Lightweight wheels
Discussion
Kawasicki said:
When you corner, the forces going through the wheel make it lose camber and to a much lesser extent toe.
The problem with putting the performance aspect of a wheel down to one characteristic, weight, is that you end up with manufacturers optimising for that… rather than for a balance of characteristics.
Example. A special high performance edition of a road car was spec‘d with freakishly expensive wheels from a renowned Japanese wheel maker. They were light and looked great. The problem was the car lost a LOT of handling precision and predictability when they were fitted. They were nearly 50% lighter than the original cheap, boat anchor alloys! I measured the camber stiffness of the wheels, how much they deflected under cornering load. They were less than half as stiff.
everyday a school day.The problem with putting the performance aspect of a wheel down to one characteristic, weight, is that you end up with manufacturers optimising for that… rather than for a balance of characteristics.
Example. A special high performance edition of a road car was spec‘d with freakishly expensive wheels from a renowned Japanese wheel maker. They were light and looked great. The problem was the car lost a LOT of handling precision and predictability when they were fitted. They were nearly 50% lighter than the original cheap, boat anchor alloys! I measured the camber stiffness of the wheels, how much they deflected under cornering load. They were less than half as stiff.
thx
CABC said:
Kawasicki said:
When you corner, the forces going through the wheel make it lose camber and to a much lesser extent toe.
The problem with putting the performance aspect of a wheel down to one characteristic, weight, is that you end up with manufacturers optimising for that… rather than for a balance of characteristics.
Example. A special high performance edition of a road car was spec‘d with freakishly expensive wheels from a renowned Japanese wheel maker. They were light and looked great. The problem was the car lost a LOT of handling precision and predictability when they were fitted. They were nearly 50% lighter than the original cheap, boat anchor alloys! I measured the camber stiffness of the wheels, how much they deflected under cornering load. They were less than half as stiff.
everyday a school day.The problem with putting the performance aspect of a wheel down to one characteristic, weight, is that you end up with manufacturers optimising for that… rather than for a balance of characteristics.
Example. A special high performance edition of a road car was spec‘d with freakishly expensive wheels from a renowned Japanese wheel maker. They were light and looked great. The problem was the car lost a LOT of handling precision and predictability when they were fitted. They were nearly 50% lighter than the original cheap, boat anchor alloys! I measured the camber stiffness of the wheels, how much they deflected under cornering load. They were less than half as stiff.
thx
Cambs_Stuart said:
That is really interesting. So how much were the wheels deforming underload? Is it enough to be seen with the naked eye?
On the bench I mounted both wheels to a horizontal hub and hung 150kg from the rim and measured the deflection with a dial gauge. You could see both wheels clearly deflect under the load.What was funny was a NVH engineer came into the workshop and laughed at my efforts to be analytical. He said you just need to tap the wheel with a hammer and measure the resulting vibrations. We tapped both wheels on the rim with a plastic hammer.
Heavy, stiff wheel made a diinngggg sound.
Light, flexible wheel made a dooonnnnnnkk sound.
How’s about that for fancy?
The other clear difference between the wheels was how the tyres looked after the test. You could clearly see that on the tyres mounted to the flexible wheel that WAY more of the outer sidewall was contacting the ground when driving. This was hard driving though, not cruising.
In cruising driving the stiffer wheels were just more precise and the steering torque straight ahead was more meaty. How much of this meatiness comes down to gyroscopic effects and how much to wheel stiffness is a test for another day.
Kawasicki said:
On the bench I mounted both wheels to a horizontal hub and hung 150kg from the rim and measured the deflection with a dial gauge. You could see both wheels clearly deflect under the load.
What was funny was a NVH engineer came into the workshop and laughed at my efforts to be analytical. He said you just need to tap the wheel with a hammer and measure the resulting vibrations. We tapped both wheels on the rim with a plastic hammer.
Heavy, stiff wheel made a diinngggg sound.
Light, flexible wheel made a dooonnnnnnkk sound.
How’s about that for fancy?
The other clear difference between the wheels was how the tyres looked after the test. You could clearly see that on the tyres mounted to the flexible wheel that WAY more of the outer sidewall was contacting the ground when driving. This was hard driving though, not cruising.
In cruising driving the stiffer wheels were just more precise and the steering torque straight ahead was more meaty. How much of this meatiness comes down to gyroscopic effects and how much to wheel stiffness is a test for another day.
Do you have any idea as to how much the weight and CoG of the car impact the deflection of the wheel? What was funny was a NVH engineer came into the workshop and laughed at my efforts to be analytical. He said you just need to tap the wheel with a hammer and measure the resulting vibrations. We tapped both wheels on the rim with a plastic hammer.
Heavy, stiff wheel made a diinngggg sound.
Light, flexible wheel made a dooonnnnnnkk sound.
How’s about that for fancy?
The other clear difference between the wheels was how the tyres looked after the test. You could clearly see that on the tyres mounted to the flexible wheel that WAY more of the outer sidewall was contacting the ground when driving. This was hard driving though, not cruising.
In cruising driving the stiffer wheels were just more precise and the steering torque straight ahead was more meaty. How much of this meatiness comes down to gyroscopic effects and how much to wheel stiffness is a test for another day.
CABC said:
everyday a school day.
thx
Your welcome. It was a fairly big surprise for me when I first drove the test.thx
I’ve done the blind test for other engineers at a few companies now, and they are all surprised.
There is no doubt that light wheels can be great. Making good light wheels isn’t easy, but they are out there.
Around the hub the wheel should be stiff, so more metal and 3 dimensional rather than 2 dimensional, if that makes sense. More spokes, with as much depth as possible and a broad connection of the spoke to the rim itself.
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