Good question! At first glance it might not make sense but if you think about the affect of the 20″ rear wheel on the gear range of the bike, it does make sense. If you’re curious and like to get into the nitty gritty technical side of why it’s sensible, read on.
Probably the most compelling feature on the EdgeRunner is the small 20” rear wheel. And we don’t hesitate to go on record to say that the rear 20″ wheel is major advancement in the evolution of longtail cargo bikes. We can think of three advantages of the 20” rear wheel to call out:
1) A smaller rear wheel makes for a stronger and more rugged wheel…a feature very appropriate for a cargo bike. That smaller wheel also facilitates a tighter and stiffer rear triangle on the frame. That stronger wheel plus stiffer frame equals a better ride with less tail wag under load.
2) Lower center of gravity. With a smaller rear wheel, it is possible to set up the EdgeRunner with shortened rear V-rack tubes and thus dropping the height of the deck 4-6 inches lower than that of a comparable 26” rear wheel Xtracycle. This lower center of gravity has a tremendous effect on the handling characteristics of the bike when loaded-and is especially better with kids as the load because kids are always carried above the wheel, high on the bike.
3) Lower gear ratios with the smaller rear wheel. With a cargo bike, having low gears is a nice feature. What is especially nice is when running a rear wheel electric assist motor like the BionX, the smaller rear wheel must spin at a higher RPM to go the same speed as a BionX bike with a larger rear wheel. With the BionX on the EdgeRunner, you get quite a bit more climbing torque because of this. The reason is, electric motors like to spin and are more efficient at turning electricity into forward motion when spinning at higher rpms.
With that said, the 20” rear wheel can pose a problem with getting a BIG enough gear. That 20″ wheel (compared to a 26″ MTB or 700c road/hybrid wheel) drops the whole gear range on the bike substantially. Essentially, it would be comparable to riding everywhere in the granny gear of your mountain bike. Too low a gear range can mean that you’re spinning your legs like a hamster in a hamster wheel while doing 17 mph on the flats and that’s for hamsters, not humans!
So, you can see that the BIG issue with the EdgeRunner- at least in regards to gearing – is not if can we get low enough gears but, can we get big enough gears?
To address this challenge, four of Splendid Cycles’ custom spec’d EdgeRunners will have optimized gearing – a gearing range set up to compensate for that small rear wheel. The two Shimano Alfine internal hub bikes (Value and Primo) will come spec’d with these optimized gears by running a 45 tooth front ring and an 18 tooth or 20 tooth cog on the rear. The two externally-geared Primo bikes with derailleurs (one with e-assist and one without)will have the optimized gears by running a Shimano Tiagra road crankset with a 53/39 tooth profile.
While a standard MTB drivetrain will get you the super low gears you desire on a cargo bike, on the EdgeRunner it fails to deliver in the mid to high range. Running the 39/53 tooth front rings with the 11-34 tooth ten-speed rear cassette gives us a very comfortable gear range of about 20 gear inches for your lowest gear (that’s quite low!) and about 90 gear inches for your highest gear (yeah, you can pedal down some hills!). From a gear inch standpoint this is perfect for loaded bike riding like touring or cargo biking.
On a side note, in order to run a road crankset, our options are pretty limited. If you want higher quality, nice looking components, proper part compatibility and good shifting performance with a flat bar shifter, there just are not a lot of options. With our spec on the Primo bikes, we run the Shimano Tiagra group with flat bar shifters, front derailleur and crankset, and a Shimano Deore rear derailleur shifting a 10-speed 11-34-tooth cassette. This selection of parts gives us everything we need: proper gearing, elegant looks, a reasonable price, excellent shifting on both front and rear derailleur, and good durability because of the higher quality components.
That’s why we do it. We think it’s a sensible and attractive option for a very sensible and attractive Xtracycle EdgeRunner.
Come see for yourself….drop by and take a bike for a ride!