CYCLINGFORUM.COM - Where Cyclists Talk Tech --- Return To Home

 

    Register FAQ'sSearchProfileLog In / Log Out

 

****

cyclingforum.com ****

HOMECLUBS | SPONSORS | FEATURESPHOTO GALLERYTTF DONORS | SHOP FOR GEAR

Return to CyclingForum Home Page CYCLING TECH TALK FORUM
          View posts since last visit

Then there's this
 

Author Thread Post new topic Reply to topic
PLee
Joined: 08 Dec 2003
Posts: 3487
Location: Brooklyn, NY

10/4/17 7:57 AM

Then there's this

http://road.cc/content/news/224277-i-was-frightened-pro-cyclist-hits-135-kilometres-hour-during-race

I can't imagine what this must have felt like. I've only gone north of 50 mph a few times. I'd be burning up my brakes way before I approach 80!!!

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 15739
Location: Portland, OR

10/4/17 9:55 AM

Last few years I actually began scrubbing speed in descents. I use never touch the brakes, just tuck and roll. And at my size and weight I would usually pass lightweight riders spinning out easily. I would need a 58/11 and still be spinning.

Not anymore, mortality seems to have occurred to me. I am pretty sure it was the ski/tib/fib in TN that began my brain not thinking I was 25 anymore..

"FDJ pro Kévin Réza says he was "frightened" during yesterday's Stage 5 of the Tour de Suisse after he hit a speed of 135 kilometres an hour."

He was on a thin line to death, @ 23-4 it would maybe not have occurred to him. ;)

 Reply to topic     Send e-mail

Jesus Saves
Joined: 16 Jun 2005
Posts: 1010
Location: South of Heaven

10/4/17 12:48 PM

Merde!

I suspect the cycle computer miscalculated. Doesn't terminal velocity kick in _much_ sooner? Either that or he rides like a ghost (ie. no wind resistance).

However, I like one of the article's comments, "FDJ race in white shorts, right?".

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 15739
Location: Portland, OR

10/4/17 1:21 PM

FDJ?, His bibs probably looked like AG2R after the 'event' subsided. ;)

 Reply to topic     Send e-mail

KerryIrons
Joined: 12 Jan 2004
Posts: 2843
Location: Midland, MI

10/5/17 9:06 AM

Terminal velocity


quote:
Doesn't terminal velocity kick in _much_ sooner?


Terminal velocity of a reasonably aero object (not feathers) is around 120 mph = 195 km/hr. What it is rolling down a hill I do not know.

 Reply to topic    

Jesus Saves
Joined: 16 Jun 2005
Posts: 1010
Location: South of Heaven

10/5/17 10:31 AM

Take the steepest decent you have ever done, compare that with slightly less steep descents you've done. Now imagine how much faster you would have gone in the most aerodynamic tuck position versus riding the drops or the hood tops.

My point is all of those differences equate to a just a few +/- s in mph. Very marginal increments. To get to a top speed of 80 mph from the often known/common 60 mph top Pro Tour descent speed is a way bit of a stretch. Way too much of a big jump, I think. Wind resistance alone increases by a squared-power to velocity, does it not?

Additionally, where will one find a paved road descent that is so steep and long enough to say even exceed 70 mph, without first having to break for a switchback, turn, or portion of roadway that flattens out, etc? Maybe a ski slope - but good luck finding a paved one. In that respect, I mean a bicycle's terminal velocity.

 Reply to topic    

Rickk
Joined: 01 Jun 2004
Posts: 491
Location: Montreal

10/5/17 12:13 PM

Good point

 Reply to topic    

Nick Payne
Joined: 10 Jan 2004
Posts: 2293
Location: Canberra, Australia

10/5/17 2:11 PM

I was watching Eurosport coverage of the Tour de Suisse a couple of years ago during a TT stage. The motorcycle camera following one of the riders panned down to the mororbike digital speedo, and it was showing 113kph. And a rider in a real aero tuck on a road bike is going to be more aero than a rider on tri bars on a TT bike, so I don't see why the 135kph has to be false. I'm pretty sure other riders reported speeds in excess of 125kph on the same descent of the Simplon Pass.

I'm only a lightweight at 65kg, but I've recorded 104kph down one of our local hills - 2.5km at an average gradient of 12%, only one bend about 2/3 of the way down. And that was recorded on a properly calibrated Cateye bike computer, not a GPS.

 Reply to topic    

Jesus Saves
Joined: 16 Jun 2005
Posts: 1010
Location: South of Heaven

10/5/17 2:17 PM

I'm still skeptical...135kph vs 113 kph .... that's nearly a 20% increase to an already off-the-top speed and 125kph is better than a 10% increase.

 Reply to topic    

daddy-o
Joined: 12 Apr 2004
Posts: 2820
Location: Springfield

10/5/17 6:06 PM

Any idea on the grade where he maxed out?

 Reply to topic     Send e-mail

Nick Payne
Joined: 10 Jan 2004
Posts: 2293
Location: Canberra, Australia

10/6/17 2:11 AM


quote:
I'm still skeptical

I found one Strava segment covering a couple of kilometres of the descent off the Simplon Pass (the last hundred metres of the segment actually goes uphill at about 10%
gradient), with virtually the entire first couple of pages of the leaderboard coming from the day this year that the TdS crossed the pass. Marcus Burghardt tops the leaderboard with an average speed of 105.6kph over the 2.1km.

https://www.strava.com/segments/11680446

 Reply to topic    

KerryIrons
Joined: 12 Jan 2004
Posts: 2843
Location: Midland, MI

10/7/17 5:35 PM

Physics


quote:
Now imagine how much faster you would have gone in the most aerodynamic tuck position versus riding the drops or the hood tops.

My point is all of those differences equate to a just a few +/- s in mph. Very marginal increments. To get to a top speed of 80 mph from the often known/common 60 mph top Pro Tour descent speed is a way bit of a stretch. Way too much of a big jump, I think. Wind resistance alone increases by a squared-power to velocity, does it not?


A tight tuck is a 1/3 reduction in aero drag compared to riding in the drops.

Power to overcome aero drag increases with the cube of speed. It takes 70% more power (in this case supplied by gravitational pull) to go 135 vs. 113, so I am skeptical too. As an example, if the grade was steep enough to hit 113 just riding in the drops, then switching to a tight tuck would accelerate you to 130. But the 113 speed was already in a tight tuck so that advantage is not possible. Call me a doubter.

 Reply to topic    

Brian Nystrom
Joined: 26 Jan 2004
Posts: 3754
Location: Nashua, NH

10/9/17 10:19 AM

Either way...

...it's a hell of a lot faster than I've ever gone on a bike, or want to!

I love descending, but that's just way too fast for comfort.

 Reply to topic    

dan emery
Joined: 11 Jan 2004
Posts: 5765
Location: Maine

10/10/17 6:02 AM

Descending into psychological uncertainty

I was reading a Top Gear report on a drive of the Alfa Stelvio on the Stelvio Pass (the scene of a legendary attack by Coppi in the Giro) and came upon this description of cyclists descending the Pass, which I think presents an interesting perspective....

>>And then there are the bicyclists. Grim-faced pedallers with hamstrings like ship chains and calves like tumorous melons, whose downhill pace borders on the disturbed, well beyond brave and into the no-man’s land of psychological uncertainty.
I followed one man on a downhill section at nearly 40mph. A man whose safety kit consisted of nothing more than a full-body condom made of lightly fluorescing lycra and a slippery-looking crash hat. On tyres the width of my finger.

Anyway, with little mechanical grip, the pedal pushers tend to run wide on the hairpins and, coupled with their general lack of fear glands, it means that you have to give them a respectful amount of room.<<

 Reply to topic    

Brian Nystrom
Joined: 26 Jan 2004
Posts: 3754
Location: Nashua, NH

10/10/17 2:51 PM

"Grim faced"

I guess he can't see the smiles on the inside. ;-)

His rather eloquent prose belies his lack of knowledge of cycling and his apparent belief that we don't enjoy descending.

 Reply to topic    


Return to CyclingForum Home Page CYCLING TECH TALK FORUM
           View New Threads Since My Last Visit VIEW THREADS SINCE MY LAST VISIT
           Start a New Thread

 Display posts from previous:   


  
Last Thread | Next Thread  >  

  
  

 


If you enjoy this site, please consider pledging your support

cyclingforum.com - where cyclists talk tech
Cycling TTF Rides Throughout The World

Cyclingforum is powered by SYNCRONICITY.NET in Denver, Colorado -

Powered by phpBB: Copyright 2006 phpBB Group | Custom phpCF Template by Syncronicity