Would the car with 18" wheels be faster to 60 because of the less unsprung weight compared to 20" wheels? If that's the case why is Tesla selling larger wheels on their Performance?
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18" vs 20" wheels 0-60 times
- Thread starter yellowcakepie
- Start date
dwalme
Member
Not a factor. You can buy the same tires for 18" and they weight the same as the 20" version:
PILOT SPORT 4S 235/35ZR20 23 lbs
PILOT SPORT 4S 235/45ZR18 23 lbs
https://www.tirerack.com/tires/tires.jsp?message=singleSize&tireMake=Michelin&tireModel=Pilot+Sport+4S&cameFrom=selectOE&width=235/&ratio=45&diameter=18&autoMake=Tesla&autoYear=2018&autoModel=Model+3&autoModClar=&minLoadRating=XL&minSpeedRating=V&partnum=345YR8PS4SXL&cameFrom=selectOE
For the record, if you lost 5-10 lbs unsprung weight, you'd find it noticeable. Losing 28 lbs is crazy good. There's a reason why racing cars go for the lightest rims they can get.
Grassright
Member
There will be no difference in 0-60 time. Handling around corners is a different story.
Might not, but it can.
High unsprung mass also exacerbates wheel control issues under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control.
Unsprung mass - Wikipedia
High unsprung mass also exacerbates wheel control issues under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control.
Unsprung mass - Wikipedia
Tesla sells the 20s because they look the part for the performance trim and they can charge more. I have a SR+ with 18s and a M3P+. The Eco tire limits show up when you push the car into a corner or stand on the brakes. The turn in is a bit sharper in the M3P+ as well. If you drive them back to back you can tell but if you have nothing to compare to then you will obviously never know.
Same reason why all high performance cars like Corvettes, Porsches, Ferraris have larger wheels. Looks, better road feel and ability to install larger brakes. Do you want a Lambo to have 15" wheels and gigantic side walls?
Please explain why you think so. All things being equal with the exception of rotational mass, there will be a very quantifiable difference between two cars. This is a very well documented fact. Now, its possible Tesla is limiting the 0-60 times but that wont affect braking.
Re cornering forces, given a smooth surface, rotational mass will have less of an effect on cornering forces. If the surface is not smooth, it can effect grip, depending on the surface, shock design and several other factors.
David
It has to do with multiple factors.
Gearing - ICE cars have low first gears to give them extra torque at low speeds. When combined with a torquey V8 and RWD, it is becomes easy to reach the limits of the even the best tires and break traction. The Teslas have AWD and one gear that is engineered for a balance of performance and efficiency. We don't get that torque multiplication effect from gearing. Porsche and others will release EVs with 2 speed transmissions, which will be interesting as EVs continue to evolve.
More Advanced Traction Management systems - The Traction Control (nannies) in an ICE car are very slow compared to the digital management controllers integrated with an EV motor. In ICE, when the Traction Control system senses wheel spin it has to pull ignition timing to reduce power to stop the wheel spin and then add timing to give it back. This back and forth process as the system senses wheel spin and then signals back to reduce power is relatively slow and lengthens the time required to put power down to the ground. If you compare that to Traction Control in the Tesla, it has a digital TC controller that monitors wheel spin but it is so much faster as it communicates directly with the drive unit. It can modulate the torque applied to the wheels so quickly that they can actually get more grip out of the Eco Primacy tires. You can think of it like ABS brakes in a way. You just mash the brake pedal and the ABS controller will pulse the brakes so quickly to maintain tire grip better than us humans trying to pulse the brakes at a much slower rate.
Combine this system with AWD and you get a lot more out of those Eco tires as it relates to 0-60 launches, tire grip does not appear to be the limiting factor. Smaller, lighter 18" wheels will improve times a bit and folks have tested this already when they swap them out. Now when it comes to braking and cornering the systems can't overcome those physics just yet. The limits of the Primacy Eco tires will show up right away. There are tests out there showing how the braking distance is reduced and the skid-pad numbers increase when you throw on some performance tires.
We're talking about rims, not tires. You can install the same tire on your 18" as on 20".
Understood. From a wheel size perspective folks have already proven faster 0-60 times (maybe .1 sec) with the 18" setup and if you swap the tires then yeah it should perform better on track as well. The 20" wheels Tesla gives us are heavy but they fill in the wheel wells and look a lot better than the 18s they offer. If you put a low profile tire on the 18s it makes the Model 3 look like it is jacked up 4x4.
The aftermarket is the solution, which is what I would do if I bought a M3P-.
They really don't. They're about the same size as the 18" with tires, you just see less sidewall and more rim.
If you want to fill the wheel well, you'll need to lower the suspension.
Grassright
Member
Because the power required to compensate for the rotational mass difference during 0-60 is negligible, compared to the total mass, friction, etc.
It is more about moment of inertia than sprung weight. Actually, it is almost entirely about moment of inertia. Lower moment of inertia, the faster the acceleration. Might all the other factors (grip, ability of traction control system, etc.) make that difference small to negligible? Sure. But generally, the lower teh moment of inertia, the faster teh body can be accelerated by the same force.
Probably by about a tenth of a second, or maybe 0.15 seconds if you really went to a very light weight wheel. But you'd be giving up some other things including steering response and of course the very popular aesthetic these days of bigger Wheels and low profile tires. They are regarded as de rigueur on high performance cars. Like everything else it's all trade-offs, and in order to get that cooler look you do give up unsprung weight, ride, and vulnerability to impact damage for both The Wheel and Tire.
beastmode13
Member
Smaller lighter wheels mean less rotational inertia and shorter gearing, those two things always mean faster acceleration. I've done testing on my current car, a tuned Golf R. With the 19" factory wheels at 26lbs vs. the 18" Titan 7's at 17lbs and found similar results as the guy in the video. .02-.03 seconds faster with the 18", you certainly can't feel the difference in acceleration, but I can feel the difference in steering response, with the 19" my car feels more responsive in the twisties. On the flip side, the 18" give a much-improved ride.
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