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dpatt67's avatar
dpatt67
Explorer
Oct 13, 2014

May not want to swap tire sizes on that Ram just yet..

I had made a post a week ago about switching wheels and tires on my '13 Ram 2500 from it's factory size of 17" to the '14's 20" size. I got the tires and TPMS sensors switched over to the 20" wheels and then took it to the dealer to have the computer flashed to recognize the new size for the speedo. No go. All the truck would recognize is the factory size. So, if you are looking to change tire sizes on your late model Ram and want an accurate speedo and odo, you are probably out of luck. I post this to let others know that late model vehicles don't want you to change them, even tire sizes.
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  • The_Mad_Norsky's avatar
    The_Mad_Norsky
    Explorer
    Oct 13, 2014
    :h

    Makes me wonder what Dave Smith Motors in Kellogg, Idaho is doing with their new Slingshot trucks.

    Here's a link: Dave Smith Motors modified new vehicles, Ram in this case

    They're putting 295/55/20 Trail-grapplers on these trucks, new, and factory warranty.

    Impressive looking vehicles, I just bought a new Ram 3500 out there. They said they could do a Slingshot conversion with my new dually.
  • BenK's avatar
    BenK
    Explorer
    Oct 13, 2014
    The most accurate OEM dash gauge is the speedometer.

    They don't want their speedo's to a reason for the LEO's to pull you over

    More than TPS & ABS computer needing to know, but the torque management for
    the whole setup and the +5 speed automatic. Toss in traction control and
    anti-sway if you have it. Maybe more computers are involved.

    Anyone know if the tuners also change those functions, other than just
    the speedo?

    PS...the computers count "rev's per mile" to calculate everything and
    the tire's OD is just what we are told
  • dpatt67's avatar
    dpatt67
    Explorer
    Oct 13, 2014
    Yeah, the dealer said it would give him the option of the 20" size, but when he selected it, it would default back to the original size. I appreciate the Hypertech option, my only problem is would be the fact that the dealer would be able to detect the programmer, albeit just for a speedo calibrator. Kinda scares me that they would say a warranty issue would be denied(although hard to prove) due to the programmer. Thoughts?
  • ScottG's avatar
    ScottG
    Nomad
    Oct 13, 2014
    There may be another way the dealer doesn't know about..
    On third gen Rams you had something like 3 different tire sizes to choose from but a little known method of solving for odd size tires (like I have) is to go through the anti-lock brake screens using either the dealers Star-scan tool or an after market programmer like the Smarty Jr. Once you get into that section you can adjust tire height in .1" increments and get your speedometer dead on.
    If you go this route, measure the height of your tires and subtract about .5" to get the closest accuracy without having it read too slow.
  • bguy's avatar
    bguy
    Explorer
    Oct 13, 2014
    If you're not changing the overall diameter of the tires there's no change needed for the speedo. IIRC anything less than 4% error is acceptable.
  • camp-n-family's avatar
    camp-n-family
    Explorer
    Oct 13, 2014
    The dealers are only able to calibrate to sizes that the truck could come stock with. The largest option are the 17's. There are aftermarket programmers that can recalibrate the speedo on the newer trucks. Hypertech and bullydog seem to be the most popular. See here

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