I BOUGHT A 93 BARTH BREAKAWAY, IT HAS 225/70R 19.5 TIRES ON IT.WHEN 1 DRIVE @ 70MPH MY GPS SHOWS I'M ONLY GOING 63 MPH.THERE WERE NEW TIRES ON IT WHEN I BOUGHT IT. I WOULD LIKE TO FIND OUT WHAT SIZE TIRES ARE SUPPOSED TO BE ON IT. I WOULD APPRECIATE ANY HELP I COULD GET.
TIM

Hi Wrongturn, and welcome to the forum.

Have you looked at the data tag yet? It will have tire and wheel sizes. It is possible that your 225/70s are a little smaller outside diameter than the originals.

While you are there, could you share the other numbers here for our database?

I have a 30', '94 breakaway and the standard tires for that are 8R19.5, I had a slight problem with the speedometer calibration even with those, the 225R70 19.5 tires are in fact a bit smaller in diameter so that probably is where your issue is.

Here is a link to my website showing how to reset your speedometer. Follow this and you will be able to set your speedometer to within 1MPH of your GPS reading.

speedometer re-cal

At the bottom of this procedure is link to VDO calibrations spec. This all should get you going.

THANK YOU FOR YOUR INPUT, IT IS VERY HELPFUL.WHERE IS THE DATA TAG LOCATED?

quote:

Originally posted by wrongturn2:
WHERE IS THE DATA TAG LOCATED?

Typically it's above you head, behind a curtain rail on the drivers side. It looks like this.



We are looking for a group of numbers that, in your case, should begin with 92xx or 93xx. In the above example, this number is 8908-0128-40RDS-C1

Also, do you have a few pictures of your coach that you can share. My email address is bill_ny@barthmobile.com

Hi wrongturn2,

When I put new rear tires on my coach, I went from an 80 series Michelin to a 70 series Toyo. Michelin is the only maker of the 80 series and I didn't want Michelins. Because the 70 series tire is slightly smaller, my odometer is no longer accurate. I didn't loose much in fuel mileage, but gained in torque while accelerating. This has actually worked out better since the coach was sluggish before changing tires. I like the new set up better and don't really bother with the speed. I know that my odometer is about 4 miles per hour slower that what the odometer reads.

Bill G

"I know that my odometer is about 4 miles per hour slower that what the odometer reads.I know that my odometer is about 4 miles per hour slower that what the odometer reads."

Bill, isn't that's what GPS data is for?