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Topic: Tires (Read 11355 times) previous topic - next topic

Re: Tires

Reply #160 –
On my recent trip to NAC and back I weighed my 2001, U320 coach and Toad at a nice new scale in Casper, WY for $9. I came up with a front axle weight of 12,860lb and the rear (no Tag) 19940.  That is a fully equipped coach on the road with full fuel and ready to go on a voyage. The Toad (Daihatsu Rocky) was 3020lbs.
I run Michelin 275/80 22.5, LRH tires.  With those weights I should run the front at 105psi and the rear at 90psi according to the FT chart.
I had been running 100psi cold on the front and 95psi cold on the rear.  NOT CORRECT as I did not take into consideration the heat build-up while running.  My fronts were showing 120psi on the TPMS and if you look at the Alcoa rims they are rated only for 120psi so I was on the upper limit.
So the answer is to have a cold pressure that gives me 105psi Front and 90psi Rear, for my weights, on the road.  My cold pressure is about 82psi. on the front and 80psi on the rear.
Others may disagree and with different tires there will be a variation, as will different weights of course. But I am a lot closer than I was before and it steers a bit better.
Next challenge is to check to alignment??  That is next weeks job.
Speedbird 1

Re: Tires

Reply #161 –
Quote from: speedbird1 –
On my recent trip to NAC and back I weighed my 2001, U320 coach and Toad at a nice new scale in Casper, WY for $9. I came up with a front axle weight of 12,860lb and the rear (no Tag) 19940.  That is a fully equipped coach on the road with full fuel and ready to go on a voyage. The Toad (Daihatsu Rocky) was 3020lbs.
I run Michelin 275/80 22.5, LRH tires.  With those weights I should run the front at 105psi and the rear at 90psi according to the FT chart.
I had been running 100psi cold on the front and 95psi cold on the rear.  NOT CORRECT as I did not take into consideration the heat build-up while running.  My fronts were showing 120psi on the TPMS and if you look at the Alcoa rims they are rated only for 120psi so I was on the upper limit.
So the answer is to have a cold pressure that gives me 105psi Front and 90psi Rear, for my weights, on the road.  My cold pressure is about 82psi. on the front and 80psi on the rear.
Others may disagree and with different tires there will be a variation, as will different weights of course. But I am a lot closer than I was before and it steers a bit better.
Next challenge is to check to alignment??  That is next weeks job.
Speedbird 1
Tire pressures are supposed to be set cold. They will always read high when hot. Fronts on my crane cold are 110 I get over 130 0n a very hot day.
Page 24 says do not exceed cold pressures marked on the wheel

https://www.arconic.com/alcoawheels/catalog/pdf/2017_service_manual_english.pdf

Re: Tires

Reply #162 –
Quote from: cubesphere –
" Looking at it I wonder if having the toad was a positive or negative factor. "

That is entirely dependent on how the braking system functions on the toad relative to the coach. The toad could be used as an anchor to help keep coach in a straight line, however, in most cases the weight of the toad just adds to a loss of complete equilibrium, not good. Most of the time in racing, there is an old saying, when in doubt gas it for good reason although, counter intuitive to most.
Funny you should say that, on a motorcycle say the same "when in doubt, power out" not quite sure how that works on a rear heavy coach with heavy rear brake bias. One thing for sure experience isn't in textbooks, and unfortunately only one way to get it.

Re: Tires

Reply #163 –
Quote from: speedbird1 –
On my recent trip to NAC and back I weighed my 2001, U320 coach and Toad at a nice new scale in Casper, WY for $9. I came up with a front axle weight of 12,860lb and the rear (no Tag) 19940.  That is a fully equipped coach on the road with full fuel and ready to go on a voyage. The Toad (Daihatsu Rocky) was 3020lbs.
I run Michelin 275/80 22.5, LRH tires.  With those weights I should run the front at 105psi and the rear at 90psi according to the FT chart.
I had been running 100psi cold on the front and 95psi cold on the rear.  NOT CORRECT as I did not take into consideration the heat build-up while running.  My fronts were showing 120psi on the TPMS and if you look at the Alcoa rims they are rated only for 120psi so I was on the upper limit.
So the answer is to have a cold pressure that gives me 105psi Front and 90psi Rear, for my weights, on the road.  My cold pressure is about 82psi. on the front and 80psi on the rear.
Others may disagree and with different tires there will be a variation, as will different weights of course. But I am a lot closer than I was before and it steers a bit better.
Next challenge is to check to alignment??  That is next weeks job.
Speedbird 1


All the tire charts are for cold tire pressure, not for hot after driving.

Re: Tires

Reply #164 –
My point was not to state the obvious (for some) but to show the numbers from a basic level as related to any similar FT coach of about the same weight.
From the forum it has been fairly clear to me that few have any idea of the weight of their coach so my numbers were to give some idea and to start at the beginning!!! 
Speedbird1.

Re: Tires

Reply #165 –
Quote from: speedbird1 –

I run Michelin 275/80 22.5, LRH tires.  With those weights I should run the front at 105psi and the rear at 90psi according to the FT chart.

So the answer is to have a cold pressure that gives me 105psi Front and 90psi Rear, for my weights, on the road.  My cold pressure is about 82psi. on the front and 80psi on the rear.

Others may disagree

"Others" include the tire manufacturers, RV Safety, Escapees' Smart Weigh, etc. 

As others have stated, your cold pressures in the second paragraph are way too low (20% or more if you are only inflating to 80 psi!).  Follow the tire manufacturer's recommendation.  You are otherwise risking serious sidewall damage and a blowout.

BTW, the Foretravel chart is for the OEM tires that were installed on your coach, which are no longer made.  Be sure to use the most current inflation tables for your tire size and load range.  They are slighly different.

Re: Tires

Reply #166 –
And, if you have a 20 PSI pressure rise (unless you had an extreme ambient temperature swing), it is quite likely you are running insufficient pressure. 

An underinflated tire flexes more, which creates HEAT which makes for a larger PSI change.

And, as all have stated, 100% of the tire manufacturer's inflation tables are for COLD PSI.  Cold is defined at "before driving" at whatever ambient temperature is.

Re: Tires

Reply #167 –
Quote from: speedbird1 –
...............  "With those weights I should run the front at 105psi and the rear at 90psi according to the FT chart"...

 ***Yes, correct - that is the COLD tire pressure to use according to the tire industry, every major coach builder, car manufacturer, trucking industry, etc. *** 

....................."I had been running 100psi cold on the front and 95psi cold on the rear. So the answer is to have a cold pressure that gives me 105psi Front and 90psi Rear, for my weights, on the road...........My cold pressure is about 82psi. on the front and 80psi on the rear"......   

  ***Incorrect.  That is the wrong answer according to tire industry experts across the board, and all vehicles manufacturers***

Speedbird 1

Just like with cars and over the road trucking, tire pressures are ALWAYS set cold -- to the recommended charts and/or manufacturer guideline. 

Yes, the pressure does increase substantially running down the road. That was already taken into consideration by the tire manufacturer, the wheel manufacturer, the coach builder, and every other type motorized vehicle running down the road manufacturer. 

You are substantially and dangerously under inflated.

Looking at your weight versus pressure, with your load range H tires, you need 105 front and 85 rear COLD pressures (minimum, another 5 psi for margin is what many of us do).
 See bottom link for newest chart of weight/pressure.

https://www.michelinb2b.com/wps/b2bcontent/PDF/RV_Tires_Brochure.pdf 

http://www.rvtirepressure.com/assets/images/extrapages/Michelin_Rv_Load_Inflation.pdf 

Re: Tires

Reply #168 –
Thank you 7880,

That chart is much different from the one that I was given by FT and my pressures will be adjusted to reflect the difference.
Again the value of this forum. Thank you all.
Speedbird 1.

Re: Tires

Reply #169 –
RV and tire companies list pressures that will give a comfortable yet safe ride. The last thing they want is a competitor that offers a softer ride.

Pierce

Re: Tires

Reply #170 –
Speedbird....sorry mised you in Nac, glad went well.

Nothing to add to this thread but to reassure you....my weights are very similar to yours so we same.  For tires I start cold at 108/90 psi.  Not unusual I use 110/90.

Perhaps you have seen variation in the inside and outside duals at times.  I recall a thread says it can happen due to heating differences during the day.  Not much different but enough my gauge could show it.

By the way, Brian, i was having some trouble getting to the 110 at times.  The air chuck was the problem...got a straight in chuck rather than angled and airing up front became easier.

Cheers, safe travel to the last best place

Re: Tires

Reply #173 –
Quote from: craneman –
Tire pressures are supposed to be set cold. They will always read high when hot. Fronts on my crane cold are 110 I get over 130 0n a very hot day.
Page 24 says do not exceed cold pressures marked on the wheel
The Alcoa wheels are forged aluminum and very tough. The maximum pressure is stamped on the wheel and has a huge margin of safety. Forged wheels don't chunk off like cast wheels and just bend. Our U300 Alcoas are stamped 120 psi cold. This is higher than any maximum recommended cold tire pressure for our sized tires I have seen. Bottom line is to check and adjust pressures cold and don't worry about the pressure later in the day no matter how hot the road or weather is.

Heat is the enemy of tires and the more the tire flexes, the hotter it gets. Dropping pressures on a hot day will cause the tire to heat up more and make it more susceptible to damage or failure.

Pierce

Re: Tires

Reply #174 –
Trent, I got it from Kelly Truck Stop, a supply parts outfit out of Nac.  But they seem available too at NAPA for I have now gotten a straight in gauge as well and find both work better for me.  The chuck was the best find for the higher pressure versus the auto tire chuck.  Had wondered why Herman Power could more easily get their chuck to fill the tire, they showed me the straight in version they use but did not sell them.


mike

Re: Tires

Reply #176 –
We just had a set of six Toyo M154s installed Friday; selection of Toyos was primarily based on economics (and info on this forum). Drove around the block a couple of times; so far, so good. Headed for Puerto Penasco (Rocky Point) late May.

roger

Re: Tires

Reply #177 –
We went with the M177 type,have had them a year.

Re: Tires

Reply #178 –
I almost had a set of Toyo M177 installed, however, elected to go with the M170 because on the M177 there is a cut close to the edge of the tire thats according to the tire tech, rip off. Now, he said it won't effect the life of the tire, he said the M170 had not had any issues. I am sure good driving habits will go a long way in saving the M177, I just opted for a non issue tire. After 2 weeks and only 1,000 miles I really like them so far and feel very stable.

Re: Tires

Reply #179 –
Tread depth:
M177 is 18/32".
M170 is 19/32".
M154 is 22/32"

They are all rated for steer, however the M154 is the only "recommended all position steer/drive" and has the deepest tread. Although I am 100% sure they will all perform well in any position on an RV, I will go with the M154 so I can have the deepest tread possible when I sell my used casings to a dump truck or regional delivery owner/operator. They will buy good tires without caring about age because they will wear them out in less than a year. My current bridgestones are probably too old to be sold, but I will still try. Sucks discarding a tire with 95% of its original virgin tread.