Technical FAQ

Technical FAQ: Will an oval chainring violate junior gear restrictions?

In this week's column, Lennard fields questions about junior gearing, bent derailleurs, and whether a bike can zap you in a lightning storm.

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

Dear Lennard,
Just a quick question regarding junior gearing and rollout. Will a Rotor Q-Ring 36-tooth chainring produce a larger or smaller rollout than a round 36 chainring? My son is interested in bicycle racing and I’m trying to get my head around junior rollouts. Currently my son is restricted to a 5.5-meter rollout and he currently runs a 36-tooth chainring with a 14/28 cassette with 25mm tire on 700c wheels. Will an oval chainring impact this rollout distance if the teeth number is the same as a round ring?
— Seb

Dear Seb,
The rollout would be the same because the number of teeth is the same, and the spacing between teeth is the same. A bike with the chain on a 14-tooth cog and a 36-tooth round chainring should roll just as far in one revolution of the crank as it would if the chainring were a 36-tooth Rotor Q-Ring.

Pablo Carrasco, founder of Rotor, says, “The rollout is exactly the same. It is just about the ratio for teeth number:
(Fc/Rc)*pi()*D
When D is the maximum diameter of the wheel (including the tire).”
― Lennard

Dear Lennard,
I’ve got some riding buddies that insist that shifting under load can bend a derailleur hanger or damage the braze-on in for the front derailleur. I can imagine the front derailleur situation because of the immense force needed to push the chain sideways across so large a gap, but I don’t agree with their theory about the rear derailleur. I would imagine that the force of the cable pulling on the derailleur doesn’t correlate with the pedaling force in a way to bend the hanger.
Would love your input!
— Mathew

Dear Mathew,
I agree with you. The chain being under high tension does not translate to having the lower section of chain being under tension. While you can do some damage to the chain and cogs and front derailleur by shifting under load, the rear derailleur jockey wheels, as they are running on the part of the chain with minimal tension, are largely unaffected by how hard you are pedaling.

The chain won’t want to derail from one cog to the next if the chain tension is high, but the rear derailleur is only touching the low-tension chain under the cassette, so, when trying to shift from one cog to the next, the side load on the derailleur, and hence on the derailleur hanger, will be no higher than when shifting from one cog to the next with low tension on the chain. It still may not make the shift due to pedaling so hard, but that doesn’t mean the derailleur would be damaged.
― Lennard

Dear Lennard,
After getting caught in an afternoon storm the other day, my buddies and I started to wonder if one type of frame material is more dangerous in an electrical storm than others. For instance, is it safer to be riding a titanium bike rather than carbon? Is carbon more dangerous in a storm than steel? While we’re at it, does the battery in a Di2 drivetrain make the bike potentially more dangerous than a traditional mechanical drivetrain during a storm? What about carbon e-bikes? They would certainly be the most dangerous bike to be riding during a storm, right?

Thanks for entertaining the musings a few old guys seeking shelter on a stranger’s porch.
— Tom

Dear Tom,
I don’t think it is likely to matter in terms of your safety. While there might be a slightly greater likelihood of a metal frame being directly hit by lightning than a carbon-fiber composite frame, the probability of either one being struck is so low that the slightly increased probability still won’t amount to much.

Rarely are people hit directly by lightning; when people are killed or injured by it, it is generally due to it flowing across the ground after a lightning strike on a nearby tree or another tall object. If the person’s feet are far apart (say, laterally), and the direction of the current is from one foot to the other (flowing from the side of the person), the electrical potential difference (voltage) between the feet can result in enough current flowing up through the person from one foot and down to the other that it stops the heart. If the current is instead flowing toward the person from straight ahead or behind and the person’s feet are laterally separated but not separated fore-aft, then the potential difference between the feet is negligible, no matter how far the feet are apart laterally, and little or no current will flow through the person. This is the reason in a lightning storm to crouch down (to not be hit directly due to being the tallest thing around) with feet together (to minimize potential difference between the feet) and not touch any other body part to the ground (again, to not have separation between contact points).

On a bike on dry roads, a lightning strike hitting a nearby tree will not bother the rider, because the tires insulate him or her from the road. Wet roads, of course, carry a higher lightning risk

If lightning strikes a tree or sign adjacent the road, causing current to flow across the road toward the bike from the side, there will be little or no electrical potential difference between the wheels, resulting in no current flowing up through the bike. However, if current from a lightning strike is flowing down the (wet) road from the front or back of the rider, there will be a potential difference between wheels. This will inspire current to flow through the bike from one wheel to the other.

A carbon frame, being an insulator, will block that flow, but if it is all wet, the current may still find a way through the dirty water. Conversely, current can easily flow through a metal frame, but to shock the rider, the current still has to get through the insulating saddle and handlebar tape and shoe soles into the rider. Since the resistance to current flow through the metal frame is low, that is where it will tend to go, from one wheel and out through the other, rather than through the high-resistance parts like saddle, bar tape, shoes, and the person’s body.
― Lennard

Regarding carbon frame damage:
Dear Lennard,
Ruckus Composites in Portland, OR offers a wonderful frame inspection service for carbon. I have had great successful with them. After no crashes but 2 very hard seasons of rough gravel racing, I had them inspect my 3T Exploro last fall to make sure it would see another season safely. The steerer was showing signs of delamination so I replaced the fork. After a bad crash in a race yesterday I’ll be sending the Exploro down to them again. Although I suspect that this frame is due for replacement the service is cheap enough to make it worth checking out first. I have also had them inspect and repair a Niner Jet 9, as well as modify it for an internal dropper post.
— Joel

Dear Lennard,
Ductility is measured as the amount of plastic deformation a material or part can undergo before ultimate rupture. The material’s yield strength is the measure of the stress a material can withstand within its elastic range. The yield strength and the part’s geometry (tube diameter, tube shape, wall thickness) determine the amount of force a part can sustain within the elastic range of the material.
— Harry

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. Readers can send brief technical questions to Ask LZ