21" Wheels Less Efficient?

[rogbmw]

I just weighed a 21" silver wheel with the standard Continental 245/35R21 Extreme Contact DW tire on it...61 pounds. Oof. Continental says the tire is 26 pounds, so that means the wheel must be 35 pounds.

Anybody have a 19" wheel/tire sitting around they can weigh? Let us know which tire it is, thanks. I've got the Pirelli 245/45R19 Sottozero Serie II winter tires on my 19's; Pirelli says the tires are 28 pounds, but I don't know the wheel weight.

I just swapped out my 19s for 21s on Wednesday evening. Both are new, and I weighed each complete wheel/tire. This is what I got repeatedly:

19 inch wheel with Goodyear tire: 59.4 lbs
21 inch wheel with Michelin tire: 61.6 lbs

 

[teslasguy]

Thanks Hans. That supports my experience as a great all season tire for winter usage in moderate winter climates (Philly), but also supports Tesla's findings re poor rolling resistance. So still in pursuit of the "perfect" all season tire in all categories including rolling resistance.


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[jerry33]

I just swapped out my 19s for 21s on Wednesday evening. Both are new, and I weighed each complete wheel/tire. This is what I got repeatedly:

19 inch wheel with Goodyear tire: 59.4 lbs
21 inch wheel with Michelin tire: 61.6 lbs

The actual effect on RR, particularly during acceleration, will be more than the difference in weight suggests because on the 21" tire:

1. The wheel's rim mass is further from the centre of rotation.

2. The tire's bead is further from the centre of rotation.

3. Has a stickier tread compound.

4. Has a wider tread width.

 

[teslasguy]

The actual effect on RR, particularly during acceleration, will be more than the difference in weight suggests because on the 21" tire:

1. The wheel's rim mass is further from the centre of rotation.

2. The tire's bead is further from the centre of rotation.

3. Has a stickier tread compound.

4. Has a wider tread width.

I just weighed my 21" wheels with the Continental DWs that came with it and they are consistently weighing 59.2 lbs.

So Jerry, sounds like from what you're saying I should be better off taking my car to the drag strip with the 19" wheels with my Bridgestones on than waiting until I put on my 21s with the Contis, even though the Bridgestones seem to get dinged for rolling resistance? At 59.2 lbs it doesn't look like the weight of the 21s with Contis should be much different than my 19s with Bridgestones.

 

[jerry33]

So Jerry, sounds like from what you're saying I should be better off taking my car to the drag strip with the 19" wheels with my Bridgestones on than waiting until I put on my 21s with the Contis, even though the Bridgestones seem to get dinged for rolling resistance? At 59.2 lbs it doesn't look like the weight of the 21s with Contis should be much different than my 19s with Bridgestones.

On the drag strip, as far as I know, the main thing is to keep the tires glued to the road without TC kicking in or spinning the tires. Top end dragsters use very low psi to obtain the maximum amount of contact area. They also screw the beads to the wheels to prevent any slippage there.

The sticky tread compound on the 21" tires will overpower all the other factors, although my suggestion would be to go for either the Michelins or see if Yokohama has some street legal competition tires (or not street legal if you don't mind changing tires at the track). For normal driving LRR is important for range.