Newbie Question - Watts going uphill


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.


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.

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.

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.


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.

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.

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.


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).

Hello All - Newbie to ZWIFT - Level 10 now waiting for level 14 for bike I want / available. So I would like to share my experiences todate and any advice would be welcomed. Im at 89 /90 kgs - and all races todate I average around 255 watts consistently for a 30km to 40km race. My FTE is around 250 average from Training Peaks guessing its pulling data from Strava/ ZWIFT. Average around 37kph to 40+kmp depending on race / elevation, and a bit slower on MTB /Dirt rides.

Great topics and raw watts on pedal equates to torque. I get to choose gear and cadence and I ride ZWIFT like I ride in a real race, drop gear round corners or accelerate , power up hard on hills and over the top, pedal hard on flats (Your example of the lighter rider battling on flats but strong on hills, I am one of those that unless I dig deep and push out 450 watts on 8% to 10% gradient and hold it I cant stay with the bunch, this is where my Wahoo really gives me a load of resistance to overcome and I WONDER IF ALL SMART TRAINERS ARE EQUAL, I have heard Wahoo Kickr4 is a hard trainer :slight_smile: as i see people coming past me at 8W to 10W per Kg or perhaps they have shed lots of virtual weight:).or their trainer overstates watts?

I have a Wahoo Kickr4 and I think gives me a heck of a workout especially on the hills. think I am a C rider 2.5 watts to 3 watts , as in C races usually in top 3rd of participants - but can not hold the front bunch that goes the watts they push are unrealistic and I would blow keeping up. I am not pushing my heart rate todate as hard as a real road race to stay with bunch, I race about 5 to 10 beats off that effort just because I can indoors and NO GRAVITY FORCE a blessing for a heavy rider. I try stay with second bunch and draft as much as i can, I actually find ZWIFT more intense as the pace just does not let up and towards end the pace hots up.

Questions and looking to experienced guys to help me here or advise;

Erg mode vs Sim mode. I am sure on initial Wahoo setup i chose erg mode - Question Is ERG mode this the best thing todo. ZWIFT is clearly communicating and instructing my trainer based on terrain. I have also left the ZWIFT
Difficulty setting in the middle - I have not played with this yet and I think it could help me I believe it can be changed real time during a ride? Need to find optimal way for climbing - I have the power on flats and gradients below 4% and prepared to put in a bit of extra work if needed ( I think difficulty to the left would be way togo?)

In a Race I am a big gear grinder have always been, that said I see the Wahoo Trainer seems to respond quicker to cadence verus pushing more power in low gear. QUESTION - The real strong racers do they opt for higher cadence 80rpm plus in say 50 X 13 / 14 /15 vs 65 rpm 50 x 10 /11/13

Going up hills 6% plus gradients that where i feel it and at 10% gradient working harder than on any roads I have ridden in South Africa :slight_smile: , I can get out of the saddle, and use raw power on 50 x 11/12/13 to get the 450 + watts but is not practical in long climbs - QUESTION - I have been pushing my big blade 50 and going up the cassette trying to spin but could not seem to get on top of the 50 for enough cadence, but now finding that small blade 34 and going for 12 / 16 range and holding say 350 watts which is a high cadence gets me up the hill but still battle with the really strong climbers as I need 400 + watts sustainably without blowing my legs. Any tips on climbing for a heavier rider.

I can push out 1100 - 1500 watts on my Wahoo Kickr4 just for a few seconds, can hold 600 to 800 watts for 20 seconds from ZWIFT stats I need to up from my current 255 Watts average for a race to 300 watts average - Question I have not done any workout rides yet - where would the maximum benefit come for me training wise doing races as I have been an loving it, or a specific training regime? I have seen some ZWIFT training rides as well.

Regards Steve