Everyday i do a 60 minute commute from Hamilton to Toronto for “work”…my question is, tractor trailors with, i dunno, 18 wheels, only use i think 10 of them. Can anyone explain why they bother putting on the other wheels? Are they spares?
They raise or lower the wheels depending on how heavily loaded the truck is. The more weight, the more wheels, to get the pounds-per-square-inch down to a reasonable level. Also, some areas have laws about how many wheels they can have on the ground, and they have to raise some off from time to time. Tour buses do this, too.
IANATD but if some axles are off the ground, it may be that the load is light enough that the load per axle is within limits. If a heavier load is on board, the “extra” axles are lowered to distribute the load. In the U.S., some large dump trucks are set up this way. When the extra load capacity is not required, the axles are raised to reduce wear on those tires. In the case of dump trucks, they may also be able to turn tighter on a construction site if those wheels are not on the ground.
Why does everybody spell it “trailor” with an O? I always thought it was “trailer” with an E. Merriam-Webster supports me, at least. But everybody spells it with an O now. What’s up with that?
As an American who has toured extensively by road (U.S. and Canada), and done the Buffalo, Hamilton, Kitchener round trip frequently…
The trailers in Canada (especially the “hopper” type, open shells with a tarp covering the load of raw material (coal, ore(?), sand, etc. etc.), the majority seem to have this ‘extra’ axle in the middle of the trailer.
I am sure the reason for this is as explained above (too many axles on the road, load dispersion, etc.).
I’d just like to point out that these “extra axle” trailers are the minority on most American highways. Yes, of course, there are some (I also see dump trucks and cement mixers with extra axles), but the majority I see (in the U.S.) do not have the extra axle. Hmmmm… different regulations between the two countries?
IAATD, but the other posts pretty much covered it.
The are put down when the loaded weight leagally requires it, if the extra axle is in the middle of the trailer it is usually to take advantage of laws on the way weight is distributed. They can be raised temporarily to make a tight turn easier and without causing excessive tire wear, particularly on trucks where the extra axel is far away from the rest. They are raised when not needed to prevent tire wear. Most states charge tolls based on the number of axles but only those being used count so this is another cost savings.
Weight laws vary widely from state to state and Canada so many trucks that stay within a state are built to take advantage of local laws. In some states dump trucks have an extra axel that is lowered about 10 feet behind the rest of the truck on a boom, this is to take advantage of the extra weight allowed on a longer wheelbase in these states.
While on the subject of truck axles, in Europe I noticed many ‘fixed chassis’ (not tractor-trailer) trucks have 2x2 configuration - i.e. 2 (steerable, I guess) axles in front, and 2 in the back. I have not seen this configuration used in North America at all (except for very heavy Cement mixers). Any ideas why?
It has to do with bridge laws. States and provinces have bridge formulas that establish axle load limits.
The vehicle weight is distributed on the axles in such a way so as not to overload a road structure (bridge) when the vehicle is loaded to it’s maximum weight.
If you were to look in a trucker road atlas,(available at any truckstop, last years edition available at a discount) most of them have the bridge formulas and weight guidelines in them somewhere.
I think Vivian is referring to the extra wide tires I’ve seen recently. I’ve never driven a truck with them and none of the trucks at our company had them. One tire replaces a set of duals so instead of 8 tires on the trailer there were 4 extra wide ones.
Those extra wide tires are called “super singles” by the tire companies. The reason for using them on trailers is to save weight. Using four tires to replace eight can save four to six hundered pounds. The trailers that can use them to the best advantage are liquid bulk trailers and dry bulk trailers. Dry bulk trailers are often loaded while parked on a scale, so the super single tires help to get the most possible payload onto the trailer. One advantage of the super single tires on bulk liquid trailers is that the tank can be built several inches lower giveing the trailer moe stability. Two disadvatages to super singles are that each tire costs a lot more to replace and that if you have a flat you have to get it fixed right there and can’t drive it in slowly for little way to a tire shop.
When you see them used of the front axles of concrete mixers and dump trucks it’s to allow higher front axle loads.
It also makes steering old mixers agony for a driver with bad shoulders.