Tire Circumference

I don't think you will see much difference either but don't think the same thought later if referring to a road vehicle...I was stopped once shortly after puting 16.5 iches rims and tires on the back of Dodge Aspen from 15 inch .... speedometer read 62.5 MPH I was clocked doing 79 MPH.

LilysDad said:

I have a '74 Wheel Horse B 80 that has a snowblower on it. Now in '74 the B 80 only had a 4 speed on it. In an effort to slow it down, I thought I would put some 22x7.50x12 tires on it in place of the 23s. Then I measured the circumference of the tires. The 22s are only 1 3/8" smaller than the others. This isn't going to make much difference in speed, is it?

I've got an 8 speed that I will put in it next year, but don't have time right now.

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For a true measure, the distance from a hard surface to the axle centerline should be used for the calculation. The rolling radius changes substantially with a difference of just a few psi. in the tire. Measuring the circumference or diameter of a tire that is not carrying the tractor, or going by the sidewall dimensions, will not give the accurate number that the tractor "sees".

I measure from the concrete to the top of the rim to check my pressures and make sure the tires will travel the same distance in one revolution. No pressure guage involved once you know what the height should be at your choice of operating pressure. Even mismatched tires can be used, but I don't recommend that. One side would be "soft" and the other "hard" resulting in different traction efforts by the two tires.

That might work to your advantage,actually--some racers use different tire pressures in the rear to fool the spider gears into acting like a posi!..

I'd like to see what that Dodge Aspen looked like with 16.5's on the back!...

I once put a pair of 36" Dick Cepeck "Quiet Giants" that were 36" tall on the back of my '56 Chevy 3100 series 2wd pickup....didn't keep them on long--first gear was like second,I could barely take off on a steep hill and had to ride the clutch--second gear was now good for 55 mph before it started winding up,used to top out at 35!--third was like overdrive,if you weren't going 65 ,you could feel every cylinder firing!..I got 3 speeding ticket "verbal warnings" withing a few weeks of installing the big tires,they threw the speedometer off a good 20+ mph!..truck looked kind of goofy with the rear "raked" up so high,and handled poorly that way,so I put stock sized 15" tires back on it..

If you really want to lower the gearing on the Wheel Horse,maybe you can find some 8" rims & tires that fit it--you'll lose a lot of ground clearance,but it'll gear it down quite a bit..

While it's not on the topic of tire size, you indicated that you wanted to slow your tractor down some. I'm guessing that there's at least one drive belt involved on your machine. Have you considered changing the belt and one of the drive pulleys? I'm guessing that the engine pulley would be the easier to change, and you would want to make it smaller. If you have to change the transmission pulley, you would want to make it bigger.