Calibration doesn't seem right

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Calibration doesn't seem right

Postby GrittyGoober » Fri May 14, 2010 2:35 pm

I have an iSport with 4.21 firmware. I have performed all of the calibration tests several time, but I have yet to feel like the data being reported is correct. It could be that I just don't know what I am looking at, but it just doesn't seem consistent.

I can be riding with what I think is very little effort and the iBike reports I am cranking mid-300 watts (seems too high). I can be cranking hard (I don't mean pedal stress, I tend to ride at an 85+ cadence unless a big hill is involved) and have it report 130-150 watts. I thought this was because of a bad tilt, but I have been very careful with my tilt calibrations to assure that isn't the problem.

I can't upload a settings file since it is an iSport, but is there any way I can check my calibration for "reasonableness"?

I have my total weight set at 216lbs.
Est Fric = yes
Fric set to 55
Est Aero is set to 71 in., weight 187 lbs, Hoods = yes

I've done the cal ride (4 miles). I do wind cal before every ride, usually in my garage out of the wind and cupping my hand over the wind port. I very carefully do a tilt before every ride using marks I made on my smooth, flat, dirt free garage floor. I haven't done any coast downs because the detailed instructions (April 2010 version) say they are not recommended for an iSport.

I'm not sure what else to provide. I don't know if these numbers help, but when I hit the left arrow button I get these numbers after the TSS numbers.

CSt Aero 1_8144
CSt Fric 13_936


Does all this seem correct?
GrittyGoober
 
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Re: Calibration doesn't seem right

Postby Velocomp » Fri May 14, 2010 3:29 pm

For a total weight of 216 your fric number of 13.9 is reasonable.

When the iBike is mounted on the handlebars the aero number can be higher than 1.0. When the iBike is mounted on the stem the aero number will generally be less than 0.6

In your case, even if your iBike is on the handlebars, an aero factor of 1.8 is likely too high. An aero number that is too high will cause high watts.

A high aero number is the result of a problem with the Cal Ride data.

Here are some things to do:

1) Make sure your handlebar mount does not rotate on the handlebars. When the green stickies are used and the mount screws are tightened normally it should not be possible to rotate the mount at all. Don't overtighten the screws--this can break the u-shaped clamp!

2) It's critical to have a good wind cal and tilt cal prior to doing a Cal Ride. Make sure to cup your hands over the wind port when doing a Cal Wind.

3) Here is a very simple test tyou can do to check calibrations at any time after performing the Fast Start and Cal Ride.

Make sure your tilt and Cal Wind is correct.

After completing the Fast Start and Cal Ride go to the User Yes menu in setup. Click the up arrow until you come to the Coast screen.

DO NOT START THE COAST DOWN BY CLICKING THE CENTER BUTTON!

While in the Coast screen, ride up to 20 mph. As you pedal to speed the watts number in the middle window will go up. This is the watts number your iBike reports during a normal ride.

When you reach 20 mph, stop pedaling. The number in the middle window will drift towards zero (you're not pedaling so applied power is zero). If your calibrations are "good" then the watts number in the center screen will drift around zero. If your calibrations are incorrect (either the Est Aero was not done properly or there was a problem in the cal ride) the number in the middle window will be far from zero (more than +20W or less than -20W).

If your iBike is reading high watts on the flats then you should see a big number in the coast window when not pedaling.

4) Perform another calibration ride. You do not need to do another Est Aero prior to the cal ride.

To get better accuracy from Cal Ride, ride out 2 miles before turning around to ride back. The iSport will tell you to turn at the one mile mark, but just keep riding until it says 2 miles. Note that you'll need to keep your bike speed above 10 mph after you hit the 1 mile mark.

After the Cal Ride look at your aero and fric numbers. If the aero number has gone down then you will get lower watts on the flats. Also, you can do the test in step 3) again to see if the coasting watts are close to zero (as they should be).
John Hamann
Velocomp
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Re: Calibration doesn't seem right

Postby GrittyGoober » Fri May 14, 2010 3:52 pm

Thanks John,

I'll perform all your suggestions and report back... it will be a few days. As you predicted, I do use a handlebar mount with the iBike almost horizontal (I find it easier to read that way).
GrittyGoober
 
Posts: 14
Joined: Sat May 08, 2010 10:07 pm

Re: Calibration doesn't seem right

Postby GrittyGoober » Mon May 24, 2010 2:50 pm

I performed all of your steps:

1) The mount is rock solid.

2) I performed a good wind and tilt cal, then did a cal ride (4 miles). My Fric and Aero number are unchanged from what I posted earlier. They are exactly the same, which seems a little odd.

3) I did the simple test using the coast down method you described. The watts went down to +- 4 watts. So I guess it is all good.
GrittyGoober
 
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Re: Calibration doesn't seem right

Postby Velocomp » Mon May 24, 2010 8:19 pm

The fact that you got the same results means that your first calibrations are good :D

We will be adding a "check calibration" feature in a future release of firmware so that you'll KNOW all is well...

In the mean time, enjoy the ride!
John Hamann
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Velocomp CEO
 
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Joined: Fri Jan 11, 2008 9:43 am

Re: Calibration doesn't seem right

Postby jazclrint » Thu Jun 24, 2010 5:53 pm

That was a very helpful thread!

One question:
1) What do you mean by, "You do not need to do another Est Aero prior to the cal ride." Is there an Est Aero test? On the iSport you just select one of 3 choices for estimating aero. Thats all there is right?
Thanks,
Rich
'98 ProFlex 5500c under construction
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