Tractor Trailer Question

[crokett]

I saw a couple rigs today that instead of having the dually tires on the tractor and trailer had a single wide tire. Why do they run with this configuration? Can the single tire carry more? Is it cheaper to do? Does a wide tire not sink in mud as much?

[TB Roye]

David

It is probably all of the above. Out here I have seen some Dump Trucks and Cement Trucks have them and I assumed it was because of the soft ground where they went to deliver their loads.

Tom

[phi1l]

Abstract from: http://www.epa.gov/smartway/document...045-110105.pdf


Paper Number 05CV-45
Effect of Single Wide Tires and Trailer Aerodynamics on Fuel
Economy and NOx Emissions of Class 8 Line-Haul Tractor-
Trailers

ABSTRACT

We hypothesize that components designed to improve
fuel economy by reducing power requirements should
also result in a decrease in emissions of oxides of
nitrogen (NOx). Fuel economy and NOx emissions of a
pair of class 8 tractor-trailers were measured on a test
track to evaluate the effects of single wide tires and
trailer aerodynamic devices. Fuel economy was
measured using a modified version of SAE test
procedure J1321. NOx emissions were measured using
a portable emissions monitoring system (PEMS). Fuel
consumption was estimated by a carbon balance on
PEMS output and correlated to fuel meter
measurements. Tests were conducted using drive
cycles simulating highway operations at 55 mph and 65
mph and suburban stop-and-go traffic. The tests
showed a negative correlation (significant at p < 0.05)
between fuel economy and NOx emissions. Single wide
tires and trailer aerodynamic devices resulted in
increased fuel economy and decreased NOx emissions
relative to the baseline tests. Decreases in NOx
emissions were disproportionately larger than increases
in fuel economy; however, this effect may be an artifact
of the particular engine being tested. These results
demonstrate that emissions reductions can be achieved
using strategies that decrease fuel use and save truck
operators money.
INTRODUCTION

[leehljp]

They supposedly lighten tire psi load on roads. I know that this concept was used back in the late '60s but I never saw it in use. My dad was a gas distributor for 3 counties in N MS in late '50s and through the '60s. Tires of all kind were distributed to service stations and truck stops also. Industry magazines became part of my reading! The purpose at that time was the weight load distribution as well as the claim for better milage, which was not a problem back then.

The real problem was if one went flat, it would in effect render the truck/trailer unusable until the tire was fixed. With duals, a rig could limp into a station if one was within a few miles. And I would imagine that the main problem was that people did not want to be the guinea pig and "change" was not something you did back then!

[Tom Slick]

From http://en.wikipedia.org/wiki/Semi-trailer_truck

Although dual wheels are most common, use of two single, wider tires (known as "super singles") on each axle is becoming popular, initially among bulk cargo carriers and other weight-sensitive operators. With a growing desire to reduce greenhouse gas emissions the use of the super single tire is gaining popularity. The three advantages of this configuration are : (1) super singles reduce fuel consumption. Testing on an oval track (Canada 2009) showed 10% fuel savings when using super singles. The savings come from less energy wasted flexing tire side walls. Fewer tire side walls equates to less wasted energy. (2) the lighter tire weight allows a truck to be loaded with more freight (3) the single wheel covers less of the brake unit, which allows faster cooling and reduces brake fade.

[cabinetman]

I would think the "savings" from the tests are due to a single setup would be load sensitive. Duals I would guess can carry more weight, and that would affect the test results.
.

[bruce hylton]

Load capacity is directly related to square inches on the road. Super singles put more rubber on the road with one 16" than can be had with a pair of 11" standard duals.

[Tamarack]

One of the biggest advantages of super singles is a very noticeable reduction in unsprung weight due to having fewer wheels. Super singles are rated to carry just as much weight per tire as duals. The only downside is that the driver must be more careful to check tire pressures frequently (something he SHOULD be doing anyway) to avoid flats out in the middle of nowhere. Most big rig flat tires are caused by running them with low pressure due to a slow leak that could have been repaired easily at a truck stop- underpressure tires heat up more and blow out. This happens far more frequently with "Company Drivers" than with
Owner-Operators who have to pay for their own tires! During my 20+ years as a weigh station enforcement officer, our biggest problem was company drivers who didn't care enough about the equipment to do a proper job of periodic maintenance. Most were blind to the fact that while the rig is broken down on the road they were losing money, because most company drivers are only paid for miles traveled.

Sorry about blowing off steam, but this issue is one of my hot-buttons.

Paul

[phi1l]

No one cares about the reduced NOx emissions???

[crokett]

Load capacity is directly related to square inches on the road. Super singles put more rubber on the road with one 16" than can be had with a pair of 11" standard duals.

Really. Thanks for the explanation. I thought maybe it was related to the reduced weight of the tire or something,

One of the biggest advantages of super singles is a very noticeable reduction in unsprung weight due to having fewer wheels. l

Is this accurate? Found it on the web and other sources seem to confirm it:

A "wheel" meaning, without the tire on it, is approximately 150 Lbs.
A "wheel" meaning, with the tire on it, add 350Lbs to equal 500 Lbs.

If so, that is a lot more than I thought and at 8 wheels saved that is 4000lbs. A considerable savings on an unloaded weight of, say, 30000 lbs.

[cabinetman]

Really. Thanks for the explanation. I thought maybe it was related to the reduced weight of the tire or something,



Is this accurate? Found it on the web and other sources seem to confirm it:

A "wheel" meaning, without the tire on it, is approximately 150 Lbs.
A "wheel" meaning, with the tire on it, add 350Lbs to equal 500 Lbs.

If so, that is a lot more than I thought and at 8 wheels saved that is 4000lbs. A considerable savings on an unloaded weight of, say, 30000 lbs.

That is a considerable amount of weight.
.

[Black wallnut]

I'd tend to think those weights are either way off track or I am a heck of a lot stronger than I thought.
Paul makes great observations into this as he has more than enough experience dealing with drivers.

The research seems to suggest that super singles enhance fuel milage savings although I question the numbers quoted. The offset in trading gross capacity for tires is pointless as there is so much variation in loads, trailer weights, tractor weights, and weight laws. As already mentioned for bulk loads super singles make the most sense and there is some benefit by reducing the weight of the track and adding more load, however in a 48 state legal operation limited to not more than 5 axles and a light sleeper truck pulling a very light van trailer the likely net load will not exceed 45,000 lbs. If you lose 8 tires at about 100 lbs each that only gives you a new net capacity of 45,800, so every 47th or so is free. Well not quite since the cost of super singles is not exactly the same. when compared to duals.

For most fleet operations super singles simply do not make sense. When they fail, and tires do fail for lots of reasons other than what Paul stated, the price of a road service call to replace a super single will buy several tires. With dual tires often it is possible for a driver to travel some distance with one flat. Been there done that many times. I've also had super singles go flat and destruct, that was long ago before cell phones.

As far as load capacity, it is measured in so many pounds per inch of tread width. In my state it is 600 lbs. However legal weights is far more complex than just one simple number. Where Paul used to work size, weight, and load was a rather complex set of laws , rules , and regulations. Although I passed through his scale many times I was never able to catch him at work.

Really. Thanks for the explanation. I thought maybe it was related to the reduced weight of the tire or something,



Is this accurate? Found it on the web and other sources seem to confirm it:

A "wheel" meaning, without the tire on it, is approximately 150 Lbs.
A "wheel" meaning, with the tire on it, add 350Lbs to equal 500 Lbs.

If so, that is a lot more than I thought and at 8 wheels saved that is 4000lbs. A considerable savings on an unloaded weight of, say, 30000 lbs.