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Old 06-27-2022, 07:45 AM   #1
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Question on tire size for my coach

All,

I have a 2004 Ford F53 chassis with a 20,000LB chassis under my Fleetwood 32 foot motor home.

The front axle is rated at 7000LB's which is indicted on the name plate inside the coach. That nameplate states the tire size of 245/70 x 19.5 F tires. I assume it came with range F tires which are long since gone. I had just replaced the H load range Continental's due to age with G load range tires on the front only which I think is more than sufficient to carry the load of the front axle rating.

My question is, other than the height difference or a 225/70 19.5 tire vs. a 245/70 19.5 tire should I be concerned about the "smaller" tire?
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Old 06-27-2022, 07:59 AM   #2
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The circumference difference is only about 3”. The 245/70 has the slightly larger diameter. It will be about 1” larger so check clearance.
I wouldn’t worry about it.
On the rear, maybe as it will change your speedometer reading.
JMHO

ChecK with your tire supplier.
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Old 06-27-2022, 08:10 AM   #3
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Go here https://tiresize.com/calculator/ and plug in you numbers to see the difference.

Going to H range could effect ride comfort. How much I don't know as I had no problem getting 245/70-195 G rated tires back in spring of 2020.
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Old 06-27-2022, 08:26 AM   #4
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Go here https://tiresize.com/calculator/ and plug in you numbers to see the difference.

Going to H range could effect ride comfort. How much I don't know as I had no problem getting 245/70-195 G rated tires back in spring of 2020.
I can attest to the ride comfort, the H tires ride like bricks. 16 ply vs. 14 ply makes a difference.
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Old 06-27-2022, 03:02 PM   #5
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If you haven't decided on a tire manufacturer the TOYO tires are a lot better ride than the stock GY tires. They were also about $1,500 cheaper for the 6 tires. We've got about 5,000 miles on them and all is well.
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Old 06-27-2022, 03:27 PM   #6
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Agility57-

If I had to choose, I'd use the same size tire, 245/70R19.5, in load range G if I could get it and H if I couldn't. I'm just cautious about using something smaller than original spec.

Per Michelin inflation charts for the XZE (link here), the load range H at 75 pounds will hold 3390 pounds single and 6410 pounds dual, both of which are lower than the maximum axle ratings front and rear. It might not provide a harsh ride.
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Old 06-29-2022, 12:10 PM   #7
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Agility57-

If I had to choose, I'd use the same size tire, 245/70R19.5, in load range G if I could get it and H if I couldn't. I'm just cautious about using something smaller than original spec.

Per Michelin inflation charts for the XZE (link here), the load range H at 75 pounds will hold 3390 pounds single and 6410 pounds dual, both of which are lower than the maximum axle ratings front and rear. It might not provide a harsh ride.
Well, now I am a bit concerned because the max load for a single on the tires that ARE now on the front of my rig are just below the max rating for my 7000# front axle rating. The 225/70 19.5 tires are load rated at 3450# at 90 PSI.
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Old 06-29-2022, 01:27 PM   #8
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Agility57-

Don't take my word for it, but I have read that two tires from different manufacturers that are the same size and load range have the same inflation charts.

If we take that as an assumption (to be confirmed by you with a tire chart for the make and model of tires you have), the chart values for the Michelin XZE 225/70R19.5 load range G are:

90 psi: 3450 pounds
95 psi: 3640 pounds
100 psi: 3715 pounds
105 psi: 3845 pounds
110 psi: 3970 pounds

The simple answer to "below the axle rating" is to inflate the tires more. For example, the chart value for 95 psi is 7280 pounds.

The better, non-simple answer is: Until you weigh your coach when it is fully-loaded, including you, any passengers and all the "typical" liquids in the tanks, you are shooting in the dark as to what pressures you should run.

For instance, while axle rating is a valid point along the spectrum, perhaps your coach never gets within 1000 pounds of that rating with the coach loaded as above.

A four-corner weigh is best, a per-axle weigh is OK, and a full-coach weight is not helpful to determine tire pressures.
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Old 06-29-2022, 04:52 PM   #9
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Quote:
Originally Posted by l1v3fr33ord1 View Post
Agility57-

Don't take my word for it, but I have read that two tires from different manufacturers that are the same size and load range have the same inflation charts.

If we take that as an assumption (to be confirmed by you with a tire chart for the make and model of tires you have), the chart values for the Michelin XZE 225/70R19.5 load range G are:

90 psi: 3450 pounds
95 psi: 3640 pounds
100 psi: 3715 pounds
105 psi: 3845 pounds



110 psi: 3970 pounds

The simple answer to "below the axle rating" is to inflate the tires more. For example, the chart value for 95 psi is 7280 pounds.

The better, non-simple answer is: Until you weigh your coach when it is fully-loaded, including you, any passengers and all the "typical" liquids in the tanks, you are shooting in the dark as to what pressures you should run.

For instance, while axle rating is a valid point along the spectrum, perhaps your coach never gets within 1000 pounds of that rating with the coach loaded as above.

A four-corner weigh is best, a per-axle weigh is OK, and a full-coach weight is not helpful to determine tire pressures.
All good points, thank you. I have weighed my coach before and I will check the paperwork tomorrow to see how close I am to the max on these tires. Hopefully not too close.
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