2022 Dually Front Tire Pressure

[SSchang]

I noticed that my dually 3500 has 80psi for the front tires on the door sticker. I had several 3500 SRW trucks in the past, and as far as I remember the sticker was 65psi for the front tires. What's different in the the front end of the dually that increases the fronts to 80psi?

 

[lpennock]

Dually fronts are 80. SRW fronts are 65. Load rating on the dually tires are less than the SRW tires which is why there is the difference.

 

[Cummins12V98]

Your DRW is a HEAVY MO-FO. It needs all of the 80psi. Rears run them at 30-35psi unloaded and rears know your weights and use the weight inflation chart and add 5psi. Load at 9,750# needs 65psi.

Do your self and your tires a favor and get it aligned to 1/64" Toe setting!!!. Rotate fronts ONLY side to side every 15k leaving the rims in the same position and the tires will be rotating the same. Never touch the rears.

Another suggestion is get a set of Michelin's and sell the POS NEXEN's as they WILL give you tread separation at around 30-35k. Dumped mine at 200 miles on the ODO. These Michelin's have 55k on them with plenty of tread doing what I suggest above.

 

[lpennock]

My Nexen slipped a belt on on front at 12k miles and the other front at 13k miles they were all replaced at 14k with General atx.

Agree on getting the toe set between 0-1/64"

BTW front axle weight of drw and srw are almost the same. The pressure difference is due to load rating.

 

[AH64ID]

DRW and SRW both have the same 6K rated axle, the difference is the rubber. The added curb weight of DRW is almost entirely on the rear axle.

The DRW tires have a load index of 120, which is 3085lbs at 80 psi, so they need 80 psi for the FAWR.

The SRW tires have a load index of 125, which is 3640lbs at 80 psi and 3085lbs at 65 psi… so 65 psi is all that is needed for the FAWR.

 

[Cummins12V98]

Loaded my front axle is 5,780# so yes 80psi is needed.

 

[AH64ID]

Loaded my front axle is 5,780# so yes 80psi is needed.

Sounds about right. I run anywhere from 5,080#-5,900# on the front axle depending on the load/loading/trailer.

 

[Cummins12V98]

Sounds about right. I run anywhere from 5,080#-5,900# on the front axle depending on the load/loading/trailer.

Thats full fuel, wife and I plus at least 500# toolbox hitch and RV pin of 6k.

 

[PRS]

So the tires on my DRW are rated for 11340# @ 80psi. The sticker on the door says my rear gawr is 9750# @ 65psi. with my current tires. Which is my actual gawr? And is it due to tires or axle capability?

 

[AH64ID]

Your RAWR is 9,750lbs, and it’s not based on tires or axle capability.

There isn’t anything solid on what dictates RAWR for the DRW, but I suspect it’s getting into design limits of the frame.

 

[User113]

So the tires on my DRW are rated for 11340# @ 80psi. The sticker on the door says my rear gawr is 9750# @ 65psi. with my current tires. Which is my actual gawr? And is it due to tires or axle capability?

Manufacturers have a lot of flexibility in how they assign weight ratings.

The relevant U.S. Federal regulations on that come from 40 CFR 1037.801:

Gross axle weight rating (GAWR) means the value specified by the vehicle manufacturer as the maximum weight of a loaded axle or set of axles, consistent with good engineering judgment.

Gross combination weight rating (GCWR) means the value specified by the vehicle manufacturer as the maximum weight of a loaded vehicle and trailer, consistent with good engineering judgment. For example, compliance with SAE J2807 is generally considered to be consistent with good engineering judgment, especially for Class 3 and smaller vehicles.

Gross vehicle weight rating (GVWR) means the value specified by the vehicle manufacturer as the maximum design loaded weight of a single vehicle, consistent with good engineering judgment.
​

Some of the considerations that companies take into consideration as part of "good engineering judgment" include things like emissions. I remember reading about one European car maker (can't remember right now which one) that, when the emissions requirements were changing from one year to the next, simply changed both the tire specifications and the GVWR for the sole purpose of placing it into a different emissions bracket so they wouldn't have to re-do the emissions systems at that time (I also don't remember if that was to avoid U.S. emissions or European emissions).

Bottom line: Nobody other than the manufacturer knows why the ratings are what they are.

 

[Cummins12V98]

80 fronts all the time, 30 rears unloaded and 65-67 full RAWR. Alignment 1/64" TOE.
[/ATTACH]

 

[slowmover]

CAT Scale phone app
https://catscale.com/cat-scale-apps/

There’s only one way to determine proper air pressure — it’s over a short range — and that’s via weight scale values. The minimum to maximum ideal for a given loading.


Tire Manufacturers Load & Pressure Table

http://www.barrystiretech.com/loadtables.html
(Plenty more informative reading here and at Tire Rack, etc. Download tech info from your tire manufacturer).

Too much air is as much a mistake as too little. Too much is a common RV’er sin. Screws up braking & handling as well as wet surface traction.

I use the phone app several times weekly. The Steer Axle doesn’t change much on a big truck or on a pickup when loaded correctly. The Drive Axle of a pickup is where one needs to know the range from typical Solo use to being loaded heavily and/or towing. From 50-psi solo to 70-psi covers almost all my range, as an example.

Part II is respecting vehicle manufacturer range as it’s inside the tire manufacturer’s range (shorter). I can run tires lower than what Dodge recommends when Solo/Empty, but found there’s no reason to do so.

A 121 Load Index tire as example is pretty much the same pressure versus load numbers across tire brands & models. I’d get the specific data and keep it in the glovebox with notes attached. CAT Scale values required for accuracy.

— Cold reading after sitting overnight before sunup is best start. Adjust up/down from cold numbers after going across weigh bridge. Ck and re-adjust following morning.

Tire warmup is lengthy in time. It’s pretty much 1.5-hrs before equalization occurs given steady-state travel. Test is after scale value pressure is correct, then a glide into rest area using minimal brakes to get a road check after that 1.5-hrs. 5-7% rise from cold is spot on. 7-8% is “okay”. 9-10% means needs more air (try 5-psi over base on 121). Find the minimum. Continue testing until the “safe” minimum established.

— Calibrated air gauges ain’t cheap. The testing above is as much about your tire gauge as it is anything else. The known variance from yours to one that’s truly accurate.

There a day one finds his tires low. But how low is too low? (Reason for knowing minimum). 10% is the red flag.


CapriRacer and TIREMAN9 are tire engineers. Both blogs worthy reads.

https://www.rvtiresafety.net/

See what is said about tire gauges (pressure and tread depth).

.

 

[Cummins12V98]

Tires pictured above have a bit over 67k on them.

 

[SSchang]

So I used an online converter to convert 1/64" to to degrees. It came out at .144 degrees per side, or .288 degrees total. Does that sound right?

 

[AH64ID]

So I used an online converter to convert 1/64" to to degrees. It came out at .144 degrees per side, or .288 degrees total. Does that sound right?

I think it's even less that that, I come up with 0.028°.

Thuren specs are 0-5°, so that's probably accurate. 1/64" would be total toe thou, not per side. I'd just take the Thuren specs to an alignment shop and have them follow those.

 

[AEdelheit]

I think it's even less that that, I come up with 0.028°.

Thuren specs are 0-5°, so that's probably accurate. 1/64" would be total toe thou, not per side. I'd just take the Thuren specs to an alignment shop and have them follow those.

To clarify Thuren specs a 0.00-0.05deg not 0-5 deg. any sort of inch measurement is very inaccurate as it would change with tire diameter.

 

[AEdelheit]

Loaded my front axle is 5,780# so yes 80psi is needed.

Curious of what the weight rating per tire is , I would assume around 3,600 per tire which would give you a tire capacity of around 7,200 so in that case 80psi is not needed? Never really seen a truck without a fairly heavy payload or added weight on the front actually need 80 psi in the front.

 

[AH64ID]

Curious of what the weight rating per tire is , I would assume around 3,600 per tire which would give you a tire capacity of around 7,200 so in that case 80psi is not needed? Never really seen a truck without a fairly heavy payload or added weight on the front actually need 80 psi in the front.

235/80R117 have a LI of 120, 3085lbs at 80 psi.

80 psi is needed for the FAWR.

75 psi is good for 5,880lbs

70 psi is good for 5,610lbs