Slab side ride quality

[TonyC]

I'm not out to start a hostile debate over it, so I make this disclaimer: My statement is based solely on my own experience and on independent references I have read, and do not necessarily demand compliance by anyone who reads it. This is guidance which only I follow, which works well for me but may not necessarily work for others. Essentially, "That's my story, and I'm sticking to it; nobody else has to, however."

Anyway, back to the original topic, these cars were considered the master-nuts in luxury back in their day. Most of the road tests would say that, though admittedly not all (and not necessarily in those words). And there are archived articles, some online and some in printed compilations (an example of the latter is pictured below), which can make for really interesting reading for those who have interest. Tom McCahill's reviews for Mechanix Illustrated are particularly entertaining.

---Tony

Just because you have your own opinion on what PSI to run doesn't mean I'm wrong. I've stated what tire manufacturers and vehicle manufacturers say- that you're supposed to run the pressure indicated for the vehicle, not on the tire. Just because a tire has a max pressure doesn't mean that's what you base your set pressure on. If that was the case the tire manufacturers and vehicle manufacturers wouldn't show any value and simply say refer to the tire sidewall.

That being said I have the pictured book and it's an interesting read. There are several in the same series that are worth getting.

I thought I had already stated that.

But anyway, yes, that book does make for fun reading.

---Tony

[George W]

If tires are to be inflated to the car manufacturer's stated specifications then shouldn't the tires be inflated to 24 psi as stated in the TSM for my 65 sedan ? Of course in 1965 radials were not the original equipment tire. When Lincoln first went to radial tires as standard ( don't know what year ) did they specify a different, higher inflation pressure ?

[TonyC]

There is something not factored into that idea: Those specs were for bias-ply tires, which were the only option in '65. Radials didn't even become optional until the near-end of that decade. Bias-ply inflation specs and radial inflation specs are by no means the same; and since bias-ply tires are for the most part no longer offered (and ridiculously expensive from the few who do still offer them, primarily for the museum show-car look), the manufacturer's original inflation specs are totally irrelevant. If you tried running radial tires with only 24 psi, especially with the massive load it has to carry, you'd wear the tires out in less than a year. Now, when radial tires became factory options, I would think the factory would place decals with totally different specs for that option, but I cannot guarantee that would have been the case. By the end of the '70s, radial tires became pretty much the standard for the industry, so those inflation decals from later cars would be more relevant today. But for the bias-era cars, the inflation specs one needs to use today are those that are embossed on the tires themselves, not the factory decals (except maybe for later cars that had radial tires as standard equipment—e.g., a 1970 Mark III).

---Tony

[action]

I would suggest inflating based on tire size and loading. It requires knowing the weight of your vehicle.

That data is available from each tire manufacturer. Get it through the tire dealer.


Action

[Mike]

There is something not factored into that idea: Those specs were for bias-ply tires, which were the only option in '65. Radials didn't even become optional until the near-end of that decade. Bias-ply inflation specs and radial inflation specs are by no means the same; and since bias-ply tires are for the most part no longer offered (and ridiculously expensive from the few who do still offer them, primarily for the museum show-car look), the manufacturer's original inflation specs are totally irrelevant. If you tried running radial tires with only 24 psi, especially with the massive load it has to carry, you'd wear the tires out in less than a year. Now, when radial tires became factory options, I would think the factory would place decals with totally different specs for that option, but I cannot guarantee that would have been the case. By the end of the '70s, radial tires became pretty much the standard for the industry, so those inflation decals from later cars would be more relevant today. But for the bias-era cars, the inflation specs one needs to use today are those that are embossed on the tires themselves, not the factory decals (except maybe for later cars that had radial tires as standard equipment—e.g., a 1970 Mark III).

---Tony

Again what's on the tire is max psi and is as irrelevant as the recommended pressures listed for the old bias ply tires.
30-35psi is probably the range you'd want to run them at. That's been the standard range for decades and should also be what was factory recommended when they were still making bigger Lincoln's in the 70s and early 80s.

[TonyC]

Again what's on the tire is max psi and is as irrelevant as the recommended pressures listed for the old bias ply tires.

I submit that to be an incorrect assessment. What the tires indicate is far more relevant than the old bias-ply stats; any tire professional will tell you that.

That said, yes, 35 psi was the standard for service tires from the '70s into the '90s. But we're not in that period anymore, and tire engineering has not been stagnant. Keep in mind that the "donuts" (the temp-use spares) have had a much-higher rating than service tires since that period when they were introduced, and they have that for a reason. Technology has moved on, and it is very plausible that the engineering that goes into "donuts" has been expanded at least to some extent to service tires, allowing them to run on higher psi.

The indicated psi limit is the COLD psi limit, not the absolute limit. If it states 50 psi, you can inflate the tire to 50 psi (or 48 to be safe) and not have to think twice about a blowout, because tires are engineered to accommodate expansion beyond the stated cold limit.

Now, if you wish to keep 35 psi, that's fine, if it does not compromise the handling, the fuel economy, or the tire's integrity. But going with 24 will guarantee that you'll need to change out those tires in less than a year because the inboard and outboard edges of the tread have simultaneously worn off.

Action also made a valid point: The load rating of the tire is critical, and it does require knowing the weight figures of the car in question, both dry and gross. I still strongly suspect that too many people and even some unscrupulous shops will disregard that factor when they're trying to sell those looney wagon-wheels.

---Tony

[action]

What is listed on the side wall of a tire is the max cold PSI for that tire.
Tires come in 3 general applications.
P = passenger tires. However many P designed tires are found on light truck and SUV
LT - Light Truck and are designed for the pick up truck or general truck market up to a 1 ton designation.
ST - Are for trailers or non-passenger vehicles

The tire manufacturer has no idea what their tire will be installed on. And because there is liability and a few other things the side wall is marked with a max cold PSI fill. And cold means a tire that has not been moved in the pervious 8 to 12 hours or so. Yes if the tire is filled to max side wall in the morning and it NOT over loaded the pressure will be over the cold fill number, however NO air pressure adjustment should be made on a tire that has been used in the previous 8 to 12 hours. (There is an exception for that but not based on the above data)

Generally a current passenger vehicle tire, P design (and this will be limited to Lincolns) will have a load rating that far exceeds actual load applied to the tire if filled to max PSI. If filled to max PSI the ride will be rather hard and not satisfactory to most drivers, especially a luxury car driver. Hey it is a luxury car!!!!

So let's put some general numbers to the discussion assuming a 5000 (US) pound vehicle
If you divide 5000 by 4 that equals 1250 #s
To have a margin multiply that by 125% and it equals 1562
Meaning one would need a tire with a load capacity of 1562 pounds (give or take) to adequately cover the load. One can have more, just not less or there will be tire issues. If the vehicle was equipped with P235/75R15 SL shown in the chart towards the bottom of the page linked below, then the air pressure could be as low as 20 PSI for 1543 pounds of load. Most won't users and vehicle manufacturers will not go that low. But it is possible. One of the reasons for going higher is greater fuel economy. And a vehicle manufacturer with a current vehicle tests that new vehicle with the published tires inflated to the pressure indicated on a (usually yellow) tire inflation decal. Part of that reason is because the vehicle is certified to get the fuel economy on the "federal test" with that tire inflated to that PSI.

As we apply this to a classic car none of the federal regs apply and the tire design nor the current tire sizing and load ratings did not exist back then. So the classic car user really needs to know the weight and then apply to the chart for the given tire that is used. And not going out on a limb much, most if not all current radial tires available will have more than enough load capacity if inflated to 30 PSI. It is the nature of the tire industry. They make tires that handle passenger vehicle loads very easily. (Unlike the 1960s when load ratings were much lower and less clear as to what the tire would handle) I think the bottom end of most passenger car tires on a 14" rim or larger is in the neighborhood of 1880 pounds per tire under max inflation. So that would be a cheap tire. Few Lincoln owners are getting that tire. Most will get a tire that has a max capacity of 2000 #s or more per tire and a max side wall inflation of 44 PSI or more.

Here is a good read about max pressure and how pressures up or down the scale increase or decrease load capacity.
https://www.tirerack.com/tires/tiretech ... techid=195


>>>>>>>Action

[Mike]

Again what's on the tire is max psi and is as irrelevant as the recommended pressures listed for the old bias ply tires.

I submit that to be an incorrect assessment. What the tires indicate is far more relevant than the old bias-ply stats; any tire professional will tell you that.

That said, yes, 35 psi was the standard for service tires from the '70s into the '90s. But we're not in that period anymore, and tire engineering has not been stagnant. Keep in mind that the "donuts" (the temp-use spares) have had a much-higher rating than service tires since that period when they were introduced, and they have that for a reason. Technology has moved on, and it is very plausible that the engineering that goes into "donuts" has been expanded at least to some extent to service tires, allowing them to run on higher psi.

The indicated psi limit is the COLD psi limit, not the absolute limit. If it states 50 psi, you can inflate the tire to 50 psi (or 48 to be safe) and not have to think twice about a blowout, because tires are engineered to accommodate expansion beyond the stated cold limit.

Now, if you wish to keep 35 psi, that's fine, if it does not compromise the handling, the fuel economy, or the tire's integrity. But going with 24 will guarantee that you'll need to change out those tires in less than a year because the inboard and outboard edges of the tread have simultaneously worn off.

---Tony

Whether you think it's an incorrect assessment or not doesn't matter. What the tire indicates is MAX psi not what it should be run at. The tire manufacturer has no idea what their tire is going on, it's handling characteristics or anything else. All the the tire tells you is what the max pressure the tire should be safely run at. Cold or hot doesn't matter it still has nothing to do with what pressure it should be run at on any specific car.

35psi wasn't just the 70s into the 90s. The majority of new cars still use that range as the standard. You're right 24 probably is too low which is why I didn't say anything about that. A newer with some modern unusual tire size or different load characteristics might be running at some other pressure but most people are still running the typical size tires on their Lincolns and 30-35psi has almost always been the typical tire pressure for them.

[Mike]

Thanks for that writeup action.

[action]

As a post script to my post above, go to that link and look at the load capacity of the two tires listed towards the bottom.

BOTH are P235/75R15
One has a SL suffix and the other is a XL suffix.
It makes a difference in capacity and likely cost.

Just know what you are buying and what you need before you open your wallet.

Action

[TonyC]

Whatever, Mike; I could go to Peerless and get all I'd need to debunk that claim of 35 being the standard to this day, not to mention your refutation about the specs on the tires and the tire companies being clueless about applications ("The tire manufacturer has no idea what their tire is going on, it's handling characteristics or anything else"—I'm sure they'd have something to say about that); but in the end those are all academic matters and not worth triggering a war over. As I said, if 35 psi works for you without any of the side-effects I listed and which you so thoroughly copied in your response, then by all means stick to it. It works for you, and that's the main matter. 42 psi works for me, and I'm sticking to it. At least we do both agree that the old bias-ply inflation figures are inadequate and as a result irrelevant for radial tires.

---Tony

[Mike]

I didn't say 35 psi was the standard to this day but 30-35 still the most common range. Even 2019 Continental is 33-35 until you get into 20" rims. At least according to this site:
https://tirepressure.com/2019-lincoln-c ... e-pressure
I looked it up because I was curious more then anything else (Ford only refers to the sticker in the door jamb).
Either way you're right we do at least agree on something

[LithiumCobalt]

OK, guys, all good and fine on the tire pressure specs. Just for the record, I have not changed my strut bar bushings yet. Has been unseasonably hot here all summer (finally had high in the 70s past couple of days for first time in months) and then I had a minor hand surgery last week, neither of which is conducive to wrenching. Will get them swapped before fall hits. May swap in my tilt column while in the process since I have to get down under there anyways.

[TonyC]

Yow...I do hope you recover quickly from that surgery, Nick. Strut rod bushings are critical for stability, and the sooner you can get them in, the better. If I were close enough, I'd volunteer to do that for you; luckily, despite the years ticking down for me, I learned I still have the ability to perform some of the less-fun tasks like removing and re-installing a brake booster within a two-hour period.

Although swapping out a steering column isn't fun either, you should have less trouble than I did, since yours is already the correct year for that design of tilt column. It's just that one 12-point 7/16" bolt head on the column side of the steering coupler that should be the biggest headache, I think.

---Tony

[George W]

It seems the general consensus is to run our 235 x 15 radial tires in the range of 35 to 45 psi. Currently I'm running 35 in my 65 sedan with BFGoodrich radials. The car seems to ride fine but my concern was/is two fold. First, how do higher or lower tire pressures effect the rim flex problem on these cars ? I'm concerned as I fear throwing off one or more of the OEM wheel covers and not being able to find an acceptably nice replacement. I would think higher pressure would put more stress on the wheel when cornering, but I may be 100% wrong on this.
The second is that no one has yet to provide what the Lincoln owner's manual or tire pressure spec. label recommended for the tire pressures for the Lincoln Continentals of the early 70s that were factory equipped with radials. Didn't radials become standard equipment in the early 70s ? Did they raise the recommended pressure spec at that time or provide pressure specs for both radial and non radial tires on the same car ?