6437 km (4000 miles)

A quick update since it's been nearly a year: The last crash took some wind out of my sails, and the MS that put me in the chair keeps progressing, but the past 1400 km have been fairly uneventful with the rubber side staying down.

• The Q-211 front tire finally gave out with a slow flat and cords showing.  Lifetime: 3629 km
• The larger 36 V, 11.6 Ah battery started cutting out, perhaps due to unbalanced cells, so I reverted back to the original 6.6 Ah one.  Lifetime:  5050 km (about 250 cycles assuming 50% depletion)

Screenshot from the VESC phone app (Android).  The electronic FREEwheel is active to improve coasting and reduce torque chatter.  The throttle holder is keeping MAXimum forwards throttle until I press reverse.

Replacement Q-211 tire before mounting.

5000 km (crash)

The past two km chiliads (since 3000 km) were notable for two accidents, keeping the rate at a stubborn one per 1000 km.  First, a minor low-speed tip-over that occurred while playing tag with a relative on roller skates.  Some people take pride in playing hard.  The second was more troubling:

Near the top speed (23 km/h), I lost steering control and crashed diagonally into a curb, causing the wheelchair to flip. I think the left Firefly attachment had separated from the wheelchair, and the right clamp by itself was too weak (picture below), causing the loss of steering. 

I don't know why the left connection let go.  Perhaps I forgot to flip the quick-release lever or the pins weren't fully seated or resonance caused the mechanism to disengage. Just before the crash, I rode over a rumble strip whose vibrations must have caused the final separation. It would be wise to check for any self-loosening in the future and maybe add latch retainers.

Fortunately, the bruising and road-rash are temporary.  I replaced the trashed right-side attachment clamp, but my wheelchair is crooked now, with the right frame leg bent back by about half an inch and downward by a quarter inch.  Considering my usual routes, the consequences of veering sideways uncontrollably could have been a lot more serious.

On a positive note, the QIND Q-211 tire continues to last beyond 2400 km with no visible cords. The front axle has stayed tight since switching to the VESC controller nearly 700 km ago, despite heavy use of regen-braking.

Tire change #3 and #4

The previous Goodyear "Street" tire was showing cords after only 369 km (229 miles).  I replaced it with a heavy-duty "electric scooter" tire (QIND Q-211).  The scooter tire is a lot beefier, but the nominal size is the same, 57-203.

Initial inflation to 25 PSI caused a little tire rub (probably at the "hairs" that hang off).  Lowering the pressure to 10 PSI reduced rubbing.  Low tire pressure makes the contact patch wider, so more rubber is available to wear.  It also improves shock absorption, but raises rolling resistance (not so important) and the risk of bottoming-out (which is hard to quantify).  The operating weight of the front wheel is only 40-60 lb¹ (measured with a bathroom scale) and I approach large bumps slowly, so I think low pressure is ok.

This tire was super tight to put on.  I used 12" motorcycle tire levers and also zip ties to hold the seated bead against the rim while working the tire on.

For unknown reasons, after the tire change I had to adjust the V-brake left and right spring tensions a lot to prevent brake drag.

I recommend this tire for anyone who wears out multiple tires per year and is willing to deal with a tight bead and minimal clearance.

Update: The Q-211 tire lasted 3620 km.  It ended with a gradual flat (first one) and some cords visible.  I had periodically pumped it to 20 psi or so.  At softer, more comfortable pressure, the tire and tube slowly rotate against the rim because of driving torque.  This would cause the valve stem to rip out.

    

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¹ Equals 18 to 27 % of vehicle weight, depending on upper body position. Shifting the wheelchair rear wheels backward would improve the Firefly weight distribution but degrade manual wheelchair handling.

Tire change #2

Old: Schwalbe Big Apple (50-203, $25)
New: Goodyear 12" Street Folding (57-203, $15)

The rubber had worn through to the light brown base material in one spot.  Schwalbe Big Apple lifetime: 515 km.

The new size has minimal clearance.  To prevent rubbing, I had to adjust the fender (loosen screw at fork, push fender away from tire & re-tighten).

Tire change steps:

1. Flip Firefly upside down
2. Disengage V-brake
3. Unplug motor cable
4. Remove disc brake (5 mm Allen wrench)
5. Remove wheel (17 mm wrench)
6. Let air out of tire
7. Remove old tire with motorcycle tire irons and replace (easy peasy)
8. Pump to 30 psi
9. Reassemble

Note that despite its name, this Goodyear tire does not actually have a street tread, and I can't recommend it.

Tire change

After 1000 km, the original tire (ETRTO size 47-203) was getting bald (not the only thing doing that), and it was time for a replacement.  The new tire is a Schwalbe "Big Apple", size 50-203.  The Schwalbe tire went onto the rim by hand and seems like a quality product.  The original was really tight and I used steel motorcycle tire levers to remove it.  Unfortunately I scratched the inner rim and didn't think of sanding down any sharpness before putting on the new tire.  Hopefully this doesn't cause a flat.

After loosening the outer wheel nuts, the axle had a 5 mm or so total gap between the inner wheel nuts and fork legs.  A pair of washers whose thickness matched the gap had been put on the outside of the fork, and the fork legs were being bent to close the gap.  Putting the washers on the inside allows the wheel to be mounted without bending the fork.

The V-brake needed adjustment to match the new wheel position.  Making this adjustment had the benefit of significantly reducing brake shudder.

PS: For reference, the inner fork spacing is 5.375" (137 mm).