I want to try zwift but am skeptical that my kurt kinetic virtual power is skewed pretty high. i use trainer road so i dno’t really care as long as it’s consistent.
right now i use 120 psi with 3.5 turns. from what i’ve found online (not much) 5 turns at 120psi matches best with readings from a power meter.
is 5 turns the general rule?
I want to try zwift but am skeptical that my kurt kinetic virtual power is skewed pretty high. i use trainer road so i dno’t really care as long as it’s consistent.
right now i use 120 psi with 3.5 turns. from what i’ve found online (not much) 5 turns at 120psi matches best with readings from a power meter.
is 5 turns the general rule?
Depends on what you call a ‘turn’. Five full rotations of the knob, after the tire touches the roller, would pretty much squish the tire right flat. I’ve generally used five half-turns and 100 PSI and that seems to provide good friction up to at least 400W-500W kind of levels. The manual says 2 to 3 full turns, and if you can grab the tire and make it slip against the roller by giving it a sharp tug, to add half a turn.
I’ve found the published power curve to be decent (i.e. +/- 10%) relative to reference power meters. The thing with it is that this is true only if you are holding a steady speed through the pedal stroke. The inertia of the flywheel will help you when you’re slowing down but it dramatically increases the power required to speed up. Not that there’s anything wrong with that - but the power derived form the wheel speed will be smoother than what you’d get from a bike mounted power meter.
I use TR virtual power with a KK road machine. I use 110# and 2 full turns after tire contact. I recently got a P2M power meter on another bike and tested it against virtual power. I found that virtual power was 7 watts higher at all power ranges 50%-100% in 10% increments.
I wouldn’t tighten 5 full turns. I’ve managed to strip the threads on 2 of the “L” shaped bolts over the years. They would fail faster if I tightened more than 2.
I mean I’m using 120 psi with 3.5 full turns (well, 3 full and 1 half) after the tire touches.
Am I right to read that you are getting similar virtual to actual power readings with 2 turns?
Yes. Always within 7 watts which is about 3% for me.
Using turns is silly. Just jerk the wheel up and down while gradually turning the knob. Whenever it mostly stops slipping, it’s good to go. Sometimes it’ll be 2 turns. Sometimes 8. Depends on the clamp, skewer, tire brand, PSI, relative humidity, temperature, etc. This method will get you the best consistency over time.
Is that just a feel thing? Yank the wheel and when it stops slipping you’re good?
With a trainer tire, 2.5 turns and 110PSI made virtual power and my Quarq match up pretty well.
Is that just a feel thing? Yank the wheel and when it stops slipping you’re good?
Yep, you want just enough pressure on the tire for it to not slip. Best way to do this is apply a little pressure, and then move the wheel up and down as you turn the knob. You’ll know when you get it tight enough.
That’s what I always did when using virtual power. Jerk the tire and if it slipped crank it down some more. When I got a powertap I found virtual to be right around 30 watts high. A little less at lower power and a little more at higher power. So around 200 watts it was close but at 350 and above it would be off a little more than 30 by just a few watts. Very consistent power curve though.
Last yeah I trained fully on TrainerRoad + Kurt Kinetic Road Machine. My FTP based on the 20 minute test was 260 Watts. I now train with Vector pedals and while I haven’t done the same FTP test on TrainerRoad I did a MAP test with my coach on Computrainer which gave me 275. This puts my FTP somewhere around 220 if not less… I am honestly not sure how come there is such a huge discrepancy honestly.
I want to try zwift but am skeptical that my kurt kinetic virtual power is skewed pretty high. i use trainer road so i dno’t really care as long as it’s consistent.
right now i use 120 psi with 3.5 turns. from what i’ve found online (not much) 5 turns at 120psi matches best with readings from a power meter.
is 5 turns the general rule?That’s some tension you have there. As with others, I use ~110psi and ~2.5 full turns (5 half turns). I read a long time ago where someone with a power tap PM had very good correlation with the published curve using a similar setup. Supposedly doing a 20mph to 0 coast down check with a cold unit took ~ 12 sec to stop spinning, after a warm up period of ~10min the coast down check was about 14 sec. I shoot for on a ~12sec coast down check before I start.
Ya it is a lot of tension so I’m happy to hear it’s probably too high.
It’s going to vary also depending on the tire and tube you use, but I run 2.5 full turns. Virtual power matches close enough.
It’s going to vary also depending on the tire and tube you use, but I run 2.5 full turns. Virtual power matches close enough.
This is bang on. There is no, “one-way fit all” with this…its virtual power for a reason…air pressure, temp, rr, pressure by flywheel…unless you can run a test run with a 3rd party meter, then try to replicate it conditions each time is the best you will get…
Yes, this is one of those cases where consistency is what matters, and the KK will be consistent if you always use the same tire and tube, same pressure, same turns after contact. So long as you make sure the tire isn’t slipping.