Tires: BF goodrich tyre pressures on Defender 90, bf goodrich tyre, landrover defender 90

Question
QUESTION: Hi Barry,
I have just bought a 1999 Landrover Defender 90 pickup. It has BF Goodrich 365/75 R16s fitted and I wanted to know what the correct pressure was/ I have search lots of forums but not had much luck - suggestions from 30-36 PSI so currently running at 33 all round! No offroad plans yet!
many thanks,
dave.

ANSWER: Dave,

On every vehicle sold in the US - and I understand this is a worldwide practice as well -  there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size.  The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

Personally, I like a car that handles crisply. So I use 3 to 5 psi above the placard pressure.  I also get better fuel economy, better wet traction, better snow traction, better tire durability, better tire wear, but I do have a degradation in ride harshness (but I am willing to put up with it.)

BTW, it doesn't matter who makes the tire or what pressure is listed on the tire's sidewall, if the tire size is the same as the placard, then the pressure listed on placard is also appropriate.

One word of caution:  Some trucks use tires with the letters "LT" in front of the tire size - and some trucks use tires with the letter "P" in front of the tire size - and some trucks use tires with the letter "C" after the tire size.  You should not use "P"'s in place of "LT"'s and vice versa.

For this situation, you should be sure the pressure on the sidewall equals or exceeds that pressure on the placard.  If you do this the issue about the letter "C" in the sidewall will take care of itself (which is not true with "LT"'s vs "P"'s.)

If you are using a tire size that is different than what is listed on the placard, then the pressure has to be recalculated.  The calculation is not difficult, but it requires tire load tables which are not allowed to be published in the Internet because of copyright laws.  However, I have a copy and would be glad to do the calculation, but the starting point is the vehicle placard: Tire size and inflation pressure.  I will also need to know the new tire size.


Ordinarily I would look up your vehicle in Tire Guides, a book which summarizes the vehicle tire placards for vehicles sold in the US - but I think you can see the problem.  The book only applies to the US.

So, please go find your vehicle tire placard and tell me what is says for the original tire size and inflation pressure.  Plus you should tell me what the new tire size is as what you wrote in your original post appears to be in error - plus is the new tire an "LT" or not?

---------- FOLLOW-UP ----------

QUESTION: Thanks Barry - you are correct on the typo and the tyres are LT 265/75 R16 Mud terrains. The original placard only has info for the original tyre sizes - for example 205/80 R16 are recommended to be run at 28 front and 38 rear for normal use, and '7.5x16 and 205R16' tyres at 28 and 35. (I am in the UK by the way! - lots of forums with recommendations but all of them different!).
I hope that this helps with answering my query.
Dave.

Answer
Dave,

Thanks.

A 205/80R16 has a load carrying capacity of 691kg at 28 psi and 844 kg at 38 psi.

In order to carry the same loads, an LT265/75R16 has to use 25 psi and 34 psi.  That is 3 psi and 4 psi lower than the 205/80R16 - and I feel comfortable with that.

But there is one other issue you need to be aware of.  An LT265/75R16 has an allowable rim width range fo 7" to 8", while a 205/80R16 has an allowable rim width range of 5" to 7", while for a 205R16 it is 5½" to 6½".  I strongly suspect the rims on your Landrover are too narrow for the LT265/75r16's - and that could lead to the vehicle wanting to follow the ruts in the road surface, as well as some sensitivity to side winds.  In other words, the vehicle may feel unstable.