I'm thinking of putting 18" wheels on my M3P. Traction question

[mrfiat74]

Hi. I have a 2019 M3P with the 20" wheels. I'm thinking of putting these wheels on it: Fast Wheels FC04

Can the M3P still do full acceleration without losing traction with 18" wheels? I would think the answer is yes, but just double-checking.

I was thinking of getting 245/45R18 tires on it. I'm hoping the sidewall would stick out a little to protect the wheels. Would there be any clearance issues with the fender when hitting bumps?

Would 225/45R18's be a better choice? (or 235/45R18's) I plan to put sticky tires on them. 9 lbs less per wheel is huge. (compared to the 20")

Thanks!

 

[mrfiat74]

I'm thinking of putting these tires on the new wheels: Discount Tire | Tires and Wheels for Sale | Online & In-Person

 

[gearchruncher]

Can the M3P still do full acceleration without losing traction with 18" wheels? I would think the answer is yes, but just double-checking.

Yes. The wheel diameter doesn't matter, only the tire (width and compound). Tesla sold the "performance stealth" with 18" wheels in the past.

I was thinking of getting 245/45R18 tires on it. I'm hoping the sidewall would stick out a little to protect the wheels. Would there be any clearance issues with the fender when hitting bumps?

People run 285's no problem. 245's will be fine as long as your wheel offset is close to stock. The issue with larger tires is less efficiency.

Would 225/45R18's be a better choice? (or 235/45R18's) I plan to put sticky tires on them. 9 lbs less per wheel is huge. (compared to the 20")

You'll never notice the 9 lbs on a 4,400 lb car. You'll get way more performance out of the right tire.
12lbs on a Miata barely mattered: Are lighter wheels really better?

 

[Gauss Guzzler]

Note that those wheels will sit about 1/2" inboard of your stock 8.5et35 wheels. 1/4" from the narrower 8" width plus another 5mm from the offset, assuming they fit your calipers, hub, hub lip, and lug nuts. 245mm tires will push that back out a little bit, but will look somewhat dune buggy-ish on 8" wheels.

Like @gearchruncher said, wheel weight can make a tiny difference in drag strip acceleration but once you're turning or on slightly imperfect roads the only thing that's holding you back on a 3P is traction.

 

[RandyS]

I just did the same thing with EV01+ wheels and Michelin Pilot Sport 4 A/S tires 245/45R18. I was blown away by how much nicer the ride quality is than the 20" setup...I used to feel every bump, and always had to be on the lookout for potholes, etc. But now the ride quality is much better. I think you'll like it. I haven't had any traction issues and have done some spirited driving...Enjoy!

 

[mrfiat74]

Thanks everyone. Randy, can you post a picture of your car with the EV01+ wheels and Michelin Pilot Sport 4 A/S tires 245/45R18? I'm not sure what Gauss meant by dune buggy-ish? Too much gap from the tire to the fender?

 

[jackmott]

Hi. I have a 2019 M3P with the 20" wheels. I'm thinking of putting these wheels on it: Fast Wheels FC04

Can the M3P still do full acceleration without losing traction with 18" wheels? I would think the answer is yes, but just double-checking.

I was thinking of getting 245/45R18 tires on it. I'm hoping the sidewall would stick out a little to protect the wheels. Would there be any clearance issues with the fender when hitting bumps?

Would 225/45R18's be a better choice? (or 235/45R18's) I plan to put sticky tires on them. 9 lbs less per wheel is huge. (compared to the 20")

Thanks!

The diameter of a wheel has no impact on straight line traction, and barely any impact on cornering traction either. The reduced weight is also not going to make a difference that you would notice if someone tested you blind. Switching to 18s to save money on tires and to have wheels that don't dent as easy on potholes is a fine idea, but don't expect efficiency or acceleration differences of any significant amount., especially when you plan to go with sticky tires instead of efficient tires.

 

[Mash]

18 is a significantly better and cheaper ride.

 

[mrfiat74]

Yes, I need new tires soon anyway, so why not new wheels too? I would think that a savings of 9 lbs per wheel (rotating weight) would make a noticeable difference in performance. I know it does in a bicycle, not the same thing I know.

 

[gearchruncher]

I would think that a savings of 9 lbs per wheel (rotating weight) would make a noticeable difference in performance.

Why would you think 9 lbs would make a difference in a 4,400 lb car? Physics doesn't work that way. Rotating mass is not 100X or even 10X more important than static mass. Dig around on this site and nobody is finding big differences due to wheel weight. Get them for the other benefits of taller sidewalls, don't expect a faster car.

 

[mrfiat74]

The rotating mass is what the motors have to get moving. (plus the static mass) What you said does make sense though. I guess the best plan is to do a couple of pulls to 60 with the 20" wheels and some with the 18's. I will do so and let you guys know the results.

 

[mrfiat74]

But certainly if I did low profile tires on the 18's it would make the car faster. That would give me a better gear ratio but without lowering the car, it would not look good.

 

[mrfiat74]

Actually this test as already been done: (not with a Tesla though)

Are lighter wheels really better?

We always hear that lightweight wheels are better, but do they actually make you go faster on track?

grassrootsmotorsports.com

The lighter wheels allow the car to accelerate faster and handle better as per the article.

 

[gearchruncher]

The rotating mass is what the motors have to get moving.

No, the motors have to get the WHOLE car moving.
A 4,4400 lb car at 60 MPH has 718,000J of energy.
9 lbs at 800 RPM (60 MPH) 12" out is about 2,000 joules.

So if you can take 9 lbs off at each corner, the car will be 710,000J instead of 718,000. That's 1%, good luck feeling that.

The lighter wheels allow the car to accelerate faster and handle better as per the article.

They added 12 LBS per wheel to a MIATA that weighs half as much as our cars and gained 0.31 seconds on a 1 minute track. 0.4 seconds 0-60, but on a 9 second car. That does not offset linearly. That would be way less than 0.1 seconds on a 3 second car.

 

[mrfiat74]

They also added dead weight to the Miata with the lighter wheels on it to somewhat equal out the weight. So the rotating weight does make a difference. Multiple people on this forum have said the M3P handles better with the lighter 18" wheels on it. Only one way to find out for sure, do it. Plus the tires will be cheaper and less likely to get bubbles in the sidewalls.

 

[tm1v2]

Wheel weight: Yes it matters! I easily felt the difference from putting lightweight forged 18x8.5" wheels on my 2021 M3P, coming from the uber-heavy Uberturbines. The power steering feels better, as if it were struggling with the Uberturbines before. Quick back-and-forth turns in the twisties especially feel better, but even just driving around town the steering feels more eager and nimble.

I've no idea if it made a measurable impact on acceleration and I don't care. I'm sure any difference there is very small, not likely relevant unless you're actually drag or street racing.

As others said everything about the change is good, it's all upside. Grip, ride quality, wheel protection, power steering feel, tire cost are all better now. I also gained some efficiency as best I can tell, despite staying with "max performance" tires and non-aero wheels.

(To be clear, grip improved because of better tires, I went with Bridgestone Potenza Sport and they grip much better dry & wet than the OE Pirelli PZ4. I'm sure they'd grip well in 20" too but the point is you don't lose grip from downsizing the wheel diameter, it's all about your tire choice.)

 

[gearchruncher]

Wheel weight: Yes it matters! I easily felt the difference from putting lightweight forged 18x8.5" wheels on my 2021 M3P, coming from the uber-heavy Uberturbines. The power steering feels better, as if it were struggling with the Uberturbines before. Quick back-and-forth turns in the twisties especially feel better, but even just driving around town the steering feels more eager and nimble.

(To be clear, grip improved because of better tires

You have no idea if the better "feel" was due to tires or weight. You changed way too much at once to know that. This kind of feel almost always comes from tire sidewall stiffness.

I've AutoX'ed multiple Model 3's back to back, one with stock uberturbines, one with lightweight 18" wheels, and I noticed no difference that wasn't due to the tires. The stock car was far from "struggling."

Do the math and you'll see how little difference it makes- realize that when you drop X lbs off a wheel by downsizing, not all of that weight comes off the most extreme part of the radius.

 

[tm1v2]

You have no idea if the better "feel" was due to tires or weight. You changed way too much at once to know that. This kind of feel almost always comes from tire sidewall stiffness.

I've AutoX'ed multiple Model 3's back to back, one with stock uberturbines, one with lightweight 18" wheels, and I noticed no difference that wasn't due to the tires. The stock car was far from "struggling."

Do the math and you'll see how little difference it makes- realize that when you drop X lbs off a wheel by downsizing, not all of that weight comes off the most extreme part of the radius.

@gearchruncher I don't buy that the power steering difference I feel is primarily from the tire, not between two "max performance" tires when I dropped about 25% of the stock wheel+tire weight. Makes sense to me that it's mostly from the lower weight.

Let me be clear, I'm not talking about "steering feel," not as that term is typically used. I'm talking about the weight and assistance of the power steering. Any improvement or change I got in steering feel was very minimal and I would chalk that up to the tires.

Yes tires do affect the heft of the steering, e.g. swapping from performance tires to soft squishy snow tires on the same wheels. Heck just inflation pressure can make a very noticeable difference. I'm somewhat calibrated on those things and it doesn't add up at all to me that this case is from the tires.

I'm not volunteering to buy extra tires that I don't want just to prove or disprove it with a 100% apples-to-apples comparison though!

 

[thesmokingman]

Steering feel and or turn in, etc etc is definitely partly due to tires. It's one of main points in Tire Rack testing.

 

[tm1v2]

Steering feel and or turn in, etc etc is definitely partly due to tires. It's one of main points in Tire Rack testing.

I'm aware, I've changed to different tires many times without changing wheels. The difference I feel doesn't match my experience with the difference between similar tires in the same category.

That said I've never used the exact same model tire when changing to a different size/weight wheel, even when I stayed in the same tire category. It just never worked out that way in terms of tire size availability and my tire preferences.

It would be neat to compare 20" Potenza Sports on Uberturbines vs my current setup, and 18" PZ4 on my new wheels vs the OE setup, but I'm not wealthy enough to buy tires I don't actually want just to settle this!