Uphill resistance explained


Maybe it has already been discussed somewhere else, but I haven’t been able to find the best answer yet. I have read about the theory that resistance during a climb also depends on the weight of a person. But can somebody tell me what the difference is in ‘User Experience’, between cycling on a smart trainer with 10% (like Tacx Flux S) or and 16% (like Kickr Core)? Because a trainer like the Tacx Flux S, with a maximum power output of 1500 Watt, should be able to give me a lot more resistance then a max of 10%? In other words, if I go uphill in Zwift, the trainer should be able to give a resistance (for example about 500W), that can be compared with about 15%

So what I really want to know is how it affects my user experience. I hope somebody can help me to explain this, it would be appreciated!!!

Max wattages are achieved at a rated speed…25 mph or so…so it will be difficult to reach max wattage on a 10%+ slope…

All trainers have a “Window” where everything is accurate but only one major provides that diagram. I forget who but it is a recent review on DCRAINMAKER and Ray also gives a pretty good explanation of how it works. I cannot remember which trainer but work backwards and you will come across it.

For me, I went from a Snap (1500 watts/10%) to an H3 (something like 2000 watts/20%) and all those 10%+ hills suddenly got a lot harder. I am a bigger fellow, 103kg or so, and riding some of the hills hurt a lot more…Subway Stairs, Richmond, etc…

Hope this helps.

Since Zwift by default halves the incline and that there are no inclines greater than 14-15% in any current Zwift world the ability to simulate a 10% grade is more than enough.

I guess you could be a glutton for punishment and ride at 100% to truly experience the joys of riding 19KMs at an average of 9% grade. :smirk:

Ah, but there are. Not very long, granted. The Radio Tower for example, hits about 18% just after the bend halfway up. The New York KOM hits 19% IIRC.


Since Zwift by default halves the incline…

Zwift doesn’t half the incline (uphill), but rather the decline (downhill), I’m fairly certain.

and that there are no inclines greater than 14-15% in any current Zwift world…

To add to what @Daren said, there are short bits in Richmond over 20%.

Im assuming they meant the default Trainer Difficulty is 50% unless you change it, ergo the halves the incline line.

1 Like

OK. Aside from a few very short segments there are no actual climbs above what I said.

Also as D Watson said the trainer difficulty slider “flattens” the incline/decline.

I was misinterpreting the comment that “Zwift halves the incline by default.” Note that with trainer difficulty set to max, Zwift simulates the stated virtual incline (so long as the trainer can simulate the value), but halves the stated virtual decline (i.e. a stated 10% downhill only acts like it’s 5%). I thought you were talking about this universal feature of Zwift, and not the particular feature of trainers being set to 50% by default.

Isn’t that more to do with going from a wheel-on trainer to direct drive? Because according to the article at https://zwiftinsider.com/how-much-trainer-resistance-do-you-really-need/ a 15% gradient only needs to provide 887W of resistance for a 100kg rider at 20km/h. So your Snap shouldn’t have had a wattage shortage there, even with Trainer Difficulty set to 100%.

All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?

1 Like

My Snap is first generation and limited to 10% gradient and would hit a max difficulty on higher grades. So the tower road would feel like a 10% gradient even though it goes up to 18% or whatever. With the H3 I can definitely feel the increased slopes.

I will let you know when I can hit 900W and 20KPH going up a 15% grade…not happening soon unless I hit a very short segment (<50M)… Though come to think of it the subway stairs might be a good place…I am usually trashed from whatever climb I did previously (usually Box Hill) to give a good effort.

1 Like

And WTF is that supposed to mean?

Never mind.

1 Like

Classic Monty Python.