Yes, 6th gear can be unlocked by anyone with the proper computer hookup to the drivetrain. But remember that most 425 and 445/65R22.5 tires have a speed rating of either 60 or 65mph. You may be within 10-15% of max load in the rear. Under those conditions I'd recommend inflating to the max pressure and not going much over 65 for sustained periods.
I personally am uncomfortable in a big truck, particularly with my 395/85R20 XZLs, at over 60mph.
We will be back travelling in Oz 2/20-4/15. Probably head for the Red Centre to avoid the rain/flooding.
One tire/wheel "issue" with the Intl's is spacers vs. wheel offset vs. track width F/R.
Charlie
We'll look at the need to unlock 6th gear after we complete the build and have a chance to road test on the highway. Thanks for the idea.
Our tires, GOODYEAR G178 - 425/65R22.5 have a speed rating of 68mph. That is plenty fast for us. I don't expect we'll run more than 65 very often. I am reviewing the manufacturer's
Load Adjustments for Speed worksheets and data. It looks like you've spent some time studying this kind of data.
FYI, the following represents our current GVW calculations:
14,333 Truck Chassis
5,500 GXV Cabin
1,200 Water
1,200 Fuel
2,000 Gear
24,233 Total Est. GVW (73% of GVWR)
Any comments?
Regarding the width of the rear axle, we spent quite a bit of time working with the engineering department at International to develop the spec'd rear axle. It is a single axle MERITOR MS-21-14X-6DCR Single Reduction, Wide Track, 21,000-lb capacity "wide-track" axle. They have assured me that it will have the identical track as the front axle.
I hope that you have a great adventure down under. Ron (GXVMogHvn) has just returned and it sounds like he had an incredible time.
Thank you, again, for sharing your wisdom with a novice like me. I am in your debt!