# Impact of wheel size.....



## Webiter (Oct 28, 2012)

If I were to change the rear drive wheels on tractor from 420/85R30 to 315/80R22.5 this would reduce the vehicles top road speed from 38km/hr to 27.6km/hr which is a reduction of some 26%.

Does the reduction in wheel size raise or lower the torque value of the engine or does it make any difference. :merry:?


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## wjjones (May 28, 2010)

Webiter said:


> If I were to change the rear drive wheels on tractor from 420/85R30 to 315/80R22.5 this would reduce the vehicles top road speed from 38km/hr to 27.6km/hr which is a reduction of some 26%.
> 
> Does the reduction in wheel size raise or lower the torque value of the engine or does it make any difference. :merry:?



You would think it would gear it down in torque in the rear diff but the engine would not be affected except it would have to rev higher for top speed.


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## Webiter (Oct 28, 2012)

So if a tractor is quoted as having say 200Nm of torque with the wheels that it has been supplied with from the factory, does the torque or horsepower deliverable to the drive wheels increase if the wheels are changed for smaller ones as indicated ?


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## X-Raycer (Jul 19, 2012)

Webiter said:


> So if a tractor is quoted as having say 200Nm of torque with the wheels that it has been supplied with from the factory, does the torque or horsepower deliverable to the drive wheels increase if the wheels are changed for smaller ones as indicated ?


My understanding of gears is that by changing to a smaller final gear, wheel in this case, the applied torque of the gear/wheel will be greater. Also in this case, given the same engine RPM and the wheels being smaller, the top speed will be reduced.

My 30 HP CTX9500, 107.25007 came with 24x12-12 Turf Tires. The top speed was advertised as 8 MPH.
I installed some 23x10.5-12 Ag Tires with 12x7 Wheels on it and the speed did seem slower.
But what bothered me was the smaller "Footprint" of the tire. The tires had a tendency to dig holes in pulling situations.
I theorize that the smaller diameter (Greater Torque) of the Tire coupled with the narrower tread concentrated the power to a smaller patch (Footprint) of ground. So it would tend to dig a hole.

My remedy was to put 26x12-12 Ag Tires on the factory 12x10 Wheels.
I'm doing the same type of work with the back blade but have not dug a hole yet.

The Top Speed is negligible as the mounted diameter is only slightly larger.


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