Accuracy of Dynotrainer

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December 7, 2013 at 1:08 am #315

Gerardbalnaves@gmail.com

I’ve had the dynotrainer for about 5 months. Power readings are up at around 430 for average watts over a 2 hr cycle.

I’ve checked the set-up of the trainer and I did it per instructions. Is it actually accurate? And if not is it covered by warranty to get a more accurate replacement?

January 26, 2014 at 2:47 am #321

jetblackcoach

Hi Gerarde, this is the reply from the manufacturer

Hi Murray,

That is obviously too high unless they are a world class athlete…

Discussing accuracy is a fairly complicated area as there are a lot of variables as I’m sure you are aware of… I will try give you the whole story so that you have all of the pieces and can understand it more clearly. Sorry for the lengthy reply.

Just to get started and check your familier, you probably already know this…
Fluid Trainers: (As this customer has an average reading issue this probably isn’t it but note that it will give the average a skewed reading)

All Fluid trainers that use Oil as the resistance medium (majority of fluid trainers use oil that is petroleum based). These trainers requires a 5-10 minute warm-up to get the oil up to its stable viscosity (like oil in a car, the oil becomes thinner and less resistance once the car has warmed up). So after the 5-10 minute warm-up the oil will reach a stable range and will then give a consistent and measurable read out on the Dynometer computer head unit. This should be within 5% accuracy when compared to say a power hub/crank or similar product. Note that this 5% accuracy will remain the same for the lifetime of the product (Only if the roller adjustment dial is set to the exactly the same number of turns after fist contact with the tyre and that the tyre pressure and tyre remains the same). This means that if it reads low by 3% then it will always read low by 3%, giving you a consistent power measurement so that you can train at power levels and measure improvements in your power output. The progressive power curve better simulates the resistance effects as your speed changes that are much more similar to riding on the road (for our trainer this is approximately 1% slope for a 75kg rider on a 23x700c road bike)

As you know wattage output for different riders riding the same piece of road varies drastically for many factors, road surface and condition, tyre pressure, tyre size, temperature, humidity, rider and bike combined mass, aerodynamic position, roller adjustment dial tension, Etc etc can all make a difference. Maybe the rider is heavier than 75kg and puts out more power than our base figures used as the based figures for the Dynometer. A 65kg rider vs. a 90kg rider will have a large difference between their power output required just to hold the same speed.

The tension of the roller against the tyre can make a difference to the resistance (note: This would be similar for other A frame bike trainers that use a roller against a tyre so is not unique to ours alone). Check that the customer always sets their bike up with exactly the same turns each session on the adjustment dial from the point at which the roller first makes contact with the tyre. Tyre pressure must also be checked regularly so that it is at the tyres recommended pressure.

(I have run some test on our trainers on our testing rig so we have some data on what this difference is and found that the roller tension can make a substantial difference to the resistance. On the Z1 when taking the adjustment from 1.5 turns to 2 turns increases the resistance by about 15% So it’s important that they keep this tension consistent between rides and ideally they set it up at the same number of turns each ride).

We recommend 1.5 turns as the base figure to match the Dynometer computer read out (75kg rider on a 23x700c road bike). With other variable already listed above, these can sometimes make it necessary for a minor adjustment to get the wattage reading more accurate.

If a rider is experiencing watts that are higher than expected or they can normally put out, this means that riding on the trainer is too easy and the resistance needs to be increased by tightening the roller adjustment dial.

If a rider is experiencing watts that are lower than expected or they can normally put out, this means that riding on the trainer is too hard and the resistance needs to be decreased by loosening the roller adjustment dial.

Make the above adjustments by quarter turn or less and check how the trainer then feels.

So for this customer I would check they have first been riding at 1.5 turns (I usually explain this as “three half turns” as people seem to understand 1.5 turns better this way) on the adjustment dial from the point at which the roller first makes contact with the tyre. Also check that they are running a consistent tyre pressure. If this is correct then ask them to tighten it by quarter turn increments or less until their average wattage is within their expected range.

If for some reason the unit is actually faulty and it is not possible to get the power reading within range by make these adjustments then yes, we would be happy to try a new computer head unit.

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