Tire RCI groups

Patch164

Member
I'm in the market for new tires for my tractor. It has 14.9 30 fronts( rci group 41) and 420 80 r46 rear(rci
group 46). I would like to go to a 16.9 front and 18.4 rear. This would change the rci group to 42 and 47.
Can I do that without effecting the lead lag ratio? A Michelin salesman said I could but I'm not sure He
might have just been trying to sell me tires because he said people do it all the time but I haven't found
anything about it online. I know I can change to 42" rim and run the 18.4 but I don't want to have to get 4
new rims.
 
It only shows what is on there now 14.9 30 and 390 90 46/ 420 80 46. Then the size if I change the rims to a 42 I can get the 18.4 or if I go to a 38 I can run the 520 and keep the same front tires. It doesn't show anything about changing front tire sizes. In my case I want to increase both front and rear tires sizes. Also the operator manual isn't original I got it off Ebay but don't think that really matters.
 
That would be a good question to ask on your tractor manufacture's support web site.

Try to keep your question to them as specific as possible, like: If I change the front tires from 14.9-30 to new tire size X (the new tire size you want), will tire size A work on the rear or what would you recommend?

You can try to work out some possible tire combinations yourself by keeping the same ratio between the loaded tire radius of the front tire and the loaded radius of the rear tire. Be aware that the loaded radius of tractor tires of one size will change with tire brand and with tire model, especially between bias ply and radial ply tires. Also, the front tires will wear faster than the rear tires, you want to keep the front tires always pulling faster than the rears, the owners manual should say how much faster that ratio needs to be.

Worst case, stay with the original tire brand and size.
 
Ha it's already got 3 different tires on it. I bought it at an auction last year so who knows what was originally on there. Had radials on the rear and bias in the front. Needs new tires now and trying to figure out what to do. I talked to the Deere dealer and they said ask the people I buy the tires from. It's like no one knows.
 
Ok I called nts tire supply and they said it was ok to go up in sizes and long as you do both front and rear. If I wanted to go just different in the rear is where I would run into problems and have to get different rims. Good information to know. They said you just have to watch the rim width then.
 
Calculate the ratio between the front and rear. As long as you keep that ratio your fine.

I do it by figuring the circumference of the front and rear tires. Then just figure the ratio between the two. Then look up the circumference on the tire your looking at. Do the math and it will tell you.
 
Yes. You will be fine if you keep the same drop. So if you had 46 and 41, you can go to 47 and 42. That is the way RCI works. You don't have to do the calculations manually.
 
Good to hear. I read somewhere that as long as you keep a difference of 5 between groups you should
be fine like 46 and 41.
 

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