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Lower tyre pressure findings

zefszefs Posts: 484
edited July 2016 in Road general
I am 65kg and I was always using 100-110 psi on my 25c tyres. On rides longer than 50k's I was getting back pain and saddle pain as well as a lot of fatigue on the legs for not so hard effort that I was doing.

Recently I tried 80psi and I noticed that I get less fatigue on the legs and also less pain both on back and saddle.
Although I feel 65-70 psi would be perfect for me comfort wise (also tried it) I might settle on 80 psi as the rolling resistance is 1-2 watts lower based on http://www.bicyclerollingresistance.com/ (for conti gp's 4000s ii).

I feel though that the rolling resistance penalty is a bit more than stated on that site. The comfort of the ride is a lot better though.
Also I am aware of the increased chance for flats but I will keep testing to see how it goes. Few questions

1) Is there a change in tyre life when using lower psi?
2) Is there a way to get that level of comfort I am getting at ~65 psi with a different setup (carbon wheels?) at ~100psi to eliminate the rolling resistance/speed penalty? I can't use 28c tyres as the frame doesn't support them.

Posts

  • cougiecougie Posts: 22,512
    2 watts in rolling resistance is not Noticeable.

    Are you using less pressure in the front? There is less weight so you can do this.

    I've swapped to 25mm an lower pressure And I've been over some godawful roads lately. Tyres have been perfect. Embrace the change!
  • BobbinogsBobbinogs Posts: 4,841
    My race weight is also 65kg (although my current preference for cold cider finds me the wrong side of that target). I have found that 80R and 70-75F to be pretty much ideal for 25s (on a very hilly route I will often go 80F though to compensate for the weight shift). I haven't detected an increase with rolling resistance or pinchflats but it does start to get 'squishy' below 70 and it started to feel sluggish. The quality of the roads makes a big difference and I found that riding in France meant that I went up 10PSI as the smooth roads seemed to be a bit more zippy at that pressure.

    A recent switch to wide rim wheels (17mm internal) has also been great...like cherries on the cake in terms of comfort and road holding.
  • zefszefs Posts: 484
    Thanks, seems like I will keep using that PSI as the roads here are bad. For me though I can feel a bit of difference in rolling resistance (maybe around 20w on strava but need to test further) and also like ~4km/h slower.
  • AK_jnrAK_jnr Posts: 717
    Strava power estimation is pure guess work so disregard that.
  • singletonsingleton Posts: 2,032
    AK_jnr wrote:
    Strava power estimation is pure guess work so disregard that.

    For a specific point in time measure I agree entirely, but for an average or a comparable figure then it's useful.

    It comes down to mathematics - moving a known weight, over a known distance and elevation with a known speed will require a calculable amount of power.
  • stevie63stevie63 Posts: 481
    Singleton wrote:
    AK_jnr wrote:
    Strava power estimation is pure guess work so disregard that.

    For a specific point in time measure I agree entirely, but for an average or a comparable figure then it's useful.

    It comes down to mathematics - moving a known weight, over a known distance and elevation with a known speed will require a calculable amount of power.
    Problem is strava does not take into account wind speed and direction and it can't know if you are drafting.
  • keezxkeezx Posts: 1,316
    Here is a set of blog postings from Josh Poertner at Silca, showing the relationships between tire pressure, ride comfort, rolling resistance, aerodynamics, and pinch flat resistance:

    https://silca.cc/blogs/journal/11839...-we-got-to-now

    I am 82 kg and never pump anything more than 6,5 / 6,0 bar.
    Never felt any resistance punishment and much more pleasant rides.
  • bigmatbigmat Posts: 5,127
    I rode Paris Roubain on 28s at 60PSI, I can confirm that this reduced the life of my rear tyre to around 100km!
  • AK_jnrAK_jnr Posts: 717
    Singleton wrote:
    AK_jnr wrote:
    Strava power estimation is pure guess work so disregard that.

    For a specific point in time measure I agree entirely, but for an average or a comparable figure then it's useful.

    It comes down to mathematics - moving a known weight, over a known distance and elevation with a known speed will require a calculable amount of power.

    I take it you dont have a PM then? If you did you would realise how wildly different the same route and average speed can be.
  • mfinmfin Posts: 6,724
    zefs wrote:
    I am 65kg and I was always using 100-110 psi on my 25c tyres.

    Which is a ridiculous pressure for your weight. So, forget any findings and experience from having ridden like this.
  • imposter2.0imposter2.0 Posts: 11,386
    Singleton wrote:
    It comes down to mathematics - moving a known weight, over a known distance and elevation with a known speed will require a calculable amount of power.

    Except for the unknown variables, like wind direction, wind speed, road surface quality, and so on...
  • cougiecougie Posts: 22,512
    Just how big are you bigmat?
  • bigmatbigmat Posts: 5,127
    cougie wrote:
    Just how big are you bigmat?

    Around 82kg. Low pressures were great for grip and got me through Arenberg, but I took a few big hits too many and blew the tyre off it's bead. You can go too low...
  • MiddleRingerMiddleRinger Posts: 678
    I've always been a "slam in 100psi and go" kind of man. A little while back I had to pump both my tyres up from flat using a little mini hand pump. I threw in as much air as my little cyclist arms would let me and rode off with no way of checking the actual pressure.

    It felt like somebody had smoothed out the road in front of me! The difference in ride comfort was very noticeable, so much smoother and none of the usual harshness. Not sure about rolling resistance but doubt it was much. When I got home I checked and I had 70psi rear with 60psi front. I don't run them that low but I've certainly backed my pressures off a little since then.
  • First.AspectFirst.Aspect Posts: 7,455
    I'd agree that a value such as the Strava power is unlikely to be either accurate or precise.

    It is entirely possible for rolling resistance to increase with increased tyre pressure, on a rough surface. We do ride on British roads after all......
  • cougiecougie Posts: 22,512
    BigMat wrote:
    cougie wrote:
    Just how big are you bigmat?

    Around 82kg. Low pressures were great for grip and got me through Arenberg, but I took a few big hits too many and blew the tyre off it's bead. You can go too low...

    Oof. I guess that is pretty extreme but is it possible you had a slow puncture taking the pressure down further?

    We've been doing some garmin route exploring of late - so basically plotting new routes to places and as a result are using a lot of lanes we've never ridden before. We've found some godawful ones but thanks to going to 25mm and lower psi things seem to be pretty decent.

    And I used to ride ludicrous pressures! 140 psi in vredesteins.
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