Hey Jeff,

When I purchased the W126, I drove it up from Florida with the stock 195/70/14 tires. With the AC operating the entire trip, the vehicle would routinely get about 26 mpg. After getting it back to New York, I switched the tires from the W123. Now, it had 215/70/14 tires that I had purchased previously. The fuel economy remained unchanged, still about 26. BUT, the vehicle traveled 3% farther because of the larger tires. I could not tell any difference at the pump based upon the larger tires. If the fuel economy stayed the same, I would have expected a drop at the pump because the odometer had not been recalibrated.

Now, 3% is such a small amount that I could be within measuring error. I really do not have enough data to confirm the 3%. But, my sense is that the fuel economy is better with the larger tires.

Brian Carlton
1984 300 SD