Jeremy McCreary
Bought it anyway
- Region
- USA
- City
- Carlsbad, CA
Rider power needed for ECO dash and climb
A recent thread made me wonder: How would an alloy Vado SL 1, a carbon SL 2, and a carbon Creo 2 compare on two very different rides — (1) a fast "dash" on the flat at 20 mph, and (2) a slow 8 mph "climb" up a 5% grade?
The focus would be on relative rider power contributions and battery consumption. Each ride would involve 30 minutes of steady speed on smooth pavement in still air under ECO (35/35) assist.
Specialized mid-drive spreadsheet model
Happen to have a spreadsheet model for questions like this. The physics comes from Wilson & Schmidt, 2020, Bicycling Science, 4th ed. Official Specialized documents provide the necessary PAS details. With realistic input parameters, results should be at least ballpark.
Dash sheet (climb sheet below)
Each bike has its own column.
Column C is just me (87.3 kg) on an alloy Vado SL 1 5.0.
Column D is me on a carbon Vado SL 2 6.0 running 47 mm Creo 2 tires but otherwise stock.
Column E is me on a stock carbon Creo 2 Comp (I wish).
Rows 5-10, 24-25, 36, and 41-42 hold the relevant bike and battery properties. The bike masses in Row 5 add 1 kg of cargo to factory values. Test parameters are in Rows 13-15, 27-28, and 43.
☆ Since the gross (bike+rider+cargo) masses here differ by at most 1%, any significant performance differences are likely to be due mainly to motor and aerodynamic differences.
Power requirements depend critically on a bike's coefficient of rolling resistance (Crr, Row 8) and drag area (CdA, Row 10). Here I used Crr measurements from www.bicyclerollingresistance.com and CdA estimates based on several sources. Gave the flat-bar SLs the same CdA and the drop-bar Creo a 10% discount for its more aero rider posture — when ridden on the drops.
The rest of the bike data comes from official Specialized product pages.
Climb sheet
Ground speed (Vg, Row 13) falls from 20 to 8 mph, and gradient (G, Row 15) rises from 0% to 5%. Rows 5-29, 36, and 43-45 are otherwise unchanged. All other rows change with Vg and G.
Some things to notice (☆ marks take-homes)
These 3 ebikes definitely differ in Pr requirements and battery consumption — but not drastically.
Power losses
☆ The Creo's the lightest, fastest-rolling, and most aero of the bunch, and it shows in the external power losses calculated in Rows 17-20.
☆ In both rides, the Creo has the lowest total mechanical power loss (Ptr, Row 20) due to air, rolling, and gravitational resistance.
Turns out, the Creo has same Ptr of 213 W in both rides. Just an interesting coincidence, but we'll make use of it by comparing all SL Ptr values to that benchmark.
In detail, the SL 1 and SL 2 respectively lose 10% and 8% more power than the Creo in the dash but only 2% and 2% more in the climb. Guessing this is mainly an aerodynamic effect.
Row 21 shows that for all 3 bikes, the weight-dependent losses (rolling + gravitational) account for 95% of Ptr on the climb but only 25-27% in the dash.
☆ As expected, bike weight differences matter much more in the climb than the dash.
Rider and motor power
In steady riding, Specialized's power-sensing mid-drive PAS doles out motor power (Pm) mainly on rider power (Pr) measured at the crank. Since all bikes in this comparo use the same 35/35 assist mode (Rows 27-28), differences in the Pm (Row 34) recruited by a given Pr (Row 32) are due solely to differences in 2 key motor properties — namely, max available motor power (Px, Row 24) and boost factor (B, Row 25).
☆ Having the lowest Px and B, the SL 1 uses the least Pm and requires the most Pr in both rides.
☆ Differences in motor torque don't affect the steady riding assumed here.
Row 38 shows the net power (Pn) from all sources and sinks. In steady riding, Pn must be zero. I manually adjusted each ride's Pr inputs till Pn = 0 for every bike. These are the Pr requirements reported in Row 32.
☆ In both rides, the SL 1 needs the most Pr, and the Creo the least, with the SL 2 closer to the Creo.
In detail, the SL 1 and SL 2 respectively need 29% and 8% more Pr than the Creo in the dash but only 14% and 2% more on the climb. Guessing this is also mainly an aerodynamic effect.
Battery consumption
Row 44 shows the electrical energy in Wh consumed in 30 minutes of steady riding under ride conditions. Since the Creo loses the same Ptr in the dash and climb, it also consumes the same 61 Wh.
☆ In both rides, the SL 1 consumes the fewest Wh, and the SL 2 the most. Good thing the SL 2 has a bigger battery.
In detail, the SL 1 consumes 13% FEWER Wh than the Creo in the dash, while the SL 2 consumes 2% MORE. In the climb, the SL 1 still consumes 13% less energy, but the SL 2 burns only 2% more.
Row 46 shows the battery consumption rate in Wh/mi. (This is the inverse of mileage in mi/Wh.)
☆ For each bike, the Wh burned varies little between dash and climb. But the Wh/mi differs dramatically due to the big difference in distance covered (10 vs. 4 mi).
For example, the Creo has only 19 mi of range under climb conditions but 48 mi under dash conditions.
☆ In both rides, the SL 1 uses the fewest Wh/mi, and the SL 2, the most, with the Creo closer to the latter. The is due solely to differences in motor parameters Px and B.
Row 47 shows the range in miles from 100% to 10% state of charge (SoC) under ride conditions.
☆ In both rides, the SL 2 has the longest range to 10% SoC, and the Creo shortest, with the SL 1 closer to the Creo. This is where the SL 2's larger, heavier battery shines.
In detail, the SL 1 goes 15% farther than the Creo in the dash, while the SL 2 goes a whopping 50% farther. On the climb, the SL 1 still goes 15% farther, but the SL 2 goes 60% farther in this case.
Some conclusions
1. This comparo doesn't cover the alloy Creo 2, but its gross mass would be only 0.4% higher, and the rankings wouldn't change.
2. Reported Pr requirements assume that all bikes use 35/35 assist on both rides. You could always up the SL 1's assist to make it as easy as the Creo in 35/35. You'd lose some battery range in the process, but not enough to matter at the 10-40 mi distances I typically ride.
3. All other things are definitely NOT equal, but if range is your primary concern, the carbon SL 2 will always go farthest.
4. If you're after the highest speed for a given Pr, the Creo 2's the ticket. It's also likely to be the most nimble. And of course, it's the only bike here with drop bars.
5. If you don't mind working a little harder for your speed — or find the carbon SL 2 and carbon Creo 2 too expensive — the alloy SL 1 is an excellent compromise. For local rides, it may well have all the battery you need, even without a range extender.
A recent thread made me wonder: How would an alloy Vado SL 1, a carbon SL 2, and a carbon Creo 2 compare on two very different rides — (1) a fast "dash" on the flat at 20 mph, and (2) a slow 8 mph "climb" up a 5% grade?
The focus would be on relative rider power contributions and battery consumption. Each ride would involve 30 minutes of steady speed on smooth pavement in still air under ECO (35/35) assist.
Specialized mid-drive spreadsheet model
Happen to have a spreadsheet model for questions like this. The physics comes from Wilson & Schmidt, 2020, Bicycling Science, 4th ed. Official Specialized documents provide the necessary PAS details. With realistic input parameters, results should be at least ballpark.
Dash sheet (climb sheet below)
Each bike has its own column.
Column C is just me (87.3 kg) on an alloy Vado SL 1 5.0.
Column D is me on a carbon Vado SL 2 6.0 running 47 mm Creo 2 tires but otherwise stock.
Column E is me on a stock carbon Creo 2 Comp (I wish).
Rows 5-10, 24-25, 36, and 41-42 hold the relevant bike and battery properties. The bike masses in Row 5 add 1 kg of cargo to factory values. Test parameters are in Rows 13-15, 27-28, and 43.
☆ Since the gross (bike+rider+cargo) masses here differ by at most 1%, any significant performance differences are likely to be due mainly to motor and aerodynamic differences.
Power requirements depend critically on a bike's coefficient of rolling resistance (Crr, Row 8) and drag area (CdA, Row 10). Here I used Crr measurements from www.bicyclerollingresistance.com and CdA estimates based on several sources. Gave the flat-bar SLs the same CdA and the drop-bar Creo a 10% discount for its more aero rider posture — when ridden on the drops.
The rest of the bike data comes from official Specialized product pages.
Climb sheet
Ground speed (Vg, Row 13) falls from 20 to 8 mph, and gradient (G, Row 15) rises from 0% to 5%. Rows 5-29, 36, and 43-45 are otherwise unchanged. All other rows change with Vg and G.
Some things to notice (☆ marks take-homes)
These 3 ebikes definitely differ in Pr requirements and battery consumption — but not drastically.
Power losses
☆ The Creo's the lightest, fastest-rolling, and most aero of the bunch, and it shows in the external power losses calculated in Rows 17-20.
☆ In both rides, the Creo has the lowest total mechanical power loss (Ptr, Row 20) due to air, rolling, and gravitational resistance.
Turns out, the Creo has same Ptr of 213 W in both rides. Just an interesting coincidence, but we'll make use of it by comparing all SL Ptr values to that benchmark.
In detail, the SL 1 and SL 2 respectively lose 10% and 8% more power than the Creo in the dash but only 2% and 2% more in the climb. Guessing this is mainly an aerodynamic effect.
Row 21 shows that for all 3 bikes, the weight-dependent losses (rolling + gravitational) account for 95% of Ptr on the climb but only 25-27% in the dash.
☆ As expected, bike weight differences matter much more in the climb than the dash.
Rider and motor power
In steady riding, Specialized's power-sensing mid-drive PAS doles out motor power (Pm) mainly on rider power (Pr) measured at the crank. Since all bikes in this comparo use the same 35/35 assist mode (Rows 27-28), differences in the Pm (Row 34) recruited by a given Pr (Row 32) are due solely to differences in 2 key motor properties — namely, max available motor power (Px, Row 24) and boost factor (B, Row 25).
☆ Having the lowest Px and B, the SL 1 uses the least Pm and requires the most Pr in both rides.
☆ Differences in motor torque don't affect the steady riding assumed here.
Row 38 shows the net power (Pn) from all sources and sinks. In steady riding, Pn must be zero. I manually adjusted each ride's Pr inputs till Pn = 0 for every bike. These are the Pr requirements reported in Row 32.
☆ In both rides, the SL 1 needs the most Pr, and the Creo the least, with the SL 2 closer to the Creo.
In detail, the SL 1 and SL 2 respectively need 29% and 8% more Pr than the Creo in the dash but only 14% and 2% more on the climb. Guessing this is also mainly an aerodynamic effect.
Battery consumption
Row 44 shows the electrical energy in Wh consumed in 30 minutes of steady riding under ride conditions. Since the Creo loses the same Ptr in the dash and climb, it also consumes the same 61 Wh.
☆ In both rides, the SL 1 consumes the fewest Wh, and the SL 2 the most. Good thing the SL 2 has a bigger battery.
In detail, the SL 1 consumes 13% FEWER Wh than the Creo in the dash, while the SL 2 consumes 2% MORE. In the climb, the SL 1 still consumes 13% less energy, but the SL 2 burns only 2% more.
Row 46 shows the battery consumption rate in Wh/mi. (This is the inverse of mileage in mi/Wh.)
☆ For each bike, the Wh burned varies little between dash and climb. But the Wh/mi differs dramatically due to the big difference in distance covered (10 vs. 4 mi).
For example, the Creo has only 19 mi of range under climb conditions but 48 mi under dash conditions.
☆ In both rides, the SL 1 uses the fewest Wh/mi, and the SL 2, the most, with the Creo closer to the latter. The is due solely to differences in motor parameters Px and B.
Row 47 shows the range in miles from 100% to 10% state of charge (SoC) under ride conditions.
☆ In both rides, the SL 2 has the longest range to 10% SoC, and the Creo shortest, with the SL 1 closer to the Creo. This is where the SL 2's larger, heavier battery shines.
In detail, the SL 1 goes 15% farther than the Creo in the dash, while the SL 2 goes a whopping 50% farther. On the climb, the SL 1 still goes 15% farther, but the SL 2 goes 60% farther in this case.
Some conclusions
1. This comparo doesn't cover the alloy Creo 2, but its gross mass would be only 0.4% higher, and the rankings wouldn't change.
2. Reported Pr requirements assume that all bikes use 35/35 assist on both rides. You could always up the SL 1's assist to make it as easy as the Creo in 35/35. You'd lose some battery range in the process, but not enough to matter at the 10-40 mi distances I typically ride.
3. All other things are definitely NOT equal, but if range is your primary concern, the carbon SL 2 will always go farthest.
4. If you're after the highest speed for a given Pr, the Creo 2's the ticket. It's also likely to be the most nimble. And of course, it's the only bike here with drop bars.
5. If you don't mind working a little harder for your speed — or find the carbon SL 2 and carbon Creo 2 too expensive — the alloy SL 1 is an excellent compromise. For local rides, it may well have all the battery you need, even without a range extender.
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