Hi guys was just wondering how bad do you think a 2.5:1 ratio would be it's a lawn tractor with and industrial 12hp and I want to try and get 30mph out of it do you think acceleration would be slim to none it's a variable speed
What do you mean by "bad"? Getting a lawn tractor up to 30 mph, when they are normally designed for sub-10 mph, means you'll want to spend time making sure the steering is tight, well aligned, and perhaps upgrade the front wheels to use bearings instead of bushings if they use them.
Brakes would also be an issue.
The tractor itself is a small not very aerodynamic brick, and you'll have fun eating bugs, but 12hp might be able to do the job of getting up to speed, but not very quickly.