Technical FAQ
Photo: Ben Delaney / Roll Massif

Technical FAQ: Tubeless road tires, glove loops, e-bike power

A reader writes in after an unfortunate crash on tubeless tires; Lennard gets more feedback on his lightning column

Have a question for Lennard? Please email us to be included in Technical FAQ.

Dear Lennard,
I’ve been riding road tubeless for a little over two years and absolutely love the lack of flats. The downside I’ve seen at least once and maybe twice is sudden and immediate loss of air pressure when the tire burped after hitting an object in the road at high speed.

The first occurrence was downhill in a straight line at I’m guessing around 35mph; both front and rear tires went flat instantly. Thankfully, I stayed upright and made a safe stop.

This last week I awoke in a helicopter ride to a hospital. Nobody was around when I crashed, and I have no memory of the crash. Only worrisome part is the front tire was flat with no punctures.

I may be adding two and two and getting five, but I am concerned that a less than desirable part of road tubeless is the sudden loss of air with a burp.

I was using Hed Ardennes wheels with 25mm Continental GP5000 TL in the last occurrence. The first burp with no crash was with 25mm Specialized tubeless.

Now I’m wondering if the rim tape failed or if this was a self-inflicted wound. After the tire was removed, it is obvious the tape needs replacing — it was pulled out of place in some areas. I assumed (I hate that word) this was from the tire losing air and the bead unlocking.

I’m laughing at myself; I hate opinions based on limited data. But I’m probably going back to tubed tires for the road. However, I just remembered a friend crashing and breaking a shoulder some years ago on the cool down lap of a crit; his front tire went flat.
— Colan

Dear Colan,
Your understatement at the “only worrisome part is the front tire was flat with no punctures” after finding yourself in a helicopter to the hospital is classic. Those are some scary incidents! Yikes!

The thing with a tubeless road tire is that it has little air volume at high pressure, so if it burps some air, the tire goes immediately and essentially flat. Compare that to a tubeless mountain-bike tire, which has lots of air volume at low pressure; if it burps some air for the same brief instant of time that would have taken a road tubeless tire from 80psi to 10psi, it may instead go from 20psi to 15psi. This is still rideable and will be much less likely to result in a crash than a road tire that suddenly goes flat. (And speeds are lower and the ground is often softer on a mountain-bike trail, so the consequences of a crash from a burp would not tend to put you in a helicopter to the hospital.)

As I have said before, I have reservations about running tubeless road tires on standard wheels (even “tubeless-compatible” wheels) with tape to seal their spoke-nipple access holes in the rim bed. A tubeless-specific rim, by contrast, needs no tape because it is completely airtight, without any spoke-access holes in the rim bed. It also, perhaps most importantly, has a narrow ridge (the “hump”) on the inboard edge of the bead ledge, a bead-locking ridge that Hutchinson designed the tires to mate with. The hump is designed to seal against the extra rubber flap extending inboard from the tire bead as well as to lock the bead on.

Without the little ridges (humps) on the inboard edges of the bead shelves inside the rim that a tubeless-specific rim has, the bead will not be locked on. Instead, having shiny, slippery sealing tape smoothing the rim contours under the tire bead, lubricated by slippery tire sealant, seems to me to offer significantly reduced resistance against the bead moving inward and burping air in the case of hard cornering, especially at the lower pressures that tubeless makes possible by eliminating the inner tube and hence pinch flats. Additionally, without the inboard bead ridge, the tire could come off of the rim more easily in the event of riding on a flat. And you identified the other thing that can happen with rim tape, namely that it can become dislodged and leak air.
― Lennard

Dear Lennard,
I read your columns on wiping tires.

I recently made the switch from old school leather palmed cycling gloves with macrame cotton backs to some more modern ones. I notice that both pairs have a little reinforcement on the middle and ring fingers, like a pocket with the opening toward the palm. On one pair this is leather, and on another it is plastic. Are these for ease of removing gloves, or for cleaning debris from tires, or some combination of both? They certainly work for removing gloves but seem to be too fine an embellishment for that to be their purpose.

I’d be hard-pressed to see how these would work for wiping tires with ease.
— Richard

Dear Richard,
My friend Henrik of Curve clarified this. Those little loops are to help take off the gloves, since some gloves are super tight, and you can’t get a hold of anything to peel them off your hands.
― Lennard

Dear Lennard,
I’m trying to figure out how much power my e-bike puts out. The specs only show the maximum torque at each setting, not the power output.
— James.

Dear James,
This is how to figure it out.

For a motor operating at constant torque over its speed range, the power delivered would be P=T*w with w representing the rotational frequency of the wheels and tires (depends on the tire’s inflated diameter) and T= torque of motor.

Here’s an example using my own e-bike, which has a Bosch Performance Line Speed motor, which is limited to 28mph (45kph).

circumference of 700 x 30C tire = 2,146mm = 2.146m

Bosch Performance Line Speed motor max torque = 63 Nm

w = 45 km/h * 1000 m/km * 1 rev/2.146m * 1 h/60min * 1 min/60s = 5.8 rev/s

P = T * w = 63 Nm * 5.8 m/s = 365 W

Incidentally, this motor has a listed power output of 350W and max power of 575W. For 2020, the Bosch Performance Line Speed motor has a max torque of 75Nm, making the average power on its highest setting instead 435Nm, using the above formula.
― Lennard

A bit more on lightning

Photo: Flickr Creative Commons

Dear Lennard,
Back in the 70’s when I co-owned a bike shop in San Francisco, a customer told us of cycling in the Sierra when lightning struck his aluminum brake lever and arced to a hydrant he was just passing by. Scared the hell out of him, but unhurt and kept riding. One of his nine lives I guess.
— Michael

Dear Lennard,
I used to be a mountain bike guide in western North Carolina. Once while riding with a group of eight and a co-leader, we were caught in the middle of a lightning storm. I was standing on the ground and so was another student to assist in a tough stream crossing. A tree nearby was hit by lightning. The two of us standing on the ground received ground current through our legs and we each “jumped” and then fell. The eight people still on their bikes received no current at all and wondered what had happened to us. Luckily, we were both fine, if not scared. In this situation where there were plenty of long conductors (thick forest) and little chance of a direct strike, it would seem that a bike offers some marginal resistance to ground strike current. The tree that was struck in our situation was within 20-30 yards for reference.
— Paul

Dear Lennard,
I don’t know why Dale suggested that the electrical potential of a lightning bolt being a billion volts. That seems to be about a factor of 10 too high as electrical potential is reported to be in the range 10 to 100 MV.

Here are a couple of references.
— Ray


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.