Downhill Speed and Effort (watts)


(Dave) #1

I’m killing myself trying to keep up on downhills… Climbing and flats seem like a perfect simulation of my outdoor road numbers, efforts, and the feel of it - but I dread all the downhills… Individuals and groups easily pull away from me on the downhills, while I’m crushing it at 4 or 5 w/kg trying to keep up. And that’s crazy compared to the real world for me - where I’m the guy coasting to the front and looking forward to rest on the downhills. I’ve tried coasting, I’ve tried smashing the watts, it doesn’t matter which bike I choose or wheels… Today on Tour of London, my riding partner was coasting with 0 w/kg and pulling away second by second, and I was struggling at 2.5-3.0 watts/kg to keep up.

This happens coming off the radio tower in Watopia, and down from l’Alp du Zwift, any and all downhills. My max lifetime watts was not climbing l’Alp, but descending and trying to keep up.

My system: Tacx/Neo 1; Windows 10 (Alienware); wired internet with 200Mb/10Mb down/up. ANT+ with no problems. I have my “realism” set to about 40-50%, and I’ve used both the Tacx “estimated” cadence, as well as a real cadence sensor on the crank. I even swapped from my Litespeed on the trainer to my Moots. I even put my aero Campy FRONT wheel on the trainer bike (yeah, the last two statements are supposed to be funny).

My avatar and I suck at downhills, I guess…


(Lin) #2

This may sound daft, but is your Neo plugged in? The Neo can be used w/out power. However, w/out power, you will not get the downhill simulation.

Verify your Neo is running the latest firmware. You’ll need to use the “Tacx utility” app on your phone.


(Dave) #3

Thanks - yes it’s powered on. And I check about every other week with the Tacx software for updates… I read on one of the forum posts that Zwift applies a 60watt brake when we’re coasting… that’s an odd thing to do.


(Lin) #4

I also use a Neo. When going downhill, I have to pedal if I want to keep up w/another rider even if I’m in the draft. I can coast momentarily on occasion, but still have to resume pedaling. If you expect to coast in the draft all the way down, I doubt that will work. Also, remember that how much your buddy weighs and how much power he is putting down will also need to be taken into account.

Below is an example of me going down Box Hill this morning during Stage 4 of the Tour of London. There were four other riders. I don’t usually coast, preferring to soft-pedal, but wanted to see how it worked. Notice, I have to put power back down in order to not get dropped all while drafting. They were not coasting (based on rider position and w/kg). Avg for the descent was 211W which is 2.89w/kg for me.


(Dave) #5

Great data and explanation - thanks.


(Anton Kovalnogov (B)) #6

Also using neo1. Hasn’t faced such issues. In draft i usually soft pedaling, even freewheeling. But if i want to chase the group, i should give it all and its still hard to catch. Trainer difficulty set to 100%


(G odmother Fox-Neo2) #7

Let me guess it has something to do with trainer’s difficulty setting and your weight …

Two days ago, while on descent from Alpe Zwift, I was not pedaling at all (my new Kickr has some nasty problem with flywheel rattling and vibrations at high speeds) … but I got the same avatar’s speed as another rider who was working quite hard … all the time he was about 2-2,5w/kg. My difficulty is set to 100% and my weight is 91kg.

If he is significantly lighter then me and his difficulty is set lower (let’s say 20 or 30%), I think he is not able to use the advantage of steep descents as I do - while I “have” 8-10% all the time … he had 4-5% grade and it should mean some difference …

But again, I’m not an expert and I just guess …


(Zach Johnston) #8

Not to hijack, but does Zwift really put a brake on you if you aren’t pedaling while going down a mountain?


(Alexander Perdon (CTWT)) #9

Your guess is right, lighter riders do have some disadvantage on Zwift both decents and ascents.


(Dave) #10

Thanks for all the great responses…

Neo 1: I have a friend who is 205 lbs (93kg) with a Neo 1 - and he says he can coast most of the time in the downhill group.

rider weight: My settings are 5’7" at 165 lbs (75 kilos) and I still need to lose 10 more lbs to get in shape - so I consider myself a hefty rider.

rider height: I haven’t heard any evidence that tall riders stick up in the wind - air resistance due to height? I don’t know of that parameter being part of the equation.

trainer reality setting: I’m at 40%, but some riders report they are at 100%. GPLama (Shane Miller) did a study of this and said overall his times were the same - but maybe for pure descending, it makes a different - I’ll ask my guys for more info on this parameter.

braking while coasting: I should have bookmarked the forum thread for this - here’s a link, but I remember there was a more definitive one… (Coasting)

Well - there’s one parameter that’s super easy to mess with - reality - so today I’ll try the reality at a higher setting and try coasting… but it may be the climbs are too hard - could be I’m getting an easier climb but harder descent because of “reality” setting.


(Zach Johnston) #11

Interesting…so not a definitive “Yes” to the auto braking but next time I go down a mountain I will do some testing and see. By definition, pedaling just 10 or so watts would be noticeably faster than getting hit with a 60watt brake so it shouldnt be too hard to notice.


(Tim) #12

Zwift will auto brake you on modest (or maybe all) slopes at speeds below 35-37 MPH (it seems to vary, but about that number). If your speed is above 35-37 then, with no power input, your avatar will adopt an aero tuck position and rocket down. If speed drops below 35-37 your avatar will untuck and the bike will slow further.

My experience is that I need to input 200+W at 85kg to try to keep pace with a tucked rider.

I also have a Neo and yesterday I descended Alpe du Zwift at about 50 MPH on a TT bike without pedalling at all once I got going.

I can’t post an image for some reason, but take a look at this analysis and look at speed vs power and cadence for the descent.

https://www.strava.com/activities/2025227083/analysis/5843/6018

Basically, Zwift has its features and you just have to get to know them.


(Zach Johnston) #13

Interesting…I almost always ride in first person view so I dont really know what my avatar is doing.

It seems weird that 35/37 is the speed at which things change…I dont understand the justification for braking you at that speed.

I barely understand the idea that it would autobrake on a descent (in order to simulate real life rider caution, like NOT going 50mph around a hairpin turn on Alpe Du Zwift in cold/wet conditions). But if its not even doing that…weird.


(Dave) #14

I’ll try to separate the anecdotal from the facts:

Here’s a great post where one guy who weighs over 200 lbs says his bike stops on a -1 or -2% grade… and another guy who says his Tacx accelerates on the downhill while coasting…

Here’s ZwiftInsider’s explanation of the difficulty setting - smart trainers are getting the short end of the stick on the downhills: One common complaint from smart trainer owners is that they get dropped by other riders on downhills.

I still can’t find something that says definitively that the Tacx/Zwift combo does X watts braking while coasting - but it must, otherwise we’d coast for ever on the flats…

Anyway - interesting discussion - in the end, I just need to try harder, and it will make me stronger when I get to ride outside again…


(Tim) #15

I can only guess that auto breaking is a feature to help riders to manage speed a little better when trying to ride in a pack. After all, we have no brakes at all in the game, so it would be very hard to adjust if the was no braking effect of some sort. Once you’re hurtling downhill at 35+ I guess it’s no longer about a social sub 2 group ride. The race is on. :grin:


(Dave) #16

NICE! (also I finally spotted my typo in the thread title and changed “Dowhill” to “Downhill”.)


(Tim) #17

The problem for smart trainer riders on descents is that IF they have a high difficulty setting they can almost spin out trying to keep up with someone on a dumb trainer or a lower difficulty setting. I know. I’ve been there myself, a long time ago. For a while I used to ride at a lower setting and now, usually, I have trainer difficulty set to zero. I still have to put out the Watts, but there is far less gear changing required and I’ll never spin out.


(Zach Johnston) #18

I ride on a Cycleops H2 with the difficulty set to max (or, realistic), but to be honest during the two Fondos Ive done so far I mostly coast down the hills. Thats why the news that it may/may not be autobraking me was so alarming, I thought I was just going as fast as Im gonna go naturally.

But when I do pedal going down, I dont necessarily feel like Im spinning out.


(Dave) #19

I just finished some tests on Box Hill and Leith Hill, using my Tacx/Neo1.

When I set the “difficulty” to about 80% (there’s no digital readout, it’s just a slider to the right), the climbing felt more difficult (just like the ZwiftInsider tried to explain to me). It felt like I was in a harder gear, and indeed the watts went up to reflect that. But for the same watts, I got the same uphill speed. The higher D-setting just made me use different gears. But for the same 200 watts, I got the same speed.

And interestingly, the Shane Miller (GPLama) video I watched on this months ago said the same thing. GPLama climbed the same hill with D=0 and D=100%, but held 300 watts steady… and he got the same times up the hill.

Downhill: The higher D-setting allowed me to coast a bit more, but the flats and sticky climbs didn’t feel right to my legs. But I would say that for the same watts, I got the same speed. It just seemed “steeper” downhill - which I guess is what the D-setting is for. It’s for an almost unquantifiable “feel”.

I set my trainer back to 40% which seems right to me - makes it feel like a normal bike, and I’ll just push harder on the downhills, and never coast when I’m inside a peloton.

IMHO - just set the thing so it looks and feels like you’re riding outside, and have fun.

RIDE ON.


(Dave) #20

Zach - I can’t prove that 100%. I wish I could find a GPLama video on this, or something from Zwift Engineers, but I can’t find it.

:wink: I suppose I could dismantle the Tacx, slap a Rohde & Schwarz spectrum analyzer, and a Rick Sanchez defraculator on it… (ok - that last sentence is a joke - I’m not tampering with the equipment…)