Page 2 - which computrainer

30-04.-2008, 09:11 AM	#16
strader Registered User Join Date: Jun 2007 Posts: 113	Re: which computrainer I ended up picking up the Computrainer after all. I did a quick test on it after a 15 minute warm up at ~200 watts, and a calibration value of 2.05 lbs. Here's how it compared to my powertap (which I remembered to zero this time) over three 5 minute trials at 300, 250, and 200 watts: Computrainer Powertap 300 watts 316 watts -5.1% 250 watts 264 watts -5.3% 200 watts 212 watts -5.6% Not bad, but I'd like them to track a bit closer. 316 watts feels a lot harder for me than 300. The unit also develops a nasty buzz at around 22 mph wheel speed. I can feel it though the bike. Could it just be an unbalanced tire? Something loose on the trainer? Right now I'm using a Michelin Carbon, but I have a conti home trainer tire sitting in a box waiting to be used.

01-05.-2008, 04:21 PM

#17

Porkyboy

Registered User

Join Date: Apr 2006

Location: Northumberland. UK

Posts: 77

Re: which computrainer

Quote:

Originally Posted by strader

I ended up picking up the Computrainer after all. I did a quick test on it after a 15 minute warm up at ~200 watts, and a calibration value of 2.05 lbs. Here's how it compared to my powertap (which I remembered to zero this time) over three 5 minute trials at 300, 250, and 200 watts:

Computrainer Powertap
300 watts 316 watts -5.1%
250 watts 264 watts -5.3%
200 watts 212 watts -5.6%

Not bad, but I'd like them to track a bit closer. 316 watts feels a lot harder for me than 300.
The unit also develops a nasty buzz at around 22 mph wheel speed. I can feel it though the bike. Could it just be an unbalanced tire? Something loose on the trainer? Right now I'm using a Michelin Carbon, but I have a conti home trainer tire sitting in a box waiting to be used.

Hi

FWIW my advice would be as follows:

Fit Conti tyre.
Inflate to 110psi.
Run routine and set calibration with trainer and tyre cold, ensure press on force is about 3lbs at this stage.
Warm up tyre and trainer for 10 minutes, at least 8 minutes done @ 175W.
Recalibrate trainer, this should now give you a press on force of about 2.4-2.6lbs.
You are now properly calibrated, perform tests at about 90RPM , away you go, post results here
Re-run calibration after tests, the reading should be VERY close to the reading obtained in step 5, if the unit and tyre were properly warmed up.

My experience is that with press on forces in the lower end of the range, and 2 is the absolute minimum, you may well get "micro slips" of the tyre, especially at higher wattages if the cadence is lowish, the above routine avoids this. Bear in mind if you are going to do any work standing up, steep gradient settings, high wattages, you may well need to set a press on force of above 3 to avoid "micro slips" which are not obvious when they are happening on any trainer.

Can't help you will the buzz!

Cheers.

PBUK

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06-05.-2008, 10:01 AM	#18
strader Registered User Join Date: Jun 2007 Posts: 113	Re: which computrainer In case anyone is interested in the follow-up, after following rmur's calibration procedure my computrainer and powertap track much closer: CT PT % diff 300 299 -0.3% 250 252 0.7% 200 204 1.9% 150 156 3.8% The slopes cross over around 280ish watts, which I call Good Enough (TM). I figure workouts paced by either one should be within a couple of TSS points.

06-05.-2008, 03:26 PM

#19

Porkyboy

Registered User

Join Date: Apr 2006

Location: Northumberland. UK

Posts: 77

Re: which computrainer

Hi Strader

Quote:

Originally Posted by strader

In case anyone is interested in the follow-up, after following rmur's calibration procedure my computrainer and powertap track much closer:

CT PT % diff
300 299 -0.3%
250 252 0.7%
200 204 1.9%
150 156 3.8%

The slopes cross over around 280ish watts, which I call Good Enough (TM). I figure workouts paced by either one should be within a couple of TSS points.

I've re-read the thread and am not quite clear in my own mind exactly which exactly is rmurs callibration procedure as based on your experiences I'd like to try following it. Any chance of a 1,2,3 noddy guide?

Thanks for your help.

PBUK

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