Bike Forums

Bike Forums (https://www.bikeforums.net/forum.php)
-   Road Cycling (https://www.bikeforums.net/forumdisplay.php?f=41)
-   -   Coasting down hill (https://www.bikeforums.net/showthread.php?t=1252423)

LarrySellerz 05-26-22 09:56 AM

Coasting down hill
 
Is putting out consistent power faster than attacking climbs and coasting down descents? Constant power and pedaling down hill are common tips for doing endurance rides. Personally I don't often pedal when im going ~26+ mph

the sci guy 05-26-22 10:25 AM

my legs love me when i give them a well deserved respite, even if only for the brief duration of a downhill

Mojo31 05-26-22 10:29 AM

If you wear a shirt and let it fly behind you like a cape, it will generate lift. The result will be less tire to road contact and reduced friction, enabling you to go faster downhill without pedaling. YMMV

Bah Humbug 05-26-22 10:48 AM

Take up running; problem solved.

genejockey 05-26-22 11:03 AM


Originally Posted by LarrySellerz (Post 22520688)
Is putting out consistent power faster than attacking climbs and coasting down descents? Constant power and pedaling down hill are common tips for doing endurance rides. Personally I don't often pedal when im going ~26+ mph

I'm not sure how much more speed you can gain by pushing harder on the descents. Mostly, I spin up to 25 or so and then coast, on the straight ones. The technical ones, I'm braking WAY more than I'm pedaling. I think you'd lose more by going less hard up the hills than you'd gain pushing more on the descents. And, geez - you say you weigh 260. How much more speed do you need than what that gives you? You could probably get more speed by rebuilding your hubs with new grease and bearings.

Seattle Forrest 05-26-22 11:24 AM


Originally Posted by Bah Humbug (Post 22520749)
Take up running; problem solved.

He said he wants to be faster!

surak 05-26-22 11:41 AM

Depends on how hilly and long the ride is, and what type of physiology you have / want to train to have.

Mathematically it's faster to go harder uphill and into a headwind, go easier downhill and with a tailwind. However attacking and going over threshold takes longer to recover and eventually you'll blow. Some riders are much better at putting out bursts of power and recovering, others are diesels that can't go into the red much at all.
​​​​​​

Bah Humbug 05-26-22 11:42 AM


Originally Posted by Seattle Forrest (Post 22520791)
He said he wants to be faster!

Oh I'm sorry; did I derail the thread?

Iride01 05-26-22 12:17 PM


Originally Posted by LarrySellerz (Post 22520688)
Is putting out consistent power faster than attacking climbs and coasting down descents? Constant power and pedaling down hill are common tips for doing endurance rides. Personally I don't often pedal when im going ~26+ mph

You'll probably find it pretty difficult to maintain a consistent power both up and down the other side. Not unless you climb with very little power and therefor will be slower overall.

If you are coasting at 26 mph, you might need a bigger chain ring or develop a faster cadence.

Broctoon 05-26-22 12:24 PM

On anything more than a moderately steep descent, your pedaling effort will be wasted. This is because aerodynamic drag (and therefore power required to increase speed) goes up by the square of your speed increase.

Going up a hill, obviously you must pedal to keep moving. It's okay, because at speeds below 10 or 15 mph, air drag is by far the smallest component of the total formula you have to overcome to maintain or increase speed. In other words, your effort is not wasted, because increasing power by 20% will bring an increase in speed of nearly 20%

On flat ground, pedaling is again required, obviously. At speeds of 15 to 20 or 22 mph, air drag starts to take over as the major component. Within this range, any increase in speed will require a progressively greater effort--actually, this is always the case, but in this range it becomes a significant factor.

When you're coasting downhill at 25, 30, 35 mph or higher, you might as well rest and enjoy the free propulsion from gravity (technically, withdrawing potential energy you put in the bank while climbing earlier on your route, or if your descent is at the beginning of the route, going in debt by using energy you haven't banked yet). To increase your speed, you'll have to exert a disproportionately greater effort. Spending any energy here does little to increase speed, therefore it's better saved for a time when it will make a bigger difference.

prj71 05-26-22 12:29 PM

If you ever drop your keys into a river of molten lava, let 'em go, because man, they're gone.

Mojo31 05-26-22 12:35 PM


Originally Posted by prj71 (Post 22520884)
If you ever drop your keys into a river of molten lava, let 'em go, because man, they're gone.

Worse than trying to catch a falling knife?

delbiker1 05-26-22 12:39 PM

I am in the flatland of Delmarva. The only "hill" for many miles is the Indian River Inlet Bridge, guessing about 50 feet above sea level, each side is about 1/4 mile long. I believe the grade is about 4%. So, this likely does not relate a whole lot to the descents the OP has in mind. Anyway, it's about half and half in regards to getting as much speed as I can, or just coasting. I would have to go over and back on the bridge about 55 times to reach 1 mile of elevation gain. On days the wind is out of the north or south at a good clip, I like to go uphill into the wind riding hard, then coast the downhill, then do the reverse coming back across. I once hit 42 mph in the downwind, downhill 1/4 mile. Recent memory is more like 32 max.

genejockey 05-26-22 01:16 PM


Originally Posted by Broctoon (Post 22520874)
On anything more than a moderately steep descent, your pedaling effort will be wasted. This is because aerodynamic drag (and therefore power required to increase speed) goes up by the square of your speed increase.

Going up a hill, obviously you must pedal to keep moving. It's okay, because at speeds below 10 or 15 mph, air drag is by far the smallest component of the total formula you have to overcome to maintain or increase speed. In other words, your effort is not wasted, because increasing power by 20% will bring an increase in speed of nearly 20%

On flat ground, pedaling is again required, obviously. At speeds of 15 to 20 or 22 mph, air drag starts to take over as the major component. Within this range, any increase in speed will require a progressively greater effort--actually, this is always the case, but in this range it becomes a significant factor.

When you're coasting downhill at 25, 30, 35 mph or higher, you might as well rest and enjoy the free propulsion from gravity (technically, withdrawing potential energy you put in the bank while climbing earlier on your route, or if your descent is at the beginning of the route, going in debt by using energy you haven't banked yet). To increase your speed, you'll have to exert a disproportionately greater effort. Spending any energy here does little to increase speed, therefore it's better saved for a time when it will make a bigger difference.

The one point I'd make here, though, is that if you come over the top of the hill at 10 mph, and then start the descent by spinning up to a decent speed, like 25 or 30, if that's less than your terminal velocity on that hill.

burnthesheep 05-26-22 01:39 PM

1. It's not just a physics problem, but a physiology one also.
2. In time trial, if you're not pedalling within 10% of your target power during the event there better be a sharp corner, insufficient gearing, or you've already passed the finish line.

If confused about #2, refer to the part after the "," in #1.

PeteHski 05-26-22 03:53 PM


Originally Posted by burnthesheep (Post 22520972)
1. It's not just a physics problem, but a physiology one also.
2. In time trial, if you're not pedalling within 10% of your target power during the event there better be a sharp corner, insufficient gearing, or you've already passed the finish line.

If confused about #2, refer to the part after the "," in #1.

If it's a hilly TT, your target power on the climbs will be higher than it is on the descents or flat. At least if you want to win. It's simple physics/maths. Any pacing algorithm (eg. Best Bike Splits) will always set higher power targets on the climbs (obviously taking account of your personal limits).

Seattle Forrest 05-26-22 04:26 PM

Last time I did a 20 minute MMP test, I was pretty done at 18 minutes, then the road went uphill at about 18:30 and my power went up with it. I don't know if hills just keep us honest, if the different position recruits more muscles, or if somebody shot me with a tranquilizer dart but filled it will speed instead. But I've heard a lot of people say hills draw more power out of them at the same feeling of effort.

LarrySellerz 05-26-22 04:43 PM


Originally Posted by burnthesheep (Post 22520972)
2. In time trial, if you're not pedalling within 10% of your target power during the event there better be a sharp corner, insufficient gearing, or you've already passed the finish line.
.

so ive heard stuff like this but it seems to contradict the idea that its more efficient to work hard when going slow because of drag. Ive also heard people talking almost derisively about riders going hard on hills and coasting on the decents, as if they are training ineffectively or are inexperienced. It also seems like people drop massive watt bombs on punchy climbs, but maybe people just like doing that? I dont really know what to think tbh

cxwrench 05-26-22 04:45 PM

Stupid question. If you can pedal you can go faster.

LarrySellerz 05-26-22 05:03 PM


Originally Posted by cxwrench (Post 22521133)
Stupid question. If you can pedal you can go faster.

Once your cadence gets high enough soft pedaling can take hundreds of watts, gassing yourself for little gain

genejockey 05-26-22 05:28 PM


Originally Posted by LarrySellerz (Post 22521151)
Once your cadence gets high enough soft pedaling can take hundreds of watts, gassing yourself for little gain

Hence, gears.

genejockey 05-26-22 05:32 PM


Originally Posted by LarrySellerz (Post 22521130)
so ive heard stuff like this but it seems to contradict the idea that its more efficient to work hard when going slow because of drag. Ive also heard people talking almost derisively about riders going hard on hills and coasting on the decents, as if they are training ineffectively or are inexperienced. It also seems like people drop massive watt bombs on punchy climbs, but maybe people just like doing that? I dont really know what to think tbh

There's a whole range of power output between on the one hand pushing the same wattage as on the flat, and on the other, charging up the hill with everything you've got. It does you no good to be the first to the top of a climb if you have nothing left when you get there.

(I confess, I do the latter for fun, where you turn off of Page Mill onto Arastradero right by 280. Charge up the hill like my life depends on it then gasp like a fish on a dock for the next 100 yards. Why? Why not?)

Sy Reene 05-26-22 06:13 PM

It's kinda a fun question. Pretend you have a course that's 20 miles long. 5 miles of flat, 5 miles up a 5% gradient; turnaround and do the 5 miles back down and the final 5 miles on the flat. If you have eg. a 200 watt FTP.. do you go out at 200 watts, and gear appropriately to keep that all the way through the ride, or do something else, and what would it look like?

datlas 05-26-22 06:15 PM


Originally Posted by Bah Humbug (Post 22520813)
Oh I'm sorry; did I derail the thread?

Reported

indyfabz 05-26-22 06:54 PM


Originally Posted by genejockey (Post 22521174)
Hence, gears.

Not sure he understands what soft pedaling means.


All times are GMT -6. The time now is 02:08 AM.


Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.