Remember- knurling is used for extremely sticky, low PSI tires. Basically any car can put 1000HP+ down to the wheels- because that's what the brakes can do and the tire doesn't care if you are accelerating or braking. It doesn't really have anything to do with the drivetrain type or power. Even with knurling, the tire will walk a bit on the rim, but it's not a big deal.
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lightweight wheels model 3 performance 0-60 testing
- Thread starter Kaz93
- Start date
Good point! With our 40+ psi tires would take a lot of power to slip the tires.
He means slip on the rim- higher pressures increase load on the bead and reduce chance of spinning the rim in the tire.
BigNick
Infamous Fat Sweaty Guy
Mark the valve stem location with chalk, crayon, shoe polish, whatever you like.
Abuse the snot out of the tires (drag launches, repeated hard braking on a twisty road course, etc.)
Check to see if the marks are still lined up with the valve stems.
Abuse the snot out of the tires (drag launches, repeated hard braking on a twisty road course, etc.)
Check to see if the marks are still lined up with the valve stems.
Lindenwood
Active Member
Guys... on these cars at 80 to 100% State of Charge you wont notice the difference of lighter wheels, but at lower SOCs you definitely will around 55% and below there is a BIG DIFFERENCE.
Can you explain why a fixed mass on a car is more noticeable as the motive power drops off?
Each pound you take off of wheels is a 0.09% reduction in energy needed to accelerate to 70 MPH. I sure can't detect a 0.5% change in acceleration as a big difference, particularly when the car is already changing the power output by 25%+ due to battery SoC.
Your math is wrong.
Check the OEM 20" turbine wheel weight vs the SV104... the difference is huge.
BTW, I am not sure a turning wheel is a fixed mass.
Gauss Guzzler
Safety Score = 42
A 0.09% change in power results in *exactly* a 0.09% change in acceleration force, per F = ma
The same is true for a change in *effective* mass, for the same reason, still F = ma. But as the car gets slower, the difference in acceleration *time* will appear greater. It’s still linear but obviously 0.09% of 3.1 seconds is a smaller number than 0.09% of 7 seconds.
And as James mentioned, wheel mass has an extra effect since the wheel needs to accelerate to 60mph *and* accelerate to 750RPM at the same time. This doesn’t change any of the simple linear relationships above, it just makes the wheels seem heavier than they really are.
The same is true for a change in *effective* mass, for the same reason, still F = ma. But as the car gets slower, the difference in acceleration *time* will appear greater. It’s still linear but obviously 0.09% of 3.1 seconds is a smaller number than 0.09% of 7 seconds.
And as James mentioned, wheel mass has an extra effect since the wheel needs to accelerate to 60mph *and* accelerate to 750RPM at the same time. This doesn’t change any of the simple linear relationships above, it just makes the wheels seem heavier than they really are.
It's not.
4,000 lb car @ 70 MPH: 888,000 joules
1 lb @ 70 MPH, 17" diameter: 182 joules
So each pound you take off a wheel is 730 joules at 70 MPH, out of 888,000. 0.09%.
Stock uberturbines are 32 lbs. SV104's are $6000+ per set, but sure, they weigh 10 lbs less (so do $250 wheels). That's a lot of coin for 1%.
No way you are noticing 1% reliably, and again, as the power falls off below 50% power, you have no idea if the wheels made any difference since the power is changing so fast vs SoC.
Maybe someone that spent $6000 for wheels that don't even list their weight as a spec would be kinda biased about how much performance they gained. Glad you like your wheels though.
Fair. So 1 lb is 182 joules turning each, and 222 joules forward (like any single pound in the car is). Yes, there is literally more energy in the linear mass than the rotational mass.
You really can't calculate the rotational energy without knowing the rotational moment of the wheels. A wheel is not a disc with evenly distributed mass. As a wheel gets larger, more mass will end up on the barrel of the wheel and thus be farther out from center. So the amount of energy required to turn the when will not have a linear relationship with total mass.
That said, this will not change your argument, but it is something to keep in mind.
Lindenwood
Active Member
Tinkered with my own math as well. Even using a whopping 10lb per corner at 24” diameter, we only save about 1.5% of the accelerational energy, or 2.5% total once you factor in both linear and angular accelerations. Interestingly, going to the not-uncommon 27” tires (I.e. 255/35R20), we also lose about 2% of effective wheel torque.
This +\- 2% is about the same as a ~8-degree (F) change in battery temp at a given SOC.
Overall, going from the factory Performance Uberturbines to light weight wheels and tires might technically be perceptible, but not significant, as it would feel like a ~10-15 HP gain in a 550hp vehicle. Of course, going down to a 26” tire almost doubles the effect, so you could approach a 5% “increase” with super-light wheels and undersized tires, which would feel like an extra 20-25HP.
In any case, I think the point still stands that shaving wheel weight is far less significant than we would all love to believe.
*edit*
And to be clear, I am not sure it is possible to reduce the wheel and tire combo by 10lb at a 1ft radius (I.e. maybe with some light 225-width tires), so the actual numbers are indeed going to be closer to what gearcruncher showed (closer to perhaps 1.5%, or about 8-10HP effective difference). This is the difference we experience between about 80 and 90% SOC, or about 10 degrees F difference in battery temp. Again, if I am really paying attention I can maybe feel it, but it is really not significant.
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oreobbq
Member
Physics has left my brain many years ago. But the perceived difference in wheel weight could also be affected by tire wear so I imagine the most accurate way to test is to swap old tires onto new wheels. Since you'd eliminate possible differences in rolling resistance between sets of tires.
My math was done assuming the 1lb was a hoop, not a disc, and that hoop was 17" in diameter. I'd say that's a pretty good estimate for taking 1lb off a 19" rim.
Of course you can't back it up because there is no data. You seem to acknowledge that power falls off as SoC drops. Given that happens, how do you know you're feeling the wheels, not just that it's 2% SoC higher? It is summer how do you know your battery isn't a touch warmer at the same SoC? There's way too much variance here to trust a butt dyno here across likely days of time difference.
Look, lower SoC's just limit kW. It's the same as driving partial throttle. You're saying that if I charge my car to 100%, accelerate at 60% throttle, slap $6000 worth of wheels on with identical tires, and then go accelerate at 60%, I'll feel a big difference?
If so, you'd think people would immediately feel a much more responsive car the instant they put on new tires, given most driving isn't at 100% throttle, and in fact is at 10% or so throttle, where you indicate the difference gets larger and larger.
What? No, lower SOCs at full throttle is where most of the difference is for me dont be silly.
The real issue is that you guys seem to be offended by the price of the wheels, an issue I never mentioned but one that you seem to repeat constantly.
I swapped wheels because I wasnt comfortable running rubberband tires, the added performances was just a bonus.
Thanks!
JC
How is 60% throttle at 100% SoC different than 100% throttle at 30% SoC?
You're the one that listed the model of wheel instead of listing the weight reduction of the wheel.
We are not able to reason together so let just leave it at that. Sorry if I offended you with the wheels I purchased.
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