Workouts with a (real) MTB

Hi all,

I know there’s differences between road bike and MTB but here what I’ve noticed:

With a MTB, when Zwift tells me " 110w at 85 rpm", it is impossible: I can either produce 110w but at like 50 rpm or be at 85 rpm but at 200+w.

Is is because of the “rings” / gears system on a MTB compare to a road bike?

Basically, I have to give up trying to follow a normal cadence. On average in free ride I’m at 65…

Any opinions and/or technical explanations?

What sort of trainer do you have?

A Tacx flow Smart. It works perfectly. I’m connected over ANT+ without issue.

Does it simulate the gradient properly on a free ride? Are you using the FE-C connection always for the controllable device?

You shouldn’t be changing gears in ERG mode. Use a gear where you can keep a comfortable cadence (roughly in the middle ot your gears) and stick with that until the workout tells you to change cadence. And give the trainer time to adjust when you change cadence.

Yes gradient is ok and I use FE-C connection for the controllable device.

What I’m saying is that with a MTB, when it tells you “110w @ 85 rpm” it is not possible. You can either be 110w @ 50 rpm or something or at 85rpm but at 180-200w

I think it is because the “rings” are completely different on a MTB compare to a road bike.

If I don’t care about rpm and only use watts, I have not problem to reach the wanted wattage. But keeping the same cadence with a MTB as if it was a road bike looks impossible.

Have you tried adjusting the “difficulty” setting in zwift.

On a related note, I started off on my MTB with trainer tire on a Kickr snap. After struggling with power output, I switched to a used road bike. This made a sizable improvement in FTP and overall experience on zwift. Ymmv. There’s another post in this forum related to MTB vs Road bikes on a trainer.

As you use a wheel-on trainer, your rear wheel effectively acts as an extra gear.

What wheel size are you using? MTBs usually have bigger wheels than road bikes, which could be part of the problem.

You should be using ERG mode when doing workouts, assuming this trainer supports it. Power/watts will automatically adjust based on your cadence, so whether you are at 50, 85, or 100 rpm the power will be constant and not change.

I use a Tacx training tyre (28x1.25 if I remember well).

Yeah, I plan to buy a road bike (even a cheap one). I think it will make everything easier / smoother.

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I use ERG mode. It works during the workout itself. But during warm up, I can match the wattage asked (85, 100, 115, etc…) But not the cadence AND wattage at the same time.

That doesn’t make sense, ERG mode works the same in a warm up or cool down as long as they are part of the workout. Are you doing a warm up (free riding around) before starting the workout or training plan?

No. I’m talking about the warm up as part as a workout. But now I realized it’s the same during all the workout. The resistance will increase by itself when needed, but in all workout that asks for a certain cadence. I can’t match both ( watts and cadence).

David,

I have found even with ERG I still needed to be in the right gear, especially with respect to cadence. I know I use a different trainer (Tacx Flux) and with road bike gearing but for higher cadence at lower watts I found I had to be in a suitable gear to do this.
I think for each gear ratio the trainer has a power range it can control (I have seen a power chart somewhere), think this is called wattage floor or similar.
In the most part you don’t need to change gear with ERG mode but I found this not to be the case for low watts high cadence.
Cheers, Andy.

This doesn’t sound like an MTB gearing issue. Are you allowing long enough for the resistance to adjust? When you’re increasing cadence to 85rpm, and you hold it there, you should then feel the resistance ease back off so that the power comes back down to match the target.

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I’m using a mountain bike too (an old hardtail with 3 by 8 gears), but on a direct drive trainer (tacx neo). In workouts (ERG mode) I’ve never had an issue with hitting power or cadence (other than with my own fitness). I put it on the big ring and somewhere in the middle on the cassette. When I’m asked to do power and cadence I just concentrate on hitting the cadence and the trainer adjusts resistance to bring the power in line with the target.

On free rides I have noticed if I’m trying to hold a certain power output for pacing the gaps between gears can make it hard for me to find a comfortable cadence.