Kurt Kinetic computer

Piotr

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 .

__________________
blog

wiredued

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?

__________________
Romans 5:10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. http://www.earnharts.com/html/reala...ecific.asp?id=3

Piotr

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?

__________________
blog

wiredued

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.

__________________
Romans 5:10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. http://www.earnharts.com/html/reala...ecific.asp?id=3

kant314

According to this link:
http://www.planet-x-bikes.com/triat...age&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?

__________________

wiredued

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.

__________________
Romans 5:10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. http://www.earnharts.com/html/reala...ecific.asp?id=3

phantoj

Isn't coast-down time going to be directly related to the inertia of your wheel?

wiredued

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.

__________________
Romans 5:10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. http://www.earnharts.com/html/reala...ecific.asp?id=3

frenchyge

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.

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/...eels_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.