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  1. #21
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by Lofty View Post
    I never knew that,480 kg? masehare
    And you believe him
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  2. #22
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by Lofty View Post
    Anton have you driven a Hilux with 2.4 kpa tyre pressure haha my tande sal uitval
    Haha.... Ek ry 2.4 bar en 2.6 bar...

  3. #23
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by KurtG View Post
    And you believe him
    haha lmao
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  4. #24
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    Default Re: Much higher fuel consumption

    I went from 65 Dueler to a 70 BFG profile on my 2.8 and it made a huge difference in 6th gear.

    Fuel consumption changed by about 2km/lt, but then again now you also drive it harder.

    I run my tyres at 1.8 bar, max 2 bar, the ride of the hilux is just to hard for me otherwise

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  5. #25
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    Default Re: Much higher fuel consumption

    Chris8d, did that 2km/L include a readjustment of your calculation for the 3% (plus minus) change in circumference of the new tyres? The new tyres will result in a change in actual distance travelled compared to the trip meter so that needs to be factored into the calcs.
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  6. #26
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by KurtG View Post
    Chris8d, did that 2km/L include a readjustment of your calculation for the 3% (plus minus) change in circumference of the new tyres? The new tyres will result in a change in actual distance travelled compared to the trip meter so that needs to be factored into the calcs.
    No I did not, but I am aware of it. Revs has also dropped due to the bigger tyre hens the "lack"of power in 6th

    What I was getting at is that at the end of the day bigger and heavier tyres makes quit a difference to fuel consumption.

    Even changing from BFG AT to BFG Mud in the same size made over 1km/lt difference.

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  7. #27
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by HugoNotte View Post
    The impact of tyre weight is amplified by the fact that they are part of the vehicle's mass which isn't suspended. It's impact is something like 8 times that of weight carried in the vehicle.
    In other words, a tyre that weighs 15 kg more than the standard tyre would be similar to at least carrying 15 x 4 x 8 = 480 kg inside the vehicle.
    Add to that a wider tread pattern, the ST Maxx is rather square and has got a wider running surface compared to e.g. a GY Wrangler of the same advertised size, which increases drag.
    Plus the tread pattern is more aggressive and got a higher rolling resistance, hence the humming noise.
    It all contributes to higher fuel consumption.
    On a petrol vehicle one might feel it more than on a diesel.
    What? (BTW this is called 'Unsprung Mass ' ) Any scientific sources on this?
    Petrol /diesel vehicle?

    Quote Originally Posted by RoelfleRoux View Post
    I refuse to accept this claim, sorry.
    Indeed, awaiting factual confirmation. Until such time I wil regard this as rubbish .
    Last edited by PieterOos; 2019/12/24 at 09:18 AM.

  8. #28
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    Default Re: Much higher fuel consumption

    https://laroverket.com/wp-content/up..._component.pdf

    For the engineers and mathematicians!

  9. #29
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    Default Re: Much higher fuel consumption

    Nothing material on tyre mass (not weight), only a glance toward:

    This effect depends on the mass ofthe tread band.
    Reducing this mass (resulting in lower rolling resistance) leads to

    lower centrifugal stiffening and therefore more excessive tyre vibrations. On the other
    hand, lower mass will increase the natural frequency of the tyre circumferential
    vibrations, and hence the critical speed. Both effects work against each other. The
    combined impact on critical speed depends also on the sidewall stiffnesses (being low
    for radial tyres).
    I did find this part interesting:
    The loss of tread material decreases the effective tyre radius.
    To get an idea of the
    significance of this change, a calculation can be made for a common tyre, e.g.
    195/65-15. The nominal diameter of this tyre in new condition is 322 mm. After the
    tread has worn from 8 to 2mm, this diameter is reduced until 316mm, which is a
    change of 1.9%. The circumference is of course also reduced by 1.9%. This
    decrease changes acceleration, fuel consumption and leads to a deviation in
    speedometer reading.
    Last edited by PieterOos; 2019/12/24 at 10:43 AM.

  10. #30
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by Waals View Post
    Hi just for interest sake where did you get the formula?

    Quote Originally Posted by RoelfleRoux View Post
    I refuse to accept this claim, sorry.
    I remember reading this claim in the tyre section of this forum in a post by one of the tyre experts here. However, after reading up on it a bit more, it seems like it's not that bad and the factor 8 is exaggerated.
    According to what I have found, it is not unsprung mass, but rotating mass, which requires a greater effort to be accelerated than static mass.
    The factor seems to be somewhere around 3 to 4. In other words, it takes about 3 to 4 times the effort to accelerate a rotating wheel than what it takes to accelerate an equal amount of mass on or inside the vehicle.

    Therefore, my apologies, it's not all that dramatic. But coming back to that example of a set of tyres mounted of which each tyre is 15 kg heavier than the original tyre, it would mean that we are looking at:

    15 kg x 4 x 4 = 240 kg

    15 kg being the difference times 4 tyres times 4 for the factor of increase in effort

    Put on heavier tyres as per example and it got a similar effect of driving around with a constant 180 - 240 kg dead weight in the vehicle on your fuel consumption.
    Last edited by HugoNotte; 2019/12/24 at 05:36 PM.
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  11. #31
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by HugoNotte View Post
    Put on heavier tyres as per example and it got a similar effect of driving around with a constant 180 - 240 kg dead weight in the vehicle on your fuel consumption.
    240 kg dead weight will effect a 1990 250D Isuzu, not a new hilux. Tyre thread type, rubber compound and pressure will have a bigger effect.
    Johan Kriel

  12. #32
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by HugoNotte View Post
    I remember reading this claim in the tyre section of this forum in a post by one of the tyre experts here. However, after reading up on it a bit more, it seems like it's not that bad and the factor 8 is exaggerated.
    According to what I have found, it is not unsprung mass, but rotating mass, which requires a greater effort to be accelerated than static mass.
    The factor seems to be somewhere around 3 to 4. In other words, it takes about 3 to 4 times the effort to accelerate a rotating wheel than what it takes to accelerate an equal amount of mass on or inside the vehicle.

    Therefore, my apologies, it's not all that dramatic. But coming back to that example of a set of tyres mounted of which each tyre is 15 kg heavier than the original tyre, it would mean that we are looking at:

    15 kg x 4 x 4 = 240 kg

    15 kg being the difference times 4 tyres times 4 for the factor of increase in effort

    Put on heavier tyres as per example and it got a similar effect of driving around with a constant 180 - 240 kg dead weight in the vehicle on your fuel consumption.
    This applies to the acceleration phase only though, and not to maintaining constant speed, which is where you sit most of the time on longer trips. Rolling resistance is the biggest factor when considering differences in consumption between tyre sizes/brands at the same speed.
    Mike Lauterbach

  13. #33
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by mikeml View Post
    This applies to the acceleration phase only though, and not to maintaining constant speed, which is where you sit most of the time on longer trips. Rolling resistance is the biggest factor when considering differences in consumption between tyre sizes/brands at the same speed.
    Indeed.
    Won't it require *relatively* less power to keep heavier wheels at a constant speed? (Kinetic energy etc). Acceleration / deceleration will obviously cost more energy wise.

    BTW some acceleration tests with different wheels : https://www.hotrod.com/articles/ligh...ls-comparison/
    Fairly insignificant gains, even with ~80 lbs less.

  14. #34
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    Smile Re: Much higher fuel consumption

    Quote Originally Posted by JLK View Post
    240 kg dead weight will effect a 1990 250D Isuzu, not a new hilux. Tyre thread type, rubber compound and pressure will have a bigger effect.
    Hey watch it my other bakkie is a 1989 SWB 250D haha
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  15. #35
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by Wandering_Soul View Post
    I was expecting about a 1L difference due to the profile change. Not the huge jump it was, however it's school fees and they are nice tyres offroad without a doubt, they breezed through 3 provinces at 1.8 bar.
    Readings will be out as well ( bigger circumference )
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  16. #36
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by cor View Post
    Readings will be out as well ( bigger circumference )
    Actually not, they are now as close to spot on as I can get.

    Speedo reads 100km/hr and GPS reads 99km/hr.
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  17. #37
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by Wandering_Soul View Post
    Actually not, they are now as close to spot on as I can get.

    Speedo reads 100km/hr and GPS reads 99km/hr.
    Can agree with that , but what about previous readings ?
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  18. #38
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    Default Re: Much higher fuel consumption

    Quote Originally Posted by cor View Post
    Can agree with that , but what about previous readings ?
    Roughly 8km/hr out.
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  19. #39
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    Default Re: Much higher fuel consumption

    Best is to compare tyre EU Label specs if available. . This will give very good insight for different tyres. .

    I run General Grabber AT3 in 255/60 R18. Standard tyre has a B rating for fuel efficiency, and the same size in LT spec has an F rating.
    But due to the deeper treads it gives more mileage on a set and has a stronger casing. Also its wet weather performance is also better. . Pros & Cons to both


  20. #40
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    Default Re: Much higher fuel consumption

    The power required from an engine to accelerate a rotating object is determined by the inertia thereof.

    For a disk, the inertia is linearly related to the mass of the object and squarely related to the radius.

    So if the tyre mass doubles - unlikely - the inertia doubles.

    If the tyre size goes up by one profile on say an 18" wheel from 235 to 255 in a 60 profile, the radius squared factor is 1.06.

    Not that much, but you are accelerating either two or 4 wheels and that is where the bigger numbers come from.
    Last edited by JJJ; 2019/12/29 at 04:45 PM.
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