It's not the radius, it's the whole axle diameter, plus the thickness of the spring pack, plus the height of the original bottom spring pad, plus the height of the new top spring pad.
You're moving the bottom of the spring pack from where it is, about 3" below the bottom of the axle tube, to where it will now be, about 1" above the top of the axle tube. This example is assuming both spring pads are about 1" high and the spring pack is about 2" thick and the axle tube is about 3" diameter.
Going from bottom to top, it's the spring pack thickness (2"), plus the bottom spring pad height (1"), plus the axle tube diameter (3"), plus the top spring pad height (1"). This totals 7", in this example. Axles can be all different diameters. Spring packs can be all different thicknesses. Spring pads can be all different heights. So it is entirely possible to end up with a measurement less than or greater than this example.
Another example could be a 2-1/2" axle, 1/2" spring pads and a 1-1/2" spring pack, which would make 5" instead of 7".
I think that happens to just about every extended length camper sometime in it's lifetime. I tore up my 10.5' camper more than once and I wasn't the first one to damage it either. That's why my next 2 campers were 8 footers!
Check the registration laws of your particular state, and ask your insurance agent about the insurance.
My F350 cab/chassis required a $1M commercial policy, which cost about double what my F350 pickup cost to insure with $300K limit. This was for a '97 F350 4x4 diesel dually cab/chassis 11,000 GVWR, versus a '92 F350 4x4 gas single wheel pickup 9200 GVWR, both with the same insurance company, same driver, same location, same full coverage comprehensive, etc, except the commercial policy did not offer roadside assistance, which the pickup policy did.
Once you do get a commercial truck policy though, the price doesn't change much from one commercial truck to another. My International cab/chassis doesn't cost much more to insure than my F350 cab/chassis did, while the International is newer and worth twice as much as the F350 was and the GVWR is 3 times higher than the F350's (11,000 vs 33,000).
One thing to consider is the hours of engine use. Many commercial service trucks have low mileage, but have high hours, because they run the engine all day on the job, powering winches, booms, compressors and other job-related equipment. There is usually a procedure to check the hours of newer diesel trucks. You would have to consult the owner's manual, or ask on a brand-specific forum, to find out how to check the hours on a truck you're interested in.
Some trucks with flatbeds or service beds started out life originally as pickups and had the beds replaced. Others, started out as incomplete cab/chassis trucks, which were then sent to an aftermarket upfitter and finished as a complete vehicle, with the bed and other equipment.
Depending on your state's laws, the cab/chassis truck may be considered a commercial truck, requiring commercial truck registration and insurance, or it may not. In AZ and CA, cab/chassis trucks over 10,000 GVWR are automatically commercial trucks, for registration and insurance purposes, regardless of how they are used.
I had two F350's, otherwise nearly identical, except one was a pickup and one was a cab/chassis truck. The cab/chassis truck was roughly double the cost on registration and insurance, versus the pickup, both in AZ and CA.
I can't imagine tow bar mounts for a Tracker costing $2000. Buy a universal tow bar for about $150, which comes with it's own mounts, and have a local welder fabricate some brackets to weld the tow bar mounts to.
I like that the full air ride suspension kit you used uses the truck's original spring hangers and places the load fully on the hangers, which is where the truck frame engineers intended the load to be placed.
With the common add-on air-assist bag kits (Firestone, Air-Lift), they take load off the springs and place it in the middle of the frame, which is where the frame is weakest, particularly with '99-up F250-550 truck frames.
There is a half-circle scallop removed from the lower flange of the frame channel, above the axle, to allow for shock clearance. The scallop is so deep that there is practically no lower flange left on the frame in that area. That is where the frames crack.
That scallop is the same spot that the air assist bags place their additional stress on the frame.
If you have a light hitch load on the truck, you may be bouncing on and off the truck's rear axle overload springs. Lots of folks use overload spring bump stop extensions to get the overloads to contact sooner and stay contacting anytime the truck is loaded. This stops the on again, off again of the overload springs and reduces some of the bouncing of the truck's rear axle.
Gears are a torque multiplier. When you shift to a lower ratio gear, you have greater torque multiplication. Therefore, the engine doesn't have to work as hard when operating in lower gears. This means less heat made by the engine.
When I worked at the RV park, most folks with motorhomes pulling toads had those full-width big hairy mudflaps under the rear bumper, in addition to the individual mudflaps just behind the rear wheels.
I guess the big hairy ones work better than the solid rubber ones?
Alot of the trucks pulling travel trailers and fifth wheels full time had those big hairy full-width flaps too.
...since it would be the diameter of the axle plus the thickness of the spring pack.Plus 2 times the height of the spring pads...
If you have a 3" diameter axle tube, 2" thick spring packs, and 1" high spring mounting pads, the lift ends up being 3 + 2 + 1 + 1 = 7
Naa man, just hacksaw off those little hooks and replace them with some heavy duty clevis hooks that fit. Get some with the safety latches... Here is an example
JeremiahThat right there is what I use, works great.