Wheel and tyre ratios

Davef1978

Hi all
Can anyone tell me about tyre ratios i have a John Deere 6210 se 16/16 power reverser gearbox. The tractor is rolling on 340 85 r24 tyres on 13x24 rims on the rear their is 420 85 r34 on 15x34 I want to if possible change over and use 15x38 rims with 420 85 r38 tyres but according to manufacture spec this will reduce overall road speed running the 420 85 r 34 the tractor runs 8.2% faster but with 420 85 r38 is 3.9% faster. What tyre combination do I use for front do I go with lower profile tyres on my tractor.
Cheers and thanks
Dave

Nekarsulm

I have a Fiat 90-90 which had 16.9x34 (85% ratio) on the back.
I came across a set of 600x38's with a 50% ratio, and their rolling circumference is identical. So no need to change the front wheels/tyres size.

If you google "agri tyre rolling circumference" you will come up with various charts. Some helpfully provide a variety of sizes that are equal in circumference. As long as they are within 100mm or so, they will be fine.

Davef1978

Cool thanks for that information I've a 40kph box and it gets slow on the hills hope I don't make it any slower. Did you change over your rims

Nekarsulm

You need more power, not different wheels....

You must be the only man in Ireland planning to fit narrower tyres than he already has....

If you plan to move to 38's, and still use 85% ration tyres, even by going down one size in width, you still are increasing the speed of the tractor (and you'll have to change the fronts as well, possibly the rims also).

The engine will still pull it up the same hill at the same speed as it's doing now, just you'll be in a ratio or two lower in the gear box.

Davef1978

I'm going from 34 up to 38 not the other way about

Davef1978

I had a 6210 se power quad rears where 420/85r38 and front was 380/85r24 front rims are both the same width on the front of both se model 13x24 the 340 85 r24 that are on the this tractor are nearly gone so I want to do a tyre and wheel upgrade on this tractor

Nekarsulm

Have a look here.

http://www.mitas-tyres.com/underwood/download/files/mitas_agri_databook_en_13th.pdf

Nekarsulm

Have a look here.. http://www.mitas-tyres.com/underwood/download/files/mitas_agri_databook_en_13th.pdf

your340/85/r24 fronts, matched to the 420/85/r34 tyres have rolling circumferences of 3420mm and 4715mm, and when you divide one into the other you get 1.37 ratio.


380/85/24's and 420's 85 38's have rolling circumferences of 3700 and 5020mm. This ratio works out at 1.35, so they would match up with the first set of tyres you listed, and keep the gearing right.

Your 420/85/38' set are going to increase the to speed a bit, because each rotation of those back tyres are covering 5020mm of road lenght, while the 420/85/34's are covering 4715mm of road. Or in other words, every turn of the back wheels will be a foot more road covered.

Davef1978

Cheers for the help answering my question thats a good help