Accuracy of Cyclosport HAC 4



sjonz3

New Member
May 3, 2003
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I was wondering if anyone has experience using a cyclosport HAC4 computer. How accurate are they in comparison to the other products on the market?

thanks
sean jones
CA, USA
 
I've got a HAC4 and I do keep a record of its power measurements. I can't say how accurate it is, but I wouldn't count on it too much. I think it is good as a relative measure in comparing different rides, however. So if you've got multiple rides with the roughly the same duration but different average power measurements, you can get a good sense of the relative difficulties of the rides.

One sanity check suggests that the HAC4 might be at least in the right ballpark. Yesterday I rode 24.7 miles (fairly hilly terrain) in 1:23:16. HAC4 said average power of 138 W. If I use the commonly reported 0.95 efficiency of a bicycle and 0.24 efficiency of human muscles, that converts to 722 (dietary) calories. The bike_power program calculates 804 calories for the ride (not accounting for any hills). So, the two numbers are within about 10% of each other, which, considering all the approximations and estimates that go into the various formulae, has to be about the best one could expect.

Stephen
 
Originally posted by sjonz3
I was wondering if anyone has experience using a cyclosport HAC4 computer. How accurate are they in comparison to the other products on the market?

thanks
sean jones
CA, USA

Because the sum of all the resistive forces that you must overcome are related to both your size (e.g., frontal area), your bike equipment (aerodynamic drag), the intensity which you're riding and friction and rolling resistances, etc. it's impossible for the HAC4 to estimate these accurately, especially when cycling on level ground. up a steep hill where speed (and thus drag) are very low it becomes somewhat easier to account for these resistive forces. Therefore, the HAC 4 is unlikely to be accurate, especially while cycling on level, rolling roads.

Ric
 
Originally posted by ricstern
Because the sum of all the resistive forces that you must overcome are related to both your size (e.g., frontal area), your bike equipment (aerodynamic drag), the intensity which you're riding and friction and rolling resistances, etc. it's impossible for the HAC4 to estimate these accurately, especially when cycling on level ground. up a steep hill where speed (and thus drag) are very low it becomes somewhat easier to account for these resistive forces. Therefore, the HAC 4 is unlikely to be accurate, especially while cycling on level, rolling roads.

Ric

Has anyone made a direct comparison between the power measurement of the HAC4 when compared to the system used by the Polar s720i which is theoretically and reputedly more accurate?

I had both hrm/cyclecomputers at one time, but do not as yet have the s720i power sensor...

Thanks in Advance

Feanor
 
Originally posted by Feanor
Has anyone made a direct comparison between the power measurement of the HAC4 when compared to the system used by the Polar s720i which is theoretically and reputedly more accurate?

I had both hrm/cyclecomputers at one time, but do not as yet have the s720i power sensor...

Thanks in Advance

Feanor

(Caveat) I've not seen a Hac 4, but i've seen other people run a comparison, plus, because of the way power is estimated it won't be and isn't accurate. On slow moving uphill sections it should be accurate, but then it's fairly easy to calculate power anyway uphill!

Ric
 
Unless you have a power chart that you are comparing yourself against, I would have thought that accuracy is less important than consistent repeatability which allows you to compare rides. If the Hac4 achieves this (and, in my experience, it does), then it can be a useful aid to training. If only the software was better - and if there was some meaningful two-way exchanges between Ciclosport and their customers, this would be an excellent bit of kit. As it is, it's merely good.
 
Originally posted by TimC
Unless you have a power chart that you are comparing yourself against, I would have thought that accuracy is less important than consistent repeatability which allows you to compare rides. If the Hac4 achieves this (and, in my experience, it does), then it can be a useful aid to training. If only the software was better - and if there was some meaningful two-way exchanges between Ciclosport and their customers, this would be an excellent bit of kit. As it is, it's merely good.

How can it be repeatable when it can't take into account the various retarding forces except gravity (i.e., air drag)? How would it be able to tell between a strong or light headwind, or even a strong headwind and a strong tailwind?

Ric
 
In short, it can't! But on your normal training route, in average UK weather, the figures returned will be similar enough that major differences due to other factors will be noticeable. On my own regular route, my variation in speed and heartrate due to wind are less significant than the variations due to other physical factors, so the power figures given by the Hac4 are pretty valid. Yes, it's a fairly sheltered route, but many are.
The point is that it's not the absolute accuracy of the power figure that's important (unless you want to compare yourself to Lance's power figures - but, note, he uses a Hac4!), but that each time you repeat a given ride at a given speed in similar conditions, the power graph returned is directly comparable to previous episodes. If it is, then changes in power performance can be tracked and used as a training guide.
If you want absolute accuracy, and a system that accounts for changes in wind effect and road conditions, then you are going to have to pay a lot more. That may be good value for you; for me, the Hac4 will do just fine - if only the software was better!!
 
Originally posted by TimC
In short, it can't! But on your normal training route, in average UK weather, the figures returned will be similar enough that major differences due to other factors will be noticeable. On my own regular route, my variation in speed and heartrate due to wind are less significant than the variations due to other physical factors, so the power figures given by the Hac4 are pretty valid. Yes, it's a fairly sheltered route, but many are.
The point is that it's not the absolute accuracy of the power figure that's important (unless you want to compare yourself to Lance's power figures - but, note, he uses a Hac4!), but that each time you repeat a given ride at a given speed in similar conditions, the power graph returned is directly comparable to previous episodes. If it is, then changes in power performance can be tracked and used as a training guide.
If you want absolute accuracy, and a system that accounts for changes in wind effect and road conditions, then you are going to have to pay a lot more. That may be good value for you; for me, the Hac4 will do just fine - if only the software was better!!

I don't mean to sound 'rude' but i don't believe you can compare one day to another. small changes in temp, wind, and air pressure that you wouldn't notice without measuring will significantly affect speed/power. i know this because i have years and years of data from lots of people riding the same routes.

Ric
 
There are limitations, obviously, and God knows the Hac4 could be improved, but for the money I don't believe there's anything better. However, the Hac4 does measure temperature and pressure. It's only the effect of wind that is missing from the equation, and only very expensive power-measuring cranks will overcome that limitation. If the Hac4's software was improved, the ability to meaningfully compare rides on the same route would be very much enhanced, even without the wind element.

At the end of the day, it all comes down to money!
 
Originally posted by TimC
There are limitations, obviously, and God knows the Hac4 could be improved, but for the money I don't believe there's anything better. However, the Hac4 does measure temperature and pressure. It's only the effect of wind that is missing from the equation, and only very expensive power-measuring cranks will overcome that limitation. If the Hac4's software was improved, the ability to meaningfully compare rides on the same route would be very much enhanced, even without the wind element.

At the end of the day, it all comes down to money!

but, on flat roads, at normal riding speed, about 85% of your power goes in to overcoming air drag. as it misses this or estimates it, it's going to be off by a long way.

from the data i've seen from it compared to srm or pt, i can get far closer estimates of power with analyticcycling.com (which is free).

ric
 
I have a HAC4 and am just beginning to understand the blasted thing. Since the software literally has no instructions, it's an effort to figure it out.

Ric is of course absolutely right -- in an area like mine (Northern Cal), I can be crawling along at 13 mph at 165 bpm because of headwinds, and then the next day be cranking at 19 mph at 145 bpm in the same spot. The longer the ride, though, the more things should balance out and return consistent results.

One thing's for sure... I don't like what power it says I'm producing! It's usually 80-140 watts. Maybe I was supposed to input my weight in pounds rather than Kg??? Can't tell in the highly ambiguous instructions!!