Newbie Question - Watts going uphill

(Jordan) #1


I’m new to cycling and even newer to Zwift. I have a Wahoo Kikr Snap. I am on ERG mode with 100% trainer difficulty and my height/weight is accurate.

On relatively flat surfaces I hold around 100w and I’m passed constantly. Even the slower riders eventually pull away from me. On uphills, however, I have noticed that my watts shoot up to 250 or even as high as 350 and I’m flying past all the people I was struggling to keep up with on the flats.

I don’t mind people passing me on flats because I’m new, but I don’t like easily passing people on the uphills because I feel like I’m cheating.

Anyone got any idea what’s going on here. Sorry if this is a stupid question or has already been covered (I did briefly search before posting), but I am genuinely brand new to cycling and don’t know anything about watts or how the trainer works.


(alan) #2

I’m relatively new to Zwift as well, my first season on the game, but I would say you are expecting “sim” mode behavior from a trainer that’s in “erg” mode. If you are actually in ERG mode, the trainer should be giving you a constant resistance(wattage) no matter what speed you are pedalling. The resistance is determined by your selected training program, and has nothing to do with what the course climb grade shown on screen is.
SIM mode is simulated riding outdoors. If your avatar is climbing a hill, your resistance increases with the grade.
In both modes, your speed uphill is just a function of your in-game entered weight and your wattage output. In ERG you simply don’t have the added resistance/effort dragging your cadence down.

(alan) #3

Also, have you done a spindown test to calibrate your trainer? This will require the Wahoo fitness app to perform, but will ensure that the wattage the trainer says you are doing is fully accurate. You will be instructed to warm up the trainer by riding for 20 minutes or so, then gradually build up to a certain speed and stop pedalling so the trainer can calibrate against any extra resistance that might be coming for your hub bearings or other environmental factors.

(Lin) #4

If using ERG mode, the trainer difficulty setting is meaningless. If using ERG mode, your watts are not going to suddenly shoot up from 100 to 250-350 when you hit a hill. In ERG mode, your watts will go up or down based on the interval you are doing, which has nothing to do with the in game terrain.

SIM mode is like riding outside. The trainer difficulty setting is in effect here. Think of that setting as a virtual cassette (another discussion entirely) When you reach a hill, it will get harder to pedal. You either push harder in the same gear or you can shift to an easier gear.

Selecting Zwift workouts will put you in ERG mode, assuming your Kickr Snap is paired as the controllable trainer. Otherwise, you are riding in SIM mode.

(Mark) #5

Make sure you pair the trainer as F-EC option to Zwift in both power source and controllable options
F-EC is what lets the software (Zwift) control the trainers resistance.

(Jordan) #6

Thanks for the responses.

I thought ERG mode was the simulation setting. I selected it on the wahoo app. Silly me. So far I’ve only done a few routes, no training plans, so the erg mode setting shouldn’t be coming into effect.

And yes, I’ve done a spin down at the start of each session.

(Joe) #7

Maybe this will help:

100W isn’t much power. On level ground, it’s enough for you to cruise around at ~ 16 mph +/- (and this is true regardless of rider weight, because gravity isn’t a factor on the flats. So, a 150 lb rider @ 100 W may go 16 mph, and a 250 lb rider @ 100W will go a bit over 15 mph). In Zwift? On a flat course. This is on the slow side.

If you want to go faster on the flats? You need to shift into a higher gear, pedal faster, or both.

When you ride up a hill in Zwift with a controllable trainer (like yours), the trainer automatically applies more resistance. Assuming you don’t shift into a lower gear when this happens, your power output increases because you’re now turning the same gear against more resistance.

The reason you’re suddenly passing people on the way up has to do with your power-to-weight ratio (aka w/kg). Based on the W you’ve posting here, I’m guessing you are probably on the lighter side, weight-wise. So, as you start climbing and cranking out more watts, your w/kg increases. And, likely, it’s suddenly higher than those around you - which causes you to climb past them.

Let’s say you weigh 150 lb (68 kg).

At 100W on the flat, you’re at just under 1.5 w/kg and going ~ 16 mph.
When you’re climbing at 300W, you’re going at 4.4 w/kg (speed depends on the % grade)

Compare that to what happens with a larger rider who is 225 lb (102 kg)…

On the flat, at the same relative effort that you put in @ 1.5 W/kg? The larger rider is putting out: 102 kg * 1.5 w/kg = 153 W, which is good for ~ 18 mph - and so they ride away from you!

But when things go uphill… the larger rider has to sustain 448 W to match your effort.

Now, there are any number of reasons why people may appear to slow down disproportionately on climbs in Zwift. It may be that they’re heavier and don’t have the strength required to fly up hills, but I think it’s just as often the case that people are riding in ‘workout mode (ERG)’ and may be in the middle of a rest interval. Or they just chose to drop down into a really low gear and take it easy because they just finished a sprint. Whatever the case, you needn’t feel bad for climbing faster than them. There’s always plenty of yo-yoing that happens with riders in Zwift.

It’s all good.

(i van) #8

The quick answer here is:

Air resistance is the main force you have to overcome while riding in a flat. Raw watts are the way to overcome this force.

Gravity is the main force you have to overcome while riding up hill. The higher the gradient, the more gravity. There is still air resistance to overcome, but not as much as the flats. Gravity is overcome by a higher power to weight ratio (watts/kg).