A couple of tire pressure issues

CarpeDiem · 11-27-2020, 02:08 PM

The inside tires had valve extensions on them when we purchased our rig new. When I check the pressure on them the Viair gage says 140 psi and my digital gage says ~76 psi. Also when I pull the trigger on the Viair it doesn’t seem like it is filling. On all the other tires including the car it seems to work fine. The tires say cold psi 110 and the sticker by the driver says
82 psi ????? Suggestions? I filled them based on what was on the tire, then just before I posted this I turned around and saw the sticker - color me confused.

**Eagle5** · 11-27-2020, 02:48 PM

Hi Carpe Diem,
I would get a third source for checking your air pressure. If you really have 140 PSI, then many compressors are not pressurizing to that level, and hence no air would flow into the tire. The digital gauge at 76 PSI is a really different reading. Very few of us own Calibrated instruments, so sometimes you need to replace with new, and when in doubt, throw it out. I use this gauge for my tires:
Oasser Tire Inflator with Tire Pressure Gauge
Eagle5

**Eagle5** · 11-27-2020, 02:51 PM

... additional ...
The maximum pressure on the tire is for its maximum load. Your recommended door label pressures mean that your tires are not loaded to their maximum. Of course, air never leaks into a tire.

rk911 · 11-27-2020, 03:12 PM

Not sure what a 'Viair gauge' is but that or your digital gauge would seem to be malfunctioning.

you don't say what sort of rig you have but from your post I'll assume it's a Class A motorhome. if so and it has 19.5" or 22.5" tires the correct way to inflate tires is...

- load your MH as you would for a trip including food, fresh water, full fuel and LP tanks, clothing, supplies, pets, other stuff and people.

- then take it to a certified scale and get individual axle weights (corner or "tire" weights are better but axle weights will do for now).

-compare the scale weights to the published GAWR (gross axle weight rating) for that axle. If the scale weight on either axle is greater than the GAWR you'll need to offload some weight on that axle before proceding.

- assuming the scale weights are less than the GAWR look online for the inflation table for your brand of tire. if you can't find it then use either the Goodyear or Michelin inflation tables. For the best and safest ride inflate all tires on the same axle to the lowest or minimum inflation for the load being carried on that axle. let's assume that the actual weight on the rear axle is 10,000-lbs. look at the inflation table, find your tire's model name/number and/or load-range and then run your finger across that line until you see the column that is equal to or greater than 10,000-lbs. that's your minimum inflation.

- i round up to the next 5-psi, some others round up to the next 10-psi, some don't round up at all. personal preference. some will advocate just inflating the tire to the max pressure listed on the sidewall. that is an option but unless your scale weight indicates that pressure your ride will be hard and stiff and there could be handling issues. Conversely, under-inflating your tires will cause them to overheat which could lead to tire failure, increased braking distance and handling issues.

- when you have time check https://www.rvsafety.com/rvweighing. these folks are commonly known as 'Aweigh-We-Go'. their mission is to help RVers ensure that their tires are properly inflated for the weight being carried. they have portable scales and show up at RV rallies around the country or if you find yourself in south Florida make an appointment at their HQ to get your corner or tire weights.

- always check your tire inflations when the tire is 'cold' meaning it hasn't been on the road. i check in the morning before we break camp. you may find a small discrepancy between tires in the shade and tires in sunlight when checking. my experience is it won't usually be more than a few psi difference. and be sure you have a good, quality tire gauge. I prefer a "trucker style", a long barreled with chucks on both ends of the head for checking inner and outer rears.

- if you use valve extensions (and I do) make sure they are quality and tight. inferior extensions can cause leaks.

good luck.

CarpeDiem · 11-27-2020, 04:26 PM

As far as my not indicating what rig I have, when I typed the post I wasn’t logged into the site. Apparently that is why my signature line wasn’t at the bottom. We have a 2020 Vista 29VE and a 2013 CRV toad. �� Thanks for all your input.

Winterbagoal · 11-27-2020, 04:27 PM

I used to run the tires on my Sunstar 26HE nearer to the high end of the maximum cold inflation pressure (110psi) range, closer to 100+psi. If that was too much for the loaded weight, running them harder improved (albeit slightly) the rolling resistance, and the fuel economy of the very thirsty V10/6spdwTH/3valve combo. If I was loaded more heavily, the extra pressure would hande the added load. So that was a win/win situation.

The 82psi number is probably the absolute lowest recommended cold inflation pressure, for a "not loaded for travel" coach, and if you load it up at that number, your tires will look like they're going flat, and it's dangerous because you're putting more strain on the sidewalls. Potential for "kaboom".

These comments are based on my personal preferences. I typically run my tires at the harder end of the scale, on everything I drive.

CarpeDiem · 11-27-2020, 04:29 PM

The Viair is a portable compressor, designed for dual wheel RV’s. Max pressure supposed to be 160 psi.

Winterbagoal · 11-27-2020, 04:44 PM

Quote:

Originally Posted by CarpeDiem

The Viair is a portable compressor, Max pressure supposed to be 160 psi.

That might be part of the problem.
Although, many on these forums worship the Viair products.

cbeierl · 11-27-2020, 05:27 PM

The pressures on the sticker by the driver provided by Winnebago should be the correct pressure for the OEM tires when the vehicle is loaded to its maximum capacity. Checking the tire manufacturer's inflation tables should validate that information. (If the OEM tires have been replaced with different tires the sticker number may no longer be valid for those new tires.)

In the absence of actual weights (ideally individual wheel position weights) you should assume that the vehicle is loaded to maximum capacity when calculating your tire pressures.

CarpeDiem · 11-27-2020, 05:45 PM

Quote:

Originally Posted by cbeierl

The pressures on the sticker by the driver provided by Winnebago should be the correct pressure for the OEM tires when the vehicle is loaded to its maximum capacity. Checking the tire manufacturer's inflation tables should validate that information. (If the OEM tires have been replaced with different tires the sticker number may no longer be valid for those new tires.)

In the absence of actual weights (ideally individual wheel position weights) you should assume that the vehicle is loaded to maximum capacity when calculating your tire pressures.

That is what is throwing me. I worked in the service dept of auto dealers for 20 years and the door sticker always matches on OEM vehicles.

Any thoughts on the inside tire question?

Wyatt · 11-27-2020, 10:06 PM

Might I suggest you read this post, dealing with many of your very same issues. Once you find Tireman’s post, follow the link to his blog. He’s an expert on tires, and will give you the exact answers you need.

https://www.winnieowners.com/forums/...ns-355847.html

Inflating to the max tire pressure on the tire scrapes the heck out of me, as once you get rolling, they will heat up and exceed the maximum inflation allowable.

Secondly, the VAIR compressor, as previously mentioned, is no doubt unable of inflating to the advertised pressure. I had a similar experience, and had to change out the pressure valve. That said, once you get the right pressure, which is probably closer to 85#, your VAIR will do fine.