Tire type impact on measure accuracy

[fuego.bluedane]

Is it possible that measure accuracy of Rampa depends of tire type used?
Few days ago I've changed my worn tires from 12k km used btwin Res5 to Conti GP II and get a feeling that I have to use a little less energy to generate the same power training at zwift. So today I get FTP test and get shocked. Last test I took month ago and generate 255W, today I get 295W so 40w more. Is it possible that rolling resistance of tire have such great impact on measure? Or the month of training make me so strong

[Elite Admin S]

Well, it is more probable that the pressure between the tire and the roller has changed.
The material of the tire can influence power - as it may cause a different friction - but the pressure is indeed more relevant.

To have a correct setting:
- check that the inner tube is well inflated
- put the lever in open position
- turn the knob until the tire touches the roller (press the plate to be sure that there's no space between the two)
- close the lever

[fuego.bluedane]

I`ve checked all this things twice. There is no error in wheel montage on roller.
Correct me if i`m wrong but shouldn`t we get the lower not a higher power readings if something is wrong with pressure between tire and roller?

[Elite Admin S]

If the pressure is not correct, the tire will slip on the roller and power will decrease. Also, the surface of contact is less if the wheel is not well in contact and this means less friction (and so, less power). On the other side, if the inner tube is not well inflated the contact surface will be more, increasing power.
If all the setting is ok, it may be due to the material of the tire. In this case, the best solution is to do a calibration (especially if you have a power sensor).

[fuego.bluedane]

Unfortunately i dont have power meter. Can i calibrate Rampa without PM? Where can i check the best P values for my Rampa?

[Elite Admin S]

You can calibrate it manually, but it requires a little more skill (as you have to "feel" the realism on your legs).

To do it, follow these rules:
- P1 refers to medium/high slopes; P2 refers to low slopes; P3 refers to flat road
- if the trainer brakes too much, increase the values; if it brakes too little, decrease the values
- increase/decrease the values by about 20-30 points at time (no more), then do a training on a course/training that you know well and check if the simulation is more realistic
- repeat until you have a good simulation

It's an empirical method, but if you have a good feeling of your effort while you ride you can achieve a very good calibration.

[fuego.bluedane]

I don't think I have enough experience, but maybe I'll try. If I mess up with p parameters where do I find the default one?

[Elite Admin S]

If you need it, simply send me the serial number of your trainer and I'll give them to you.

Regards

[fuego.bluedane]

Thanks for default P values.
Now correct me if i`m wrong. Calibration have impact on trainer behavior at slopes and road simulation. But if i`m going with a structured workout (something like 10min at 150W, 10min at 200 etc in Zwift in EGR mode.) does the trainer recalculate using P values or just getting braking force from flywheel speed rotation?

[Elite Admin S]

Every trainer has its own power map inside. It's a table, that map the power at every speed and resistance position.
When you do a calibration, the power map inside the trainer is modified basing on the three calibration points. This means that every app that connects to the trainer will "use" the new calibration.


Let's do an example.

Before the calibration, suppose that you had 200W at 20km/h with the resistance at 42%.
This means that when the software/app you use ask the trainer to develop 200W, the trainer will set the resistance at 42%.

Suppose that you feel that, in reality, the trainer is braking more. So, you calibrate the trainer increasing the calibration points.
Now, at 42% the resistance will be more in the power map. Suppose it's 250W at 20km/h.
Instead, in the map you'll have 200W with a resistance of 36%.
When the software/app asks the trainer 200W, the trainer will set the resistance at 36%.


I think now it's more clear