While maximum RPM is a readily marketed feature for most impact drivers, there are problems with relying upon manufacturer claims. Firstly, testing RPM output across manufacturers isn’t standardized, resulting in difficulty for consumers when comparing models to find the best impact driver.
Secondly, manufacturer-provided RPM testing is limited. We’ve not found any manufacturers (or third parties) that rigorously test more than the maximum RPM output, including testing RPM for each impact driver’s speed settings in forward and reverse.
When designing our RPM testing methodology, we set out to fix these problems and fill in the gaps so consumers can easily compare impact drivers across brands and know all the details before purchasing.
Below, we discuss our RPM testing methodology, including how we test RPM output and why RPM performance matters. Check out our impact driver RPM test results to see how each model in our test fleet fared in our lab testing,
What we test
Using a contact tachometer, we test the no-load RPM output for each impact driver in our test fleet.
How we test it
We use a Reed Instruments R7100 contact tachometer to measure RPM output in a no-load scenario in both forward and reverse. The RPM output is tested for each speed setting an impact driver offers. For example, an impact driver with three speed settings produces six RPM test results. The RPM test data is displayed in each review produced on-site in a standardized manner to simplify comparing results across impact driver models.
Impact drivers increase RPM output the longer the trigger is held, reaching their maximum output within 10 to 15 seconds after depressing the trigger. Knowing this, we run each RPM test with the trigger fully depressed for 15 seconds and record the maximum readout generated by the tachometer.
Why it matters
The RPM profile is one product design feature that determines how quickly an impact driver drives screws. The faster a job is completed, the more time is saved, which is especially important for repetitive tasks and professionals on the job site.
But if you’re looking for the fastest impact driver, the simple answer isn’t to select the model with the highest RPM output. Speed depends on the task.
Torque and RPM are inversely related, working together to determine how quickly screws and fasteners can be driven in different scenarios.
An impact driver with high RPM output and moderate torque will likely drive short screws faster than a model with high torque and average RPM output. However, the latter model will almost certainly reach higher RPM levels in heavy-duty tasks, resulting in more quickly driving big screws and lag bolts.
This relationship explains why it’s critical to understand what tasks you want to finish quickly and which ones are acceptably slow. Some high-end impact drivers, including Milwaukee’s M18 Fuel lineup, design their RPM and torque profiles to quickly finish demanding tasks, such as driving long screws and big lag bolts.
For most homeowners, a high-end 18V impact driver is a waste of money since weekend warriors and DIYers don’t frequently push tools to the limits for extended periods. Instead, most non-professionals should look for an impact driver with moderate torque output and a high RPM for better performance outside heavy-duty tasks.