Why do the men run so slowly at PTO races?

The 20m draft rule is fantastic for fairer racing, and the weak bikers are paying for it on the run.

The Homestead-Miami Speedway is flat, but the wind can blow across the course and during the opening T100 men’s race, the wind blew pretty hard.

The T100 series has begun in triathlon and true to form from the other PTO races, save for a couple of exceptions, the run speed from the men has been really slow. Well, slow relative to the run splits these guys have produced in the past and myWindsock, combined with a look into the rules at other races regarding the distance they’re allowed to ride. Previously, we talked about Race Ranger and the differences it can make – but the pro men seem to have ignored this message so today we will look into the physics of race tactics at 20m… 

The rules stipulate that you can ride 20m behind the rider in front, does that actually provide any benefit?

According to CFD simulations done (check here for more details), the saving at 20m is about 3% and this will form the basis for our discussion here. There’s a point worth making though, this number is probably wrong and most definitely not constant. You won’t always be getting a 3% reduction in drag 20m off the wheel, sometimes it will be more and sometimes less. It’s just 3% under the conditions done in this simulation.

This is how the drag is calculated and there’s two things worth noting, a reduction in drag is worth more at higher speeds and it’s linearly related to the change in power.

This is the drag equation rearranged to show us the relationship with drag and power. We can see that the two are linearly related which means a 3% reduction in drag from the simulations above lead to a 3% saving in power required to ride at a fixed velocity.

How much power is saved at 20m?

The answer is 3%, so if the bloke in front is doing 370W as Magnus Ditlev reportedly did in Daytona, the man behind him is doing 358W under our fixed conditions at a speed of 47kph. If they’re at the legal IRONMAN distance of 12m from the front wheel, the following rider would be doing around 315W – it’s clear that a change in tactic is necessary to prevent over-biking.

This leads us to a key takeaway –  if the drafting distance is 20m then your in-race decision making must be different to if it’s 10m or 12m.

Ok, so should I follow a rider like Magnus Ditlev? 

If you’re riding at 20m, you should only follow a rider who you’re sure that your abilities on the bike are similar to. This is a decision that Sam Laidlow has got wrong on a couple of occasions, including in the recent PTO race – when he rode with Ditlev then blew up on the run. Riders in the T100 should cede the time on the bike as it’s clear many of them are riding too hard. 

It would also seem that the female athletes are better decision makers. Despite there being many amazing riders in the women’s field (Paula Findlay finished 25th at TT world champs and was outridden in the T100 in Miami) – the run times in the women’s field don’t appear to be any slower than at a “normal” race. 

If you remember one thing from this blog, let it be this: If the rider in front of you is more than 3% stronger than you, then you being 20m off their wheel is not an advantage, but a disadvantage.

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