Do tires make a big difference on a turbo?

littledove44
littledove44 Posts: 871
edited January 2014 in Training, fitness and health
I have switched from a 25mm Continental Four Seasons at 100 psi to an Espoir Sport 23mm at 90psi. I think the turbo wheel pressure is about the same.

However, I am really struggling to do 90% of the power I was doing before, and to do it I can see my heart rates 10% higher than they were.

Its not me, I am feeling fine.

Do the tires really make that much difference.

If so I will have to redo the FTP test. Joy!

Comments

  • amaferanga
    amaferanga Posts: 6,789
    Is this real, measured power or virtual power?
    More problems but still living....
  • MartinGT
    MartinGT Posts: 475
    Why not keep them the same pressures?
  • diamonddog
    diamonddog Posts: 3,426
    It's 23mm that usually run at a slightly higher pressure than 25mm IME.
  • littledove44
    littledove44 Posts: 871
    amaferanga wrote:
    Is this real, measured power or virtual power?
    Virtual power, so it is all calculated by turbo rotor speed.
  • littledove44
    littledove44 Posts: 871
    diamonddog wrote:
    It's 23mm that usually run at a slightly higher pressure than 25mm IME.
    I know that. That's what I do on the road. This just happens to be what they actually were at when I used the turbo.

    My question is, does pressure and tire size make that much difference to power?

    I am quite happy to keep the setup identical in future, but before I start redoing FTP tests I want to see if others have experienced such big differences.
  • GBY73
    GBY73 Posts: 20
    I'm sure if you used a "real" power meter you would see no difference whatever tyre you used . Your turbo is not measuring power, only an estimate based on a calculation. Your effort is the same whatever the tyre.

    I have found, however, that perceived effort can change with a different tyre.
  • littledove44
    littledove44 Posts: 871
    GBY73 wrote:
    I'm sure if you used a "real" power meter you would see no difference whatever tyre you used . Your turbo is not measuring power, only an estimate based on a calculation. Your effort is the same whatever the tyre.

    I have found, however, that perceived effort can change with a different tyre.

    Yes, but that much?

    The point is that the turbo measure how fast you spin it. To spin it at the same speed as before I need to use a lot more energy and am working at 10% more of my max heart rate for the same programme.

    Trainer road workouts are based on the assumed power reading, so by changing tire I appear to have given myself massive extra efforts required to follow the plan. Not good.

    I don't care what the number is, I just want to work in the right training zones and using power is more accurate than heart rate, so long as the conditions are the same.

    My simple question is how much difference will the tire thing make?
  • michaelede
    michaelede Posts: 152
    Could there be a reasonable difference in the circumference of the tire? If your new tyre had a bigger circumference you would be turning the turbo faster for the same cadence which would be harder.
  • diamonddog
    diamonddog Posts: 3,426
    littledove44 wrote:
    diamonddog wrote:
    It's 23mm that usually run at a slightly higher pressure than 25mm IME.
    I know that. That's what I do on the road. This just happens to be what they actually were at when I used the turbo.

    My question is, does pressure and tire size make that much difference to power?

    I am quite happy to keep the setup identical in future, but before I start redoing FTP tests I want to see if others have experienced such big differences.

    Stickier compound on new tyre could make a difference to effort required for same results, just to say I have turbo tyre fitted so different set up to you.
  • mattv
    mattv Posts: 992
    Grippier tyre with different tread pattern will make it harder work as will the low tyre pressure. Crank it up to 110 and see if it's easier!
  • xavierdisley
    xavierdisley Posts: 159
    Yes, it (rolling resistance) will make a difference to your reported power if you're using a turbo speed based option. It's exacerbated if you ride on rollers (as you have two tires in contact with the rollers) but will happen on a normal turbo too. If you're using something like Trainerroad then for consistency you must use the same tyre and pressure (and type of inner tube! ie. butyl or latex) each time.

    Xav
    twitter@xavierdisley
    http://www.rstsport.com
  • imposter2.0
    imposter2.0 Posts: 12,028
    Did you do a roll-down test with your previous tyre? If you did, just adjust the roller pressure to give you the same reading with the new tyre..
  • littledove44
    littledove44 Posts: 871
    Imposter wrote:
    Did you do a roll-down test with your previous tyre? If you did, just adjust the roller pressure to give you the same reading with the new tyre..

    Sorry, but no I didn't.

    What is it, how do I do it?
  • littledove44
    littledove44 Posts: 871
    xavierdisley wrote:
    Yes, it (rolling resistance) will make a difference to your reported power if you're using a turbo speed based option. It's exacerbated if you ride on rollers (as you have two tires in contact with the rollers) but will happen on a normal turbo too. If you're using something like Trainerroad then for consistency you must use the same tyre and pressure (and type of inner tube! ie. butyl or latex) each time.

    Xav

    Thanks. As the setup is now finalised I guess it's a new FTP test. Lovely.
  • imposter2.0
    imposter2.0 Posts: 12,028
    littledove44 wrote:
    Imposter wrote:
    Did you do a roll-down test with your previous tyre? If you did, just adjust the roller pressure to give you the same reading with the new tyre..

    Sorry, but no I didn't.

    What is it, how do I do it?

    Wind the bike up to a given speed (say 20mph) and then stop pedalling and time how long it takes for the wheel to come to a complete stop. By adjusting roller pressure on the tyre, you can use this measure to set up any other wheel/tyre combo to give pretty much the same performance.
  • dw300
    dw300 Posts: 1,642
    Imposter wrote:
    Wind the bike up to a given speed (say 20mph) and then stop pedalling and time how long it takes for the wheel to come to a complete stop. By adjusting roller pressure on the tyre, you can use this measure to set up any other wheel/tyre combo to give pretty much the same performance.


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  • gotwood25
    gotwood25 Posts: 314
    Imposter wrote:
    littledove44 wrote:
    Imposter wrote:
    Did you do a roll-down test with your previous tyre? If you did, just adjust the roller pressure to give you the same reading with the new tyre..

    Sorry, but no I didn't.

    What is it, how do I do it?

    Wind the bike up to a given speed (say 20mph) and then stop pedalling and time how long it takes for the wheel to come to a complete stop. By adjusting roller pressure on the tyre, you can use this measure to set up any other wheel/tyre combo to give pretty much the same performance.

    Nice tip, I am in a similar position in that I did my FTP test and the first week of training on my 'good bike' and have since used my 'winter bike' which I reckon is costing me around 40 watts (virtual power). In fact I can't even get close to my FTP for short intervals so torn between putting the good bike back on the turbo (don't really want to do that) or doing an FTP test on the winter bike which I really don't want to do as it would give me terrible numbers :D

    Will give this method a go first and see if it saves me any unnecessary pain.

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