Cadillac Owners Forum banner

1 - 20 of 30 Posts

·
Registered
98 STS
Joined
·
42 Posts
Discussion Starter #1
I know what the door panels say, but what pressure do you find is the best for a balance of ride, performance, economy, and tire wear? I have always used ~35psi.
 

·
Registered
01 Eldo ETC, 02 Deville SOLD!
Joined
·
1,815 Posts
Remember also that the door pressure sticker is apropos only to the factory installed set of tires - if you're not on the originals, I'd check the sidewalls of what you do have on. But Ranger is right, usually for most normal duty passenger tires, a range between 30 and 35 should do the job.

Of course, be sure to not use the ol' 'eyeball' method - the fronts on my Deville look low (sidewall bulge) but repeated checks with trusted gauges show 32 psi - it's just the added weight up front that sometimes fools us.
 

·
Registered
1999 STS - diamond white
Joined
·
5,229 Posts
JimHare said:
Remember also that the door pressure sticker is apropos only to the factory installed set of tires - if you're not on the originals, I'd check the sidewalls of what you do have on.
That is incorrect. Google on "correct tire pressure" and you will find articles on what to use. The pressures listed on the tires is what the tire can support - not the recommended tire pressure for the application. Start with what the car manufacturer lists. You can try a higher pressure but remember handling, wear and traction are affected by different pressures.

Car Advisor
Car Talk (same guys)
Transport Canada
Myths

I could go on...
 

·
Registered
STS
Joined
·
132 Posts
Since getting my 2003 STS in August, I've had some experimentation with this.
I'm still running on the OEM Michelin Tourning tires... MXMH? somethin like that.
(WHY CADDY DIDN'T PUT AN ALL-SEASON PERF TIRE ON THE STS IS NUTS???)
Anyway... I HATE those tires... They are gummy, especially aruond turns.
I also noticed the bulge up front with all the weight too!
I'm running 37 PSI all the way around... The additional 2 PSI helps alot.
Ride doesn't seem much firmer and the difference in handling and roll is noticable. If it causes quicker wear, then I'm all for it... I HATE THESE H RATED MICHELIN's... I plan to put 255/50/17's on it soon! Hankook Ventus ST RH06 actually... They are incredible tires! I rode them on my Lincoln Mark VIII for over a year!!! All-Season Performance Radials. Smooth Ride, Awesome handling with an aggressive tread design and a UTQG Rating of 420-A-A. The big tire guy in our area, runs a shop with a huge warehouse attached... He can run his Mercedes E55 on any tire he wants! When he showed me he's running these Hankook Ventus on his car I was SOLD.
 

·
Registered
01 Eldo ETC, 02 Deville SOLD!
Joined
·
1,815 Posts
EcSTSatic said:
That is incorrect. Google on "correct tire pressure" and you will find articles on what to use. The pressures listed on the tires is what the tire can support - not the recommended tire pressure for the application. Start with what the car manufacturer lists. You can try a higher pressure but remember handling, wear and traction are affected by different pressures.
I stand corrected. I just checked one of my Conti's and it says "Max Recommended Pressure 44 PSI"..

I wonder if this is a recent change - I seem to remember, back in the old days that a tire read something like "Recommended pressure 32-36PSI" or some such. But, like many other things, my memory may be failing..

Thanks, EcSTSatc, for catching me on this.
 

·
Registered
STS
Joined
·
132 Posts
Yeah... Keep in mind Jim that MAX means MAX... You'll get all kinds of warning messages if you have the Tire Pressure Monitoring System on your car. Your correct... The "Recommended Tire Pressure" is usually between 32-36 PSI.
I'm running 37, and it seems fine... BTW, I don't take to heart the TPS numbers. I've got digital calibrated Tire Pressure Guages to check the PSI and they tell me 37 all the way around. But the TPS in the car indicated that one was 39 and others were at 36... LOL External guages all indicated 37 SOLID!
 

·
Registered
1999 STS - diamond white
Joined
·
5,229 Posts
JimHare said:
I stand corrected. I just checked one of my Conti's and it says "Max Recommended Pressure 44 PSI"..

I wonder if this is a recent change - I seem to remember, back in the old days that a tire read something like "Recommended pressure 32-36PSI" or some such. But, like many other things, my memory may be failing..

Thanks, EcSTSatc, for catching me on this.
You are welcome Jim. I'm from the old school too. I used to think the same way. It has been a recent revelation for me as well.:thumbsup:
 

·
Registered
Joined
·
166 Posts
my tires have a maximum rating of 44 pounds.
i run mine at 40 pounds because i want the performance.
i travel mountain roads every day and freeways.., and desert roads up to about 115mph every day.

kevin
 

·
Registered
1999 White Diamond ETC
Joined
·
2,540 Posts
The resident expert said once that the minimum recommended tire pressure is on the door jamb, and the maximum is on the sidewall.

Running lower than that indicated on the door jamb, you risk a blowout from overheating of the sidewalls. The owners manual indicates that if one plans to drive at 100 MPH or higher, to pump pressure up to 35psi cold (assuming 30psi is the recommended), then to bring them back down to norm when normal speed resumes.

I like 35-37 personally... I do notice a difference in handling especially with sharp maneuvers.

Tire pressures too high may wear your tires and shocks prematurely (the tire becomes bouncy and guess who has to work extra?)
 

·
Registered
1999 STS - diamond white
Joined
·
5,229 Posts
That's what I said but I'm not the resident expert.
"Start with what the car manufacturer lists. You can try a higher pressure but remember handling, wear and traction are affected by different pressures. "
 

·
Banned
1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
Joined
·
7,971 Posts
I run 1-2 under the max listed on the tire for less wear, better economy, and better handling, my ETC needs all the handling it can get. The ride is still acceptable.
 

·
Registered
94 Eldorado, and a 99 ETC
Joined
·
3,887 Posts
It really depends on three factors: the load rating of the tires, the maximum psi rating of the tires, and the weight of the car.

If you give me this information I can do the math for you to get your optimal tire pressure.

Please remember that the front of the car weighs more than the back, so it would be more accurate to give me those weights separate from eachother.

Too much pressure would give you better gas milage, BUT you would also be sacrificing the life of your tires. Too little pressure not only gives you bad gas milage, but it also reduces the life of your tires.
 

·
Registered
Joined
·
136 Posts
I just puchased Goodyear's Triple treads for my 92 Eldorado. I run 44psi, the ride is excellent! The tires suck up the expandtion joints, very quite, and a 6 hour drive netted 28.2mpg at 72mph. These tires are really good I would recommend them. Car Handles great as these tires are H rated. They are stock size.
 

·
Registered
1999 White Diamond ETC
Joined
·
2,540 Posts
Krashed989 said:
It really depends on three factors: the load rating of the tires, the maximum psi rating of the tires, and the weight of the car.

If you give me this information I can do the math for you to get your optimal tire pressure.
Ok Krashed989, you got me curious.

Tire load index: 98 (max load = 1653 lbs)
Max cold PSI 51

Cadillac Eldorado Touring, Curb weight 3876 lbs

I weigh ~ 155 lbs (fuel weighs about 120 when full tank, but curb weight is with all fluids)

Static Weight Distribution (assume @ curb weight above):
64% front = 2480.64 lbs (1,240 lbs per tire )
36% rear = 1395.36 lbs (697.68 lbs per rear tire)


Edit: I messed up with the calculator, corrected it.

So what are my numbers and how do you arrive at them?
 

·
Registered
94 Eldorado, and a 99 ETC
Joined
·
3,887 Posts
ok here we go.

1653 divided by 51 = 32.2411764705882352941176470588235 for the sake of brevity I'm just going to round that to the nearest 0.01.

That means that for every 1psi your tires can hold 32.24 lbs.

For me to be able to take into account the drivers weight, I need to know both the width of the car and the length of the wheel-base (so I can find what % of the drivers weight is on what wheels).

1653-1240 = 413

413 divided by 32.24 = 12.180173697270471464019851116625 again for the sake of brevity I'm going to round that to the nearest 0.01.

51 - 12.18 = 38.82psi

front = 38.82psi

1653-697.68 = 955.32

955.32 divided by 32.24 = 29.631513647642679900744416873449 again for the sake of brevity I'm going to round that to the nearest 0.01.

51 - 29.63 = 21.37 ?? that doesn't sound right so I'm going to add the weight of the fuel to it, and maybe 100 lbs of cargo

697.68+120+100 = 917.68

1653-917.68 = 735.32

735.32 divided by 32.24 = 22.807692307692307692307692 again for the sake of brevity I'm going to round that to the nearest 0.01.

51 - 22.8 = 28.2

WOW that's a huge difference from the front to the back. Are you sure you got the weight of the back right?

So:

Front = 38.82psi
back = 28.2psi (I would round this up to 30 psi just to be safe)
 

·
Registered
2003 STS w/BoseNav, 1993 Deville, 1985 Deville
Joined
·
1,089 Posts
When I got my STS last Friday, the pressures in the Michelin MXV4 Plus tires were like 25 or 28. When the weather turned colder, the TPS gave me a low pressure warning. I took that opportunity to air them up to 35-36. Jury is out if I like these Michelins or not. I'm already shopping for the next set of H-rated tires. I won't need them for prolly another year, so I'm not in any hurry.

I have been running Toyo Spectrums on my 93 Deville at 44 PSI. It has a 65,000 treadlife waranty, but I ran them to 110,000 miles. Tells you what proper maintenance will do for ya. I bal and rotate them every 10,000 or so. Costs me about $35 or $40 at Sears. Pay that once, and you never have to pay it again as long as you own the car even if you get different tires. I drive fast, so that's why I keep the pressure to the max listed on the sidewall.

I liked those tires sooo much, I got a second set. The original Michelins were so frickin' noisy, I couldn't believe it. These ride soooo much better.
 

·
Registered
94 Eldorado, and a 99 ETC
Joined
·
3,887 Posts
I guess I should summarize my math because it looks really confusing (makes sense to me :bigroll: ).

1.Divide the maximum load of the tires by the maximum psi of the tires to get how much lbs each psi can lift.
2.Find the difference between the cars weight on the tire and the load it's rated for.
3.Divide that difference by what you got for #1 to get how much extra psi the tire can hold.
4. subtract that psi from the maximum psi rating on the tire to get the minimum psi your tire should be kept at.

I say it's the minimum because that's what the tire would be kept at if there was no driver, passengers or cargo.
 

·
Registered
1999 White Diamond ETC
Joined
·
2,540 Posts
Krashed989 said:
I guess I should summarize my math because it looks really confusing (makes sense to me :bigroll: ).

1.Divide the maximum load of the tires by the maximum psi of the tires to get how much lbs each psi can lift.
2.Find the difference between the cars weight on the tire and the load it's rated for.
3.Divide that difference by what you got for #1 to get how much extra psi the tire can hold.
4. subtract that psi from the maximum psi rating on the tire to get the minimum psi your tire should be kept at.

I say it's the minimum because that's what the tire would be kept at if there was no driver, passengers or cargo.
It's creative. The only thing that kind of worries me is that I don't know where heat comes into consideration as the sidewall bends while rotating. I guess a better formula would have to consider what speeds the tire will encounter.

When you came up with 21.27 lbs for the rear. I believe that was derived from curb weight. Curb weight includes all fluids (a full tank of gas) but no cargo. Typically I ride by myself so my 155 lbs or so in the front drivers side would probably not have much of an effect on the result of the formula.

Another factor which is immensely important is inertia and momentum and how they push and tug on the vehicle as it goes at different velocities, in different directions. The weights shift to the back when accelerating and dramatically to the front when braking. This would mean that the tires likely encounter a whole different set of numbers.

But your method is creative and that's a very good start. :thumbsup:
 
1 - 20 of 30 Posts
Top