I posted in chat room but no reply. I need new tires - both front tires are Steelmark 225/70R 19.5 radial tubeless, new 5 years ago. Left outer rear has used Michelin 8R 19.5 last year; right outside rear is Bridgestone 8R 19.5, 12 ply and has bad cracks in sidewarll. No idea of what the inner duals are. One tire dealer is willing to move the front ones back, replace the others with good used 225/70R 19.5's, or put all new Roadmasters. RV doc says they should all be replaced with 8R 19.5 as that is the original size tire for my RV. What's the best recommendation? Braley

Not sure on the size, but keep in mind that RV tires should be replaced every 7-10 years regardless of mileage or exterior tread. They are usually pushed to their max as far as weight capacity, and the rubber breaks down internally long before you see cracking or dry rot on the outside.

I would highly recommend AGAINST putting any used tires on an RV. The potential for blowouts is higher, and an RV tire failure can cause extreme damage to the underbody and various components of the rig.

Best option is to pony up for a new set of 6 (and keep your newest "used" one for a spare) once you determine the correct size.

Here is your data tag.



Notice that your rim size shows a 19.5 x 6

The 6 is the important part here. If your 225 tires are rated for 6" rims - then yes, it'll be fine. Had your tag said 19.5 x 5.25 - then it would be NO. The 8R19.5 could have fit on a 5.25" width rim.

Here is a tire conversion chart from Goodyear

http://www.goodyearrvtires.com/size-conversions.aspx

The 245 70 R 19.5 has a 33.3" radius - That's almost the same size as your 8R19.5 which comes in at 33.1"

The problem is, the 245's are made for a 6.75 width rim so it's not going to work for you.

You can also get wider rims - you'd have to check with Spartan to see what options are available to you if you think the 2.5% difference is too much.

Here is another conversion chart from Michelin for you to ponder. Click on the "SPECIFICATIONS TAB"

http://www.michelinrvtires.com...ireInfo.do?tread=XRV

From the research I did, I think you would be wise to put NEW metric radials all the way around.

Braley returned to the chatroom,and we discussed tires. Bill N Y's posts usefully expand on the chat.

Thank you all for your quick responses. I'll be putting the original size tires back on. I should have remembered that data tag!

On Breakaways with the 4 speed, (3.73:1 diff) original tires, 8R19.5 are the best choice. By going to the smaller 225 metric tires the engine RPM at 60 MPH will increase by 66 RPM.

At 60 MPH:
8R19.5 625 RPM = engine 2331 RPM.
225/70R19.5 648 RPM = engine 2397 RPM.

Above 2400 RPM (engine RPM) your torque and power goes down dramatically.

In my case with the 6 speed (and 4.1 diff) I loose about 61 engine RPM but I cruise at 60 MPH now with 225/R7019.5 at 1723.

On my 91 Breakaway, existing tires are 8R19.5. Sounds like that is what I should replace them with. I don't want to add another 63 RPM to the engine, especially if it's already close to the maximum power and torque for the engine. I don't know what rim width is on the data tag. Was it the same on all the 91 Breakaways?
Jim