What tire pressures are you running?

HandyDan · December 02, 2015, 12:41 PM

Just who at the factory decides what the air pressure should be? I'm picturing several guys in white coats doing scientific tests, like on Mythbusters, to determine the optimum pressure for the average load. In reality, it is probably Joe Blow at the end of the assembly line that says his brother's next door neighbor swears that 65 is what he always uses for his Chevy step van and it has always worked for him.
And, I'm surprised that on the official data plate the name of the manufacturer is Chevy. That doesn't sound very legal to me.

Rickf1985 · December 02, 2015, 08:08 PM

Dan, Check the rims on a spin balancer. I will bet you find some of them are not round. That is the problem I found on mine. I thought I had it made when I found a guy that had a full set of brand new never used rims left over from a stock of spare tires for utility trucks. The tires aged out so they had to throw them out, brand new tires!. The utility company decided they were not going to stock tires anymore and just buy new ones as needed so he had these rims. I bought them for 40 bucks a piece but wanted them checked before he put the tires on. He was a little upset with the time wasted but did it anyway and damn if three of them were not bent! Brand new rims. bent! I still have two on my rig that are just bent a little bit nut you sure do feel it right at 65 just like you.

Rickf1985 · December 02, 2015, 08:11 PM

Remember that the tire tech has changed a LOT since those pressures were posted. The old Michelins on mine had 65 lbs in them and looked fine but these Samsons look low at 65. If the sidewall is hotter than the tread then they get more air, no if, ands or buts.

Rickf1985 · December 02, 2015, 08:15 PM

And I also notice that the tire your door sticker calls for is a bias ply tire, not a radial. Stiffer sidewalls did not need as much pressure in some cases. Still needed to check temps. Before IR guns I always felt all my tires at every stop. As I did my walk around I would feel the tread and the side. You could tell if they needed air before even getting the gauge out.

DRMousseau · December 03, 2015, 03:10 AM

I do the same Rick,... feel those tires immediately at every stop. I also have an IR temp gauge. The ol' Winnebago had small tires and carried a heavy load. Hot roads were a problem so much I sometimes waited for cooler night and mornings to run.

But I learned a lot this year. Most importantly,.... these are "TRUCKS", not cars!!! While lower tire pressures in a car may be "comfortable", they are a REAL hazard in trucks, especially an RV, with or without a load!!! While those "stickers" state a vehicle manufactures recommendations, they are mostly for comfort. HA! Comfort in a truck!?!? I'm still not convinced that radials belong on a truck!

I now follow the "TIRE manufactures" recommendations on the sidewalls, and have learned there's no harm in running maximum pressures as stated on them. Jus check mine on the Cruise Air II last week due to cold weather,... brought 'em all up to 100psi as stated on sidewall. Ya,.... like driving on "wooden wheels", solid and positive handling, and slick as hell on the icy roads here!!! But what should I expect,... IT'S A TRUCK!!! LoL!!!

TripleJ · December 04, 2015, 01:47 AM

Believe it or not, the factory put load range C (or D, I cant remember which) tires on my 1985 28'. The max inflation pressure would be 65 psi or 75 psi respectively.

I put load range F tires on it when I replaced them, which according to the factory placard should be wildly overkill. The max psi on these tires is 110 psi which is 15 psi OVER what the rims are rated at. 95 psi max is stamped into the steel

I believe the ride and handling on my rig are negatively affected by these tires. Luckily I only replaced the two steer tires. Before I return to the tire store I will have a weight slip with me, and a more educated idea of what I want. While I cant imagine a load range C tire is appropriate (I don't even think double coin makes an 8R19.5 in C) their inflation chart shows the load range D tire to be good for 2835 lbs single at 80 PSI. I doubt my front end weighs 5000lbs (I guess I could be wrong) But I believe this would be a much more appropriate tire than trying to run the load range F tires at 20-30 psi UNDER their max inflation pressure (that's 20% or more underinflated!).

That is, its better to run the load range D tire within a few % of max psi, than run an overkill tire WAY under its max inflation pressure (both within the vehicle's weight safety margin of course)

I believe theres more to it than just the weight numbers. An overly stiff tire stresses the chassis and the driver unnecessarily. It affects the vehicles ability to drive in a straight line and affects the traction characteristics, wears the tread unevenly, etc.

The place I got my tires services big rigs, I think they were a little out of their element with my little RV...

legomybago · December 04, 2015, 11:09 AM

I've heard of guys running F rated tires at lower PSI and loving the handling characteristics. I think you put the wrong tires on for your application though, you would be fine with an E rated tire. Probably be fine with a D, but you need to weigh the rig to be sure.

Rickf1985 · December 04, 2015, 11:42 AM

You do not have to run the tire at the max rating on the sidewall! This is a mistake that is made by way too many people and it is also bad advise that is given out far too often. That number is just that, MAXIMUM SAFE PRESSURE for that tire. It is NOT the recommended running pressure for the tire in your application. Unfortunately neither is the tag on the door since those tires do not exist anymore. Like I said, you have to experiment with temps on the tires. If the sidewalls are getting warmer than the tread then you need to go up on the pressure a few pounds. Too much pressure will just wear out the center of the tire and also give you less traction.

Elandan2 · December 04, 2015, 12:30 PM

I still think the safest way is to use the "Load and Inflation" tables for the size and brand of tire you have. That way, you know what the minimum amount of air you need to carry the load on each corner. Of course, that will require a trip to the scales to get accurate weights. Rick

TripleJ · December 04, 2015, 01:13 PM

I bet there are a lot of people in older 20-30 foot rvs that are in the same boat as me. In my situation theres no safe number to run my tires on the inflation pressure chart, the numbers dont go that low. If they did it would be telling me to run my tires at like 50 psi which cant possibly be a good idea. Of course i could be way underestimating my front weight.... Theres a scale down thhe street, i gotta stop in a see how to do it

Rickf is your sidewall vs tread temperature thing supported by literature anywhere or is it your own best method? It seems logical enough but id like to hear that a tire maker supports it too

Sasquatch · December 04, 2015, 03:36 PM

The only way to properly find what pressure YOU should run in YOUR coach is to stop at a truck stop or roadside weigh station and weigh your coach by axle. Write this down. Then go to the website of the tire manufacturer you are running and download the inflation table for those tires. Look up what the manufacturer recommends for pressures for the load you have loaded. As a safety margin I add 5psi to those numbers.

What I run in my coach may be very wrong for you in your coach, even if we have the same rig because we would load them differently. In my '76 Executive with 225/70/19.5 Toyo radials I run 75psi in the front and 70psi in the rear. If my Triumph goes on the rear bumper rack, the rears go up to 80psi and the fronts down to 70psi.

I run a Smartire TPMS system that displays pressures as well as temperatures for each tire inside (more accurate). It is not uncommon on a hot day to see 150 degrees in a tire. This is well within the safety margin of the tires. Manufacturers set the warning at 194 degrees where the tire will start failing.

Rickf1985 · December 04, 2015, 05:55 PM

What these guys are saying about weight/inflation charts is right on the money, BUT, as Triple J is saying sometimes the charts don't go that low or some companies just don't have them. Triple J, To answer your question, that is how we did it in trucks along with the very scientific "tire beater bar" where you would just go around with a bat or metal bar and beat on the tires. (Honest officer, that is all it is for) You could tell by the sound if they were good. That was just an indicator and if there was question you got the gauge out. With full size trucks it was a little easier since you ran 110-120 lbs. in all tires since you were usually hauling maximum load. Same principals applied though, if the sidewalls were getting hot then the pressure was most likely too low and you better check it. You know all those road gators you see on the road? (Tire carcasses) 99.5% of them are there due to low pressure and carcass failure due to heat.
Once you establish your best pressure for your rig then you are set after that. Probably the best invention ever made is the TPMS that mounts inside and warns you if a tire is getting hot or low. Most of the over the road trucks use them nowadays.

tmsnyder · July 14, 2016, 02:50 PM

Anyone try the external TPMS systems? They screw on instead of a cap, on each valve stem. The display plugs into a cig lighter port and shows the pressures inside the vehicle. I see them on amazon for about $100. Pretty neat but wondered if anyone had first hand experience.

Rickf1985 · July 14, 2016, 04:35 PM

I haven't see a quality system that covers 6 tires for under 300.00. High two's if you can catch them on sale. You will want a system that is expandable to cover a trailer just in case. The TPMS sensors are usually around 45.00 apiece.

joanfenn · July 14, 2016, 05:10 PM

We will let you know when we pull our trailer. Bought a system after tire blew and took out floor on trailer. It also took out the furnace, water lines and electrical under the dinette. So after buying the system, a new furnace, new tires on the trailer and a few feet of water line. Seems like a darn good idea to us. Plus we can use it on the motor home also.

Rickf1985 · July 14, 2016, 05:19 PM

Basically the same reason I want one, what system did you get and how much did it cost?

FN Duck · July 14, 2016, 07:12 PM

I use this type of valve cap. They work and have had no problems
http://accu-pressure.com/eShop/product_info.php?products_id=31&osCsid=2703b16a2fde19c3c3a79c9bf5166500

If I was rich and famous I might try these .
http://www.accu-pressure.com/cgi-bin/Store/index.cgi?exact_match=yes&product=pro_wireless_monitors&cart_id=4021672.92301

joanfenn · July 14, 2016, 07:22 PM

those two are the same product.

joanfenn · July 14, 2016, 07:23 PM

Rick I will have to get back to you on that. Hubby has it hiding right now so will have to ask him when he gets home

M & J · July 14, 2016, 08:16 PM

He must be rich and famous already Joan.

joanfenn · July 14, 2016, 08:19 PM

Yes I guess so...........

Rickf1985 · July 14, 2016, 08:41 PM

He must also be able to run REAL fast to see what they read while driving down the road. If I need to stop and check I can use a tire pressure gauge.

joanfenn · July 14, 2016, 10:09 PM

We have The Hawkshead SystemTAL6C. 339.00 us. Don't know how it works yet but it seemed to have good reviews on it. Cheaper then replacing everything again for sure.

tmsnyder · July 15, 2016, 08:09 AM

There are 8 tires just on my RV, no plans on towing anything. But I have the dash area where I tore out the old CRT screen TV and was going to make a panel for charging phones and holding stuff. For $99 each for 4 tires, I would put in two power ports for two systems and have the pressures on all 8 tires displayed. IF the systems work. Something like this, $89 x 2:

https://www.amazon.com/SNAN-Pressure-Monitoring-Interface-Temperature/dp/B01C064XJU/ref=sr_1_10?s=automotive&ie=UTF8&qid=1468584518&sr=1-10&keywords=tire+pressure+monitoring+system

Just to stay on topic, my RV came with load range D tires originally, based on the fact that the dry rotted spare is still on the back and the owner's manual says so. I imagine that they were inflated to 65psi, a pretty typical LR D tire max pressure.

At some point, load range F tires were put on, overkill for the application but my assumption is that since these are more common than D's they may have actually been less money for better tires. Max pressure on the sidewall is 110psi on these, cold, I inflated them to 90psi.

Quote from: Rickf1985 on July 14, 2016, 04:35 PM
I haven't see a quality system that covers 6 tires for under 300.00. High two's if you can catch them on sale. You will want a system that is expandable to cover a trailer just in case. The TPMS sensors are usually around 45.00 apiece.

Rickf1985 · July 15, 2016, 12:28 PM

Mine calls for 65 lbs and if I put that in the radials that are on it now instead of the bias tires it came with the sidewalls get far too hot. I have to run 80 lbs in a load range E tire to keep the sidewalls happy on the radials. That is on 19.5 tires.