Tyre pressures with larger tyres




Results 1 to 20 of 20
  1. #1
    Join Date
    Nov 2010
    Location
    Jhb
    Age
    38
    Posts
    580
    Thanked: 48

    Default Tyre pressures with larger tyres

    Hi all,

    So after upgrading to a 265/65/17 (GY Adventurers), the ride seems slightly harder. This made me think about whether, with a bigger tyre, I should be reducing tyre pressure. I have them at VW's recommended 2,3/2,5.

    Any way, found a few web pages talking about this with differing opinions.

    Interestingly, I found this page that provides a formula to calculate optimal tyre pressure:

    http://www.uklegacy.com/forums/index...yre-pressures/

    When I use my vehicles figures:

    Weight: 2,137kg
    Max load per tyre: 1,120kg
    At PSI: 51

    Optimal tyre pressure = 1,68 bar

    At 2,350kg = 1,84 bar.

    Interesting...

    Any thoughts / comments?

  2. #2
    Join Date
    Aug 2012
    Location
    Okahandja, Windhoek
    Age
    66
    Posts
    3,314
    Thanked: 386

    Default Re: Tyre pressures with larger tyres

    Yes as pressure must be increased with adding weight, increase size (contact area) you can reduced a bit pressure.
    Johan Kriel

    LC PU's and a Prado

  3. The Following User Says Thank You to JLK For This Useful Post:


  4. #3
    Join Date
    Mar 2008
    Location
    De Wildt
    Age
    55
    Posts
    29,675
    Thanked: 6015

    Default Re: Tyre pressures with larger tyres

    It is correct to reduce pressure when the tyres get bigger.

    I reckon 2 bar would be best at the start and you'll have to check how they wear.
    2012 Jeep Sahara Unlimited 3.6 V6
    Ela Diablo: Land Rover S2A 109 PUP: SOLD

  5. The Following User Says Thank You to jelo For This Useful Post:


  6. #4
    Join Date
    Aug 2007
    Location
    Carletonville
    Age
    52
    Posts
    6,105
    Thanked: 372

    Default Re: Tyre pressures with larger tyres

    From 29" to 31" on my Sani I already dropped from 2.2 to 2. In fact I initially ran them at 1.8 for the first year and experimented with 2bar to get better fuel consumption (which seemed to work). Now on 33" I find 2bar very hard and grip levels utter rubbish (could just be the brand/model standard performance, this is the first time I have Mitchilens).

    I also see the 33s bulge out in the middle on the 15" 8J rims, and I have dropped to 1.8bar. Ride and performance is better, but the fuel consumption looks to be worse, but I can't say for certain as my van has not had a full, or measured tank fill, since 2015.

    Mine may be an isolated case, as I am running 12.5" wide rubber on 8" wide rims. But based on the trend of lower pressure on bigger rubber, I'm curious to see what pressure I will need to run, when I go to 35". My personal feel is that 1.8 is as low as I would like to go, but the tread contact patch will ultimately dictate the pressure.
    David/Hillbilly - 1997 SFA Nissan Sani 2,7 TD - 5" lift on 33" tires - Dual Transfer with 4.1 gears

    http://www.youtube.com/user/davidabcab



  7. #5
    Join Date
    May 2016
    Location
    East London
    Age
    66
    Posts
    1,551
    Thanked: 1681

    Default Re: Tyre pressures with larger tyres

    It is related to the 'contact patch' of the two tyres.

    If the original tyre had a contact patch of A1 and a pressure of P1

    and the contact patch of the new tyre is A2, then the pressure for the new tyre will be P2 where

    P2 = P1 * A1/A2
    "Nothing in the world is more dangerous than sincere ignorance and conscientious stupidity" - Martin Luther king Jr

    2006 VW Touareg V10 TDi
    (currently done more than 385 000 km)

  8. The Following 2 Users Say Thank You to 4eTouareg For This Useful Post:


  9. #6
    Join Date
    Jun 2010
    Location
    Port Elizabeth
    Age
    34
    Posts
    4,967
    Thanked: 697

    Default Re: Tyre pressures with larger tyres

    Iíve learned a lot now.

    Now that we are on the topic. My Jimny was on 205/70/15 and upped to 215/75/15. On standard I was running 1.6 front and 1.8 rear (even with bigger size).

    Does it mean I can go down by 0.1 to 1.5 front and 1.7 rear?
    Sent from my iPhone


  10. #7
    Join Date
    Aug 2007
    Location
    Carletonville
    Age
    52
    Posts
    6,105
    Thanked: 372

    Default Re: Tyre pressures with larger tyres

    Thats a bit low on tar I think. Check your contact patch and see how much the tyre bulges. Then see over a period how tyres wear. If they wear more in the centre, then you are running to low pressure. If they wearing on the edges, you to hard. ***EDIT.. Its the other way round***

    Those are fairly small tyres you have there, I would be running 2-2.2 bar. Although the Zook must be fairly light. My experience is on a 2.2ton rig, so I may just be totally wrong with my advice.
    Last edited by bfreesani; 2018/05/06 at 07:52 AM.
    David/Hillbilly - 1997 SFA Nissan Sani 2,7 TD - 5" lift on 33" tires - Dual Transfer with 4.1 gears

    http://www.youtube.com/user/davidabcab



  11. #8
    Join Date
    Jul 2010
    Location
    Pinetown
    Age
    69
    Posts
    1,773
    Thanked: 644

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by bfreesani View Post
    Thats a bit low on tar I think. Check your contact patch and see how much the tyre bulges. Then see over a period how tyres wear. If they wear more in the centre, then you are running to low pressure. If they wearing on the edges, you to hard.

    Those are fairly small tyres you have there, I would be running 2-2.2 bar. Although the Zook must be fairly light. My experience is on a 2.2ton rig, so I may just be totally wrong with my advice.
    Is it not the other way around?
    I would have thought that with higher pressure the centre of the tyre (width) would tend to be pushed outwards from the centre?
    Just a question.
    Answering the call of the wild is just so much beter than answering the telephone.
    ISUZU KB 280 DT LE NOW POWERED BY THIS AMAZING COMMUNITY
    Modified Glider Hunter trailer fitted with RTT.
    Platkar = Chevy Spark 1.2

  12. The Following User Says Thank You to Peter1949 For This Useful Post:


  13. #9
    Join Date
    Aug 2007
    Location
    Carletonville
    Age
    52
    Posts
    6,105
    Thanked: 372

    Default Re: Tyre pressures with larger tyres

    Totally correct. Somewhere between Alzheimers and dyslexia, I duffed that post completely.

    Best thing is, this is the second time I've done it on the same subject, on two different threads in probably two years. I'm getting worried about myself..

    Sorry about that
    David/Hillbilly - 1997 SFA Nissan Sani 2,7 TD - 5" lift on 33" tires - Dual Transfer with 4.1 gears

    http://www.youtube.com/user/davidabcab



  14. #10
    Join Date
    May 2009
    Location
    Hillcrest, Malaysia
    Age
    62
    Posts
    17,213
    Thanked: 3946

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by bfreesani View Post
    Totally correct. Somewhere between Alzheimers and dyslexia, I duffed that post completely.

    Best thing is, this is the second time I've done it on the same subject, on two different threads in probably two years. I'm getting worried about myself..

    Sorry about that
    At least you can still spell altshymers and dislexihere.
    Cheers

    ZS5KAD Yeasu Ft-897D
    3 V8's
    A V6 and an inline 4
    The nice thing about going the extra mile - the road is never congested.

  15. #11
    Join Date
    Aug 2007
    Location
    Carletonville
    Age
    52
    Posts
    6,105
    Thanked: 372

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by Fluffy View Post
    At least you can still spell altshymers and dislexihere.
    I may hate electronics and gadgets on cars, but I love my spell checker on my phone.
    David/Hillbilly - 1997 SFA Nissan Sani 2,7 TD - 5" lift on 33" tires - Dual Transfer with 4.1 gears

    http://www.youtube.com/user/davidabcab



  16. The Following User Says Thank You to bfreesani For This Useful Post:


  17. #12
    Join Date
    Apr 2007
    Location
    Nigel
    Age
    57
    Posts
    15,013
    Thanked: 1194

    Default Re: Tyre pressures with larger tyres

    Yes, I like hard pressures on tar. Gives me even wear and directional stability.
    LC 78 Troopie 1HD-FTE
    +27 zero eight 2 four 95 9252

  18. #13
    Join Date
    Jul 2010
    Location
    Pinetown
    Age
    69
    Posts
    1,773
    Thanked: 644

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by Henris View Post
    Yes, I like hard pressures on tar. Gives me even wear and directional stability.
    Agreed and the higher pressure most definitely improves fuel consumption without any doubt.
    Answering the call of the wild is just so much beter than answering the telephone.
    ISUZU KB 280 DT LE NOW POWERED BY THIS AMAZING COMMUNITY
    Modified Glider Hunter trailer fitted with RTT.
    Platkar = Chevy Spark 1.2

  19. #14
    Join Date
    May 2009
    Location
    Hillcrest, Malaysia
    Age
    62
    Posts
    17,213
    Thanked: 3946

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by Peter1949 View Post
    Agreed and the higher pressure most definitely improves fuel consumption without any doubt.
    Do you think that if I pump my tyres to 5 Bar I will be able to get the V8 from one petrol station to the next

    I am not a believer in these tyre pressure calculations.

    The calcs don't work out for any of my cars - nowhere near in fact.

    I have two almost identical RRS. A Petrol V8 and a Diesel V8. The Petrol is 200Kg heavier, yet the tyre pressures are the same. With 20" rims the pressures are 2.3 and 2.6 BAR. But here is the clanger, with the smaller 19" rims the pressure is 4.2 Bar all round with all loads.

    My Ford Tourneo van, which only weighs 2000Kg uses tyre pressures of 3.8 Bar in the front and Between 2.7 and 3.5 Bar on the rear depending on load.

    I think a lot depends on other factors like sidewall strength and the profile.
    Cheers

    ZS5KAD Yeasu Ft-897D
    3 V8's
    A V6 and an inline 4
    The nice thing about going the extra mile - the road is never congested.

  20. The Following User Says Thank You to Fluffy For This Useful Post:


  21. #15
    Join Date
    Aug 2012
    Location
    Okahandja, Windhoek
    Age
    66
    Posts
    3,314
    Thanked: 386

    Default Re: Tyre pressures with larger tyres

    Yes tyre pressure ( force per area ) must counter act the weight of a vehicle per tyre footprint area, the trick is however to decide what is the length of the contact area , to be able to calc that pressure, when the contact area has the same pressure right through.
    Last edited by JLK; 2018/05/06 at 10:54 AM.
    Johan Kriel

    LC PU's and a Prado

  22. #16
    Join Date
    Jul 2010
    Location
    Pinetown
    Age
    69
    Posts
    1,773
    Thanked: 644

    Default Re: Tyre pressures with larger tyres

    What I mean is on the same vehicle, same conditions, same load, same tyres, same ??, - you will get better fuel consumption with higher pressure.
    That does not mean that you should pump your tyres to MAX to save fuel - depends on what you are doing at the time.
    Eish.
    Fluffy getting all technical again.
    This is just such a great forum - love it.
    Answering the call of the wild is just so much beter than answering the telephone.
    ISUZU KB 280 DT LE NOW POWERED BY THIS AMAZING COMMUNITY
    Modified Glider Hunter trailer fitted with RTT.
    Platkar = Chevy Spark 1.2

  23. #17
    Join Date
    Apr 2007
    Location
    Nigel
    Age
    57
    Posts
    15,013
    Thanked: 1194

    Default Re: Tyre pressures with larger tyres

    On mine, I go to 2.5bar on the front and to 3bar, on the back, on tar. Gravel I will go down to 1.5bar in the front and 2bar in the back.
    LC 78 Troopie 1HD-FTE
    +27 zero eight 2 four 95 9252

  24. #18
    Join Date
    Jul 2010
    Location
    Pinetown
    Age
    69
    Posts
    1,773
    Thanked: 644

    Default Re: Tyre pressures with larger tyres

    Yebo

    PS:

    EISH !
    Last edited by Peter1949; 2018/05/07 at 04:44 PM. Reason: Eish !!
    Answering the call of the wild is just so much beter than answering the telephone.
    ISUZU KB 280 DT LE NOW POWERED BY THIS AMAZING COMMUNITY
    Modified Glider Hunter trailer fitted with RTT.
    Platkar = Chevy Spark 1.2

  25. #19
    Join Date
    Apr 2011
    Location
    Sandton
    Age
    47
    Posts
    1,428
    Thanked: 172

    Default Re: Tyre pressures with larger tyres

    Quote Originally Posted by Fluffy View Post
    I think a lot depends on other factors like sidewall strength and the profile.
    Agreed
    '06 TJ Wranger | 4.0L Auto| 4.5" Lift | 35" Copper STT | 15" MT Classic II Black | 4.88 Gears

  26. #20
    Join Date
    Oct 2016
    Location
    Melkbosstrand
    Age
    43
    Posts
    521
    Thanked: 64

    Default Re: Tyre pressures with larger tyres

    2015 VW Amarok 4motion Auto
    2011 Conqueror Companion

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •