Do different tyres have effect on power

Wilby_89

I'm using two different bikes with the same gear ratios and the same power meter on the same turbo trainer.
One has the gatorskins 25c on and the other has the veloflex master 25c.
I'm doing the same cadences on the same resistance on both bikes but I am constantly getting around an extra 10watts to my overall average power on the veloflex masters.
So my question is does tyres have an effect on power?
I'm using the exact same bike fits on both bikes somehow on the gator skins It almost feels a little harder to maintain certain watts where as on the veloflex I can keep a smooth cadence.

fat daddy

Yes ..... If you go to http://www.bicyclerollingresistance.com they review loads of tires and me are the rolling resistance by use of a power meter

sungod

yes they do, it's called rolling resistance, i'm sure the rolling resistance of gatorskins will be significantly higher than the veloflex

but if you're using the turbo a lot, i wouldn't use either tyre as they may wear out/fail much faster, instead use a turbo-specific tyre

BrandonA

Wilby_89 wrote:

So my question is does tyres have an effect on power?

The simple answer is no. The different tyres due to rolling resistance and how you've configured the bikes on the turbo will affect how much power is required to turn a certain gear at a certain cadence.

Assuming you have a crank based or pedal based power meter means that your power is computed very lose to source, I've your legs turning the pedal. Power is not generated at the wheels so tyres will not affect power. Assuming you have two different chains this might affect power delivery effectiveness, for example if one chain is more worn or one is more dirty it will take more power to go a certain speed.

What you need to do is learn how to configure your turbo for each bike so the same pressure I turn on the tyres and thus the same cadence in the same gear takes the same amount of effort.

markhewitt1978

The OP doesn't say but if they are using a smart trainer then the power calculated is that put down 'on the road', so to speak, so presumably the tyre will have an effect here. As you say if it's an on bike power meter then it won't have any effect at all.

slowbike

BrandonA wrote:

Wilby_89 wrote:

So my question is does tyres have an effect on power?

The simple answer is no. The different tyres due to rolling resistance and how you've configured the bikes on the turbo will affect how much power is required to turn a certain gear at a certain cadence.

Assuming you have a crank based or pedal based power meter means that your power is computed very lose to source, I've your legs turning the pedal. Power is not generated at the wheels so tyres will not affect power. Assuming you have two different chains this might affect power delivery effectiveness, for example if one chain is more worn or one is more dirty it will take more power to go a certain speed.

What you need to do is learn how to configure your turbo for each bike so the same pressure I turn on the tyres and thus the same cadence in the same gear takes the same amount of effort.

Sorry - but I think you're wrong. The fact that you go on about the chain just confirms the fact that you don't know what you're talking about - if tyres don't affect power then chain certainly isn't going to - but fact is - both do.

The OP is comparing power - to cadence at a set resistance - so the tyre DOES make a difference as it has to deform on contact with the roller. Gatorskins are pretty tough - and I guess less flexible than the veloflex masters - but there may be a difference in the diameter of too - so if it's a clamp up roller then that may need slacking off for the gatorskins to get the same pressure against the tyre.

markhewitt1978

He's not wrong given that he assumes a power meter on the bike rather than the trainer.

Man Of Lard

Exactly - it depends where the power is being measured: Crank/chainring, hub, trainer...

Crank/chainring should always give a higher reading than a hub-based measure (given inevitable frictional and other losses in the chainring/chain interface, losses in the chain & the chain/sprocket losses) and both of those readings should be independent of anything mechanically connected beyond (rim, tyre, trainer) since all of the "downstream" appears only as a resistance load to be overcome.

slowbike

markhewitt1978 wrote:

He's not wrong given that he assumes a power meter on the bike rather than the trainer.

Man Of Lard wrote:

Exactly - it depends where the power is being measured: Crank/chainring, hub, trainer...

Crank/chainring should always give a higher reading than a hub-based measure (given inevitable frictional and other losses in the chainring/chain interface, losses in the chain & the chain/sprocket losses) and both of those readings should be independent of anything mechanically connected beyond (rim, tyre, trainer) since all of the "downstream" appears only as a resistance load to be overcome.

Yes he is ... the power required to achieve the same cadence at the same resistance setting with the same gear ratio on an identical turbo will have some dependancy on how easily the tyre deforms.

You're not wrong in that measuring the power at different places will result in different results due to power loss and accuracy of the power meter - but crux of it is - assuming everything else equal - so the OP is using the same bike, same power meter, same wheel, just swapping the tyre over - then yes - it's down to the tyre.