I need new tires & am just wondering how much you can deviate from the OEM size...for example, can you go from 235's to 225's or 245's...& what about the next number...from 60 to 55 or 65?

I have found some attractive deals for like new tires but a lot of times the size is one number off.

Also, any truth that you should ideally stick with the OEM brand/type (or something similar) because the manufacturer selected them as ideal for the car/truck's make & model?

Thanks to all...I've always been kinda dumb about tires.

 

It is the numbers that matter wear ratin, temp, load rating. You can change the
aspect ratio to a lower profile for better handling, But there is always a trade off
and the first number is the height, the second number is the aspect ratio and relates
to the width. Here is a calculator to figure out the height difference of the tires in
inches.https://www.ford-trucks.com/calculat...re_sizes/a-td/
Just input the sizes and see the difference. Of course the height will affect your
speedo to a certain percentage and even the gas mileage if you change it by a big
factor, Depending on your type of driving if you tailor the tire size to say highway
and get taller tires(to a point) you can get a bit better mileage. and Versa
vice!!

 

Hate to call you on this.......but the first number is WIDTH, The Aspect ratio is the percentage of width that the sidewall is.
In other words if you had a "100/75" series tire, the tread width would be 100mm and the radial distance from rim to tread surface would be 75mm

245/55 series tires are only 55 percent as 'tall' as they are wide.

 

I think I'm just going to stay with the exact same tires...that way I don't have to figure it out!

 

First off, we are all better off these days vs. the "good old days" when the mfg intentionally undersized tires to save a couple $ per unit, to the detriment of wear, braking, etc.

However, the first thing to look at is the OEM size and the particulars of your vehicle. Are we talking about your 2000 F250? What size tire is on it?

Once the base line info is supplied, better suggestions may follow.

With respect to the tires, here is an example of what you can do.

235/75 x 15 can be swapped for 255/70 x 15, maybe 265/65 x 15, and then if you want new wheels, 275/60x 16 and so on, as long as it fits in the well and doesn't hit the suspension. Usually, in swaps like this, you seek to keep the diameter of the tire the same so speedo and ABS issues don't crop up.

There are conversion calculators on line as well as fitment charts from tire sellers.

If you were 100% (or even 90%) satisfied with the OEM tires, nothing wrong with going back to a proven thing if you still feel uncomfortable with the idea of changing sizes.

 

The good old days? You had better go measure a few tires and see they are still
very much undersizing tires to save some "resources" mostly their money.
Flotation tires are almost always off the sidewall measurement they say 36" tall
but they can be only 34 or 35 1/4 inch tall, Each manufacturer has their own ruler
I guess and it is not a standardized drift from the stated size. Measure 3 or 4 brands
and and even different models in the same maker almost all will be different.
Don't hate to call me on it it was a mistake and actually the whole thing is one big
math problem and the rim size ends up figuring in the height or diameter.
Play with the calculator and compare sizes http://www.dakota-truck.net/TIRECALC/tirecalc.html

 

[QUOTE=blue beast]The good old days? You had better go measure a few tires and see they are still
very much undersizing tires to save some "resources" mostly their money.
Flotation tires are almost always off the sidewall measurement they say 36" tall
but they can be only 34 or 35 1/4 inch tall, Each manufacturer has their own ruler
I guess and it is not a standardized drift from the stated size. Measure 3 or 4 brands
and and even different models in the same maker almost all will be different.
Don't hate to call me on it it was a mistake and actually the whole thing is one big
math problem and the rim size ends up figuring in the height or diameter.
Play with the calculator and compare sizes http://www.dakota-truck.net/TIRECALC/tirecalc.html[/QUOTE]

I do not doubt what you are saying at all. What I was talking about is when they put 7.35 x 14 where a 7.75 should have gone, or 6.50 x 13s where a bigger tire should go etc, including 8.25 x 15 car tires on a F100 4x4 and stuff like that there.... AND the fact that for the most part, 13 & 14 inch wheels are history and 15s are at least the minimum, and rim widths aren't 4 1/2 or 5 " any more. Not that this point really applys to the OP.