GM Cadillac - Determine proper TIRE PRESSURE
#1
05-06-2007, 01:34 PM
GM Cadillac - Determine proper TIRE PRESSURE
from an GM Cadillac automotive engineer that spends a great deal of time
with the testing of concept cars at tracks....
with the testing of concept cars at tracks....
ORIGINAL name witheld by request
Tire pressures on the door are the recommended values for ride quality and encompass safety, tire durability, traction, fuel economy, etc. concerns as well. The recommendations are obviously a compromise as some of the "requirements" are mutually exclusive in a fashion.
Practically speaking I would consider the door recommendations a MINIMUM inflation value and the rating molded into the specific tire you are using to be the MAXIMUM. Somewhere in between you will have to find a value that suits your driving and driving style.
Since any type of car is used differently by different owners and the personality and requirements of every owner are different there is no "correct" answer for tire pressure. If you like a soft, compliant ride then you'll probably tend toward the door sticker recommendations. If you drive fast, hard and like hard cornering and/or a more sporting ride quality then you'll probably tend toward the maximum ratings on the specific tire's sidewall you are using.
I like the firmer ride and cornering characteristics of increased tire pressures so I tend to run toward the maximum rating ..i.e..44 PSI...in the fronts of a TFWD car and about 38-40 PSI in the rear.
The wear characteristics of modern , belted, radial tires allows some higher inflation pressures without "wearing out the middle" of the tire. You'll see perfect wear with 44 PSI and the tires will last much longer and lear more evenly the higher you run them without exception. You just sacrifice ride quality and increase the impact harshness with the higher inflation pressures. In an Allante this can be miserable sometimes as any convertible has less structure than a car with a full top so the cowl shake and general "squeek and rattle" quotent will undoubtable get worse.....
A lot also depends on the sidewall height and the aspect ratio of the tires. The original inflation pressures were for the OEM tires....which, don't forget, were produced at least 10 years (Allante) ago... Tires have changed since then and so have available sizes. If you read the door sticker it ALSO says what the tire size is for the car and that is what the inflation recommendations are for. Lower aspect ratio tires will have different (higher) inflation pressures.
Don't forget that a MAIN purpose of the tire is to protect the rim in potholes, curbs, etc..... Sounds funny but true. The higher the inflation, the better the rim protection. Especially true of lower aspect ratio tires.
Don't be afraid to experiment with the tire pressure just keep it within the borders of the door recommendations (if you still have OEM size tires) and the maximum molded into the tire sidewall.
Tire rolling resistance is a main factor in fuel economy and top speed so the higher inflation pressures help here too by lowering rolling resistance.
Really, the only reason for not running the maximum inflation pressures is for ride comfort and/or balancing the car for handling purposes.
When you increase the tire pressure you are increasing the spring rate of the tire which can dramatically affect handling. That is why you hear so much talk of tire inflation pressures in racing....it is a way of rapidly tuning the car for handling. If you drive hard and drive at the tires limits on a closed course you can really tell the difference in the inflation pressures and will undoubtable gravitate toward the higher end of inflation pressures if you experiment.
Don't forget, the tire pressure increases as the tire warms up so check them HOT if you are running at the maximum inflation pressure. If you air them to the max cold and then hop on the interstate you will be over-inflated by 3 or 4 PSI. This is readily apparent in the current model cars with the tire pressure monitoring systems.
[align=center](Note: this last paragraph in italics is in disagreement with the manufacturer's instruction stamped
on the sidewalls that clearly state MAX xxx psi COLD. The paragraph is kept here as it
is preferable to not modify or alter this engineer's recomendations - Stealth)
[/align]
Tire pressures on the door are the recommended values for ride quality and encompass safety, tire durability, traction, fuel economy, etc. concerns as well. The recommendations are obviously a compromise as some of the "requirements" are mutually exclusive in a fashion.
Practically speaking I would consider the door recommendations a MINIMUM inflation value and the rating molded into the specific tire you are using to be the MAXIMUM. Somewhere in between you will have to find a value that suits your driving and driving style.
Since any type of car is used differently by different owners and the personality and requirements of every owner are different there is no "correct" answer for tire pressure. If you like a soft, compliant ride then you'll probably tend toward the door sticker recommendations. If you drive fast, hard and like hard cornering and/or a more sporting ride quality then you'll probably tend toward the maximum ratings on the specific tire's sidewall you are using.
I like the firmer ride and cornering characteristics of increased tire pressures so I tend to run toward the maximum rating ..i.e..44 PSI...in the fronts of a TFWD car and about 38-40 PSI in the rear.
The wear characteristics of modern , belted, radial tires allows some higher inflation pressures without "wearing out the middle" of the tire. You'll see perfect wear with 44 PSI and the tires will last much longer and lear more evenly the higher you run them without exception. You just sacrifice ride quality and increase the impact harshness with the higher inflation pressures. In an Allante this can be miserable sometimes as any convertible has less structure than a car with a full top so the cowl shake and general "squeek and rattle" quotent will undoubtable get worse.....
A lot also depends on the sidewall height and the aspect ratio of the tires. The original inflation pressures were for the OEM tires....which, don't forget, were produced at least 10 years (Allante) ago... Tires have changed since then and so have available sizes. If you read the door sticker it ALSO says what the tire size is for the car and that is what the inflation recommendations are for. Lower aspect ratio tires will have different (higher) inflation pressures.
Don't forget that a MAIN purpose of the tire is to protect the rim in potholes, curbs, etc..... Sounds funny but true. The higher the inflation, the better the rim protection. Especially true of lower aspect ratio tires.
Don't be afraid to experiment with the tire pressure just keep it within the borders of the door recommendations (if you still have OEM size tires) and the maximum molded into the tire sidewall.
Tire rolling resistance is a main factor in fuel economy and top speed so the higher inflation pressures help here too by lowering rolling resistance.
Really, the only reason for not running the maximum inflation pressures is for ride comfort and/or balancing the car for handling purposes.
When you increase the tire pressure you are increasing the spring rate of the tire which can dramatically affect handling. That is why you hear so much talk of tire inflation pressures in racing....it is a way of rapidly tuning the car for handling. If you drive hard and drive at the tires limits on a closed course you can really tell the difference in the inflation pressures and will undoubtable gravitate toward the higher end of inflation pressures if you experiment.
Don't forget, the tire pressure increases as the tire warms up so check them HOT if you are running at the maximum inflation pressure. If you air them to the max cold and then hop on the interstate you will be over-inflated by 3 or 4 PSI. This is readily apparent in the current model cars with the tire pressure monitoring systems.
[align=center](Note: this last paragraph in italics is in disagreement with the manufacturer's instruction stamped
on the sidewalls that clearly state MAX xxx psi COLD. The paragraph is kept here as it
is preferable to not modify or alter this engineer's recomendations - Stealth)
[/align]
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