Yesterday I rode (raced?) the long-distance version of Tour de Zwift‘s stage 3 group ride.

This was one lap of Watopia’s Big Loop which begins in downtown Watopia then travels over the Epic KOM to the Jungle Circuit before returning to downtown by way of a ride around the volcano. With the Epic KOM included I knew I wasn’t going to finish in the front group–but I knew it would be a great workout anyway, plus I was anxious to try an experiment… for science!

The Big Question

Before the ride began I knew I would be swapping from my road bike (Specialized S-Works Venge with Zipp 858 wheels) to a mountain bike (Specialized Epic) for the Jungle Circuit portion of the route. Some Zwifters aren’t fans of the swapping idea, but I think that’s just because they haven’t tried it. 😄 I find it’s a fun challenge to swap bikes as quickly as possible, then work to pass other riders in the Jungle while I have a speed advantage before swapping back to the road bike.

If you’re wondering–I chose the Epic because of its performance in our speed tests. And because I like Specialized!

But the bigger reason for my swapping was a desire to test a theory. This ride would answer the question: how well does the MTB perform against packs of roadies in double draft mode?

If you recall, I first wrote about how well the MTB swap worked in my post about the Le Col Metric Century. But that ride used Zwift’s standard draft, not double draft. With the draft effect being doubled I was sure the MTB would offer less advantage since the packs of roadies would be moving faster. But would the swap strategy still prove valuable? There was only one way to find out!

The Swap, Part 1: Losing

Abou to hit the Jungle dirt

As we hit the Jungle dirt I was in a pack of ~15 riders, putting me somewhere between 134th to 169th place overall in the field of 689. (This is an important number to look at before you swap bikes, because the goal, obviously, is to move up in the placings by the time you’re back on your rode bike after completing the Jungle Circuit on the MTB.)

My bike swap was pretty fast, but still by the time I was back up and riding my group was 10 seconds up the road. Now the fun began–how many riders could I catch?

The start of the Jungle: time to chase!

The first portion of the Jungle Circuit is a descent to the lap banner. Here I noticed that, unlike previous swaps, I wasn’t gaining time on the group I was chasing. They stayed 10s-11s ahead during the entire descent. Double draft was definitely working in their favor.

Then it got really ugly at the bottom as we hit the wooden boards/bridges on either side of the lap banner. I had enjoyed a rolling resistance advantage in the dirt up to this point–my Crr was .014 vs the road bikes’ Crr of .025. That’s a big difference – nearly 100 watts at 40kph!

But on wood, the Crr of a road bike is .0065 (nearly the same as pavement) while for MTB wheels it is .01 (see more on specific Zwift Crr values here). That’s a ~40 watt disadvantage at 40kph. Plus they were working together in double draft mode, while I was soloing!

There are also some “hardpack dirt” sections on either side of the wood which look like the dirt around the volcano. It’s noticeably different from the Jungle dirt (it rolls fast, and no dust is kicked up). This surface has the same Crr as pavement, meaning I was at a 60-watt disadvantage here. Ouch.

Thanks to the wood and hardpack sections at the bottom of the Jungle I lost another 10 seconds on the group I was chasing, putting me about 20 seconds behind as we began climbing up and out.

The Swap, Part 2: Winning

As speeds slowed from ~40kph on the descent and flat to ~20kph on the climb, I knew the double draft advantage was mostly gone since air resistance isn’t much of a factor at slow speeds. If I was going to catch that group, it had to happen here!

I kept my watts steady and saw the time gap steadily drop. I passed a few stragglers, then caught the group I’d been chasing as we neared the rope bridge at the top of the Jungle Circuit.

Finally caught the group!

I stayed on the MTB until the dirt ended. That’s where I made the swap back to my road rig, put in a good dig for about 20 seconds to catch the group up ahead, then assessed the swap situation.

Was it worth it?

I don’t think it was. Not today. The group I rode out of the Jungle with was basically the same group I started with–the front place in the finishing group was 137th overall (it was 134th when we entered the Jungle).

It’s possible that the roadie group was working significantly harder than I during the Jungle portion, but based on the effort level I saw from them for the remainder of the ride, I don’t think that was the case.

I think double draft, combined with the Crr disparity at the bottom of the Jungle, made the swap strategy a wash in this ride.

Roving Gangs of Hairy-Legged MTBers

Here’s how the MTB swap could still work well in a double draft race: if several riders all swapped to the MTB then rode together, taking advantage of the double draft.

There would still be a slight disadvantage at the bottom of the Jungle through the wood sections, but the MTB gang would certainly gain time on all the dirt sections, especially the higher-speed descent where double draft matters most.

What About You?

Have you tried the swap in a double draft event in the Jungle? What is worth it? Share your experience below!