Tire temps

[neoneddy]

Been soldering on while we've had a few issues here and there this summer.

Anyway  I measured my tires coming back to MN from the Dells with an IR gun as part of my walk around during stops.  I measured my steers and tags around 105f, my drives where 135f , I'd expect them to be similar.

I run my fronts at 110 psi, and my rears around 100.   I did have full water tank but empty waste.

Is this cause for alarm? Should I push my drive tires up some? 

[richard5933]

I'd first get an accurate weight by axle. Better even if you can find a scale to weigh the end of each axle, but at least you should know the weight on each axle when the coach is fully fueled and loaded as you normally travel.

Once you know the weight on each tire, you can use the manufacturer's inflation charts to calculate the proper inflation for the tires on the axles. I follow the recommendations of http://www.rvtiresafety.net/ and here is a link to a post of his that details how to determine the proper inflation using axle weights and tire inflation charts for anyone interested: http://www.rvtiresafety.net/2018/06/setting-motorhome-inflation-for-newbie.html

After the tires are set at the recommended pressures, then I'd say it's time to try and figure out the reason for a temperature difference. Might be due to a benign reason like the weight difference on each axle, might be because of the way the airflow is under the coach, or it might be something more serious like a problem with the axle (bearing, brakes, etc.)

[chessie4905]

Heat from engine, trans, brake drums, and drive axle, also restricted air flow will cause higher temps than front. Did all 4 dual tire temps equal?

[luvrbus]

If the temp was the same on both sides of drive axle don't worry about,the drive axle carries the most weight on all buses so they run warmer.  It has always been a practice if you can touch a tire with your hand it's ok.If you follow the inflation chart on your bus and forget about all the axle weighing crap your tires will last longer and the bus will be happy to   

[richard5933]

If you follow the inflation chart on your bus and forget about all the axle weighing crap your tires will last longer and the bus will be happy to

How is it possible to follow the inflation chart on your bus if you don't know how much the axle weighs?

Sorry to disagree, but the chart that came with my bus was calculated for bias belted tires, not modern radials, and there is no way I'd trust it to set the pressure on the Firestone FS400 tires on the bus at the moment. It takes all of about 10 minutes to run a bus through the scales after fueling, and then it's pretty simple to follow the tire manufacturer's inflation chart based on the actual weight the tires are carrying.

[luvrbus]

How is it possible to follow the inflation chart on your bus if you don't know how much the axle weighs?

Sorry to disagree, but the chart that came with my bus was calculated for bias belted tires, not modern radials, and there is no way I'd trust it to set the pressure on the Firestone FS400 tires on the bus at the moment. It takes all of about 10 minutes to run a bus through the scales after fueling, and then it's pretty simple to follow the tire manufacturer's inflation chart based on the actual weight the tires are carrying.

They all sell tires all manufactures will tell you a fully inflated tire will wear longer and improve the fuel mileage. lol and they all tell you if park for long periods of time on concrete place a board under the tire how many people do that.
Folks do what they think will work best and in the trucking and tour bus world they don't care about weighing each axle the chart is their bible and they get 100,000 miles from a set of tires @ 70 mph 
I have a Teltex weight gauge in my bus I can sit in the seat and watch the weight change and no way am I going to adjust tire pressure for a weight difference  JMW I don't care oneway or the other what people do I do what is best for me the 315/80/22.5 costs a lot and I run just below the max loaded or empty 

[neoneddy]

I see my drives are rated at 125PSI... I think I'll push them up and see if I notice any change.

[chessie4905]

People weigh their coach, check the tire charts, set their tires to the recommended pressure at 85 to 90 psi or so. Then after driving it, they don't like the squirmy feeling, then raise the pressures to 100 to 110. If you notice, almost all use that pressure range. Only ones that go higher on front or rear have pretty heavy rigs, close or over rated gvw, especially on front axles.
Neodaddy, hit a pothole with them at 125 and then put your fillings back in.lol

[luvrbus]

If you weigh all the axles on a bus if you go by the tire manufactures pressure chart and not the bus manufactures chart you will be buying new tag axle tires in hurry.Tag axles don't carry a lot of weight but they take a higher PSI so don't always believe what you read on a chart supplied by a tire co.You guys with the 2 axles buses maybe can get by   

[richard5933]

Don't know about those with a third axle - never had one and don't want one. Always driven two axle coaches and buses. Here's the chart that is in the Operator's Manual for our 4108a. Even using the GM chart that came with the bus, you'll need to have some idea of how much weight you're carrying. I'm also posting a piece of the Firestone chart for the tires currently on our coach, FS400.

Now factor in the vast difference between the tires that are the subject of the charts (bias belted) and those on most buses today (higher pressure radials) there's no way I'd use the GM bus charts. The max on the GM chart is 100 psi while the max on our FS400 tires is 130 psi.

Based on our actual weight plus a safety buffer our minimum cold inflation is about 85 psi, but we run at 95 - 100 psi since handling at 80 psi was a bit too sloppy for my taste. No way I'd run at 130 psi unless I wanted to shake my teeth loose going down the road. Besides, running at too high a pressure can actually reduce traction, reduce tread contact area, and cause premature tire wear.

There is no need to readjust every time a few pounds are added - I weighed the coach with full tanks (fuel, water, and LP) and then add a small buffer for safety's sake since I know we're going to pick up more weight as we shop along the journey.

[luvrbus]

Richard , the cross belted bias tire and radial belted tires have always used the same air pressure when carrying the same weight with the same size tire, I feel bad for the Prevost and Newell  people running 130 psi shaking their teeth out I run 125psi and don't have that problem and my DL3 rides excellent,it could be 9 inch wide rims take that away who knows and you can still buy bias tires 

[chessie4905]

Richard, you need also to take in ply rating. 12 ply, 16 ply, 20 ply, load range g, h, j, k. Each has different load carrying capacities and at rated pressures which are different. Without looking, I'm thinking the bias ply tires were 12 ply in the GM manual specs.

[DoubleEagle]

Tire pressures are all up and down depending on whose opinion prevails. I would go with the opinion of the manufacturer of the bus who has an interest in the safe and efficient operation of the bus. I drove tanker tractor-trailers for a while, and my company required that each tire be checked physically each day, and the pressures recorded. They mandated that every position be set at 90 psi, which they judged was a good balance of tread contact for braking, and for mileage, even though the maximum allowed pressure was 110 or 120. My 1984 Eagle calls for 105 psi on the front, and 90 psi everywhere else. That level tracks well, and the ride is good. Whether going to higher pressures will increase mileage or cause a different wear pattern, I do not know, but I don't want to experiment with my new expensive Dunlop's.

[Ed Hackenbruch]

Keep in mind that no matter what pressure you start out at, in just a matter of a few miles it will go up about 10-12% due to the tires warming up.  

[richard5933]

I guess what's confusing about all of this is the notion to just 'go what the bus manufacturer' recommends. The recommendations GM made were based on speed, load weight, and tire size. The charts gave a minimum psi and there was an allowable range above that.  They made their recommendations based on the tires available at the time and with the bus intended for commercial revenue service.

According to the chart in the Operator's Manual my coach left the factory with G-rated tires, while I'm running L-rated Firestones at the moment. The Firestones also have a chart which is also based on multiple factors. The pressure I run is based on the load being carried as well as how the pressure affects handling, as I mentioned earlier. The pressure I chose does coincidentally fall in the range of pressures on the charts in the GM manual, so in a way you could say that I am following their recommendations if you wanted.

Pressure will go up in all tires as they are driven, but its my understanding that the engineers take this into account when they develop the inflation charts. Our TPMS does monitor temperature, but I don't focus on that too much unless one of the tires spikes differently than the others. Otherwise, all tires are inspected by me at the start of the day and periodically throughout the day when we stop for breaks.