AT4 - MPG Issue & Tire PSI on new Nitto Ridge Grappler Tires & Fuel Rims

[JerseyMikeAT4]

Hi All,  Hoping for some help or feedback here.

 

I replaced my stock AT4 18in Rims and Wrangler Duratrac tires (275 65 18) with 20 x 9 Fuel Rims and Nitto Ridge Grappler tires (275 60 20).  

 

I was getting about 15-16 MPG on the Duratrac's and now only getting 12-13 MPG on my Nitto's which I thought would have improved over the Duratrac's.

 

I have driving approx 300-400 miles thus far in different conditions and my PSI is at around 40.

 

Im hoping that someone here has some incite? 

 

 

Edited April 13, 2020 by JerseyMikeAT4

[steve841]

You're gonna pay a fuel penalty when you go bigger ....

[AdamAT4]

Which nitro tires? 275 60 20 are not much bigger, but if they are 10 ply load E those tires are like 20 pounds each heavier and that will make the truck drink fuel to accelerate.

Most tire companies make all tires over 32" in 10 ply, very few 4 or 6 ply tires in 33 and I csnt find any in 35 that's not 10 ply.

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[Black02Silverado]

Major change in wheel/tire weight.  That will  effect your mpg.

[newdude]

2 hours ago, JerseyMikeAT4 said:

Hi All,  Hoping for some help or feedback here.

 

I replaced my stock AT4 18in Rims and Wrangler Duratrac tires (275 65 18) with 20 x 9 Fuel Rims and Nitto Grappler tires (275 60 20).  

 

I was getting about 15-16 MPG on the Duratrac's and now only getting 12-13 MPG on my Nitto's which I thought would have improved over the Duratrac's.

 

I have driving approx 300-400 miles thus far in different conditions and my PSI is at around 40.

 

Im hoping that someone here has some incite? 

 

 

 

Are they LT tires?  If so, more air wil decrease roll resistance = a bit of MPG increase.  What Grappler did you pick?  Grappler is a loose description as there is the Mud, Trail, Ridge, Dune and Terra Grapplers.  

 

The bigger size isn't helping either as they are now heavier wheels and tires.  

 

Edited April 13, 2020 by newdude

[JerseyMikeAT4]

6 minutes ago, newdude said:

 

Are they LT tires?  If so, more air wil decrease roll resistance = a bit of MPG increase.  What Grappler did you pick?  Grappler is a loose description as there is the Mud, Trail, Ridge, Dune and Terra Grapplers.  

 

The bigger size isn't helping either as they are now heavier wheels and tires.  

 

Yes they are LT tires and are Ridge Grapplers. I dont believe they were that much heavier than OEM.  Even if they were 15lbs heavier or 60lbs total, Im shocked id lose 3 MPG with essentially the same overall size as OEM.

 

With that ratio, if I had my family in the car, Id get 3 miles to the gallon. 

 

Thanks for all the responses thus far.

 

 

[AdamAT4]

Yes they are LT tires and are Ridge Grapplers. I dont believe they were that much heavier than OEM.  Even if they were 15lbs heavier or 60lbs total, Im shocked id lose 3 MPG with essentially the same overall size as OEM.
 
With that ratio, if I had my family in the car, Id get 3 miles to the gallon. 
 
Thanks for all the responses thus far.
 
 

No no, theres a huge difference in rotating mass, 10 pounds per tire would be more like 1500 pounds of payload equivalent.

My uncle did 10 ply tires on his 5.3 8 speed and his fuel economy took a good dive.

The HD diesels dont take much of a hit on 33s vs 35s but o boy do these gas jobs sure do if you add heavier tires whether they are larger or not.

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[Ianwelch001]

Yes they are LT tires and are Ridge Grapplers. I dont believe they were that much heavier than OEM.  Even if they were 15lbs heavier or 60lbs total, Im shocked id lose 3 MPG with essentially the same overall size as OEM.
 
With that ratio, if I had my family in the car, Id get 3 miles to the gallon. 
 
Thanks for all the responses thus far.
 
 

You are looking at 15lbs difference per tire so 60lbs of unsprung weight which is equivalent to 240lbs total. 1lb of unsprung weight is equivalent to 4lbs sprung weight. So 60x4=240lbs. Most mlm people see a 3mpg or so difference moving up to a hybrid tire.

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[blckblt]

Rotational weight of tires can have a huge impact.  On my previous truck (2016 ram rebel) I went from the stock Toyo tires to General Grabbers ATX in the same size and saw a loss of 1-2.

 

If you went larger have verified that your speedometer is correct?  If it is off then any MPG calculated from info from the truck (DIC or manually from trip) may be wrong.

[eppieguy]

Plus your speedometer is off in which will play with your MPG calculations as well.

[newdude]

1 hour ago, JerseyMikeAT4 said:

Yes they are LT tires and are Ridge Grapplers. I dont believe they were that much heavier than OEM.  Even if they were 15lbs heavier or 60lbs total, Im shocked id lose 3 MPG with essentially the same overall size as OEM.

 

With that ratio, if I had my family in the car, Id get 3 miles to the gallon. 

 

Thanks for all the responses thus far.

 

 

 

The tire you've put on is 59.08lbs.  The Duratracs in OE size are 49lbs, so a 10lbs difference per tire.  The tread design is more aggressively interlocked than the Duratrac so that would add resistance there alone.    

 

Not sure what Fuel wheel you picked, but you've also gained 10+lbs minimum per wheel.  OE wheel that came on your truck is 30-31lbs.  Some of the Fuel 20" wheels I was looking at scaled at 49lbs.  

 

What I'm going to suggest is this.  Stop by your local dealer with the information below.  Short story is that if your truck could have been optioned with the 20" wheels from the factory, which on the AT4 is possible, that GM would be able to issue a calibration file that the dealer can then flash your truck with.  The stock 20" tire is the same size you put on, 275/60R20 so GM would have a calibration to do that.

 

If doing this doesn't get everything back to about where you were before changing to what you put on the truck, then I'd be looking at the tires you put on next.   

 

Quote

 

#PIT3271J: Guidelines When Changing Tire And Wheel Size - (Nov 12, 2019)

 

Supersession Statement

This PI was superseded to update the Condition, Recommendation, and Model Years. Please discard PIT3271H.

 

Condition / Concern

A request may be made for a variety of reasons to change the tire size on a vehicle. 

 

Recommendations / Instructions

General Motors will ONLY support a tire calibration for tires that have been sized, tested and designed for the vehicle in question and its applications.  The only way to confirm that a calibration is available would be to visit YOUR sales department. Using the sales order guide, if you can build a vehicle, using the same make, model year, trim, and meet any restrictions listed in the tire section, GM will have a corresponding calibration available. 

 

Note: When changing tire size for new vehicles prior to the first sale and/or a tire/wheel size that may require a different pressure or alter the cargo carrying capacity of the vehicle, refer to #12-00-89-007B: Dealer Responsibility for Cargo Carrying Capacity Labeling.  

 

Once the tire application has been confirmed per the sales guide, contact Techline Customer Support Center (TCSC) (English: 1-800-828-6860, French: 1-800-503-3222 ) to determine calibration availability. 

 

Please do not call Technical Assistance Center for these concerns. 

 

Note: There may be a cost to the customer for this service. This is NOT a feature that is covered under the manufacturer's warranty. 

Examples: 

 

First example -  A customer with a 2019 Chevrolet Silverado 1WT Regular Cab built with 255/70/R17 tires would like to install a set of wheels and tires from a 2019 Silverado 1CX Double Cab, which came with 275/60/R20 size tires. Based on the order guide, the 1WT trim is only available with either 255/70R17 or 265/70R17 size tires. For this reason, a calibration will not be offered for this application.

 

Second example - A customer with a 2018 Chevrolet Colorado 2LT Crew Cab built with 255/65/R17 size tires would like to install a set of wheels and tires from a 2019 Chevrolet Colorado Z71 with 265/65/R17 size tires.  From the order guide, the 2LT trim is only available with either 255/65/R17 or 265/60/R18 size tires. For this reason, a calibration will not be offered for this application either.   

 

 

[Giantpeaches]

Don't just add more air to reduce rolling resistance. too much air = uneven tread wear

[JerseyMikeAT4]

19 minutes ago, Giantpeaches said:

Don't just add more air to reduce rolling resistance. too much air = uneven tread wear

Is 40 PSI considered too much air?  

[JerseyMikeAT4]

43 minutes ago, newdude said:

 

The tire you've put on is 59.08lbs.  The Duratracs in OE size are 49lbs, so a 10lbs difference per tire.  The tread design is more aggressively interlocked than the Duratrac so that would add resistance there alone.    

 

Not sure what Fuel wheel you picked, but you've also gained 10+lbs minimum per wheel.  OE wheel that came on your truck is 30-31lbs.  Some of the Fuel 20" wheels I was looking at scaled at 49lbs.  

 

What I'm going to suggest is this.  Stop by your local dealer with the information below.  Short story is that if your truck could have been optioned with the 20" wheels from the factory, which on the AT4 is possible, that GM would be able to issue a calibration file that the dealer can then flash your truck with.  The stock 20" tire is the same size you put on, 275/60R20 so GM would have a calibration to do that.

 

If doing this doesn't get everything back to about where you were before changing to what you put on the truck, then I'd be looking at the tires you put on next.   

 

 

Thank you very much for your detailed response.  

[JerseyMikeAT4]

1 hour ago, eppieguy said:

Plus your speedometer is off in which will play with your MPG calculations as well.

Maybe a stupid question but is comparing my speedometer to to using Waze and another GPS device (they all report the same) sufficient?