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Old 01-08-2018, 07:45 PM   #1
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1994 30' Excella
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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, 02:44 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, 05:35 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, 06:16 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, 06:25 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, 08:15 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, 01:42 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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Old 08-03-2020, 11:11 PM   #8
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1984 34.5' Airstream 345
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2 years later - how are the G647s performing?

I need to replace all 8 tires on a newly bought 345. Just curious how the G647s worked out for you? Would you still recommend them?
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Old 08-06-2020, 06:33 AM   #9
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Quote:
Originally Posted by marcvl View Post
I need to replace all 8 tires on a newly bought 345. Just curious how the G647s worked out for you? Would you still recommend them?

I am bias and just replaced all 8 tires with Goodyear G647 on my latest 350 purchase. (the 2018 350 purchase fell through).
The rim width is correct and the heights is correct, so i am sticking with stock size as long as quality tires are available. I would not use cheaper knock offs, they will cost you more over time and are just dangerous.

The drawback is cost and availability. I had to special order them and it took a few weeks to get them. They are made in special runs by Goodyear and may not always reflect the latest DOM. Combine the G647 with a set of Centramatics wheel balancers and you have a fine ride.
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Old 08-08-2020, 01:38 PM   #10
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Thanks Peter. I’m assuming you are using the 8R19.5 size, correct?

As for the wheel balancers, interesting! Do you need 8 of them as well? Or just 6? Do dualies require one for each wheel as well?
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Old 08-08-2020, 02:38 PM   #11
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Quote:
Originally Posted by marcvl View Post
Thanks Peter. Iím assuming you are using the 8R19.5 size, correct?

As for the wheel balancers, interesting! Do you need 8 of them as well? Or just 6? Do dualies require one for each wheel as well?

Yes, Goodyear G647 8R19.5 . They have a nice almost 7" wide thread, which is more than most 8R19.5
On the Centramatics, you will need 3 sets, 1 for the tag and one for the drive, mounted between the duallies (see second picture) and 1 set of the steer axle (third Picture)
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Old 10-02-2020, 07:15 AM   #12
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Just don't use G159
https://www.usatoday.com/story/money...ims/488815002/
I followed this case closely. I also have family that worked for a truck design company that sourced all tires from goodyear... they were not without issue, though they could have gotten better...

I'll probably be buying michelins
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Old 10-02-2020, 03:34 PM   #13
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Quote:
Originally Posted by Magnet18 View Post
Just don't use G159
https://www.usatoday.com/story/money...ims/488815002/
I followed this case closely. I also have family that worked for a truck design company that sourced all tires from goodyear... they were not without issue, though they could have gotten better...

I'll probably be buying michelins

cant get 8R michelins anymore. I would think twice before I mount 225's on 8R rims. 225 require 6.75 rim, 8R are 6" rims, plus the 225 diameter is less by 1 1/2 "
Goodyears G647 are the best on the market, probably followed by Bridgestone R187. Dont fall for the Toyo M120Z, they have max speed rating of 60MPH or the Samson tires. They will fall apart after 4 years.
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Old 10-03-2020, 08:09 AM   #14
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In this document
http://ddwt.us/Michelin_RV_Tire_Information.pdf

I found the attached table on page 12 stating both 6.00 and 6.75 " wheel widths are ok

The dagger on dual spacing is

(‡) Overall widths will change 0.1 inch (2.5 mm) for each 1/4 inch change in wheel width. Minimum dual spacing should be adjusted accordingly

So by mounting on 6.00s you gain 0.3" of dual spacing as well
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Old 10-03-2020, 08:25 AM   #15
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Quote:
Originally Posted by Magnet18 View Post
In this document
http://ddwt.us/Michelin_RV_Tire_Information.pdf

I found the attached table on page 12 stating both 6.00 and 6.75 " wheel widths are ok

The dagger on dual spacing is

(‡) Overall widths will change 0.1 inch (2.5 mm) for each 1/4 inch change in wheel width. Minimum dual spacing should be adjusted accordingly

So by mounting on 6.00s you gain 0.3" of dual spacing as well

Rob, I stand corrected on the Michelins 225's. Its the 245's Michelins that can not be mounted on 6" rims. When I was looking to replace my tires, I had a truck shop refuse to mount 225's on 8R rims, but they were not Michelins.

I always run Centramatics on all axles so the spacing of the duals has to be a consideration, since they are mounted between the duals. The heights difference is not a huge issue, but throws of your speedometer and reduces ground clearance.

Besides all of the above, i always prefer michelins.
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Old 10-03-2020, 04:08 PM   #16
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Quote:
Originally Posted by PeterH-Airstreamer View Post
Rob, I stand corrected on the Michelins 225's. Its the 245's Michelins that can not be mounted on 6" rims. When I was looking to replace my tires, I had a truck shop refuse to mount 225's on 8R rims, but they were not Michelins.

I always run Centramatics on all axles so the spacing of the duals has to be a consideration, since they are mounted between the duals. The heights difference is not a huge issue, but throws of your speedometer and reduces ground clearance.

Besides all of the above, i always prefer michelins.
No worries Peter, I appreciate your concern

I had just been assuming they fit based on the 4 or 5 members that have claimed they're running them without issue. You prompted me to actually verify

I have centramatics to put on so I'll update with the dually clearance. Installing a GPS speedo so no issues there
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Old 10-03-2020, 04:25 PM   #17
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I use Michelin all round
TV: cross climate suv Ltd, 255/ 45r20 105w extra load rated

AS: DEFENDER lt 225/75r16 Ltd load range e

Very happy with then after 3 years
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Old 10-05-2020, 07:22 AM   #18
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Quote:
Originally Posted by waninae39 View Post
I use Michelin all round
TV: cross climate suv Ltd, 255/ 45r20 105w extra load rated

AS: DEFENDER lt 225/75r16 Ltd load range e

Very happy with then after 3 years
Appreciate the input, but you wandered into the motorhome section
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Old 10-05-2020, 06:14 PM   #19
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As you all know Iíve been running the 225/70R19.5 XZEís on the 370LE for 3 years.....no issues. The first 2 years I ran with 8 ozs. of beads in each tire. Last year I got the Centramatics. Top speed this year was 92 MPH. We cruised at 80-82 MPH going to Yellowstone and back. Regards, Bob
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Old 10-06-2020, 06:34 AM   #20
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I see you thuroughly ignored the 75mph speed rating

We don't all have bus chassis', I don't push my P-30 above 75 anyway.
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