68 Camaro Alignment for Polyglas Tires - Team Camaro Tech
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post #1 of 12 (permalink) Old Mar 27th, 11, 06:26 AM Thread Starter
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68 Camaro Alignment for Polyglas Tires

I have been doing a lot of searching for information regarding front end alignment specifications for my 68 Camaro convertible. I understand that the factory specs are for bias ply tires, and I have seen recommendations for radial tires. I am probably going to be putting on a new set of Polyglas F70-14 tires, so I want to be sure to get the alignment correct. The car has no suspension modifications, and I plan to drive the car about 500-1000 miles per year. I would like the car to handle as good as possible considering my tire choice, and I would hate to ruin a new set of Polyglas ($$$) due to improper alignment.

So, I have some questions:
1) Should I just try to achieve the target factory specs, or are there other settings recommended for Polyglas tires?
2) Why do bias ply tires require so much toe-in (1/8" to 1/4")?
3) Why do bias ply tires require positive camber (1/2 deg. target)?

For questions 2) & 3), I guess I am used to the specs for more modern cars with radials. It would seem that the combination of positive camber and 1/4" toe-in would tend to wear the outer edges of the tires.

I was thinking about shooting for the negative side of the camber spec (1/4 deg. neg.), and going with minimum toe-in (1/8").

Any info or feedback on experience with bias ply tire alignment would be greatly appreciated.

Thanks,
Jeff
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post #2 of 12 (permalink) Old Mar 27th, 11, 09:32 AM
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Re: 68 Camaro Alignment for Polyglas Tires

Imagine each front tire is a motorcycle leaning out at 1/4 degree. They would turn away from each other. Imagine a rope running between them & the force that would be pulling on it. This effect is called "Camber Thrust" since both wheela are pulling in opposite directions, some toe in must be added to cancel this force. Bias ply tires require more toe in than Radials. If you set camber to zero, a little less toe in can be used but you will still need 1/8"'or so. In addition since our cars have a lot of bumpsteer, when the car settles, toe in will be reduced or even go to toe out fairly quickly. Even changes in passenger load will affect toe.

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post #3 of 12 (permalink) Old Mar 27th, 11, 10:15 AM Thread Starter
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Re: 68 Camaro Alignment for Polyglas Tires

Thanks for the simple explanation, David. You obviously know your stuff, so I'm going to try to pick your brain a little if you don't mind. I'm trying to understand bias ply technology versus radial.

You stated that bias ply tires require more toe-in to cancel out camber thrust. Is this because the bias ply tires create more camber thrust than radials for the same camber setting? Or is it because the bias ply create less "toe thrust" (if there is such a term) than radials for the same toe setting?

Is there a good reason to run positive camber with bias ply tires per the factory spec.? Do you think it would be best to run zero camber or slightly negative with the repro Polyglas tires?

If I run negative camber, would my camber thrust be in the opposite direction and actually require toe-out to help cancel it out?

Any recommendation for target alignment specs? The front springs are original, so hopefully they have already settled as much as they are going to. All suspension bushings are new original rubber type. My car has the F41 suspension, but I'm not sure that matters here. The car will be a cruiser, no trying to push the limits of the Polyglas.
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post #4 of 12 (permalink) Old Mar 27th, 11, 01:48 PM
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Re: 68 Camaro Alignment for Polyglas Tires

When radial tires came out the general recommendation was to run a little less toe in. I don't have any special info on why, without doing a lot of research, & there is very little in print about bias ply dynamics. Remember your suspension even precedes the use of belted tires, let alone Radials.
With bias ply tires the tread & belt are affected more by the wheel in a turn, but radials are not 100% radial either, they do have some bias to the cord angle, just not as much as a bias ply tire.
If you ran around 1.5 deg neg camber you should run zero toe in. At 2 to 3 deg neg camber you start using toe out, but for autocrossing you can be more aggressive.
Near zero camber to .5 deg neg or positive, I'd run 1/8" toe in total.
More positive caster is great too, so except omfor a little extra toe in, I'd set camber at zero to .25 neg, max out positive caster, woth 1/8" toe but re check toe if the car settles even a tiny bit. I did this with the last Goodyear polyglass tires I had on my 67, & it worked well.

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post #5 of 12 (permalink) Old Mar 27th, 11, 05:29 PM Thread Starter
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Re: 68 Camaro Alignment for Polyglas Tires

Quote:
Originally Posted by davidpozzi View Post
... I'd set camber at zero to .25 neg, max out positive caster, woth 1/8" toe but re check toe if the car settles even a tiny bit. I did this with the last Goodyear polyglass tires I had on my 67, & it worked well.
Thanks. That's what I'll shoot for. I appreciate your help.
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post #6 of 12 (permalink) Old Mar 27th, 11, 10:42 PM
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Re: 68 Camaro Alignment for Polyglas Tires

Just a word to the wise, Jeff. Keep close tabs on those "Polys", even if you're putting on few miles. I had a blow out a while back (a rear)...the tread was like new. Was glad I was loafing down the road when it went!

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post #7 of 12 (permalink) Old Mar 28th, 11, 07:39 AM Thread Starter
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Re: 68 Camaro Alignment for Polyglas Tires

^^ Aye aye, Capt! Was it a reproduction Polyglas or an old original?
Is this a common issue with repro Polyglas? I hope not/
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post #8 of 12 (permalink) Old Mar 28th, 11, 08:46 AM
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Re: 68 Camaro Alignment for Polyglas Tires

i went to a Bear alignment class in 1980. Here's what i remember (or what I think I was told). Radial tires need less toe in because they have less rolling resistance. Ideally you want zero toe in while moving and radials deflect less so less toe in. We were also told to set camber no more than 1/4 positive so that might be some of the reason for the minimum toe. Toe in recommendation on rear drive cars was 1/16, toe out is used on front drive cars. I remember being told the early Monte Carlo was the first American car designed from scratch for radial tires. Seems the engineers felt it needed to 7 degrees positive caster for high speed stability.

Because I'm almost as old as dirt I thought our first gens came with Polyglas tires as an option. The white book shows them as options PY4 and PY5 from 68 up.

Jeff
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post #9 of 12 (permalink) Old Mar 28th, 11, 09:49 AM
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Re: 68 Camaro Alignment for Polyglas Tires

Jeff, being a 67 owner my thoughts were about what was available that year. Kinda narrow thinking on my part, but just where my head was at. My 67 came with Uniroyal Laredo 7.35 - 14 tires, but a Firestone Wide oval Redline tire was an option in E 70 profile. I just can't remember if those were fiberglass belted or what. I should look it up, or hopefully someone will post that info here.

Lower rolling resistance & less heat are benefits of radials, this allows softer tread rubber to be used with lower wear, they transition over parallel pavement seams much better.

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post #10 of 12 (permalink) Old Mar 28th, 11, 10:58 AM Thread Starter
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Re: 68 Camaro Alignment for Polyglas Tires

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Originally Posted by davidpozzi View Post
My 67 came with Uniroyal Laredo 7.35 - 14 tires...
My car came from the factory with 7.35-14 tires as well. When they wore out, my father put on a set of Polyglas F70-14. If I go for the Polyglas, I'm going for 'period-correct' versus 'factory correct'.
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post #11 of 12 (permalink) Old Mar 29th, 11, 07:38 AM
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Re: 68 Camaro Alignment for Polyglas Tires

Quote:
Originally Posted by davidpozzi View Post
Jeff, being a 67 owner my thoughts were about what was available that year. Kinda narrow thinking on my part, but just where my head was at. My 67 came with Uniroyal Laredo 7.35 - 14 tires, but a Firestone Wide oval Redline tire was an option in E 70 profile. I just can't remember if those were fiberglass belted or what. I should look it up, or hopefully someone will post that info here.
David, my thoughts were just the opposite, if 69's had them, they all did. LOL

67 tire options
PQ2 7.35 X 14 2 ply nylon white stripe (no charge with SS)
PW6 D70 X 14 2 ply nylon red stripe (standard with SS)
P58 7.35 X 14 2 ply whitewall original equipment

68 tire options

PW7 F70 X 14 2 ply white stripe (no charge with SS)
PW8 F70 X 14 2 ply red stripe (no charge with SS)
PY4 F70 X 14 2 ply fiberglass belted white stripe ($26.55 charge with SS)
PY5 F70 X 14 2 ply fiberglass belted red stripe ($26.55 charge with SS)
P58 7.35 X 14 2 ply whitewall original equipment

69 tire options
PK8 E78 X 14 2 ply whitewall, original equipment
PL5 F70 X 14 2 ply white letter, original equipment
PW7 F70 X 14 2 ply white stripe original equipment(no charge with SS)
PW8 F70 X 14 2 ply red stripe original equipment (no charge with SS)
PY4 F70 X 14 2 ply fiberglass belted white stripe ($26.25 charge with SS)
PY5 F70 X 14 2 ply fiberglass belted red stripe ($26.25 charge with SS)

My Bear alignment spec book is not at my fingertips but my thought is they didn't specify tire size/style with specs.(seems to me all first gens used same spec)

Jeff
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post #12 of 12 (permalink) Old Mar 29th, 11, 07:45 AM
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Re: 68 Camaro Alignment for Polyglas Tires

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Originally Posted by jeff68 View Post
^^ Aye aye, Capt! Was it a reproduction Polyglas or an old original?
Is this a common issue with repro Polyglas? I hope not/
They were orig... had been keep in the basement wrapped...no signs of deterioation on them what so ever... treads like new, one went. Could be the inherent structure of this style of tire? It was the bridge between the 2 ply and the newer radials. But even if a repro, I'd still keep an eye on them.

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