Kurt Kinetic computer

[squidwranglr]

I opened up the old one to see if I can fix it. They use a VERY flimsy method of passing the electrical signal through to the screen. It is essentially two small rectangular pieces of foam that have conductive channels that sit on the top and bottom of the screen. They are barely glued into place and if they ever move out of place, realignment is a nightmare.

Just so you know (and assuming I'm not misunderstanding what you're describing), the compression polymer with conductive strips is a very common and industry-accepted way of passing signals from circuit boards to small LCD screens:

http://www.shinpoly.co.jp/business/connector/type_e/zebra.html

I can tell you, for example, that Polar heart rate monitor and cycling watches also use the same method. This technology has been around for decades and is very mature, so I very much doubt is the fundamental issue with the Kurt Kinetic power computer.

And, for disclosure's sake, I'm a very happy Kurt Kinetic Road Machine user of a number of years, but I don't own the power computer (I used to use a laminated power curve I prepared in Microsoft Excel using the published formulas).

Berend

 

[Ade Merckx]

Hi guys,

I'm just about to put my damn KK trainer on ebay...I've just about had enough of it.
Don't get me wrong, I love the trainer. It has a great feel to it.
It's just the bloody crapy power computer they sell with it. £25 for something that looks like it was made in China in the 70's.
I've already sent 2 back and I'm on my third now. After a few weeks of use these things just seem to begin to go wrong.
The first one I had the buttons kept sticking so that you couldn't change the display screen without resetting everything. Then it started blanking out and going back to zero in the middle of a session. The 2nd one they sent me was dead on arrival and the third one resets the tyre calibration size half way through a session and changes to km/h. That's if it makes it through a 20 min session at all.

I real really wish I'd gone for another trainer with power.

I'd heard bad things about the KK power computer before I bought it but TBH I thought it really can't be that bad.

How wrong I was.


(rant over)

Hey John I just read your blog that a shame about you needing a knee op. Are you going to see how effective your training (311wattFT) has been by doing 1 or 2 races before you go under the surgeons knife? There's lots of 4th cat and 3rd cat races comming up and its a chance to really test yourself in the real' world. With that kind of sustainable power under the hood you should be fairly comfortabe. If you give me a shout I'll even come and join you

 

[kant314]

Hi Ade,

Yes, I'd like to try a few before I go under the knife....assmuning the weather warms up a bit.
I've got a business trip to Hong Kong coming up soon though. I'll be away for a couple of weeks with that, so that means 2 more weeks training lost.

cheers
John

 

[Ade Merckx]

Hi Ade,

Yes, I'd like to try a few before I go under the knife....assmuning the weather warms up a bit.
I've got a business trip to Hong Kong coming up soon though. I'll be away for a couple of weeks with that, so that means 2 more weeks training lost.

cheers
John

Ok lets see how it worksh out, even just a 40min - 60min job at Hillingdon would be a nice psychological boost. Having ridden with the 19mph group quite a bit I'm sure your pack riding skill are ok. Have a look on http://www.britishcycling.org.uk/web/site/BC/eve/eventsfuture.asp in the south east region and let me know if you can make any of the races. If you post on the ACC site perhaps others may come along too. Anyway whatever happens keep training when you can. Its great to see you can now comfortably bang out 3 x 20's when last year you wouldn't go near a 2 x 20 with the proverbial barge pole

 

[kant314]

Hi Ade,

It's all about the mindset, I think.
When I started, I found it harder mentally rather than physically to do 20 mins on a TT.
Once you get used to the pain you kind of become accustomed to it or are better able to deal with it and see a session through..
That's my take on it , anyway.

 

[Ergoman]

I hate to discourage you all who are using the KK computer or are doing calculations or using the KK curves to determine your power...BUT, there's no way you're going to get accurate results. There are at least two reasons:

1. The KK machine itself is affected by temperature. As it warms up and cools down, power readings will vary significantly.

2. The power required to turn the KK is greatly influenced by the clamping pressure to the wheel. Further, it's very difficult to get the clamping pressure exactly the same every time you ride.

Finally, the KK computer is nothing more than a cheap speedometer and the reading it gives assumes a constant clamping pressure, a standard temperature for the trainer and no wheel slip plus and accurate calibration for wheel size. These conditions are not likely to occur with any predictability.

In general, if you want accurate power, get a real power meter. The KK computer can easily be off by 20% or more in the 200 to 300 watt range, and even more than that at lower powers.

 

[frenchyge]

I hate to discourage you all who are using the KK computer or are doing calculations or using the KK curves to determine your power...BUT, there's no way you're going to get accurate results. There are at least two reasons:

1. The KK machine itself is affected by temperature. As it warms up and cools down, power readings will vary significantly.

They do shift during the warmup and cooldown, but are actually pretty stable (as advertised) in between. See this little experiment that I did with mine: http://www.cyclingforums.com/showpost.php?p=3160616&postcount=56

2. The power required to turn the KK is greatly influenced by the clamping pressure to the wheel. Further, it's very difficult to get the clamping pressure exactly the same every time you ride.

I think the folks that are serious about using their KK computers do a coastdown test before each ride to try to standardize those factors, but you are correct. Most just seem to be looking for something cheap, yet more consistent than HR.

 

[Yojimbo_]

Here's something I found re the KK power calibration. This is a comparison against a PT power meter.

It looks surprisingly good to me.

http://www.planet-x-bikes.com/triathlon/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=189

 

[kant314]

The KK computer can easily be off by 20% or more in the 200 to 300 watt range, and even more than that at lower powers.

where do you get those figures from?

 

[Ade Merckx]

I hate to discourage you all who are using the KK computer or are doing calculations or using the KK curves to determine your power...BUT, there's no way you're going to get accurate results. There are at least two reasons:

1. The KK machine itself is affected by temperature. As it warms up and cools down, power readings will vary significantly.

2. The power required to turn the KK is greatly influenced by the clamping pressure to the wheel. Further, it's very difficult to get the clamping pressure exactly the same every time you ride.

Finally, the KK computer is nothing more than a cheap speedometer and the reading it gives assumes a constant clamping pressure, a standard temperature for the trainer and no wheel slip plus and accurate calibration for wheel size. These conditions are not likely to occur with any predictability.

In general, if you want accurate power, get a real power meter. The KK computer can easily be off by 20% or more in the 200 to 300 watt range, and even more than that at lower powers.

Hey it would be nice if you could back up some of your claims of how innaccurate KK's are. I just wanted something that would help me train with a greater deal of accuracy than HRM and 'feel' and KK does the job. I will get a powermeter one day but I can't justify one at this point...Group rides with racers have shown I'm stronger than ever and thats what I'm after so hopefully it will show in races later this year.

 

[Ergoman]

where do you get those figures from?

I've got thousands of miles on a KK, and I've used it with the KK "power meter", an Ergomo, a Polar CS600 and a PT. I've run comparisons among the power meters and temp tests and clamping pressure tests on the KK.

Bottom line: With the exception of the KK "power meter", all the real meters are relatively consistent to within a few percent across the board. What they have conclusively shown me is that the KK is a fine exercise device but that the power that it takes to turn it varies considerably with setup and temperature.

As a typical example at a room temperature of 68 degrees F and a ball park correct clamping pressure, when cold at an indicated 16mph, the KK requires a real power of about 175 watts to turn it. When warmed up, at the same speed it takes more like 155. At 19mph cold, power required is about 265 watts, warm about 230. Again, all this assumes accurate clamping pressure. Clamping pressure can cause the results to vary in the range of about 30 watts.

With too much clamping pressure and a cold KK, power could be off as much as 75 watts at 19mph, which would be an error of over 30%. I was being generous when I said 20%.

 

[phantoj]

At 19mph cold, power required is about 265 watts, warm about 230.

The calculated power from Kurt's equations is 231 W at 19mph.

Extra power to turn the cold resistance unit would explain why the beginning part of my workouts hurt so much.

 

[kant314]

thanks for that Ergoman,

that's pretty damning stuff!
For what it's worth, I bought I Trek rear wheel cycle computer the other day.
It's a Trek Incite 11i
http://www.evanscycles.com/product.jsp?style=12359
Its really nicely made and the difference between this and the KK computer is night and day.
However, one thing I've noticed is that with the exact same wheel calibration size put into the computer, the KK gives a higher speed read out compared to the Trek computer.
Up to about 10mph they are pretty similar, but when you get to around 15mph the KK comp is about 0.3 mph faster than the Trek which is about 7 watts or so at that speed.
However one you get to over 20mph the discrepancy is over 10watts.
Now I don't know which computer is right, if any of them are, but just going by looks and build quality alone, I would plump for the Trek.
But who knows.

 

[daveryanwyoming]

...Extra power to turn the cold resistance unit would explain why the beginning part of my workouts hurt so much.

It could, as could the very normal warming up many folks find they need when doing long SST/L4 intervals during training. Even after a moderate warmup a lot of folks(myself included) find it's a good idea to ramp into L4 efforts a bit below target power and then ramp the power up after five to ten minutes. I get my best 20 and 30 minute power numbers using this approach even after warming up. That approach works best whether I'm riding indoors or out and when I try to hit my target power right from the start I tend to hurt a lot more in the early going until my legs have opened up.

That's different than a full out time trial where I'll get forty to fifty minutes of warmup including some short L4 and L5 efforts prior to lining up for the start. In that case I'll go out very close to my target power but still try to err on the low side.

YMMV,
-Dave

 

[frenchyge]

that's pretty damning stuff!

Really? Don't most people spin an easy gear for a few minutes at the start of a trainer ride before really worrying about their power output anyway?

My typical 10-min warmup (~60% FTP) with a couple high-cadence spin ups is more than enough to get the KK trainer warmed up and into the 'accurate* range' for the computer.

* assuming you've taken some measures to ensure consistent rolling resistance.

For what it's worth, I bought I Trek rear wheel cycle computer the other day.

FWIW, all those damning problems that Ergoman mentioned will still be issues with your new computer.

 

[wiredued]

Polar power meters on indoor trainers have issues and Ergomos have issues indoors and out. I believe the Powertap results but does any one actually workout cold without a warm up? If coast down is 13.4 seconds from 20mph and the KKR is warmed up isn't it fairly accurate?

I've got thousands of miles on a KK, and I've used it with the KK "power meter", an Ergomo, a Polar CS600 and a PT. I've run comparisons among the power meters and temp tests and clamping pressure tests on the KK.

Bottom line: With the exception of the KK "power meter", all the real meters are relatively consistent to within a few percent across the board. What they have conclusively shown me is that the KK is a fine exercise device but that the power that it takes to turn it varies considerably with setup and temperature.

As a typical example at a room temperature of 68 degrees F and a ball park correct clamping pressure, when cold at an indicated 16mph, the KK requires a real power of about 175 watts to turn it. When warmed up, at the same speed it takes more like 155. At 19mph cold, power required is about 265 watts, warm about 230. Again, all this assumes accurate clamping pressure. Clamping pressure can cause the results to vary in the range of about 30 watts.

With too much clamping pressure and a cold KK, power could be off as much as 75 watts at 19mph, which would be an error of over 30%. I was being generous when I said 20%.

 

[phantoj]

FWIW, all those damning problems that Ergoman mentioned will still be issues with your new computer.

The biggest issues I see with using power from a KK are (in decreasing order of importance):

1. There is a published calibration curve for a KK trainer. But you have no way of knowing how closely your KK trainer follows this calibration curve, unless you test it yourself. How do you know your trainer didn't get overfilled by 10% or it ended up with a slightly less efficient impeller shape due to manufacturing tolerances? Self-calibration is not a bad idea if you know someone with a power meter.

2. Rolling resistance issues, primarily clamping force against the rear wheel, but tire selection and pressure also probably affect things.

3. Temperature effects are unknown. How long does the KK take to warm up? Once warmed up, it it stable, or will resistance drift downwards during an extended effort (sure doesn't feel like it does). Does resistance rise again between intervals?

 

[frenchyge]

The biggest issues I see with using power from a KK are (in decreasing order of importance):

1. There is a published calibration curve for a KK trainer. But you have no way of knowing how closely your KK trainer follows this calibration curve, unless you test it yourself. How do you know your trainer didn't get overfilled by 10% or it ended up with a slightly less efficient impeller shape due to manufacturing tolerances? Self-calibration is not a bad idea if you know someone with a power meter.

IMO, the fact that they actually publish an equation, rather than a vague power chart (like other manufacturers) actually gives me more comfort that quality assurance steps are taken to promote consistency between units. Plus, the fact that they tuned their resistance unit design to match the power generated by a road model would be pretty much a waste of time if they didn't then try to make sure individual units conformed to the design.

Edit: actually, in reading the website, it looks like they pulled the equation from empirical test data from a group of production units, rather than trying to manufacture units to a design equation -- even better.

2. Rolling resistance issues, primarily clamping force against the rear wheel, but tire selection and pressure also probably affect things.

Yep. Not a KK issue, however, and completely user-controlled. It's a valid criticism only because of the extra steps that KK has undergone to make their units consistent, and the additional user expectations associated with having a power equation (vs. chart). It's understandable, though, since they do set the expectation that their power computer will be usably accurate. I'd move this one to #1 if users aren't taking steps to ensure consistency.

3. Temperature effects are unknown. How long does the KK take to warm up? Once warmed up, it it stable, or will resistance drift downwards during an extended effort (sure doesn't feel like it does). Does resistance rise again between intervals?

Believe I covered that one in post #27, above.

Edit: if anyone is getting the feeling that maybe this has been discussed before, you might check out this thread: http://www.cyclingforums.com/showthread.php?t=380967

 

[kant314]

FWIW, all those damning problems that Ergoman mentioned will still be issues with your new computer.

Yes , I know.
I only mentioned it to add weight behind the doubts surounding the veracity of the KK power data.

 

[frenchyge]

I only mentioned it to add weight behind the doubts surounding the veracity of the KK power data.

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.