Alternate Tire Sizes

[byez]

My Dodge Ram has three alternate tires sizes. I currently have 275/60/20 tires on the vehicle.

The alternate size is 265/70/17 which is 4.2% faster and the second alternate size is 245/70/17 which is 7.5% faster than my current size.

How does Dodge get away with recommending tire sizes with such variance in circumference? Whats the maximum deviation from stock tire size allowable? Would running 235/65/17 be ok to run? It seems like my choices for winter tires are very limited at anything larger than that size.

 

[CapriRacer]

Byez,

I hate the way Dodge does their vehicle placard. Multiple tire size listings creates confusion and can lead folks somewhere they don't want to be.

Dodge adjusts the axle ratios and the speedometers to account for what goes on the vehicle. The problem here is that unless you are sure what originally came on the vehicle you could mistakenly think that changing tire sizes is going to have no effect - and that is obviously not true. Plus I wonder if all the rims will clear the brake rotors - I'm going to guess they will, but I now have much doubt.

My suggestion is to call Dodge and ask your question there. That is the only way they are going to realize the confusion they are creating - and perhaps they will fix it in later models.

But to answer your question, the federal government has told the car makers that the speedometer has to be accurate to within 3%, so the common rule is that tires have to be within 3% as well.

I'm going to assume that Dodge also intended to show that even the smallest tire on the placard has enough load carrying capacity, but the 235/65R17 you mentioned has less than the smallest, so don't go there.

 

[alreadygone]

Have been told dealerships can re-program computer to match different diameters? No personal experience, is this true?

Bob

 

[92saturnsl2]

The dodge speedometer is microprocessor controlled, so yes, the calibration can be changed with a simple program (flash memory) update.