18” to 19” - car feels slower

[nigeldodd]

I don't understand some of this. Surely the overall diameter (wheel plus tyre) must remain the same for the speedometer to be accurate? The speedometer uses wheel revolutions rather than gps, presumably. So therefore the gearing must remain the same, mustn't it? The only difference I can see is that less rubber means, other things being equal, less deformation and consequently less energy loss. Carrying this to an extreme, if you had solid cart wheels on the car with just a wrapping of a strip of rubber then the friction losses would be minimal even if the ride would be intolerable.

[Splashalot]

As I understand it, the weight of the wheel is critical in response.  That is, the heavier the wheel, the slower and less responsive the car's handling and performance will feel.

[nigeldodd]

I can see that if the all up weight i.e. wheel plus tyre is greater then the moment of inertia would be greater and the angular momentum needed to be overcome would be greater thus, as you say, resulting in less responsiveness.

But is it true that a 19 inch wheel plus tyre is generally heavier than an 18 inch plus tyre?

Steel is stronger than rubber for its weight and so I don't see why the above should necessarily be true. Of course the rubber is inflated to give it strength.

[Gnasher]

I can see that if the all up weight i.e. wheel plus tyre is greater then the moment of inertia would be greater and the angular momentum needed to be overcome would be greater thus, as you say, resulting in less responsiveness.

But is it true that a 19 inch wheel plus tyre is generally heavier than an 18 inch plus tyre?

Steel is stronger than rubber for its weight and so I don't see why the above should necessarily be true. Of course the rubber is inflated to give it strength.

You'd be surprised how much more material there is in a 19" wheel compared to an 18" one and how little difference in weight there is between an 18" and a 19" tyre of the same rolling radius.

The only thing that bucks the trend is that (sometimes) larger wheels tend to be forged, which for a given size of wheel, tends to be a lighter wheel than a cast one.

I've got 19" BBS SR alloys on mine and they're really quite heavy in comparison to the Austins I took off. Mine are on there primarily for looks - if I were going for performance over anything else I'd have ended up with 18" Team Dynamics Pro Race wheels as they're strong and light.

[nigeldodd]

Thanks. I understand the bigger wheels feel heavier and the two different sizes of tyres don't feel much different in weight. Do you actually have weights of the wheels and tyres?