33” tire reprogram?

[21SilverRam]

You would think if you went to a 33” tire the dealership would be able to reprogram your speedo and shift points since that tire size is available on our truck. Am I right or no? Or they can do it but probably won’t!! Has anyone been successful having the dealership reprogram their tire size?

 

[RamDiver]

You would think if you went to a 33” tire the dealership would be able to reprogram your speedo and shift points since that tire size is available on our truck. Am I right or no? Or they can do it but probably won’t!! Has anyone been successful having the dealership reprogram their tire size?

You might be able to sell a dealership on including that tweak, if you buy a set of tires from them, although, I've never heard anyone speak of this.

I adjusted my tire sizes using AlfaOBD and an old TomTom GPS unit. AlfaOBD has many other tweaks for our trucks too.

Have a look at the AlfaOBD thread if you're curious.

AlfaOBD

Please Read!!! Supported years: 2013 to 2018 Make a backup of your original BCM configuration before making any changes. While we have a few BCM configs to compare with, there is nothing like comparing to your own pre-changes. Instructions: Uploading System ID (BCM) Information: Thank you...

www.ramforum.com

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[1999 White C5 Coupe]

You would think if you went to a 33” tire the dealership would be able to reprogram your speedo and shift points since that tire size is available on our truck. Am I right or no? Or they can do it but probably won’t!! Has anyone been successful having the dealership reprogram their tire size?

Most dealer programming or reprogramming on newer vehicles is done based upon their VIN - which has specific features and options associated with it.

Since your vehicle was not originally optioned with the 33-inch tires, a dealer probably could not program your vehicle’s computer to show it has 33-inch tires (and make the necessary adjustments for the speedometer, odometer and shift points).

I would also suspect that much larger tires would affect the ABS and stability control systems too.

 

[Daw14]

You would think if you went to a 33” tire the dealership would be able to reprogram your speedo and shift points since that tire size is available on our truck. Am I right or no? Or they can do it but probably won’t!! Has anyone been successful having the dealership reprogram their tire size?

I think if you found the right dealer , they could take care of what you want easily. However it’s finding the right dealer, they may be out there . Maybe contact an off-road 4x4 shop , they might have the equipment since it’s something they probably use often.

 

[RamDiver]

I think if you found the right dealer , they could take care of what you want easily. However it’s finding the right dealer, they may be out there . Maybe contact an off-road 4x4 shop , they might have the equipment since it’s something they probably use often.

That's a great idea.

One of the aftermarket parts/tire stores I used to use for my Tundra, bought a Toyota Techstream unit to access Toyotas.

Some jobber parts place, offroad shop, or tire shop is likely to have AlfaOBD for tweaking FCA vehicles too.

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[Jeepwalker]

If a person has the 'right' scan tool, or knows someone who does, it's as simple as navigating to the Tire/Wheel section of the scan tool, and selecting the size tire/wheel from the drop down list.

 

[BWL]

What size did your truck come with? The 275 60 20 is a 33 and the 275 55 20 is a 32. It looks like your truck is a classic so if it came with the 20" wheels it came with 33s. A lot of 33x12.50 tires are closer to 32.5 though so either way you're probably not far off as is.

 

[RamDiver]

What size did your truck come with? The 275 60 20 is a 33 and the 275 55 20 is a 32. It looks like your truck is a classic so if it came with the 20" wheels it came with 33s. A lot of 33x12.50 tires are closer to 32.5 though so either way you're probably not far off as is.

That's a good point.

The OP might want to look at the tire manufacturers spec to see how close the tire circumference spec is to the original tires that came on the truck.

The tire manufacturer will spec all the dimensional sizes and the revolutions/mile.

Or, there are many online tire calculators.

Tire size calculator: compare tires online

Our tire size calculator will help you estimate the difference of external dimensions of the wheels, height clearance, revolutions per mile and other characteristics, when installing tires of other sizes on your vehicle. This calculator allows you to tell the difference between the tires in...

tire-calc.com

I used my winter wheels for 1.5 winter seasons before fixing the 2.5 mph error. I just added the difference in my head. LOL

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[Jeepwalker]

The various choices of tire/wheel packages (hence different tire sizes) actually resides within your truck's computer software. It's there...you just need the software tool to access and allow it to be changed.

But because your (OP) truck is 2018 and newer it'll take a dealer scan tool, or 3rd party software/tool and a Secure Gateway Access (SGA) component to allow a user into the TIPM (computer). The reason for that is security. There was a famous video published on youtube back 11 or so yrs ago where hackers demonstrated how they hacked into a Jeep G/C (real-time..at the time) in CA, and took over remotely. Locks/brakes/other functions/maybe steering??. It rocked mfgrs and Chrysler wisely added a layer of security/safety. But for home mechanics it also means a little more work to work-in a SGA device. But after that a scan tool, like a Snap-on tool, for example, or another scan tool, can access the data and make changes. I'm just putting it out there to give a somewhat understanding of what and why..

 

[21SilverRam]

What size did your truck come with? The 275 60 20 is a 33 and the 275 55 20 is a 32. It looks like your truck is a classic so if it came with the 20" wheels it came with 33s. A lot of 33x12.50 tires are closer to 32.5 though so either way you're probably not far off as is.

265/70/17 with E rated tires

 

[GTyankee]

A 265/70R17 tire has an approximate height, also known as the overall diameter, of 31.7 inches (804 mm). This height can vary slightly depending on the brand and model of the tire, as well as the amount of air pressure in the tire

 

[crash68]

You would think if you went to a 33” tire the dealership would be able to reprogram your speedo and shift points since that tire size is available on our truck. Am I right or no?

If memory serves me correctly, there have been a few people reporting that dealerships are limited to OEM tire sizes for the vehicle. As someone else mentioned it comes down to whether the dealership is willing to adjust the wheel size. It possible to change the speedo adjustment with AlfaOBD and there is plug in modules like Taser that can calibrate the speedo for non-factory tire sizes also.

 

[Jeepwalker]

33's are within the computer selection. That's the easy way to do it.

As was suggested a couple times in previous posts, If the OP has the desire and some computer skills (or knows a kid, neighbor, etc who does). Just buy the AlfaOBD software, an OBD device/cable like the MX Plus (Amazon), and connect in a SGA (search on this forum or Youtube how to do it). Then he can do it cheaper than a dealer would charge and have the software for any future issues/customizing ...or read codes and do troubleshooting, etc. Works on some other Chrysler vehicles too.

 

[BWL]

265/70/17 with E rated tires

In a bfg all terrain the difference between the two 265/70-17 and a 33 12.50 -17 is roughly ,8 inch height and revs per mile is 657 vs 640 a roughly 2.5% difference. So at 100 mph you'd actually be just shy of 103 on the 33s. Not enough to be concerned, but as said there are ways to change if you have the will. As it happens the stock 275 60 20 is actually a taller tire and 630 revs per mile so roughly 1.5% off the other way.

 

[Racer9]

This 'site was pointed out by another member an it's great for comparing tire sizes. https://tiresize.com/comparison/

 

[GTyankee]

I seem to remember, that Discount Tire once told me that the difference between a 20" tire from a company like General & my Michelins , would measure to be 3 miles off per 100 mile drive

 

[RamDiver]

I seem to remember, that Discount Tire once told me that the difference between a 20" tire from a company like General & my Michelins , would measure to be 3 miles off per 100 mile drive

Yup, the online tire size calculators are only a guesstimate.

The tire manufacturer's spec is better.

The best method to calibrate the speedo is using AlfaOBD with an old standalone GPS and a calculator.

It all depends on how well your medication is working or not working, for the importance of the accuracy.

What's the point of a speedo if it's only close to the true velocity.

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[BWL]

Even worn vs new makes a big difference. Closest you'll get is using the tire manufacturers rotations per mile

 

[RamDiver]

Closest you'll get is using the tire manufacturers rotations per mile

That's the next best thing to using AlfaOBD and a standalone GPS.

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[21SilverRam]

That's the next best thing to using AlfaOBD and a standalone GPS.

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I would have no idea how to use this or how to get one the AlphaOBD