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MG MGB Technical - rear anti roll bar?
|I was helping my brother in law to check a rear shock absorber on his 77 mgb when I spotted that it has a rear anti roll bar fitted. |
It has been converted back to c/b spec (a nice conversion too)
Shouldn't the rear a/r bar have been removed when the conversion was done leaving just the front a/r bar in place?
Would the car handle better without it now that it has been lowered back to the c/b suspension setup.
|If the car is now at chrome bumper ride height, the rear bar could be removed and the handling should be similar to the original car. The MGB was designed to understeer gently at first, then as cornering speed increases the tail was allowed to roll causing gradual and controllable oversteer. This made it a very safe and forgiving car to drive for the average driver.|
Jacking up the ride height on the rubber bumper cars, as well as hanging those heavy bumpers on either end, caused the once gentle roll to become worse, and so a rear ARB was fitted to compensate.
|Rear antirollbar is bad news on any B. The car feels flatter in corners (nice) but the ARB results in additional weight transfer at the rear. With the live axle there is no geaometry gain at the rear to offset the weight transfer (unlike a front ARB, in which the weight transfer it causes at the front can be offset by the wheel remaining more upright). The result is a reduction in ultimate grip at the rear and the car reaches its limit earlier than without the ARB.|
Best thing is to remove the rear bar and fit a 3/4" one at the front.
|Thanks guys, that's what I suspected, I will have to give him a hand to remove it and sort a new 3/4 " front bar too.|
I bet it will be a lot better when we have sorted it.
|When fitting a 3/4 one at the front, it's a good idea to plate the chassis rail around the mount as (admittedly after years of hard work) they can break the rail around the capitve plate. Very easy to do now, much harder to do once it's cracked and broken!|
|Didn't the Ron Hopkinson handling kit include a rear ARB for chrome bumper B's?|
|Dave O'Neill 2|
|I have a 67GT that has a rear bar installed by the previous owner. The car is definitely flat in the corners. |
I have not yet experienced loss of grip as Paul describes even after some pretty tight cornering.
|Yes, the Ron Hopkinson kit did have a rear ARB. Definitely feels better, but loses the tail early. I had a number of customers who didn't believe me on this but found (particularly on the track) that it was indeed true and the car swapped ends quite easily.|
The Hopkinson rear bar was fitted to balance things up once a 7/8 bar was fitted at the front, as with this size of front bar the geometry gain is less than the weight transfer loss so there is net understeer if nothing else is done. The addition of the rear ARB balance this understeer by reducing grip at the back; to restore balance, much better by far is to increase grip at the front by introducing a bit of static negative camber there. This scenario gives an increase in total grip rather than a decrease.
Rear ARBs certainly work on IRS cars where the flatter ride also produces geometry gains from better wheel angles at the rear, and that can balance the weight transfer. But for a rear live axle car the wheels stay at a fixed angle to the road so the only way you can increase total grip at that end (o a given set of wheel+tyres)is to reduce weight transfer. This can be achieved by lowering, by fitting softer springs at the rear, or by getting the front to take more of the roll load by stiffening it up.
Though there are some enterprsing types who have put a bit of negative into the rear of a live axle by jacking the rear axle housing into a slight banana (1/2" of bend would be 1 degree of negative) though what this does to the wear rate on half shaft splines would be another question :-)
This thread was discussed between 10/08/2014 and 11/08/2014
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