The small and light Bosch Performance SX is rated at 55 Nm of torque. It’s obviously been designed to be less powerful than the Performance CX. The SX is made for the mild and lightweight embs, often referred to as Super Light emtbs. Still, Bosch claims it has a peak power output of 600 W. That’s the same as many other full-power motors with more torque. How strong is the SX really?
The 55 Nm Bosch SX too needs high motor rotation speed to unleash its power potential. A common full-power ebike motor can be very strong from the get go, but the power can start tapering off well before 100 rpm. The Bosch SX needs to go beyond 100 rpm to deliver 600 W. Does that mean the Bosch SX can compete with the stronger motors in some situations?
The bike must have a setup that matches a 29er rear wheel and a gear ratio of around 34/51. The hill is about 100 m long with 20 m of elevation, and it’s ridden at 65, 80 and 100 cadence. We measure how hard the rider pedals using Garmin Rally pedals. If the rider puts less force to the pedals, we know the motor has done more of the work as the bikes will have completed the segment in the same amount of time with similar cadence. We intended to do a 60 cadence test, but it was difficult riding that slow and all aour results were above 60 rpm, so it ended up being the 65 cadence test.
We also ride a short trail loop of just under one kilometer. The loop starts with a section of smooth surface where we briefly go above cut-off speed, before entering rocky and rooty trails. There is little elevation difference in elevation, and we are riding all-out. There are so many variables in this test. Weather will affect speed, and the rider shape will vary throughout the season. Bikes have different tyres, suspension properties and geometry. We will be riding different lines on pretty much every run. Comparing results set the same day eliminates a few variables. This test is done to say something about ride feel and to determine if there are any huge, obvious differences in motor performance.
We’re comparing the Bosch SX to the 85 Nm Shimano EP801 and Bosch Performance CX. All tests were done on the same day by the same rider. You may already have seen some of these results in our EP8 vs Performance CX article.
As the Bosch SX is said to peak at above 100 rpm, we decided to do a run with even higher cadence. The run ended up being 126 rpm, and we couldn’t go much higher. The rider averaged 347 W, which is 108 W more than the 100 rpm test. But it’s also much faster, at 34 seconds. Unfortunately, we didn’t do this test with the other motors. It's possible the SX might have beaten them.
Clocking in at 1 min 47 seconds means the SX is around 4 seconds slower than the full-power CX and EP801. That’s not a whole lot and one could argue it's insignificant. This is totally acceptable for me to get a lighter bike on a gentle trail like this. The SX did well, but if you ride in a group with full-power emtbs, you will be working noticeably harder.
I always appreciated having a motor that can shuttle me uphill, it allows for some mid-ride rest. The Bosch SX will do this. Sure, the shuttling is a bit slower than I’m used to, but it doesn’t matter to me. When pedaling hard and fast, there is little downside riding the SX. And when going faster, above motor-cut speed, the small Bosch has the advantage. It feels easier pedaling without motor support.
How can a weaker motor have high power output?
A small motorcycle engine can have a surprisingly high power output considering its size and torque. Even though it might have less torque than the Bosch SX, the high motor rotation speed makes up for it. Many motorcycle engines will go well beyond 10.000 rpm. That means the engine will have much more power than a way bigger tractor engine. Still, the tractor will pull a much heavier load up a hill.The 55 Nm Bosch SX too needs high motor rotation speed to unleash its power potential. A common full-power ebike motor can be very strong from the get go, but the power can start tapering off well before 100 rpm. The Bosch SX needs to go beyond 100 rpm to deliver 600 W. Does that mean the Bosch SX can compete with the stronger motors in some situations?
About the test
There are two sides to testing motor power, peak power and power amplification. If we ride uphill in a low gear while pedaling slowly, we’re very likely not getting maximum power. This is a test of power amplification. If we push hard, we’ll be limited by the peak power. It’s interesting testing both. Before we start, we make sure the motors are set to the highest power settings in the app, that means +5 for the Bosch SX. The test is ridden in the highest assistance mode.The bike must have a setup that matches a 29er rear wheel and a gear ratio of around 34/51. The hill is about 100 m long with 20 m of elevation, and it’s ridden at 65, 80 and 100 cadence. We measure how hard the rider pedals using Garmin Rally pedals. If the rider puts less force to the pedals, we know the motor has done more of the work as the bikes will have completed the segment in the same amount of time with similar cadence. We intended to do a 60 cadence test, but it was difficult riding that slow and all aour results were above 60 rpm, so it ended up being the 65 cadence test.
We also ride a short trail loop of just under one kilometer. The loop starts with a section of smooth surface where we briefly go above cut-off speed, before entering rocky and rooty trails. There is little elevation difference in elevation, and we are riding all-out. There are so many variables in this test. Weather will affect speed, and the rider shape will vary throughout the season. Bikes have different tyres, suspension properties and geometry. We will be riding different lines on pretty much every run. Comparing results set the same day eliminates a few variables. This test is done to say something about ride feel and to determine if there are any huge, obvious differences in motor performance.
We’re comparing the Bosch SX to the 85 Nm Shimano EP801 and Bosch Performance CX. All tests were done on the same day by the same rider. You may already have seen some of these results in our EP8 vs Performance CX article.
Uphill test
65 cadence
The Bosch SX is noticeably weaker at low cadence. But pushing 161 W isn’t that hard for most people weighing 80-90 kg. The full power motors require much less than 100 W of rider input, making the climb feel easy.80 cadence
Pedaling at 80 rpm is still a noticeably lower cadence than 100+, but the SX performs well. Sure, pedaling 184 W is noticeably more than on the full power motors. But we only pushed 23 W harder than on the 65 cadence run. The Bosch SX offers much more support at 80 rpm and there is little reason pedaling slower.100 cadence
Expectations were high for the 100 cadence test. We hoped to find the difference in rider input would continue dropping. But it didn’t, the test pilot had to pedal 239 W on average, that’s 55 W more than the 80 rpm run. The two other motors required 154 W of rider input.As the Bosch SX is said to peak at above 100 rpm, we decided to do a run with even higher cadence. The run ended up being 126 rpm, and we couldn’t go much higher. The rider averaged 347 W, which is 108 W more than the 100 rpm test. But it’s also much faster, at 34 seconds. Unfortunately, we didn’t do this test with the other motors. It's possible the SX might have beaten them.
Short trail loop results
The SX performed well on the trail loop. We tried to keep the pedals spinning and play to its strengths. That was a bit difficult as we had to shift a lot and predict which gear we needed after having coasted for a bit. Out of all the three test bikes, this was the one most suited for the test trail. The Schwalbe Nobby Nic rear tyre rolls faster than the Maxxis Minions, and it’s at no disadvantage on this flat and dry trail.Clocking in at 1 min 47 seconds means the SX is around 4 seconds slower than the full-power CX and EP801. That’s not a whole lot and one could argue it's insignificant. This is totally acceptable for me to get a lighter bike on a gentle trail like this. The SX did well, but if you ride in a group with full-power emtbs, you will be working noticeably harder.
Conclusion
The SX didn't win in any of our tests., but it’s not far behind on flat terrain. The term “mid-power” is used to describe the SX, and it seems fitting. The SX is surprisingly strong for a small 2 kg motor. You can ride the bike uphill and arrive well rested if you play to its strengths. Picking a lighter gear and pedaling faster than you might be used to will yield better support. The motor characteristics inspires me to pedal faster. It’s an exhilarating rideI always appreciated having a motor that can shuttle me uphill, it allows for some mid-ride rest. The Bosch SX will do this. Sure, the shuttling is a bit slower than I’m used to, but it doesn’t matter to me. When pedaling hard and fast, there is little downside riding the SX. And when going faster, above motor-cut speed, the small Bosch has the advantage. It feels easier pedaling without motor support.
