Jims92CTD

I have located a set of 245-75-16 used snow tires. I am aware if the speedo problems since they are smaller in diameter but for a wider rim by 1/2". A chart I looked at said they are for rims 6.5 to 7.5". I'm running the steel rims that came on the truck which are 6" wide. I'm running the correct tire size now - 235-85-16. Can this switch work safely or should I bite the bullet and buy new?

Any adcice will be appreciated.

JIm

Forrest Nearing

they'll be fine, but with that small of a tire, you're really going to want an E rated tire...

BearKiller

Make sure that they are LT245-75-16, and not P245-75-16.

LT=Light Truck

P=Passenger

If they are LT, it would be rare for them to be any other than LR-E.

G1625S

I ran some LT245's. They were waaaayyy small when compared to the stock 235's (imo), but they were e-rated...and free. I know where you're coming from. If you don't mind giving up a couple MPH for the winter, go for it.

sixshooter

I think they are safe but in my experience the center of the tread will wear faster than the edges.

apwatson50

YOu just need to adjust your air pressure to compensate, or at least to try to compensate.

4x4dually

Those will fit the rims fine. I'm running 285's on stock rims and have no problems. The specs are just for suggestion...kind of like speed limit signs and those stupid "click it or ticket" signs.

Ace

The rule of thumb is tread width no more than an inch wider than the rim (each side). So 6" rim = max 8" tread width. You can go a little more or less either way, usually with minimal problems, but they won't always wear or handle the best outside that range. The 285s on my stock rims seem just "OK." They're wearing fine at 50psi, but I don't think they handle very well on the pavement, probably due to too much sidewall flex caused by the extra tread width on too small a rim.

james1

Ace:

That sounds like a good rule of thumb. Thanks.

At risk of explaining the obvious, the number 285 specifies the width of the tire in millimeters. To convert to inches, multiply by 0.0254. (A 285 tire is 7.24 inches wide, a 235 tire is 5.94 inches wide, etc.).

sixshooter

The tires I was using were too mushy at low enough pressure to get full tread contact. They were some load range D piece o' #@*&% tires the previous owner put on there to get the truck sold. I now am riding on some 235 85 16 Bridgestones which seem like pretty good tires.

BearKiller

Tire designations are at the casings widest point, inflated, on manufacturer's specified rim width.

For instance, 235-85-16 is 235mm wide at the sidewall bulge, when inflated.

The 85 means that the distance from bead to tread-center is 85% as much as width.

The only number in this mess that makes sense is the 16, which means 16" wheel size.

I hate the communist way that tire manufacturers size car and truck tires.

A much superior method of sizing is the way 4-wheeler tires, off-hi-way equipment tires, and specialty 4x4 tires are sized.

For instance:

A common 4-wheeler/ATV size is 25-10-12, which means the tire is 25" tall, 10" wide, and fits a 12" wheel.

A common 4x4 size is 33-12.50-15, meaning 33" tall, 12.5" wide, and 15" wheel.

Now, which do you think is the more sensible method of tire sizing??

Without doing any math, how tall in inches is a tire that is size 225-55-17??

Hope this information is of some use.

Forrest Nearing

actually, on a metric tire, 235 is the tread width in mm, and the 85 is the sidewall height... it's 85% of the width.

makes perfect sense

Ace

This is probably the most important point. Anytime you go outside the recommended rim, be it OEM spec or rule of thumb, the ratio between the height and width changes to the point where the tire no longer performs as designed. Far enough out and the contact patch won't sit right at all.

BearKiller

You are almost right.

The 235 is casing width at widest point when inflated on recommended rim width.

4x4dually

Ah, who cares....THEY ARE TOO SKINNY!