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Tire Pressures
Posted by: vairygood ()
Date: February 06, 2018 01:53PM

I haven't found anything addressing this,When upgrading tire sizes (14 & 15") and radial tires,do you still maintain the factory specs for air pressure?I would assume so but I was asked that question and I really don't know for a fact.

Buster Tindel
Gulfport Mississippi
63 vert
65 Corsa 140 4 speed

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Re: Tire Pressures
Posted by: stitch ()
Date: February 06, 2018 01:58PM

I have 15's and still run 32/34 rear. 24 front. Handles Great! smileys with beer

"If you can't fix it with a Hammer, you have an Electrical problem."
Stitch...
Schertz, Texas.
(Smallish town/burg 17 mi. NE of San Antonio)

!967.. 4th body
8th off the line

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Re: Tire Pressures
Posted by: MattNall ()
Date: February 06, 2018 02:00PM

same differential between front and back...

to determine correct tire pressures for the new tires...

To find your correct pressures use the talcum powder method, starting at max. tire press. on sidewall and lowering until you get full tread contact as you roll over it.





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
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Re: Tire Pressures
Posted by: vairygood ()
Date: February 06, 2018 03:43PM

Thanks guys,I'll pass that on and I learned something as well.

Buster Tindel
Gulfport Mississippi
63 vert
65 Corsa 140 4 speed

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Re: Tire Pressures
Posted by: BobV66Vair ()
Date: August 10, 2018 12:49PM

Is the differential really 10 PSI? That seems extreme. Mine are all set to 30 PSI (cold). I can try the talcum method but wonder about the big differential.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Tire Pressures
Posted by: RobertC ()
Date: August 10, 2018 01:05PM

BobV66Vair Wrote:
-------------------------------------------------------
> Is the differential really 10 PSI? That seems
> extreme. Mine are all set to 30 PSI (cold). I can
> try the talcum method but wonder about the big
> differential.

Yes... Haven't you read the owner's manual? Of course, the owner's manual is for bias ply tires. You can use higher pressures with current tires.

Your car must understeer dangerously. Unless you drive it real slow in corners. Unless you carry 500 lbs in the trunk...

As stated, the talc test is the best.

I have ran 8 lb differential at times.

To me, it depends on the tires that you run - across brands and across different tires in the same brand.

A "generic" street radial can handle a little different than a H-speed rated radial.

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Re: Tire Pressures
Posted by: MattNall ()
Date: August 10, 2018 01:13PM

Bob... this car of yours is a casual driver... sometimes racer? right?

Unless you've taken the time to "cross Weight / Balance" your car...

Each tire will be a different pressure...

Then when you practice or race... you take tire temps...HF Infared gun..

Many use white shoe polish on the sidewall next to the tread... to see if the tire is "rolling over"





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Tire Pressures
Posted by: richard1 ()
Date: August 10, 2018 02:07PM

BobV66Vair Wrote:
-------------------------------------------------------
> Is the differential really 10 PSI? That seems
> extreme. Mine are all set to 30 PSI (cold). I can
> try the talcum method but wonder about the big
> differential.


Definitely different. Most of the handling problems with rear engine cars are due to people putting the same pressure in front and back.
I use 35-36 in back, 24-25 up front in my 60 with 14" tires.
and in the Dauphine, I use 14 up front and 23 in the back, as per the manual with 135R-15

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Re: Tire Pressures
Posted by: joelsplace ()
Date: August 10, 2018 02:13PM

The powder method works great for best tire wear in a straight line but won't give the best traction or stability. At the point the tires need maximum traction they will have a lot more weight on them than they do at rest so they will need more air.
60-63 with no sway bar need the most pressure differential and lates need the least.

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Re: Tire Pressures
Posted by: joelsplace ()
Date: August 10, 2018 02:17PM

Actually using too much pressure in the front causes oversteer.

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Re: Tire Pressures
Posted by: Phil Dally ()
Date: August 10, 2018 02:44PM

For a stock application I go with 20/30 because it's easier to remember.

Buying four new 185/80R-13's for Gem next week...my guy has them in stock.

Using date code correct original willow green steel wheels and 500 hubcaps.

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Re: Tire Pressures
Posted by: RobertC ()
Date: August 10, 2018 02:59PM

joelsplace Wrote:
-------------------------------------------------------
> Actually using too much pressure in the front
> causes oversteer.

Well, I would think that too much tire pressure in the front would cause the front to lose traction first?

Smaller contact spot, but whatever...

I can immediately tell when a tire shop puts too much pressure in the front of my Corvair.



Edited 2 time(s). Last edit at 08/10/2018 03:01PM by RobertC.

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Re: Tire Pressures
Posted by: 66vairman ()
Date: August 10, 2018 03:55PM

First check the tire manufacturers maximum tire pressure rating. Not all modern radial tires are rated the same.

I run a 205 X 14 up front and a 235 X 14 in back on a LM. I found that even with the wider tire in back the car DID NOT like equal tire pressure all around. Handling became a lot more stable (straight line and in turns) when I set the front tire pressure 8PSI less than the rear.

I suspect if I had the same tire width front and rear I'd set the front tires 10PSI less than the rear.

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Re: Tire Pressures
Posted by: stitch ()
Date: August 10, 2018 05:00PM

Once went to an NTB tire place to have my 13" white walls installed. They were finishing it up and I told them about the 10 psi difference in front-to-back. They didn't believe me so I showed them the 'Decal' in my glove box. Well, they wouldn't have any of that, Their policy was "32 all they way around, before they would release it. After they parked it on the lot, for pick-up, I let 10lbs out of the fronts. (I always carry a tire pressure gauge in glove box) smileys with beer

"If you can't fix it with a Hammer, you have an Electrical problem."
Stitch...
Schertz, Texas.
(Smallish town/burg 17 mi. NE of San Antonio)

!967.. 4th body
8th off the line

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Re: Tire Pressures
Posted by: joelsplace ()
Date: August 10, 2018 07:44PM

Radials get better traction with more pressure up to a point. The lower pressure in the front was to compensate for oversteer even with the original bias belted tires. The lower pressure caused them to have less traction and push or understeer rather than stick the front and oversteer. Most US cars from that area had severe understeer and an oversteering car was more than most unskilled drivers could handle. RobertC I'm guessing you have an LM since the oversteer isn't as pronounced on them but it's still hard for me to see how anyone could not notice. I spun my '62 several times when I first got it and didn't know about the pressure requirements. Equal pressure will have the rear end come around on you in a hurry.

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Re: Tire Pressures
Posted by: Seth Emerson ()
Date: August 10, 2018 09:38PM

If you want to test the theory about the tire pressure, put 32 PSI in the front tires - do this in your flat driveway. Then drop down and look to see how much rubber is actually touching the driveway surface. Too much pressure in the front tires causes understeer. You turn the steering wheel, but the front tires do not bite and the car refuses to turn, so you drive off the road front first. The only difference, in this case, is that radial tires don't look as stiff at rest.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: Tire Pressures
Posted by: BobV66Vair ()
Date: August 11, 2018 05:57AM

Ran on the track yesterday. The car oversteered and understeered at speed. I will work on the tire pressures using a PSI differential. I also need to sort this car out for the track. The handling was not great overall. Sucks being passed by everything. It was a totally modern group of cars though. My little 140 was underpowered by half. Still, I should have been able to keep up in the turns.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Tire Pressures
Posted by: MattNall ()
Date: August 11, 2018 07:41AM

Congrats!! And you didn't blow the engine!! Much better luck than Barry Ellison!





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Tire Pressures
Posted by: joelsplace ()
Date: August 11, 2018 08:15AM

I don't think I've ever disagreed with you Seth but you are dead wrong in this one instance. At some certain overpressure I'm sure you would be correct but 32 in the front causes oversteer in most situations. The factory wasn't concerned about understeer as evidenced by the way all the front engined cars from the era handled. Oversteer is very dangerous for the general public. No one would have cared if their grocery getter understeered. All this being said I haven't ever tried equal pressures in a LM. But I have in EMs and 32 certainly didn't make them push with stock size tires on dry pavement at any speed stock
engines are capable of. It's been a few years duo maybe I need to go try it again just for fun. I haven't spun any of my Corvairs lately.

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Re: Tire Pressures
Posted by: robert wilkinson ()
Date: August 11, 2018 11:03AM

I've wondered about this. My car is a 63 Conv with AC (heavy), owned since 64. Stock 13" K-H rims. Somewhat short (185/70) radials for decades. I put 35 PSI in the rear, but 29 or so in the front because for some reason the steering is heavy otherwise (I do have Clarks quick steering arms, so that's one reason). I have a 64 sway bar.

As I understand it, the idea was to induce understeer (to compensate for swing axle oversteer) by deliberately reducing cornering traction of the front tires. Less than optimum pressure does this, but doesn't more than optimum pressure do the same thing?

I ask because I wonder if overinflating my front tires would work just as well but make it easier to steer.

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