Factory Tire / Wheel sizing Questions.

[Herckules35]

There are also several other issues that you need to consider:
TPMS will still think you need 17” pressures, and act accordingly. It also affects how your ABS reacts.


FCA has released new coding software recently that will allow your technician at the dealership to do a vehicle configuration change In the Body Control Module. The ABS, ECM and other modules ***** to the BCM so the veh config change will affect the entire computer.
I’m not sure as to the roll out status. Check with your dealer.

 

[Jeepwalker]

I was kind of wondering that too:

Does changing tire size (or axle ratio) in AlfaOBD or a Snap-on/Dealer scanner only adjust the speedometer readout, or does it transmit the changes across other affected sub-systems (fuel mapping, shift points, braking, TPM, Traction-control, etc)?

In order to make that work, it would require Ram to have a universal 'Master' program with logic steering already installed in the TIPM such that when selections were changed it selected certain programming blocks of other system. But then again, having a one-size-fits-all program (with options) would make it a lot easier and cleaner to program various factory options on the assembly line and changes made at the dealership.

Has anyone had direct experience with this? What have you noticed?

 

[TommyGuns777]

Looked right after I read this, at the Warlock net door tgo me and see his fctory label says the stock tire for the 20" rims is a 275/55r20 - that is what is on it. Curious as to why the difference. who knows ? cheers

That’s interesting… I thought for sure they all came with the 275/60’s. 55 would get me more within spec I think.

Thanks for the info. I’m going to look into this.

 

[Blue Truck]

To get an idea of how much difference there is between tire sizes, this is my favorite site:

Tyre Size Calculator

A better easy to use tyre size calculator. Use our tyre size calculator to find tyre diameter, width, sidewall, circumference, and revolutions per mile.

tiresize.com

If you use the "Tyre Comparison" tab, you can plug in two tire different sizes and get all sorts of info. Using your two sizes shows 1.4" increased diameter. This gives you about a 4.4% height increase, or 4.1% decrease in tire revolutions per mile.

Different manufacturers build their tires slightly off the nominal measurements, so you can usually get the specifics from the manufacturer's site.

Personally, I'm running a 3.5% larger diameter tire than stock and never felt the need to correct anything.

 

[Elkman]

Going from 30" to 31.5" tall tires is a difference of only 5 percent and nothing to worry about. You will be going 5% faster than the odometer reading but you can allow for that. It will be easier to break a bead if you actually go offroad but few people actually leave the pavement.

 

[Atcer2018]

TPMS sensors. Running two sets of rims/tires you’ll need to reprogram the TPMS system to the proper sending units in the different rims or use clones unless you like the bright yellow dash light. +1 on AlfaOBD. The GUI is old but it can do more functions than most owners will ever need. OP if you at some point level your Warlock LT275/65/20 easily fit. That’s a 34 inch tire. The tire size and TPMS thresholds are easily changed with AlfaOBD. Not to mention you can run LED lighting without using resistors, add keyless n go, program fobs, reprogram TPMS transmitters, do diagnostics and monitor just about every system on the vehicle. 2018 and up will need the bypass module or harness.

 

[pacofortacos]

That’s interesting… I thought for sure they all came with the 275/60’s. 55 would get me more within spec I think.

Thanks for the info. I’m going to look into this.

This is the stock size on the later models and is the same diameter as your 17's, so straight out swap.
Truck will handle much better with the 20's but if offroading the 17's will be a softer ride.