50mph+ instabilty

[User16625]

Why is it that when I aproach 50 mph on a very steep downhill I cant pedal anymore? What I mean is when I DO pedal at that speed, my bicycle leans over dramatically to the side of the pedal stroke. Basically my bicycle is extremely unstable at high speed down extreme declines. 18% apparently but more like hardbastards pass in Cumbria, ****in ell!

 

[slowmotion]

Your giant swinging testicles might be making the bike a tad unstable???

 

[Louch]

I'd say stop Peddling, 50 is plenty!

 

[ColinJ]

Because you are trying to pedal, but you do not have a high enough gear to do it smoothly! In a 53/12 gear you would have to pedalling at about 141 rpm which is a pretty high cadence.

If you are on a very steep downhill, you should be able to hit 50 mph very quickly without pedalling at all, unless there is a headwind. I hit 55 mph on one local descent just freewheeling and that is only about 7.5%.

 

[Shut Up Legs]

Often you can gain more downhill speed with a low aero tuck position than by pedaling hard.

 

[summerdays]

You're all mad! My brain forces my hands to pull the brakes at anything over 40 and even some over 30. Interesting replies though as to why

 

[Cuchilo]

Its not the bike becoming unstable , its you . Have a go in a higher gear at slow speed and you will see what happens when you spin out . Once you are peddling as fast as that gear will let you , you start to bounce around on the saddle . Bounce around like that at 50MPH and things could get messy

 

[Garethgas]

You're all mad! My brain forces my hands to pull the brakes at anything over 40 and even some over 30. Interesting replies though as to why

Madness indeed!
At 30mph my jowls start flapping...not a dignified look at all.

 

[sidevalve]

I used to get a speed type wobble at 50 ish but I just power through it and accelerate away to a proper speed [only on the uphills of course].

 

[GrasB]

Because you are trying to pedal, but you do not have a high enough gear to do it smoothly! In a 53/12 gear you would have to pedalling at about 141 rpm which is a pretty high cadence.

^^ this.
Basically you either haven't got enough resistance to balance your pedal forces properly or your spinning faster than you have coordination in your muscles. Either way you wobble about.


Either way there's not much point in peddling on an upright at those speeds as is likely to be adding about 2-3mph to your speed!

 

[PpPete]

I'd say NO point pedalling beyond 40 mph.
Concentrate instead on
a) getting as aero as possible on the straighter sections
b) getting your line through the corners as efficient as possible.

Hoever if you really want to improve your pedalling efficiency at high cadences - get yourself fixed.

 

[PpPete]

However if you really want to improve your pedalling efficiency at high cadences - get yourself fixed.

Sorry that should read get yourself a fixed [wheel].

 

[GrasB]

I'd say NO point pedalling beyond 40 mph.

5% down hill, no peddling = 41.3mph, 5% downhill & peddling at 150w (a nice base/active recovery power for me) = 47.9mph. That's including the aero disadvantage of peddling the bike. I'd say putting power in at 40mph is worth it for me.

 

[KneesUp]

5% down hill, no peddling = 41.3mph, 5% downhill & peddling at 150w (a nice base/active recovery power for me) = 47.9mph. That's including the aero disadvantage of peddling the bike. I'd say putting power in at 40mph is worth it for me.

Imagine how much faster you'd go if you hadn't sold the bike

140 rpm (52/11 gearing 700c wheels @ 48mph) is beyond me I think.

 

[GrasB]

Imagine how much faster you'd go if you hadn't sold the bike

Sold which bike? The one I did the calcs for I rode this morning.

140 rpm (52/11 gearing 700c wheels @ 48mph) is beyond me I think.

52t? That's middle ring territory. I run 33/48/70 with an 11-30 cassette on a 559x28 or 622x20 rear tyre depending on my mood... that's 100km/h or 107km/h at 135rpm in top gear (my maximum sustained speed rpm)... oh sorry you're on one of these inefficient up-wrong contraptions