29er Tyre Pressures

The_Wicker_Man
The_Wicker_Man Posts: 338
edited November 2016 in MTB workshop & tech
Just upgraded my tyres on my 29er and wondering what pressure is best for them. Mainly forest trails and some tarmac too.

My old tyres were Specialized Ground Control 2.1 set at 2 bar front and rear.
My new tyres are Continental Trail Kings. 2.2 on the rear and 2.4 on the front.

My current weight is 99kg

Comments

  • The Rookie
    The Rookie Posts: 27,812
    Less than that! About 26-28psi.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • N0bodyOfTheGoat
    N0bodyOfTheGoat Posts: 5,845
    On the road, I inflate my 38c Marathon Crosses to ~73PSI front and 80PSI rear, at ~79Kg (lost ~11Kg since mid summer) plus ~5Kg of clothes and shoes while chasing my own personal Strava segment times.

    For off-road, I could easily drop the pressures by another ~10%+.
    ================
    2020 Voodoo Marasa
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  • LimitedGarry
    LimitedGarry Posts: 400
    Depends on the tires, where you ride, and whether tubeless or tubes. I'm at around 108-111Kg (depending on how much I'm working out, eating and riding), running tubes.
    Maxxis Ardent 2.2 on the front gets around 28PSI.

    Maxxis Ikon 2.25 on the rear gets anywhere between 35-45PSI, depending on the trip expectations. I prefer to put more pressure into the tire when not sure, since it's easier to let air out than put more in when out there.
  • JBA
    JBA Posts: 2,852
    2bar is 29psi. Try that in the front and maybe up the rear to 36psi and see how it feels.
    “Life has been unfaithful
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  • kajjal
    kajjal Posts: 3,380
    Its really personal preference, far too low and the tyres roll off the rims, too high and you get a rougher ride.

    I have both tyres at 40psi on my xc hardtail as it gives me the consistent handling i want. I ride mainly natural trails.
  • The Rookie
    The Rookie Posts: 27,812
    At that pressure that would be consistently no grip I think!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • kajjal
    kajjal Posts: 3,380
    The Rookie wrote:
    At that pressure that would be consistently no grip I think!

    My massive honed muscular physique pins the bike to the trail :)
  • The Rookie
    The Rookie Posts: 27,812
    Argh, so weight/strength changes mu does it, silly me!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Rightarmbad
    Rightarmbad Posts: 216
    Kajjal wrote:
    The Rookie wrote:
    At that pressure that would be consistently no grip I think!

    My massive honed muscular physique pins the bike to the trail :)

    The conti's have pretty good sidewall stability so low pressures are possible on a modest rim.
    But 99kg is pretty heavy for a 2.2, so you will more than likely be well over 30 psi in the rear.
    High 30's wouldn't surprise me at all.
  • mugensi
    mugensi Posts: 559
    I have Rapid Rob/Tough Toms and inflate to 36psi front and 44psi rear. I'm 76kg and those pressures work good for me.
  • The Rookie
    The Rookie Posts: 27,812
    'Work good' compared to what? Unless you are doing very light XC that's stupid hard and will reduce grip AND increase rolling resistance.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Rightarmbad
    Rightarmbad Posts: 216
    MugenSi wrote:
    I have Rapid Rob/Tough Toms and inflate to 36psi front and 44psi rear. I'm 76kg and those pressures work good for me.
    I can only assume that you ride fast open gravel roads at those sorts of pressures.
  • The_Wicker_Man
    The_Wicker_Man Posts: 338
    MugenSi wrote:
    I have Rapid Rob/Tough Toms and inflate to 36psi front and 44psi rear. I'm 76kg and those pressures work good for me.

    Too hard for the trails. I've came down to around 28psi, only been out for a few rides and seems ok but could probably lower it a bit more on the front.
  • whyamihere
    whyamihere Posts: 7,702
    The Rookie wrote:
    Argh, so weight/strength changes mu does it, silly me!
    How exactly is the tyre pressure going to change mu? :wink:

    The lower the tyre pressure, the more deformation you'll get - This increases grip as (to simplify things) the rubber can wrap around any bumps more easily, so makes a larger contact patch. Also, for a given pressure, a heavier rider will get more grip (if we ignore for a moment the effect of the added mass on the centripetal force...) due to greater tyre deformation. Coefficient of friction is essentially a constant between 2 materials (not that you ever really get the same materials consistently on an MTB).

    In answer to the original question: Start at what you know, then experiment. It's free, so you may as well...
  • The Rookie
    The Rookie Posts: 27,812
    whyamihere wrote:
    The Rookie wrote:
    Argh, so weight/strength changes mu does it, silly me!
    How exactly is the tyre pressure going to change mu? :wink:
    It doesn't, but Kajjal says it does, you may have heard of sarcasm?
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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