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Tire size change - need a little help

R

Rick Kr

Well-known Member
Looking for someone to tell me I am on the right track.

I am switching my NH3930 4wd from 9.5-24s and 14.9-28s to R-4s. I need to keep the ratio the same for the 4wd.

Using Titan/GY specs:
For my current tires I came up with [b:6b3b4a6287]78.8%[/b:6b3b4a6287] front/rear.

Switching to 12.5/80-18s and 16.9-24s, [b:6b3b4a6287]75.1%[/b:6b3b4a6287]. (rear tires going faster)
12.5/80-18s and 17.5L-24s, [b:6b3b4a6287]79.9%[/b:6b3b4a6287] (front tires going faster)

Do you agree I need to go with the 12.5/80-18 & 17.5L-24 combo? It will be off by only 1%. Plus air pressure in the tires will vary that a little.

I can put the 12.5s and 16.9s on, as I already have them all, but thinking I should switch out the 16.9s for 17.5s.

FWIW, the R-4 option on this tractor was 11.2R20/16.9-24. The 20" rims are impossible to find. The tires I have worn out and need replaced, and I need to switch to the R-4s.

Thanks
Rick
 
IIRC, fronts should run a bit faster than rears. Maybe cuz they"re smaller, and wear faster? Plus, they carry less weight (less traction?) than the rears? Some op manuals have the recommended combos in the book.
 
JMS,
I agree with you, I have read the front should run a little faster. No such luck on any info in the owners manual for the R-4 combo.

Talking with the 2 local Ford/NH dealers, the one had never seen the combo on any he sold, and did a lot of digging to find out the about the 20" tire size.

The second dealer said the same thing... "that"s rare, nobody ordered them that way" This is a big dealer, they handle the majority of the ditch bank mowers for the counties and state of Michigan.

Rick
 
For all practical purposes you'll never know the
difference between 78.8% and 79.9%. Depending on
how your tractor is loaded and what your inflation
pressures are the dimensional data from the tire
book can have quite a bit of variation anyway. If
the factory setup had a large overspeed for the
fronts, for example 5%, even the 75.1% could still
result in the fronts running faster than the
rears.

You always want the fronts to be over-running the
rears by 1-5%. The tractor will not steer as well
if the fronts are being pushed.
 
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