
2017 Hilux 2.4 SRX D/C 4x4 2012 Cross Polo [mamma s'n]
http://travel.webshots.com/album/558867451ncpSPZ
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
Toyota Land Cruiser 79 DC V8
Toyota Hilux 2.8 GD6 4x4
Toyota RAV4 2.2 D4D
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.
2014 Pajero 3.2DiD SWB
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.
Toyota Land Cruiser 79 DC V8
Toyota Hilux 2.8 GD6 4x4
Toyota RAV4 2.2 D4D
What? (BTW this is called 'Unsprung Mass ' ) Any scientific sources on this?
Petrol /diesel vehicle?
Indeed, awaiting factual confirmation. Until such time I wil regard this as rubbish .
Last edited by PieterOos; 2019/12/24 at 09:18 AM.
https://laroverket.com/wpcontent/up..._component.pdf
For the engineers and mathematicians!
Nothing material on tyre mass (not weight), only a glance toward:
I did find this part interesting: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).
The loss of tread material decreases the effective tyre radius.
To get an idea of thesignificance of this change, a calculation can be made for a common tyre, e.g.
195/6515. 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.
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.
2012 FJ Cruiser
1983 FJ60 Landcruiser
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...lscomparison/
Fairly insignificant gains, even with ~80 lbs less.
2017 Hilux 2.4 SRX D/C 4x4 2012 Cross Polo [mamma s'n]
http://travel.webshots.com/album/558867451ncpSPZ
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
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.
If my post insulted you, wonder where the smiley went .
Johnie
Volvo XC60 T5
180kW/350Nm (1500  4800 rpm)
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