Tyre pressures

[MilkyNoSugar]

I am 48 hours into C3 ownership, with a 1972 454 convertible and living the dream. The car came with new tyres fitted to the rally-style wheels. They are 225/70/15 from memory.

The original manual suggests that the type pressures should be 24 psi all around. However, they came from the dealer at 32 psi.

I appreciate I am opening a can of worms, but what are the recommended pressures for modern tyres on the C3?

 

[Roscobbc]

Its likely you'll find 24 psi way too low------tyres will be screaming like a 'stuck pig' when you go around corners.......I'm sure others on here will also say that perhaps 32 psi is a little too high and it'll perhaps ride a little harder - perhaps 28 psi would be a 'happy medium' ....... guys?

 

[Forrest Gump]

Congratulations on getting a C3 .

Tyre pressure were being discussed on here recently on this thread if you fancy a bit of reading - New Boots.

Theres no definitive answer other than peoples experiences. I like 28psi. Less and you might start to lose some sharpness (if there ever was any!!) and possibly uneven tyre wear, but going into the 30's and it might start feeling skittish on our typically uneven road surfaces.

 

[teamzr1]

I am 48 hours into C3 ownership, with a 1972 454 convertible and living the dream. The car came with new tyres fitted to the rally-style wheels. They are 225/70/15 from memory.

The original manual suggests that the type pressures should be 24 psi all around. However, they came from the dealer at 32 psi.

I appreciate I am opening a can of worms, but what are the recommended pressures for modern tyres on the C3?

Due to sidewalls are 70s tall, the 24 PSI is when cold and as being driven temps raise and tire pressure goes up to 30 PSI
IF sticking with the OEM tire size and type, go to 26 PSI will help lessen too much sidewall flex

I attached below the 165 pages of the GM engineering design in PDF form,
download and save this as highly in-depth of how your 1972 Corvette was designed and all specs

Specs show tire info:

 

[MilkyNoSugar]

Due to sidewalls are 70s tall, the 24 PSI is when cold and as being driven temps raise and tire pressure goes up to 30 PSI
IF sticking with the OEM tire size and type, go to 26 PSI will help lessen too much sidewall flex

I attached below the 165 pages of the GM engineering design in PDF form,
download and save this as highly in-depth of how your 1972 Corvette was designed and all specs

Specs show tire info:

View attachment 23028

Many thanks for the attached guide. An extremely useful resource.

 

[MilkyNoSugar]

I will give 26 and 28 a try over the next few outings and see how it feels.

Thanks for the advice.

 

[GiuG]

Hey guys around this range, I found that you need to put little less pressure on the front, 26 front 28 back? Could be possible?

 

[teamzr1]

Tire pressure setting can create or solve under or oversteer
So staggering tire pressures, front/rear or left/front is a simple no cost way to correct or if on a track bias direction
Also, other ways to correct or bias under/oversteer

Oversteer

Rear tire drift is greater than that of the front, and the rear tends to “spin out.”
The vehicle will end up closer to the center of the circle because the rear tire drift changes the direction inward.

Or, simply: Oversteer takes place when a car turns more than the amount commanded by the driver.
Oversteer is common in rear-wheel-drive cars and generally caused by a lack of traction at the rear tires.

When you break loose, oversteer is occurring.

Ways to Correct Oversteer

• Lower front tire pressure
• Raise rear tire pressure
• Stiffen front shocks
• Soften rear shocks
• Raise front end
• Lower rear end
• Install narrower front tires
• Install wider rear tires
• Stiffen front sway bar
• Soften rear sway bar
• Reduce front negative camber
• Reduce positive caster
• Stiffen front springs
• Soften rear springs

Understeer

Front tire drift causes the vehicle to refuse to turn as sharply as the direction the wheels are pointed.
If the wheels and throttle are held steady, the vehicle will make an ever-widening circle.

Or, simply: Understeer occurs when a car turns less than the amount commanded by the driver.

It’s “push” in racing lingo.
It’s a natural handing characteristic of front-wheel-drive and all-wheel-drive vehicles.
You turn the wheel, but you just go straight. Which is bad.

How do you fix it?

Ways to Correct Understeer

• Raise front tire pressure
• Lower rear tire pressure
• Soften front shocks and stiffen bump
• Stiffen rear shocks
• Lower front end
• Raise rear end
• Install wider front tires
• Install narrower rear tires
• Soften front sway bar
• Stiffen rear sway bar
• Increase front negative camber
• Increase positive caster
• Soften front springs
• Stiffen rear springs

Oversteer and understeer are more common problems in racing than in street driving.
As such, weather and track conditions, as well as varying driving styles and abilities will also play a role.

Also using air pressure to better launching from a dead stop like at a drag strip
Up the tire pressure in the front to reduce drag, lower rear pressures to create more traction off the stop/launch
to reduce the 0-60 feet times

 

[MilkyNoSugar]

An update on progress, 26 Front and 28 Rear seems ok, but I do get a bit of tyre squeal from the front until they warm up. Anything lower than that and the car was grounding on the country lanes and tyres complaining quite a bit. 28 Front and 30 Rear is my next set of pressures to try.

 

[teamzr1]

When you are testing different tire pressures
Do you also than when test-driving if the pressures induce more over or under steer ?

 

[Roscobbc]

Do you know something Jon........ I seriously doubt whether most of our members ever drive around corners in 'extremis' sufficiently to care about understeer or oversteer. So many seem to be more concerned about how 'pretty' the tyres look and how well defined the white lettering is...................

 

[teamzr1]

I must be odd, then,
as I select tires on how they help handle the Apex

They would have a fricking fit as I only wash the tires/wheels like twice a year

 

[Roscobbc]

I must be odd, then,
as I select tires on how they help handle the Apex

They would have a fricking fit as I only wash the tires/wheels like twice a year

Whenever I suggest members will get the best advantage from stepping-up a few inches in tyre diameter and get vastly improved traction, braking and cornering it seems that most still prefer the old school high profile rubber.........not that it'll be around for too many year now.......

 

[Forrest Gump]

An update on progress, 26 Front and 28 Rear seems ok, but I do get a bit of tyre squeal from the front until they warm up. Anything lower than that and the car was grounding on the country lanes and tyres complaining quite a bit. 28 Front and 30 Rear is my next set of pressures to try.

How old are your tyres? Tyre squeal can be a sign that the rubber has hardened with age. For the same reason, older tyres will feel harsher on the road.