Rebuilding a busted MX5 was quite an education in gearboxes and ratios... I could have slowed down or sped up the blade tip speed with the replacement, but I just went with the stock ratio. There could be a number of configurations in any gearbox series, depending on what the manufacturer/customer intended it for. If you don't have the specs on the unit to check on, you can either try it out or count the splines in the gearbox to figure out the speed. Where its a tiller I think you've got a pretty wide effective speed range to play with. If it performs well in your tractors powerband, and gives you good results, its a good deal.