Who wants to do 50mph?

Ollieda

PeteMadoc wrote:

I drop both them at the same time from the same height. I know that in a vacume they will hit the ground at the same time. How does that change when air is present. They're the same size and shape so isn't air resistance the same for both balls?

Air resistance would have to exert more of a force to slow the havier one down the same amount as the lighter one however it will only exert the same amount of force on both.

If you think about the sudden stopping force of the ground the heavier ball will make a bigger impact. The same stopping force would have been applied to both balls but it took longer to stop the heavier one and there was more displacement of energy upon impact.

Jez mon

PeteMadoc wrote:

Rick Chasey wrote:

Drysuitdiver wrote:

galileo proved things many years ago a 50kg weight and a 100kg weight released at the same time from the same height will hit the ground at the same time- they fall at the same rate.

the 100kg will exert a greater force on the ground when it lands than the 50Kg weight but regardless of weight of an object they will still fall at the same rate 9.8m/s sq

Yeah, but that's not including air-resistnace.

Given that air-resistance is a big deal on the bike, you need to consider that.

On Earth in normal air, a heavier ball for the same shape will fall quicker...

Sure on the moon everything falls at the same speed, but we're not on the moon!

Right I'm getting confused here.

Let's make this as simple as possible. I have two balls exactly the same shape and size but one weighs 1Kg and the other weighs 2Kg

I drop both them at the same time from the same height. I know that in a vacume they will hit the ground at the same time. How does that change when air is present. They're the same size and shape so isn't air resistance the same for both balls?

Air resistance will be the same for both balls yes. So if the are falling at the same speed, the retarding force will be the same


but the 1 kg ball has less weight accelerating it down. Approx 10 newtons

As the balls accelerate, this air resistance will increase, until it equals 10 newtons, at which point the 1kg ball will have reached equilibrium. However, the 2 kg ball would still have a net resultant force at this speed, as it has a force of approx 20 newtons accelerating it down.


So the heavy ball wins

petemadoc

So it's confirmed! The heavier you are the faster you go downhill because it takes longer to reach the equilibrium with air resistance. Got it!

So all this showing off of speeds 55mph + must be from the fatties

rick_chasey

PeteMadoc wrote:

So all this showing off of speeds 55mph + must be from the fatties

Quite.

bexley5200

ive done 60 mph down edge hill many years ago

balthazar

PeteMadoc wrote:

So it's confirmed! The heavier you are the faster you go downhill because it takes longer to reach the equilibrium with air resistance. Got it!

So all this showing off of speeds 55mph + must be from the fatties

Moreover, it's the chance for "normal people" like us to ride faster than the professional racers we admire. Above 50mph, nobody is pedalling usefully, so the "engine" is only mass, and they don't have any.

I go 50-60mph nearly every ride, simply because I have a very steep straight hill nearby (a newish bypass) which I usually finish with. Top speed depends on the wind direction, which frustratingly prevails from ahead.

thecrofter

Hit 45-ish down the Bealach last year. I'll try for 50 in two weeks time when it's on again. But I'm not convinced there's much more speed available from my legs/the hill. I was giving it the berries last year.

Don't think about the damage you could cause it'll just slow you down. My legs are pretty f****d from motorbike crashes at less than 50mph while wearing full leathers etc. Doesn't bear thinking about in just Lycra.

meanredspider

balthazar wrote:

PeteMadoc wrote:

So it's confirmed! The heavier you are the faster you go downhill because it takes longer to reach the equilibrium with air resistance. Got it!

So all this showing off of speeds 55mph + must be from the fatties

Moreover, it's the chance for "normal people" like us to ride faster than the professional racers we admire. Above 50mph, nobody is pedalling usefully, so the "engine" is only mass, and they don't have any.

I go 50-60mph nearly every ride, simply because I have a very steep straight hill nearby (a newish bypass) which I usually finish with. Top speed depends on the wind direction, which frustratingly prevails from ahead.

I'm heavy-ish (94kg) but I'm also quite broad and, as wind resistance squares with speed, being skinny helps top speed. Wind direction makes the world of difference to that last couple of MPH too for the same reason.

trooperk

Be interesting to know how many of you out there have accurate speedo's, so easy to put a longer wheel settings, not saying that you would.

Pross

55mph plus on the descent of Snaefell with closed roads on the Mannin Veg RR in 1990 (I'd been dropped on the climb and had the descent to myself), not sure of the exact top speed as 55 was the most the speedo went to but hit that within the first 500m so may have gone faster. Gear is pretty much irrelevant though, I was on a 52 x 13 but probably only pedalled for the first 100m or so, this is why I always get amused by the number of people who say they won't ride a compact in case they spin out!

stephenswindley

Jez mon wrote:

PeteMadoc wrote:

Rick Chasey wrote:

Drysuitdiver wrote:

galileo proved things many years ago a 50kg weight and a 100kg weight released at the same time from the same height will hit the ground at the same time- they fall at the same rate.

the 100kg will exert a greater force on the ground when it lands than the 50Kg weight but regardless of weight of an object they will still fall at the same rate 9.8m/s sq

Yeah, but that's not including air-resistnace.

Given that air-resistance is a big deal on the bike, you need to consider that.

On Earth in normal air, a heavier ball for the same shape will fall quicker...

Sure on the moon everything falls at the same speed, but we're not on the moon!

Right I'm getting confused here.

Let's make this as simple as possible. I have two balls exactly the same shape and size but one weighs 1Kg and the other weighs 2Kg

I drop both them at the same time from the same height. I know that in a vacume they will hit the ground at the same time. How does that change when air is present. They're the same size and shape so isn't air resistance the same for both balls?

Air resistance will be the same for both balls yes. So if the are falling at the same speed, the retarding force will be the same


but the 1 kg ball has less weight accelerating it down. Approx 10 newtons

As the balls accelerate, this air resistance will increase, until it equals 10 newtons, at which point the 1kg ball will have reached equilibrium. However, the 2 kg ball would still have a net resultant force at this speed, as it has a force of approx 20 newtons accelerating it down.


So the heavy ball wins

Just to add a bit to this, as this makes it sound as if heavier objects accelerate faster. If you have two objects of different masses but the same surface areas (and therefore the same aero drag), then they will both accelerate at the same rate (aprrox 9.8ms sqaured) but the heavier object will continue accelerating at that acceleration for longer and reach a higher terminal speed. So applying this to cycling; two people of the same surface area but different masses will accelerate at the same rate as each other but the less dense rider will stop accelerating while the denser rider continues accelerating at the same rate until he/she reaches a higher terminal velocity due to his/her greater density.

nwallace

Tend to aim for 64kmh on the descent from work, GPS claims 59kmh tonight, never really checked the speedo.
Best I've ever had on a speedo was 89kmh, descending Glen Ogle.

Rapid acceleration tends to freak me out especially when I can't see too far ahead or need to turn. So I can easily find myself hanging onto the brakes at 30 on a short sharp hill, yet will happily tank past 60ks on something longer.

mrushton

PeteMadoc wrote:

So it's confirmed! The heavier you are the faster you go downhill because it takes longer to reach the equilibrium with air resistance. Got it!

So all this showing off of speeds 55mph + must be from the fatties

In theory, but the likes of Paolo Bettini and Fabian Cancellara will descend a lot faster than us and they prob. weigh less. Also, as mentioned earlier, a tandem will descend spectacularly quickly and a touring one fully loaded with panniers even more so.

FocusZing

Everybody in this thread wrote:

Blar blar, blar de blar...blar blar blar mph!

+1 mph

Stuy-b

freehub wrote:

Stuy-b wrote:

micken wrote:

Stuy-b wrote:

52.96mph is my fastest so far this year, there was a big cross wind so lost my nerve at 52.96, and was on the training bike. i think i can hit 58ish on a good day on that road

Where's that road?

dropping down to the goyt vally from the top of long hill.

I've heard someone did well over 60 on that road.


The fastest I've done is 52.8.

60+ on that road wouldn't surprise me. im waiting for a nice windless day on my race bike to really go for it.

rake

PeteMadoc wrote:

Rick Chasey wrote:

Drysuitdiver wrote:

galileo proved things many years ago a 50kg weight and a 100kg weight released at the same time from the same height will hit the ground at the same time- they fall at the same rate.

the 100kg will exert a greater force on the ground when it lands than the 50Kg weight but regardless of weight of an object they will still fall at the same rate 9.8m/s sq

Yeah, but that's not including air-resistnace.

Given that air-resistance is a big deal on the bike, you need to consider that.

On Earth in normal air, a heavier ball for the same shape will fall quicker...

Sure on the moon everything falls at the same speed, but we're not on the moon!

Right I'm getting confused here.

Let's make this as simple as possible. I have two balls exactly the same shape and size but one weighs 1Kg and the other weighs 2Kg

I drop both them at the same time from the same height. I know that in a vacume they will hit the ground at the same time. How does that change when air is present. They're the same size and shape so isn't air resistance the same for both balls?

the trouble with that theory is that you're not dropping vertically off a cliff on your bike with the acceleration of gravity. The angle of the slope comes into play, so your forward vector is resolved from the downward weight and the angle of slope using simple physics.

Jez mon

rake wrote:

PeteMadoc wrote:

Rick Chasey wrote:

Drysuitdiver wrote:

galileo proved things many years ago a 50kg weight and a 100kg weight released at the same time from the same height will hit the ground at the same time- they fall at the same rate.

the 100kg will exert a greater force on the ground when it lands than the 50Kg weight but regardless of weight of an object they will still fall at the same rate 9.8m/s sq

Yeah, but that's not including air-resistnace.

Given that air-resistance is a big deal on the bike, you need to consider that.

On Earth in normal air, a heavier ball for the same shape will fall quicker...

Sure on the moon everything falls at the same speed, but we're not on the moon!

Right I'm getting confused here.

Let's make this as simple as possible. I have two balls exactly the same shape and size but one weighs 1Kg and the other weighs 2Kg

I drop both them at the same time from the same height. I know that in a vacume they will hit the ground at the same time. How does that change when air is present. They're the same size and shape so isn't air resistance the same for both balls?

the trouble with that theory is that you're not dropping vertically off a cliff on your bike with the acceleration of gravity. The angle of the slope comes into play, so your forward vector is resolved from the downward weight and the angle of slope using simple physics.

It's mainly air resistance

If the two balls were on a slope, in a vacuum then they both would fall at the same rate..

I'm fairly sure anyway, I haven't got any paper to check :oops:

rake

i stand corrected. i fell into the trap of weight not the same as mass.

swagman

Ah youre all lightweights,
50mph on fullloaded touring bike on a 48x11
and 62mph on 52x14 steel racer 20 years ago which goes to prove older bikes are faster.

Homer J

65mph on slight up hill.

My name is Bhima, I thank you and good night.

Pokerface

My Garmin clocked me doing 90MPH. However, it turns out I just forgot to turn it off when I put the bike in the car after a race and drove home.

borisvanhalen

47 going into wilton (wiltshire)... regularly hit 45+ going down snakey pass outside salisbury, scares the pants off the car drivers when you are catching them up hand over fist, just a shame you have to brake half way down to avoid going straight on at the junction at the bottom

porker33

I have had a few 47 and one 51mph this year, obviously both down hilll!

Last year pedalling down Westerham hill, I managed 52mph, I kept pedalling to get past 50mph.......at that point I noticed the left turn I wanted to take,,,an important lesson on how ineffective road cycle brakes are, I over shot the left turn by maybe 30 feet....which was ok on this occasion, but would have been a disaster of someone had pulled out...maybe I have done the 50+mph thing on the roads now?

lifecyclist2010

I did some AMAZING speeds when i was in Italy few years back but wouldnt do that speed in the UK...road conditions and other motorists just arent in your favour going that quick.

BarryBonds

Rick Chasey wrote:

Fasted I did was in the Pyrenees - 70kph.

wimp

snipz

Hit 57mph down Titsey Hill on a 53-11 around 1999. Surface was a lot better then and I was more foolhardy.
61mph in the Pyrenees once, the only time I broke the 60 mark!

andi1363

max888

andi1363 wrote:

The last time I saw a video of someone doing that their bike snapped in half. Not good.

Here we go,

http://www.youtube.com/watch?v=JLRDRzMWIsg&oref=http%3A%2F%2Fwww.youtube.com%2Fresults%3Fsearch_query%3Dmtb%2Bworld%2Bspeed%2Brecord%26aq%3D0%26oq%3DMTB%2Bworld%2Bspee&has_verified=1&oref=http%3A%2F%2Fwww.youtube.com%2Fverify_age%3Fnext_url%3Dhttp%253A%2F%2Fwww.youtube.com%2Fwatch%253Fv%253DJLRDRzMWIsg

Max

Crispybug

I hit 46mph on a training run this morning going down Essex Way (which heads down towards Canvey Island which is not somewhere you'd normally want to get to in a hurry!) this morning, road was very quiet and I thought I 'd put it into top gear and see what happened. Have to say that it scared the living shoite out of me and I sat up and applied the brakes a bit long before the bottom.

mgittings

i was averaging about 50mph at herne hill behind the big motors for about 10 laps all be it on 59X14

but when i go over 40 going downhill i think holy sh*t what if i hit a pot hole or a stone then im on my brakes straight away lol

only worth going for it if you know the decent and have been down it that day to check the road