Tire Size Question

[jerichorick]

Originally Posted by Pbac

I am looking to replace all six tires on my coach. My current tires are Toyo M147 295/75R22.5. Toyo doesn't make the M147 anymore, or I would buy them again.

I'm hoping to replace them with Toyo M144s, but that model does not come in my current size. My reasonable options are: 1) 295/80, which is 1.2" taller and same width, or 2)305/70, which is about .5" shorter and about .5" wider.

I would like to hear from this knowledgeable crowd which one you would choose, and why?

Thanks a bunch!

Flip
1999 Holiday Rambler Imperial, Cummins 8.3 ISC

I put the Toyo M154's on my coach about 8 months ago. 295/80's work fine. Great ride. Went to 16 ply. This model has 14 & 16 ply ratings.

[flywithcoop]

Try to stay as close to the original size as possible. this is so your speedometer stays fairly accurate. larger or smaller tires change the accuracy of the speedometer. TOYO's are good tires.

[jerichorick]

Originally Posted by flywithcoop

Try to stay as close to the original size as possible. this is so your speedometer stays fairly accurate. larger or smaller tires change the accuracy of the speedometer. TOYO's are good tires.

It's not that complicated to change tire sizes and still be close on the speedometer accuracy. In my case, I am getting a closer reading than I did with the original Michelin's. All tire manufactures have a RPM column in their spec sheets. If you know what the original tire is you can find a tire with a different profile that will satisfy your original spec withing reason. But the buyer must do the homework. Tire dealers simply sell tires to make money. Not all the sales folks have the knowledge details up front that we are requiring. Most folks simply replace tires by picking a brand that they heard is good on their car or whatever. We need to be a bit more picky and I think you will agree to this idea. We do have a broader range of choices in tires than one might think was available. It simply takes a bit of googling to find the good way to go.

[barmcd]

Check this out:

https://www.tacomaworld.com/tirecalc....5-295-80r22.5

[Dale70]

On the speedometer side, if you have a VDO speedometer/odometer with the digitial display that should be an electronic speedometer.
There is an easy procedure (available online) to recalibrate the speedo.

I did nine about two weeks ago and am within 1/2 MPH of a GPS.

Easy Procedure with a VDO Gauge.

thx Dale

[jleamo1]

Are you sure your 99' Imperial actually came with that size tire. Double check the label inside. Ours came with the 295/75R22.5 (just as yours) and they were the incorrect tire, also over loaded on the steer axle!
I just switched our 02' Imperial to 12R22.5 from 295/80R22.5 that was supposed to be on it. The 295/80's are hard to find and with only a few manufactures making them. The 12R was the closest overall size, weight, load rating that would fit on the Roadmaster wheels plus its a common size in the trucking industry, so if we need a replacement it shouldn't be hard to locate.

[Pbac]

That's a good point jleamo1. I was wondering if that was even the original tire size. The coach came with a ton of original brochures and paperwork, so I'll dig through and see what I can find.

I'm fortunate that the previous owner preserved all the manuals and took meticulous notes on servicing and replacement of parts.

[jleamo1]

Originally Posted by Pbac

That's a good point jleamo1. I was wondering if that was even the original tire size. The coach came with a ton of original brochures and paperwork, so I'll dig through and see what I can find.

I'm fortunate that the previous owner preserved all the manuals and took meticulous notes on servicing and replacement of parts.

Behind or along side of the drivers seat on the exterior wall is a label, that should have the tire size that came with it as well as a bunch of other good information. If not call REV at 1-877-466-6226, they should have that information when you give them your VIN number.

[Crasher]

Going from a 295X75/22.5 t0 a 295X80/22.5 results in 2.5% increase in circumference. That's 1.3 mph at 60 mph. On our 2003 Phaeton, I went from a 255X80/22.5 to a 275X80/22.5 which was a 3% increase. Freightliner reprogrammed the computer to correct the speedometer. I'm not sure if they changed the shift points or not. I ran them for six years and 45,000 miles with no issues and do not recall any change in mileage. If there was any change in performance, I didn't notice it. The coach did ride a little better, but not enough to change for that reason alone. I did it for increased load capacity and Tiffin paid 50% of the cost.

[flywithcoop]

Originally Posted by Dale70

On the speedometer side, if you have a VDO speedometer/odometer with the digitial display that should be an electronic speedometer.
There is an easy procedure (available online) to recalibrate the speedo.

I did nine about two weeks ago and am within 1/2 MPH of a GPS.

Easy Procedure with a VDO Gauge.

thx Dale

Interesting. Pls post the web link. My speedo is 2 mph faster than 3 different GPS systems. I had always assumed it was due to time delay between GPS and the satellite signal.

[Dale70]

Here is what I used to calibrate my VDO speedometer.

VDOCALIBRATION

if this does not work -- just search for
VDO speedometer calibration pdf.
was the top search result for me.

hope this helps --- -Dale

[Pbac]

Thanks for the tip jleamo1. I called REV and they were able to confirm that the 295/75R load range H (16 ply) is the correct tire for my rig. I spoke with Deb (says she's been there FOREVER), and she was able to search in some hard to find places to confirm. They are a very valuable and helpful resource!

I decided on getting TOYO M177s all the way around. They get installed in St. Louis on Friday. Out the door for $2,966, including balancing beads.

Thanks again!

[jerichorick]

Originally Posted by Dale70

Here is what I used to calibrate my VDO speedometer.

VDOCALIBRATION

if this does not work -- just search for
VDO speedometer calibration pdf.
was the top search result for me.

hope this helps --- -Dale

Thanks Dale but I can't see how this will help me on my Freightliner chassis. No obvious button to push. Now, on my CR-V this method just might work.

We have been focusing on RPM for the last several posts. There is a factor that is a bit more critical, IMO. Width. On the duels this is very important to keep the running clearance of the tires correct. You don't want the sidewalls to touch when traveling. The friction will heat the tires and cause premature failure. Width on the front or tag is not as critical as long as there is no fender rubbing when the suspension is deflated.

No matter if OEM size is used or a custom size tire, this story holds true. A friend told me of someone he knows who forgot to straighten his front wheels before setting up for the night. Blew the fenders when they came in full contact with the tires. That was an expensive camping night.

[Dale70]

If you don't have an electronic VDO the procedure will obviously not work.
I was asked by flywithcoop to post the link.

I posted the link -- thx Dale