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Technical FAQ: Feedback on lightning strikes and junior gears

Lennard receives ample feedback from his recent column about lightning strikes and frame material, plus some insight into proper junior gearing

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Dear readers,
I had another column prepared for today until I started reading my inbox. I think it makes more sense to run these letters about lightning instead. Regarding last week’s column on bike riding in lightning storms and junior gear rollouts on oval chainrings, I received a lot of feedback and have reconsidered my answer about lightning. Here is some of it, starting with the junior gears:

— Lennard

Dear Lennard,
I just saw today’s technical FAQ question from Seb about juniors riding oval gearing. As you answered, the shape of the chainring makes no difference to rollout. My son has been riding RideA cranks with Oval power rings on road and mountain bikes since he was 10 years old and loves them. Particularly, since he has developed Osgood-Schlatter, the oval rings seem to be easier on his knees. (Anecdotally, reducing knee pain is a benefit for the many juniors we know on oval rings. But I know that has been discussed repeatedly in columns including your own.)

The main reason for me writing though is to warn parents of junior riders that tire choice can have a significant impact on rollout. A bike with legal gearing can fail junior rollout when equipped with increasingly popular high-volume tires. I have witnessed junior riders being disqualified when racing on tires from 25c and up. It is very important to verify rollout when switching tires, even if gearing remains the same. My son has had very good experience with Challenge tires at 700x24mm. The diameter is consistent as labeled, where that is not always the case with other brands/diameters. The 25mm width seems to be the limit for juniors, as long as the 25mm measurement is accurate, which seems to be hit or miss.

Fortunately, this year we are seeing rollout performed on the way to staging, before our SoCal races, instead of after. This gives riders a few minutes to correct a rollout discrepancy before the race rather than be disqualified after. But that is not the case everywhere.

I am happy to share info with respect to junior racing and equipment with any parent seeking advice. I know USA Cycling has numerous resources as do many junior teams and clubs. Our Velosport Junior Development program is a great example (shameless plug intended).
— Ted

Dear Lennard,
Confused as to why Seb states that his son needs to be compliant with a 5.5-meter rollout. The USAC website shows all age juniors rolling out 7.93 meters on the road and 6.05 meters or higher on the track (depending on riders age)

• Ages 6-18: 7.93 meters (26’)(52×14)
• Ages 17-18: Unrestricted
• Ages 15-16: 6.93 meters (22’9″)(50×15) **
• Ages 13-14: 6.45 meters (21’2″)(50×16)
Ages 10-12: 6.05 meters (19’8”)(52×17)
— Scott

Dear Lennard,
A couple years ago, I was just coming to the crest of Loveland Pass when there was a simultaneous blindingly bright flash boom. I didn’t go down but kept riding and made an immediate U-turn.
The weird part was that the next time I looked down, my Garmin head unit was dead and was unable to be revived. Power meter survived (as did I).

That was interesting – nothing more.

I’m dubious that your discussion of frames, insulation from tires, etc. has any pertinence or validity whatsoever however in the face of the large potential differences involved in a lightning strike. You might want to rethink that one or get an expert to comment on it.
— Rick

Dear Lennard,
Carbon fiber is not an insulator but rather an excellent conductor. I agree that lightening isn’t a concern on one frame material vs. another, but there’s a reason fishermen switch from graphite rods to fiberglass when a storm blows up.
— Christopher

Dear Lennard,
Wait… so a lightning bolt that travels miles through air will get stopped by a 1 inch piece of rubber? Me thinks not.
I was driving in a pickup which was struck by lightning; blew off the old pig tail cell phone antenna, popped a bunch of fuses, and took out the alternator. The pickup tires should have substantially more insulating qualities than a bike tire but the fact remains, the truck was hit. Talking to the local Chevy dealer, he told me I was lucky to have so little electrical damage, most of the time the entire wiring harness is fried.

I’m no electrical engineer or physicist but do have that one experience plus logic tells me a bike tire is not going to stop a billion volts.
— Dale

Dear Dale,
If the truck itself was hit by lightning, then this is not really addressing what I was trying to write about, and I apparently could have written that more clearly. My point was about lightning that had hit the ground (or a tree or sign) and traveled across the road (or along it lengthwise) to get to the bike. In re-reading my answer from last week, I guess I didn’t make it as clear as I’d intended that if the person or the bike were to get hit directly, the rider would presumably not survive.

As for your truck, the current from the lightning strike was trying to get to the ground. It seems to me that if it had actually gotten to the ground through the truck’s tires, at least one of them would have been burned or melted, and you didn’t mention that happening. Perhaps I’m wrong about this, and it flowed around the tires (they were probably wet, which would have facilitated this) to the ground without burning a hole or other visible marks in any of them.

The antenna, fuses and alternator were between the lightning and the truck’s own internal ground and hence got fried. I suppose that the fact that the rest of your wiring harness was not burned the way the Chevy dealer said often happens could indicate that the current got back out of the truck to the road before frying anything else. The reason you were fine inside the truck is that electric fields don’t exist inside closed surfaces, so even though the voltage of the exterior of the truck had gone up by thousands of volts, you felt nothing inside of it.
― Lennard

Dear Lennard,
I liked your explanation of the touch and step dangers due to lightning.

I do want to address the frame material effect. It is as close to 0 as you can get. The potential difference between the Earth and the sky is great enough that a spark can cross several thousand feet of air, which is usually a pretty effective insulator. 5000V per inch of air gap (dry of course). The under four-inch of gap between the top tube and rims will not resist that spark significantly different between metal and any other frame material. Yes, aluminum is probably the most conductive frame material, but carbon is not a pure insulator; regardless, the spark gap is insignificant. This also applies to the tires. They won’t hurt but they don’t help either.

At least in a car we are surrounded by a faraday cage which shunts the electricity around us.

A lot of electrical professionals lump all high voltage into one experience. Tires can certainly help isolate a car with a power line contact, but lightning can be a million volts, and we have little ability to insulate for that voltage level.

Best advice is to do as you say. Squat down at a location that is low to the terrain and stay away from tall things like trees. Keep feet together, and if you must move, shuffle with feet close together. Hopping can work, but a trip and fall could spread you out for touch and step dangers. Still, you did a pretty good job on the advice. As always, I love your contributions
— Mike

Dear Mike,
Thanks. I take back my answer about any insulating effects of anything on the bike. Your point about lightning jumping across thousands of feet of dry air makes any insulating effect of a 23mm-tall rubber tire or a frame being irrelevant; it’s absolutely clear how naïve my answer was. Unless the strike was at quite a large distance from the rider, the tires probably won’t be enough to keep the current from going up into the bike if lightning hits the road or a tree or sign adjacent it.
― Lennard

Dear Lennard,
I have no experience with carbon frames and electrical conductance, however, I do have experience with raw carbon fiber. Raw carbon fiber will conduct a current. Our fiber ring spinning equipment continually needed cleaning when we used carbon fiber “string”. This was used in experiments for a major tire manufacturer that wanted a CF reinforced passenger tire.

Thanks for your helping to educate me.
— Mike

Dear Lennard,
I live in Florida, which is touted as the lightning capital of the U.S. Very recently a motorcyclist was struck in his helmet by a bolt of lightning while riding down the highway. In the pictures of the helmet you can see the holes that the lightning blasted through his helmet. It is unclear if the lightning bolt or the resulting crash was the cause of his death, but the circumstances of this crash are different than the scenarios you mentioned. It is also worth noting that this crash occurred on a clear day, so this was in fact a bolt out of the blue. A link to an article with further details is attached.

Over the past 10 years on average 10 people in the U.S. die from lightning every year and five of those deaths on average occur in Florida. People worry about the wrong things in Florida such as alligator attacks or shark bites while they are much more likely to die from lightning or even a mosquito bite.
— Peter

Dear Peter,
Wow. That’s brutal. Similarly, a bike rider hit by a direct strike would have no chance, and I guess I didn’t make that clear enough last week.

Interestingly, a friend of mine was hit by lightning while hiking many decades ago. He has led a full life since, thanks to it having knocked him off of a small cliff. The doctors said that the lightning had stopped his heart, and the fall revived him, as his heart restarted from the impact. Clearly, he must not have been hit by as powerful of a strike as the one that burned right through the motorcyclist’s helmet; his burns were not of that kind of severity.
― Lennard

Dear Lennard,
I have been reading your column for more than a decade, and you are typically a great source for facts and clarifications.

Your recent comments about lightning strikes and various bicycle frame materials needs revisiting.

I am a physician practicing in Brevard County, Florida. We have many lightning strikes to various objects annually in our county. This past year I have had two persons directly struck by lightning while riding a motorcycle, of which one survived. The year prior we had a person killed while riding his bicycle (steel frame cruiser). There is no safety while riding a bicycle in a lightning storm despite its rubber tires, etc.

Frame material: The material type is irrelevant when high powered electrical strikes are searching for a ground. Additionally, your comment “A carbon frame, being an insulator, will block that flow ” is completely wrong. Carbon fiber is not an insulator, but rather it is the perfect electrical conductor. If you don’t believe me, go connect two terminals of a car battery with a single piece of carbon.

For liability and safety concerns, please publish a clarification.
— Tom

Dear Tom,
Done. Thanks. I have learned a lot today not only about lightning but also about Florida!
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, 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. Readers can send brief technical questions to Ask LZ

Follow @lennardzinn