Marcus, the problem with the timer is something else that @Alex can respond to.
I’m coming back to you about calibration for wheel-on trainers.
What you should know:
- Wheel-on trainers can be consistent if you do it right but usually have low accuracy. Manufacturer specs are somewhere +/-5% - +/- 10%
- The calibration procedure from the manufacturer will only allow you to get within the above range, but if you have a power meter, you can do better
- Wheel-on trainers are very dependent on tire pressure and wheel tension. A higher tire pressure results in lower resistance. A higher tension of the roller contacting your tire results in higher resistance
- Tire pressure changes quite drastically with temperature. This means that riding your trainer at higher resistance creates a temperature change of the air in the tire, pressure rises and resistance lowers.
- PowerMatch in TrainerDay is not perfect and can’t handle big corrections very well. Alex will surely improve this one day but they have a lot to do and are a small group
If you have already a big “overall” offset on power and then add the power differences caused by the temperature changes, PowerMatch is unable to handle it correctly.
But if you have a Power Meter, you can limit the “overall” difference and then PowerMatch works quite well.
To limit that static difference you need to be consistent and NOT follow the manufacturer’s calibration procedure.
- Set your tire pressure at 7 - 7.5 bar. You have it at 8.5 but that is probably a bit high because you set it when cold and it will raise even more once you start riding. Too much pressure causes slippage and then you will tighten the tension too avoid slippage. You will end up with too much resistance…
- Turn the tension knob as per instructions from the manufacturer. You mentioned 2 full turns after contact with the tire.
- Ride a bit to warmup your tire (yes, it is the tire you are warming up and not the trainer
). Do some accelerations just to make sure that slippage is minimal. Make adjustments as necessary if there is too much slippage. Lowering pressure a little bit or raising tension slightly will reduce risk of slippage. - Now with this situation, do the Spindown calibration. And this is the ONLY time you should do this unless there were significant changes in your setup. What they call Spindown Calibration is no more then a very awkward way to get you close to the specs. Remember that this is not at all accurate because there is simply nothing to verify accuracy against!
- Ride your trainer in high endurance zone for about 10 minutes and then a couple of minutes in low tempo zone while having PowerMatch disabled. On the left you have the target sent to your trainer and on the right the real power measured from the power meter. Check the difference in the last couple minutes at low tempo.
- If the power meter is higher then the target, your trainer creates too much resistance and you need to decrease wheel tension a bit. Maybe even raise tire pressure a bit. But be conservative, small changes have a big impact! If power reads lower, you have to do the opposite.
- Ride again for 10-15 minutes and check the result. Try to get too a difference smaller then 5W.
- And now a very important bit: NEVER do the spindown test again because it will throw of all the work you did above. From now on, try to leave your bike on the trainer as much as possible and check tire pressure before every workout. Be precise! Make a mark on your pressure gauge to match it as close as possible. Make a mark on the tension knob to reproduce the same setting when you remove and reinstall your bike on the trainer.
I know, it seems like a lot of work. But if you do this once at the start of the indoor season, you only have to carefully check tire pressure and wheel tension before starting your workout. Just hop on and and after roughly 10 minutes of warm-up, your power values will be close. PowerMatch will do the rest and compensate little differences caused by temperature drift. During you ride (after warmup) you should never see corrections higher then about 10W.
Let me know how things went! 