Mustang II Front Supension

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frnkeore
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Mustang II Front Supension

Post by frnkeore »

I have a Austin Healey kit car, that uses factory, Must II suspension. I'm putting in a 9" 35 spline, 52.5 track rear axle. It's located with a 3 point arms and a Panard rod for roll center.

It will mostly do duty at the drags but, I will do some road racing with it, too and I need the Must II front roll center, to set the basic (adjustable) rear roll center.

Does anyone have the front roll center height for this suspension or a drawing of the suspension, with dimensions, so I can calculate it?
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dannobee
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Re: Mustang II Front Supension

Post by dannobee »

It's not that easy. Where you put the control arm mounts matters, as does frame height. You'll need to carefully measure the suspension points, at your chosen ride height, then find the roll center. Putting it on an 8.5"x11" piece of paper isn't really that accurate. The easy way is to get a chalk line and a flat floor. Carefully measure your control arm mounting points and ball joint heights, then transfer your readings to the ground, full scale, by snapping chalk lines. Then run some scenarios by changing what you can; usually the upper control arm mounting points.

Front roll centers for performance cars *usually* fall somewhere in the 2"-4" above ground level range. Rear roll centers for live axles *usually* falls somewhere between 1/2 and 3/4 the width of the rear wheel. Generally speaking, YMMV depending on a bunch of variables, but that should get you in the ballpark.

https://www.racecar-engineering.com/tec ... ll-centre/
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frnkeore
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Re: Mustang II Front Supension

Post by frnkeore »

Thank you for your input.

I've understood how to calculate RC and the instant centers, as well as roll couple, since about 1963, in a book by Colin Chapman.

I'm not looking for a exact RC, just within 1" so I can set my Panard bar above that, to start with. I'll have 1.25 adjustments, from there.

I can not measure the suspension positions w/o dissembling the front end, not to mention finding the center of the ball joints. So, that's out.

Can you explain this more:
Rear roll centers for live axles *usually* falls somewhere between 1/2 and 3/4 the width of the rear wheel.
It has always been my understanding, that the roll center will be where the Panard bar crosses the center line of the chassis. I make my Panard bars as long as possible and as parallel to the ground as I can, using multiple points on both axle and chassis.
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Re: Mustang II Front Supension

Post by Chris_Hamilton »

I've used this in the past to get a starting point on a Mustang II front suspension. The demo is free and it has Mustang II suspension in the samples. Should get you started.

https://www.performancetrends.com/download-2018.htm#sa
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http://www.spiuserforum.com/index.php?t ... inia.9030/
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Re: Mustang II Front Supension

Post by dannobee »

What I meant was that the height of the rear roll center is dependent on the size of the rear tire. I.E., if you have 10' wide wheels, 5-8" rear roll center is a good starting point. 15" wide wheels and you would need a rear roll center about 10" or so.
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Re: Mustang II Front Supension

Post by frnkeore »

Thank you, Chris. I couldn't get anything to run. I'm going to have to close a few things first and maybe re boot.

dannobee, that's a interesting rule of thumb. Do you know the theory behind it? My pictured avatar car (Formula Atantic) has 13" wheels that are 15" wide, I don't think it would apply on that. I've always just used a higher rear roll center, by 2 - 4" to transfer weight to the front, in cornering.
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Re: Mustang II Front Supension

Post by dannobee »

The rule of thumb applies to your current type of build, ie front engine, rear wheel drive, with a live rear axle.

Yes, there's theory and practical experience behind it.

IIRC, the Mustang II front end had a roll center of about 7/8" from the factory. BUT, obviously changing anything will alter that. If it's a kit car, I doubt that ANY of the mounting points are in the factory location.
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Re: Mustang II Front Supension

Post by frnkeore »

danobee, is there any site that I can go to, to read about this?

Thank you,
Frank
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