MG Motorsports Forum

Hi all, it’s been a while since I’ve been on here. It thought this might be the best place to discuss my new project – Another MGB GT V8 race car.

The focus of this car is to try something a bit different with the suspension within the class rules to see what happens. My question to you guys is, if there were no practical limits as to where the roll centres could be located, where would we put them? My understanding is that a lower RC is better as you get less push on the outside of the contact patch and obviously more effort through the springs rather than the wishbones etc. So I guess that it is best to locate the RC relatively low and control the roll with springs and sway bars.

I have designed a Mumford linkage with enough adjustability to locate the rear RC anywhere between ground level and 8” above. I have built in the bracketry to allow the use of a rear ARB (I've not used one on any of my previous race cars!) and am at the stage where I need to choose what rear spring rate to go with. I will start with the rear and then locate the front RC an inch or so above the rear, I have a massive range of front springs and bars to try.

Effectively there will be adjustability, just need to choose a starting point.......

The car will weigh 925kgs (class lower limit) and I think a CoG height of 15.5 is achievable. Max track width is 58” to the outside of the tyre sidewall. 195/50/15 tyres are to be used (class rules)

Any thoughts or suggestions?

Ollie, I'm not familiar with the term "Mumford linkage". Please describe.

Hi Dave. If you go to GOOGLE and type in Mumford Link, there are a lot of links and pictures of Mumford Links. Here is a good one with discussion and pictures.

http://www.not2fast.com/chassis/mumford.shtml

VintageBob.
Alvin, TX
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Looks overly complicated vs a panhard rod.

Thanx. Being a big believer in K.I.S.S. this does not excite me. AT ALL!

Opinion

On production based cars you don't want the rear roll center below ground. All my reading says it should be about the same distance below the cg as the front roll center is below the front roll center. Rear roll center should be located with respect to the sprung weight rather than the unsprung (that means don't mount the watts propeller on the rear axle). This shuld prevent the rear end from wiggling as the rear suspension articulates and the distance between RCH and CG over the rear axle changes

Further opinion

Since we aren't running diffusers in vintage, there is little to be gained by running a Mumford over a well set up watts, panhard or even one of Dave's clever lateral location devices.

I think a Mumford has a place, probably on sports racing cars like the live axle U2's that Mallock built, that have low CG heights and diffusers. Think they are probably overkill (but way cool overkill) on a proddy car.



Edited 1 time(s). Last edit at 2017-02-23 03:35 PM by twentyover.

K.I.S.S ? What's that?

American colloquialism meaning Keep It Simple, Stupid

Related to the concept of simplicating and adding lightness. Easy to say, usually harder to do in practice .than one might think



Edited 2 time(s). Last edit at 2017-02-24 06:00 AM by twentyover.

Actually, "Keep It Simple Symon" for the polite crowd

As in, don't make it any more complex than required.

Ollie,

In your original post you state: "I will start with the rear and then locate the front RC an inch or so above the rear"

I don't think that's what you want. When you turn the steering wheel the front tires develop a slip angle and start to generate lateral force... the rear tires lag behind the front, if the rear roll center is higher it helps the rear to "catch up" with the front which is why the roll axis almost always slopes down toward the front tires.

The following link is primarily about US Muscle cars being raced in a class called Pro Touring. The size of the cars, the horsepower and other variables are vastly different than an 1800 pound 150 horse power MG... but the thinking and the engineering is spot on. The author shares insights and formulas to design and develop (in this thread) suspension for race/performance cars.

http://www.lateral-g.net/forums/showthread.php4?t=42568