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

[dpatt67]

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.

[Grit_dog]

Don't know about the new Rams in particular but find another dealer.
Better yet find a shop that does a lot of lift kits and big wheels and ask them where they take their trucks.
On my old 13 F250, 3 dealers told me the tpms threshold could not be adjusted. Another issue with bigger aftermarket tire options. Went to Les Schwab and they told me the dlr they use for their customers trucks. Those guys adjusted down the tpms thresholds in like 10 min for me.

[camp-n-family]

You can swap from 17's to 20's without needing to recalibrate as long as the overall diameter is the same. The factory offers different sizes but doesn't need to recalibrate because the diameter is the same.

For example the base Tundra comes with 265/70R17s while my Limited comes with 275/55R20s. The overall diameter differs by 0.9% which is negligible. The smaller rim has a larger sidewall profile (70%) vs the larger rims low profile (55%) which gives similar diameters.

Just find a 20" tire with the same diameter (or close)as the stock 17s and you don't need to do anything. Here is a tire size comparison chart where you can plug in different sizes.

[dpatt67]

It irks me, because I want my gauges to be as accurate as possible. Changing tire size is one of the most common upgrades people do to a truck. Cars and trucks have been built well over a hundred years and there's always been a way of correcting the speedo, whether it was a speedo pinion or easy computer change. Why stop it now? I understand manufacturers not wanting huge tires on trucks because of the additional stress on parts, but changing to a factory size tire?

[The_Mad_Norsky]

mrkoje wrote:
Most likely on those slingshots Dave Smith will have a disclaimer to sign so that you are "aware" of the risks. I bet though that nobody reads them ...

Now you've done got me to thinking. Dangerous indeed! :B

I did sign such disclaimers while getting my truck. The one I can recall off-hand is one which said about putting larger tires and such on the vehicle. I do believe there is at least one more, but gotta go look for that one.

[jus2shy]

The Mad Norsky wrote:
: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.

Those tires are actually slightly shorter than the OEM tire size which is just over 33" (something like 33.2" or whatever). Those Nittos are actually 32.8". No need to calibrate for that.

My OEM tires are 275/70R18 which is 33.2".

[mrkoje]

The Mad Norsky wrote:
: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.

Mostly I don't think Dave Smith would have to deal with to many issues as most of their customers (99%) are not local. Meaning a local dealer will break the news to the customer that their "slingshot" conversion could be a reason for Chrysler to deny a warranty claim.

It's fairly clear in the factory warranty (both 3/36 and 5/100) that a failure of a covered component by a non-covered component will not be covered under the warranty. So if the big tires, lift and programmers could potentially cause an issue - you're done for.

Most likely on those slingshots Dave Smith will have a disclaimer to sign so that you are "aware" of the risks. I bet though that nobody reads them ...

[ScottG]

To answer a couple of posters questions, yes, changing the dimensions in the ABS section takes care of all concerns by fine tuning the tire specs.
But I like the GPS idea the best. Since the speedo is only off about 5%, a GPS will give you the best accuracy (even if everything is totally stock).

[dpatt67]

Apparently it can affect, as mentioned, more than the speedo. Trans shift schedules, Abs ,etc. The trucks at Dave Smiths are interesting as well, and I've read of other dealers, when modifying their trucks, using the Hypertech themselves and just charging the customer for the programmer. I have a local dealer that also modifies their trucks, so I think I'll call and ask what they do. Thanks for your replies..

[stickdog]

If just for the speedo get a cheap GPS that gives speed, ours is right on with our F350 but shows our Focus to be 2 MPH off at 60.

[bguy]

BenK wrote:
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

You speedo is going to read about 5% too high. Meaning you're not going as a fast as you think. You odometer, however, should read pretty well dead on.

[The_Mad_Norsky]

: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]

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]

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]

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.