20’ MH Tire size?

[Don B]

Hello everyone. What a great forum!
We bought our 1974 20’ MH a few weeks ago and what fun it is to drive around. We think we got so many waves and thumbs up is because it looks so funny (short & tall). Had to stop driving it because we need some tires bad, the more I drive it the worse the tires get. It had 875 16.5s on the rear and 950 16.5 LTs on the front, very cracked but made the drive home ok. I wanted to change to 16” rims so bought 7 and mounted some LT235 85R16s on them. TOO BIG! Even though my manual list them as an acceptable size. While changing the tires I discovered that the 875 16.5s had been rubbing the plastic inner fender on the rear. Well, the 235 85R16s rubbed too. I need to know what tire size you 20 footers (16in rims) are running and what seems to work best. Any and all help will be appreciated.

Thanks, Don B

[ALANSD]

I am guessing no one has replied because of the lack of 20' owners....sure is a rare bird.

[thenewkid64]

Don,

I am going to make a SWAG here, but I would bet that the tires are rubbing due to suspension age. The springs, leaf/coil have held up the weight for so long that they have sagged a bit and are allowing the "properly sized" tires to rub. You may need to add some helper airbags or find a good spring shop to have them reworked.

Barring that I will check my 87 manual tonite and see what it says regarding tire size for you. Mine may be different due to suspension changes, but on the 20 footers I bet it is the same.

Congrats on owning a rare model!

[74Argosy24MH]

'74 20 ft. 10,500 gvw is 7.50-16 or 8.75-16.5

My manual states:

"Radial tires are not recommended in that they are not approved for use with these wheels." But the wheels were split rims so that makes sense.

Along with the spring height how is the body roll? Like you said, it is short and tall and that makes a lot of roll. My wheel wells had a few scuffs inside but nothing serioius. Also watch the cross section of the radial. Could be you will need a narrower tire or different offset on the rims. How much clearance between the duals?

John

[Don B]

Thanks Guys

You’re both right. The springs are not like new any more and it does have body roll, but the tires are rubbing on the side of the tire. I checked a chart on tire sizes and found that a 8.75-16.5 = 29.5 in. tall, a 7.50-16 = 31.5 in. tall and a LT235/85R = 31.5 in. also. This just doesn't make sense! Two inches difference in diameter will make a huge difference in the gear ratio that the engine sees. I mounted a LT225/75R16 (narrower) and they won't rub, so now I know the width I need, but that tire is only 29 inches tall. I really would like some input from MH owners with 16-inch rims or 16.5-inch rims. I'm out of tires to test with. I guess if I don’t hear from anyone running 16.5 / 16 inch tires I will try the middle of the road, a 30.5 inch tire. I don't have a tach but it sure seemed like the engine was turning faster than I like at 60 MPH on the 29.5-inch tires. Thanks again. Hey, if you see any other 20-ft. MH out there stop them and check their tire size, OK?

Don B

[Bfrank]

My 79 Excella 24 uses 8.75R 16.5 and it has rear air bags
but even running with no pressure they dont rub the wheel wells
but with air in the bags they raise the coach height about an inch or two. I just bought four of these tires at tires.com 95 bucks each from california to tennessee in the door. Sounds like it is possible that it could be springs but would try anything as I'm sure that new springs would not be very cheap.

[Don B]

Bfrank,
Are you happy with the engine RPMs with that tire size? Seems like I am turning higher RPMs than I need to but I don't have a tach to know for sure. I just wanted to buy the tallest tire I could without being geared too high.
Thanks, Don B

[Bfrank]

I'm turning about 3000 rpm at 62 - 65 mph. I don't know if thats
good or bad I would prefer to run lower rpm at that speed but
that would mean replacing the gm 400 tranny.