Tire Pressures

67 ragtop

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What tire pressures should be run with newer radial tires. I am running 32lbs but when I read the post about tire pressure labels I saw that it was only supposed to run 24lbs if under 5 passengers. I am concerned that that could ruin a modern radial tire.
For all loads up to full rated it dos state it does state 28 front 30 rear.
I think the lower pressures were to create a soft ride Just like the super aggressive no feel power steering.
 
From a Goodyear guy for 40 years. You can be between 28 and 30 which ever feels good for your ride. The newer cars/suv's call for about 32 psi. I think older cars like our (67 Chrysler & 66 Fury) need a little softer ride (just my personal/professional opinion). Enjoy your car.
rsh1966vip
 
Have you looked to see what the manufacturer says on the tire. Every automotive tire I've seen in the last several years shows the max at 44psi. I've been running closer to that in my vehicles. The only one I really notice a difference in is the little DD I run, because it is a small car.
 
I run 35 front, 32 rear on my '65 with Hankook Optimo.

I was taught by a Michelin man (not that one) that tires blow out due to too low pressure. Over pressure only causes rough ride and bad wear patterns. I was told that a properly inflated tire should gain approximately 10% in pressure cold to running temp.
 
As a tire guy for 25 years....whatever the bias ply tire pressure is factory spec, add 6 psi to the radial.
Done.
 
Good Afternoon
The '65 with Hankooks: 40 psi front/back
Same for the radial red lines on the '68 Bee and '66 GTO.
Wear pattern is fine. Ride is good.

Omni
 
Can you explain your reasoning here?
As you may already know, bias ply have a totally different construction verus the radial.
Radials offer a wider/flatter footprint and run cooler compared to bias ply.
Its been an industry standard as I was taught to add 6 psi to radials on a car that originally came with bias to extend tire wear and better handling.
Bias ply have stiffer sidewalls and given the technology at the time,car manufacturers were more concerned about ride quality over handling . They also acted as a spring. Hence the lower tire pressures. Bias ply tires had a lot of squirm in them and when pushed hard in corners they do curl over onto the sidewalls much more than a radial tire will allow.
Hope this helps.
 
In the '66-'70 owners manuals for our '66 Newport and my '70 Monaco, the base tire pressure is listed on the door decal (along with the mininum tire size for the car). Reading the owners manual, I discovered that to that base pressure, you ADD 4 psi for driving over 75mph, which puts things at an adjusted base pressure of 28psi. From there, there is the "Max Load" pressures which went up to the Max Rated Inflation Pressure of 32psi. In the '70 manual, no mention was made of whether for bias ply, belted-bias ply, or radials as to inflation pressures.

When P-metrics came out in the earlier 1980s, they had a stated max pressure of 35psi and the carcass plies for the radials were a bit softer in configuration to allow for the higher inflation pressures, from what I could tell. The higher inflation pressures were for less "flex" and higher potential fuel economy levels.

Usually, the front tires were spec'd at 2psi less than the rear tires. In '66, the front tires on the station wagon models were spec'd at 22psi, as the rears were closer to 32psi!

In the earlier 1970s, a Firestone tire salesman told me that ALL of their tires were designed to run at 26psi, no matter what. High speeds, full loads, light loads, etc. He was firm in that recommendation, back then.

Usually, front tires wore sooner than the rear tires did. As the front ends were heavier, I formulated a theory that tire pressures should relate to the load the axle was carrying. After finding a chart which had tire pressure and load capabilities in it, I discovered that starting with the "75mph pressure" (28psi) and adding 2psi would balance the loads the tires saw between the front and rear tires. Which resulted in 30 frt/28 rr. Which also resulted in even tire wear between the front and rear tires. Steering response was also better with very little ride quality decrease. This was on 14x5.5 factory wheels on the Newport and 15x6 on the Monaco.

Back when everybody was seeking to navigate the differences between P-metrics and earlier radial tires, there seemed to be some disagreements in what fit where. The "industry sources" claimed that you worried about tire load carrying ratings, which generally resulted in smaller (physically) tires getting installed and the inflation pressures used being the max inflation pressures on the sidewalls. My orientation was to go by the tire diameter, to maintain cosmetics of the earlier tires, which also kept the odometers reading more accurately, too! With the latter being where things ended up years later, by observation.

Later, I discovered the "Revs/Mile" spec in some BFG Radial T/A brochures, later in the Spec charts at TireRack.com. Which can be related to the same specs in the SAE Specs guides you can find at www.Hamtramck-Historical.com, too.

IF your car has the 8.25x14 tire size spec, which later became G78-14, you can convert the "8.25" numbrer into metric 209.55mm, which would be a very close match to P215/75R-14. Which would result in having a tire with adequate load-carrying capabilities for your car and its equipment. That's the first step. With the second step being to aim for about 30-32psi inflation pressure in the rear tires, then add 2 more for the front tires. Which should cover a majority of the vehicle loading situations, other than trailer towing or a trunk full of heavy stuff with people in the back seat (where you might need to go to the max inflation pressure on the sidewall instead).

ALSO be aware that "air" shrinks with colder ambient temps and expands in hot ambient temps! Which means that you probably need to adjust tire pressures in the fall/winter and then again in the spring/summer months.

From my experiences . . .

Enjoy!
CBODY67
 
32 PSI in my old cars with Radials is what i run.
 
Remember the Firestone/Ford Exploder tire debacle? It was due to pressure recommendations being far too low for the vehicle and the tire. It caused the tires to run hot and when cornering hard for the tire to fold under, causing the vehicle to overturn.
As mentioned earlier, they set pressures low on the big vehicles to promote a soft ride. Unfortunately this can cause a hard impact when you roll over.
Learn to read your tire wear. Wear on both outsides of tire-too low. Wear in the middle-too high.
And the pressures on the sidewall are MAX pressure, not normally recommended pressure.
 
Having watched much of the federal inquiries into the Ford/Firestone deal, I was amazed that the Bridgestone/Firestone execs seemed to know so little about things! It was also revealed that Ford wanted 29psi for the recommended tire pressure and the tire engineers wanted 30psi. Ford won out. BUT 1psi difference wouild not cause a tire to fail, I suspect, especially when the tire psi is already in the "good range" NOR would that little difference result in a smoother ride that most people would notice, by observation. I, indivually, determined that there were MANY side issues which were not admitted to, on both sides (consumer and seller) of the deal. BTAIM

IF you go back into the 1957 era, base tire pressures went as low as 20psi for normal driving. Tires were much more substantial back then and would tolerate such things. BUT reading the owners manual would probably indicate higher pressures for high speed driving or carrying heavy loads. By the middle 1960s, 24psi was the industry standard of sorts for normal driving (and a smooooth ride, "acceptable tire wear", but sloppier handling) with 32psi being the max recommended pressure (for a stiffer ride, much better steering response, and much better tire wear) and for carrying heavy loads. With some optiional-in-some-cases 6-ply-rated tires going to 36psi (and later 40psi in "XL" radials).

Here's an additional little test I devised. With the rear tires at the "high speed" psi level, and the front tires too, I would find some clean and reasonably smooth concrete and park the car there. Then, with the car in "Park", turn the steering wheel one way all the way, then go the other direction, all the way, ending in the "center" when done. Then move the car backwards and look at the "patch" of rubber left on the concrete. At 28psi, the H78-14 tires on 14x5.5 wheels would usually have a light spot in the center. Upping the front inflation pressure up to 30psi would have only a faint light spot, if any, in the middle of the rubber patch. Which meant that the center of the tread was in more complete contact with the road, driving straight. With 28 in the rear, the tires wore "flat" with no evidence of over-inflation with just me and a little bit of stuff in the trunk, which was good. This was on bias-ply and later bias-belted H78-14 tires on the standard 14x5.5 wheels.

It was also normal for the tire's tread width to need to be within 1" of the tire's rim width, back then. With the wider rims (on non-radials) probably needing a bit more pressure to keep the tread flat against the pavement. Radials, with their more flexible sidewalls, are not quite to sensitive to tread width/rim width issues, by observation.

These were/are my experiences on the '66 Newport Town Sedan and the later vehicles we had/have. Your experiences might vary. Your judgment call.

Enjoy!
CBODY67
 
I thought I heard "29", but even at 26, and how those three psi might decrease the total load capacity of the tires, but for the particular size of tire, even the "Standard Load" versions (which should have been on the vehicle) should have been good enough, I suspect. Reason I say that is that at the time, I figured the total capacity of the tires at 35psi. There was enough load capacity there that IF the vehicle was carrying that much additional weight, the back bumper would have been close to the ground, it would seem. Even if the vehicle had been ccarrying its "full-rated load", I suspect there would have been enough capacity reserve to not run hotter or suddenly blow out. But this is my speculation as I haven't seen a load chart segmented in 1 or 2psi increments (as I did in the later 1960s for tire sizes back then).

Which raises the question of "Just what might under-inflation be?" Is it related to total capacity inflation? Is it related to the minimum-recommended inflation pressure? Or is it generally low enough for the tire to look significantly under-inflated? Considering when I started paying attention to tire pressures (circa 1962), the normal base inflation pressure was 24psi, no matter what. Anything under that was under-inflation. With the additional qualifier that the tire was big enough to carry the weight of the car in the first place, at that pressure.

I also saw the video of the simulations which one major car magazine ran on a similar vehicle, which they found on a used car lot. Presumed to be representative of a used Explorer. They rigged the lh rr tire to completely deflate within one second. Their degree of repeatability was also in the mix. In all cases, the tire deflated and that corner of the vehicle just dropped as the vehicle drove straight. No drama.

The one item which could not be repeated, without destroying the tire by a bullet, was the sudden instability a sudden tire sidewall failure might cause. BUT from one experience I had several years ago, that might not have happened quickly.

I was in a company Tundra and had been to a customer's shop where the rh rr tire apparently picked-up something which punctured it and it deflated slowly. After about 5 more miles of driving, I started to hear a roaring noise from the lh rr, but the truck still drove straight and smooth. After several more miles, the sidewalls of the Michelin radial was shredded, but still attached, at which time I was limping to an exit and safe place for the tire to be changed. No drama, other than the loud noise being louder than the radio could be. There were contact marks on the shock absorber from the sidewall segments hitting it. Got the tire changed and replaced, no other issues. BTAIM

End of published thoughts on this subject,
CBODY67
 
The problem was a combination of the low tire pressure and the size of the tires Ford used. They used the same size tires as used on the Ranger. Undersized for Exploders.
 
Actually the recommended tire pressure was 26 psi.
Originally? With bias ply tires. Radials are different. It is best to read on the tire to see what the manufacturer recommends.
 
Originally? With bias ply tires. Radials are different. It is best to read on the tire to see what the manufacturer recommends.
The Exploders had radials.
And the pressure on the sidewall is MAX pressure. The car maker recommendation is on the B pillar. Two different pressures.

The car maker seems to prioritize soft ride over handling.
 
The Exploders had radials.
And the pressure on the sidewall is MAX pressure. The car maker recommendation is on the B pillar. Two different pressures.

The car maker seems to prioritize soft ride over handling.
Those were defective Firestones if I remember correctly. Most of the issues were in Texas and Ariz at high temperatures.
 
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