PSI accuracy Viair vs Ford

[SaltyJim]

Question: which do you all think would give a more accurate psi reading? The inflator gauge on my Viair compressor? Or the factory tpms in the Ford e450 chassis on my 2023 Greyhawk 29MV? I checked the tires and added a bit of air before leaving on my current trip. Cold readings about 77 front, and about 82 in the rears using the Viair. Yes a couple pounds extra vs the door sticker. I have the tpms on the dash all the time. Cold reading in the mornings have been around 82 on the fronts, and 86-88 in the rears. Seems weird that the cold readings would be so different. Should the Ford tpms get reset somehow? I would think the Viair would be pretty accurate.

Then while driving the Ford tpms shows psi’s increasing anywhere from 10-15 pounds. Sometimes the rears approach 100 psi. Seem right?

Thanks for all the great knowledge out there.

Jim

[Raines]

I do not know which one would be more accurate but if I were you , I would simply check them with a tire gauge. I do know on my after market tymate tpms that the tire pressures increase 10 to 15 lbs after driving for awhile, so that part is accurate. Also, I personally would not intentionally overinflate the tires. It does not provide you a safer tire but actually makes it a little less safe plus gives you a rougher ride. You would be surprised what a couple psi difference will make.

[craigav]

My bet is the Viair is inaccurate. I ran into a similar issue with mine quite a while back and it (Viair) also reads low (but only ~2psi). Also you have 6 pressure sensors on the Ford (although a common TPMS component), vs the one for the Viair.

What I ended up doing was to purchase an Amazon recommended digital tire pressure gauge and I verified on 3 different vehicles that the tire gauge I purchased matched the TPMS displayed pressures in all three vehicles, so I trust the accuracy of the gauge, and in my case I was able to verify the Viaiar was reading low. I still have and use the Viair but adjust the pressure accordingly. If you have other TPMS equipped vehicles, you could just use the Viair on one of them and see if the gauge on it matches the vehicle's TPMS or is off like it is on your Greyhawk.

It is normal for the tires to increase in pressure once you start driving, which is why it is important to check the pressures when they are cold. I try to check mine very early in the morning as even the sunlight on one of the tires for an hour or more changes the pressure. You might even see more than 15psi increase in the heat of the summer on a very dark/black highway, although I don't recall seeing anything past 18~20 increase at most. ~CA

[SaltyJim]

Thanks, guys! Looks like I'll be bleeding a few pounds before leaving this campground.

[norty1]

You can go nuts trying to get 3 different pressure reading tools to be the same. I check mine cold before leaving with a digital meter. If my truck and my TSPS don't match it, I just note that and keep on trucking, unless it's over +/- 3 psi!

[Hilltopper9]

I use a digital tire gauge and the readings are always within 1 psi of the TPMS readings on my E450. Given that, I would probably trust your TPMS readings more than the VIAIR in the short term, but I'd spend the $20 to get a reliable tire gauge for peace of mind.

[LuckyDuck]

Originally Posted by Hilltopper9

I use a digital tire gauge and the readings are always within 1 psi of the TPMS readings on my E450. Given that, I would probably trust your TPMS readings more than the VIAIR in the short term, but I'd spend the $20 to get a reliable tire gauge for peace of mind.

Any recommendations out there as to a proven reliable brand of gauge? I have several, plus my Viair, and assume the reading that is the same on the majority of them is likely most accurate. I know 1 or 2 psi off isn’t a huge deal, but I’m kind of a perfectionist…

[Hilltopper9]

I use the AstroAI Digital Tire Pressure Gauge 230 PSI Heavy Duty Dual Head. $21 on Amazon.

[SmokeyBear]

Originally Posted by LuckyDuck

Any recommendations out there as to a proven reliable brand of gauge?

I used to do autocross with the SCCA. I still am involved with sports car races. Believe me, tire pressure is a really big deal in racing. The tire gauge I would find most often up and down the paddock is Longacre. That is what I use still, although just on my passenger cars. If you want precision, this is the one to buy. However, I did a search and could not find a Longacre that goes above 60 psi.

[pconroy]

Like Norty, I went around w/ two gauges plus an after-market TPMS, a few weeks ago. None were the same, the largest difference was about 5 psi. In the end, I decided to just pick the digital one. The aftermarket TPMS will just be there to monitor extreme conditions - like a blow out or overheating.

Like craig, I've easily seen 15psi swings.

[billcf7]

None of the gauges from Viar, Amazon or whoever will be calibrated. You just have to get used to the differences and go with it. I would use what Ford has for the TPMS and adjust the rest accordingly

[TCNashville]

I use a Milton gauge, specifically this one. Recommended on the truck forum. It matches my TPMS every time.
https://miltonindustries.com/collect...il-pack-s-986w

[Raines]

Originally Posted by LuckyDuck

Any recommendations out there as to a proven reliable brand of gauge? I have several, plus my Viair, and assume the reading that is the same on the majority of them is likely most accurate. I know 1 or 2 psi off isn’t a huge deal, but I’m kind of a perfectionist…

I love my Jaco digital tire gauge and I love their lightning T series air chuck for getting to the rear dually rims. They make great products

[Jagiven]

Personally I would not trust either. I have a good analog gauge I compared to a calibrated gauge at work. My DW's car is reads, about 4 psi off of that gauge.

[CAG]

I don't get caught up in a pound or two with the reading. Even with today's accuracy, if you think it is a gnats ass you need to think again. It is not going to be that close and if you do, well, get over it!

[LuckyDuck]

Originally Posted by CAG

I don't get caught up in a pound or two with the reading. Even with today's accuracy, if you think it is a gnats ass you need to think again. It is not going to be that close and if you do, well, get over it!

Thank you for the thoughtful advice.

[pconroy]

Originally Posted by CAG

f you think it is a gnats ass you need to think again. It is not going to be that close and if you do, well, get over it!

Slow day at the cabin?

[Scoutmaster253]

Originally Posted by CAG

I don't get caught up in a pound or two with the reading. Even with today's accuracy, if you think it is a gnats ass you need to think again. It is not going to be that close and if you do, well, get over it!

x2

[craigav]

Keep in mind the OP is reporting 5+ difference in PSI. While a pound or 2 isn't a great concern, if you have a pressure gauge that isn't consistent with is reading (vs consistently off by the same amount) you could run into an issue where one tire is 2psi low next to a tire that is 2psi high resulting in a 4+ psi difference.

I know the offset for the gauges I use most often and some read low and some read high, as long as they remain consistent then I am less concerned and adjust for that. However, if you find that the same gauge on the same tire (for example if you check the psi say 5~6 times in a row), if the gauge doesn't read the same or very close to the same each time then I would likely throw the gauge away (depending on how far off each reading was).


I am not sure how much pressure tolerance is OK for dually tires side by side, but with an accurate digital tire pressure gauge that reads in the 10th of a psi, I prefer to match both tires on both sides up with each other and I am less concerned if the gauge is off a little vs if it is consistently off.

BTW, I grew up using the pencil stem pressure gauges with 5# increments (5# for the higher psi gauges), it was very hard to even read them to within 5psi, but now we have digital gauges so having the tires within 1 psi from each other isn't really a challenge. I will add again, that if you check the pressure late in the morning until evening, if any of the tires are in the sun they will read a couple psi higher than they read prior to having the sun on them, which is why I like to check mine very early in the morning whenever possible. (not that I like to get up at sunrise checking my tire pressures.) If none of the tires are in the sunlight, say it is parked in a shady location, then the pressures should be consistent with each other even later into the day. ~CA

[CAG]

Originally Posted by pconroy

Slow day at the cabin?

Not there and won't be for another month. Still two feet or more of snow there at 8K feet and more coming but, to the point, a garage that I took vehicles to, often, had a company come in, monthly to calibrate the air system because they just don't stay where they are put so I use a digital, actually several because there is one in each vehicle, and if they all come out close together I am happy. I also have a gauge on the Viair, and another "rod type" that I keep in the Jeep for airing up and down. The Viair is the most inaccurate of the bunch but it still is not over five pounds and my Jeep lets me know if it is off too much.

There is just not something that you get from China that is going to be that accurate, so as I said don't worry about it unless it is way, way off and then you get another and not use the bad one.


I am terribly OCD, but there are some things that I have learned, are just not worth the stress and worry.