Tire size change.8R19.5's to 225/70R19.5

Yep, I did the same thing 2 years ago. Mileage went down slightly, Engine noise/RPM went up and the handling did not change. The tires are a lot heavier. It did straighten out my speedometer it does register the proper speed now. I would swap back if I could.

I switched to 225/70/19.5

I made the swap on mine, and I love it.

If anyone wonders why I bother posting, this thread is a good example. No one has given a correct or complete answer.

An 8-19.5 is 8.0" wide on a 6.00" rim, with an allowable rim width range of 5.25 to 6.75, an overall diameter of 33.8", a minimal dual spacing of 9.1", and a load carrying capacity of 3195# at 95 psi (Load Range E).

A 225/70R19.5 is 8.9" wide on a 6.75" rim, with an allowable rim width range of 6 to 6.75, an overall diameter of 31.9", a minimal dual spacing of 10.0", and a load carrying capacity 3195# at 80 psi (Load Range E)

So not only are the tires 2" different in diameter, they are also different widths and don't completely share the rim width compatibility.

Summarizing:

If the rims you have a 5.25", then you can not change from an 8-19.5 to a 225/70R19.5.

If there isn't 3/4" clearance around the 8-19.5 in all positions (Including the front suspension completely collapsed AND the steering wheel fully turned), then a 225/70R19.5 is likely to rub. Very bad.

Note: Collapsing the suspension to verify clearances is very difficult to do. It can be estimated by someone with experience - and if you don't have that level of experience, seek help.

For those who are interested, the width difference when mounted on the same rim width is 0.6".

So if there is only 0.6" between the duals, then you CAN NOT use a 225/70R19.5 in place of an 8-19.5. In the OP's case, depending on how he measured the 3/4", he might be OK.

And lastly, use the same Load Range with 15 psi less.

84 Brougham wrote:
My dually spacing is about 0.75 inches. I have to say though, with the new tires I like the idea of having a little more rubber on the road.
Is three quarters of an inch enough space? Once again, thank you all
so much for the prompt feedback, It's nice to feel welcomed!!!
And to anyone else who has done this swap, were you happy with the results as far as handling and mileage are concerned?

Did the swap when i had a gasser, was very pleased with the results. Keep the tires you will not be sorry.

.75 is a little close. i beleive the tire manufacturers suggest min 1 inch.
I put wider front tires on mine and stayed with the 8R-19.5 in the rear. 8R-19.5 are very common around here.

My dually spacing is about 0.75 inches. I have to say though, with the new tires I like the idea of having a little more rubber on the road.
Is three quarters of an inch enough space? Once again, thank you all
so much for the prompt feedback, It's nice to feel welcomed!!!
And to anyone else who has done this swap, were you happy with the results as far as handling and mileage are concerned?

If the tire has a smaller diameter, yes your mpg will be lowered, and your speedometer will be just for a bit off. And the tire you are asking is the proper swap and should work just fine. You will probably never notice any difference, and the tires he recommended should improve your motorhomes handling.

The salesman said that it was a less expensive alternative, easily available and more modern. He also said I would get better fuel economy.
I figured he's the tire expert so I trusted him. I called another tire place and they told me to go back and return the tires.
Thank you for responding so soon. I need to do something asap.

84 Brougham wrote:
I just purchased new tires for my 1984 29' Brougham. with the advice of the tire salesman I bought the B F Goodrich 225/70r19.5's to replace my
old 8R19.5's. He said that a lot of people were converting to this tire
and that it was only about a half inch shorter. I was concerned about my gas mileage and speedometer accuracy, he said I would get better mileage
with this tire. when I got the RV home I compared it side by side to an 8R19.5 and it seems to be more than a half inch smaller. Did I get steered in the wrong direction?

They should be right at 1 inch smaller diameter...and yes you can swap out your 8R 19.5 for them with no problem. Lots do it and I even did it myself when I was running a gasser