Racing in the wind - is deeper better after all?

Racing in windy conditions can be a worry for many riders.  However, we caught up with pro triathlete Laura Siddall to find out how riding a Disc wheel in Lanzarote actually helped improve stability.

Back in May, I headed to Lanzarote for a training camp in preparation for racing Ironman Lanzarote in July. I was aware that the island was renowned for its wind and conditions. I used to pride myself in wanting races to be the windier the better.

Two years earlier, in May 2019, I came off my bike on a corner but due to the wind zipping down off the mountains and dumping me on the road, breaking my collarbone. Since then my confidence has been rocked, and I’m still working to build that back up.

Arriving in Lanzarote in May, I wasn’t fully sure what to expect. As said, I’ve never found wind an issue for training and racing, but have lost significant confidence in these conditions. I happened to arrive for a week that was particularly strong winds (yes yes I know everyone says that right), but when part way through the week the locals were asking if you’d prefer or need to borrow a turbo trainer as they aren’t even going out, I guess you do start to second guess yourself. I’d be lying if I didn’t say my time in Lanzarote in May didn’t worry me. I had a few times where I was blown across the road, having to suddenly unclip to save myself. Times where I was almost getting blown backwards down a hill I was trying to ride up. I even had a situation at the top of a climb, getting ready to descend where I honestly wasn’t sure I was going to get down with the direction and strength of the wind. I also found I couldn’t put any power down as was too busy trying to just keep the bike upright and on the road. Getting down on my aero bars and doing race efforts and training sessions was a real challenge. How the heck can you race in these conditions, I’m just trying to keep the bike upright?!

I did consider whether I should race or whether I should choose another one. But I’d committed, in my head at least, and felt I now needed to see it through, and almost attack it head on, rather than shy away and potentially always then have that looming over me. I don’t like something beating me without trying, and so needed to go through with the race and challenge, even though I couldn’t see how you could actually ‘race’ in the wind and those conditions.

I’m grateful to work with Dov at Parcours and before any race, we always talk about my wheel choice for the course terrain and conditions. A go-to race set up would be a Chrono front / rear Disc wheel. For Ironman Lanzarote, with the wind element, a Strade front / rear Disc was recommended. I knew also that good friend, fellow triathlete and also the 2019 Ironman Lanzarote Champion, used a disc wheel for her race. Only a handful of other athletes did. I know in my head that the theory says in wind, it’s actually the front wheel that is issue, not the rear. That’s because all of our weight is on the rear wheel, and it’s the front (depending on depth) that gets blown about and makes riding in the wind challenging. Yet I’ve never actually tested this in real wind. Many races ban disc wheels in windy conditions.

Race week and I headed out a few days later than I normally would, so that I could get my last few key sessions in, in Girona, whilst not getting battered for days on end by the wind, before the race even started. My first session on the bike on arriving back in Lanzarote, was just with my training wheels, but I was getting blown all over and battered by the wind. To be honest this time it didn’t phase me, because I’d been preparing myself for the worst, so to speak, and I was here to race and it was too late, so just deal with it. In fact I actually just ended up laughing, it was almost that comical. Yet I was still conscious of the wind, and controlling the bike. I usually don’t put my race wheels on till the day before the race, but having never ridden a disc wheel in Lanzarote, and with the wind conditions, I thought I’d best see what it was like, a few days before the race. I guess whilst I knew I would probably ride a Disc, I’m not sure I was 100% convinced.

Now, I did ride a different part of the course, to the previous day with my training wheels, so the wind conditions were slightly different. However, I’d hardly ridden 100m and I felt how stable the bike was. It blew my mind how I could notice such a difference, and how much more confident I felt, with the Disc, in blowing conditions.

I messaged Dov to find out the why. Why does riding a disc in the wind make the bike feel so much more secure and stable? When everything about it in your head is telling you different. It’s another part I like about the support and relationship from Parcours. Dov always has time to explain and make it understandable.

The Sciencey Bit!

When you ride a spoked rear wheel, the centre of pressure on the bike is roughly positioned between the front and rear wheels. Think of the pressure profile of the bike. i.e. the difference in air pressure from one side of the bike to the other and the flow through the wheels.

When you ride a rear disc wheel, this blocks the air flow from one side of the bike to the other (e.g. through the wheel). It results in increasing the pressure differential at the rear of the bike, moving your centre of pressure further back.

Therefore, when riding in cross winds, the major impact on stability is the front wheel as this is freer to turn on its axis, whereas the weight / pressure is on the rear wheel.

The stability of the bike will be affected by the distance of this free axis (front wheel) from the centre of pressure (in the rear wheel, or nearer the rear of the bike). Therefore moving the centre of pressure further back increases the distance from the free front axis, and the centre of pressure, therefore improving the stability of the bike.

This may help it to click and make sense:

The principle is similar to centre of gravity. Think about someone standing up straight, with someone else trying to push them over (or put the bike upright on its rear wheel). Then think about if they lower their centre of gravity (i.e. moving it further away from the point at which the second person is trying to push them over). With a lower centre of gravity, or a centre of gravity that is further away from the point where pressure is being applied, they can resist a far bigger force before they topple. Exactly the same with the bike. By moving the centre of pressure further from the free axis that you’re trying to stabilise (i.e. the front wheel), you can exert a higher sideways force (i.e. cross wind) without causing instability.
Bingo! And that’s why you can look to ride a rear disc wheel in windy conditions and in fact it’s more stable and secure than a rear spoke wheel.

So, the ideal set up is a Disc rear wheel and a shallower front wheel (e.g. the Parcours Strade is the perfect option).