Front -v- Rear tire press?

[Tomthepilot]

Will I typically have higher pressures in the rear dual drivers vs front steer tires?
I know this simple tire pressure thing has been discussed at length but the more I read the more confused... well let's just say there remains an element of uncertainty for me and I may have had things bass-ackwords.

2 axle DP
Goodyear G670 RV
255/70R22.5

I realize I need actual weights but for simplified discussion:
assume a GVW of 25,500 lb
assume equal weight distribution over 6 tires:
25,500 / 6 = 4,250lb each tire.

So... I'd inflate the front steering tires to 82 PSI. + a bit more for grandmother <grin>
And... the rear dual driving tires to 90 PSI. + ""

?Correct?

From Goodyear info I interpolated to one PSI below:
Single Dual PSI
4190 3970 80
4226 3971 81
4262 3972 82 front tires
4298 3973 83
4334 3974 84
4370 3975 85
4406 4035 86
4442 4095 87
4478 4155 88
4514 4215 89
4550 4275 90 rear tires
4575 4302 91
4600 4329 92
4625 4356 93
4650 4383 94
4675 4410 95

Regards,
Tom C.

[Steve Ownby]

Originally Posted by Tomthepilot

Will I typically have higher pressures in the rear dual drivers vs front steer tires?
I know this simple tire pressure thing has been discussed at length but the more I read the more confused... well let's just say there remains an element of uncertainty for me and I may have had things bass-ackwords.

2 axle DP
Goodyear G670 RV
255/70R22.5

I realize I need actual weights but for simplified discussion:
assume a GVW of 25,500 lb
assume equal weight distribution over 6 tires:
25,500 / 6 = 4,250lb each tire.

So... I'd inflate the front steering tires to 82 PSI. + a bit more for grandmother <grin>
And... the rear dual driving tires to 90 PSI. + ""

?Correct?

From Goodyear info I interpolated to one PSI below:
Single Dual PSI
4190 3970 80
4226 3971 81
4262 3972 82 front tires
4298 3973 83
4334 3974 84
4370 3975 85
4406 4035 86
4442 4095 87
4478 4155 88
4514 4215 89
4550 4275 90 rear tires
4575 4302 91
4600 4329 92
4625 4356 93
4650 4383 94
4675 4410 95

Regards,
Tom C.

Looks good Tom. That inflation pressure will support your GAWR which is what you should do until you can get a corner weigh done. Be aware that many suggest inflating 10% over the Goodyear table in the steer axle to minimize "river wear" which G670 tires are prone to developing on the steer axle.

[Cbones]

Originally Posted by Tomthepilot

Will I typically have higher pressures in the rear dual drivers vs front steer tires?
I know this simple tire pressure thing has been discussed at length but the more I read the more confused... well let's just say there remains an element of uncertainty for me and I may have had things bass-ackwords.

2 axle DP
Goodyear G670 RV
255/70R22.5

I realize I need actual weights but for simplified discussion:
assume a GVW of 25,500 lb
assume equal weight distribution over 6 tires:
25,500 / 6 = 4,250lb each tire.

So... I'd inflate the front steering tires to 82 PSI. + a bit more for grandmother <grin>
And... the rear dual driving tires to 90 PSI. + ""

?Correct?

From Goodyear info I interpolated to one PSI below:
Single Dual PSI
4190 3970 80
4226 3971 81
4262 3972 82 front tires
4298 3973 83
4334 3974 84
4370 3975 85
4406 4035 86
4442 4095 87
4478 4155 88
4514 4215 89
4550 4275 90 rear tires
4575 4302 91
4600 4329 92
4625 4356 93
4650 4383 94
4675 4410 95

Regards,
Tom C.

Tom,
Without a 4 corner weight, you really are guessing. I don't think the tires evenly distribute the weight the way you are figuring. If that was the case, there would be no need for a 4 corner weight. Additionally every coach that I have owned has higher pressures on the steer tires than on the duals. I would go by the recommended tire psi plate on your driver side wall until you get an accurate weight. It is safer to be over inflated for a while until you get a weigh rather than be under inflated and overloaded on the tires.

[Skip426]

I'm , sorry but you cannot " assume equal weight distribution over the six tires"
Until you get actual weights, assume that you are loaded to your axle weight ratings.
Example . FAWR 10,000 lbs = 5,000 lbs per tire, single.
RAWR 16,000 lbs = 4,000 lbs per tire, dual.

I've always heard of more pressure in the steer tires that the duals , and that's the way mine works out from scale weights . 95 front 90 rear. with a 5 psi cushion at each.
Set your pressure high , until you get your weights , then with cold tires , lower the pressure according to the chart.
Easier to lower on the road than , find a place to pump tires up.

I see , Cbones , types faster than I do.

[Steve Ownby]

Originally Posted by Skip426

I'm , sorry but you cannot " assume equal weight distribution over the six tires"
Until you get actual weights, assume that you are loaded to your axle weight ratings.
Example . FAWR 10,000 lbs = 5,000 lbs per tire, single.
RAWR 16,000 lbs = 4,000 lbs per tire, dual.

I've always heard of more pressure in the steer tires that the duals , and that's the way mine works out from scale weights . 95 front 90 rear. with a 5 psi cushion at each.
Set your pressure high , until you get your weights , then with cold tires , lower the pressure according to the chart.
Easier to lower on the road than , find a place to pump tires up.

I see , Cbones , types fast than I do.

Guys,

I looked up the OPs coach and his GAWR is as follows:

Steer axle 8500
Drive axle 17000

Based on those weights then the inflation that he is using will support the coach at the maximum axle weigh rating. Agreed, he should gat a corner weight when he can but he is protected from over loading his tires at these pressures. I agree that it doesn't seem typical but the facts support him.

[Skip426]

Originally Posted by Steve Ownby

Guys,
I looked up the OPs coach and his GAWR is as follows:
Steer axle 8500
Drive axle 17000
Based on those weights then the inflation that he is using will support the coach at the maximum axle weigh rating. Agreed, he should gat a corner weight when he can but he is protected from over loading his tires at these pressures. I agree that it doesn't seem typical but the facts support him.

Wow, .

[Tomthepilot]

I do thank everyone for the quick and great responses. I do realize the need to work with actual four corner weights. For legal purposes I don't want publish numbers that might be... ah... slightly north of legal GVW. My actual tire pressures are higher than stated.

I just wanted to make sure I'm using the Goodyear data correctly.

This is our first motor home. We've had this coach for a bit over a year now. Put about 6,000 mi on it so far and I must say it's handling and predictability is far better then I ever expected and we've become very comfortable driving it.

Thanks to all,
Tom C.

[JFXG]

Originally Posted by Tomthepilot

Will I typically have higher pressures in the rear dual drivers vs front steer tires?........assume equal weight distribution over 6 tires......

Originally Posted by Skip426

I'm , sorry but you cannot " assume equal weight distribution over the six tires".....

Tom, you have what appears to be a highly atypical situation. Your numbers and premise seem accurate, but it would be wrong to assume that always to be the case. This may be why you had ongoing confusion.

As a very general rule, the GAWR breakdown runs approximately 1/3 front and 2/3 rear (as it does in your coach). In my coach its just a bit forward at 12K/19K, for a GVWR of 31K. My front tires carry 5900 lbs each (110psi), my rears about 4600 (90psi). Everyone I've talked to since I've had this coach has similar weight spread.

Now, as to your "...I don't want publish numbers that might be... ah... slightly north of legal GVW. My actual tire pressures are higher than stated...". Some may think that sounds pretty clever, but mostly its not.

[Barbaraok]

Originally Posted by Tomthepilot

I do thank everyone for the quick and great responses. I do realize the need to work with actual four corner weights. For legal purposes I don't want publish numbers that might be... ah... slightly north of legal GVW. My actual tire pressures are higher than stated.

Get rid of some weight. Someone you love life might depend upon it. Why would you knowingly overweight an axle/tires?

[Tomthepilot]

Barbara or David wrote:
Get rid of some weight. Someone you love life might depend upon it. Why would you knowingly overweight an axle/tires?

I agree. We're seriously working on it. weight is an ongoing struggle.

Thanks,
Tom C.

[Koop]

I've weighed my coach and my situation is similar to the OP's. Approximately one third of the weight is carried by the front axle and two thirds by the rear.
Since I have six tires, one third of the tires are on the front axle, two thirds are on the rear.

This suggests a fairly evenly balanced load per tire. The load and inflation chart indicates a dual wheel set-up needs about 10psi higher inflation than a single to carry roughly the same load.

Therefore, my rear tires are inflated 10psi higher than the front.

[ecurb74]

But on the rear you have 4 tires on the Axle so it seems to me that if you had 20k(arbitrary number) on rear you would divide by 4 to get the individual tire load, 5k, thus the rear would run at a lighter pressure.

[Steve Ownby]

Originally Posted by ecurb74

But on the rear you have 4 tires on the Axle so it seems to me that if you had 20k(arbitrary number) on rear you would divide by 4 to get the individual tire load, 5k, thus the rear would run at a lighter pressure.

That would be true, except for the fact that tires run in a dual configuration are de-rated somewhat and so must be inflated to a higher psi to carry the same load as a tire in a single configuration. That's why the tire tables have two max weights listed at each psi level. One "S" and one "D".

[Tomthepilot]

Mike wrote:
I've weighed my coach and my situation is similar to the OP's. Approximately one third of the weight is carried by the front axle and two thirds by the rear.
Since I have six tires, one third of the tires are on the front axle, two thirds are on the rear.

This suggests a fairly evenly balanced load per tire. The load and inflation chart indicates a dual wheel set-up needs about 10psi higher inflation than a single to carry roughly the same load.

Therefore, my rear tires are inflated 10psi higher than the front.

Mike... and everyone else,
Thanks! Very helpful info. I feel better now about utilizing the Goodyear data to derive proper tire pressures. I'm also using a TST press/temp monitor system and it also provides a measure of comfort as we travel.


-irv2- I've learned so much about so many things here.


Regards,
Tom Charlton