Cost-Benefit Comparison: Felt Mountain or eBike?

Mike leroy

Active Member
What benefits justify additional eBike costs? Scroll to the last post for the answer.

The aim of this article is to relate an eBike's benefits to technical detail, your physical ability and subjective opinion. A cost-benefit picture is drawn that reflects your situation, that is easy for everyone to interpret. The technical details and personal information is rated on a scale from 1 to 5. The ratings are the data for the cost-benefits picture.

A Google Sheet to associate 50+ major eBike features (i.e., costs) with benefits. Benefits are rated on a scale from 1-5. Associate any bike feature (i.e., costs) with a benefit. The benefits are categories tailored to your situation. The seven benefit categories in this example are based on Bosch research. The features (i.e., costs) are taken directly from bike manufacturer spec sheets.



Google Sheet sorted by Cost(above) or Benefit(below)



The technical features are classified under six benefit categories, according to the relevance for your particular purpose or environment. The benefits score is the average of the ratings that comprise that benefit. Most people refer to this approach as a "software algorithm".
  1. Economy
  2. Elegance
  3. Excitement
  4. Endurance
  5. Enjoyment
  6. Ease
We might refer to the two personas in this article as Ms. Ease and Mr. Endurance, due to the characteristic tradeoff decisions. Mr. Excitement is introduced at the end when full suspension eBike and mountain bikes are compared.

The NINEe 20 electric bike and NINE 60 mountain bike look very similar, but the structural differences are significant. Some of reasons are:
  • Additional weight and motor forces
  • Reinforced frame and rims for additional weight and acceleration.
  • Additional braking power due to higher speeds.
  • Stronger drive chain due to motor.
 
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Mike leroy

Active Member


The electric bike and NINE 60 mountain bike look very similar. The structural specifications are very different. The ebike is more similar to the NINE3, which costs $2K more than the NINE 60 shown below.

 

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Mike leroy

Active Member
The eBike is more similar to Nine 3, which costs $2K more than the Nine 60. Specification sheets are the basis for comparison. The Nine 3 is used for the remainder of the comparison.
 
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Mike leroy

Active Member
Discomfort, shortness of breath, sweat and a strong urge to strike the ground with your heels are signs that a hill is too steep for your fitness level.

To know how steep of a hill a person can climb with a particular bicycle, a calculation is made. The relationship between the distance travelled by the wheel and one turn of the pedal is called the "gear display".

"Gear Display" for the Nine 3 mountain bike is measured in meters (1.6m):
"Gear Display" = 24 front teeth / 36 rear teeth x 0.74m (29") x 3.14 = 1.6m

To know if Mr. Endurance or Ms. Ease can pedal a hill of a certain "grade percentage", we find the 1.6m "gear display" in the following table.

The power of Ms. Ease's legs are "100 Watts", located in the first column. Ms. Ease cannot climb hill more than 7.5% grade, which is considered moderate by most people.

The power of Mr. Endurace's legs are "200 Watts", located in the second column. Mr. Endurance can climb hills below 12.5% grade, which are considered steep by most people.

To optimize your bike, match this table to your gears, local environment and leg + motor power!



Note: see calculations to increase torque by 25%, i.e., 2.0m display, by changing chainring.
 
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Mike leroy

Active Member
Cost-Benefit Ratios

The eBike is clear benefit to Ms. Ease. Ms. Ease can climb hills that were beyond her ability.

For Mr. Endurance, the eBike provides benefits when the motor can push 50 pounds of groceries from a store closer to home, but with extremely steep hills. The less expensive mountain bike is a better choice for the store that is further away on a much less steep route.

Another calculation is required to assess whether the motor provides enough power.

I estimate 5Nm torque per grade-percent. So, the 60Nm Bosch drive can handle 60Nm / 5 = 12% grade. Another way to state Mr. Endurance's situation is the need for 90Nm of torque, 18% grade x 5Nm.

The Bosch drive does not help Mr. Endurance up the steep 18% hill. Mr. Endurance chooses the NINE 3 conventional Mountain Bike. A 750W, 48V, 120Nm motor for the NINE 3 kit better achieves his objectives for the very steep 18% grade hill.

Your decision is highly dependent upon personal leg strength. Mr. Endurance six feet tall. His weight varies +- 10 pounds from 175. Mr. Endurance's 2.4 weight-to-height ratio is ideal for hill climbing. Check out the Tour de France champions for the past decade, (i.e., 2.1).
 
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Mike leroy

Active Member
The automobile industry has a long-standing history of using "Star Plots" to visually diagram differences between cars. Suppose we rate aspects of a bike ride on a scale from 1 to 5. We can also include personal information, i.e., our Heart Rate.

The following Star Plot illustrates a typical ride. All bike considerations are rated a "3", on a scale from 1 to 5. We also score our personal information , i.e., Heart Rate, as a "3", or average.

The following Star Plot tries to convey an under-powered bike because the outcome, Heat, has the highest score of "5". The bike was overheated.

If we scored Heat as too cold, "1", for another bike, then that motor is over-powered. The potential power was never utilized, so we overpaid for the bike.





Now that the concept of star plots has been introduced, we will compare the Felt 3 Mountain and NINEe bikes in a star plot.

To evaluate the bike from a holistic viewpoint, we considered the outside temperature, bike speed, additional weight, steepness, etc.... To make this comparison relevant we will compare:
  1. Economy - eBike rated as 3/5. Mountain bike 5/5.
  2. Elegance - eBike 5/5. Mountain 3/5.
  3. Excitement - both 4/5.
  4. Endurance - eBike 5/5. Mountain 3/5
  5. Enjoyment- eBike 5/5. Mountain 4/5.
  6. Ease - eBike 5/5. Mountain 3/5.

The Star Plot for the NINEe electric bike tradeoff decisions made by Ms. Ease:




The Star Plot for the Nine 3 mountain bike tradeoff decisions made by Mr. Endurance:

 

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Mike leroy

Active Member
The eBike is well suited for a particular type of person. Both bikes scored 5 of 5 in the "Results" part of the star plot graph. The star plot is a visual aid to comparing vehicles. Star plots should remove a great deal of the effort required to find the most appropriate bike for a particular person or purpose.

The tradeoff decisions made by Ms. Ease and Mr. Endurance illustrate the benefits that appeal to different types of people.

Mr. Endurance
protects his bike from overheating by adding a thermometer. Electric motors operate most efficiently at 140F. Because Mr. Endurance carries 50 pounds of food up an 18% grade hill, he runs the risk of overheating the electrical system on hot days. Products like CycleAnalyst display temperature.

Ms. Ease uses an FLIR lens on her cellphone to get temperature readings.
See Cellphone Camera Reveals eBike "just right for you" post.
 
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Mike leroy

Active Member
Let's compare Felt compulsion full suspension mountain bike with Felt DUALe electric bike.

To judge a bike we relate conceptual benefits to the corresponding technical detail. The conceptual benefits are:
  1. Economy
  2. Elegance
  3. Excitement
  4. Endurance
  5. Enjoyment
  6. Ease
The previous comparison contrasted Ms. Ease with Mr. Endurance. The approach taken in this example is solely for one person, rather than two different types of people. We introduce a new persona, Mr. Excitement. Mr. Excitement like jumping his bike, so he needs to relieve the motor/pedals/spindle of some of the pressure. The rear suspension absorbs some of the landing impact, so the motor is less stressed.

The two bikes are:



The DUALe electric bike:
 

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Mike leroy

Active Member
How does Mr. Excitement relate conceptual benefits to the corresponding technical detail?

The process is fitting a motor to a bicycle, rider and terrain. Just like a bike shop fits a frame to a rider, this process configures a motor to the rider, bike and terrain. Essentially, the goal is to customize the following table correspond with personalized Pedal Assist levels.



The six benefits are categories that he assigns features and personal feelings to. The ratings and graph are only for the Felt Compulsion 10 mountain bike.
  1. Economy
    • Power Consumption Bosch rated 5, mountain bike rated 3. More power requires two batteries for same time period.
    • Battery replacement cost Bosch rated 2, HPC 48V rated 5.
    • Cost your personal rating (scale 1-5), relative to total cost and budget. Rated 5.
  2. Elegance - measured in performance, rather than fashion.
    • Fork - eBike 4, Mountain 5
    • Shock - Mountain 5
    • Wheelset - eBike 4, Mountain 5
    • Frame - Mountain 5
    • Bottom Bracket- Mountain 5
    • Chain- Mountain 5
    • Freewheel- Mountain 5
    • Brakes- Mountain 5
    • Rims- Mountain 5
    • Tires- Mountain 5
    • Spokes- Mountain 5
    • Hubs - front and rear
    • Weight - Mountain 5
    • Your personal rating from demo rides.
  3. Excitement - how much fun, access to remote places, etc...
    • Torque Acceleration - Bosch 3, 8Fun 5.
    • Steepness - Bosch 12% grade rated 3, 8Fun 20% grade rated 5
    • Your personal rating from demo rides. - Mountain 5
  4. Endurance - how much longer he can play.
    • Heat - 36V Bosch rated 3, 48V NTS Works rated 5
    • Throttle - Bosch 0, 8Fun 5.
    • Your fitness level rating - Shortness of breath, sweat and a strong urge to strike the ground with your heels are signs that a hill is too steep for your fitness level. (5)
  5. Enjoyment - new types of thrills
    • Speed - Bosch 3. 8Fun 5.
    • Jumping - Bosch 3. Mountain 5. Suspension.
    • Contentment - Your personal rating from demo rides. - Mountain 5
  6. Ease - access steeper grades that were not previously climbable
    • Gear switching torque sensor - Bosch 5, 8Fun 2.
    • Pedal Assist Levels 1-9 - Bosch 5, 8Fun 2.
    • Components - Mountain 5
    • Derailleur front and rear- Mountain 5
    • Chainwheel- Mountain 5
    • Drivetrain - EBike rated 4, mountain bike rated 5
    • Head tube angle - constrains max. Slope one can climb. (69 degrees)
    • Discomfort - Your personal rating from demo rides.
    • "Gear Display" mountain = 1.6meters
    • Your leg power (100, 200 or 300 Watt category)
    • Your max steepness grade for mountain bike 12.5% (Mr. Endurance 200W)
HPC gear display (25% more torque)
Custom Single Speed 38T sprocket for nearly 25% more torque and higher efficiency.
38 front teeth / 42 rear teeth x (0.7m) x 3.14 = 2m
32 front teeth / 42 rear teeth x (0.7m) x 3.14 = 1.7m


Felt gear display calculations

  • Chainwheel
    RaceFace NW 30T 1x11-speed
  • Freewheel:
    SRAM X1 11-speed 10-42
  • Tires: 27.5" x 2.35" (0.7 meters)
  • 30 front teeth / 42 rear teeth x (0.7m) x 3.14 = 1.6m
High gear ratio = 30 / 10 x 0.7 x 3.14 = 6.6m
Gear percentage = 6.6m / 1.6m = 412%. Rohloff is 526% (+124% or 22% improvement)

Rohloff gear display 26" wheel 1.44 to 7.56
 
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