Medium Duty Ambulance FAQ (Freightliner, International, GMC, Chev)
- Thread starter Ozrockrat
- Start date
Just curious. The 29378SP you mentioned lists "Trailer or Drive Use Only" on their site. Are you using it on the front anyway?
Link: https://buytruckwheels.com/collecti...zero-offset-accuride-standard-polish-aluminum
Ozrockrat
Expedition Leader
Goes to prove you shouldn’t let the dyslexic guy punch in numbers. I don’t know what I meant to put in there but that is the centered one. The steel ones for the front I have out the back are basically flush with the bead on the rim.
I am guessing that I would need to measure the distance between the front axles to the rim interface, then do the same for the back. Cut the difference in 1/2, and look for that offset? Either that, or I further need to account for the wheel flange thickness, and divide that in half too, then add it onto the difference. Example (using purely BS numbers). Front distance 100", rear distance 90". Difference 10". Divide by two = 5" offset from center. Rim thickness is 1/2", so add half of that for a 5.25" offset.
Am I thinking along the correct terms? Then to get the tires to run in the same plane, run the front offset to the inside, and rear offset to the outside?
Am I thinking along the correct terms? Then to get the tires to run in the same plane, run the front offset to the inside, and rear offset to the outside?
Coachgeo
Explorer
search is your friend.
https://www.4wheelparts.com/tire-wheel-package-guide/wheel-offset-backspacing.aspx
Ozrockrat
Expedition Leader
FYI the axle widths on my FL60 were 71” on the back and 91” on the front. Mounting face to mounting face. I ran 11” rims that had the mounting surface about 1” inset from the edge of the rim. Flipping them back to front got the track within a inch or so.
My choice if I was leaving the current axles in my truck would be the front wheel rims off a cement truck 12.25” and 385/65R22.5.
My choice if I was leaving the current axles in my truck would be the front wheel rims off a cement truck 12.25” and 385/65R22.5.
Britboaters
Observer
Trestle,
Using Oz's numbers, you'd need wheels with with a 5" offset (ignoring the thickness of the center).
On the front, the wheel centerline would be at 81", and on the rear, turning the wheels around, would be 81" also.
If the wheel center is 1/2" thick, you'd need a 4.75" offset, to give 81,5".
Then to get the outside width of the tires, add the width of the tire.
So again using Qz's choice of 385/65R22.5 (nominally 15" wide) you'd be at 96.5" outside width and 81.5" inside width. Make sure you clear all the steering links and so on at full lock to maintain a good turning circle
Just a thought, the 385/65R22.5 Load Range "J" is designed for an axle load of 18,740 lbs at 120 psi. (Michelin databook)
You'll see them on the front axle of very heavy dumptrucks or concrete mix trucks.
To get the best performance out of the tire it's best to match the air pressure to the load.
The minimum recommended air pressure on this tire is 75 psi; this gives a load capacity of 13.440 lbs. (Min 75 psi to avoid issues of bead unseating).
This is a very high load capacity tire, and would probably be very hard and stiff riding.
It may be better to go to a smaller tire so that the minimum air pressure better matches your axle load.
Bob
https://www.michelinb2b.com/wps/b2bcontent/PDF/Truck_Tire_Data_Book.pdf
Using Oz's numbers, you'd need wheels with with a 5" offset (ignoring the thickness of the center).
On the front, the wheel centerline would be at 81", and on the rear, turning the wheels around, would be 81" also.
If the wheel center is 1/2" thick, you'd need a 4.75" offset, to give 81,5".
Then to get the outside width of the tires, add the width of the tire.
So again using Qz's choice of 385/65R22.5 (nominally 15" wide) you'd be at 96.5" outside width and 81.5" inside width. Make sure you clear all the steering links and so on at full lock to maintain a good turning circle
Just a thought, the 385/65R22.5 Load Range "J" is designed for an axle load of 18,740 lbs at 120 psi. (Michelin databook)
You'll see them on the front axle of very heavy dumptrucks or concrete mix trucks.
To get the best performance out of the tire it's best to match the air pressure to the load.
The minimum recommended air pressure on this tire is 75 psi; this gives a load capacity of 13.440 lbs. (Min 75 psi to avoid issues of bead unseating).
This is a very high load capacity tire, and would probably be very hard and stiff riding.
It may be better to go to a smaller tire so that the minimum air pressure better matches your axle load.
Bob
https://www.michelinb2b.com/wps/b2bcontent/PDF/Truck_Tire_Data_Book.pdf
shortbus4x4
Expedition Leader
All the newer D-maxes come with them, including pickups and have since about 07 I think. Variable geometry turbo with computer programming and a switch. Google variable geometry turbo and it explains it better than I can.
Coachgeo
Explorer
one issue with that is you can not open door till you tilt up the awning..... and for my set up..... that would be no go cause I got at least two vertical doors on each side could not open with out lifting awning up (former ambulance box). Also awning mount would have to sit high enough to open door when awning out.
Which reminds me.... to do use this awning idea at all got to plan for how to accommodate for opening door(s)
qcdstick
Member
Any idea what type of air connector this may be? It is on the vehicle for standby air to keep the vehicle aired up while at the station. At first glance I thought it was a standard 1/4" female air connector, but when I went to connect one it was quite obviously far too small. So today, I went out and bought a 3/8" connector and it doesn't fit properly either. Pictured are both the 1/4" and 3/8" next to the vehicle connector. It's like the 3/8" fitting is too big to fit in far enough to push open the valve, but IS about the right size for the retention collar (if it could go in far enough, which it won't).
Can probably just replace the entire thing with at standard 1/4" connector, but at this point I'm just curious what in the world this thing is?
Edit: Since I'm pretty sure it's 3/8", and local options in that size seem limited, I opted for the sensible thing and just swapped it out for a 1/4" universal that should work well enough with about anything I plug into it. Thanks everyone for the help, I didn't realize there were so many different types!
Can probably just replace the entire thing with at standard 1/4" connector, but at this point I'm just curious what in the world this thing is?
Edit: Since I'm pretty sure it's 3/8", and local options in that size seem limited, I opted for the sensible thing and just swapped it out for a 1/4" universal that should work well enough with about anything I plug into it. Thanks everyone for the help, I didn't realize there were so many different types!
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cjken
Explorer
A lot has changed recently in terms of electric stuff. I’m wondering if we will start to see an electric front axle option for med and heavy duty trucks at some point. What I mean is like a eztrac type deal, but electric. Just to engage below 20 mph or so.
There could be a small battery pack to operate it along with charging from the main engine.
Anyone have any insights into this as a possibility. I believe the technology exists, but so have yet to see one.
qcdstick
Member
I've often thought the opposite. Tons of otherwise useable space is lost with rear axle and driveshaft for road going vehicles. Seems to me the optimal new RV configuration would be a FWD based platform, with help as needed from electric hub motors in the rear.
I see several significant advantages:
1. You get a completely blank slate for rear buildouts, a low floor flat floor build becomes a real possibility, as does monocoque or tube frame chassis from the cab back which would make the possible configurations and uses nearly endless.
2. The engine could be smaller than normal, only needing to provide enough sustained power to maintain cruising speed on the open road plus some extra for topping up batteries, and could be optimized around that much more narrow criteria. Acceleration would be aided by the electric rear drive as needed, such as getting up to speed or climbing hills. Also gives you all wheel drive capability if needed for getting unstuck or poor road conditions.
3. You have a giant battery bank already built in which is awesome for an RV. Less time having to be tied to shore power or running a generator, especially if you incorporate some solar.
4. Fuel efficiency should be drastically better due points to #1 and #2. Lower floor means less overall height for the same useable space. Couple this with the lower displacement / better optimized ICE up front, regenerative braking, etc... This would not end up being an insignificant difference. Also, depending on the specs of the batteries and electric motors, you could potentially drop some of the lower gears from the transmission. Or, keep the 6 (or however many speeds the trans would have) but make them very close ratio near the top end. IE, a gear optimized for 40mph, 50, 60, 65, 70, 75 mph which would allow one to tune the engine to a very narrow RPM range for maximum power with little displacement. Koenigsegg has taken it even a step farther on their Regera hypercar, eliminating the transmission completely.
The old GMC motorhomes were built somewhat along these lines, without the electric rear drive. Probably not ideal for the off-roading lots of you guys like to do, but for how most people use an RV, I'm really surprised to not see some manufacturers moving this way. Certainly not an entry level budget option, but with what some people spend on RVs... I'm surprised someone isn't going this route yet.
I see several significant advantages:
1. You get a completely blank slate for rear buildouts, a low floor flat floor build becomes a real possibility, as does monocoque or tube frame chassis from the cab back which would make the possible configurations and uses nearly endless.
2. The engine could be smaller than normal, only needing to provide enough sustained power to maintain cruising speed on the open road plus some extra for topping up batteries, and could be optimized around that much more narrow criteria. Acceleration would be aided by the electric rear drive as needed, such as getting up to speed or climbing hills. Also gives you all wheel drive capability if needed for getting unstuck or poor road conditions.
3. You have a giant battery bank already built in which is awesome for an RV. Less time having to be tied to shore power or running a generator, especially if you incorporate some solar.
4. Fuel efficiency should be drastically better due points to #1 and #2. Lower floor means less overall height for the same useable space. Couple this with the lower displacement / better optimized ICE up front, regenerative braking, etc... This would not end up being an insignificant difference. Also, depending on the specs of the batteries and electric motors, you could potentially drop some of the lower gears from the transmission. Or, keep the 6 (or however many speeds the trans would have) but make them very close ratio near the top end. IE, a gear optimized for 40mph, 50, 60, 65, 70, 75 mph which would allow one to tune the engine to a very narrow RPM range for maximum power with little displacement. Koenigsegg has taken it even a step farther on their Regera hypercar, eliminating the transmission completely.
The old GMC motorhomes were built somewhat along these lines, without the electric rear drive. Probably not ideal for the off-roading lots of you guys like to do, but for how most people use an RV, I'm really surprised to not see some manufacturers moving this way. Certainly not an entry level budget option, but with what some people spend on RVs... I'm surprised someone isn't going this route yet.
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