WhyFi

Like all things, it depends. At those speeds and with the right kind of vehicle, there can be a pretty generous pocket, enough so that you'd still have time to avoid hazards like potholes and road debris.

billridesbikes

Stick your cycle computer in your car and drive down.

There is a Strava segment near me that is 1.5miles long along a road with a posted speed limit of 45mph. The ‘winning’ Strava time? 55 seconds.

Zaskar

^THIS^

So many Strava KOMs are team (group) efforts, e.g. lots of guys giving that one guy a readout - whether they intended to or not. One day Strava's algorithm will see that - based on multiple similar uploads - and categorize it that way.

I have a few KOMs that "just happened" - part of a fast ride and I guess I was moving forward relative to the group... KOM.

genejockey 

I know that road well enough to know there aren't any potholes, which is a plus. OTOH, drivers can be...capricious.

genejockey 

One thing I never have to worry about is getting a Strava KOM. There are SO MANY cyclists here, and we all ride the same roads, everybody from me to national champions, so on most segments I'm happy if I'm in the top couple thousand. For example, there's a 5 mile segment I do every Sunday where my PR is 5638th out of 31,809.

Rides4Beer

At 40+mph, aero is playing a big part, still pedaling, without being able to add power, you'd need more gear as mentioned, will actually hinder your effort. Aero and weight will def matter, I've had rides where I could sit full upright and still pass lighter riders on descents.

There was a really short -15% hill on my old regular route, I used to sprint on the flat leading to the descent and then tuck down (just a regular tuck, no super tuck for me lol), I could easily hit 50mph on that short hill, but I'm 185lbs and that was with a somewhat aero setup (tight kit, aero road helmet, deep wheels).

jonathanf2

Come to think about it, on my earlier attempt when I wasn't even trying the car in front of me actually waved for me to pass him. I was close enough that I was probably benefiting from a free draft down the hill which resulted in my faster time.

SoSmellyAir

Don't worry about the water, and please don't be tempted to drink less on the ascent. Water weighs the same regardless of whether it is in your bottle(s) or in your body. Instead, wear a super tight rain jacket to keep more sweat from evaporating.

jonathanf2

This road is plenty safe with very little to no traffic, it's fairly wide with lots of visibility, no blind corners and the pavement is smooth. Plus the descent ends on the flats with plenty of time to brake. Plus it's not like I'm racing anyone and I never said I wanted the KOM, I just wanted to become quicker on this particular segment.

rm -rf

On Strava, when viewing the segment details inside your ride, you can click "compare" to match against your best efforts, or select the KOM, etc from the list underneath. The chart shows how far you are ahead or behind all through the segment--hit the play button or drag the position. (This might be a strava premium feature?)

There must be diminishing returns up near 40 mph. For example, using this bike speed calculator:
I took the defaults, except for Position=drops, grade=-10%.
Rider A does 150 watts for 47.25 mph, Rider B does 600 watts for 52.24 mph. 4 times the power to go +5 mph, 10% faster. (Or coasting at zero watts gets 45.20 mph.)

I would try full speed through the start, and spinning any flatter sections, then tucking.

Equipment
A while back, HED announced a specialty set of downhill wheels. Woah!

rm -rf

I no longer try to max out fast downhills, it's not worth it to me. Shallower ones, sure -- 32 mph instead of 27? Yeah! I can reach the highest heart rate of a ride on these sometimes. Go, go, go!

Your KOM downhill sounds safer than many others, with good sight lines, no side roads or driveways, smooth pavement.
But I've pinch flatted on a nice newly paved downhill, on that one big piece of gravel that was kicked out from a driveway. I didn't see it. At slow speeds, I would have bounced over it instead of flatting.
No deer or dogs to run out suddenly? Or even squirrels.
I do let myself go faster on roads like the Blue Ridge Parkway with swooping curves, good sight lines, no drivers pulling out, and few animals darting out.

Stopping distances go way up.
One thing that got me to slow down on steep downhills: Stopping distances are extremely long, and it takes a while to burn off even the first portion of speed.

This math puzzle applies to bikes as well as cars. There's a limit to how much braking force you can put into a bike before the rear tire starts lifting off the ground. Just like a car has a maximum braking force on it's tires.
https://www.roadandtrack.com/new-car...mph-heres-why/

The question in the embedded youtube video is: (No, I sure didn't guess the answer.)
A car is going 70 mph as another identical car passes at 100 mph.
There's a sudden obstruction ahead, so both start maximum braking right then.

The 70 mph car just barely stops before the barrier.
How fast is the 100 mph car going when it hits the barrier?

~~~~~~~~~~

Stopping time is related to kinetic energy from the speed & mass, which increases by the square of the speed.
This would apply to a 30 mph cyclist vs a 40 mph (with 78% more kinetic energy) or 50 mph cyclist (178% more than 30 mph) too. With wind resistance to help slow down, the faster speeds wouldn't be "quite" this much worse.
After the video, I started noticing how much easier it is to slow from 25-30 mph compared to 35-40 mph.

Branko D

The way I try to maximize speed downhill - and I run a compact 50-34, too - for me is to go briefly well in the red on the flatter bits - spin out if need be - then tuck in as best I can to recover. Over some speed it's just not worth pedalling because the aero losses eat it up, unless you're really laying on the power, so go in the red, tuck in, recover, and go again seems to be overall faster.

It's fun when the visibility is good and you get a workout downhill.

SapInMyBlood

1lbs of far is 3500 calories
Ergo 10lbs = 35,000 calories
I've burnt up 15k + in 2 days riding
I think with a high level of fitness it would be possible. A lot of ultra endurance athletes pack on a few extra pounds before racing because they know they cant eat as fast as they're burning

WhyFi

I'm aware of the math and I'm also aware that burning calories != burning fat. Exceptionally few people can operate at a 5k+ cal deficit 7 days in a row and those that can/do are almost certainly eating in to more than just their fat supply. I'll stand by my "damn near impossible," statement.

burnthesheep

I see this topic and went to reply, then saw this.............and typical BF going off the rails on a topic. What in the world. From super unsafe Strava segment chasing to weird nutrition fat burn talk in one page.

WhyFi

Let sleeping dog specious claims lie for the greater good of the very important and useful thread topic? What fun would that be?

GhostRider62

It takes a lot of miles. Not impossible but pretty damned hard. I lost 20 pounds in 3 weeks and 5 pounds of fat in 2 days. The three weeks was a tour in remote area doing 100+ loaded touring miles per day in very hill, wet, cold terrain. The 2 days was a 1200k. BF measured with skinfold calipers. Normally, 2 pounds is easy but 3 pounds of fat loss per week is about as much as I can do week over week. I have ridden many 1000+ mile weeks and never lost 10 pounds of fat in a week, but then again I was eating at will.

tomato coupe

But, there's guy on TV that says I can do it, without exercising.

genejockey 

AND earn $1000/week!

rumrunn6

beware the devil. beware the intoxication that an exciting descent offers. on several attempts, to beat personal records, on public roads, I've had safety related regrets afterwards

I'm reminded of the scene in "The Right Stuff" where Chuck Yaeger attempts too much altitude, goes into an unrecoverable flat spin & has to eject

- on one of my favorite hills I pedal like crazy, then tuck. on that one I have to feather my brakes due to a curve & yes, traffic!
- on another, this summer, I just kept cranking. got passed by a car, while I was doing 37 in a 30 zone. at least the guy waited until the other side of the yellow line had room for him, but he was annoyed that he had to kick it up to 40+? to get passed me

jonathanf2

Fully hydrated I'm just under 150 lbs. On summer bike rides I can sweat out down to 140 lbs. in about 4 hours. I can also shred weight via carb cutting and send my body into ketosis which I've done before. At my height I have quite a bit of weight flexibility to drop down maybe another 20-25 pounds and still be considered healthy. I bike ride and power lift on my non-riding days. The only reason I haven't opted to cut more weight is due to my weight training, but I've been thinking of dedicating a few weeks to focus on becoming faster and lighter on my bike. People make it sound like it's impossible, but many athletes who compete in weight classes cut weight or shred prior to a competition.

tomato coupe

To be picky, he ejected because his plane was in an unrecoverable flat spin. He did not pass out.

genejockey 

Well, THERE'S your PROBLEM!!!

woodcraft

High wind warning for today- pack on those pounds and go for it!

GhostRider62

I would sprint into the hill and down part of it until around 60 km/h, then, I would tuck tight.