KPRA question for California

Yes, you can be less than that as that is California's maximum. I do not know their minimum distance. You may be able to find it either in the CHP website or the Caltrans website.

 

I'm not sure how much less you could be, since the tandems will generally be pretty much all of the way forward as it is. The bridge law is found in the front of your motor carrier atlas (or here if you'd rather just click), and you'll notice an exception to the bridge formula which states that 2 consecutive sets of tandem axles may carry 34,000 pounds each if the overall distance between the first and last axles of these tandems is 36 feet or more. Seeing as how the trailer pin is usually around the mid-point between the drive axles, even at the 40' pin to rear axle setting, you've still got about 8' to spare before the federal bridge law starts limiting your axle weights.

Generally speaking, you're going to have more problems being overweight on your trailer axles with the tandems slid that far forward than you will with overweight drives.