Light Riders not part of Zwift

I have been zwifting a while, as a 53Kg rider I can handle to hold wheels on flats but is almost impossible to do it on descents, even on flats I have to put a lot more power holding wheels than people pulling. The thing is, no matter if is flat or descent heavy riders have advantage, the other thing is that someone could say “ok, find some hilly races” but there´s like zero mid to long hilly races on zwift for PM America zone time, just flat races… Please: Enforce hilly races events and improve phisycs for light riders… Thanks

Bad news. Hilly races aren’t going to help. Heavier riders are faster uphill as well.

An 8kg bike is a 10% weight penalty for an 80kg rider but a 13.3% weight penalty for a 60kg rider. If both riders are doing the same w/kg then the 80kg rider will be faster as the additional weight of the bike is a smaller weight penalty for them.

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LOL, so, heavy riders just not have advantage on flats but also on climbs and descents. Cmon Zwift =D

You could try eating more I guess :rofl:


By “more power” presumably you mean a higher w/kg? (I mean, if you’re putting out more raw wattage than someone else, you’ll leave them in the dust.) But if you’re light, then of course you’re going to be putting out a higher w/kg than a heavier rider, right?

And this is the problem with the Zwift race category system. If you’re 53kg putting out 3.1w/kg in C cat then you will always have a speed disadvantage to heavier riders putting out the same 3.1w/kg. If you put out more w/kg to compete with the heavier riders then you’d be over the cat limits and should move up to cat B. And if you thought it was tough being a light rider in cat C wait until you try it in cat B.

If we had a proper race cat system then light riders with a higher w/kg would be able to compete against heavy riders with a lower w/kg. The bigger riders would have an advantage on the flat and in sprints but the lighter riders would have an advantage on the hills.


Well, yes Zwift should move to a results-based categorization system. That’s true.

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If it were so easy :frowning:

Right, high w/kg

Right now I ride on B based on zwiftpower categorization (4.3 FTP but 233 watts or so), and sometimes just for fun on A cat, but at the end of a race I was putting 4.2 on average and winner 3.8 or less, good for fitness and I enjoy it but just not fair, some other light riders just got dropped so fast

A 53kg rider can do 3.77w/kg before they’re at risk of being promoted to B. That’s exactly what the secondary outright power qualifier is intended for.


This is a real issue. You hear heavy riders joking that they are so disadvantaged in races because of climbs (what climbs?) but it’s not true. As long as you are below the average weight in a race you are definitely at a disadvantage, not the other way around.

Now, the same thing would be true outdoors as well if on the flats against a heavier rider with more muscle volume pushing heavier Watts with the same ease as your chicken Watts, wouldn’t it? Yes, but… it doesn’t stop there.

First, more of a sidenote, there is something off with Zwift’s simulation. It’s too simplified. I’m pretty sure they calculate air resistance assuming that everyone has the same Cd. And that weight doesn’t affect CdA. Of course it does! Although the effect is small, it still hurts tall light riders.

Second, the really important part: The light rider’s problem in cycling in general is exacerbated in Zwift by the uniquely stupid W/kg cat system (which needs to go and be replaced by a results-based cat system instead - for a lot of completely different reasons already).

Anyone ever participated in a group ride where the target avg W/kg was supposed to be just about what you can manage, only the ride leader was a lot heavier than you and he never told you his weight? Not fun. You end up having to push a far higher W/kg than him just to keep up with him - and you’re both in draft!

If we move to racing we have a big problem related to the group ride example. There is, as we all know, a performance ceiling in cat B-D. You are not allowed to go over a certain W/kg. Which means if you are on a heavier rider’s wheel, and you are both in draft, and he is already on the W/kg limit of your cat, then you as a light rider are not permitted to keep up with him per definition. Which is completely absurd!

We’ll repeat that: You are not allowed to compete with a heavier rider riding at your cat limit!


Please repeat after me:

You can’t have performance ceilings in a sport!

You can’t have performance ceilings in a sport!

You can’t have performance ceilings in a sport!

You just can’t!

But we have that in Zwift. And so we also get the Light Rider’s Curse. It’s is very difficult to get on the podium as a light rider in the lower categories, where the average weight is higher than in cat A or B, even if you are fit enough to put out the max W/kg allowed. You will get upgraded before you start to take podiums. And become pack fodder in the next cat. Light riders go on a detour around the podium moving from one cat to the next.

The solution is not to enforce hillier races. If a heavier rider destroys you on the flat, he will also destroy you in some Watopia hills. You need AdZ or Ven-Top to make a difference. And even then he is not that far behind if you look at cycling physics. Not enough to make up for his advantage on the flat. Being light is not enough. You need to pair it with good VO2Max and good recovery and hurt him repeatedly in the climb, says cycling science. Now we’re talking outdoor climbing. In Zwift it’s a bad solution to enforce hilly races because it tries to circumvent the real problem. The W/kg cat system.

The solution is to change the cat system and make it results based. Then you will be grouped with riders you both can compete with and are permitted to compete with, regardless of weight.

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I think the Zwift speed algorithm is very good, I have tested it with empirical formulas for IRL riding and it compare very well. There are super long threads on the forum about that.

But the problem is the racing categories that is based on weight that skew all the results.

If you take a mass start event on Zwift and you plot the Rider position against weight you will see that the lower weight riders are at the front.

this was a quick one I did.

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first of all I doubt that Zwift does a fully realistic calculation of air resistance. I have no proof, but I’m pretty sure the modelers were lazy and that Zwift assumes that every rider of a certain length has the same frontal area (the A in CdA, or Cd x A). We don’t. A 180 cm rider @ 90 kg does not have as small a frontal area as a 180 cm rider @ 65 kg, no way. Amateur riders pay thousands of dollars/euros for aero frames that give far less reduction in air resistance than the difference between those two bodies.

So one rider may have 50% more muscle volume but still somehow “the same” frontal area as a lighter rider riding next to him in a race? And hence both have the same air resistance? How can that be fair?


Secondly, we’re on the same side concerning the W/kg category critique, I believe, @Gerrie_Delport. But you’re wrong about the importance of weight in races. It is exactly like I said in the previous post. And that is a direct consequence of the W/kg system, which favors heavier riders, like I said.

To illustrate the point I grabbed some fresh data off of ZwiftPower, a sample of 50 consecutive cat C races of all sorts, starting from yesterday night and backwards.

I only skipped races where 1) weight data was missing, 2) there were fewer than 6 cat C finishers according to ZP, or 3) the race type didn’t lend itself to this test (e.g. Hare & Hounds or age category races).

Then I compared the average weight of the 3 riders on the podium to the average weight of the other riders in the race (hence why I wanted at least 6 finishers).

The podiums in the races had an average weight of 81.3 kg.
The remaining riders in the races had an average weight of 77.5 kg.

This nearly 4 kg difference between the average podium winner and the average loser turns out to be highly statistically significant, even at the 1% level (p = 0.00118). For those who aren’t into statistics, this means that it is extremely unlikely that this difference wouldn’t appear again and again if we picked some other random set of 50 races from the ZP history.

This difference simply can’t be random. There is an underlying cause. And it is bad to be light in Zwift races. The results prove it.

You could blame the algorithm Zwift uses to model cycling physics in the virtual world of Watopia, but it seems far-fetched to me, even when taking into account the possible rider frontal area issue I started the post with. That could be a partial explanation but the fact remains that the W/kg cat system screws light riders, and this should be the main problem. I will give an example why.

Assume the following:

You are racing in the front group in cat C (for some reason there are no sandbaggers this time…)
The group keeps a steady pace and you are at least 20 min from finish
You weigh 75 kg
You are on the wheel of a bigger guy @ 85 kg
You are both in draft
The big guy is able to hold a 20 min average of 286W, i.e. 3.2 W/kg according to ZP (286 x 0.95 = 272. 272/85 = 3.2)

The only way you can stay on his wheel is by matching his 286W. This would put you at (286 x 0.95)/75 = 3.6 W/kg. Keep at it for 20 min (if you can) and ZP will give you a DQ. People might even call you a sandbagger! You simply can’t win this race as a light rider and get away with it on ZP!

Guys weighing 75 kg with a 1 hr FTP of 272W according to ZP will already have been upgraded to cat B. They will have seen very few podiums back in cat C if they were up against heavier riders. Which they were. The results above show that.

The W/kg cat system just plain sucks. And this is only one of the reasons. Another very important reason is that the system promotes cruising races (=cheating and getting away with it on ZP), a completely different story. There is a neighbor thread that I started about that. What should move you between categories has to be your previous race results, like in any other sport, not your Watts and your weight. It’s completely absurd! What were they thinking??

Yes Zwift has to estimate some data like cda, they do have weight and height and from that they need to calculate a lot of things. But it give a very good estimate. People don’t get as aero while riding Zwift as they would be irl.

I totally agree with your calculations if you look at w/kg grouped categories. The w/kg categories skew the data that’s why we don’t like it.

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The drag issue is a minor one compared to the W/kg cat issue. But it’s still interesting. I found this interesting link by Coggan himself, where he discusses various ways to estimate, among other things, the impact of mass (hence weight) on both the rider’s drag coefficient and his frontal area.


I have absolutely no idea how simplified the Zwift physics algorithm is. I just have this strong hunch that they probably didn’t make it overly complex. I could be wrong. But I thought I’d test this too before I criticize it too much.

How could you test the mass/weight effect on drag at all? And can you do it reliably enough to actually spot subtle differences in drag between riders of the same height but with different weights, as to not mistakenly rule out that the algorithm actually already accounts for that?

The best I can come up with, unless someone else has a better idea, is I create a short workout that I run in ERG mode. I’m not very strong, though, and drag increases expontentially with Watts, so high Watts would be ideal. To make things worse, I need to make the workout easy enough (low enough Watts) to be repeatable directly, because I’m too impatient to wait between trials… :stuck_out_tongue:

I need ERG mode to keep Watts reasonably steady. Then I alter my weight and run the workout on a TT bike (to avoid draft) on Tick Tock or somewhere really flat with different weights (let’s say 3) and see how far I got with each weight as the fixed Watt workout block ends. I probably have to run each weight a few times and take an average because there will be some variability in the Watts produced. Then I can try plot the results.

If the algorithm is actually advanced when it comes to drag, could you still expect to see a difference, or would it just get blurred out by “noise” such as not matching Watts properly or something? I think it should be possible. People have already compared different bikes and concluded that some bikes are faster than others. And the bikes’ CdA are all lower than the rider’s.

So if there are no differences in distance covered, then the algorithm simply isn’t taking weight (mass) into account when calculating drag. If there is a difference, then that’s a good thinkg, but I will have to figure out how they calculated it, if possible, and if it seems reasonable.

There should be a difference because it is more realistic and because it mitigates the lower muscle volume of a lighter rider somewhat and thus reduces the light rider penalty a little. But we’ll see.

Oh and, I won’t hold my breath, but if anyone actually wants to chip in and provide some data with his or her own tests, then that would be most welcome of course. The more data the better. Just be diligent and careful if running a test so we can trust the data.

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I don’t think we need to test Zwift’s drag algorithm until we have proper racing categories. :shushing_face:

I have done a few tests using these formulas.

I would guess Zwift use something similar.

Zwift Insider has already done these tests (they use an Ant+ simulator to get a constant wattage rather than using ERG mode or worrying about rider fatigue). Yes, rider weight (and height) affects drag.

@Umi_Sonada , indeed you’re right. I knew about that article, read it earlier but never noticed it actually also addresses drag and in a good test. Sloppy reading.

I don’t want to be wrong when I criticize something, so I’ll edit previous posts to point that out. That I was wrong in my suspicions concerning drag and rider mass.

But then that means the Light Riders Curse in Zwift could only be attributed to the W/kg cats - because my test results still stand. In fact, the Light Riders Curse is basically a matter of simple logics and not not data even, although data proves it.

And no, that’s not the same thing as the light rider penalty on the flat outdoors (due to naturally lower muscle volume). With a results-based categorization instead of our W/kg categories light riders would still have to push higher W/kg to compete on the flat with heavier riders, but there would be no difference between the average weight of the winners and the average weight of racers outside the podium.

And this I have said and agree with you. W/kg categories is weight classes and if you are the heaviest in the class you have advantage.

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