Tires Tire SLR's and MFWD.

[AKfish]

There have been a number of posts regarding bigger tire and rim combinations. And of course, discussions about R4's, R3's and R1's and a current thread about JD790-770 tires and "rolling circumference".

I recently purchased the OEM tire/rim combo for the JD990 for use on my older model JD970.

Can you do that...? Will it mess up your MFWD? What's the "rolling circumference" and SLR?

AKfish

 

[irwin]

hi Akfish:
I'd be willing to bet your okay.. If you want to pm me with the size and brand of your original tires, frt and rear.. and the same with the new tires..I should be able to find the rolling circumference on all and check ratios for you.. If you message deere from their site you should be able to get the mfwd ratio for both tractors--but from my findings , most likely they are the same..

When I get home from work I can get related info on lead percentages and post a link for you..

tim

 

[irwin]

Can I use a different size tire on my 4wd tractor

Akfish here's that link, use the formula with the mfwd ratio for your 970, along with the rolling circuference of your tires. Let me know if ya got any questions.

Heres how it works.. the 770 and 790 ratio is 1.571. The front tire (23x8.50-14) rolling circumference (from the titan tire site) Titan® 2006 Tire catalog is 71" so multiple 71 by 1.571. This equals 111.541..Divide this by the rear tire r.c. in my case it's 110" this equals 1.014. Then subract 1.0 this equals .014 multiple by 100=1.4 this is the front wheel lead percentage, anything from .5 to 6.0% is okay. I have read a few differences on acceptable lead percentages, but this appears to be correct (.5-6.0).



let us know ...Tim

 

[AKfish]

Thanks Tim. If I use the rolling circumference of the tires or the "static load radius" (SLR) method of calculating the front tire slip --- either way it looks like I should be OK.

I have seen mention that the rolling circumference calculation should not be used for tires that have less than a 24 inch diameter. You ever hear that claim before?

The gear ratio for the JD970 is 1.691. And from the Titan website you posted -- the SLR for the front's is 13.9 and the rear's is 22.7.

The circumference is 91 and 150, frt. and rear. Thanks again, for the links.

AKfish