[M_Power Rob]

Originally Posted by sl0m0

The MAD one is not boxed so it might save a little weight. A cf strut brace as zero21 has mentioned is also a great option, definitely a cost savings that bmw took. It's on my potential list.

I would not (and have no plans to) run an open CAI on the streets in South Florida. That would be a recipe for disaster.

[Xspeedracer]

This would be a good way to loose weight in the back of the car

[zero21]

Originally Posted by Xspeedracer

This would be a good way to loose weight in the back of the car

True but the weight bias shouldn't get any worse than it is. Ideal weight balance isn't really 50:50 like BMW likes to claim.

[aerobod]

Originally Posted by zero21

It's definitely not steel, and definitely not light either.

I would expect it will be about 2/3 the weight of a steel one. Typically an aluminium skin will be about double the thickness of a steel one plus the support structure making up about 50% of the weight. So a panel skin of that size will have a weight of about 9kg, for about 18kg (40lbs) total weight. You could probably halve that with carbon fibre, if it is optimised in structure, unfortunately most aftermarket ones aren’t optimised, so they may not be significantly lighter.

[LCDRJohn]

Originally Posted by zero21

True but the weight bias shouldn't get any worse than it is. Ideal weight balance isn't really 50:50 like BMW likes to claim.

Remember something about weight bias and why it is not a major consideration in this case:

1) track days ain't "racing". No one will notice a percent either way. 30 laps of real racing....maybe...even then, probably not.
2) the removal of weight near the battery as is currently located, would be a 1% reduction in weight in that area. If it were such a big deal, no one would drive with less than a full tank, for fear of lightening the rear.
3) the car is tuned for the 52/48 balance, so it already is part of BMWs plan to have a little more weight on the nose.
4) removing weight is less of a problem than adding it.

Whenever we set up a class-conforming track car, we never really obsessed over the front-back balance beyond a certain point. There are plenty of poor handling cars with 50/50 balance and lots of good ones with a heavy nose or tail. All of our cars (except 911s and vettes) are nose heavy at the end of a race, because we are on fumes. I've never noticed anything outside of just the tires getting greasy, which is normal after 30 laps. I think for street driving, the loss of the 30lbs (which is pretty much unnoticeable too) is the bigger target. BTW, love your Threads! keep em' up!

[JustinHEMI]

After seeing the newest video with the stock car on track, I'm no longer doing anything except cosmetics. Anything else would be wasted on me as a weekend warrior. I'll spend the money on road trips.

[kyrix1st]

If one is fairly serious about HPDEs, it would be advisable to at least remove the rear seats to install a half cage/brace that supports 5-point seatbelt&HANS, bucket seats, and square setup wheels. That accounts for roughly 70~100 lbs, which is pretty significant weight reduction.

[M_Power Rob]

Originally Posted by LCDRJohn

Remember something about weight bias and why it is not a major consideration in this case:

1) track days ain't "racing". No one will notice a percent either way. 30 laps of real racing....maybe...even then, probably not.
2) the removal of weight near the battery as is currently located, would be a 1% reduction in weight in that area. If it were such a big deal, no one would drive with less than a full tank, for fear of lightening the rear.
3) the car is tuned for the 52/48 balance, so it already is part of BMWs plan to have a little more weight on the nose.
4) removing weight is less of a problem than adding it.

Whenever we set up a class-conforming track car, we never really obsessed over the front-back balance beyond a certain point. There are plenty of poor handling cars with 50/50 balance and lots of good ones with a heavy nose or tail. All of our cars (except 911s and vettes) are nose heavy at the end of a race, because we are on fumes. I've never noticed anything outside of just the tires getting greasy, which is normal after 30 laps. I think for street driving, the loss of the 30lbs (which is pretty much unnoticeable too) is the bigger target. BTW, love your Threads! keep em' up!

+1000000

I have been trying to convey this but it seems to fall on deft ears.

[sl0m0]

Originally Posted by M_Power Rob

I would not (and have no plans to) run an open CAI on the streets in South Florida. That would be a recipe for disaster.

Is this because of the heat/humidity?

[M_Power Rob]

Originally Posted by sl0m0

Is this because of the heat/humidity?

No, dirt on the streets and in the air plus we have a nasty extensive rainy season with sranding water/puddles quite common. Dont want any of that having direct contact with the filter and into the intake.

[sl0m0]

Originally Posted by M_Power Rob

No, dirt on the streets and in the air plus we have a nasty extensive rainy season with sranding water/puddles quite common. Dont want any of that having direct contact with the filter and into the intake.

Ahh, gotcha. I'm still figuring out the road conditions where I just moved, and initially intended this car to be more of a DD, but am now that I'm on the list for a m3cx it will probably come out in drier conditions.

[M_Power Rob]

Originally Posted by Xspeedracer

This would be a good way to loose weight in the back of the car

For those who have run and/or considering lithium batteries...do these have the risk of thermal runaway? With the difficulty of extinguishing a lithium battery fire and being in the trunk near the gas tank, is there a risk above the risk of the "standard" battery in the trunk?

[M2PDX]

Originally Posted by M_Power Rob

For those who have run and/or considering lithium batteries...do these have the risk of thermal runaway? With the difficulty of extinguishing a lithium battery fire and being in the trunk near the gas tank, is there a risk above the risk of the "standard" battery in the trunk?

These are well engineered, well thought out batteries, not the cheap ones found in scooters or other small appliances.

I've had no problems whatsoever.

[Squidget]

Originally Posted by M_Power Rob

For those who have run and/or considering lithium batteries...do these have the risk of thermal runaway? With the difficulty of extinguishing a lithium battery fire and being in the trunk near the gas tank, is there a risk above the risk of the "standard" battery in the trunk?

Technically, yes. If a full battery shorts, the car may be totalled by fire, smoke, and/or firefighter dousing. Technically there's some marginal risk over a lead acid, everything else being equal. Practically, tho?

Ignoring crashes for a sec, I don't think they are significantly more dangerous than the other electrical and explosive risks in the car. (I'm looking at you, airbag recalls and electrical fires.) LI tech is mature.

So that leaves us with crashes. I am not an automotive engineer, but I assume any rear-ender that crushes the battery will total the car anyway.

Everyone has their own risk tolerance, but personally I wouldn't worry about it.

[Squidget]

Also, and I'm sure this is in the instructions, but don't jump start a dead lithium battery.

[aerobod]

You could also protect the car from a Li Ion battery fire like they did with the Boeing 787 APU starting battery - 1/8” thick stainless steel sealed box around it. Although that would add about 6kg additional weight.

[JohnnyBeagle]

I've had an Antigravity H6 40Ah battery that's lived in my 718 Cayman T, 997 GT3, and is currently in my Camaro SS 1LE. No issues with it, built in jump start is nice although I've never needed to use it, and the weight savings is pretty incredible.

[zero21]

Originally Posted by JohnnyBeagle

I've had an Antigravity H6 40Ah battery that's lived in my 718 Cayman T, 997 GT3, and is currently in my Camaro SS 1LE. No issues with it, built in jump start is nice although I've never needed to use it, and the weight savings is pretty incredible.

I was going to suggest that Porsche has been offering Lithium batteries since I believe 2013? I knew when I spec'd out a Boxster Spyder you could request an Li battery.

[zero21]

Originally Posted by LCDRJohn

Remember something about weight bias and why it is not a major consideration in this case:

1) track days ain't "racing". No one will notice a percent either way. 30 laps of real racing....maybe...even then, probably not.
2) the removal of weight near the battery as is currently located, would be a 1% reduction in weight in that area. If it were such a big deal, no one would drive with less than a full tank, for fear of lightening the rear.
3) the car is tuned for the 52/48 balance, so it already is part of BMWs plan to have a little more weight on the nose.
4) removing weight is less of a problem than adding it.

Whenever we set up a class-conforming track car, we never really obsessed over the front-back balance beyond a certain point. There are plenty of poor handling cars with 50/50 balance and lots of good ones with a heavy nose or tail. All of our cars (except 911s and vettes) are nose heavy at the end of a race, because we are on fumes. I've never noticed anything outside of just the tires getting greasy, which is normal after 30 laps. I think for street driving, the loss of the 30lbs (which is pretty much unnoticeable too) is the bigger target. BTW, love your Threads! keep em' up!

I don't disagree.

But it's more of a personal preference that I don't exacerbate "baked-in" weakness. In my opinion, it is a weakness having a forward weight bias - I believe everyone who knows about suspension and chassis engineering will say the same.

I'm not saying I'm going to go "pro racer" on everyone. The point that you and others are making on the one hand saying: "no one will notice it"; and then on the hand saying, yeah take away 20lbs here - I'm saying no one will notice that either. But:

The accumulation of the weight will be noticed in due course and with proper experience in the vehicle. So I'm back to my original point, if you're going to remove 100lbs, 150lbs, 200lbs - you're chasing performance and handling with that kind of investment. Why not focus on the nose and replace the front spring rates with lighter load springs once you drop the weight? It seems obvious to me if you're going to dump money into the car that's a clear thing to reduce front tire wear which will dramatically improve lap time consistency and on-road handling, and ultimately traction for launches, low-speed acceleration, and braking stability/direction changes.

[Squidget]

I also forgot to mention that motorcycles have been using lithiums for a while.

[Ravenseal]

Lots of super useful information in the OP. Thanks for this! Looking forward to shedding some weight starting with the wheels.

[goldfz8]

Hey All,

g8x uses a oem lithium battery. So m2 doesn't? that makes sense even more why it's so heavy. The back lower section is probably 10 to 13lbs and the uppers are heavy probably close to 46 like in the g8x. There is alot to lose.

I will be getting one soon for drag racing so intend to take some weight out.

ig is vrsix_aj if you Wana see how I took out 300lbs on a x3m lol.