Questionwhat is the difference between tire and vehicle manufacturer's information specifications?
AnswerSean,
This is a difficult question to answer because I'm not sure what you may mean.
If you mean the difference between the inflation pressure listed on the vehicle tire placard vs the pressure listed on the sidewall of the tire, then let me break this down into 2 parts:
Tire sidewall pressure: All tires conform to tire standards published by tire standardizing organizations. There are 3 major organizations: The Tire and Rim Association (TRA# - for the US, ETRTO #European Tyre and Rim Technical Organization# - for Europe, and JATMA #Japanese Automobile Tyre Manufacturers Association# - for Japan. There are others, but those are the major organizations and the others follow their lead.
Among the things those organizations do is define the relationship between load carrying capacity and inflation pressure by tire size. All of these organizations consult with one another and even though there are slight differences, the standards are reasonably close - particularly considering they are working with different measuring systems #Metric vs English units).
What appears on the sidewall of a tire is based on those standards. You need to be aware that certain types of tires do not have load and pressure information printed on the sidewall - like mining tires. While those types of tires are standardized, the service conditions are highly varied and things like inflation pressure need to be tailored to the work they are being asked to do. No one answer fits. But let's just talk about passenger car tires, recognizing that lots of what follows applies to other types of tires.
There are regulations that require passenger car tires to list the maximum load and pressure on the sidewall. Notice that I said maximum load, but it is not clear if the pressure has to the corresponding inflation pressure or a maximum inflation pressure - and that's what way the regulations are written.
So you will see passenger car tires that will say: Max Load XXXX at YY pressure - and - Max Load XXXX, Max pressure YY. These are not equivalent statements.
In the case of passenger car tires, it is clear what the max load is, but there are situations where additional inflation pressure is called for - such as high speed operation.
As a result, you will find inflation pressures listed on the sidewall of standard load passenger car tires as either 35 psi, 44 psi, or 51 psi - even though the max load occurs at 35 psi.
Now the vehicle tire placard.
vehicle manufacturers also look at those tire standards and base the tire size and the inflation pressure specification on the loads on the tire at each wheel position. What happens next depends on the vehicle manufacturer's internal practices.
Some vehicle manufacturers will want to use the same pressure front and rear - knowing that tires should be rotated regularly. Others will use a differences front to rear. but in every case, the pressure is more than enough to carry the max load of the vehicle.
Once the vehicle manufacturer decides what pressure to use, they will select springs, shocks and sway bars that give them the kind of ride and handling characteristics they want. This takes quite a bit of experimentation to get this right. In particular, they want the vehicle to be predictable in even the most extreme maneuvers.
There are regulations that require the vehicle manufacturer to post the original tire size and the inflation pressure specification on the vehicle somewhere. The common term for the label is the tire placard. Currently the US regulations require the placard to be on the driver's doorpost, but prior to 2008, this placard could also appear in the glovebox, the trunk, or the fuel filler door.
The above is the long way of saying that the vehicle manufacturers tire specs are specific to the vehicle, while the tire manufacturers specs are maximums, because a given tire might appear on different vehicles.
If this does answer your question, post a followup with more detail about what you are looking for.
