SELF LEVELING SUSPENSIO I AUTOCROSS

[golfpin]

HOPE THIS IS NOT TOO FAR OFF THE POINT,
WOULD ANYBODY CARE TO COMMENT ON THE FOLLOWING.
CIRCA 1982 THE AUSTIN 1100, NAMED THAT IN RSA, WAS LAUNCHED, I WAS AN APPRENTICE AT THE TIME ON THE FLOOR ABOVE US WAS THE BODY SHOP.
I NOTICED THAT THERE WAS AN ABNORMAL NUMBER OF THESE CARS WERE IN FOR REPAIRS TO THE REAR ENDS SEEMING TO INDICATE THAT THESE VEHICLES WERE STOPPING TOO QUICKLY FOR OTHER MAKES? THEY WERE EQUIPPED WITH THE HYDROLASTIC SUSPENSION. MY CURIOSITY WELL AND TRULY ROUSED I EVENTUALLY GOT MY HANDS ON ONE AND WENT FOR A "TEST DRIVE" AND TO MY SURPRISE THIS VEHICLE DID STOP ON A "TICKEY" MY DESCRIPTION OF THE EVENT WAS AKIN TO THE WHOLE VEHICLE SQUATTING IT LITERALLY JUST STOPPED. HENCE PERHAPS THE PLETHORA OF REAR ENDERS IN THE PANEL SHOP. PART OF THE SALES PITCH [PUN] WAS THE HYDRO WAS REFERRED TO AS SELF LEVELLING
THERE WAS NO DIVE, NO APPARENT BIAS TO THE FRONT IN TERMS OF DIVE OR LOCKING OF WHEELS, I HAD DONE QUITE A BIT OF COMPETITIVE DRIVING BY THIS TIME SO I THINK I HAD REASONABLE FEEL FOR THE CAR.
I KNOW COLIN CAMPBELL MADE MENTION OF IT IN HIS BOOK "AUTOMOBILE SUSPENSION" AND COOPER PLAYED WITH IT IN I THINK A FJ OR F3 HAVE DONE A BIT OF DESIGN WORK ON OFF ROAD VEHICLES BUT HAVE ALWAYS HAD THE HYDRO EXPERIENCE TUCKED AWAY IN THE GREY AREA. WONDER IF THIS HAS AN APPLICATION IN AUTO CROSS OR SIMILAR, ANYONE CARE TO COMMENT.
HOPE TO SEE SOME VERY ERUDITE POINTS/EXPLANATIONS.
CHEERS GOLFPIN

 

[gt6racer2]

Hi Golfpin,
I think your observations have merit.
The Austin suspension was coupled front to rear in an in/out coupling, meaning that if the front suspension was compressed, the rear would extend and vice versa. This coupling was good for single axle bumps (speed bump for example) as when the front hits the rear suspension would push out, keeping the car more level. You'll have seen those images in the advertisements.
However, for braking this coupling removes the resistance to pitch, such that when the front suspension is compressed under braking, the rear will extend. This exagerates brake dive, and would thereby give the impression of strong brakes. It could be argued that greater brake dive (pitch) puts more load on the front wheels - and thereby more stopping power, but I suspect the greater effect was that the build up of load on the front wheels with the dive ( especially if an suspension travel end stop such as a compression bumper is encountered) meant that drivers slowed more quickly than they expected.
Does this have race application ? I doubt it as the brake dive and light rear end will give challenging turn in, and I don't think the at the ultimate stopping power will be improved much.
But, if you couple the front/rear suspensions to be in/in ( if front compresses, the rear wants to compress - opposite of the Austin) then you can provide pitch stiffness. Pitch stiffness is especially important in aero based cars such as F1, where you need to keep the car level to the ground in the pitch axis, and I believe that they have developed just such a device. They call in FRIC (Front/Rear Interconnect). Unfortunatley, given the secrecy around F1 little is known about their exact systems, but basically that is what it does. Try a quick google on FRIC and you'll find lots of opinion....

 

[Tmoose]

In a Car Life/ R&T/ Car and Driver road test of a small block Cobra back in the 60s there was a reference to an MG 1100 sort of keeping up with the Cobra on a twisty bumpy road despite "all that lovely horsepower."

 

[BrianPetersen]

Pitch stiffness as described (front/rear try to operate together) won't provide roll stiffness, though. If you want to go this route, the trick may be to diagonally connect them ... compressing the left front causes the right rear to try to be driven up.

The other thing is that the tendency for the front to compress and rear to extend during braking can be compensated for by the geometry of the suspension. I do know that the various British Leyland cars that used Hydrolastic suspension, used pure trailing arm rear suspensions, and those have very strong anti-lift under braking. (The braking torque tries to pull the trailing arm pivot point down. If you locate the trailing arm pivot point correctly, it can come very close to canceling out the unweighting of the rear end.) Front suspensions were double wishbone. On a front drive car, a weight shift forward has a much greater percentage-wise effect on unloading the rear compared to adding load to the front, so it might not be necessary to do anything about it. If needed, you can build anti-dive into the front end geometry by tilting the axis of the upper arm, for example.

 

[NormPeterson]

used pure trailing arm rear suspensions, and those have very strong anti-lift under braking. (The braking torque tries to pull the trailing arm pivot point down. If you locate the trailing arm pivot point correctly, it can come very close to canceling out the unweighting of the rear end.)

Anti-lift doesn't reduce the unweighting, only the outward appearance that is commonly associated with unweighting. The suspension spring is unloaded less, but the rear tires see both the elastic and geometric unloading effects. If anything, a greater amount of anti-lift unloads the rear tires faster because it doesn't have to wait for the suspension to travel to a new equilibrium position.

Pretty much the flip side of rearward load transfer and squat on acceleration with a RWD vehicle. The load transfer happens with or without visible suspension movement.


Norm

 

[BrianPetersen]

That is a good clarification - the geometric anti-... functions change the amount of suspension movement but not the actual total amount of load transfer. Still, it's useful for keeping the spring and damper within a useful part of the travel range. On a Hydrolastic suspension with front/rear connection in opposition (the way British Leyland did it - and for that matter, the way the Citroen 2CV did it mechanically), there is very little to stop the front suspension from going completely to the bump stop in compression and the rear suspension from going completely topped out when one slams on the brakes, if it were not for the geometric anti-dive on the front and anti-lift on the rear.

 

[GregLocock]

Incidentally Moulton insisted that BL had interconnected the Hydrogas units incorrectly, but I can't remember his preference.

Cheers

Greg Locock


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[golfpin]

TO ALL WHO REPLIED TO MY THREAD A VERY BIG THANK YOU, MY EYES HAVE BEEN TRULY OPENED TO MY IGNORANCE LOTS TO THINK ABOUT. ONE MORE POSER CAN ANYONE PERHAPS EXPLAIN MY EXPERIENCE IN THE INCREDIBLE STOPPING POWER OF THIS VEHICLE, OH AND BY THE WAY THE DATE SHOULD READ 1962 NOT ,82 WITH THANKS GOLFPIN RSA