GEN V Tire RPM issue Dash full of Lights

[AllAboutViper]

Hi,

I used to have a Custom 20" wheels for my 15' which caused me to buy new tires

Installed Nitto 20"s front and rear, whenever We drive the car, immediately after a while the ABS, Traction, Gauges all will be turned off with the dash full of lights, checked that nothing is wrong with the wheels

Someone advised to check the Tire RPM before buying,

That this issue is because of a tire RPM which is much different than the Stock 19/18" PZeros

So how do i know which 20" tires would fit (same OEM tires RPM)?


Thanks

[Jack B]

One option is to contact Prefix, they can reprogram the PCM. I have used a mixture of tires, some taller and some shorter without issue, i am surprised the pcm set a code, A good scan tool or the dealers witech should give you the answer.

[AllAboutViper]

Contact Prefix, they can reprogram the PCM

The car is currently in Qatar, Taking the PCM to prefix is so hard

No other choice than buying new tires with close RPM

[Jack B]

The car is currently in Qatar, Taking the PCM to prefix is so hard

No other choice than buying new tires with close RPM

Look at my edit

[Lawineer]

The PCM measures speed of the car by wheel speed, not "ground speed." It has no way of knowing how fast you're actually going (hence why the speedo goes up on a dyno). The actual diameter of the tires doesn't matter. What DOES matter is the ratio of the tire diamters stock to new. StockF/StockR vs NewF/StockR.

The only way the PCM would know you changed tire sizes is if the ratio between the front and rear diameter changed. If you exactly doubled the size of the front and exactly doubled the rear (you're talking about 56" mud boggers at this point) the PCM would have no problems (other than incorrect speedo).

IE: Stock: 100 rotations of the front = 90 rotations of the rear. The computer for TC/SC/ABS/etc knows that this is the ratio when the car is going straight. If the front is rotating 100 RPM and the rear is at 600, it knows your rear tires broke loose.

If you lift the car and put 44" mudboggers on the front and 40" rear (that's roughly 90%) it will have the same 100:90 ratio. The speedometer will be off (because it thinks every rotation is about 26" on stock tires and now it's 103") but it will have no way of knowing it's "GPS" speed. But if you made it 44" front and 40" rear (or even 44 square) , you'd have a problem.

I seriously doubt you can, without doing something wild like lifting the car or running big slicks and small skinnies or something, change enough of the ratio to mess up the PCM. It may make SC slightly less effective, but that's about it. You'd probably have t do something that would be silly and perhaps intentional.


There is a ton of leeway in there. Tires wear at uneven rates and it would be a disaster if you couldn't run different track tires or change wheels lol. It can't be that precise and sensitive.

[Jack B]

What is the true diameter of the new tires. BTW do not give us the published spec.

[JonB ~ PartsRack]

The car is currently in Qatar, Taking the PCM to prefix is so hard

No other choice than buying new tires with close RPM

You can purchase a performance PCM pre-programmed as you need. Ships in few days. Cheaper and more beneficial all around than than 4 more tires shipped to UAE

[AllAboutViper]

What is the true diameter of the new tires. BTW do not give us the published spec.

OEM Fronts Diameter: 25" (RPM 832)
OEM Rears Diameter: 27.4" (RPM 727)

Nitto (20") Fronts Diameter: 26.73" (RPM 754.5)
Nitto (20") Rears Diameter: 26.65" (RPM 756.7)

Seems Like It's because of the Slightly Smaller Rear Diameter

Rears Diameter should be bigger,

[Lawineer]

Can you get a lower profile front or taller rear?

[AllAboutViper]

Can you get a lower profile front or taller rear?

That's what i'm planning to do
I'll go 335/30/20 Rear (Diameter 28") RPM 744

[Arizona Vipers]

That's what i'm planning to do
I'll go 335/30/20 Rear (Diameter 28") RPM 744

I still don't think that's going to work. The problem is you raised the fronts almost 1.73" and are only raising the rears .6". So you're gonna be 1.1" off stock, that's too much.

[darbgnik]

Yeah, those tire ratios aren't even close. My car threw a Christmas tree worth of dash lights at me years ago too, when an alignment shop got the steering wheel position way off.

And to add extra planning, it seems some years of Viper are more tolerant to tire discrepancies than others. And without knowing what your car likes, you should probably aim close.