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tyre pressure in the heat

Discussion in 'New Riders and Riding Tips' started by twistngo, Jan 3, 2008.

  1. Had low tyre pressure coming home the other night when it was cool after a few hot days. So I've been checking it regularly since and notice a lot of variation with temperature, which is from 15-40 in Melbourne these days.
    It was around 16 this morning and my front was 36. Came home this afternoon, temp around 30 and tyre pressure was 41. The bikes been sitting in the shed all morning. So WTF do I set my tyre pressure to?

  2. 36 at cool and leave it there.
    Always inflate/check your tyres when cool, regardless of the weather.
    Just make sure you check them again when the weather cools down.
  3. Check with your tyre recommendations also.

    My mechanic dude said for my rear tyre (Metzler something or other), it needed to be 40 and my front 38.

    I would check my tyres every week when I filled with petrol.

    As Smee says, I always checked when cold. I think it's about 200 metres to the servo from home!

  4. I bought a michelin foot pump from K-mart $29.00 and check them each time i leave home.

    great quality pump and gauge and can be used for most other things filled with air.
  5. I've got one of those pumps but I've only been checking every week or so. Might mend my wicked ways. Just starting to believe the gauge as it seems very close to my digital one.
  6. Yeah but what ambient temperature is 'cool'? I know it goes against traditional thinking, but it almost makes more sense to check tyre pressure when fully warmed up as the discrepancy may be less. I had a similar question here:

  7. I meant your tyres being cool, it doesn't really matter what the ambient temperature is.
    In the summer months especially where we have more variable temperatures check them more often.
    In all reality it would make diddly squat because under hard riding your tyres get hot, the air expands inside and they "seem" fuller when measured with a guage.
    Just make sure your tyres are not underinflated when its hot.
  8. Ah, gotcha, sorry mate. Thing is, with the variation in ambient temperatures, the pressure reading from a 'cold' tyre varies too. A few days ago I left home with a reading of 32.5 (coolish early morning, maybe 17 degrees?) and the next morning got a 35.5 :shock:
  9. Well assume an ambient temperature of 25°C if you like, but like Smee says, it doesn't matter. When your tyres are up to temperature from riding, the air pressure is going to be much higher than when you tested, like 42 or 44 PSI. Maybe more.

    It's easy to remember:
    If you want your tyres to warm up faster, you need a lower pressure so that the side walls will deflect more, and heat up the tyre. Try wiggling a bit of rubber hard for a while. It gets hot. So lower pressures in Winter.

    If the weather is hot, you don't want to heat your tyres up more than necessary, as they are already hot from the road and ambient temperature, so you want high pressure in the tyres when you check them. Less side wall flex means less heat build up in the tyres from ridding. Under inflation leads to overheated tyres. So higher pressures in Summer.

    But the difference when testing a cold tyre in Winter or Summer shoud be only 2 to 4 PSI.
  10. but if your psi is to hig couldnt your tyres pop, as stupid as that sounds its the one thing that really scares me.
  11. 44-45 for a rear when they are hot is fine.
    You risk a blowout more if your tyres are underinflated rather than vice versa.
    I don't understand the physics behind it.
    Just inflate your tyres to the manufacturers specs ususally written on the side of the tyre and all will be well.
  12. can you fill bike tires with nitrogen?

    i had the cage tires filled with nitrogen once upon a time as apparently it is more stable then then normal air

    it was $6 bucks but free refills bob jane or beaurepairs whichever it was did it for free when i bought new rubber
  13. Yep but you gotta consider your tyres are filled with 70% nitrogen already.
  14. Manufacturers work out the maximum cold tyre pressure, taking into account the maximum pressure that will occur when the tyre is hot. You can't really measure the maximum hot tyre pressure, since the tyre is rolling when it happens. :eek:

    The max cold tyre pressure is what is written on the side of the tyre. As long as you only fill a tyre to the maximum cold tyre pressure specified, it wont pop when it gets hot.

    Don't push bike racers run tyres at 60 or 100 PSI or something like that? With those thin walled tyres and all. They only pop when abused by hitting large pot holes or ruts, pinching the tyres, or if extremely worn.
  15. Depends on the tyre, it can go up to 130psi though normally i put 90 front and 105 rear on my road bike.
  16. Hey has anyone thought of adding those electronic tyre pressure monitors to bike wheels,

    You can buy them aftermarket and retrofit them to a car,

    so why not for a bike?

    other than the unit size - what restriction is there?
  17. Hi guys.

    Total newbie (get my first bike tomorrow), but I am a competent car driver :? and have done a few defensive driving courses, and the topic of tyres and pressure was covered.

    May be a bit irrelevant for bikes, but similar to what RoderickGI was saying works for car tyres:

    When the tyre pressure is low before you start out, the tyre walls flex more - usually you'll notice this at the bottom of the tyre :) - this in turn generates lots more heat and results in higher tyre pressures.

    If the pressure is 'normal' when cold, then the type wall flex is less and therefore the heat generated is less, meaning the 'hot' pressure apparently can be the same or even lower than the 'low start presure' tyre.

    Also, with cars the typical pressure for tyres is about 32psi - the instructors all called this level "comfort while you crash" and suggest it makes the cars and tyres seem 'better' by providing more cushioning for the occupants, while reducing your road handling significantly.

    They all recommended much high car pressures of at least 40 psi. And some of us where also concered about the tyres 'popping' but apparently for cars the tyres can be something like 80psi easily without risking a 'pop'.

    I don't know how much of this applies to bikes, but I've driven my car with these rules for >12 years now and I always believe my car handles beter as a result.
  18. The latest Audi A6s come fitted with them as a factory option ($3,900)! I saw them in use - pretty cool! Shows tyre pressure and temperature.

    Cheap, huh!

    (Bu then, their factory option GPS option is $6,900! - but you get a TV with that!)
  19. New Kawasaki 1400GTR has then standard. I have watched the temp change a few times but its not all that exciting :LOL:
    There is quite a bit of variance.
  20. Seems like alot of you blokes are'nt paying enough attention to your tyres!!...
    Your tyres are NOT jus the black things that keep the rims off the ground...they play a very active role in your bikes handling, grip, and feel.

    You all should be riding your bikes and feeling what those tyres are saying to you....Forget what the manufacturer says...THAT is a general rule and you should treat it as a default only.

    Tyre pressures will depend on the day, what kind of riding you intend to do, and you should set your tyre pressure accordingly.
    After alot of listening to what my bike has been trying to tell me, and some input from riders with similar bikes, I have settled on Front 34psi and Rear 38psi...With the way I like my suspension to be set up, these pressures fit well on MY bike with ME on it. Your own bike might/will be different.

    I try to set these figures at night before I go to bed, when the air temps are at their lowest, and it also provides some reasonable consistency of measurement.

    I may vary the pressures a pound or two from my own settings if the weather is going to be extremely hot or cold, but I don't do it that often.

    Pay close attention to what your tyres are telling you, and find the settings that suit you the best. You can't mistreat them like alot of people do on their cars.
    Remember...you've only got two. :eek: :)