Team BKool CycleChat

[JLaw]

Jeff, if you fancy joining in tomorrow (Tuesday) from 8pm GMT (UTC) then you could just start alongside Whorty at 2 mins underway and see how you get on.

Geoff (spelled the correct way!)

Will try to -- it hits right in the middle of my workday, coinciding with the end of a meeting that always seems to run long... Sounds like a hell of a good time...

 

[BILL S]

How do you know this Bill? Just through feeling that the resistance doesn't change above 10% or do you have a more technical way of knowing? I've never really thought about it as I'm usually too busy just trying to breathe at inclines more than 10% to do anything else!

As LB says, done loads of steep rides, but also I run fairly high gearing at 11-25 and at 10 percent I need to be in first gear and have no further gears to change down after that. The high gearing is great though because none of my 11 speeds are wasted. Anyone able to make a steady 300 watts or so who hasn't tried an 11-25 on a compact should consider trying it.

 

[LBHIFI]

WARNING: layman struggling to remember A level physics spouting half understood concepts...

The more I look into this, the more factors are involved in the physics of the electro-magnetic brakes used in trainers like the bkool and KICKR, etc. and hence the more variables that are involved in what can be simulated. It's not like in the real world, where the major factors are gravity and aerodynamic drag, which have no practical limits to their predictable effects.

Maximum resistance is not "directly" related to weight, but to simulate a gradient for a given weight you would need a greater resistance for a greater weight, so maximum gradient is "indirectly" related to weight.

You would expect it should also be related to speed, in as much as the faster you can cycle at a given gradient, the sooner you will reach the maximum resistance, since the force you are producing is greater and therefore requires a greater resisting force. However, the physics imply this cannot be an entirely linear relationship...

In an electromagnetic trainer the resistance is created using circular eddy currents induced in a rotating metal disc by magnetic fields and these eddy currents are related to speed, so at slow speeds you get much lower resistance (as pointed out by AAAC and hence the on/off technique). As you increase speed the resistance increases, but at some point the resistance will then then reach a practical maximum and cannot increase any further.



If you cycle very slowly, you get less resistance, but if you cycle very quickly you will reach a point where you can get no more resistance for a given system of magnets and conductor.

But if you are cycling slowly you are by definition getting less resistance, even when the electromagnets are on full, so you will have a lower maximum resistance than if you cycle quicker, until you reach the maximum resistance of the whole system, i.e. the eddy currents generated can produce no more resisting magnetic forces and dissipate no more heat.

So cycling slower will give a lower maximum resistance, but cycling faster can reach the maximum resistance of the whole system.

Weight is a bit easier to predict, as being heavier should always reduce the gradients at which these maximum resistances are met.

There must be a range of gradients for each weight that can be simulated over a range of speeds, but above or below those speeds the resistance will reach a limit or begin to fall off.

A heavy/powerful rider will reach maximum resistance sooner than a lighter/less powerful rider, but a slower rider will have a lower maximum resistance, therefore the simulation will only be accurate between both a minimum and a maximum speed for each given riders weight and power.

Edit: This implies that a heavy slow rider will have a lower maximum gradient than a light fast rider, which seems to fit reported observations here.

This makes it hard to get a one size fits all rule for how steep a gradient can be simulated by a given trainer, as it depends on weight and speed/power, but also temperature (and humidity), airflow (for cooling), not to mention the usual manufacturing tolerances (and undoubtedly other factors not considered)!

The systems are limited by the maximum strength of the electromagnets, the size and magnetic properties of the metal disc, the maximum speed of the disc that the rider can maintain and the maximum heat the system can dissipate in the given environment. Since the energy is dissipated as heat, beyond a certain level the heat can no longer be dissipated and this will limit the energy and hence the resisting force.

Finally, an electromagnetic trainer with a larger rotating disk and/or stronger electromagnets should be able to produce larger resisting forces and hence simulate greater gradients, all else being equal.

These capabilities always tend to be quoted in Power but since power is force times velocity (when force and velocity are constant) this is misleading as it depends on velocity.

Where these capabilities are quoted as a maximum gradient, these are doubly misleading, as it also depends indirectly on rider weight.

So unless the maximum resistance is quoted in Newtons and the maximum gradient is for a specified weight (and speed) then take them with a pinch of salt.

However, I think it is safe to assume that a trainer with a higher quoted maximum power will be able to simulate a higher gradient for a given rider, unless they employ much more misleading marketing staff...

Geoff

But what I'm wondering is how much of the resistance is self generated and how much is applied by external power. If it relies on self generated power to apply the higher resistance, then the only thing they can do to counter the on/off effect, would be what Zwift apparently have done: use calculate speed in the initial stages of a sprint and then slowly letting it rise as the resistance kicks in and then eventually use the actual speed.

 

[Randyberlin]

I'm getting the same max as Bill: 10-11 %. Bill and I have done plenty of crazy slopes in the UK 100 climb league to have reached this conclusion.

As LB says, done loads of steep rides, but also I run fairly high gearing at 11-25 and at 10 percent I need to be in first gear and have no further gears to change down after that. The high gearing is great though because none of my 11 speeds are wasted. Anyone able to make a steady 300 watts or so who hasn't tried an 11-25 on a compact should consider trying it.

Does your speed turn blue on climbs?

 

[gbrown]

Ditto
That puts me in the heavy slow category too as it only simulates up to 10 percent for me

Ah, but because you go faster, even though you can generate a higher resistance, you need a higher resistance to resist your power and so exceed that resistance...

...I think!

 

[BILL S]

Does your speed turn blue on climbs?

I don't know TBH. I'm going to have to have a look tonight.

 

[bobinski]

So, is the test the to set up an incline ftp test were the gradient slopes gradually from 2% up to say 15% and see what happens?

 

[LBHIFI]

But what I'm wondering is how much of the resistance is self generated and how much is applied by external power. If it relies on self generated power to apply the higher resistance, then the only thing they can do to counter the on/off effect, would be what Zwift apparently have done: use calculate speed in the initial stages of a sprint and then slowly letting it rise as the resistance kicks in and then eventually use the actual speed.

Actually, now that I think about it, It must have the ability to generate enough power purely driven by the external power. A few times I have been caught in a big gear on a steep hill, and it was virtually impossible to pedal. Cadence must had been something like 10.

 

[BILL S]

Looks like we have a new contender for first spot in the Mountain Goat League

The Stig 50+ has just taken first place in the Ovaro Zoncolan stage and at the same time moved up to Pro1 level.

Well done The Stig . Excellent work

And I almost forgot the massive kudos for not bailing after 30 minutes. I know I would've.

 

[Goldwolfie]

OK, I suggest we go for an 8PM start on Tuesday, as it seems to suit more people and gives an alternative to the 7PM starts on Thursdays. Let's see if the slightly later start is popular?

See you all on Tuesday. I'll start the warm up at 7:50 pm, hopefully TheBoxers can join me, and I'll update the Handicap thread with the start times and post a reminder here.

Should all be done before 9PM...

Geoff

Geoff - I was just checking to see if my Saturday ride had appeared on Bkool, and noticed that the Handicap League Stage session expired yesterday - will that impact tomorrow's live ride.

I'm starting to think my result is lost in the Cloud somewhere, which is a pity as I wanted to check the old heart rate, as i think I was probably a bit close to my suggested sustained limit. (220 - age=156). I'll keep a closer eye on that tomorrow night.

 

[RickB]

....lots of stuff.....

Just what I was thinking...

...... only simulates up to 10 percent for me

I'm getting the same max as Bill: 10-11 %. .

I agree with Bill and Lars

Even though I weigh more I dont see any difference from somewhere between 10-11% - just did a mountain goat stage there and definitely doesnt feel any different past 11% - like Bill I'm in my lowest gear so I'd feel it if it got harder (though my smallest is 26 tooth on a 9 speed cassette with a compact chainset.)

 

[LBHIFI]

Does your speed turn blue on climbs?

Only when the gradient is > 11 % and not the way one would imagine: the speed slowly decrease from my initial value when hitting it. E.g. if I was doing 25 mph on a flat section and hit a 12% slope, my speed would slowly decrease from 25 mph downto ?. In real life It would of course be more like hitting a brick wall.

 

[Add]

OMG, just logged on, and you're all talking gibberish! I thought I was going to have to use a translator.
I just about got my head round Geoff's 'brief' version, although even that was an effort.
I might go and play Candy Crush for a bit until the conversation swings back round to something I can relate to....like lighting farts.

 

[RickB]

New Chaingang league will be up and running this week in time for the Thursday Race

You can check out the new stages here: http://www.bkool.com/league/showFutureLeagues/72022

Nothing too frightening I think! Nice straightforward 10 mile Time Trial for stage 2 which could well be the next Handicap stage.

 

[AAAC 76C]

Only when the gradient is > 11 % and not the way one would imagine: the speed slowly decrease from my initial value when hitting it. E.g. if I was doing 25 mph on a flat section and hit a 12% slope, my speed would slowly decrease from 25 mph downto ?. In real life It would of course be more like hitting a brick wall.

Got you all thinking!.

One of my points is that a few weeks ago I was climbing the Mortirolo and there were some bazaar 25%+ gradients in it.
I was on my, as then, unmodified Classic.
I was bought to a stand up 4 kph grind on these slopes and an individual (ghost) by the name of Bills flew past me at a rate of knots.
The ride would have taken me over an hour but the leauge leaders time was about 30 minutes or less.
I would have been on a 34/29 standing up and the trainer was pushing back big time.
I have now modified my Classic by fitting a Pro PCB and Stepper motor with magnets.
I only changed the stepper motor because that was what was proably used when the, as was, Pro unit was calibrated in the factory, whatever they do to do that, so the only difference between my 'Hybrid' and anyones elses Pro Unit, bar the frame, is the Flywheel.
The Classic flywheel was better made but other than its weight the only differnce there could be that would have an impacct is the conductivity of the ring that is fitted to the flywheel in which the eddy currents are created and I can't really see that they should be any different.
Breaking News, this disc is bonded to the flywheel on the Pro and if the bonding goes it sounds like your flywheel is not balanced.
I wont get onto heat dissipation as the bulkier flywheel would probably win there as well and hence improve the max resistance.
So now with my, what I can rightly call a Pro, Turbo the max slope resistance has been limited but not physically probably more to do with the SW/FW programmes saying we are not going to bother going above (lets say)11% anymore so whatever the rider does simulate the (lets say) 11% resistance untill such time the slope reduces below that level.

Boblinski's point about making a stepped slope session is exaclty what I proposed to do.

However go look at the Goats top ten Zoncolan stats and see how similar eveyones speed graphs are because they are all literally flat and we all know how many slope changes there were that went above 11% so I kind of rest my case, the only question is where is the limit.

I do get Geoffs point about the limitation of the magnetic brake but the flywheel spins pretty fast even at a slow road speed due the circumferance of the roller being only 10cm
Therefore to cover 1km/1000m/100 000cm it has to rotate 10 000 times
Therefore at 1kph it spins at 10 000/60 rpm = 166rpm.
No one rides a bike much slower than 4kph (apart from Whorty) because is becomes more efficient to walk
At 4 kph the flywheel is spining at 664rpm
And at 6kph 1000rpm.
And to add to that the effective circumferance of the flywheel as a 'brake' is about 50cm, 5 times that of the roller so when you're doing 6kph there relative speed of the disc to the magnets is 30kph or 8.3333 meters per second/27 feet per second.

Lets hope one does come adrift as it could shoot of like a rocket