Tyre size and rolling resistance

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Mon 2 Jun 2008 10:20
Tyre size and rolling resistance - Henrythenavigator
With the apparent trend toward larger rim sizes and lower height of tyre sidewalls, which configuration gives the lowest rolling resistance, large rims and low sidewall height, or small rims and large sidewall height? (Assuming all other variables are the same)
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Mon 2 Jun 2008 11:33
Tyre size and rolling resistance - NARU
When I've seen data on CO2 outputs, models using the larger wheels have higher CO2 levels - ie are using more fuel. This may be because the larger rim sizes are typically shod with wider tyres.

Edited by Marlot on 02/06/2008 at 11:33

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Mon 2 Jun 2008 12:38
Tyre size and rolling resistance - George Porge
Larger rims allow larger brake disks and calliper combinations
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Mon 2 Jun 2008 13:24
Tyre size and rolling resistance - Group B
Lower sidewall height should give less flex and therefore less rolling resistance, all other things being equal. Flexing of sidewalls generates heat, so the lower the sidewalls, the less energy wasted as heat.

The other big factor is weight: the heavier the car, the greater the rolling resistance, all other things being equal.
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Mon 2 Jun 2008 13:31
Tyre size and rolling resistance - FotheringtonThomas
models using the larger wheels have higher CO2 levels - ie are using more fuel.
This may be because the larger rim sizes are typically shod with wider tyres.


It may also be because they've more powerful engines. This is a much larger factor in CO2 emissions/fuel use than mere rolling resistance!
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Mon 2 Jun 2008 16:10
Tyre size and rolling resistance - NARU
>> models using the larger wheels have higher CO2 levels - ie are using more
fuel. This may be because the larger rim sizes are typically shod with wider tyres.
It may also be because they've more powerful engines. This is a much larger factor
in CO2 emissions/fuel use than mere rolling resistance!


I'm not that dim! My comparisons were for otherwise identical cars - when I was deciding whether I wanted to pay the additional company car tax of some non-standard wheels.
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Mon 2 Jun 2008 13:29
Tyre size and rolling resistance - FotheringtonThomas
Large rims and low sidewall height should give lowest rolling resistance (probably lowest comfort, too!).
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Mon 2 Jun 2008 13:37
Tyre size and rolling resistance - moonshine {P}

I would imagine a large but narrow rim would be the best (in terms of lowest rolling resistance).

As an extreme example, imagine a cartwheel with a low profile skinny tyre.

I wonder what a tyre shop would say if you went in and asked for a 115/50/21
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Mon 2 Jun 2008 13:47
Tyre size and rolling resistance - MVP


I watched an interesting Discovery Channel program a while ago about the pneumatic tyre.

Logically, I would have thought a solid tyre on a solid rim would be the most efficient, but it doesn't work like that. If you hit a bump with a solid tyre, you use a lot of energy to lift the whole vehical vertically to get over the bump.

A nice absorbant tyre means the vehical doesn't lift up as much, as this vastly improves efficiency.

Suspension being equal, I would think a fat narrow tyre would offer the least rolling & wind resistance.

MVP

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Mon 2 Jun 2008 14:12
Tyre size and rolling resistance - L'escargot
As an extreme example imagine a cartwheel with a low profile skinny tyre.


My granddads pony-powered trap certainly had large diameter wheels fitted with low profile rubber rims. The ride was most uncomfortable.
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Mon 2 Jun 2008 13:56
Tyre size and rolling resistance - *Gongfarmer*
HJ's test of the mega-economy Bluemotion version of the Polo notes that "The car gets 5J x 14 alloy wheels with unfashionable deep section and narrow 165/70 hard compound tyres".
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Mon 2 Jun 2008 16:34
Tyre size and rolling resistance - George Porge
The area the tyre touches the road would be the same given the same weight and pressure in the tyre, the contact patch would have a different shape though. A wider tyre would have more frontal area and create more drag because of it.
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