Kurt Kinetic computer
- Thread starter kant314
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Simply because I'm on my third KK computer since November and all have broken and proven completely unreliable.frenchyge said:Ok, but I think the doubt surrounds the method of using rear wheel speed to *calculate* power in general. That's why I'm not sure why you would abandon the flimsy KK computer for a beefier model which uses the same dubious methodology.
At least with a better computer I can get a consistent idea of how much I'm improving, even though I don't know the exact numbers in terms of wattage.
What's the alternative? Buy/rent a powertap? I don't really want to buy a cycle accesory that's worth more than my bike. .
For those who have KK Power Computers, how does it calculate the "average wattage"? Is it really just taking your average speed and calculating the power required to hold that speed? That would be a weak method that would underestimate average power.kant314 said:
Or does it track total energy expenditure and divide that by total time?
I am reposting the information I provided earlier, since judging from the discussion in this thread it looks like no-one has bothered to read it.
http://www.planet-x-bikes.com/triathlon/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=189
This link is a comparison between the KK computer output in Watts and a PT SL hub. The guy describes his methodology, presents results, and discusses uncertainties. The comparison looks damn good to me, and there is no way it's off 20 or 30 percent.
Don't you people warm up anyways before you start intervals?
http://www.planet-x-bikes.com/triathlon/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=189
This link is a comparison between the KK computer output in Watts and a PT SL hub. The guy describes his methodology, presents results, and discusses uncertainties. The comparison looks damn good to me, and there is no way it's off 20 or 30 percent.
Don't you people warm up anyways before you start intervals?
Has anyone else noticed how the KK gets suddenly noisier around 2.5 - 3 min into warmup (@100-130W)? I wonder what the explanation for that is? I also wonder if I'm the only rider who listens to the white noise from the KK road machine instead of loud musicphantoj said:
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Haven't noticed the noise change but there are times when I ride without music I will try to pay more attention...I do notice slight vibration as I pass through 12mph but not at any other speed although I've never gone higher than 37.8mph on the thing have you noticed that?... Has any one taken a KKR higher than 38mph besides Lucy?
Piotr said:Has anyone else noticed how the KK gets suddenly noisier around 2.5 - 3 min into warmup (@100-130W)? I wonder what the explanation for that is? I also wonder if I'm the only rider who listens to the white noise from the KK road machine instead of loud music
That's strange. The noise picks up suddenly as if some kind of turbo charger kicked in every time without fail around 3 min.wiredued said:Haven't noticed the noise change but there are times when I ride without music I will try to pay more attention...I do notice slight vibration as I pass through 12mph but not at any other speed although I've never gone higher than 37.8mph on the thing have you noticed that?... Has any one taken a KKR higher than 38mph besides Lucy?
I don't do sprints indoors, but my question would be did the KKR go 37.8 mph or just your rear wheel?
It may have slipped a little as I accelerated between 24 and 30mph but no slippage after that I had it clamped down pretty good for the sprint. I don't sprint very often or do any structured sprint workouts yet because it causes knee problems for me.
Piotr said:That's strange. The noise picks up suddenly as if some kind of turbo charger kicked in every time without fail around 3 min.
I don't do sprints indoors, but my question would be did the KKR go 37.8 mph or just your rear wheel?
According to this link:
http://www.planet-x-bikes.com/triathlon/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=189
the clamp pressure is crucial to getting accurate power readings from the KK comp.
I'm not sure I fully understand why that is.
I mean, shouldn't it be the case that as long as there is no tyre slippage, the power results should be the same.
The force on the roller from the clamped tyre is vertically downward on the roller whereas the force required to move the roller is horizontal at the point of contact of the tyre. IE at 90 deg to the clamping force. So the two forces, since they are perpendicular to each other, shouldn't affect each other.
Any thoughts on this?
http://www.planet-x-bikes.com/triathlon/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=189
the clamp pressure is crucial to getting accurate power readings from the KK comp.
I'm not sure I fully understand why that is.
I mean, shouldn't it be the case that as long as there is no tyre slippage, the power results should be the same.
The force on the roller from the clamped tyre is vertically downward on the roller whereas the force required to move the roller is horizontal at the point of contact of the tyre. IE at 90 deg to the clamping force. So the two forces, since they are perpendicular to each other, shouldn't affect each other.
Any thoughts on this?
The more you squish the tire the more resistance you will have it doesn't make a big difference but if you want to be as accurate as you can get on the cheap then coast down should be about 13.4 seconds from 20mph. I usually don't do a coast down test I just adjust the tension so the tire won't slip during my workout a few watts one way or another doesn't matter much to me.
kant314 said:
If you are talking about the difference between a 32 spoker and a 36 spoker you are looking for a higher level of accuracy. If you have an SRM and some different wheels you could know for sure what the difference between wheels is... As long as you use the same bike and set up procedure on your KKR you can do repeatable SST and L5 workouts and see improvement in FTP without a big investment. If you want more accurate numbers then you need to spend more money on a powertap or SRM.
phantoj said:
Tire rolling resistance can vary in the neighborhood of ~25w depending on the speed, type of tire, inflation pressure, and clamping pressure. When you squish the tire with that small-diameter, round, resistance wheel the effect is exaggerated compared to a flat road surface.kant314 said:
Yes the forces are perpendicular and the other stuff you said, but there's a lot more involved. Learn more with this *excellent* article by poster Tom Anhalt: http://slowtwitch.com/mainheadings/techctr/wheels_tires.html . Tom, can't wait to see part 2.
It's related to the combined inertia and friction of the entire rolling system. Since the KK road machine's flywheel is 6lb and spins much faster than the lighter bicycle wheel, it dominates the inertia portion, and the friction is what you're trying to match between different setups or runs. I think the person briefly mentioned something to that effect in the writeup, but the effect of a few hundred grams difference in the wheel won't make a noticeable difference.phantoj said:
