QuestionI have a 2002 Land Rover Discovery, with original 255-65-16 Michelin tires on it. I went to a local BFGoodrich dealer to buy a set of LT255-70-16 BFG All-Terrains. They were put on the vehicle, and the next day I noticed it handling terrible, and when I hit a little curb by mistake, I had a loud noise and feedback through the steering column.
I immediately checked the inflation pressure, and all four tires were at 70 lbs! I went back today and found the manager. He said that these were at the correct pressure, and I showed him the pressure placard on the door, which stated 28 front and 44 rear. I understood that going up a a a half size and an LT rated tire that the inflation might change a bit, but not to 70 lbs. I pointed out that 70 lbs is higher than max inflation for that tire, and that is a no-no. He said becasue I have more (4) plies in the tire, I need to run it at a higher psi, because if I don't, the tire will heat up and have a failure. I told him he was nuts and needed retraining, and if that was store policy, he was going to loose a lot of customers that don;t understand all of this; all they know is that the tires feel and handle like crap.
This is a major chain of tire stores on the west coast and I think BFG should know about this.
AnswerJim,
Let's do the math first.
According to Tire Guides, a 2002 Land Rover Discovery Series II came with 2 different tire sizes, and one of them was 255/65R16 105H inflated to 28 psi front / 46 psi rear. That's a little different than what you said the placard reads. I going to assume the book is wrong, but in either case it doesn't much matter, because the rear pressure specification is well over the point where the maximum load carrying capacity occurs.
That means the load carrying capacity of the tires is: 825 kg (1819#) front / 1030 kg (2271#) rear.
In order to get the same load carrying capacity, an LT255/70R16 needs to use 38 psi front / 53 psi rear - and since Land Rover chose to use 16 psi more in the rear, we should, too! That's to maintain the handling balance front to rear. A tire's spring rate is pretty much a linear relationship to pressure.
So that leaves us with 38 psi front, 54 psi rear.
I am not a fan of replacing regular passenger car tires (the kind that came on your Land Rover from the factory) with LT metric tires - and vice versa. As you can see, even though the tire is physically bigger, it still requires more inflation pressure to carry the same load - and I think that results in a vehicle that rides and handles quite differently than the vehicle manufacturer designed for.
In your case, I don't know why this was done.
Was it because you specified the BFG tire and the closest size available was LT255/70R16?
Or was it because that was the only thing that was available at the store that closely matched?
Whatever the case, I think this is not a good fitment for this vehicle. There are a lot of better choices - I just don't know why that particular choice was made - and without more information, the only thing I can do is second guess, which is never a good idea.
