pression tyre 225 75 15

[cquisuila]

Hello

I read in the user's manual riviera 1966 that the pression of the original tyre 8.45-15 are 24 psi or 1.7 BAR.

 

I put in my car EQUIVALENT MODERN TYRES

225/75 R 15 - 102 H

 

So i am wondering what pression for this tyre ?

Because 1.7 bar IS light not ?

 

 

 

 

Edited September 18, 2023 by cquisuila (see edit history)

[RivNut]

What ever pressure is called for on the sidewall. Don't try to inflate radial tires using bias tire data.

[cquisuila]

2 minutes ago, RivNut said:

What ever pressure is called for on the sidewall. Don't try to inflate radial tires using bias tire data.

ORIGINAL tyre and modern are totally different

That is what I thought

You must rely on the inscription on the side of the tire with the maximum pressure.

[Jim Cannon]

I inflate mine to 2.2 bar.

 

[NTX5467]

Some modern radials have pressure ratings up to 45psi stamped in the sidewall as "MAX PRES", but using the older-style 30psi (cold) should work well, with respect to ride, handling, and longevity.  Might even lower the rears down to 28psi, but not the fronts, or add 2psi for 32 psi front and 30psi rear.  Try and see what you like best.

 

In later owners manuals, the 24psi recommendation is for a soft ride and decent handling.  If speeds above 70mph were to be driven, then the base recommendation was increased to 28psi.  With any significant load in the trunk, with more passengers, up to 32psi (which was the old bias-ply "max load recommendation" for the vehicle).

 

With the old bias-ply tires, the more air pressure the more firm the tire became.  Less flexing over bumps and in turns, or under hard braking.  Less flex also meant longer tread wear and slightly better fuel economy, too.

 

Regards,

NTX5467

[RivNut]

You also have to remember that bias ply tires were effected by heat caused by the rolling friction of the tires against the road surface.  I wouldn’t be surprised that pressures starting out at 24 psi cold grew to 28-30 after a few miles down the road at 70 mph.

[Bloo]

Circa 1980s, there were large numbers of 1960s and even older cars still in daily use in my area. 35psi (2.4 bar) or 32psi (2.2 bar) were normal pressures for radials on cars that originally had bias tires. At that time, these were the maximum pressures listed on the sidewall. Anything less than 30psi (2.1 bar) and the tires were unlikely to survive in hot weather or at high speeds. Going higher than 35psi (2.4 bar) if the specs of the tire allow it would not be a problem, but in those times very few tires were rated higher.

 

It is true that some 1970s and 1980s cars with factory radials had a recommended pressure below 30psi (2.1 bar), but that just generated complaints from drivers about "flat tires". Most of them got higher pressure right away. In those days the US had a national speed limit of 55mph (88kph). Too much sidewall flex just generates heat for no benefit. In my area, where it gets over 95F (35C) regularly in July and August, there were a lot of heat related tire failures, even though the speeds were slower at the time.

 

[NTX5467]

3 hours ago, RivNut said:

You also have to remember that bias ply tires were effected by heat caused by the rolling friction of the tires against the road surface.  I wouldn’t be surprised that pressures starting out at 24 psi cold grew to 28-30 after a few miles down the road at 70 mph.

Yes, no doubt the tires starting at 24psi would build up several pound after running a while.  But with the decreased flex of 30psi (cold) to start with, they built up less as they were flexing less at these times.

 

Whatever works,

NTX54657

[cquisuila]

ok

32 psi or 2.2 bar is the average value😙

[EmTee]

I typically use 32 psi in the front and 30 psi in the rear for my '67 Riviera with radial tires.  My rationale is that most of the weight is on the front wheels.  If carrying lots of luggage or rear seat passengers, then 32 psi on all four tires.

[Seafoam65]

For passenger cars, 35 psi is usually the recommendation on radial tires, but published pressures

are arrived at considering a smooth ride as a factor. I always have run my tires at 40 psi and don't ever let 

the tires get lower than that and I never have tire failures and have gotten as many as 75,000 miles out

of my yokahama tires, which are the best tires out there in my opinion. Yokahamas never pull, never get out of round,  never crack, and will outlast any other tire there is in terms of miles of use before they hit the treadwear indicators. Running your radials at 40 psi will help your gas mileage and will cut down on cornering wear.

[65VerdeGS]

Seafoam65 - Are Yokohama tires still made in Japan? 

 

I've always run my tires (presently Hankooks) at 32psi, all around.  But after reading your post I will up that to 40psi in the interest of fractionally higher gas mileage and possibly lowered tire wear. 

 

Would you inflate radial tires in other cars to 40psi, or just the Riviera?  I have a set of older Bridgestone radials on my '67 Corvette, which is why I'm asking.

[RivNut]

The investigation into the cause of the 2013 accident that killed the actor Paul Walker revealed that the Porsche Carrera GT in which he was riding had 9-year-old tires. The California Highway Patrol noted that the tires' age might have compromised their drivability and handling characteristics, according to the Los Angeles Times.

 

No federal standards on tire age but most manufacturers say that 6 to 7 year old tires should be replaced regardless of tread depth or storage conditions.  My 63 was in storage and sitting on some Michelin Pilot tires. One day I noticed that one of them was not only flat but it had exploded. 

[EmTee]

I would not inflate any tire beyond the maximum load inflation pressure shown on the sidewall.  Watch tread wear; if the center starts wearing faster, reduce the pressure.