# What speed of wind gust will cause a cyclist to swerve by 1m or more?

Today's weather forecast for London predicts gusts of 45mph. While there are many factors in determining whether its safe to ride, the possibility of getting blown into oncoming traffic rules out a ride.

Given a typical road lane width of 3m, and assuming I cycle in the middle of the lane, I'd like to know what speed of wind gust could push me close to the centre of the road.

• Well it would depend on several factors which there is not information given on such as shielding from buildings, which direction the wind is blowing relative to your direction of travel... I can say from experience that I have wheelied a street motorcycle and got a strong crosswind and it threw the bike offline very quickly and forced me to set the motorcycle back down very quickly so for an even lighter bicycle, I would think the effect of wind would be even more pronounced. People have died because of wind. Butch Laswell for example. link: youtube.com/watch?v=8SOIPXTmN4U Feb 8 '16 at 13:21
• It's quite unpredictable. Depends on the angle of the wind, the configuration of the bike (bags? rider upright or aero? handlebar style?), and how quickly the gust comes up (if the rider has any time at all to correct then there will be no significant deviation). The gust from a truck passing in a crosswind is worst, since the wind quickly changes directions twice. Feb 8 '16 at 13:26
• There is not enough information given to answer this specific question, nor is there likely to be. The same cross wind will affect a large slab-sided lorry differently than a small car; the same cross wind will affect a thrown ping pong ball differently than a speeding bullet. From this you can see that it's not so much about the wind as about the characteristics of the object, and we would need much more information about the object (in this case, a cyclist) than simply the speed of the wind. Feb 8 '16 at 15:47
• It depends on how used you are to riding in the wind as well. I found I got a lot better at riding in wind when riding through tornado warnings while outside (not that this is in any way a good idea or something you should do). Feb 8 '16 at 16:44
• It's more a matter of how quickly the windspeed changes. It'd be rather easy to ride with a 45mph crosswind if it is completely constant. Feb 8 '16 at 17:15

Having ridden near Bristol this morning in a similar forecast gust speed, I'd say you're right to be worried, but keeping aware of the wind direction and speed can make a huge difference. For example: passing side roads on your left, if the wind is coming from the left, you may want to aim slightly towards them so that you get blown back towards the middle of your lane (swap left/right for US readers).

Considering my ride this morning: I was lining up for a left turn at a T, then was suddenly closer to a right turn position as the gust coincided with me leaving the wind shadow of a house. That was probably a sudden smack of 45mph wind broadside on, I'm tall and ride a hybrid with a rear pannier, and tend to sit up tall approaching that junction to see better (also loose clothing, so close to worst case). It probably moved me 1-1.5m sideways. I was already braking and unclipped.

If you're already riding in the middle of the lane you're in a good position. But don't forget that when that wind is in your face you'll be doing something like walking pace, so you have to balance your right to the road with the behaviour of drivers, and that balance is shifted both because of your reduced speed and the worse-than-normal effects of close passes. Taking the lane, but not slightly left of centre would make a big difference here.

Also:

• Use your ears - you can normally hear a gust coming before it hits you.
• Remember that when around queued vehicles the wind may change unexpectedly and you may lose most of your headway.
• Don't forget that you will be going more slowly than normal, giving you more time to react (some of that wind will be in your face).
• Don't fight to hold a perfect line - if drivers can see you being blown about they'll give you more room (I'm not saying exagerrate it either).

There are more factors:

• bike speed
• bike style / tire size
• rider skill

I ran the math

• If you are going 10 kph, get pushed off 20 degrees, and it takes 1 second to correct (point into the wind) then that is 0.95 meters
• If you are going 20 kph, get pushed off 20 degrees, and it takes 1 second to correct (point into the wind) then that is 1.90 meters
• If you are going 10 kph, get pushed off 45 degrees, and it takes 2 seconds to correct then that is 3.9 meters

It is a lot easier to get pushed around 1 meter than I thought it would be.

The equation is

speed km/hr * sin(angle) * correction time sec * 1000/k * hr/3600sec

A nimble bike with wider tire is clearly going to be more maneuverable.

The first reaction may be to turn into the wind and that just delays the actual correction. You actually need to initially turn away from the wind so you can lean into the wind. You see riders that immediately turn into the wind and just get pushed over.

Also city versus county. In the country you can watch trees and grass to see it coming. In the city you can get wind tunnel effect and hit with a blast on just mildly windy day - in that case you can look at pedestrians.

• But delaying the correction may be exactly what's needed if it buys you a little time. It would take someone following with a camera to be sure but it felt like I was throwing my weight into the wind. +1 for calcs etc. although 1s reaction time seems pessimistic. Feb 8 '16 at 17:22
• @ChrisH I fail to understand how delaying a correction buys time. Plug in what you think. React is not reaction time - I am going to know I got with with wind in 0.1 seconds - how long does it take me to get the bike pointed into the wind is what matters. Feb 8 '16 at 17:34
• I think you need to know how big is the wind force and the mass of the bike & rider. The bike speed only affects how the bike resists the wind, i.e. whether it's going 50 kph or 100 kph, 1 Newton force will push it the same distance side ways. Feb 9 '16 at 2:13
• @imel96 Really, you think you could hold a line the same 5 kph versus 50 kph with the same gust of wind? Feel free to post an answer. Feb 9 '16 at 2:35
• @Frisbee my comment was regarding the physics, not so much about the question. Like, certainly bike & rider's mass is a big factor here but not included in the math. Regarding speed, a ball would be good example to show how speed doesn't matter much because no matter how fast, it will still roll side way in Y meter for X Newton of force. I don't think there's enough details to answer this. Feb 9 '16 at 6:03