Better straightaway feel

[pitts64]

I have a 64 Bonneville with a few suspension additions like AGR 12-1 steering box, Addco 1-5/8" front sway bar, front disc conversion with adjustable proportion valve, Bilstien shocks and 225/70-15 Firestone Firehawk 500 tires.
Its a smooth as glass up to 120-130 mph.
It handles bends very well but I would like to get a better straightaway feel though.
It has rear steering like the Comaro/Firebird so it tends to over-steer more than under-steer.
When at speed, its like I under-steer then over-steer while trying to hold it steady.

Any ideas?

Thanks, Jeff

Update 7-16-15, 7-8 degrees of positive caster did the trick along with 1.5 degrees negative camber with a slight tow out...

[BonzoHansen]

For one, you are pushing those tires far beyond their design limits.

[6'9"Witha69]

For one, you are pushing those tires far beyond their design limits.

Correct. Time for an updated wheel/tire package.
Try calling Marcus at SC&C (a sponsor here) ---------->
He will be able to help with some control arms and such to increase the handling and stright line feel.

[vanzuuk1]

I have the same issue with my car, I run a little less air in the front and it seems to help,next step is the dse box. (more feel i hope) The lower front pressure makes the steering a little sluggish,less twitchy.

Dont talk about speeding on this site, some guys will yell at you.


Also , tall ****ty tires seem to feel great on the highway,more flywheel effect. Cool wide low profile tires seem to hunt all over the road as you go faster.

[pitts64]

I don't drive for miles at those speeds, I'll take it up there for a moment or two when the road is clear with no wind, then back down to around 75-80. We have long stretches of roadway here that you can see for miles ahead.

My 83 Olds 98 has 225/75-15 Pirelli touring tires that are narrow and have a better straightaway feel.
I like having 7" diameter tires when I go into corners we have a lot of them here too.
Western Pennsylvania is all hills and turns.

My wheels are vintage American T-70. I bought them before finding out E-T still makes wheels.
The E-T is the best looking wheel in my book and 100% American made.

I'm going to experiment with more positive caster but my car was designed to run negative so I don't have much to go.
From what I hear the new Camaros and Firebirds are set up for 0 caster.

[Norm Peterson]

I have a 64 Bonneville with a few suspension additions like AGR 12-1 steering box, Addco 1-5/8" front sway bar, front disc conversion with adjustable proportion valve, Bilstien shocks and 225/70-15 Firestone Firehawk 500 tires.
Its a smooth as glass up to 120-130 mph.
It handles bends very well but I would like to get a better straightaway feel though.
It has rear steering like the Comaro/Firebird so it tends to over-steer more than under-steer.
When at speed, its like I under-steer then over-steer while trying to hold it steady.

Any ideas?

Thanks, Jeff

The oversteer is courtesy of the compliance in the control arm bushings. That negative caster spec may have been an attempt to minimize this compliance (over)steer with the tires of the day by dialing out front grip/increasing front slip angle as the total steer angle increases.

Since there is more "give" in OE/OE replacement bushings than in the steering linkage, lateral force steers the wheels more or less about the outer tierod pivot in such a direction as to effectively add more steering input (sharper curve/tighter radius/oversteer). Stiffer control arm bushings should minimize this effect, or at least tame it a bit, without completely eliminating it. Rod-ended control arm pivots in all locations might if you could put up with their downsides.

Assuming that the centerlines of the chassis side pivots for each arm are coaxial, Del-A-Lum / delrin / poly - kind of in that order of preference.

That may let you run a slightly positive caster setting, but I'd experiment cautiously. Besides the altered (read: unfamiliar) compliance steer characteristics, changing caster too far from OE is apt to bring about some bumpsteer issues.


Norm

[boodlefoof]

Could add some more caster.

[pitts64]

I want to replace the upper and lower control arm bushings this winter when I take the front suspension apart.
I've heard good and bad things about poly.
I need to do more research the Del-A-Lum, I don't know anything about them.
I have new upper control arm shafts with new rubber bushings i'm going to install.
I have a feeling the tech that installed my present upper control arm bushings tightened them up with the car in the air.
I do all of my own work now.

[BonzoHansen]

My 83 Olds 98 has 225/75-15 Pirelli touring tires that are narrow and have a better straightaway feel.

Pirelli made tires that size for Jags and such. My guess is they are V rated - probably a P6. Much stiffer carcass than that 20 year old tech Firestone hoop that is probably S rated at best.

Also agree on more caster.

[6'9"Witha69]

I need to do more research the Del-A-Lum, I don't know anything about them.

Go for it if at all possible. Having solid bushings does not take away from ride comfort. In fact, the Del-A-Lum gives a smoother ride IMHO and has 0 deflection. All bonuses. When I converted from OE Poly bushed arms to the GW Del-A-Lum arms, the difference was night and day. Same springs and shocks, but a smoother ride!

[pitts64]

I was looking at my upper control arm bushings today and they are shot. They only have around 15,000 miles on them.

Do you send the control arms out to have the Del-A-Lums installed or can my machinist do it?

[6'9"Witha69]

If they are available for your application, any wheel/tire/suspension place can do the press work. If they are not available then your machinist will be needed.

[MonzaRacer]

As for the bushings yeas you need new bushings and delalum or even properly installed and lubed ploy bushings will tighten things up.
I have pmed you about some better tires (Firehawk PV41 cop car tires V rated).
I will bring home my older car spec listing for alignment specs and see if we can work on the factory specs to make it handle better.
I have been doing performance alignments for years so it woint be real hard.
Lee Abel
AFTERMARKET PERFORMANCE