205 75 15 C2 tire air pressure recommendations

[Jim R.]

I have them at 30psi now, wondering what other like.

[Duke W.]

Re: 205 75 15 C2 tire air pressure recommendations

32 psi front and rear on small blocks. Add 2 psi to the fronts on big blocks. This is cold pressure and the maximum placarded on the sidewall is likely 35 psi.

You can run as low as 26 in around town driving if the higher pressure is too harsh, but I would not use less than 32 on a long freeway trip.

Regardless of tire pressure, signficant rear ride harshness arises from compressed and hardened spring link cushions, which will also reduce rear ride height, so all should check the status of those cushions and replace, if necessary.

32 psi is still adequate pressure for high speed rated tires that may be placarded as high as 51 psi maximum cold pressure because the Corvette is rather light compared to total tire load capacity, which is nearly double GVW.

Duke

[Jim R.]

Re: 205 75 15 C2 tire air pressure recommendations

Thanks Duke. JR

[Rich C.]

Re: 205 75 15 C2 tire air pressure recommendations

I asked a similar question before about tire pressure with new radials on an older vette, and was told to go by the door jamb sticker which was 20 p.s.i., which seemed low?? I had been running them at 30 p.s.i.


1973 LS-4 454 coupe owned 24 years (7 of those with a respectable front bumper)
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Leif A.]

Re: 205 75 15 C2 tire air pressure recommendations

I certainly hope that wasn't the only reply you received when you asked your question. Your door jam sticker was tire pressure recommendations for the old bias ply (nylon/rayon) tires of the day. Today's radials are much happier and last much longer at between 32-34psi.

[Russ S.]

Re: 205 75 15 C2 tire air pressure recommendations

No it wasn't. 1973 vettes came out with steel belted radials and the door placard was 20 PSI.

I certainly hope that wasn't the only reply you received when you asked your question. Your door jam sticker was tire pressure recommendations for the old bias ply (nylon/rayon) tires of the day. Today's radials are much happier and last much longer at between 32-34psi.

[Jim T.]

Re: 205 75 15 C2 tire air pressure recommendations

I believe the pressure on my 1968 was for 24 LBS for 1968 tires.

[Rich C.]

Re: 205 75 15 C2 tire air pressure recommendations

I certainly hope that wasn't the only reply you received when you asked your question. Your door jam sticker was tire pressure recommendations for the old bias ply (nylon/rayon) tires of the day. Today's radials are much happier and last much longer at between 32-34psi.

No I didn't lower them...tire wear looked perfect with running them at 32 p.s.i.. As pointed out by Russ, '73 was radials, which seemed strange that the tire info on door still read 20 p.s.i.!


1973 LS-4 454 coupe owned 24 years (7 of those with a respectable front bumper)
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Duke W.]

Re: 205 75 15 C2 tire air pressure recommendations

The recommended TP on the placard or in the owner's manual is for "average driving", and is usually biased toward a soft ride. Owners manuals will often recommend higher pressures for "high speed driving".

I'm shocked that the new for '73 radials were placarded at a mere 20 psi. No wonder they suffered a high rate of tread separations. What was GM thinking?

When I first drove my SWC on the OE General Jetaires with the recommended 24 psi it felt like I was driving on slime, and I quickly increased cold pressure to 35 psi, which was much better.

The Jetaires' tread started chunking at my first day hot-lapping Kent, so when the car was a year old it got a new set of 6.70-15 Michelin X radials. I started out at 35 psi and ended up at 45. Those tires survived a half dozen days at Kent and lasted 47,000 miles.

Duke

[Leif A.]

Re: 205 75 15 C2 tire air pressure recommendations

Russ,

I had forgotten about the early radial tire placards. I had a '73 454 back in 1976 and I never ran the pressure that low...they looked like they were flat and ran very hot and the handling sucked. I've always run between 32-34psi in radials and have enjoyed long tire life and comfortable ride and drivability...but, thanks for setting me straight

Leif

[Jim R.]

Re: 205 75 15 C2 tire air pressure recommendations

Duke the side of the tire shows max 44psi would you still run 32. JR

32 psi front and rear on small blocks. Add 2 psi to the fronts on big blocks. This is cold pressure and the maximum placarded on the sidewall is likely 35 psi.

You can run as low as 26 in around town driving if the higher pressure is too harsh, but I would not use less than 32 on a long freeway trip.

Regardless of tire pressure, signficant rear ride harshness arises from compressed and hardened spring link cushions, which will also reduce rear ride height, so all should check the status of those cushions and replace, if necessary.

32 psi is still adequate pressure for high speed rated tires that may be placarded as high as 51 psi maximum cold pressure because the Corvette is rather light compared to total tire load capacity, which is nearly double GVW.

Duke

[Duke W.]

Re: 205 75 15 C2 tire air pressure recommendations

That's what I said in the last sentence of my post that you quoted, however, you are free to experiment.

If a tire carries substantially less than maximum vertical load, as is the case with vintage Corvettes running typical replacement 15" tire sizes, then running tire pressure at or near the maximum may, especially on high-speed rated tires that are placarded at 44 or 51 psi, actually reduce grip and make the car more twitchy at the limit.

For example the 195/60HR-14, 225/60HR-14 summer high performance tires on my '91 MR2 work best at 32 psi. At 36 the car has a more rapid transition to oversteer. But the same size DOT legal recing tires work best at 36 for road or track and have an even milder transition to oversteer.

The original rear tire size was 205/60HR-14, and it oversteered like an early 911 no matter how much tire pressure bias I tried, so I applied a simple analysis. The vehicle weight distribution is about 43.5/56.5, but the OE tire capacity load distribution was only 48/52. Increasing the rear section width to 225 mm added 200 pounds load capacity to each rear tire, which brought tire load capacity distribution in line with the vehicle weight distribution. It also eliminated the 5 percent optimistic speedometer reading, and brought it to within one percent of true, and the 7" rear wheel width (6" on the front) was adequate for the increased section width.

The only way to determine for a specific vehicle and tire combination is to experiment with different pressures and choose what you think best meets your requirements for ride and handing.

I ran the 6.70-15 Michelin X radials on my SWC at 45 psi because they were rather skinny. When I later ran Pirelli 205VR-15 CN72s and then 225/70VR-13 CN73s, both on 7" wide wheels, I found that 32 psi was best for road use.

Duke

[Jim R.]

Re: 205 75 15 C2 tire air pressure recommendations

Thanks Duke. JR