Tires: from 255/70R22.5 to 275/70R22.5 Rev/Mile Adjustment

[smalexander]

It time to change my tires, all six. The FMCA Michelin deal looks good. I've talked to other MH owners, Thor and Freight Liner, and tire dealers. It is close to decision time. I'm thinking of moving from my GY G670 255/70R225 to Michelin 275/70R225. (Some of the newer models using the same chassis use the 275/70's) I have made the measurement of wheel well, minimum dual spacing (spacing is 13").

Now the questions:

1) How do I adjust the Rev/mile? I've looked at the Operators manual for Freight Liner, and don't see an adjustment on the menu setup. (I thought I did at one time.) Is it a user setup or must I take it to Freight Liner or Cummins?

2) A friend told me that if I make the change to the 275 that my GCVR should increase from 5000 lbs (now) to 10000 lbs as with the later models of my 2008 Damon Astoria. Does anyone know it this is true. Freight Liner said check with Thor and Thor said check with Freight Liner.

Thanks in advance for any help.

Steve

[desertdeals69]

The revs/mile is set in the engine computer by a person with a laptop and the right program. Cummins or Freightliner dealer will have the necessary skill and equipment.

[wildebill308]

Go to one of the big tire web sites like Michelin. They have charts that give the rolling diameter of each tier size. Compare the two different sizes and calculate the percentage of difference. Then you can calculate your real mileage and speed.

Bill

[wolfe10]

Those same charts also give "Revolutions per mile" for each tire.

[hermanmullins]

Steve,

One more thing I would check is the gap (called "dual spacing) between the Rear dual wheels. You may need a spacer between the rims.

Herman

[RoySchoepf]

We made this change a number of years ago - the peace of mind that comes from the increased tire capacity is wonderful! Chassis capacity is determined by a number of factors - tire capacity is only one of the factors. Brake capacity, spring capacity and many others must be considered in determining chassis capacity.

[racer478r]

I made this same switch years ago and the difference on my speedometer was 2.75 miles per hour. This help me as before the switch it was off by 5 mph!