Speed limit in corners

see also: archived feature request: Braking/speed limiting in corners. This is very similar but with additional detail.

The Dolphin City crit course highlights a limitation of the bike model: that there is no slowing in corners. This is a critical part of actual crit racing, and a motivation to be at the front of a pack going into corners.

The lateral force on a bike when cornering is proportional to v²/R, where R is the cornering radius of the center of mass. Since it could well be assumed that this is limited by traction, and since there is no crashing in Zwift that riders brake to avoid exceeding the traction limit, in corners of local cornering radius R, the bike speed should be limited to sqrt( R A ), where A is the maximal transverse acceleration at the traction limit. I’m not sure what this is but any reasonable approximation should work.

The effect of this will be the following:

  1. pedaling power in excess of the power needed to reach this speed is wasted.
  2. coming out of a corner, power goes into re-accelerating the bike, in addition to maintaining speed.
  3. As packs reduce speeds going into corners, collision avoidance will force riders near the back of the pack to slow more than riders near the front, allowing the lead riders go maintain more speed thru the corner at the same average power than riders near the back. This will further provide a small advantage to breakaways, who will avoid this additional slowing. So bike speed would be reduced further if the traction limit for the corner would result in colliding with the rider ahead.

At present, corners are little more than decoration: it’s full gas, all the time. “Super-tuck” provides a reason to pedal less, on straight downhills. This would provide a further tactical aspect to power, reducing power going into a corner, and increasing it coming out of the corner.

This topic has been brought up previously (of course) and presents some potentially interesting aspects for racing. I think one of the biggest questions, though, is how much like road riding does Zwift need to be? Some people would really like that, of course, while other are fine with the gameification of Zwift (see some of the comments about the new Boost mode).

I think another question is this; if you want it to be like real riding , how far down that path do you want/need Zwift to go to achieve your desired outcome? I mean, if braking into turns is introduced, you’re still missing the aspect that some folks are technically better at cornering than others. And some people will be able to move up in a corner while others will drift back. And there might be some folks tailgunning that, IRL, would let up early and then coast right back onto the group through the corner. I think it might end up just being a rabbit hole if you try to make it too much like reality. And, or course, there will always be some people who will be unhappy with some aspect of it.

In the end, it’s not a real bike ride, it’s Zwift. It’s a great training tool and we may just have to take it at that, just like we seem to be ok with the amount of abuse a car can take and keep running, like GTA.

Agreed: it’s a balance between real life simulation and watts-based video game. But I’ve never seen a car game where corners were literally irrelevant. Skill and risk-taking are real-life factors, in real life and on Repack Ridge, but I think it’s a reasonable approximation here that everyone handles their bikes perfectly. The only accommodation to corners I propose that it’s beneficial to get into them sooner rather than later, and that they provide another opportunity for constant power to not be faster than smart application of power (as is the case with super-tuck, which I feel adds a lot to the feel of the game, even if it’s extremely simplified): less power going in, more power emerging, is faster. And it would help promote the formation of splits in the crit, which would make the racing more exciting.

The downside I see is that it’s sort of a many-body problem, where if a group of 150 riders goes into a sharp corner such as exists in Dolphin City than that could create a computational challenge, but Zwift seems to deal with amazing computational challenges already.