Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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roverman
Art Gertz
Winchester, CA.
(3005 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Suspension Design, Revisited.
Posted by: roverman
Date: May 09, 2012 01:52PM

I just read the BV8 article, May 20008, by Larry Shimp and assistants, Thank You. As I understand this, only the lower control arm mounting height/angle, determines roll center height for that end of vehicle. Semi trailing arm roll center height would be similar only veiwed/ measured from side of vehicle vs. front/rear for a-arm supension. In theory, it seems, if roll centers were at CG of vehicle, and there was NO roll center migration, anti roll bars would be un-needed as there would be zero roll, dive or squat. I've read that taller spindles on sla suspensions, generate less roll center migration. I haven't grasped how this works. I suspect if lca is too short and/or too much angle pointing down toward wheel, "jacking" could occur, just like a swing axle suspension. I suppose this all factors into the "roll axis coupling" ? I suspect most important geometry is when suspension height is at most highly loaded in turns and maximum starting and stopping positions ? How do the instant centers relate to the roll centers and CG ? Thanks, roverman.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5821 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Suspension Design, Revisited.
Posted by: BlownMGB-V8
Date: May 09, 2012 05:11PM

Art, I've heard it said that having the roll center below the CG is advantageous because it transfers weight to the outside tire in a turn, allowing more grip. Now I'll confess this seems counter-intuitive to me. I would think that having the tires loaded as equally as possible would allow them all to be run with the softest grippiest compound possible, and that this would be an advantage. (NASCAR has recently learned to equalize loading for each side of the car, resulting in higher cornering speeds, why wouldn't it be the same across the vehicle?)

But conventional wisdom says, no, you want to load the outside tires and then use a sway bar to keep the car from leaning. Who am I to argue with convention?

Jim


roverman
Art Gertz
Winchester, CA.
(3005 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Suspension Design, Revisited.
Posted by: roverman
Date: May 09, 2012 06:50PM

JB argue with conventional wisdom - NEVER !/lol. As I think I understand this, if the lateral g-force remains constant and the verticle load increases on a tire,(weight transfer), that tire will grip better because it's contact patch got bigger. Reportedly it's a ratio of lateral load to verticle load-maybe. As I see it, pretty much impossible to overload the inside tires, other than too stiff of springs or overkill sway bars. An anti-roll bar trys to lift the inside tire off the pavement. A "Z bar", does just the opposite. Onward all ye non-drifters, roverman.


roverman
Art Gertz
Winchester, CA.
(3005 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Suspension Design, Revisited and revised
Posted by: roverman
Date: May 15, 2012 12:12PM

So, how do you change the amount of Akerman, without bending the steering arms ? I thought of "undersize" bolts to hold the arms,(angle change). How to clamp securely ? Ball sockets/washers ? Anybody ? Thanks, roverman.


Bill Young
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

authors avatar
Re: Suspension Design, Revisited.
Posted by: Bill Young
Date: May 15, 2012 02:13PM

Art, the usual method is either heat and bend the steering arms or bolt on new steering arms with the correct angle. The problem with MGs is that they are front steer so the arm turns out towards the brake disc which can create clearance problems with the brakes and wheels if the wheelbase is being shortened. For a longer wheel base then it should be fairly easy to heat and bend them and then shorten the outer tie rod ends just a bit and have the ackerman right on without losing the bump steer settings. The other solution would be to make up a steering system similar to that used by GM for years with a drag link and idler arms and move that with the rack. You could just about dial in anything you want in the way of bump steer and ackerman with that sort of design, but it takes a lot of engineering to get it right and then you'd have to source the parts or have them made. Forged steel arms should bend without any problems provided the correct amount of heat is used and they aren't quenched to make them brittle. I've done a lot of early Ford steering arms for hot rods and never had a problem.


roverman
Art Gertz
Winchester, CA.
(3005 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Suspension Design, Akerman revised
Posted by: roverman
Date: May 18, 2012 11:29AM

Since tire technology has changed so much, since this GT-1 was built,(used bias-ply slicks). I suspect trying increased Ackerman, might help. How about mild steel arms cut from plate, with multiple/offset tie rod holes ? The offset holes should additionally increase Akerman, as result of approach angle, to the arm. Onward, roverman.


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