work for the back of the car. Im not convinced this is entirely safe as the bellhousing will be taking all the twisting forces brought on by the rear wheels in cornering and bump. unless there is more to the rear frame that is not shown in the pictures.

A benefit of pushrod suspension in open wheel cars is reducing aerodynamic drag.

All of the GT40 suspensions ive seen on this site have had radius rods, in the rear, which is kind of an old suspension style. This style you are seeing in the picture is used today in open wheel racing.

Chris Melia · 05-21-05, 03:42 PM

Hi All

I have my doubts about this as Clay said, this Renault bellhousing and gearbox was not designed to become a stressed member.
I also wonder about the exhaust system? you would have trouble with the regular crossover system and heat transfer into the shocks?

regards

Chris.

Paul Thompson 'Hooligan' · 05-21-05, 08:26 PM

Hi Joseph -

check THIS LINK for more on the setup you show above.

The front connections of the upper and lower suspension arms actually bolted to the steel adapter plate that connects engine to bell-housing and only the rear was attached to the G-box, via the cage to transfer loadings across the box. This car was only generally used as a track car and was very light, so whilst the G-box was not designed for the loads applied, it did not fail in operation. If used regularly on our (UK) bumpy roads, the story might have been different??? [img]/ubbthreads/images/graemlins/blush.gif[/img]

On track - I try not to think about what might go wrong, if I did, I'd never be quick enough. [img]/ubbthreads/images/graemlins/grin.gif[/img]

Actually, the above is only true when I'M driving, when I'm a passenger, my mind seems to consider just about EVERYTHING that could go wrong [img]/ubbthreads/images/graemlins/frown.gif[/img]

Russ Noble · 05-22-05, 03:26 AM

[ QUOTE ]

Actually, the above is only true when I'M driving, when I'm a passenger, my mind seems to consider just about EVERYTHING that could go wrong

[/ QUOTE ]

I know what you mean, but only if it's my car. I hate the thought of having to fix it if it's totalled! [img]/ubbthreads/images/graemlins/frown.gif[/img] If it's the drivers car then I don't worry. He'll have to fix it! [img]/ubbthreads/images/graemlins/grin.gif[/img] If you're worrying about your life, don't, we're all going to die eventually anyway! [img]/ubbthreads/images/graemlins/shocked.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]

Regards

Bob Putnam · 05-22-05, 08:40 AM

[ QUOTE ]
That is a push rod inboard suspension, there are several benefits to this. Mounting the coilovers horizontally on top of the gear box removes the coilovers from the unsprung mass, and essentially makes it sprung mass. You can tilt the coil overs any which way as long as the lever arm is situated in such a way that it will input forces directly into the coil over. This way of mounting the coilovers is convenient considering the ammount of space you're working with....

[/ QUOTE ]

You do not remove the dampers from the unsprung weight simply by using linkage. They still have inertia and require force to be accellerated. In fact, unsprung weight is added by the linkage. Inboard dampers originated as an effort to get them out of the airstream on formula cars. Once there, designers figured out it was much easier to make adjustable anti-sway bars with the inboard setup, and the layout migrated to closed-wheel cars. The horizontal setup is probably a space and structural variation to allow more room for the driver's feet.

Chris P. · 05-23-05, 04:45 PM

Another advantage to inboard shocks: with a belcrank transferring the suspension loads to the shock, you can easily control the motion ratio between the shock and the wheel. You will notice on many Formula cars the distance from the belcrank pivot to both the pushrod and and the shock are vastly different. Cars with much less suspension travel will typically have belcranks that have a very short distance to the pushrod and a longer one to the shock. This INCREASES shock travel for a given amount of wheel travel. If you kept this ratio at 1:1 then on a car that is very stiffly sprung, you won't have much shock movement and you lose resolution in damping.

By controlling the belcrank ratio (and the inclination of the pushrod or pullrod) you control that motion ratio. It's nice to have one belcrank with different mounting points for the pushrod and shock to test different wheel rates. Or, you can move the shock to a different hole, change the spring so the wheel rate stays the same, but now you have changed your damping!

Clay · 05-23-05, 10:54 PM

Sorry about the misinformation about the unsprung vs. sprung mass info, I was sure i read that in one of the suspension books i read, but when i went back to look for it to double check i couldnt find it. Now im wondering if i actually ever read it at all lol.
The only info i found was that half the coilover assembly is sprung, and half is unsprung.

Chris_K · 05-24-05, 02:54 AM

Ramble on!!

I am hardly an expert, but the benefits of inboard suspension are the compactness of the layout (coil-overs out of the underbody airstream as indicated above) and a reduction of the unsprung weight *ratio* when compared to outboard systems.

As Bob points out, there are complexities when you're adding pivots, bellcranks, etc, but the net result is the lightening of net suspension components outboard of the pivots leading to improved handling. The same arguement/benefit applies to inboard vs. outboard brakes: the mass of rotors, calipers moves from 100% unsprung to 100% sprung weight.

Given the comparatively lightweight suspension components when directly compared to the weight of the body of a car, knocking 10 lbs off any corner vs dropping overall weight of the car by 40 lbs (10 lbs per corner), you will feel a much greater effect with the unsprung reduction.

To further the effects, reducing the unsprung weight while simultaneously adding sprung weight will enhance the perceived performance gain (ie adding bellcrank systems and weight while reducing the unsprung weight makes the body feel like it's riding more smoothly while the suspension more nimbly dances down the surface of the road). Kind of a self-fulfilling prophesy...

All this said, the effects on a standard road may be minimal. Intuitively, highest benefit will be felt by the overall lightest car which is why these systems seem to show up on the formula cars but get left off of the heavier rides.

Ramble off...

Chris

Bob Putnam · 05-24-05, 09:31 AM

[ QUOTE ]
Ramble on!!

I am hardly an expert, but the benefits of inboard suspension are the compactness of the layout (coil-overs out of the underbody airstream as indicated above) and a reduction of the unsprung weight *ratio* when compared to outboard systems.

As Bob points out, there are complexities when you're adding pivots, bellcranks, etc, but the net result is the lightening of net suspension components outboard of the pivots leading to improved handling. The same arguement/benefit applies to inboard vs. outboard brakes: the mass of rotors, calipers moves from 100% unsprung to 100% sprung weight...

Chris

[/ QUOTE ]

That's not what I said.

There is no enherent weight loss when using extra linkage to move the spring/damper mounts. In fact, the chassis usually has to be stronger in more places - and that adds weight. Unsprung weight is also increased by the new linkage. The only way to reduce suspension weight is through locating a damper pushrod to take all bending loads off the lower control arm so that it can be made lighter.

Bill Bayard · 05-30-05, 06:45 AM

This front suspension looks pretty interesting. I'd like to see the upright/linkage, but I couldn't find any "exposed" shots. It looks similar to the rear of a Porsche 956/962.

Bill Bayard · 05-31-05, 06:23 AM

Found a better shot which shows the bellcrank from the upright to the shock. Very interesting.............

Triangulated and gusseted as it is, this this bellcrank setup sure does look STRONG! [img]/ubbthreads/images/graemlins/cool.gif[/img]

Chris_K · 05-31-05, 07:22 AM

The preceding pictures illustrate the point I tried to convey earlier. There is no inherent weight reduction in adding the linkage and bellcranks, etc... But it is the reduction of the unsprung weight RATIO which is important.

An example using the pics above and assuming a few things like:

weight of unsprung suspension components - 400# (100# x 4 corners)
weight of vehicle - 2400# (sprung + unsprung)

One arrives at a ratio of 400:2000, or numerically .20. My contention is the weight is not removed from the vehicle but simply transferred from one side of the ratio to the other. Isolating the heavy components from the vertical travel of the suspension (ie, outboard of the pivots) will have a profound effect on that ratio. If you bring suspension elements inboard of the pivots properly, their CG will undergo minimal displacement through the range of suspension travel. The dampers are virtually completely removed from the unsprung weight (depending on geometry, their center of mass may slightly move vertically during suspension travel as shown in the design pictured above).

Let's say that of the 100# at each corner, 25# was the spring and shock combination. The new ratio would look like:

4 x 75# = 300# unsprung weight
2100# spring weight
ratio = 300:2100 or .143

This yields ~28% improvement in the ratio.

Let's say that you also now need another 20# at each corner split evenly between sprung and unsprung to acheive the inboard suspension. The numbers become:

340# unsprung
2140# sprung

340:2140 gives a numeric value of roughly .16, which is still ~20% better than where we started (.20), but will cost us 80# to acheive. The trade off is where to balance the weight gain and complexity for feel and performance.

Granted, I did choose the numbers to make the math easy but also with some eye toward reality... Figure 30# for a wheel and tire, another 30# for a rotor and caliper, 40 for the remainder of the components.

The end result is that reducing the weight or presence of components moving grossly with the suspension will have a pronounced effect on the unsprung to sprung weight ratio of a car. With more stuff grounded to the chassis at both ends the car will be more inclined to handle better.

I hope this makes sense as it's been ages since I thought about anything of this subject and I may be a bit rusty, but I enjoy the mental exercise though.

Chris

Bill Bayard · 05-31-05, 10:36 AM

Chris,

Well put and easily understood!

FYI:
The car in the photos is a Venom Racing Attack. It has a 4 cylinder, 250HP engine, 5spd, 1850 lbs, 150MPH, and supposedly handles extremely well. I swiped the photos from an auction on ebay with a 49.5K Buy It Now price tag.
Pretty neat little car! Mid-engined too! [img]/ubbthreads/images/graemlins/cool.gif[/img]

Bill

Bob Putnam · 06-01-05, 08:28 PM

Isolating the heavy components from the vertical travel of the suspension (ie, outboard of the pivots) will have a profound effect on that ratio. If you bring suspension elements inboard of the pivots properly, their CG will undergo minimal displacement through the range of suspension travel. The dampers are virtually completely removed from the unsprung weight (depending on geometry, their center of mass may slightly move vertically during suspension travel as shown in the design pictured above)

In reality, if the damper is run "upside down" as is typical nowadays, the unsprung weight of the damper is small. Furthermore, since the stroke is shorter, the damping force must be proportionally larger, requiring a heavier piston and rod. Add the linear and rotational inertia of all the linkage and you've got negligible unsprung weight advantage, if at all.

ingvar · 08-01-05, 04:24 AM

Hi
I'm curios aboat this chasssie. It seems to me that I have exactly the same. I bought a unstarted kit with very little information regarding manufacturer. I was told that it was one of five aluminium monocoques that ray cristopher built circa 1987.The top picture was supplied as information with of how to build the car.Suspension components hat came with the kit is from march formula car, probably formula 2 car. I have tried before to get more information but nobody seems to know aboat these five monocoqes.
Would be nice to have some support in my building effort.
Ingvar