[Squidget]

Originally Posted by baron95

The 1LE and DH have so much more/better tires than the others though - don't know why in the US BMW does not offer even Cup 2 240s.

It's a little weird BMW doesn't offer it as an option.

Of course, if you are the kind of person that will buy Cup 2s, that won't stop you. So it doesn't really matter.

[M_Power Rob]

Originally Posted by Squidget

It's a little weird BMW doesn't offer it as an option.

Of course, if you are the kind of person that will buy Cup 2s, that won't stop you. So it doesn't really matter.

Jyst to stay on topic, Cup 2s are road race, not drag (and not the greatest either). As far as being offered...what would be the point in offering them on the cast boat anchors?

[M2siast]

Originally Posted by M_Power Rob

Jyst to stay on topic, Cup 2s are road race, not drag (and not the greatest either). As far as being offered...what would be the point in offering them on the cast boat anchors?

They are offered everywhere else but in the US.
The point is that they could offer more longitudinal grip for launch. As well, obviously, as faster laps.

Why do you always call the wheels boat anchors?

[Squidget]

Originally Posted by M2siast

Why do you always call the wheels boat anchors?

I mean, they are pretty freakin heavy. Especially since they are unsprung weight.

[M2siast]

Originally Posted by Squidget

I mean, they are pretty freakin heavy. Especially since they are unsprung weight.

How much do they weigh more than the lighter wheels and how does that extra weight affect performance in seconds to 1/4 mile, speed at 1/4 mile, and lap times?

[aerobod]

Originally Posted by M2siast

How much do they weigh more than the lighter wheels and how does that extra weight affect performance in seconds to 1/4 mile, speed at 1/4 mile, and lap times?

The fronts are about 1.5kg heavier than the stock 825M or 826M wheels on the M3 (6% more weight per wheel and tyre) and the rears are about 2.5kg heavier (9% more weight per wheel and tyre). The load/strength rating of the BMW wheels whether cast or forged seems to be 815kg to TUV standards. Most of the rotational inertia is in the tyres, so with the same tyres, there is only a few percent difference between the cast and forged wheels.

[M_Power Rob]

Originally Posted by M2siast

They are offered everywhere else but in the US.
The point is that they could offer more longitudinal grip for launch. As well, obviously, as faster laps.

Why do you always call the wheels boat anchors?

Cup 2s are road race, not drag radials. For road racing tires, I would go with Nankang or Nitto (NT01s). For drag radials, Nitto (555R2s or NT05Rs) would be my first choice but they just arent available on demand. I am using Atturo AZ850DRs which seem to be better than Iexpected. Toyo R888Rs are also an option but due to Toyo not making them in the size I need, its not an option for me.

The stock CAST rims are heavy (the boat anchor comment), weak (due to being cast) and not recommended for any true performance use.

[aerobod]

Originally Posted by M_Power Rob

The stock CAST rims are heavy (the boat anchor comment), weak (due to being cast) and not recommended for any true performance use.

They are the same load rating as the forged wheels (this is embossed in the back of one of the spokes, 815kg for all the BMW M2/3/4 wheels AFAIK) the weight is the main difference, but even so that will be more obvious in suspension bump absorption than measurable acceleration difference when comparing 825M and 930M wheels as follows.

Front 930M - 12kg, 925M 10.5kg. Rear 930M - 14kg, 925M 11.5kg
Front MP4S tyre - 11.8kg, rear MP4S tyre - 12.3kg

The tyres have an effective mass centre from a rotational inertia perspective at about 0.33m radius. The wheel barrel has an effective radius of about 0.24m for the front wheel and 0.25m for the rear wheel. The effective radius of the wheel faces is about 0.15m. The wheel barrel is about 60% of the wheel mass. This gives rotational inertias as follows:

Front 930M - 12 x 0.6 x 0.24^2 + 12 x 0.4 x 0.15^2 + 11.8 x 0.33^2 = 1.81 kgm^2.
Front 825M - 10.5 x 0.6 x 0.24^2 + 10.5 x 0.4 x 0.15^2 + 11.8 x 0.33^2 = 1.74 kgm^2 (4% lower than 930M).
Rear 930M - 14 x 0.6 x 0.25^2 + 14 x 0.4 x 0.15^2 + 12.3 x 0.33^2 = 1.99 kgm^2.
Rear 825M - 11.5 x 0.6 x 0.25^2 + 11.5 x 0.4 x 0.15^2 + 12.3 x 0.33^2 = 1.87 kgm^2 (6% lower than 930M).

[Squidget]

Originally Posted by aerobod

The fronts are about 1.5kg heavier than the stock 825M or 826M wheels on the M3 (6% more weight per wheel and tyre) and the rears are about 2.5kg heavier (9% more weight per wheel and tyre). The load/strength rating of the BMW wheels whether cast or forged seems to be 815kg to TUV standards. Most of the rotational inertia is in the tyres, so with the same tyres, there is only a few percent difference between the cast and forged wheels.

Of course, the 825Ms themselves are considered relatively heavy (24.3lb) when compared to, for example, Apex SM-10RS (18.9lb).

While the 930Ms are not the heaviest wheels on the planet, they are also far from the lightest.

[aerobod]

Originally Posted by Squidget

Of course, the 825Ms themselves are considered relatively heavy (24.3lb) when compared to, for example, Apex SM-10RS (18.9lb).

While the 930Ms are not the heaviest wheels on the planet, they are also far from the lightest.

The Apex wheels only have a TUV load rating of 725kg, though, compared with 815kg for the BMW wheels, so that narrows the strength to weight rating somewhat.

In terms of the effect on acceleration, at about 100km/h the wheels are rotating at 780RPM, or 13RPS. At that speed in 3rd gear it takes about 1 second to accelerate to 15RPS (about 15km/h), that equates to an angular velocity increase of 12.6 radians/s and with a wheel/tyre inertia of about 1.9 kgm^2, 24Nm of torque per wheel is required.

Torque at the wheels in 3rd gear at 100km/h is about 2500Nm (550Nm at crank, 12% driveline loss 5.33 gearing). Therefore 4 wheels consuming 24Nm each are using 3.8% of the wheel torque, at 15RPS at the wheels / 80 RPS / 4800RPM at the engine in 3rd gear, the engine is making 276kW (370bhp), so losing 10.5kW (14bhp) to accelerating the wheels.

The 930M wheels would therefore lose about 5% of the power to accelerate the wheels or 0.5KW to the 925M wheels (due to the inertia difference). This would be around 1kW loss compared to the Apex wheels.

[Squidget]

Sure, but in additional to rotational inertia, there's also translational inertia, you are reducing the car's weight almost 40 lbs. And it's unsprung weight, so you are getting a handling advantage too.

My point is that it collectively may not be a massive difference, but it is a perceptible one.

Also, pragmatically speaking, working with mounted tires is hard work and my back appreciates lifting lighter things.

[vrooooom]

Myb the car to get is the M240i Xdrive.

[Chris13002]

Originally Posted by Blue Angel

Camaro 12.2 @ 118 - Going out with a bang!

M2 is a freight train once it gets moving. Wow.

I did a friendly pull against my buddies 2022 Camaro LT1 with 10 speed auto (intake and exhaust), against my stock G87 6MT. It was a rolling race from 60-115 and I was surprised to see my G87 pull ahead by a car length. This video doesn't lie about that 3rd gear; it's stupid fast. I also only shifted gears once while I heard his car do at least 3 shifts in the race.

[M_Power Rob]

Originally Posted by Chris13002

I did a friendly pull against my buddies 2022 Camaro LT1 with 10 speed auto (intake and exhaust), against my stock G87 6MT. It was a rolling race from 60-115 and I was surprised to see my G87 pull ahead by a car length. This video doesn't lie about that 3rd gear; it's stupid fast. I also only shifted gears once while I heard his car do at least 3 shifts in the race.

As to shifting, the Camaro is a 10AT, of course it will be doing some shifting.

[c1pher]

Originally Posted by AZG87

A few comments. The race would have been different if the DH had the A10 in it. That said, my previous Mustang was much faster and more handling goodies than this DH and I am still enjoying the power delivery and weight of the G87 over it. Not to mention much nicer interior.

Would have also liked to see the A8 M2.

[c1pher]

Originally Posted by LCDRJohn

Do you mean what is wrong with autocrossers?? (I could fill a book, lol!)

or

What makes the Emira a hot-mess?

Try to picture all of the folk-lore horrors of british cars, baked into one shell and you will get the idea. I put my deposit in 3 years ago, and noticed a Loooonng delay in getting US cars. Turns out that the QA was so bad that they were holding them back from our market. When the first brits got their cars, they tried to drink as much Kool-aid as was available, but did not work. Head over to the Emira forum to get the whole scoop. Ignore the guys who swear their cars are perfect. There are 3 of them and they are chumps (every board has them). For the rest, it is like a scaled down Mclaren: Paint drips, water leaks, bad seals, broken seats,bad trannys, and electrical/computer issues that stop the heart. The latest one, which is gaining traction, is that they do not produce the HP/TQ they are supposed to. I think we just saw that in the vid, where the car with the best power/weight (Emira) lost handily. In a street-start, it would have been even worse.

So, when I read that, I had a PTSD-like flashback to my Mclaren, and immediately got my $5k back. Judging by how the dealer was begging me not to take my money back, I think it is happening a lot now. It's a shame, really. I want so badly to want this car.

I'll wait until mid-cycle on the car, and may jump back in. I love Lotus, and just wish they would stop being so arrogant. Porsche can do it, because they deliver the product. Lotus, not so much.

I had gotten my deposit back too. I was initially very excited by the early reviews and knew if I ever wanted one this century I needed to put money down. Fortunately I was way down on the list so people ahead of me started getting theirs and there were a lot of issues. I just don’t think I should deal with that for a $100k car.

[c1pher]

Originally Posted by vrooooom

Myb the car to get is the M240i Xdrive.

If just going as fast as an M2 to 60 is all you’re concerned about, sure. As much as the 240i tries, it will never be a full M car.

[MMMGuy60]

Originally Posted by c1pher

If just going as fast as an M2 to 60 is all you’re concerned about, sure. As much as the 240i tries, it will never be a full M car.

If 0-60 is what you want, the M2 auto will still be faster than the M-light 240ix.

[aerobod]

Originally Posted by Squidget

Sure, but in additional to rotational inertia, there's also translational inertia, you are reducing the car's weight almost 40 lbs. And it's unsprung weight, so you are getting a handling advantage too.

My point is that it collectively may not be a massive difference, but it is a perceptible one.

Also, pragmatically speaking, working with mounted tires is hard work and my back appreciates lifting lighter things.

Of course, the weight reduction is about 1% going to the lightest wheels, so giving you about 1% change in power to weight ratio, several times the effect of the wheel rotational inertia change on acceleration. As I previously mentioned, bump absorption change will be the biggest thing that will be noticed.

[tuffode]

Jason makes great vids, but never goes into super into his thoughts about how he feels about the car. He talks about the M2 in this podcast, basically saying how it's fast but there's basically no joy left in the car. He says it feels like a luxury car with suspension made out of cinder blocks.

"What happened, Jason admits, is that the M2 is a perfect example about how the automotive world has gone in the wrong direction, prioritizing isolation and speed above the experience.
Measured against its modern peers, perhaps the M2 is okay, but every enthusiast owes it to themself to try some old experience-first cars."

https://podcasts.apple.com/us/podcas...=1000613087249

[aerobod]

In terms of the manual G87 acceleration vs the automatic, as chris719 mentioned, a lot of the off the line difference may actually be due to 1st and 2nd gear torque reduction. With this in mind and looking at acceleration over 100km/h as being more important for track work, it looks as though the 6MT may actually have the same acceleration at higher speeds compared to the 8AT.

Autobild show an instrumented 100-250km/h for the 8AT of 19.5 seconds and 100-230km/h at 14.4 seconds (https://www.autobild.de/artikel/neue...-22846107.html), Car and Driver have the 60-150mph (96.6-241.4km/h) for the 6MT at 17.6 seconds. The 96.6 to 100km/h difference is about 0.2 seconds and 241.4 to 250km/h about 2.2 seconds, giving 19.6 seconds 100-250km/h compared with the 19.5 seconds for the 8AT.

This reinforces 2 observations - the 6MT loses out mainly in the 0-100km/h range to the 8AT and the strong 3rd gear acceleration may indicate torque reduction to protect the 6MT in 1st and 2nd gear. Therefore I wouldn't expect to see any lap time advantage for the 8AT on a road track, only on a drag strip where the initial advantage off the line before 3rd gear is reached is maintained throughout the 1/4 mile.

[M2PDX]

Originally Posted by tuffode

Jason makes great vids, but never goes into super into his thoughts about how he feels about the car. He talks about the M2 in this podcast, basically saying how it's fast but there's basically no joy left in the car. He says it feels like a luxury car with suspension made out of cinder blocks.

"What happened, Jason admits, is that the M2 is a perfect example about how the automotive world has gone in the wrong direction, prioritizing isolation and speed above the experience.
Measured against its modern peers, perhaps the M2 is okay, but every enthusiast owes it to themself to try some old experience-first cars."

https://podcasts.apple.com/us/podcas...=1000613087249

As someone who's owned 9 previous M cars (and still owns a '98 e36 Dinan Stage 3 Supercharged M3) I couldn't disagree with him more.

As I've gone through the G87 break in period I've even had to hold up a bit and try to keep the motor under 4,000 rpm, but even then, the car is an animal.

And it STICKS to the road. Steering isn't perfect, but a lot better than on my F80 M3. And the 6MT is pretty darn good. Much better than expected.

The car is quick, powerful, nimble and fun. And I haven't even started any real mods yet (except HAS).

I experience overwhelming joy every time I drive it.