[Logan Cade]

Hey Guys,

Does anyone have some recommended alignment specs for a 1969 Grand Prix.

My old shop manual from 1969 is showing this for bias-ply tires:

Camber +1/4
Caster -1.5
Toe- in “0” to +1/8

If I remember correctly, with radial tires I would want Neg. Camber and Pos. Caster.

What are you guys running? Any info would be appreciated.

Thanks

[69lm69gp]

I would just try to get as much positive caster as you can. This helps with high speed stability (highway driving)

The deal with the negative camber is not the tires (radial vs. bias) so much as it is to get the car to corner better. The A/G body did not have a camber curve that was well suited for the best handling, so guys set the camber a little negative to counter act the camber becoming more positive under compression. I doubt if you would notice a difference on a stock suspension with the stock 14 inch wheels and tires. If that is what you are running. If you are running 15's or 16's I wound set the camber to about a -1/4 negative. IIRC this would be the max allowable negative camber (+1/4 +- 1/2).

[Bill Eveland]

Camber and toe in could stay the same, it's the caster thats needs to be increased. You may need to go a little negative on the camber to help increase the caster. For handling the lower camber is better but not really needed for a cruiser. Too low and it will wear the inside edge of the tires.

[Logan Cade]

Thanks Guys!

[moegoat]

I have a 69 GP that I did the + caster & - camber alignment on. I am trying to find the printout but it is MIA. I helped the tech do it since the car was built way before he was born & he had never done a shim type alignment. You would be surprised how much adjustment you can get by just moving the front shims to the back to get the caster more positive, that car still has the stock 0 offset shafts, I think we got about 3-3 1/2 degrees positive caster & around 0-1/4 negative camber. The car drove much better & was more responsive to the steering wheel input. Another plus was steering return after completing a turn was much better. Just so you know a lot of European cars, especially Mercedes run up to 15 degrees of positive caster (the last time I checked) for high speed stability, 100mph plus. Once I had a customer come in with a broken tie rod end, didn't even know (late 90's Mercedes). He had driven the car in for something else with no problems. With lots of positive caster the wheel will follow the direction of the car without even a tie rod hooked up to it. Our old cars would just swing the offending wheel out & drag us into the ditch, median or another car.

Way too much info, but I like to keep people informed: Technically speaking.

[Logan Cade]

Great Info!

Thanks Moegoat

[amcmike]

Originally Posted by 69lm69gp

I would just try to get as much positive caster as you can. This helps with high speed stability (highway driving)

The deal with the negative camber is not the tires (radial vs. bias) so much as it is to get the car to corner better. The A/G body did not have a camber curve that was well suited for the best handling, so guys set the camber a little negative to counter act the camber becoming more positive under compression. I doubt if you would notice a difference on a stock suspension with the stock 14 inch wheels and tires. If that is what you are running. If you are running 15's or 16's I wound set the camber to about a -1/4 negative. IIRC this would be the max allowable negative camber (+1/4 +- 1/2).

That is not entirely true. While static negative camber improves handling in general, it is even more important on radial tires to keep the contact path consistent. -1/4° is a good start, and -1/2° would be even better. Dial in as much positive caster as possible to get high speed handling. Toe-in should be minimal.

[69lm69gp]

Originally Posted by amcmike

While static negative camber improves handling in general, it is even more important on radial tires to keep the contact path consistent.

If you are building a g-machine yes. Aligment specs are a comprimize between handling and tire wear. I read the original poster's question as "What do I need to set the alignment too, to run radial tires?" the answer is same as bias ply is fine. Changes the the alignment specs are not required to run radial tires. I believe the original poster was reading the setups guy are running for best handling as changes to the factory alignment spec needed to run radials.

[moegoat]

Originally Posted by 69lm69gp

If you are building a g-machine yes. Aligment specs are a comprimize between handling and tire wear. I read the original poster's question as "What do I need to set the alignment too, to run radial tires?" the answer is same as bias ply is fine. Changes the the alignment specs are not required to run radial tires. I believe the original poster was reading the setups guy are running for best handling as changes to the factory alignment spec needed to run radials.

I was just suggesting for a more well rounded more responsive driving car. I am not sure what Logan's plans are, wheels/tires suspension, etc, but those archaic alignment specs blow chunks. I know I have been spoiled by driving newer cars & do as much as I can to make the old ones drive & handle better. Makes for a more pleasurable overall driving experience.
Just my.

[amcmike]

Originally Posted by 69lm69gp

If you are building a g-machine yes. Aligment specs are a comprimize between handling and tire wear. I read the original poster's question as "What do I need to set the alignment too, to run radial tires?" the answer is same as bias ply is fine. Changes the the alignment specs are not required to run radial tires. I believe the original poster was reading the setups guy are running for best handling as changes to the factory alignment spec needed to run radials.

I read the posters request same as you which is why I answered that it needs to be changed. You don't need to run a road course to justify using the correct alignment settings for the type of tire used. In not doing so you are reducing safety and increasing tire wear. Would you put on front disc brakes and keep the pressure the same as when you had front drums? No, as this would reduce performance from your baseline. And when do you need those brakes to perform their best.... when it counts such as accident avoidance. Why would you put all that sweat and money into something and then not invest in a $70 alignment to match the tire setup?

Softer sidewalls and stiffer tread belts make radial tires more sensitive to camber. It takes more camber to generate significant camber thrust with a radial tire. Since he is not improving camber gain (chamber change as the tire is loaded) this needs to be addressed in the static camber. Therefore, instead of possibly having positive camber as specified by the factory for bias plys, he needs to ensure there is negative static camber (in the neighborhood of -1/4° to -1/2°). If I was specing this for a g-machine, it would be more like -1/2° to -1.5° depending on how much street time versus track.

The factory setup already has a backwards camber gain setting on these cars. Instead of gaining negative camber when the suspension is under compression and therefore keeping the contact patch correct, it goes the other way. So with the increased sensitivity a radial will therefore have increased tire wear as you drive the car unless you always drive in a straight line on a perfectly smooth road without ever braking or accelerating.

For safety and tire wear different alignment specs are required. Yes there are plenty of people out there who don't do this, but it does not make it right.

[69lm69gp]

Originally Posted by amcmike

For safety and tire wear different alignment specs are required. Yes there are plenty of people out there who don't do this, but it does not make it right.

Funny because I drove a 69 GP, 69 Le Mans, and a 71 Chevelle all with radial tires and all set to factory specs over 200,000 miles all totaled and all the cars handled just fine and showed no abnormal tire wear.

So unless you can point to a manual, service bulletin or some other authoritative text, because all my books and manuals say nothing about a separate spec for radial vs bias ply tires, I will remain unconvinced.

[amcmike]

Actually the first two sentences in paragraph 2 that I wrote are quoted from SAE Publication no. R-351 last paragraph on page 108.

This also talks briefly about radials needing more negative camber due to the difference in camber thrust.
http://www.tamusae.org/index2.php?op...do_pdf=1&id=29

Also, I believe if you review the alignment specs over the course of a period where radial tires started replacing bias plys on 2nd Generation Firebirds ("Radial Tuned Suspensions"), that even though the suspension geometry remained the same, the aligment specs changed to more negative camber and more positive caster.

As I stated before many have done it, but there are differences in the construction which means differences in how the tire responds to input, and therefore to keep the equivalent performance you need to correctly setup the suspension for this. Would you put on different designed cylinderheads without retuning your carburetor or timing? Lots of people still do, but it doesn't make it right. And in the case of tires it can be more of a safety issue. You may depend on your suspension to avoid an accident or maybe that corner was just a little tighter than you expected... that extra grip might be helpful. Why put addition risk to yourself and loved ones? It makes no sense not to put the proper alignment on especially since you should be realigning the car anyways when putting on any new tires. Put in the negative camber, add as much positive caster as possible, and enjoy all the benefits of radials.

I really don't care if I convince you or not. It's clear you have already have your opinion set. I'd just like the others out there to know the facts and make an informed decision. Therfore this is my last response to this thread. Peace out.

[69lm69gp]

I see that both publications you cite are focused on racing, so I go back to my original response.

Originally Posted by 69lm69gp

If you are building a g-machine yes. Alignment specs are a compromise between handling and tire wear.

The original specs are designed to give you basically 0 camber and toe while driving in a strait line. Street cars will see way more straight line driving than a race car so more negative camber(more that spec), while great for handling, will only lead to excessive tire wear. Again a compromise.

I could build a carb or engine that would be perfect on the track and suck out on the street. Racing and the street are apples and oranges. Also second gen F-Body spec could have changed for a several reasons. So unless you show me a spec that say set to 0 degrees for bias ply and -1 degree camber for radials I am still not buying that more negitive camber is required.