How fast can a road bike go?

Ash

Warming-Up
Apr 23, 2006
686
1
0
shakujiidai, nerima ku, tokyo
#1
Hmmm...I found the following on Velonews this morning from Leonard Zinn's column. I have his 'Zinn and the Art of Road Bike Maintenance', which as far as I am concerned is the best maintenance book ever written, so I usually look at his columns.

I am not a mathematician, but I think I could have figured out to pedal fast over the top of the hill before descending without doing a Phd in the subject. Thought you might like this Thomas, you are a technical geezer!

Here it is:

When cycling, you must consider the forces of rolling resistance, air resistance and gravity, which when added together, give the power the rider puts out to maintain his or her speed, "s." From DiPrampero et al., 1979 (sorry, I only found it in Portuguese), the equation looks like this:

P = krMs + kaAsv2 + giMs
where P is power, kr is the rolling resistance coefficient, M is the combined mass of cyclist and bicycle, s is the bicycle speed on the road, ka is the air resistance coefficient, A is the combined frontal area of cyclist and bicycle, v is the bicycle speed through the air (i.e. road speed plus head wind speed), g is the gravitational acceleration constant, and i is the road incline (grade; however, this is only an approximation, as the sine of the road angle to the horizontal should technically be used).
When you coast downhill, you are adding no power, so you reach terminal velocity when the gravitational force pulling you down the hill equals the drag forces resisting your motion. So, terminal velocity is when:

krMs + kaAsv2 = giMs
When you are moving fast downhill, the aerodynamic drag forces are huge compared to the rolling resistance forces, so you can ignore them. And you clearly want to know the answer in general, meaning on a calm day, rather than how fast you go into a headwind, so s = v, making the equation become:
kaAs3 = giMs
or
sterminal = (giM/kaA)1/2


Obviously, the heavier the rider and the steeper the hill, the bigger the giM term becomes, and the bigger sterminal becomes. Similarly, the lower the frontal area, A, of the bike and rider, the higher the terminal velocity becomes. This, of course, is the reason for tucking on your bike when you descend.

An interesting thing that you can see from this terminal-velocity equation is that there is a terminal velocity beyond which you will not go unless you pedal or the hill becomes steeper. This means that you will get down the hill the fastest the sooner you get to terminal velocity. So it always pays to sprint over the top of the hill and the beginning of the descent before you go into your tuck. You will arrive at the bottom sooner than if you had simply gradually coasted up to sterminal.
Lennard
 

WhiteGiant

Maximum Pace
Nov 4, 2006
1,192
240
93
Kita-Ueno
#2
Top speed

Nice post Ash!
One thing I can say about rolling resistance is; WHEELS!
I recently upgraded to Campagnolo "Scirocco"s, and I get about an extra 2km/h on flat ground on a windless day - now I'm wondering what the more expensive wheels would be like.
Anyway, my top speed on a descent: 71km/h (44mph), coming down Iroha-zaka from Chuzenji-ko (It's all switchback tight bends until you get to the last bend, and then it goes down wickedly - from about a 10% descent to 15% DOWNHILL; almost straight.)
And I was pedalling like a bitch! When I finally tucked into a crouch on the drops without pedalling, I held 60km/h (37.5mph) for almost a whole 5km stretch.
What an awesome feeling!
Does anyone out there have a high top-speed descent to share?
 

thomas

The Crank Engine
Nov 1, 2005
1,811
218
93
多摩区
#3
Ash, that was interesting indeed. Though I've never been good at math.

Travis, 71km/h must be awfully exciting! My speed record on flat road is 60,5km/h, returning from Boso via Route 16 with strong tailwind, and it's a modest 61,3km/h downhill on Route 246. I have told you already before, but two excellent "Tokyo race grounds" are Yasukuni Dori down from Yasukuni Jinja into Jimbochou and National Road 1 descending westwards into Gotanda. If you wait for the green light at the peak, you can easily do up to 60...

I also intend to upgrade my wheels. Any recommendations?
 

Newton

Senior Cyclist
Feb 15, 2006
127
0
36
Tokyo
www.fotolog.com
#4
Wow, 71km/h !!
My max speed was 68km/h but it very difficult to reach my max speed in tokyo area because I could'nt find a nice place to ride like crazy yet. :)

I also tried Yasukuni Dori with Thomas once but you have to be lucky to get the green light.
 

Ash

Warming-Up
Apr 23, 2006
686
1
0
shakujiidai, nerima ku, tokyo
#5
My top was 63kph coming down from the Kusatsu hill race this year. It was a real buzz, I had never really descended on a road bike before like that. The Pinorello really handles beautifully on a decent though. Chuzenji sounds like something I would like to try though!

My top on a flat road was 53 on Shinmejiro dori coming into takadanobaba...there is a short decent when you cross yamatedori and then if you get the lights and the right traffic conditions there is a 2km stretch on which you can really fly...:eek:

Ash
 

luc59457

Warming-Up
Feb 26, 2009
2
0
0
Canada
#6
No More than 60mph As It is the Point of overboard heating and friction

No more than 60mph (around 96km/h) as the bearings and chassis parts can

no longer handle the increased heat and friction. The bike will not last long. I

make electric bicycles of different kinds. The fastest one I've built can go 69

km/h on flat, and 71+km/h downhill. At 71km/h it starts to get to the point

where steady handling becomes a factor unless the roads have no bumps, and

over factors such as wind and curves, etc make it more risky handling on thin

tires. Bicycle tires no matter what are not meant to handle much more than 70

km/h. Here's a video of a 71km/h downhill ride. http://www.youtube.com/watch?v=pVqIh6rYbms&feature=channel_page

Here is a video showing the speedometer of a 69km/h ride on flats.
http://www.youtube.com/watch?v=Ls1K8LSvf_E&feature=channel_page

And here's simply an awesome 120Vac e-bike I've created:
http://www.youtube.com/watch?v=HnIS4c3R0Lg&feature=channel_page
 

trad

Maximum Pace
Dec 4, 2006
393
30
48
Tokyo
#7
Ton of variables, but I think aero drag is the big x factor.... There's a hill back in California that I used to get up to 53 mph (85 kph) fairly regularly in a tight tuck (hands/elbows/chin at stem). The best I got pedaling while in the drops was about 45 mph (74 kph) on the same hill. In Japan, i think my best is around 47 or 48 - those dreaded anti drifting rumble strips and anti hydroplaning groove in corners take a bit of fun away.
 

trad

Maximum Pace
Dec 4, 2006
393
30
48
Tokyo
#9
Second vote for aero position

I got curious why my top speed pedaling/spinning is slower than a tuck and poked around the internet. Found that your speed on a 125 inch gear (53x11 set up) @ 100 rpms gives you 37.5 mph or 60 kph. Same gearing @ 120 rpms is good for 45 mph or 72 kph - roughly the highest speed I got while pedaling/spinning....

http://en.wikipedia.org/wiki/Bicycle_gearing
 

echothree

Speeding Up
Sep 8, 2008
170
1
38
Mitaka
#11
During a race in Perth I got up to 92kph... it was an open road and cars were coming the other way and pulling out of driveways... Plus some clowns were losing water bottles... Crazy.

The wife and I just got back from a ski trip to Hokkaido and we took a GPS, and she took out the record and clocked 94kph coming down the piste. I was on a snowboard and there was no way I was coming close to beating that. :eek:
 
Jan 14, 2007
2,514
213
83
Noda
japanichiban.com
#12
During a race in Perth I got up to 92kph... it was an open road and cars were coming the other way and pulling out of driveways... Plus some clowns were losing water bottles... Crazy.

The wife and I just got back from a ski trip to Hokkaido and we took a GPS, and she took out the record and clocked 94kph coming down the piste. I was on a snowboard and there was no way I was coming close to beating that. :eek:
What had she been drinking? :D
 

Richard

Warming-Up
Feb 28, 2009
11
0
0
Shibuya
#16
96kmh fast!!!

Quite a few years ago I managed to reach 96kmh while going down a 3 lane highway in NZ on my old mountain bike which was fitted with road tyres. The speed limit on this particular stretch of road is 100km so I was going the same speed as the cars which I imagine would have surprised one or two drivers. Part way down the road there's a slight curve and going around it you often get some mean cross winds coming at you which makes it even more fun, although on this particular day there was little wind (thankfully).

I wouldn't dream of even trying to go that fast now (I'm happy if I make it over 60kmh nowadays), especially on my current bike (one of Giant's earlier carbon fiber road bikes) as I felt my mountain bike was more stable at extreme speeds due to its sturdiness and geometry giving it a lower centre of gravity.

There used to be a semi-professional cycle race that also went down that same road, and I heard one year they were cycling so fast (well over 100kmh:eek:) that they passed the police motorbike escort who was leading the peleton!

I've also reached 90kmh+ on a number of other occasions on the flat, but am sure it wasn't my legs peddling that fast but more likely some interference with my wireless computer ...:D
 

WhiteGiant

Maximum Pace
Nov 4, 2006
1,192
240
93
Kita-Ueno
#19
How's your hand...?

During a race in Perth I got up to 92kph... it was an open road and cars were coming the other way and pulling out of driveways... Plus some clowns were losing water bottles... Crazy.
The wife and I just got back from a ski trip to Hokkaido and we took a GPS, and she took out the record and clocked 94kph coming down the piste. I was on a snowboard and there was no way I was coming close to beating that. :eek:
...After your crash?
We're all a little disappointed that you can manage to go skiing, but can't make it out for a ride in the hills with your fellow riding mates;)

After the recent weather reports, it doesn't look like the roads in our area would be much different from Hokkaido anyway.

Hope you're getting better!...at skiing!:cool:
T
 

echothree

Speeding Up
Sep 8, 2008
170
1
38
Mitaka
#20
Well, I was on a snowboard, which didn't require the use of my hand. On the occasions I stacked it I managed to keep it out of the way, which was surprising. :)

I was riding around in Tokyo after my crash, but it was on a mama-chari with one hand... so the mountains would have presented quite a challenge.