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Old 01-08-2018, 06:45 PM   #1
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Tires revisited

Need to decide on tires of the 350 before I make the trip back from Phoenix.
Manual says 8R19.5, as all the classics use. Hankooks is an option, but I am also looking at Goodyear 8R19.5 G647, which supposedly is an RV specific tire.
I am not very comfortable switching to the 225/70 19.5, due to the factors below
Comments?

Wheels

To convert from 8R19.5 to 225/70 R19.5 tires may require the purchase of new wheels. The 8R19.5 size can fit on a 5.25-inch-wide wheels, and the low-profile 19.5 tires require 6-inch-wide wheels. Besides a better fit of tire to rim, the wider wheels will provide enough dual-wheel spacing for 225/70 R19.5 tires. Dual-mounted tires should never touch, and the 5.25-inch rim is too narrow to give proper dual-wheel spacing for the newer tire.

Tire Diameter

Tires sized 8R19.5 have a diameter of 33.1 inches, and 225/70 R19.5 tires are 32 inches in diameter. Changing tire sizes will result in a speedometer that indicates faster than the vehicle is actually moving. 8R19.5 tires will rotate 628 times in a mile, and 225/70R19.5 tires rotate 644 times. The result is a 2.5 percent speedometer error with the new tires. The Goodyear website states that no gearing change is required for this amount of error.



Load Capacity

Both the 8R19.5 and 225/70 R19.5 tires have load range F capacity ratings. This makes the capacity for the two tires sizes similar but not exact. The low-profile 225/70 R19.5 tire has a load capacity of 40 to 140 lbs. higher depending on the vehicle location of the tire. A set of six 225/70 R19.5 tires mounted on a truck, replacing 8.R19.5 tires, would increase the tire set load capacity by 440 lbs.
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Old 01-09-2018, 01:44 AM   #2
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The G670 is the RV tire https://www.goodyeartrucktires.com/t...rodline=160023 and the G647RSS is delivery and utility https://www.goodyeartrucktires.com/t...rodline=160002. (Click on the tire size to get the specs.)

The 225/70 says 10" dual spacing and the 8x19.5 says 9.3" dual spacing. The G647 is also M&S rated.

I have been running G647's for about 10 years now and just bought 4 new tires for the rear. The old ones look great but the thread is getting thin. New wheels is not an option for a P-30 with 5 lugs up front and 10 lugs in the rear if you want aluminum.

I personally don't see a need to change size. The book says 8x19.5 and the G647's have been good for me and are easy to find. And yes I have been caught in the snow a few times.
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Old 01-09-2018, 04:35 PM   #3
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Thanks for your input, Dan. I ordered the Goodyear G647 8R 19.5 tires.
I would have preferred to go with Michelins, but I remembered installing 225 on the drive and tag axle of the 87 345 and I was not happy with loosing the 1" in heights. I dont remember having spacing or rim width problems, but overhang is always in issue on these long coaches.
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Old 01-09-2018, 05:16 PM   #4
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The Michelins ride extremely better than the Goodyear's, which are on my 325LE, you could have just adjusted the air bag height to compensate.......oh that's right.....,it's a 350 not a 370, well, good luck with the new tires ! Regards, Bob
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Old 01-09-2018, 05:25 PM   #5
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Quote:
Originally Posted by bobmiller1 View Post
The Michelins ride extremely better than the Goodyear's, which are on my 325LE, you could have just adjusted the air bag height to compensate.......oh that's right.....,it's a 350 not a 370, well, good luck with the new tires ! Regards, Bob
Yes, Bob you are right and I think I did adjust the airbags to compensate, but it still does not solve the speedo, rim width and somewhat negligent performance issues, when using 225's.
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Old 01-10-2018, 07:15 PM   #6
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FWIW, the 310 is now running 225ís on the front and 8Rís on the rear. This happened pretty much by chance as I wanted new front tires quick and 225ís were all the shop could find, but I may stick with it. Speedo is still correct, and I have more rubber on the road in front.
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Old 01-18-2018, 12:42 PM   #7
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Sorry for not catching the thread sooner.
I find a BS R238 225/70R19.5 LR-G 32.2 oD x 8.7 3870@110 & 3750@ 110 Dual

8R19.5 is 33.8 OD x 8 wide
LR-G 3525 & 3305@110 S -D

so load capacity is ok but I am concerned about the minimum dual spacing causing some potential problems on rear fitment. Some carefule measurement of current wheels would be needed to learn the offset to ensure sufficient clearance.
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