Single versus Dual Wheels
Using Single Wheel Tandem Axles Versus Dual Wheels Single Axles?
The question often arises as to whether it is feasible to just mount one wheel on each hub instead of removing one of the tandem axles. The idea is to have the same number of tires (four) on the road reducing the tire friction of a tandem dual configuration while not incurring the cost of singling the truck.
To properly use single wheels on the hub, the wheel need to be close to zero offset instead of the typical offset wheels used on a dual wheel setups. The typical wheel hub offset (about 7") needs to position the rim such the each tire on the dual doesn't touch. If the same offset wheel is used in a single wheel setup, either in the inner or outer position, the rim will be offset from the center line of the hub bearings, causing a lever load on the hub bearing
A PDF on the subject of 10009934-RevF-12142011.pdf
So if single wheel hubs are desired, you should think about wheels with a much smaller or no offset.
Because you would still only have four tires, your rear axle load capacity would be about 19,000 lbs., the same as a single dual wheel axle if 0 offset wheels are used. If the offset wheels are used, the combined load capacity of the four single wheel tandem axle configuration would be about 18,000 lbs., or a loss of about 1000 lbs. of carrying capacity.
Your available cargo capacity will be about 1000 lbs. less will tandem axle single wheels compared to single axle dual wheels because of the second axle.
Using single offset wheels on tandem axles means about a 2000 lb. reduction of rear capacity. This may not be an issue for just a truck and trailer. However a heavy deck load may need those 2000 lbs.
You will have four brake drums/shoes with a single wheel tandem axle setup compared to just two brake drums/shoes with a dual wheel single axle configuration. At first look this may seem to be a positive for braking effort. But you have to remember that the braking effort of the brakes are applied to the friction of the tire patch (the area of the tire on the ground) With single wheels, there is only one tire patch per brake while the dual wheel has two tire patches for twice the area.
Pros and Cons of a Single Wheel Tandem Axles Versus Dual Wheel Single Axle:
Single PROS/Dual CONS:
- More brake shoes.
- No expense of the conversion to single the truck out.
- More unsprung weight (extra axle) means more sidewall loading for a better ride.
- Some claim better off road traction.
Single CONS/Dual PROS:
- Use existing wheels.
- Smaller turning radius.
- Less preventative maintenance.
- Fewer brake shoes, air bags, shocks wheel bearings etc. to replace down the road.
- Some claim a better resale value if and when you sell the truck as an HDT.
- The ability to continue with one tire out of a dual set..
- 1000 lbs. more rear load capacity for dual axle.
- 1000 lbs. less vehicle weight without the extra axle
- Cheaper tolls if you frequent Eastern states.
Basically, it all boils down to your preferences or to what you'll be loading on the deck of your truck.
Super Singles Tires:
Super Singles are a new tire in the commercial marketplace. The Super Single is about the same width as the dual tire pair of tires, meaning more tire patch surface as the center gap between dual tires now has tread. By the reduction of a pair of sidewalls, the Super Single is about 400 lbs. less than a dual wheel set.
Fleets are implementing Super Singles for the reduced weight, which means more billable cargo capacity and better mileage.
Old truckers don't like the Super Singles because if they have a flat, they can't continue on like they can when they lose one tire is a dual set. The problem is that if the load is high enough, like a normal cargo load, the remaining tire will be overloaded.
In the RV HDT role, the issue of continuing on one tire is mitigated by the lower loads present. At full pressure, one tire can handle the typical loading as long as you have the ability to raise the tire pressure.
Unless you buy a truck with Super Singles, the cost of changing over is basically prohibitive.