LDowney - -
I did a VERY quick look at Kubota build website, and pasted it here:
Agricultural Tires - Bias (R1)
FRONT - 9.5-24 R1 Titan Tru Grip Lug
REAR - 16.9-30 R1 DURA TORQ 17 mm holes
FRONT - 9.5-24 R1 Goodyear Dura Torque
REAR - 16.9-30 R1 Goodyear Dura Torque Cast
FRONT - 9.50-20 R1 Bridgestone Farm Service Lug M
REAR - 16.9-24 R1 Titan Hi Traction Lug TL 2.8"offset
Agricultural Tires - Radial (R1)
FRONT - LSW320/70R24 GDYR OPTI R1W
REAR - LSW 420/75R34 GDYR OPTI R1W
FRONT - LSW320/70R24 GDYR OPTI R1W
REAR - LSW 420/75R34 GDYR OPTI R1W CST
FRONT - 320/85R20 R1W ALCE FRMPRO
REAR - 420/85R30 R1W ALCE FRMPRO CAST
Turf Tires (R3)
FRONT - 9.50-24 R3 Goodyear All Weather TL
REAR - 18.4-26 R3 Firestone All Non Skid (ANS) 17mm holes
FRONT - 29x12.50-15 R3 Titan Multi Trac 8stud
REAR - 21.5L-16.1 R3 Firestone Turf & Field
FRONT - LSW305-521R3 Titan Grizz LSW Soft Turf
REAR - LSW570-648 R3 Titan Grizz LSW Soft Turf
FRONT - 13.50-16.1 R3 Firestone (ANS)
REAR - 18.4-26 R3 Firestone (ANS)
Industrial Tires (R4)
FRONT - 14-17.5 R4 With 0.55" Inset
REAR - 16.9-24 R4 Titan Industrial Tractor Lug
Looks like R1's will get you 16.9" (Bias) or 16.5" (Radial - 420mm) width
R4's are the same 16.9, which surprises me is not wider...Is that right?
I honestly expected a difference in width....like 15.5 vs. 18.4, or something like that...
But, the R1's will have the narrow lugs, maybe 1/3 or 1/4 that of R4, and possible uneven compaction track like bucktail mentions.....
I can certainly see your concern with the issue, given gravel driveway work is such a big part for you....
For a hard driveway in dry conditions, R1's might be fine. But with one a little soft or wet, R1's might make a washboard when it hardens up, even with the box blade behind it...
I like to do my driveway early spring, when it's a little soft and wet. Oddly, the R1 9.5 fronts might be more of a problem if your doing a lot of loader work.....R4's are 14...
I'll be curious what others say.
I tend to lean toward R4's even though width is comparable. It's also what you obviously know for a big part of your work. They may also wear better given your other work, like snow, some of which might on paved ground?
Best wishes and Good luck! Be curious which way you go!