Proper tire inflation

#1

I have a 97 Discovery. I just put new tires on yesterday. BF Goodrich 235 70 16’s. These are the recommended tires for the car. The tires were filled with Nitrogen, as per my request. The factory recommended tire pressure is 26 front and 36 back. The dealer, who has been in buisness for 40 years, put 40 psi in all the tires,4 psi less than max.This is his recommendation. In the past I have adjusted the tire pressure on my other vehicles ie pickup, van, sedan to get the max foot print and still keep the tire upright, not sagging or flexing too much. The Rover rides like a BRICK now. Should I bite my lip and accept the rougher ride on the say of my dealer or adjust the tires to get a smoother ride.

#2

The tires are not inflated properly. They need to be set at the vehicle manufacturer specs.

#3

Ditto. Follow whatever is recommended for the vehicle.

#4

And ditto again.
Perhaps he’s putting in 1 psi for every year he’s been in business!

#5

Hmmmm…Maybe this guy has been making mistakes for 40 years. You know–I’ve always done it this way, so it must be right! In theory, experience helps someone to do his job properly, but here is an excellent example that this maxim is not necessarily true. (If anyone wants to expand this example to political campaigns, that was not my intention, but…)

I would not be very worried about the inflation of the rear tires, since they are apparently only about 4 psi over the vehicle mfr’s specs. However, if you leave the front tires as is–with pressure 14 lbs. over the vehicle mfr’s specs–you are putting a great deal of additional stress on components such as ball joints and tie rods, and this could result in some very expensive repairs. Just as you are taking some bodily abuse from these rock-hard tires, the front end is also experiencing abuse.

Additionally, since a vehicle mfr comes up with recommendations for tire pressure as a result of factors including tests for safe handling, you could well wind up with some very unusual and unexpected handling characteristics with tire pressures that are so far out of whack.

If I were you, I would inflate both front and rear tires to about 2 or 3 lbs. over the mfr’s specs in order to get better tread life and better gas mileage, with only a very slight penalty in terms of ride quality. The present tire pressures are totally wrong and this tire guy’s expertise is definitely in doubt.

#6

I’ve found that over-inflation of new tires is quite common at tire dealers. I can only guess they think it will be longer until they are under-inflated, since so few people bother to check the pressures. Regardless, the dealer is wrong.

I suggest reducing the pressure until it is at the pressure on the vehicle sticker, or perhaps a few psi above that.

#7

Your dealer is incorrect. With a good (preferably dial) tire gauge, adjust them to the recommended 26/36 first thing in the morning, before any driving. 28/38 would be OK. You didn’t ask, but nitrogen is not needed, no benefit.

#8

Thanks for the suggestions. I went to the local Welding Supply that was offering Nitrogen for tires. The owner had an older model Blazer and said when he filled his tires he had a similar problem, with tires of similar size. His explanation was that nitrogen does not compress as easily as air; it does not squeeze or give when the tires are rolling on an uneven surface ie: interstate roads at 65-70 mph. His solution was to lower the pressure one pound at a time untill he got the right feel and response of the tires at speed. He managed to get a good foot print and maintain a proper side wall profile at 33psi on the front and 35psi on the back. He also noted that his tire pressure does not notably change from winter to summer or, after long trips on the interstate when tires normally heat up. That being said: After a couple of hours of tweeking, I settled on pressures of 30psi in the front tires and 34psi in the rear. The ride smoothed out, the foot print is flat and even across the tred and the side walls are straight and taught enough to prevent swaying when the steering is moved side to side at speed. Thanks again. We will see what happens after a couple of months and when the weather gets warmer.

#9

The car manufacturer recommends tyre pressure on the specific car you own, The tyre manufacturer does no recommend tyre pressure, in fact they tell you to use the car manufacturers recommendations.

OK so what is that pressure on the side of the tyre. It is the MAXIUM the tyre can handle so if the car manufacturer says you need 45 psi and the tyre shows a maximum of 44 psi, you know that that tyre is not recommended for your car, it can’t handle the weight.

BTW good old air we all breath and put in our tyres is 78% nitrogen.  You really get very very little benefit from using nitrogen.  Mostly it is usually dryer.  If someone will put it in for free, great, it is no worse and in a very minor way it is better, but never pay extra for it.
#10

Adjust your tire pressure according to Land Rover’s guidance. They developed it specifically for your vehicle for a number of reasons. These include roll stability, wet and dry traction, temperature control, evenness of tire wear, ride height, stress reduction on other suspension components, suspension alignment, and braking performance.

So…you can turn a no-brainer, no risk, no hassle process into a huge project and watch while your tires slowly wear away unevenly, or you can just read the owner’s manual and know that you’re doing the right thing.

#11

The owner had an older model Blazer and said when he filled his tires he had a similar problem, with tires of similar size. His explanation was that nitrogen does not compress as easily as air; it does not squeeze or give when the tires are rolling on an uneven surface ie: interstate roads at 65-70 mph. His solution was to lower the pressure one pound at a time untill he got the right feel and response of the tires at speed.

Likely he believes all that. However he is wrong.

The difference between air (78% Nitrogen) and 100% nitrogen is almost zero.

As for his method of determining the proper air pressure, well it is incomplete. The car manufacturer does all he does, but they also have high speed test tracks and test the tyres under all conditions and temperatures. While many years ago the auto companies did tend to put comfort over safety on tyres, that all ended with the Ford/Firestone rollover problems.

Use the numbers in the owner’s manual, unless you really believe that the owner of the welding shop really knows more than the engineers and test track people at the auto company.