Spedometer

[Newsa]

Does the spedometter run off of the rear differential on 4th gens?

 

[gsbrockman]

What's a "spedometter" ???? :-laf

 

[Deleted member 995608]

What's a "spedometter" ???? :-laf

It's part of the Muffler Bearing assembly.

 

[jus2shy]

Does the spedometter run off of the rear differential on 4th gens?

No, just about all new vehicles now a days use the wheels-speed/tone rings on each corner of the vehicle. They need to monitor speeds at all 4 positions in order to make a choice on what ESC or ABS routines are needed. That's why when you re-gear the truck, you don't really need to re-program for speed accuracy. Mostly just to change the shift points.

 

[Newsa]

Speedometer

 

[Newsa]

So if I put one inch bigger outside diameter wheels on, my speed won't be accurate?

 

[Cummins12V98]

So if I put one inch bigger outside diameter wheels on, my speed won't be accurate?

Me thinks that is correct!

 

[Newsa]

http://tire-size-conversion.com/speedometer-calibration/

Ok. I found this to answer my question. See above.

If I go from stock 245/70/17 's to Stock (bought someone else's stock rims and new tires on ebay)

To stock 275/70/18's, I will actually be going 5 MPhil faster than my speedometer reads at highway speeds.

Thanks for all your input . .... Even you GSBman.

 

[TRAMPLINEMAN]

My factory tires were 275/70 18's. I put 35's on and now at 73 on my speedometer I'm actually going 75.

 

[TRAMPLINEMAN]

Here's your tire difference.

 

[Newsa]

View attachment 93513

Here's your tire difference.

That confirms what I saw on a different ture calculator.
I'm focusing on the 8.7% Increase in circumference which means a 8.7 % increase in speed.

60 mph × 1.087 = 65 mph. Etc

 

[gsbrockman]

So if I put one inch bigger outside diameter wheels on, my speed won't be accurate?

Hard to answer that question.......without knowing the overall diameter of the tire you'd be using.

Now......if you were driving it on wheels ONLY.....yes, there'd be a difference in spedometter. :-laf

 

[Newsa]

Hard to answer that question.......without knowing the overall diameter of the tire you'd be using.

Now......if you were driving it on wheels ONLY.....yes, there'd be a difference in spedometter. :-laf

What part of outside diameter did you not understand?

 

[Newsa]

Actually, I was thinking actually an increase in closer to 2 inches diameter. One inch on the rims, and another inch on the tire .

But hadn't measured. I was thinking an inch increase on the radius.

 

[gsbrockman]

What part of outside diameter did you not understand?

There was NO tire information in post #6 that I originally quoted..... correct???

I do see the tire info from Tramplineman though...
In all seriousness though :-laf if one opts to go with a different OEM size, especially with a 3.42 axle truck, it would be in their best interest to visit a dealer and get that size changed in the ECM to more optimize shift points.

 

[TRAMPLINEMAN]

^^^^^I agree, except if you have a G56!!

 

[Newsa]

There was NO tire information in post #6 that I originally quoted..... correct???

I do see the tire info from Tramplineman though...
In all seriousness though :-laf if one opts to go with a different OEM size, especially with a 3.42 axle truck, it would be in their best interest to visit a dealer and get that size changed in the ECM to more optimize shift points.

I agree. I haven't actually put the new ones on yet. I am waiting closer to my trip up north this December/January to make the switch.
I'm getting as much mileage out of the 17th as I can before switching. I'm going to wear the old ones down to 1/8 before seeing the dealer.
Anyone know how much a visit like that to the dealer costs ?
Much appreciated if you could advise me on that.

These Firestone HT's that came stock on my 2500 are atrocious on wet roads. I don't want to be driving on the why and hit a slick.patch in HT's. Not even in 4x4! Can't imagine how bad these HT's are on Ice/snow. I might put the HT'S back on after out winter trip because they are fine for Miami, Fl.

Some day, I'll get off the pot and visit the dealer. Lol

 

[Newsa]

Actually, since I have a g56. I will optimize the shift points by adjusting my driving.
But will visit the dealer to get the speedo recalibrated if it's not cost prohibitive.

 

[Newsa]

Had the rear wheels break loose and spin while entering the freeway for a few seconds on wet roads.
The MPH on the speedometer seems to record what the rear wheels are doing. Seems like the ESCAPE only applies brakes for when one wheel per axle is spinning out. If you have the limited slip differential, and both rears are spinning, it doesn't trigger ESC.

 

[jus2shy]

Had the rear wheels break loose and spin while entering the freeway for a few seconds on wet roads.
The MPH on the speedometer seems to record what the rear wheels are doing. Seems like the ESCAPE only applies brakes for when one wheel per axle is spinning out. If you have the limited slip differential, and both rears are spinning, it doesn't trigger ESC.

ESC = Enhanced Stability Control. I had a different experience. I was in the snow and accelerating. Before my tires could spin-out, the engine was immediately pulling throttle and not allowing any wheel slide. I think the Speedometer setting is to read the highest value. However, the computer does record values at all 4 corners, this is how it figures out to apply stability control and abs on which corner (for braking).