Tyre pressures

pedalbasher
pedalbasher Posts: 215
edited April 2014 in Road general
Can anybody tell me how I work out my ideal tyre pressures?

65kg, running 25mm Continental GP4000s on Reynolds Assault wheels. Dry conditions, decent roads.

Much obliged!
«1

Comments

  • KevChallis
    KevChallis Posts: 646
    I use trial and error, but 120psi is what I run, practically all the time :)

    I'm 69kg, on 23c tyres (can't remember what off the top of my head)
    Kev
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  • stanthomas
    stanthomas Posts: 265
    Conti recommend 6.5 bar (95psi) for those tyres. You're light enough to run them a little lower, especially in the front. Try that as a starting point to play around and see what works best for you.
  • Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
    Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
    Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
    Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33
    Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
    Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67
  • mmacavity
    mmacavity Posts: 781
    Trial and error is probably the only real answer.
  • macleod113
    macleod113 Posts: 560
    mmacavity wrote:
    Trial and error is probably the only real answer.

    this ^^ is what i would suggest. i'm 100kg and run 110 rear and 100 front on 25mm 4000s's. seems fine by me but trying a few ways might tell you more than a forum
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  • ai_1
    ai_1 Posts: 3,060
    Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
    Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
    Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
    Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33
    Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
    Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67
    Is that front, back, average or suggesting they should be the same?

    Those calcs seem to give reasonable pressures for the rear tyre but I'd be inclined to drop the front a little - especially in the wet or on bad roads.
    In my case I'm ~87kg using 25mm Continental 4 Seasons. On good roads and if I may be doing some climbing or sprinting I'll go for about 95F/110B. If it's wet or I'll be on bad roads I prefer lower pressures around 80F/95B. I've never had a pinch puncture with these pressures. I do find the front can start to feel a little mushy when sprinting or climbing when i get down towards 80psi at the front.

    I'd say use the above as guidance for the rear and drop 10-15% on the front as a starting point. Then play around with higher and lower pressures and see what you like. Your riding style, preferences and location will have a bearing. Some people sit further forward and stay lower so load the front more, others sit back and upright. Some rarely get out of the saddle others get out regularly. Some hit bumps hard, others are good at dodging them or unloading the bike as they hit them. You may have nice smooth roads where you ride or you may spend most of your time on road acne. Lower pressure will increase grip and obviously smooths the ride. Higher pressure can feel crisper and more connected or can feel harsh.
  • ai_1
    ai_1 Posts: 3,060
    Your weight in pounds minus your IQ.
    Some people are going to have a mighty harsh ride and may rupture some tyres!
  • Moonbiker
    Moonbiker Posts: 1,706
    Vittoria have an app for it

    http://www.vittoria.com/en/app/
  • owenlars
    owenlars Posts: 719
    I wouldn't get too hung up on it. A dollop of sound common sense should see you alright. If you get a pinch flat crank up the pressure a bit, if you get a very harsh ride crank it down a bit in other words trial and error is right.
  • ai_1
    ai_1 Posts: 3,060
    Moonbiker wrote:
    Vittoria have an app for it

    http://www.vittoria.com/en/app/
    Oddly I don't see any option to select the tyre size. This seems odd given it's one of the crucial variables along with rider & bike weight, and road conditions which are requested. Not sure this is much use as a result.
  • BrandonA
    BrandonA Posts: 553
    I weigh the same as you.

    I don't think it really matters as long as you stick within the guidelines for the tyres. Personally my Mavic 23 mm tyres say up to 125 PSI. I quite like pumping them to the max.

    If I get a puncture though at the side of the road I usually manually put in 80-90 and I don't have an issue completing the ride with this.

    What I don't like is a lower pressure in the front tyre because if you really sprint hard you can feel the bike going up and down.
  • drlodge
    drlodge Posts: 4,826
    I pump it up until its hard. Same for the tyres.
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  • kajjal
    kajjal Posts: 3,380
    Your weight in pounds minus your IQ.

    Thats way over the max tyre pressure ;)

    I am about 100kg and use 105psi front and back with no problems.
  • Initialised
    Initialised Posts: 3,047
    You'll have to use lbs for this one: http://www.dorkypantsr.us/bike-tire-pre ... lator.html
    I used to just ride my bike to work but now I find myself going out looking for bigger and bigger hills.
  • Mikey23
    Mikey23 Posts: 5,306
    Conti 25s at 100
  • Ai_1 wrote:
    Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
    Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
    Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
    Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33
    Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
    Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67
    Is that front, back, average or suggesting they should be the same?

    Those calcs seem to give reasonable pressures for the rear tyre but I'd be inclined to drop the front a little - especially in the wet or on bad roads.
    In my case I'm ~87kg using 25mm Continental 4 Seasons. On good roads and if I may be doing some climbing or sprinting I'll go for about 95F/110B. If it's wet or I'll be on bad roads I prefer lower pressures around 80F/95B. I've never had a pinch puncture with these pressures. I do find the front can start to feel a little mushy when sprinting or climbing when i get down towards 80psi at the front.

    I'd say use the above as guidance for the rear and drop 10-15% on the front as a starting point. Then play around with higher and lower pressures and see what you like. Your riding style, preferences and location will have a bearing. Some people sit further forward and stay lower so load the front more, others sit back and upright. Some rarely get out of the saddle others get out regularly. Some hit bumps hard, others are good at dodging them or unloading the bike as they hit them. You may have nice smooth roads where you ride or you may spend most of your time on road acne. Lower pressure will increase grip and obviously smooths the ride. Higher pressure can feel crisper and more connected or can feel harsh.


    If it's wet you should raise tyre pressure, never lower! By lowering the pressure you're allowing the tread to close up therefore restricting water dispersal therefore lowering grip!
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  • ai_1
    ai_1 Posts: 3,060
    Ai_1 wrote:
    Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
    Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
    Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
    Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33
    Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
    Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67
    Is that front, back, average or suggesting they should be the same?

    Those calcs seem to give reasonable pressures for the rear tyre but I'd be inclined to drop the front a little - especially in the wet or on bad roads.
    In my case I'm ~87kg using 25mm Continental 4 Seasons. On good roads and if I may be doing some climbing or sprinting I'll go for about 95F/110B. If it's wet or I'll be on bad roads I prefer lower pressures around 80F/95B. I've never had a pinch puncture with these pressures. I do find the front can start to feel a little mushy when sprinting or climbing when i get down towards 80psi at the front.

    I'd say use the above as guidance for the rear and drop 10-15% on the front as a starting point. Then play around with higher and lower pressures and see what you like. Your riding style, preferences and location will have a bearing. Some people sit further forward and stay lower so load the front more, others sit back and upright. Some rarely get out of the saddle others get out regularly. Some hit bumps hard, others are good at dodging them or unloading the bike as they hit them. You may have nice smooth roads where you ride or you may spend most of your time on road acne. Lower pressure will increase grip and obviously smooths the ride. Higher pressure can feel crisper and more connected or can feel harsh.


    If it's wet you should raise tyre pressure, never lower! By lowering the pressure you're allowing the tread to close up therefore restricting water dispersal therefore lowering grip!
    By raising pressure you're reducing the contact area of the tyre thus reducing grip.
    Tyres are flexible but fairly unstretchable. There'll be very little change in tread openness or closeness due to tyre pressure and treads shouldn't be, and I believe are not, that critically designed anyway.
  • JackPozzi
    JackPozzi Posts: 1,191
    Water dispersal in bicycle tyres isn't an issue, definitely lower pressure (if anything) for extra contact area in the wet!
  • Moonbiker
    Moonbiker Posts: 1,706
    My rubino have tread pattern chervons on tyres so they have to be the right way round not that it would probably make a difference if they were fitted the wrong way round?

    I always thought the tread pattern was to the shed water from the tyre.Tyres designed for wet seem to have more tread pattern than dry weather tyres which are more slick.
  • nawty
    nawty Posts: 225
    Even Continental admit they only put grooves on their road tyres because people think they work and therefore like to see them, but they don't actually do anything. Narrow road tyres grip is all about contact area, more the better in the wet so I run as low as I dare to avoid pinch flats.

    I'm 75kg and in the dry I run 24mm tyres @ 90psi on 23mm wide rims.
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  • i must agree to disagree on this one. Any professional racer of motorsport will tell you that you have more grip in the wet with a higher tyre pressure than the dry (on the same tyres) due to the tread remaining open and also another factor is that the tyres remain cooler so less expansion of the tyre through heat
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  • ai_1
    ai_1 Posts: 3,060
    i must agree to disagree on this one. Any professional racer of motorsport will tell you that you have more grip in the wet with a higher tyre pressure than the dry (on the same tyres) due to the tread remaining open and also another factor is that the tyres remain cooler so less expansion of the tyre through heat
    However, I believe motorsport is quite a different animal with respect to tyres. The tyre pressures are significantly lower (compared to road cycling), the energy transfered is far greater, the tyre width is far greater and the ratio of surface area to volume is much greater. Tyre temperature isn't a significant problem for cycling due to greater surface area relative to the energy levels involved - and cooling is helped when wet. Tyre deformation is much greater in motorsport due to higher energy transfer, higher volume tyres, and lower pressure. Hydro-planing is a much bigger risk in motorsport due to tyre width which makes treads much more relevant.
  • DiscoBoy
    DiscoBoy Posts: 905
    i must agree to disagree on this one. Any professional racer of motorsport will tell you that you have more grip in the wet with a higher tyre pressure than the dry (on the same tyres) due to the tread remaining open and also another factor is that the tyres remain cooler so less expansion of the tyre through heat

    Water dispersion is not an issue for bicycles. Bicycles cannot aquaplane at normal speeds.

    http://sheldonbrown.com/tires.html
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  • I'm 80kg and run 90psi on the front and 100psi on the back. That said I don't even know if the gauge on my pump is accurate so I'd agree that trial and error is the way forward.

    Also,or higher pressures in the wet - bike tyres are not the same as car tyres. Road bike tyres generally don't have tread for starters and when they do they're usually just there for show. Personally I can't see any advantage to changing the pressure in the wet.
  • Sprool
    Sprool Posts: 1,022
    There seems to be general agreement on road tyres amongst those who know, such as Sheldon et al, that groove patterns are merely cosmetic and of no practical use, therefore there is no 'right' or 'wrong' way to put the tyre on, despite having searched for 10 minutes for the tiny embossed rotation direction arrow. Wider tyres can be run at lower pressures thus are more comfortable, and road tyres will cut through the water film on the road surface if they are 80 psi or 110. I used to run 23's at 105-110, now I run 25's at 95-100, I am 78kg.
  • neeb
    neeb Posts: 4,467
    i must agree to disagree on this one. Any professional racer of motorsport will tell you that you have more grip in the wet with a higher tyre pressure than the dry (on the same tyres) due to the tread remaining open and also another factor is that the tyres remain cooler so less expansion of the tyre through heat
    Err, yes, but we are talking cycling here, not motorsport... :):)

    Firstly, road bike tyres don't generally have any tread. And temperature is clearly much less of an issue than it is with a motor bike travelling at 200mph or whatever... :)

    This is actually pretty dangerous and misleading advice. Any professional road cyclist will tell you that you get better grip in the wet at lower pressures.
  • neeb
    neeb Posts: 4,467
    As far as general tyre pressure in dry conditions goes, the biggest factor is the quality of the road surface IMO, which isn't taken account of at all in those calculations based on weight.

    I think most of the disagreements and arguments about this issue are caused by people talking past each other because they are riding on very different road surfaces.
  • Monty Dog
    Monty Dog Posts: 20,614
    A lot of riders misinterpret harsh feel with speed: Higher pressures = more bounce i.e. the tyre is not in contact with the ground and therefore not transmitting power. Generally, the rougher the surface, lower the pressure, which also means the carcass can flex and allow the rubber to keep in contact, particularly on corners. Treads have no function on a road tyre - the pressure of the tyre simply displaces the water.
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