Hardware update gained 15% range

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wh05apk
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Re: Hardware update gained 15% range

Post by wh05apk » Wed May 15, 2019 5:12 pm

But presumably once Up to speed, they will act like a gyroscope and effectively help maintain speed, like a heavy flywheel having more torque?


FENorway
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Re: Hardware update gained 15% range

Post by FENorway » Wed May 15, 2019 6:17 pm

smithy2167 wrote:
Tue May 14, 2019 11:02 pm
Well FENorway, before you swap the wheels, can you do some controlled tests of consumption in various conditions with the 22's. Then repeat the tests as closely as possible with the 18's.

I'm personally quite skeptical that there'll be anything like 15% difference.
I will try. But will not switch to 18" this week.
FE Corris grey light oyster/light oyster Performance 22" 5069 & 18" 19C_19.46.4-458817 and 18.2


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anorak
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Re: Hardware update gained 15% range

Post by anorak » Wed May 15, 2019 6:49 pm

The 22" tyres have a 7% bigger contact patch than the 18s with the same loading applied.

In the UK the bigger tyres specified as OEM also have a lower efficiency rating ('stickier' compound = more grip - and more friction). I understand this is not the case in all markets though.
I Pace EV400 S, Caesium blue, Oyster leather, 18" wheels
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FENorway
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Re: Hardware update gained 15% range

Post by FENorway » Wed May 15, 2019 7:16 pm

22" tyres in Norway are Conti PremiumContact. They have C im RR-rating. The 18" Michelin have A and are rated as Ultra Low Rolling Resistance ULRR-tyres.
I dont know the reason why JLR chose Conti over Pirelli. The Pirellis are better on both RR and noise.
FE Corris grey light oyster/light oyster Performance 22" 5069 & 18" 19C_19.46.4-458817 and 18.2


DougTheMac
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Re: Hardware update gained 15% range

Post by DougTheMac » Wed May 15, 2019 8:16 pm

There’s a lot of incorrect pseudo science on this thread. Confusion between mass, inertia, weight, losses.
Heavier wheels will increase rolling resistance losses in direct proportion to the increased WEIGHT. A very small effect.
If the wheels have more of their mass distributed at a larger radius, that will increase their INERTIA. It will NOT in itself affect the rolling resistance losses or economy at a steady speed. It will slightly increase the ENERGY required to accelerate to a given speed, but also increase the energy regenerated. A tiny net increase in overall losses.
Fatter tyres will increase aero losses, but I doubt if the effect is significant. I may be wrong.
So, none of these factors explain the large observed difference in range.
I believe larger wheels with fatter, flatter tyres do have a higher RR, but I don’t understand why. The physics (stiffer tyres) would suggest the opposite.
The larger/wider contact area will give greater scrubbing losses on cornering or if the wheels have toe-in. No idea how significant this might be.
But I suspect the dominant factor by far is the tyre compound. If, as FENorway reports, 22s have a C-rating and 18s have ULRR As, then I think that’s the main factor.
Why have JLR done this? Probably to get the best “headline” figures for range based on ULRR rubber on 18s, while they assume anyone choosing 22s is more interested in handling/cornering than range.
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BillCB
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Re: Hardware update gained 15% range

Post by BillCB » Thu May 16, 2019 2:23 am

My earlier post saying skinny tyres have less RR is apparently wrong, according to Mr. Google. Still, Jaguar's own figures clearly show they are more energy efficient.

My comment was based a book I bought many years ago, "Chilton's More Miles to the Gallon", where he advised "hypermilers" to install the thinnest tyres possible and pump'em up as high as possible. This was during the oil crisis in the 1970s and I guess the technology has changed a bit since then!
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anorak
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Re: Hardware update gained 15% range

Post by anorak » Thu May 16, 2019 2:20 pm

No, you were right first time, in most instances at least. The 18" tyres have a lower rolling resistance and hence a higher efficiency rating than either the 20"s or the 22"s.
I Pace EV400 S, Caesium blue, Oyster leather, 18" wheels
MY19, delivered 01/2019
IMC: S19B_19.40.4-436082 || Telematics: 17.2
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ELray
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Re: Hardware update gained 15% range

Post by ELray » Fri May 17, 2019 1:43 am

BillCB wrote:
Thu May 16, 2019 2:23 am
My earlier post saying skinny tyres have less RR is apparently wrong, according to Mr. Google. Still, Jaguar's own figures clearly show they are more energy efficient.

My comment was based a book I bought many years ago, "Chilton's More Miles to the Gallon", where he advised "hypermilers" to install the thinnest tyres possible and pump'em up as high as possible. This was during the oil crisis in the 1970s and I guess the technology has changed a bit since then!
The technology has changed, but the laws of physics remains the same :)
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scm
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Re: Hardware update gained 15% range

Post by scm » Fri May 17, 2019 11:25 am

ELray wrote:
Fri May 17, 2019 1:43 am
... the laws of physics remains the same :)
But our understanding of those laws changes .... ;)


TryLean
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Re: Hardware update gained 15% range

Post by TryLean » Sun May 19, 2019 1:55 pm

BillCB wrote:
Thu May 16, 2019 2:23 am
My earlier post saying skinny tyres have less RR is apparently wrong, according to Mr. Google. Still, Jaguar's own figures clearly show they are more energy efficient.

My comment was based a book I bought many years ago, "Chilton's More Miles to the Gallon", where he advised "hypermilers" to install the thinnest tyres possible and pump'em up as high as possible. This was during the oil crisis in the 1970s and I guess the technology has changed a bit since then!
Assuming that the 18 inch wheels are more efficient -has anyone experimented with tyre pressures? In all my other cars increasing the pressure to the top end of the manufacturers recommended pressures has resulted in better economy -is this true on the iPace?


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