Tires: Tire Sizing for a 1999 4Dr 4WD tahoe, tire guides, oem tires

Question
QUESTION: I'm looking to replace the tires on my 1999 Tahoe.  The OEM tires were P245/75R16, but the tires on it now are p265/70R16.  I have a few questions about this.  First, I am wondering if I could safely put a slightly bigger tire on this (265/75R16).  Secondly, I'm wondering what the advantage is of going to a larger tire (if any from both a cross section and sidewall standpoint).  My impression is that wider tires give better handling and smaller sidewalls due the same, but that larger sidewalls would also increase ride comfort.  Third, I know that the "P" in the tire model stands for passenger and "LT" stands for light truck, on tires that are going on a full size SUV, are the differences between the two types of tire really notice able and if so what are they?  Lastly, you keep mentioning this "book" you have about tire sizing.  Is there anyway to purchase this book or find it online for reference to figure out which size tires are acceptable for different vehicles?

I know that's a lot of questions, but I'm curious about these things as I make my final tire decision.

Thanks!


ANSWER: Dan,

While I can not guarrantee it, there is usually enough room to go up one size - so the P265/75R16's will probably fit.

Larger sidewalls generally improve ride comfort, but the difference between tires can greater than the effect of a single size change - so this is more a function of the tire that you select.

The advantage to LT tires is that they can hold more load for a given size - but they do that with additional inflation pressure. Since your vehicle came with P metric tires - and you are going larger - there is no advantage to using LT metric tires.

"The book"?  Actually I refer to 2 books - Tire Guides - which is a compilation of what the vehicle placards say (and some other stuff) - and the Tire and Rim Association Yearbook.

Tire Guides is going to be very useful for a tire dealer, but has limited use for a consumer.  But it's only $16.00  You can order it over the net.  Just typwe in "Tire Guides" and follow the link to Bennet-Garfield Publishing.

TRA Yearbooks are fairly expensive - $60 or so - and while they list the loading information, this is more for design engineers than consumers.

Unfortunately, there isn't a book for "What fits".  This requires that the fenderwells be measured and the folks that do that think it gives them a competitive advantage, so they don't share the information.


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

QUESTION: Hi Barry,

Thanks for the quick response.  I have one follow up question.  You stated that I'd have no advantage from going to an "LT" instead of a "P" tire.  Would I have a disadvantage?  I seem to find the tires in the same size for the LT version are much cheaper.  I think I read somewhere that if my truck came with passenger tires, that the suspension etc. is designed for that type and putting on LT tires could make the suspension do more work and make the ride harsher.  Any truth to this?   I'd prefer to stick with the "P" type, but I'm wondering if there is any real difference other than the load values (will the ride be different/less safe, etc.?)

Cheers!
ANSWER: Dan,

Actually there is a disadvantage that I hoped I wouldn't have to address.

LT metric tires require more pressure to carry the same load as a P metric.  I know this sounds counter-intuitive, but that is the way it is.

This means your rims may not be up to the task, not to mention that the ride is going to be a bit rougher.

The fact the you're finding LT tires in the same size cheaper just doesn't make sense.  I suspect that means that the construction is weaker and more likely to fail.

My recommendation is to stay with P metrics if your vehicle came with them.

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

QUESTION: Barry,

Thanks again for the info.  I have one last question.  It became apparent to me over the weekend that my tires have the legal amount of tread on them, but they are worn unevenly.  The spots with the most wear are still legal, the other areas have better depth.  The outside of all the tires seems to be worn worse.  Is it possible to switch the mounting of the tires (not simply rotate them) so that the inner part of the tread now would ride on the outside?  My tires are not a design that is blatantly directional (thought it might obviously be so but unknown to me).
Thanks,
Dan

Answer
Dan,

You could do what you are suggesting, btu remember, there will probably be a fee associated with that.

Plus you will probably get a vibration.

But one thing for sure, you ought to get an alignment.  BTW, "in spec" isn't good enough.  The alignmemt should be within the middle half of the tolerance.