Rear anti-roll bar. Is it worth installing on a BN1?

[55modified]

So I am trying to upgrade my suspension wherever I can. Koni shock kit installed in the front, lowered 1/2" with original coil springs. Rear has original panhard rod and tracking arms. Car has GM 12 bolt rear. I was looking at Dennis Welch or other upgraded rod. Any suggestions or advice from anyone who has done this would be appreciated.

 

[John Turney]

I have the Denis Welch front anti-roll bar and 1.5 deg. negative camber in front, track bars in the back to limit rear spring wind-up. I upgraded the original Panhard rod with Poly bushings and broke the welds on the axle bracket. Steve Gerow (steveg) broke his also with the Cape International modified Panhard rod. Make sure your rod brackets can take the additional load. I've modified the axle mount to, I hope, prevent further breakage.

I don't recommend the rear anti-roll bar as it increases understeer. What I would recommend if you don't have it as a limited-slip differential.

 

[Michael Oritt]

John--

A rear anti-roll bar will decrease understeer as it stiffens the back and increases grip in front.
Conversely a stiffer front anti-roll bar tends to induce understeer as it decreases front lean and--relatively--lessens the grip of the front tires.
Of course all of this is theoretical and YMMV in the real world.

On my car I have both increased the diameter of the front anti-roll bar and added the DW bar in back to reduce total body roll which keeps, relatively speaking, the car's tendency to have inherent understeer.

 

[John Turney]

Michael,

You're correct. I had a brain fade.

 

[55modified]

I have the Denis Welch front anti-roll bar and 1.5 deg. negative camber in front, track bars in the back to limit rear spring wind-up. I upgraded the original Panhard rod with Poly bushings and broke the welds on the axle bracket. Steve Gerow (steveg) broke his also with the Cape International modified Panhard rod. Make sure your rod brackets can take the additional load. I've modified the axle mount to, I hope, prevent further breakage.

I don't recommend the rear anti-roll bar as it increases understeer. What I would recommend if you don't have it as a limited-slip differential.

Thanks I think I will leave it alone. I do have a limited slip recently installed when I did a gear swap from. Traction bars from PO too.

 

[steveg]

Thanks I think I will leave it alone. I do have a limited slip recently installed when I did a gear swap from. Traction bars from PO too.

Have to say, after my experience, I regard the whole idea of the "uprated" panhard bar as a crock. The racers can chime in on this, but the stock bar with rubber bushings at both ends is more than up to the job.

 

[DerekJ]

Steve, I agree with you re the Panhard rod. The load is the same whether the rod is original or thicker. If the original holds up, which it does, then there isn't a problem. A rear sway bar just isn't necessary as we already have a solid rear axle which is pretty much doing the same job.

 

[Michael Oritt]

Derek--

I agree that simply increasing the diameter of a panhard bar brings nothing to the table and so long as the original one is heavy enough to not break while locating the axle under transverse loads that's fine. What can be helpful is to modify its attachment points to the frame and/or the axle so that it is on the same plane as the axle and replicates its geometry as much as possible.

I don't agree that a rear anti-sway bar is unnecessary and it performs the same job in the rear as does a heavier bar in the front: It resists the tendency of an opposite wheel to lift and thus increases traction. The rear axle's being solid provides some, but not much, of this effect. But if we are talking about increasing suspension performance such a bar in back is no less necessary than having one in front--or upgrading suspension performance in the first place!

 

[DerekJ]

Michael

The front needs a sway bar much more than the rear due to the independent suspension set up as opposed to the solid axle at the rear.

i agree on the necessity of the Panhard Rod being on the same plane as the axle. If not it can produce weird effects such as rear wheel steer.

 

[Michael Oritt]

Derek--

I am not saying that a rear anti-sway bar is absolutely necessary. However I believe we have been talking about increasing the diameter/weight of the front bar and to my mind doing that modification alone will produce excessive understeer which a rear bar would offset. In other words if you increase/decrease the body lean/traction at one end you should do it at the other or face what would be an undesirable change in handling, etc. etc.

Again, one's mileage may vary....

 

[55modified]

So is anyone here running a rear sway bar on their car?

 

[DerekJ]

Well, you definitely do not need one on a road car and the racers who I have spoken to over here don't run them either.

 

[Michael Oritt]

So is anyone here running a rear sway bar on their car?

Yes,me--to balance the effect of the heavier front bar and mimize rear inside wheel lift.

 

[DerekJ]

I think its important also to differentiate between normal road use and setting up a track car. A rear sway will increase the tendency to oversteer which is not what you want in a road car.

 

[Deleted member 19315]

I think its important also to differentiate between normal road use and setting up a track car. A rear sway will increase the tendency to oversteer which is not what you want in a road car.

Hi Derek, when rebuilding my 100/6 I did fit a rear anti roll bar from DW. My thinking was that while I was under the car I my as well weld in the fittings and if it didn't suit its easy to remove the bar. I agree with most of the preceding discussion by the way. To get to my point, this car has all poly bushes the 7/8 front bar, negative trunnions ( which only give a measured 1 degree) up-rated lever arms. It has worked over BJ8 front springs and reprofiled rears to give a 1 1/2inch lower all around. I have 72 spoke 5.5 rims with veredstien tyres. I also have a tight plate type lsd.

My thinking with the rear bar was it may counteract to some extent the understeer affect that the lsd tends to generate when not 100 % committed to corner entry. What do you think?

By the way I recognise the difference between road and race and am no race driver I just like the feel of a more competition flavoured car.

 

[steveg]

As I understand, if you do your front and rear bars a certain way, you'll have a neutral-handling car - i.e. one where the front and rear wheels let go at the same time. Most say an understeering car is safer for ordinary drivers.

If Mike Salter's reading this discussion, he may want to contribute his bad experience with a rear bar.

 

[55modified]

It has worked over BJ8 front springs and reprofiled rears to give a 1 1/2inch lower all around.

Tell us more about your coil springs. They aren't just chopped are they?

I have looked for shorter springs and can't find them or anyone to custom fabricate. So I got Tom's 1/2 lowering kit.

I tried BJ8 springs on advice and they sat taller than stock BN1.

 

[Randy Forbes]

When my Healey was an active autocross contender, I ran a 3/4" rear bar in conjunction with a heavier 7/8" front bar, both sourced from Addco, IIRC. Under those conditions it was a big improvement over the stock configuration (and easily rotated with the throttle).

Tube shocks were still a no-no in the street prepared category, so the valves in the stock (new replacement) Armstrong shocks were shimmed and tightened up a bit, along with variety of Castrol motorcycle fork oil viscosities.

When I tore the car down for restoration in 1986, I did away with the rear swaybar AND the Panhard rod, and fitted an articulated A-arm to locate the axle instead. Try as I might, it is very difficult to induce either under or oversteer__I don't know if the tires are that much better, or if I just lost my nerve, but the car seems to be very well planted now, with neutral balance

Overall, my impressions through decades of modifications align with Michael's observations.

 

[Deleted member 19315]

Tell us more about your coil springs. They aren't just chopped are they?

I have looked for shorter springs and can't find them or anyone to custom fabricate. So I got Tom's 1/2 lowering kit.

I tried BJ8 springs on advice and they sat taller than stock BN1.

Hi. I had the end coils closed up to reduce the overall height but keep the standard "rate". They were done for me so I don't have any detail I'm afraid.

 

[55modified]

I had the end coils closed up.

What does that mean "closed up?"