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HAC4 Computer- how accurate is the watts reading?(11 posts)

HAC4 Computer- how accurate is the watts reading?Coolhand
Sep 8, 2003 9:25 AM
Is the computer reliable? Interface ok?

Currently using an old Polar HR watch and a older Cateye cyclo-computer. Thanks,

re: HAC4 Computer- how accurate is the watts reading?PMC
Sep 8, 2003 10:04 AM
The HAC4 wattage reading is a joke. Go to and do a forum search for HAC4 if you want the dirt.
You need actual power measuring devicesKerry Irons
Sep 8, 2003 5:14 PM
No "calculated" power output is worth much from exercise equipment. Same applies to many hokey units in fitness centers. You can estimate power requirements in specific situations knowing your weight, the grade, wind speed, etc. but your HRM has none of that data. The numbers are typically a joke, most often estimated way high to make you feel better about the effort you're putting in.
No free lunch huh?Coolhand
Sep 9, 2003 5:21 AM

My current HRM doesn't do power at all, actually. I had just seen a few claims regarding the HAC4 and though it was a bit too good to be true. Guess it is.

I guess I will stick with my older Polar HRM and Cateye computer for now.

What power measuring device do you reccommend if I was to get one this winter for training?


Nope, no free lunch but...PMC
Sep 9, 2003 6:07 AM
The two I really like are the Power Tap and the SRM cranks.

SRM are just too dang expensive for most of us at around 1800 for the amateur road model.

Graber's Power Tap can be had for a lot less and is what I use. The software that comes with the PT is less than desirable but really good software can be had from for less than you'd expect to pay. The newer Power Taps are pretty reliable, as they've gotten the seals figured out in the rear hub. That was the big weak spot of prior generation hubs. The computer head units are user friendly although they burn through batteries awfully quick. It can also be made Campy compatible with an American Classic 10-speed cassette so you're not limited to ShimaNo only.
Sep 10, 2003 5:22 AM
A buddy of mine just picked up this new one, the ergomo.
check it out at
What seems really cool about it, is that you can use any wheel that you choose to, i.e. training racing etc..
I think I am going to pick one up myself next month. plus it also comes with that cool software.
Sep 11, 2003 8:02 AM
The Ergomo actually look fairly interesting but does have a couple of drawbacks that I see.
- The head CPU unit is big. If I'm not mistaken, it's around two and a half times larger than the PT unit. Not an issue for some but I'd rather not give up that much bar space.
- The whole set-up is, from what I've heard, around 1200 USD which is out of my price range for this type of equipment.
- The bottom bracket unit needs to be sent back to Europe for service. To have the bearings replaced costs around 350 USD (from memory so may not be totally accurate).
- The bottom bracket unit only measures power from the drive side crank arm. There is some question, or was, as to how the unit figures out total power output.
Sep 12, 2003 6:50 AM
Accorrding to the latest Velonews article comparing power meters your memory is correct on all accounts.

Sep 12, 2003 1:23 PM
Certainly each one of the power meters has it's issues.
As far as price goes, I think that Ergomo is a bit more compared to SRM then PT.

The head is a bit big I guess, but if it does everything it says it does, I'm ok with that.

I think that they are replacing the bearings in the US now, but I am not sure of that.
re: HAC4 Computer- how accurate is the watts reading?noveread
Sep 9, 2003 1:21 PM
I have the HAC4, I love the unit itself, but I don't really pay any attention to the power readout. However, I just got my hands on a powertap so it is going to be interesting to see the two side by side this winter...

The Empty Wrapper
I've been using the 436M for a while.Mike P
Sep 10, 2003 10:38 AM
On the 436M, the power function is not a real world measurement of power as it just estimates power based the programmed in weight and the measured gradient; I assume the HAC4 is simular.

Except for hill work, I do not pay attention to the power readings at all; it just can't be accurate (and I don't think Cyclosport markets it as a power measuring device, it's just a neat little tool). On the hills I have found the power measurements to be very valuable. While working hills the power reading is consistant, as best I can tell by perceived effort and my heart rate. I find it useful in guaging effort during a climb and after the ride to evaluate the workout with the software.

The software is a pain in the rear until you figure it out. One feature I like is the ability to compare rides by overlaying one ride on the other.