Editing Semi-trailer truck (section)

===Wheels and tires===
Although [[Glossary of the American trucking industry#Dual wheels|dual wheels]] are the most common, use of two single, wider [[tire]]s, known as ''[[Glossary of the American trucking industry#Super single|super singles]]'', on each axle is becoming popular among bulk cargo carriers and other weight-sensitive operators. With increased efforts to reduce [[greenhouse gas emissions]], the use of the super-single tire is gaining popularity. There are several advantages to this configuration. The first of these is that super singles reduce fuel consumption. In 1999, tests on an oval track showed a 10% fuel savings when super singles were used. These savings are realized because less energy is wasted flexing fewer tire sidewalls. Second, the lighter overall tire weight allows a truck to be loaded with more freight. The third advantage is that the single wheel encloses less of the brake unit, which allows faster cooling and reduces [[brake fade]].

In Europe, super singles became popular when the allowed weight of semitrailer rigs was increased from 38 to 40 tonnes.<ref>{{Cite journal |url=http://www.comt.ca/english/programs/trucking/Pavements/European%20Commission%20COST%20334%20Study%20-%20Effects%20of%20Wide%20Single%20Tyres%20and%20Dual%20Tires%202001.pdf |title=COST 334: Effects of Wide Single Tyres and Dual Tyres |publisher=European Union | journal=European Commission, Directorate General Transport |date=29 November 2001}}</ref> In this reform the trailer industry replaced two {{convert|10|t|lb|adj=on}} axles with dual wheels, with three {{convert|8|t|lb|adj=on}} axles on wide-base single wheels. The significantly lower axle weight on super singles must be considered when comparing road wear from single versus dual wheels. The majority of super singles sold in Europe have a width of {{convert|385|mm|in|abbr=on}}. The standard 385 tires have a legal load limit of {{convert|4500|kg|lb|abbr=on}}. (Note that expensive, specially reinforced 385 tires approved for {{convert|5000|kg|lb|abbr=on}} do exist. Their market share is tiny, except for mounting on the steer axle.)