Is lower pressure on longer road rides a thing?

Discussion in 'General Cycling Discussions' started by Hopey, 10 Feb 2019.

  1. Hopey

    Hopey Well-Known Member

    Location:
    Edinburgh
    I have one bike; a cross/gravel bike that acts as my do-it-all bike. I tend to just change tyre pressure depending on what I'm doing. I use schwalbe landcruisers - 40mm up front, 35 up back.

    If I'm doing a longer road ride I usually pump up the PSI to around 60-65 on both tyres to roll better. If I'm heading up the pentlands or going off road, I'll drop down to ~39-40PSI on the front and 43 on the back, which gives me enough grip.

    I've found that when riding with the lower pressure, I generally stay comfortable and happy for longer. Even with the bumps and roughness that comes with off-road riding on a rigid bike, my back particularly is usually fine. I'm finding that on road rides though, even when the ride is more smooth, I get tired quicker and my back gets stiffer quicker.

    I'm starting to wonder if this is due to my tyre pressure. My question is; is lowering tyre pressure for longer road rides a thing? I'm planning on doing a 40 miler tomorrow all on road, and am considering bringing the pressure down a bit to see if that helps, but don't want to do it if the comfort thing is all in my head and I'll just be making the ride draggier for no reason.
     
  2. lazyfatgit

    lazyfatgit Veteran

    Location:
    Lawrence, NSW
    Do what's comfortable. If the tyres are not squirming or getting pinch flats at the lower pressures off road then give them a try?
     
  3. Finding the balance is key IMO too high and its too harsh to ride to low and its energy sapping and you risk pinch p'tures. I'm 65kg and my sweet spot seems to be around 85-95psi. I'll usually pump to around that but dont top up for a bit. I find they dont get energy sapping until there below 60psi and I've usually topped up before that. Touch wood I've never found pinch p'ture a problem or I might be inclined to top up more regularly.

    Edit Ive have narrower road tyres. The last time I had 40mm it was a sweet spot around 35-45psi and I didn't get an energy sapping ride until nearly 25psi IIRC.
     
    Last edited: 10 Feb 2019
  4. YukonBoy

    YukonBoy Extra solar

    Location:
    Ultima Thule
    It may just be that you move around more when off road. Staying in the same position on a bike for long periods can lead the numbness and pain. Regards pressures experiment and see what works for you. Tyres have a range and somewhere in there will be a sweetspot for you on road. 65 psi does sound high for a 40mm tyre.
     
    Reiver likes this.
  5. Ajax Bay

    Ajax Bay Veteran

    Location:
    East Devon
    If you and the bike weigh 100kg then from the authoritative BQ article (attached), on road go for 40 on the front and 60 on the rear.
    For every 2kg less, drop one psi in each tyre (for 37mm wide tyres) - data drawn from graph in article.
    As an aside, from a pressure PoV, you're better off with the wider tyre on the rear.
    I rather doubt that the pressures you're running your tyres at on the road are the reasons for you getting tyred ;) and stiff(er) quicker. Perhaps your effort is more sustained on the road. Perhaps you could wear a heart monitor for two rides of similar length and compare the data.
    Dropping the pressures in your tyres will increase the rolling resistance without (at this width tyre) making much suspension difference.
     

    Attached Files:

  6. Slioch

    Slioch Veteran

    Location:
    York
    Just be careful not to drop the pressures so low it affects performance in emergency situations.

    I was running a front tyre on a lot lower pressure than normal, and whilst going downhill on a bend had to haul on the anchors hard. I could feel the tyre "squirm" and thought I wasn't going to make the turn. A seriously squeaky bum moment.
     
  7. andrew_s

    andrew_s Guru

    Location:
    Gloucester
    Lower pressure is indeed a thing, and not just for long distance.

    If you reduce the tyre pressure, the rolling resistance of the tyre goes up, by an amount that depends on the tyre model and what the high and low pressures actually are, but could be 5 - 10 watts per tyre in some cases.

    However, that's not the only thing going on.
    As you ride along, road vibrations feed through the bike into your body, where the energy used to do the vibrating gets absorbed. You can take discomfort as the sign that a significant amount of energy is getting absorbed. That energy has to come from somewhere, and that somewhere is your legs, in the form of extra work. It's this extra work that makes an uncomfortable ride tiring. Lower tyre pressures reduce the vibration, and hence the extra work required.
    The amounts of extra work can be large - more than 200 watts has been tested on a particularly rough surface.

    In practice, there's a sweet spot between increasing pressure for lower losses in the tyre, and before the tyre gets uncomfortably hard and the losses vibrating you increase too much.
    See graphs here: https://silca.cc/blogs/journal/part-4b-rolling-resistance-and-impedance

    I take the view that if it's uncomfortable, I reduce the pressure (with due regard to the limitations of pinch punctures and squirm). This generally ends up with me riding somewhere about 50 psi in 35c tyres, though this does depend on road surface.
    If in doubt, a bit soft is generally better than a bit hard.
     
    Last edited: 11 Feb 2019
  8. Heckler

    Heckler Active Member

    FNAR FNAR!:giggle:
     
  9. OP
    OP
    Hopey

    Hopey Well-Known Member

    Location:
    Edinburgh
    Very helpful replies folks, thanks. Didn't make it out today due to a mechanical issue, but will try 50psi on road when I'm back on the road.
     
  10. Cuchilo

    Cuchilo Prize winning member X2

    Location:
    London
    I normally use 120 psi on my road bikes and top up before every ride .
    I put 100 psi on my road bike with marathon plus and only check that now and then , normally when i feel its slow and the pressure is about 60-70 psi when i check it .
     
  11. Fab Foodie

    Fab Foodie hanging-on in quiet desperation ...

    Yes it’s a thing. As is a general move towards fatter tyres for the road.
    Every rider/tyre combo has a sweet spot between comfort wnd efficiency. Whilst once narrow tyres and high pressures were the thinking, now lower pressures and slightly larger tyres are the case. No doubt tyre technology has influenced this greatly.
    In addition, UK roads are becoming like gravel tracks anyhow....
     
  12. Zofo

    Zofo Senior Member

    Location:
    Leicester
    Now riding on 28mm on front with 25mm rear -as frame is too tight for larger size. Pressures are 80 front and 85 rear, Ive found this to be ideal for me -weight is 75kg.
     
  13. YukonBoy

    YukonBoy Extra solar

    Location:
    Ultima Thule
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