Tire pressure

Discussion in 'Cycling Training' started by grizzlybxl, Aug 7, 2018.

  1. grizzlybxl

    grizzlybxl New Member

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    This will probably sound totally dumb or silly but we all ask dumb questions when we're noobs so bear with me and hear me out. Coming to the sport late, but better late than never.

    I was way into cycling a few years ago and started riding my bike (a Centurion CitySpeed 8) on a regular basis. (Really, I wanted a road bike but I ended up with this city bike for various reasons.) I stopped for a while because I grew increasingly frustrated with a relatively recurring problem - pinched tires, often the back one.

    I recently caught the cycling bug again and managed to make it some 215km before getting another pinched tire. This time, I took it to a bike shop where they were actually helpful: rather than simply fixing my tire, they explained that (yes, I know, shocking) my tires were at around half the bar they should have been.

    So now I know, but riding my bike home from the shop I felt uncomfortable because the tires were so hard that I could feel every little bump in the road and it felt kind of similar to what it feels like when you get a flat - it's a totally different sensation and I found myself riding 20kph instead of 30 because I was worried about pinching my tires again.

    Any tips for how to get used to the new tire pressure?
    Also, will it guarantee that I don't pinch my tires, or just lower the risk?
    Last question - since it's often the rear tire that gets affected, could it have to do with my position on the saddle?
     
    #1 grizzlybxl, Aug 7, 2018
    Last edited: Aug 7, 2018


  2. Henrywrites

    Henrywrites Member

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    It is not easy to adjust to the tire pressure, but it does not mean that it is something which you can get used to. The only thing I would advise is that you continue that way since it is one of the ways to get everything working right.
     
  3. dabac

    dabac Well-Known Member

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    Get a pump with a pressure gauge.
    If you’re intimidated by flats, inflate to the pressure listed on the tire sidewall at least weekly.
    If your rate of flatting was almost tolerable at half the recommended pressure, then your rate of pinch flats should drop to near nothing at the correct pressure.
    Really, for road riding, pinch-flatting should only happen if you hit a bad pothole or a curb at speed.
    Short of going to solid aka airfree aka airless tires or foam inserts, correct air pressure can never fully protect you against pinch flats.
    Air is compressible. Hit something hard enough and the tire will compress to the point where a pinch flat can occur.
    The rear carries more weight anyhow, so it isn’t your position on the saddle as such that’s to blame. Rather that you’re sitting too heavily, too inert in the saddle.
    You might merit from a little technique called ”going light”.
    This means getting out of the saddle, arms and legs lightly bent. Let the bike move beneath you when you hit a bump.
    If you find the right pressure unpleasant, you can get suspension seat posts.
    Or you can fit the widest tire your frame will accept and lower the pressure some.
    Why not start with riding some more, get acclimatized?
     
  4. Corzhens

    Corzhens Well-Known Member

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    @dabac, thank you for posting the information on tire pressure. To be honest, I am a newbie when it comes to technical aspects of bicycles. My habit is to use the bike when I don't see anything wrong and check it when something is amiss. Pinched tires or flat tires can happen and I attribute it to luck. Our car had 2 flats in a span of 1 months but it happened only when our car was already 5 years old. With the bike, it's the same thing. I got a flat after a long time and that is due to the dirty road.
     
  5. DenisP

    DenisP Member

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    I live in an area with really poor road infrastructure, and the local council doesn’t really care much to fix things. It’s a rural town so everything is on a tight budget, and apparently roads aren’t in that budget. As a result, I always have to keep my tire pressure on the higher end of the spectrum because occasionally I’ll have to stick to the side of the road while a car passes and I won’t be able to swerve out of the way of a pothole. Keeping my pressure on the lower end almost guarantees a pinch there.

    That being said, it’s kind of a moot point given that besides for transportation, I use my bike for mountain biking where I find harder tires to be much more important.
     
  6. Froze

    Froze Well-Known Member

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    There is a science behind having the correct psi that's been around for a very long time, back when I use to race in the 70's and 80's we used a paper graph (chart) to get the correct PSI, today we have the handy dandy internet and you can go to this site: http://www.dorkypantsr.us/bike-tire-pressure-calculator.html It's easy to use, simply go to the second calculator (not the first one) input your total clothed ready to ride body weight and your total ready to ride bike weight, add those two figures and enter the answer in the box that says "rider + bike"; then go to the next box that says "40%/60%" and leave it alone; move on to the third box that says "front tire width" open that box and put in your tire width which I think yours is 37mm; go down to the last box that says: "rear tire width" and do the same thing; once you've entered the last value the psi will pop into the boxes that say "inflate front/rear to_________PSI, and that's it you're done.

    Now that calculator will get you darn close, you can go 5 pounds either way, for example if comfort is more important or you have rough roads reduce the psi by 5, if speed is more important and you have smooth roads increase the psi by 5, but that whole thing is based on load much like car tires, you never put in the max rated psi found on the sidewall of your car tire, you put in what the manufacture put on the sticker near the front door, same with bicycle tires, this is to give you max tread life, max handling, and lowering your watts needed to propel the bike forward. Now on rainy days you could reduce the psi by 10 to gain a bit of traction due to putting a tad bit more rubber to the ground but that's only for rainy days. There are a few tires who will give you a chart for their PSI, follow that chart instead of the calculator, but I doubt you'll be running into that issue with those tires but I felt I needed to make you aware of it.

    By the way you have a cool looking bike.
     
  7. BrianNystrom

    BrianNystrom Active Member

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    I used that calculator and it suggested a much higher rear pressure than I typically ride and a 19 PSI difference between the front and rear, which is ridiculous with a 45/55% weight bias (the 40/60 recommendation was even more ridiculous). From experience, I know that I can run 25mm tires at 70/80 front/rear at my 170# weight and have no issues with pinch flats. The calculator suggest 78/97, which I wouldn't consider unless I was using panniers and a handlebar bag. Considering that the source for the calculator is a site geared toward touring, perhaps it's biased that way.

    The first calculator seems to be broken, as it recommended 185psi! The third one recommended 100psi, which is way too high, especially in front.

    To the original poster, if you don't already own a good pump with a pressure gauge, get one. You should not be getting pinch flats with any regularity unless you're either letting your tires get too low or you're just clumsy and hit potholes and curbs frequently. Conversely, you shouldn't be getting pounded by overinflated tires that make riding unpleasant.

    Unless you're over 200 pounds, you should be comfortable at 40/50 to 50/60psi front/rear without getting pinch flats. Top off your tires at least every other day and you should be fine. Don't be afraid to experiment with your tire pressure to determine what works best for you. If you're light weight, you may find that lower pressures than the above will work for you. The key is to keep them consistent from ride to ride.
     
  8. Froze

    Froze Well-Known Member

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    That calc is based on tried and true science, so unless the tire manufacture gave you a chart of recommended pressures than it's darn close to being right. Even Vittoria tire company puts that same chart that the calc is based on on their packaging for every tire they sell; here is a similar chart that Vittoria uses: http://www.biketinker.com/2010/bike-resources/optimal-tire-pressure-for-bicycles/ and it's a chart that's been around a very long time.

    The issue isn't pinch flats although that's part of it especially if it's way under inflated, the main issue is optimal tire wear, traction, rolling resistance (to a lesser degree), and handling. You can't judge your tire pressure due to whether or not you get pinch flats. You may be 5 pounds above the pinch flat zone but your tires will wear faster and not handle nor roll as well (to a lesser degree) due to underinflated tires, plus you subject your sidewalls to damage and flats.

    Now why you may argue that pros use less pressure in their tires when riding on cobblestones, but one has to remember their using tubular tires so pinch flatting can't happen.

    If all you're after is ride comfort then yes you can drop your PSI down to 10 psi less than the calc recommends which would be the same psi you would run on rainy days.

    It's just a suggestion that's all, you can run whatever pressure you want it's your tires.

    On this site note the example and plug the weight they give into the calculator I gave and see what happens: https://www.bicycling.com/repair/a20009629/4-ways-your-tire-pressure-is-wrong/

    More discussion on this: http://www.biketinker.com/2010/bike-resources/optimal-tire-pressure-for-bicycles/

    https://www.compasscycle.com/wp-content/uploads/2015/03/BQTireDrop.pdf
     
  9. BrianNystrom

    BrianNystrom Active Member

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    That's all well and good, but the trend is toward lower pressures, particularly with wider rims that increase the tire volume. I also don't see how there can be a single "magic number" of 15% for all tire, tube, rim and road surface combinations; it simply doesn't make any sense.

    There is no way that I'm ever going to ride the recommended 97 psi in a 25mm road tire, as it would rattle my fillings loose and skitter all over the road. When I mentioned pinch flats, it was only to indicate that they weren't an issue, not that they were a significant consideration in my tire pressure selection, as I've only had one since I switched from tubulars (which I had ridden exclusively since 1974) back to clinchers 8 years ago. I arrived at the pressure I use after trying a lot of different settings until I found the sweet spot where the tires don't feel bouncy (too soft) or harsh (too firm).

    Old habits and myths die hard, and I still see a lot of people, often lighter than me, that insist that they have to run 100-120 psi in their tires. I have to chuckle a bit as they rattle down the road, wincing on every minor impact. The inefficiency is obvious when you can actually see their bikes bounce around from every surface imperfection.

    On a trip in Glacier National Park that we just completed a week ago, one of our guides mentioned a study of tire pressures that he used to convince people that they didn't need rock-hard tires to be efficient. I'll see if I can get a copy or a link to it. He indicated that he had the same problem convincing people that they didn't need high tire pressures. I lowered the pressure in some of the other riders' tires and they were all surprised at how much better their bikes felt and handled on the rough western pavement (apparently there's lots of gravel in their aggregate, but very little sand to fill the gaps between the chunks).

    The fact that the calculator suggests a 19 psi difference front-rear with 45/55% weight distribution indicates to me that it's seriously flawed. It doesn't make sense to run 27% more pressure in the rear tire than the front, when the difference in weight distribution is only 10%.

    The front pressure it recommended (78psi) is higher than I use, but at least reasonable. The rear pressure suggestion (97psi) is just plain ridiculous. I realize that I run things on the low end of the pressure spectrum for my weight, but increasing the rear pressure by 18 psi (21%) from what I run now is ludicrous.
     
  10. Froze

    Froze Well-Known Member

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    Like I said you are obviously free to use whatever pressure you like, you like a more cushioned ride which there is nothing wrong with that; I know people who run 10 to 20 pounds more PSI then the calc would suggest but they like a firm fast ride. I tend to ride about 5 psi less than the calc recommends because I like a bit more cushioned ride myself, but I also want my tires to last a long time and have max control should it be needed, and be less subject to flats although today's tires are far better in the flat department then they were even just 10 years ago.

    It's true that the newer wider rims don't require as much PSI as the older rims do but that hasn't been put into a calc format yet so I can't quote psi ratings.

    Pro racers using tubulars will run very high pressures, as much as 145 psi for smooth roads and depending on rider weight, while cobblestone racing will see the pros lowering it to 70 psi depending on rider weight of course, but on cobbles you see mostly tubeless tires and those that use tubes use latex and they'll start the race near that 70 level knowing that the latex will lose some psi during the race. I read somewhere that Cavendish used 105 psi and he only weighed 145 pounds which according to the calc would be way too high. During the TDF the range of psi is typically between 95 to 110, however when the TDF race hit the gravel this year they were using between 30 to 50 psi depending on tire width and rider weight, but again these guys were riding on either tubeless tires or tubulars so the lower psi wouldn't cause pinch flats, if they had to use tubes the pressure would probably be 50 to 70 range depending on rider weight, but the lower psi on gravel is necessary because at higher pressures the tires simply skip off the gravel and you lose traction and forward power. Having said that I've rode on gravel roads without altering my psi...BUT, I wasn't trying to see how fast I could go either, plus I didn't want to bother releasing air for the gravel section of the ride, stop when the gravel ends and put air back in then continue my ride, so I just dealt with it; if I know I'm going to be riding on a lot of chip and seal I will reduce my psi by 10 to smooth out the ride.

    Keep in mind too that the reason most non pro or non racers, use higher psi then recommended is because they are overly consumed with going faster, and they perceive that higher PSI as being faster; it's the same reason they'll spend, for example, $40 more for a product that weighs a gram less than they were using because they perceive that weight loss as being faster. It's all part of the placebo effect that real high psi in tires has and the minute weight savings has.

    Side discussion concerning words. I used the word minute to describe small, but the word is spelled the same for minute of time though both are not pronounced the same, shouldn't the small meaning be spelled mynute since that's the way it phonetically spoken? Kind of like the word in the American language for tire is something on car or bike, but it also means someone is tired, which the English spelling of tire for a car or bicycle is tyre which in my opinion would be the better choice. Or some words use unnecessary letters like knife could easily drop the k and just be nife. Language is weird. Sorry for the bunny trail side trip, I think of weird schit like that! LOL
     
  11. rfield54

    rfield54 New Member

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    I also ride 25mm's at 70/80psi, but I weigh 143lbs. After a lot of experimentation, I found this to be perfect for my tires and weight. If I weighed 170 (and I did at one time), I would definitely raise my pressure, likely to at least 80/90psi.

    With 23mm tires, I go with 80/90 to achieve the same feel as the bike with 25mm's.
     
    #11 rfield54, Sep 1, 2018
    Last edited: Sep 1, 2018
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