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Steering Geometry

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Bob_Spidell

Bob_Spidell

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I've started thinking about ways to modify my cars'--BJ8 and BN2--steering geometry in order to improve handling. I'm a 'tourer,' not a racer, so I'm mainly looking for ways to improve all-around handling, not at the limits. Both my Healeys, esp. the BN2, exhibit the same behavior: a little too much effort, it feels, required to start a turn--understeer?--then, once in the turn, a bit of oversteer. When I acquired my BJ8 it had excessive--2-3deg--positive camber. Offset bushings got some of that out, and an alignment shop got some more out by bending the A-arm brackets (and creating a crack at the chassis, which I welded-up). The BN2 had excessive negative camber, which we remedied by installing Kilmartin adjustable shock plates (which were manufactured incorrectly, but that's another story; chassis measurements were nominal and it didn't appear to have front-end damage, so we never figured out why). Both cars track straight on flat pavement, so that's not an issue. I haven't driven the BN2 enough to tell, but the BJ8 always seems to wear out the outside of the front tires (but so does my Mustang as I do like to 'challenge' corners). The BN2 has stock, 48-spoke wheels with 165/80 tires; the BJ8 has 6-in, 72-spoke wheels with 185/70 rubber, and Torrington bushings to help mitigate turning effort. The BJ8 has an uprated anti-roll bar, which helped keep it flatter in turns.

I don't have any of my shop manuals handy, but I think they call for just a degree or two of positive(?) caster, which seems a little light compared to other cars. An alignment shop recommended 0deg camber for the BN2, but couldn't achieve that (I think because they didn't realize the bolts on the rebound buffer had to be loosened to move the sub-plate). The BJ8 still has 1deg+ positive camber.

So, what settings do y'all recommend to get a better-balanced car, agile but not too squirrely? One that will engage a corner, but not want to swap ends? Or, should I leave well enough alone?
 
Bob:

I set my camber to zero so that it goes slightly negative when the car is lloaded.
 
My BN4 has, IIRC, 1.5 deg negative camber and 1/8" toe in. There is no caster adjustment for the Healey without some modification. Can it be changed with the adjustable camber plate, or does the plate only move in and out? I have a 7/8" anti-sway bar and 195/65R-15 tires on 72 spoke wheels.
 
John Turney said:
... Can it be changed with the adjustable camber plate, or does the plate only move in and out? I have a 7/8" anti-sway bar and 195/65R-15 tires on 72 spoke wheels.
Click to expand...

The adjustable plates I've seen--Kilmartin, DWM and Tom's Import--only allow camber in/out. But, since I'd be welding new mounts I could tweak the caster.
 
I know of one steering adjustment done to big Healeys to one of both idler arms that a couple of guys in our club did. I’m not sure how it improved the steering or handling. Another one was called, I believe bump steering modification. Maybe someone knows more about this?
 
Patrick--

Bump steer--the amount of steering induced by suspension travel--is a product of steering and suspension geometry and short of limiting vertical wheel travel by putting in heavier front shocks/springs (which leads to even more understeer than is already there) there is not too much you can do without changing steering and suspension components and/or changing the height of the steering box and idlers, etc. I could be wrong but I don't think these "modifications" can be made without different suspension components to modify the geometry since a Healey's front end is not adjustable beyond alignment and toe and perhaps a bit of shimming to get things straight.

When I bought my Ginetta it had a lot of bump steer that a previous owner had somewhat dealt with by putting in very heavy front springs which limited vertical travel but induced understeer. I was able to eliminate a lot of the bump steer by modifying the location of the rack and the length/motion of the A-arms, etc. but its suspension is fully adjustable and a lot could be accomplished by making changes to geometry. NOT easily done on a Healey without replacing components.
 
Steve--

Technically the term describes the amount of steering induced by vertical travel of the front wheel without any input from changes to the steering wheel. If you want to see it in action you disconnect/remove the springs and shocks and then jack a wheel. The steering/suspension geometry will induce (or not) changes in steering angle depending upon the amount of bump steer present. To change the amount of bump steer you essentially have to change the geometry.

I have heard the term applied to the way a car, especially a solid-axled car with leaf springs, etc. such as a Healey, responds to turns on a bumpy road but that's really a different thing, generally called crappy handling.

BTW why stop at a De Dion rear which, though better than a live axle, falls short of a full IRS system. People have installed Miata IRS rears in spridgets and I am sure that, given enough money, some car's IRS system could be adapted to fit into a Healey. That said, an IRS system is not always an improvement and the benefits are also a function of the weight savings, if any.
 
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I agree with what DerekJ said, you can lower the front a little by putting spacers under the pan.

Tire pressure can make a bit of difference too, I like to run higher pressure by 2-4 lbs up front vs. rear, like maybe 32 lbs front and maybe 30 or 28lbs/in. rear. as a starting point.

Some of the handling characteristics come from the big old lump of cast iron sitting in the front.

If you want vintage light and agile feel stay with skinny tires, renew bushings and all the ball joints in the steering if you haven't already. It will never feel like a Sprite rack and pinion, but should feel much better. You can minimize toe in to make it feel a little more "darty" but the more it likes to turn, the less it will like to go straight (wander), so a bit of a trade off.

If you want a more modern feeling g machine there are all sorts of parts you can get from Denis Welch and AH Spares. Personally, if driving pleasure and not speed around cones or track are not the ultimate goal I would stick with light and agile.
 
I have measured the bump steer in my current BJ8 and found it pretty good. Not bad enough to try and modify anything. On an earlier BJ8 I did try to slide the steering box up a little bit just within the clamp but that was a long time ago and I probably didn't accomplish much.
 
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