SB20 Dream Drive

SB20 Dream Dream provides equally spaced virtual gears across the SB20's Resistance Range. Define a configuration with 10 gears and you get 10 equally spaced virtual gears. Create 25 gears, and you get 25 equally spaced gears. 

How does this compare to traditional 2X gearing with its 2 front chainrings and rear cassette?  Let's find out.

What are Virtual Gears?

First, let's understand virtual gears.  How do they differ from an indoor trainer and why are virtual gears often considered better?

Smart bikes and trainers expect apps like Zwift to control electronic brake resistance.  This allows the indoor bike to simulate riding conditions like flat or hilly terrain along with different riding surfaces like dirt or asphalt. 

Trainers use the attached bike's physical gears to add the resistance that represents the effort needed to move a bike over the simulated terrain. 

Smart bikes accomplish the same by simply increasing the electronic brake resistance. You get the feel of physical gears without the drivetrain noise, clunky shifts and chain lube on the floor.  

Resistance Range

The SB20 has 100 internal resistance levels. Level 1 is equivalent to a 39t/36t gear on a road bike. Level 100 is equivalent to a 55t/10t gear.

🔬Note: I'm not 100% certain about these numbers. Stages documentation is seriously out-of-date.  Overall resistance range has been extrapolated from the latest release of the Stages Cycling app that shows a larger resistance range than previous versions. 

GEAR RANGE

A gear inch is an integer number that lets you compare relative resistance for different gear ratios.  The formula is simple:

Wheel Size (in inches) x Number of Front Teeth / Number of Rear Teeth

Here's the range of road bike gears supported by the SB20: 

Traditional Gearing

Default SB20 gearing simulates a traditional 2X drivetrain with 53t/39t chainrings driving a 12 speed 10t/36t rear sprocket.  Gearing looks like this:

The range of gear ratios are shown for each chainring. Like a real road bike, the shaded portion of the chart highlights the gears that are duplicated on both chainrings. This means that out of 24 possible gear positions, only 16 of the gears are unique.

Dream Drive Gearing

Dream Drive maps the number of virtual gears you select to the SB20's 100 resistance levels. The resistance range never changes. You get greater or fewer virtual gears with smaller and larger gaps respectively. It's like a 1X drivetrain with equally spaced gears.

Dream Drive 25

Here's what a 25 gear Dream Drive configuration looks like:

 (The highlighted 🔵 ratio is the initial gear after power up)

Unlike traditional configurations, there is no duplication of gears. All twenty five gears are unique and evenly spaced. 

One potential concern is: the gaps in higher gears are equivalent to fractions of the rear sprocket. For example, gears 23, 24 and 25 are equivalent to physical road bike gears of 55t/10.7t, 55t/11.3t 55t/10.0t respectively.  

Dream Drive 12

To avoid fractional rear cogs in higher gears, it is worth considering a 12 gear Dream Drive configuration:

Higher gears are now better spaced but overall range has larger gaps.  Good but not perfect for many riders. It can be hard to find a comfortable gear when riding in a pace line.

Dream Drive 18

For many riders, a Dream Drive 18 gear configuration may be closer to ideal:

This configuration has more unique gears than the traditional 2X Drivetrain. It has no gear duplication and better spacing.

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My Dream Drive Configuration

I use a Dream Drive 25 gear configuration with custom buttons that resemble a SRAM shifter (even though I don't have SRAM on any of my bikes). 

SRAM shifting works well with Dream Drive. Buttons on the left of centre shift to a smaller gear. Buttons on the right shift to a bigger gear.

When using the Stages Cycling App at the same time as Zwift, it's easy to visualize the shifting pattern:

⏪  ◀️   Gears   ▶️  ⏩