Do Treadmill Desk Weight Ratings Really Matter?
If you’re comparing treadmill bases should you really take into account whether they’re rated for users at 250 lbs., 300 lbs., 350 lbs. or 400 lbs.? Yes, it matters a lot more than you might think.
The first thing to realize is no industry standards exist for determining the weight rating of a treadmill. Each manufacturer determines weight ratings using their own methodology, which generally remains their trade secret. Those who are old enough to remember what it was like to determine the true MPG performance of an automobile before EPA government standards can perhaps best relate to the current situation with treadmills. There is no regulatory standard for how this is to be done so it’s entirely up to the manufacturers’ marketing departments to claim whatever they wish.
Our favorite example of this is Exerpeutic’s marketing claim that their WorkFit 2000 Treadmill Desk has been “Tested up to 400lbs of user weight.” Notice they only “tested” it with a 400 lb. user, probably someone they pulled out of the IT department to give it a quick test run. They don’t actually reveal the results of the test, much less the testing methodology. What this belies is the complete lack of any kind of industry testing standard. The best way to know if your treadmill manufacturer claims are true is an in-depth review. Check our roundup of treadmill desk reviews or our roundup of treadmill bases reviews for more information.
Residential treadmills are usually designed with low output (and less expensive) DC motors, which generate full power only at high RPMs. At lower speeds, such as a 1 -2 mph stroll, you will only be using a fraction of the motor’s power. This is not necessarily a problem for standard users but a heavier user can place an extraordinary load on the motor and controller, causing the system to run hot. The motor and/or controller could eventually overheat and fail while you’re walking on the treadmill, typically very abruptly and without warning.
So what do treadmill weight ratings really mean to you, the consumer?
Does a weight rating of 300 lbs. mean the manufacturer tested the treadmill with a 305 lb. user and the unit failed but it didn’t when testing with a user weighing 300 lbs.? Not likely. Does it mean the unit failed after 6 continuous hours of use by a 305 lb. individual? Maybe, who knows? The fact is, while many of these manufacturers do have considerable knowledge around what works for the intended application, they do not share common standards on how weight ratings are derived. Most treadmills sold in the US have only a UL certification, which addresses safety of use, not truth in advertising.
Weight ratings as marketing fluff
Weight ratings are used more than anything to allow manufacturers to position different treadmill models towards different audiences. If a manufacturer makes two models – one robust and another not as robust – they might give the more robust unit a 350 lb. rating and the weaker one a 250 lb. rating to position them in the consumer’s mind as premium versus economy models.
Many factors go into the true weight bearing capacity of a treadmill. Lower-end treadmills generally specify a weight limit between 200 and 300 lbs. Higher-end models generally provide a more forgiving weight limit between 300 and 500 lbs. (The ultra-premium treadmill manufacturer Woodway actually claims an incredible 800 lb. limit on some of their treadmills!).
A key component of weight bearing capacity is the thickness of the treadmill deck. Wearing of the deck’s lamination yields to higher friction and eventually the need to replace the deck (or flip it over for a second lifetime if you followed our advice to purchase a treadmill with double-sided laminated deck). A ¾” deck is much more likely to have its lamination degraded from heavy pounding than a more costly and heavier 1″ deck will.
Another factor to pay attention to is the motor’s horsepower rating. Keep in mind, though, that horsepower alone is not necessarily a meaningful indicator of a treadmill’s ability to handle heavier users. Along with horsepower, factors that determine the overall capability of a treadmill include the weight and diameter of the flywheel (moderates the abruptness of speed changes when you constantly replace your weight on the belt surface with each footstep), the gear-down ratio of the drive belt, the roller diameters and the friction coefficient of the belt against the deck.
What matters most is torque – the motor’s ability to overcome the friction between the belt and the deck at specific RPMs, i.e. specific speeds and inclines. Incline is an interesting variable because even a modest incline can significantly reduce the load on the motor – although we strongly discourage working-while-walking at an incline, so let’s assume for purposes of this discussion that we’re looking at treadmills’ weight limits at zero incline.
Getting technical for a moment
The thing about torque is it can’t be quoted as a single figure from a spec book. The torque rating of a motor is measured with a dynamometer and it changes over the RPM range of the motor, so it is normally expressed on a graph such as the one shown here. You can get a rough idea of torque output by looking at the HP rating and the Maximum RPM of the motor. Since horsepower is a function of torque and RPM, at lower RPMs the horsepower output will be lower. In other words, right when you need the greatest number of horses pulling – at slow strolling speeds – the motor will be running at lower RPMs and may not be able to deliver to deliver enough torque to move the belt smoothly.
A low-torque motor at high RPMs can have the same performance as a high-torque motor operating at lower RPMs. While most treadmill manufacturers don’t publish their motors’ torque output, some DC motor manufacturers will state a torque constant, “ torque/amps.” The more amps you provide to the motor, the higher the torque. This is where the limitations of the motor and controller come into play. The limit of the motor to produce higher torque depends on how many amps it can take, which is a function of its design. The job of the controller is to vary the amps delivered to the motor, and to limit it on the upper end to keep from overheating the motor. This usually works, until it has been asked to deliver too much power for too long, causing either the motor or the controller to fry.
Treadmill designers generally select motors that have their highest torque ratings at the RPMs generated at the most common speed settings they expect customers to use. For standard exercise treadmills this speed setting will be a running, not walking speed. In practice, torque characteristics are more a function of motor design than a selectable feature, and all other things being equal, the designer is constrained mostly by the HP and RPM of the motors that meet their cost target.
Walking is harder on treadmill motors than running
While it may appear counterintuitive, this is true. At walking speeds the motor really has to haul your body against the friction of your full weight pressing the belt down to the deck. When you run, you’re kicking the belt backwards and lofting yourself into the air half the time. This is why even the finest, most expensive running treadmills can die within weeks or months of being used in a treadmill desk application.
If you’re going to select a treadmill base for your workstation you will want to find one that was originally designed to be a walking treadmill, if at all possible. Its motor would have been selected for walking loads, not running loads, and its weight rating would also have been determined under a walking regimen. The best are treadmills originally designed for rehabilitation clinics. These normally top out at ~4.0 MPH. Don’t be fooled by running treadmills that have been artificially limited to 4 mph through a software change. They still won’t have the torque needed for long hours of continuous use at 1 – 2 mph and may burn out on you after a few weeks or months of use.
Because treadmill manufacturers don’t publish their performance specs in a way that consumers can compare apples-to-apples we always recommend opting for treadmill bases that have the most solid warranties. Practically speaking this is the best indication of how confident the manufacturer is in the reliability of their design, and therefore probably the best indicator of equipment’s reliability for the lay consumer. (A notable exception is the Exerpeutic WorkFit 2000 mentioned above, which has a remarkable five year warranty on the motor. Exerpeutic is probably hedging its bets against the fact that something else will fail on this flimsy treadmill before the motor will, and it will wind up in the trash heap or on Craigslist within a year of purchase.)
Motor performance in daily use is the more important issue than potential motor failure
So to sum up what we’ve discussed above, an underpowered motor is more likely to fail sooner than a properly-suited one. But that’s not the issue you’re going to encounter day-to-day. During daily use, underpowered treadmills will groan and hesitate when you step on the belt. A 300 lb. individual using a 300 lb.-rated treadmill will likely sense a discomfiting belt hesitation much more than a 200 lb. individual will. To the user this will just be annoying, although if severe enough it could cause them to trip or fall. To the motor this will be damaging over time.
Motors most commonly fail from short circuits in the coil windings, not from shaft fractures (although this can happen as well). The short circuits are caused by wire insulation failure from too many hours of continuous use at high loads (i.e. high temperatures). And if the motor doesn’t fail the controller board that has to deliver so much more power to the motor at these straining loads can blow a capacitor or some other component first. Controller boards are no cheaper to replace than the motor itself, and no less of a hassle.
Here’s a practical test you can perform if you’re comfortable around mechanics and electronics and have an understanding of the safety precautions required. Walk on a treadmill continuously at 1 – 2 mph for at least an hour. Then remove the motor housing cover and put an oven thermometer to the motor casing. You’ll probably smell the wire insulation burning even before you touch the temperature probe to the motor’s outer casing. If the motor is too hot to touch without getting burned you probably have an impending failure in the works.
The bottom line
You can’t use weight ratings to compare two treadmills from different manufacturers. You can only use the weight ratings to compare two units from the same manufacturer to determine their relative power, usually at running speeds.
Continuous load is what matters and you’ll often be walking for several hours at a time, not running for 45 minutes at a time. So here are some yellow flags to watch for when comparing manufacturer’s performance claims:
1) Read all the user reviews you can find to see if people in your weight class commonly complain about belt hesitation, creaking and squeaking, or worse, warm motor housings when used at slow walking speeds. Keep in mind the motor housing can be cool to the touch even when the motor underneath is at metal-melting temperatures.
2) If the manufacturer sets “hours of daily use” limits for their treadmills this may be an indication their treadmills were originally designed for running and are under-torqued for long periods of use at walking speeds. Some manufacturers have out clauses in their warranties if it is found that the treadmill was used for more continuous hours in a day than their published limits.
3) Any treadmill that can be set to speeds over 4.0 mph generally shouldn’t even be considered unless they’re really cheap used units found on Craigslist and you won’t mind hauling them to the dump every few months and replacing them (fixing them will cost a lot more than replacing them).
So even if you are planning to use a conventional running treadmill in your DIY setup, you’re going to want to buy a unit with a significantly higher weight rating than your own weight. Some manufacturers overstate their weight limits by 50 to 75 lbs., if not more, and that’s at running speeds, not even at walking speeds. For this reason we recommend you purchase a treadmill with a user weight limit that is at least 100 lbs. greater than the heaviest person who will be using it.
Lastly, it bears mentioning that friction is the enemy. Please read our comprehensive advice in How to Lubricate Your Treadmill – it will pay big dividends in the long run. Most people don’t bother, or don’t do it often enough, the result of which is a build-up of dirt between the belt and the deck that gradually increases the friction load and burns the motor out that much faster. This is why professional gyms usually clean their treadmills daily, re-lubricate them weekly, and replace their decks and belts every six months.