Most bikes can easily go 25 mph or more on flat roads. But how fast can a bike go downhill? Let’s look at this question in detail so you don’t have to try it out yourself.
Because as it turns out, it can be quite dangerous to try this at home.
How fast can a bike go downhill?
Tour de France racers can go downhill at speeds of 110 mph (177 km/h) or more. But this is under perfect racing conditions. The average person can expect to reach speeds of around 35 to 45 mph (56 km/h to 72 km/h) while staying relatively safe.
3 Conditions that affect how fast a bike can go downhill
These 3 conditions determine how fast a bike can go downhill: The rider, the bike, and the road conditions.
Let’s look at them one at a time and how they affect downhill speeds.
The Rider
A fit rider can pedal harder to reach higher speeds than a couch potato. That’s pretty obvious.
And being in shape certainly helps in reaching higher speeds.
But one of the single most significant factors is the willingness to take risks.
Speed is subjective
Speed is a very subjective experience.
Some riders may consider 40 mph fast while others don’t break a sweat until they hit 80 mph.
The willingness of a rider to push the bike to its limit is one of the biggest factors in reaching high downhill speeds.
Most bikes can be safely ridden downhill up to speeds of about 40 mph.
At speeds higher than that, your bike choice becomes more important (see below).
At these speeds, it’s not only about the type of bike, but also the individual components themselves.
But someone who is willing to push a little further than the bike allows is going to reach higher speeds.
Even if can be very dangerous.
How to limit drag (wind resistance)
Did you know that a smaller (and skinnier) rider has a speed advantage?
It’s true.
On one side, a smaller rider is lighter. That has two benefits:
- Less rolling resistance since less tire surface will touch the ground.
- Less energy is needed to accelerate – resulting in higher speeds.
But on the other hand, a smaller rider also creates less drag (wind resistance).
The smaller the frontal surface area of the rider, the smaller the drag.
That means wearing tighter clothes is beneficial – wide coats and pants essentially act like parachutes, pulling you backward.
The riding position
The proper riding position helps reduce the drag even further.
By lowering your handlebars and raising your saddle, your back goes up and your head goes down.
That reduces your body’s frontal surface to a little more than your head, shoulders, and legs.
The gain in speeds is significant.
The riding position is one of the biggest reasons why a road bike can reach speeds of 100mph or more, while a hybrid bike simply can’t.
Check out the gif below. It shows how the riders’ drag has a bigger impact on downhill speed than any fancy-schmancy gear ratios or even pedaling itself.
The Bike
The bike choice is essential when trying to reach maximum downhill speeds.
And it’s more than just deciding between a road bike and a mountain bike.
Let’s look at the individual parts a bike needs to go fast (and safely).
Breaks (Disk Brakes!)
You could argue that the question of this article should be: How fast can a bike go downhill – and still safely stop?
Because it’s not just about reaching high speeds, it’s also about living to brag about it after.
In this scenario, it is simply not safe to use rim brakes downhill. At all. Period.
A rim brake needs significantly longer to come to a full stop than a comparable bike with disk brakes.
Even if it looks like an otherwise fast bike – Skip it if it doesn’t have disk brakes.
Tires
Apart from the brakes, tires are the most critical point of failure.
Tires have to be slim to reduce rolling resistance on paved roads.
And they have to be light to reduce the overall weight of the bike.
But at the same time, they also have to remain sturdy at high downhill speeds.
Popping a tire while trying to break a personal speed record is a very real danger.
So check your tires before trying to go very fast. And do not try to go fast on old or brittle tires.
A Sturdy, lightweight frame
A sturdy, lightweight frame helps in reaching top-speeds downhill.
The materials of choice are carbon fiber, aluminum, and steel. In that order.
Gear Ratio
The more optimized your downhill gear ratios, the faster you will be.
Because it’s not just gravity pulling you down the hill, it’s also your legs pushing you downward at the same time.
A common gear ratio on dedicated downhill bikes is around 3.3:1, like on a 36t/11t.
That is a chainring with 36 teeth in the front and a cassette with 11 teeth in the back.
A setup of a giant chainring combined with a small rear cog gives you immense downhill pedaling power.
Caution! Be wary of speed wobbles
Speed wobble (or shimmy) can happen on any bicycle at speeds over 25 mph.
Speed wobble happens when the handlebar starts jerking faster than you can correct it.
It often starts slowly and escalates to a violent jerking motion that is too fast to react to.
This is a hazardous situation at a downhill descent.
If you feel that your handlebar starts a life of its own, RELAX, push your legs into your bike’s frame, lean forward, and DON’T BREAK.
The worst thing you can do in this scenario is to panic and hit the brakes hard.
Instead, you want to gain control of your bike with your legs by clamping it between your legs. Make sure that this crazy horse can’t throw you off.
Then, lean forward to reduce the impact of speed wobble. This will make a crash much less likely.
Last but not least, resist the urge to break until you have fully regained control of your bike.
Hitting the front brake can be a deadly mistake.
If you follow this procedure, a crash becomes much less likely.
To see a speed wobble in action, check out this video. Thankfully, no one got hurt.
Road bikes vs Downhill bikes vs Gravel bikes vs Hybrids
A road bike (or gravel bike) is always going to be faster than a hybrid bike. On the flats and downhill.
But depending on the road surface, a dedicated downhill bike (a form of a mountain bike) may be even faster.
Even the best gravel bike won’t be as fast down a road with lots of potholes or a trail with roots sticking out and rocks in the way.
The Road Conditions
The road conditions break down into six factors:
- Dry roads, no winds.
- Good visibility: Clear weather, no glares, no hidden corners along the road.
- A long, straight descent or gentle curves. The longer, and straighter the hill, the safer it is to go fast downhill. In fact, the length of the hill makes as much of an impact as the incline itself.
- No traffic: If you are crossing other roads, and you can’t see if any vehicles are approaching, you really shouldn’t go down very fast. that includes train tracks and crosswalks as well.
- Surface material: Paved roads make every bike faster downhill. They are ideal to break speed records. But not all pavements have the same quality. Look out for potholes and cracks. Also, make sure that there are no rocks or glass on this stretch of the road.
- Speed limits: Even the best road will have a speed limit – and they apply to bikes as much as to cars. Maybe you think you could go down a certain road at 60 mph. But the speed limit is 30 mph. Then that means YOU can also only go 30 mph. These speed limits exist for a reason that is not always apparent. It can be a sharp twist in the road you can’t yet see, or a logging road crossing your way that leaves a lot of debris on the road over a 20 ft stretch. Whatever the reason, respect the speed limit.
So how fast can a bike go downhill now?
There is a physical limit to how fast a bicycle can go. But we don’t know what the theoretical top speed is.
The average rider, with an average risk profile, on a good hybrid or mountain bike (not a downhill bike), can expect to reach downhill speeds of around 50 mph safely on most hills.
More experienced riders on better bikes can reach speeds of over 100 mph on dedicated race tracks.
Under perfect conditions, the average guy on his average bike probably still can still go as fast as 70 mph at times.
But I would not advise you to try it out.
And if you want to know how a basic 7-speed bike fares on hills, check out the article Is a 7-speed bike enough for hills?
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