F-220

[frank99]

Hi

I have an F-220 and I'd like to change the tyres to 320/70 and 240/70 to reduce ground pressure. The original Japanese tyres (for rice crops) have very large lugs. Tyres are 6-14 and 9.5-22.
I'm looking for the transmission ratio between front and rear wheels to determine the correct tyre sizes.


Thanks in advance,

 

[Mickey_Fx]

Knowing the mechanical ratio between the front and rear axles may not be the best way for you to determine new tire sizes. I think you'll find the axle ratios are set up so the front axle drives ~2-3% faster than the rear. What I'd suggest is for you to measure the dia of the stk front and rear tires and look at the ratio between them. You can then select a set where the tire dia ratio is close to the stock tires.

 

[frank99]

Thanks, Mike.

I thought like you first but I ran into trouble.

What I know of these things: the front axle runs 2-5% faster than the rear axle. If I measure the diameter and calculate the current ratio between front and rear, then included in this calculation is the 2-5% 'forerun' ("Voorlop" in Dutch). To maintain this 'forerun' I'd have to get me front and rear tires that both have exactly the same old/new ratio. If not, the 'forerun' easily falls outside the 2-5% limitation.

However, new tire sizes are not exactly fitting this calculation. It may well be that any approximate tire sizes will lead to less than 2% or more than 5%. So I need to know the exact ratio in order to stay within the 2-5% limits. Since the tire size is common to many Yanmar tractors, the front/rear axle ratio of any model with front tires 6-14 and rear tires 9.5-22 is the ratio I'm looking for.

Unfortunately Yanmar refused to provide assistance.

Thanks again,