Calibrating Slope on SRM

A light bike doesn't replace good fitness.

Moderator: Moderator Team

Geoff
Posts: 5093
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

fankozola101 wrote:Geoff, are you saying...

If: You manually enter a new slope constant in the Power Control (head unit)

Then: the Power Control (head unit) sends a signal to the Power Meter, which changes the slope constant stored on the Power Meter.

And: This new slope constant stored on the power meter is what a Power Control (head unit) will detect (in future) when in "auto detection" mode.

Sorry for missing this (Canada Day, etc.) I also think that this answer may cover-off some of the other stuff you have asked. The answer is a qualified 'no'.

The 'auto-detect' feature is unique to the wireless SRM PowerMeter (i.e., not found on wired PowerMeters), so by default, only the PC6 and PC7 PowerControllers can 'benefit' from it. When you change the slope in manual mode using the SRM software, the slope stored in the PowerController is not then changed so that the 'auto-detect' feature will, thereafter, apply the new slope. Rather, the PowerMeter will default to the original, factory slope setting.

I know. It's lame. I imagine that this will lead to another round of comments about SRM seeking to further secure 'repeat' business. There is a way to do it, though...

by Weenie


User avatar
Vallinotti
Posts: 90
Joined: Mon Sep 21, 2009 11:12 pm

by Vallinotti

Tapeworm wrote:I pinched this from a forum somewhere, been sitting in my docs files for ages. Easy as it gets.

How to recalibrate SRM?

1. Look for a weight of about 30 to 40 kg. Hang it on a cable of about 25 cm, so that the weight does not touch the floor when it is hanging on the horizo ntal crank pedal, or take a longer cable and put the bike on a table.

2. Calculate the weight in Newton. E.g. 30 kg = 30 * 9.81 = 294.3 N 3.

3. Calculate the torque you get when the weight hangs on the horizontal pedal crank.
E.g. at 172.5 mm cranks : 0.1725m * 294.3 N = 50.77 Nm (Newton meter).

4. Switch the Powermeter on by pedalling backwards. Do this with a middle gea r so that the chain is in a line, e.g. 53/15.

5. Notice zero of Powermeter (MODE + SET, right number)
e.g. F0=500 Hz.

6. Bring crank in horizontal position and hang the weight on the left pedal.

7. Notice frequency output-left of Powermeter (MODE + SET, right number)
e.g. Fleft=1450 Hz.

8. Bring crank in horizontal position and hang the weight on the right pedal.

9. Notice frequency output-right of Powermeter (MODE + SET, right number)
e.g. Fright=1550 Hz.

10. Calculate frequency change of Powermeter with this weight as (Fleft+Fright)/2 -Fo
e.g. (1450+1550)/2 Hz - 500 Hz = 1000 Hz at a torque of 50.77 Nm.

11. Calculate average slope of Powermeter.
Slope = 1000 Hz/50.77 Nm = 19.90 H z/Nm.

12. This slope is the calibration of Powermeter and must be set in Powercontrol.
We recommend to check the slope monthly.


Is it possible to make these steps with a Garmin 810 unit?

User avatar
devinci
Posts: 3039
Joined: Sat Jan 03, 2009 9:43 pm
Location: Canada

by devinci

I am pretty sure it is NOT possible without a SRM head unit

User avatar
Giant DK
Posts: 1311
Joined: Mon Jan 23, 2006 3:03 pm
Location: Denmark

by Giant DK

It is posible and even easier with a Garmin Edge unit as it doesn't leave the zero offset screen in the middle of the meassurements.
Technical editor at Cykelmagasinet Denmark

My Simplon Pavo II

User avatar
devinci
Posts: 3039
Joined: Sat Jan 03, 2009 9:43 pm
Location: Canada

by devinci

but then can you adjust the slope afterwards?

wetpaint
Posts: 82
Joined: Sat Feb 06, 2010 2:55 am
Location: USA

by wetpaint

Yes, you can manually enter the slope on a Garmin

Post Reply
  • Similar Topics
    Replies
    Views
    Last post