MONTREAL, Que. - The reason why wheels are tightened to a truck or a trailer is pretty obvious: to maintain them on the vehicle so you can drive it. And many people think that wheel tightening is just...
MONTREAL, Que. – The reason why wheels are tightened to a truck or a trailer is pretty obvious: to maintain them on the vehicle so you can drive it. And many people think that wheel tightening is just as simple: screw the nuts on as hard as you can. Well, think again.
Legislators have started to be particularly concerned about wheel losses since the end of the 90s when several incidents occurred, in some cases causing the deaths of motorists. Since then, regulations have been strongly reinforced everywhere in Canada, but perhaps even more in Ontario.
Beyond safety, correct wheel tightening and maintenance can translate into big savings for a fleet. Maintenance savings, but also savings because the trucks face less downtime due to wheel-related issues.
Like any other job, if you want to do proper wheel tightening, you have to use the proper tools. There are basically three of them. The first is the very well-known hand torque wrench; the second is the calibrated air impact wrench. Last but not least, the extended accu-torque wrench, which is effective because while using it, one cannot apply more torque than desired. Also, it is less vulnerable to de-calibration than other tools, which have to be re-calibrated once a year in order to remain accurate. And keep in mind that many factors can affect the precision of calibration on an air wrench: the constancy of power conveyed by the compressor, the condition of the hose (added fittings can modify the pressure), the length of the hose, etc.
Between 450 and 500
Generally speaking, a truck wheel should be tightened at 450 to 500 ft.-lb., 475 ft.-lb. obviously being the ideal compromise. During an interview with Truck West, Olivier Bellavigna-Ladoux, a senior engineer working at Prolad Experts (www.prolad.ca, consulting and training for motorized vehicles), says that the most common misconception among mechanics is that the more you tighten a wheel, the better it is.
“I often hear mechanics say ‘550-600 pounds, that’s good’ when in fact it’s not at all,” he says, adding that you run more risks and you are more likely to damage your truck by over-torquing the nuts than if you were to under-torque them. Of course, that’s no reason to purposely under-tighten the wheels of your trucks but, as Bellavigna-Ladoux says, “under-torquing is not a good situation but it’s the lesser of two evils.”
Before even installing the wheel and tightening it, you should check for any damage that could eventually lead to wheel loss. Make sure that:
* Studs and nuts are rust-free;
* Threads on the studs and nuts are in good condition, not stripped;
* The nuts’ washers are not stuck;
* The right kind of nut is used (tapered or non-tapered);
* The wheel itself is not cracked or otherwise damaged (elongated stud holes for instance).
“The best way to tighten a wheel at the correct 475 ft.-lb. of torque is to make a ‘pre-torque’ with an air impact wrench. Then you finish the job with the precision of a well-calibrated hand torque wrench,” explains our invited expert.
Never tighten a wheel solely with an air impact wrench and then validate the torque with the hand torque wrench.
It might “click,” indicating that the 475 ft.-lb. mark has been reached, but it won’t tell you if you have exceeded it, let’s say to 600 ft.-lb.
Bellavigna-Ladoux adds that one should always screw the nuts in a cross pattern in order for the wheel assembly to be correctly balanced.
For instance, start with the one at the top, follow with the one at the bottom, then the one at the extreme left, followed by the one at the extreme right, etc.
A hub-piloted wheel will have eight or 10 studs while a stud-piloted wheel will have either six or 10. After a wheel has been installed, it will need to be re-torqued after 80 to 160 km to ensure that everything is well balanced.
Over-torquing is an accident
waiting to happen
While under-torquing can lead to incidents, over-tightening a wheel is even more risky.
“It’s more dangerous because studs will be under stress and the driver can’t see it during his pre-trip inspection. It can break on the road anytime, without any warning sign, even years after the over-tightening and even if the wheel has been correctly torqued afterwards,” says Prolad’s owner.
After the metal of the studs has been stretched more than it should have been, it shows signs of fatigue and there is no way of telling when that fatigue will lead to a break.
On the other hand, if a wheel is not tightened hard enough, a driver with a good eye can see it during his pre-trip inspection because some studs will have more threads coming out of the nut than others.
Chances are there will also be marks on the rim. A loose wheel, even if it doesn’t actually detach from the truck, will lead to damage. With each acceleration or braking event, nuts will loosen and studs will hit on the stud holes, damaging the studs and the wheel itself.
Elongated stud holes are a sign that a truck has been driven with wheels under-tightened. Damage can be even worse if the truck runs with a bad suspension or tires that are not in good condition, since each of the above-mentioned shocks will be amplified in such a situation.
Should a stud break on a disc wheel, make sure to replace it as well as the two on each side of it, since they likely have been damaged by the additional load put on them after the first stud broke. If two or more studs are broken, don’t take any chances and replace all of them. And make sure to use the exact same model and the exact same length as on the original assembly. Different stud lengths on the same wheel could lead a driver to think the wheel is loose while he makes his pre-trip inspection (remember the number of threads coming out of the nut indicator?)
Lube, paint and bearings
While some people recommend lubricating the studs on aluminium wheels, Bellavigna-Ladoux says it’s not absolutely necessary.
“What is really important is to put a drop of oil between the nut and the washer. If corrosion gets in there, it might falsely lead you to think you tightened the wheel hard enough even if it’s not the case,” he warns. Besides, lubricating the studs on the truck’s aluminium wheels and not those on the trailer’s steel wheels would be complicated and unnecessary, according to him.
But if you do insist on lubricating the studs on your aluminium wheels, you should drop the torque pressure by 100 ft.-lb., as the lube will ease the nut going down the stud.
Also, when you refurbish a steel wheel, there should never be more than 0.012″ of paint around the stud holes. Any more than that and the paint could be crushed during tightening and may chip over time, loosening the wheel. And even though wheel bearings are not really part of the wheel tightening process, remember to install them according to the torque recommendation of the manufacturer. Because a bad wheel bearing can lead to a wheel loss, and also reduce its life expectancy to 200,000-300,000 kilometres instead of nearly a million.
That results in maintenance savings and a truck that spends more time on the road and less in the shop.