Chances are you’ve seen a pit crew furiously working on changing the tires of a car at some point or another. One guy wheels the air compressor in, while another is already on his knees just ripping the wheel lugs right out, then plugs them right back in after yet another guy lifts the new wheel into position.
That small power tool can do it faster than you can even bring over the lug wrench - it just goes to show what this combination of impact and torque in a handy package can do for your garage or workshop.
How An Impact Wrench Does Its Magic
An impact wrench is an incredible tool in more ways than one. With it, even a grandma can easily take out a lug nut that will have you sweating and swearing at your lug wrench. The secret is in the power storage mechanism used in the tool.
In some electric models, it’s a heavy rotating mass inside the tool, a sort of flywheel that builds up and stores energy, then releases it very rapidly to drive the output shaft in the direction of its rotation. Pneumatic impact wrenches rely on compressed air to drive a hammer against the output shaft to generate the necessary amount of torque, with minimal effort on the part of the user.
It’s like taking a hammer and hitting your lug wrench along the direction you want to turn it. Now imagine doing that at hundreds of times per minute. Impact wrenches are a prominent example of a tool that does the work for you and once you do get used to having one, you will probably start to wonder why you didn't buy one sooner.
Which Type of Impact Wrench Should You Get?
Impact wrenches are tools that do a narrow subset of jobs. They can loosen or tighten lugs, nuts and bolts, and that’s about it. They are not to be confused with the impact driver, which has a 1/4 inch hex opening that can accommodate sockets or bits. Impact wrenches, like ordinary wrenches, can only take sockets of various sizes.
That said, if you run a garage or an automotive workshop, the demand for a tool that can remove nuts is so high that manufacturers have come up with a tool that does exactly that. The time savings alone is already worth the investment, not to mention the reduced risk of injury that the tool provides versus doing it by hand.
As far as form factor goes, impact wrenches come in three common formats – the pistol grip power tool shape that they share with so many others, the inline impact wrench, and the angle impact wrench.
Your other choice in the matter mostly comes down to the power source of the impact wrench. In that regard, you have three types to choose from: pneumatic, corded electric, and battery powered impact wrenches.
Pistol Grip Impact Wrenches
Pistol grip impact wrenches share the same general shape as the other power tools you are likely familiar with and they work in the same point-and-shoot mode of operation. One hand goes on the pistol grip to work the trigger, while the other hand aims the socket while bracing the tool at the same time – simple.
Most battery-powered pistol grim impact wrenches will have their battery packs placed under the hand grip. It’s a similar arrangement with many pneumatic and corded electric impact wrenches, with the cord or compressed air hose sticking out from under the hand grip as well.
Features to Look For in Pistol Grip Impact Wrenches
- Variable speed triggers allow you to control the torque and rotational speed of the impact wrench.
- Integrated LED lighting helps see illuminate the area which is especially helpful when working on vehicles.
- Soft grip handles and balanced, ergonomic designs provide increased comfort during use and can also help in decreasing user fatigue.
Inline Impact Wrenches or Palm Grip Impact Wrenches
Inline impact wrenches look more like over-sized screwdrivers and they share the same shape as some power saws, minus the blade of course. The larger inline impact wrenches often come with a D-shaped grip at the end that also holds the trigger, and in some models, a T-shaped grip is used instead.
Smaller inline impact wrenches, the ones with smaller drive shafts of 1/4 inches to 3/8 inches, are often simply held at the body. These inline impact wrenches are often used to loosen or tighten many small lugs or nuts, especially in tight spaces.
Features to Look For In Inline Impact Wrenches
- Butterfly throttles give you comfort and control while palming the tool.
- A low profile inline design lets you use the tool even in cramped, smaller spaces.
- Soft grip D-handles or T-handles on larger inline impact wrenches provide increased comfort and stability during use.
- Accessible forward and reverse switches let you change the direction of the rotation.
- Two-stage or variable speed triggers let you control the torque and rotational speed of the impact wrench, which is always appreciated.
Angle Impact Wrenches
Angle Impact Wrenches, which are also known as right angle impact wrenches usually come with an inline handle, but with the drive bent at an angle similar to an oscillating multi-tool. Since the drive rotates at a 90 degree axis from the rest of the tool, the force of reactionary torque is minimized, which can save you from scraped knuckles, in certain situations.
These impact wrenches are designed for close quarter access like inline impact wrenches or power ratchets and they often come in models with smaller drives as well.
Features to Look For In Angle Impact Wrenches
- Using a low profile angled head lets you insert the tool into apertures and small spaces.
- Integrated head covers protect the tool drive even while using the tool inside cramped spaces.
- Combined variable speed and direction control rings allow you to control both torque and reversing.
Compressed Air Impact Wrenches
It’s safe to say that the compressed air impact wrench is the tool that started it all for the rest of the impact wrench family. The air powered impact wrench still remains a "classic air tool", having been around since the early advances made in automotive tools.
Like all air tools, air impact wrenches require a source of compressed air – either a compressed air tank or a suitable air compressor. Compressed air impact wrenches have one major advantage over other types, in that it does not need a motor. This means that air powered impact wrenches are relatively simpler tools that are lighter than other types and they have fewer parts that can break down or malfunction.
It’s not uncommon to find air powered impact wrenches weighing as little as four pounds, which makes them some of the easiest power tools to handle, especially when you're working with them all day long. In addition to that, air powered impact wrenches are the quietest type of power wrench, if you don't count the noise produced from the compressor.
On the downside, there is the added expense and inconvenience of the compressed air tank or air compressor unit required to power this tool and an air hose.
Corded Electric Impact Wrenches
If you are using an impact wrench in the garage where an AC outlet will always be available, a corded impact wrench is not a bad choice at all. Electric impact wrenches used to lag behind compressed air impact wrenches in terms of power, but modern electric motors have all but erased that gap nowadays.
The corded models will be one of the least expensive types to own if you factor in the cost of buying a compressor for a pneumatic model and spare batteries for a cordless model. I like the simplicity of the corded models myself, just plug it in and go!
Battery Powered Cordless Impact Wrenches
Since impact wrenches are such power-hungry tools, the early battery powered impact wrench models were quite impractical in their time. With modern battery and electric motor features nowadays, cordless impact wrenches are now getting more affordable all the time, while offering similar torque and power as corded impact wrench models.
For changing tires on the road, a battery powered impact wrench is a great asset you will be glad you brought with you. There will always be a place for the trusty lug wrench in your car trunk, but you will be glad you added a cordless impact wrench on top of that.
These will require a lot of battery juice and I would recommend using at least a 4.0Ah battery for these tools and be sure you have 2 or 3 charged up too because they usually require extended charging times due to their higher capacities.
Hydraulic Impact Wrenches
These impact wrenches deserve a mention here although chances are, you will not find them in your local hardware store. They are used in heavy industrial applications, and these tools are not the ones you can toss in the trunk of your car – rather, you hitch a vehicle to them so they can be moved around.
Comparing Impact Wrenches
When it comes to situational tools like impact wrenches, you have to consider several factors. First of all, do you have an air compressor? Having a good one can shift your choice towards an air impact wrench, since they are powerful tools for their price, especially when you already have a compressed air source.
Do you want to bring it with you on the road? That calls for a cordless impact wrench in your trunk. Or do you prefer the convenience of plugging in the tool and going for it?
Torque
When it comes to impact wrenches, torque is a huge factor – you are basically buying an impact wrench for the torque it provides. Torque is often cited in terms of feet-pounds. For loosening tougher lug nuts, do not settle for anything less than 150 ft-lbs.
Impacts Per Minute and RPM
Impacts per minute, of course, is given in IPM, and this figure tells you how many times the hammer strikes the output shaft’s anvil over a minute's time. The higher the IPM, the quicker the tool can loosen a tight nut, coupled with enough torque, of course.
The free speed Rotation Per Minute of the tool describes how quickly the output shaft spins with no load, and can vaguely indicate how quickly a tool can pull off or drive in a lug nut that is already loose. This metric is usually not as important as torque given how few turns you need to put on a lug nut to remove it. Then again, in extremely time-sensitive applications like in pit stops where every split second counts, this can make a difference.
Drive Size
The drive size of your tool should be your other major factor in picking a specific model for the task you need to do. For most automotive jobs, a 1/2 inch drive is the standard and will do for most applications. There are impact wrench drive shafts that are 3/8 inches or smaller as well, so take care to check the drive size before committing to an impact wrench model.
Inline impact wrenches and angle impact wrenches often come with drives that are smaller than the usual 1/2 inch drive (3/8" or 1/4", usually).
On the larger side of things, the 3/4 inch drive impact wrench is usually only found in pistol grip impact wrenches. Going up from that, the 1 inch drive models are limited to large pistol grips and the inline impact wrenches with the D-shaped handles. Most inline impact wrenches with drives this big often have a second handle installed, allowing you to brace the tool using two grips.
For bigger nuts and bolts impact wrenches with drives of 1 1/4 inches or more usually come in inline form with T handles. Beyond that, and we’re talking major construction, industrial-grade fasteners here.
On a side note, there are impact wrenches with drives measuring 3 1/2 inches or more. These are usually oversized inline impact wrenches with T-shaped handles, in a shape that begin to resemble a jackhammer more so than a handheld power tool.
Torque Adjustment Features
If you will be attaching lug nuts and bolts using your impact wrench, keep in mind that it can be easy to apply too much torque to a fastener without you noticing it. Putting too much torque on a nut or bolt can twist or shear off the threads, making removal very difficult. In the worst case, you can twist and snap the bolt head right off, putting you in a very time consuming position.
Variable speed controls and torque stages help you manage the torque output of the impact wrench, which can be important if you are using a tool with a 400 lb-ft torque rating.
