Yesterday, Zwift enabled an adjustment/fix for drafting which will be particularly noticeable on descents. Here’s what was posted on their forum:

What Was Fixed?

Zwift says, “Up until now our drafting algorithm didn’t properly use road incline/decline percentage in the equations and this change will fix the issue.” So what was actually broken (and fixed)?

It’s an interesting little bug that is easy to understand. In Zwift, as in real life, every rider casts a draft “shadow” behind them as they cut through the wind. If you’re in another rider’s draft shadow, you’re hitting less air resistance, making it easier to move forward. Cycling 101.

But Zwift’s algorithm was calculating perfectly horizontal draft shadows regardless of road pitch. This works fine on flattish roads, but as the gradients get steeper, horizontal draft shadows will impact riders behind less and less! Zwift confirmed with me that the draft shadows now now extend parallel to the slope of the draft-giving rider.

How Does It Feel?

In my tests, the results of Zwift’s draft update are exactly as described above. It’s particularly noticeable on descents, where the draft is simply stronger than it used to be. Riders used to have to put out some power to hold the wheel of a supertucking rider, but you can now sit on that wheel at 0W, because the draft off that supertucking rider is stronger.

So while supertuck is still a fast and easy way to descend steeper hills, its utility as a weapon of attack has been blunted.

One important result of this change is that it’s now easier for lightweight riders to hold a good pack position on descents, as they sit in the stronger draft.

Coming Soon: More Tests

It’s time for me to run fresh tests and update this post, which showed how much power it took to sit on another rider’s wheel while they were descending in the supertuck or at certain wattage, in race events or group rides.

Questions or Comments?

Go do a test ride or two, then report back your thoughts on the updated draft for climbing and descending. Chime in on the Zwift forum topic, or comment below!

In 2024, Tadej Pogačar won both the Giro d’Italia and the Tour de France, joining Fausto Coppi and Eddy Merckx among only eight male riders and Annemiek van Vleuten as the only female rider to complete the feat.

Prior to Pogačar‘s Giro-Tour double, this hadn’t been achieved since Marco Pantani in 1998 and no one has ever won the Giro, Tour and Vuelta a España in the same year. 

Pogačar went on to win the World Championship, cementing his place alongside Merckx, Stephen Roche and van Vleuten as one of four riders to win cycling’s triple crown in a single season.

• 442 watts for 40 minutes: Study estimates Tadej Pogačar‘s power output on Tour de France climbs

Is there a metabolic limit?

A new study by a team of North American researchers published in Current Biology possibly helps to explain why it’s so difficult to sustain the high energy expenditure needed to win multiple grand tours in a season.

Their study suggests that there’s a metabolic ceiling that limits the maximum sustainable rate of calorific expenditure over longer periods to around 2.5-times basal metabolic rate, which is how many calories you need to burn just to keep the lights on. 

The research, reported in Scientific American magazine, looked at the metabolic output of 12 male and two female, mostly professional, elite ultramarathon runners, triathletes and cyclists, finding that they could burn as many as 11,000 calories in a day. But the researchers found that there was a limit to how long they could sustain this level of energy expenditure.

Previous studies have looked at cyclists in the Tour de France and found that over the 23 days of the race they were expending between four and five times their basal metabolic rate. In shorter races such as ultramarathons and Iron Man triathlons, athletes have been found to reach close to ten times their basal metabolic rate.

The new research supports the hypothesis that, although elite athletes can sustain very high metabolic rates over shorter periods, over durations of 30 weeks or more their calorie burn cannot exceed 2.5 times their basal metabolic rate.

That equates to around 3,750 calories per day in a fit 70kg athlete.  

In the study, athletes were asked to drink double-labelled water, which contains heavier, non-radioactive isotopes of hydrogen and oxygen. Testing how quickly this is passed into urine allows the calculation of how fast food is being metabolised to produce energy.

The study results indicated that, although participants could reach up to seven times their basal metabolic rate during races, over a 30 week period, their metabolic rates fell to 2.5 times their basal rate or less.

Scientific American quotes evolutionary biologist Amanda McGrosky of Elon University in North Carolina, who says that there’s evidence that intense physical activity has pay-backs including a slowing of digestion, lowered immunity and temporary shrinkage of brain tissue, as well as lowered sexual arousal. 

The root cause of the putative limit is not clear. There’s a suggestion that it may be related to a limit in the body’s digestion and nutrient absorption, but it’s something that it’s thought possible could be exceeded thanks to advances in modern sports nutrition.  

For now, the research suggests that it’s very hard to peak for two three-week grand tours in a season, let alone three, and may help explain why Pogačar‘s main priority after winning the 2025 Tour de France was a well-deserved rest, even if he did bounce back to win the World Championships for a third time eight weeks later.

The US Consumer Product Safety Commission issued a warning linking some Rad Power Bikes electric bike batteries to fires, stating they “pose a risk of serious injury and death”.

The batteries can “unexpectedly ignite and explode” especially when the battery or the harness has been exposed to water or debris, according to the CPSC, adding that it is aware of 31 reports of fire, including 12 reports of property damage totalling approximately $734,500. 

The CPSC says: “Some of these incidents occurred when the battery was not charging, the product was not in use, and the product was in storage.” 

Rad Power Bikes issued a statement in response to the CPSC’s warning, refuting the claims and stating that it “firmly stands behind” its batteries.

The CPSC says the affected batteries were sold with the following Rad Power Bikes electric bikes:

• RadWagon 4
• RadCity HS 4
• RadRover High Step 5 
• RadCity Step Thru 3
• RadRover Step Thru 1
• RadRunner 2
• RadRunner 1
• Radrunner Plus 
• RadExpand 5

The batteries were also sold as replacement models. They have the battery model number HL-RP-S1304 or RP-1304, which is printed on a label on the back or rear of the ebike battery.

CPSC urges consumers to remove the battery from the electric bike and dispose of the battery following local hazardous waste disposal procedures. “Do not sell or give away these hazardous batteries,” it adds. 

Rad Power Bikes has refused to agree to a recall and is unable to offer replacement batteries or refunds due to its financial situation.

The Seattle-based company filed a Work Adjustment and Retraining Notification with the Washington state regulators just last week, as part of an “advance written notice of a potential cessation of operations that could occur as early as January 2026,” a spokesperson told Geekwire. 

The shutdown would affect 64 jobs at the company’s headquarters, including the CEO and CFO, but Rad Power Bikes said no final decision has been made and that it is seeking buyers and investors to continue operating. 

In its statement in response to the CPSC warning, Rad Power Bikes said: “Reputable, independent third-party labs tested Rad’s batteries, both as part of our typical product testing and again during the CPSC investigation, and confirmed compliance with the highest industry standards. Our understanding is that the CPSC does not dispute the conclusions of these tests. It is also our understanding that the battery itself was not independently examined per industry-accepted test standards.”

“The incident rate associated with the batteries in the CPSC’s notice is a fraction of one per cent. While that number is low, we know even one incident is one too many, and we are heartbroken by any report involving our products.

“It is also widely understood that all lithium-ion batteries – whether in ebikes, e-scooters, laptops, or power tools – can pose a fire risk if damaged, improperly charged, exposed to excess moisture, subjected to extreme temperatures or improper modifications to the electrical components, all of which Rad repeatedly advises against in user manuals and customer safety guides. Contrary to the CPSC’s statement, mere exposure to water and debris does not create a hazard; rather, significant water exposure, as warned against in our manuals, can pose a hazard,” the statement continued.