Wheels: Smaller rims, taller sidewalls?

[Bicycle Bob]

Originally Posted by oldtamiyaphile

I find it telling that (almost) no no other MPG car has gone that route. All the current day EV's have pretty wide tyres, so I wouldn't read too much into the i3's tyre spec.

Aerovironment had to constantly fight GM to keep them from putting wide tires on the EV-1 for styling reasons.
Unfortunately, there is no good data on belted tires in the public domain, but racing bicycles still win on narrow tires for pavement. Also unfortunately, after a century of everyone understanding the basic engineering behind rolling resistance being inversely proportional to diameter, which operates on steel wheels and ball bearings, Greenspeed published a major test of bicycle tires all based on using a small diameter roller instead of a flat road surface, completely masking the difference.
Once they lay the rubber on the road, narrow tires leave it there for support for longer than a wide tire at the same pressure. However, a belted tire does not have to distort and scrub to create a contact patch. It can have a lower sidewall, and that is important because the strength needed there is directly proportional to the radius that it bulges out with to take the pressure.

[CapriRacer]

Originally Posted by Bicycle Bob

...… Once they lay the rubber on the road, narrow tires leave it there for support for longer than a wide tire at the same pressure. ...…

My emphasis!

Part of the problem with testing bicycle tires is that narrow tires require MORE pressure to carry the same load than wide tires. The testing needs to be done at the same load carrying capacity - ergo, different pressures.

This problem is also present in passenger car tires, but to a much lesser extent because a difference of 10 mm width is almost nothing for a passenger car tire.

[oldtamiyaphile]

Originally Posted by Bicycle Bob

but racing bicycles still win on narrow tires for pavement.

Racing bicycle tyres are getting wider and wider too. The 23mm tyres of a few years ago are nowhere to be seen and the pros ride as wide as 28mm. 18mm tyres are just history now.

[rob.e]

ok, so i've FOUND a 5x114.3 wheel that's only 3.5" wide and made of aluminium - woohoo!


https://www.ebay.co.uk/itm/Genuine-L...0/262841685517

should fit right on to the honda, bit expensive but that's not the issue, i can't find any suitable tire to fit this. Only things i can find that are narrow enough are temporary use only

looked at i3 tyres but these are only 19" or 20". Also researched adapters to fit some i3 wheels but the increased height of the narrow tyre wont' fit in the arches..

[cRiPpLe_rOoStEr]

Decent-quality 13-inch tyres with a good efficiency rating are getting harder to find in my country, but recently my mother inquired me if it was worth replacing the 14-inch rims on her Toyota Etios for 13-inch ones to use tyres with taller sidewalls. I'd go that route if it wasn't for the harder availability of 13-inch tyres back here...

[Daschicken]

Originally Posted by CapriRacer

My emphasis!

Part of the problem with testing bicycle tires is that narrow tires require MORE pressure to carry the same load than wide tires. The testing needs to be done at the same load carrying capacity - ergo, different pressures.

This problem is also present in passenger car tires, but to a much lesser extent because a difference of 10 mm width is almost nothing for a passenger car tire.

A recent test at bicyclerollingresistance addresses this issue. They did tests with multiple controls, the important one here being same tire drop(probably load capacity too). The rolling resistance turned out to be extremely close.

https://www.bicyclerollingresistance...000-comparison

[Bicycle Bob]

Originally Posted by Daschicken

A recent test at bicyclerollingresistance addresses this issue. They did tests with multiple controls, the important one here being same tire drop(probably load capacity too). The rolling resistance turned out to be extremely close.

https://www.bicyclerollingresistance...000-comparison

Thanks, but that is still not the right way to test a tire. You need a flat "road" surface. I'd use a bench model belt sander with a worn belt that produces the same friction as asphalt. The wheel rides in a frame with load weights on each side, below the belt to keep it balanced. A cage keeps the rig from going off the test area, and once it is up to speed, the operator adjusts the inclination to get the tire running in the middle. The inclination reading is the payoff.

[Daschicken]

Originally Posted by Bicycle Bob

Thanks, but that is still not the right way to test a tire. You need a flat "road" surface. I'd use a bench model belt sander with a worn belt that produces the same friction as asphalt. The wheel rides in a frame with load weights on each side, below the belt to keep it balanced. A cage keeps the rig from going off the test area, and once it is up to speed, the operator adjusts the inclination to get the tire running in the middle. The inclination reading is the payoff.

The absolute readings may not be correct, but I don’t see why the relative readings would be incorrect.

[Bicycle Bob]

Originally Posted by Daschicken

The absolute readings may not be correct, but I don’t see why the relative readings would be incorrect.

The deformation of wider vs longer contact patches will not be the same on a drum.

[basjoos]

Going to a taller sidewall means you are less likely to dent your rims when you hit a pothole.