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Gradient Simulation

Old 09-27-21, 09:18 PM
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Arbaaz11
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Gradient Simulation

Hi everyone,

Hope you are doing well and staying safe.

I have a Wahoo Kickr Core which can simulate gradients up to 16% and I am using it with Rouvy which is always at 100% in TT mode. My bike is a Specialized Tarmac SL6 with 11sp - 11-28T on the trainer.

I have been training on a local mountain indoor - however I note that the incline of the mountain at some points are above 25%. Given that the Kickr Core simulates only up to 16% - I am wondering whether I could use my gears to add the additional 9%.

So - in my mind - it works like the below examples:
  • on gradients of 11% - the Kickr Core will simulate 11% at 100% using Rouvy TT Mode - so when I am on my easiest gear - 34T & 28T - I am getting 11% of incline simulation
  • on gradients of 16% - the Kickr Core will simulate 16% at 100% using Rouvy TT Mode - so when I am on my easiest gear - 34T & 28T - I am getting 16% of incline simulation
However,
  • on gradients of 25% - the Kickr Core will only simulate 16% at 100% using Rouvy TT Mode - so when I am on my easiest gear - 34T & 28T - I am only getting 16% of incline simulation
What happens if I am on a gradient of 25% - I change gear to 34T & 25T - would this add to the 16% simulated by the Kickr Core?

If yes then how much more gradient would I add on the 16% gradient simulated by the Kickr Core just by shifting to 25T?

If I shift to the hardest gear - 11T - would that simulate even more gradient on top of the 16% by the Kickr Core? Is there a way to know how much more gradient it will add?

If my understanding is wrong - can you guys please explain why?

Thank you
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Old 09-28-21, 07:25 AM
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spelger
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i read this last night and it hurt my head. i don't think it works that way. when on the road having easier gears (larger cogs) makes the climb easier. that same grade with harder gears (smaller cogs) just makes that same gradient harder. the same would be true with a simulated grade. shifting to an 11 tooth cog will just make the 16% grade harder to ride. but if harder is what you want then do it.
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Old 09-28-21, 08:24 AM
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unterhausen
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I have never seen the maximum power a trainer can take expressed as a gradient before, but that's what I think they are doing. If I'm right, then it won't matter what gear you are in. But now I'm having doubts about this interpretation.
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Old 09-28-21, 10:03 AM
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The mechanical resistance will stay the same regardless as that is fixed by the trainer, using a bigger gear means that you will have to use more power to rotate at the same cadence, but will increase your speed as a result.
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Old 09-28-21, 10:07 AM
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spelger
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Originally Posted by unterhausen View Post
I have never seen the maximum power a trainer can take expressed as a gradient before, but that's what I think they are doing. If I'm right, then it won't matter what gear you are in. But now I'm having doubts about this interpretation.
most smart trainers i have seen express gradient as a specification. my kicker claims a max simulated gradient of 20%. this is a typical parameter supported by the ANT+ FEC standard.
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Old 09-28-21, 08:49 PM
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Arbaaz11
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Ok maybe I should have mentioned in terms of how hard it feels not taking into consideration speed and cadence. But purely on how hard it becomes to even turn the pedals.
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Old 09-30-21, 07:33 PM
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pennpaul
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Rouvy user with a Core here, too.

If you ride the route in Training mode rather than TT, in settings you can adjust the Reality level up to 150%. Theoretically, the Core would then simulate up to a 24% gradient by applying more resistance. I don't know if you can vary the reality level during a ride, but I think you can. If so, when the gradient is <=16%, set it back to 100%.
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Old 10-01-21, 08:47 AM
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A 25% climb at 250 watts is going to feel the exact same as a 16% grade at 250 watts. The gear doesn't matter. The only variable will be your speed. You're still applying the same power to the pedals (250 watts) in both situations, you're just going slower on the steeper climb.

On a trainer, we don't have factors like the angle of the bike, available traction, or the difficulty of balancing at slower speeds. So the only difference is power vs speed. A 25% grade will only feel harder than a 16% grade because you either have to go slower (so it takes longer to cover the same distance) or you have to ride at a higher power output to maintain that same speed. If speed and cadence aren't a factor to you, then gradient is also irrelevant.

To get an idea of "how hard", you can calculate how much power you need to ride a 16% or 25% climb at a specific speed (Bike Calculator):
  • A 160lb rider on a 20lb bike will need 250watts to ride a 16% climb at 4mph. A 5 mile climb at 16% using 250 watts of power output would take 75 minutes.
  • That same rider on a 25% climb would either need to slow their speed down to 2.6mph at 250 watts, or increase their power to 385 watts to maintain 4mph. A 5 mile climb at 25% using 250 watts of power output would take 115 minutes, or it would take 75 minutes if you could maintain 385 watts.

Last edited by msu2001la; 10-01-21 at 09:02 AM.
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Old 10-03-21, 09:40 PM
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Arbaaz11
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Oh I see now. Makes sense. Although one question, 250 watts on flat and 250 watts on a 16% climb does not feel the same though. Well obviously though because on a flat I have a much higher cadence to produce 250 watts compared to the cadence on the climb. Maybe that's the difference i'm feeling. Having a restricted cadence and producing the same level of power makes me feel like i'm getting more tired and doing harder work. But in reality i'm producing the same amount of power. I understand now. Thanks.
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Old 10-03-21, 09:54 PM
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Originally Posted by msu2001la View Post
A 25% climb at 250 watts is going to feel the exact same as a 16% grade at 250 watts. The gear doesn't matter.
I would argue the gear can matter, if your doesn't have the available gears to ride at the desired cadence. At the same power (e.g. 250W), grinding up a climb at 50-60rpm is going to be different from spinning up at 80-100rpm.
But assuming that's not true, then yeah 250w is 250w (at the same cadence) regardless of gradient.
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Old 10-04-21, 04:52 PM
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I'm no mathematician but I think I see where you're coming from. When I first started Zwifting, I just used a dumb wheel on trainer with a speed and cadence sensor. My system would talk with Zwift and let me ride along but it wouldn't simulate grade, drafting, etc... so when I used to ride up hills, I would change to the harder gears to get that real life feeling. Clearly it made no sense if you were trying to simulate real training numbers but it worked for me.

Are you sure you have the Rouvy settings and trainer set so that you can maximize the simulation of climbing at 16% grade? I don't ride Rouvy, but when I'm on Zwift climbing Alpe De Zwift on my wheel on smart trainer which only simulates 10% I believe, and the effort settings only at the mid mark, I am giving er.
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Old 10-11-21, 04:12 AM
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Yes my trainer is set at 100% therefore I am getting the full effect of the 16% and I can feel it.

But my local mountain - it is THE mountain for me - my most formidable opponent lol - it has a few sections of 25% +. And I wanted to know how I could prepare myself for that using the trainer.

Unfortunately it is not always opened to cyclist else I would go out and train on it. I don't know other places I could go with my road bike having the same kinda 25%+ gradients.
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Old 10-11-21, 05:45 AM
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There are several 25 % grade routes on Rouvy.

https://my.rouvy.com/virtual-routes/detail/55271

https://my.rouvy.com/virtual-routes/detail/36054

https://my.rouvy.com/virtual-routes/detail/45152

Of coarse can your smart trainer simulate a 25%
grade. You could also video your route and record the ride and upload it to Rouvy.
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Old 10-12-21, 01:53 AM
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I realize no one has directly answered the OP's question yet and while I can't give the exact answer that the OP needs, but for what it's worth:

If my understanding is wrong - can you guys please explain why?
No, you're not wrong, but I don't have the math to help determine the gear you need to simulate the harder gradient. My guess (and emphasis guess) is that it will be proportional to the difference in grade. So an increase from 16% to 25% grade is a +56% increment, so I imagine you might need a 56% increase in gear inches to match the difficulty? Which could mean from 34/28 to something around 34/18, assuming standard 700x25c tires.

However, there are two caveats:

1) The assumption only works in simulation mode (e.g. where the resistance of the trainer simulates the gradient of the terrain) and at 100% emulation; it won't apply in ERG mode (where the resistance of the trainer varies according to your cadence in order to hit a target power).

2) Besides maximum grade emulation, trainers also have some sort of maximum power rating. Which means at some point, when it's at the maximum (e.g. 16%) emulation, and if you're theoretically strong enough to hammer the thing at 50/11 at 90rpm, then at some point the trainer is going to hit a limit and is no longer able to resist the amount of power you're putting out.

On point #2, I think technically this would actually be better represented as a maximum torque rating, but I'm not sure if any trainers actually publish this so we'll just have to live with their standard "max wattage and max grade" ratings.

Last edited by atwl77; 10-12-21 at 02:13 AM.
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Old 10-12-21, 08:34 AM
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Use a higher wattage to simulate the steepest parts. It's proportional to the grade at the slower climbing speeds. So: if you can maintain 250 watts on a 16% grade: for 25%, try (25%/16%) = 1.56*250w = 390 watts. On the real hill, you'd be in your lowest gear, at a slow speed. On the trainer, I'm guessing you'll see a faster mph if the grade limit is 16%, for example, so the cadence won't quite match with the real climb. I don't know how the trainers work: can you program a 250w resistance, a short 400 watt resistance, then another 250w for the rest of the climb's estimated elapsed time, instead of using the grade% settings? Oh, I like that plan.

There's going to be a time limit on how long you can maintain the higher wattage if the 250 watts number is your full hill power. The same as on a real hill with a short, steep pitch for part of the climb. (and my example watts sounds correct to me: 250w at 16% would be near 400w on that extreme 25% to maintain enough speed to not fall over.)

(The reason that cyclists stall out on steep grades is that they can't ride slow enough to stay under their maximum power. With a trike, they could just slow way down and handle the extreme grades, assuming they have somewhat reasonable gearing.)

Last edited by rm -rf; 10-12-21 at 08:49 AM.
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