Weight Reduction vs. Weight Distribution (for track use not for drag..etc)

[glamcem]

As you may know our cars have 53/47 weight distribution from factory and easiest way to reduce the weight is from the trunk area since there are more easily accessible items which don't hurt the driveability such as spare tire, tools, seats, aftermarket exhaust etc . It looks somewhat harder to reduce the weight without hurting the balance of the car.

In addition to that, I learned when GM was working on the Camaro Z28 they decided to put back the back seats instead of completely eliminating them (Like the Boss 302) since it reduces the rigidity and they ended up adding denser foams and changed the materials to reduce weight. I never really thought about this (the impact on our cars might be smaller or negligible of course, due to weight and size differences )

Please briefly share your opinion/experience

[tahdizzle]

While weight and power to weight ratio is very important.

I chose distribution, based on my opinion that it is easier to add HP/lb than to reduce lb to HP.

[7thgear]

both are important


the question thought is what is more important to YOU


I've been leaving my spare inside the car for a better planted rear, which translated into more confidence FOR ME, which translates into better consistency, which under my current circumstances generates the best results


the most confidence I've ever had in my car was when I was with an extra two people and 50 kilos in the trunk, I felt like I could be as aggressive as I wanted to and it wouldn't snap on me


is it slower? yes


but confidence tends to build speed


so you do what fits your needs

[rice_classic]

"Percentage"

What percentage of the weight of the car are you removing? How much power-to-weight are you changing? Percentage change on weight distribution? Changing to 54/46 is different than changing to 60/40 for example.

"Variables"

What's the car's shock/spring/tire combination? Configuration of the track; long straights that are all about power or all corners with little to no straights?

"Data"

Take the weight weight out, run at the limit. Put the weight back in, run at the limit. Look at Data and you will have your answer. Before that I would put the car on scales to check the corner balance before and after weight removal. That will give you good baseline idea of the change you've induced to the balance.

[glamcem]

Originally Posted by 7thgear

both are important


the question thought is what is more important to YOU


I've been leaving my spare inside the car for a better planted rear, which translated into more confidence FOR ME, which translates into better consistency, which under my current circumstances generates the best results


the most confidence I've ever had in my car was when I was with an extra two people and 50 kilos in the trunk, I felt like I could be as aggressive as I wanted to and it wouldn't snap on me


is it slower? yes


but confidence tends to build speed


so you do what fits your needs

I actually tried to emphasis that on the poll question by saying "if you have to pick one" but maybe I should've mentioned that in the thread title too

Also, I tend to get better lap times maybe it's because I don't want to scare the passengers with me

Originally Posted by rice_classic

"Percentage"

What percentage of the weight of the car are you removing? How much power-to-weight are you changing? Percentage change on weight distribution? Changing to 54/46 is different than changing to 60/40 for example.

I am not exactly sure about the exact numbers at this point and I do understand the differences between too.. Ideally, I would prefer removing from the front and keep the balance in controls.. battery relocation kits for trunk might be a good example but with the added complexity and efforts I am not sure if it's worth it.. at that point lightweight battery also makes sense..

"Variables"

What's the car's shock/spring/tire combination? Configuration of the track; long straights that are all about power or all corners with little to no straights?

R compounds, relatively stiff coilover setup and you know I attend the events at local tracks in PNW region (PR,RMP and ORP)

"Data"

Take the weight weight out, run at the limit. Put the weight back in, run at the limit. Look at Data and you will have your answer. Before that I would put the car on scales to check the corner balance before and after weight removal. That will give you good baseline idea of the change you've induced to the balance.
good idea, I will try to get more data with and without seats next time to see if there's any quantifiable difference between two..I will report back

Please see above

[juliog]

OP what is your question exactly?

[jvincent]

No real opinion here, but I wanted to chime in with a comment about weight distribution that has annoyed me for a while.

From a physics point of view, splitting the car into equal halves isn't really that meaningful for weight distribution IMHO. There are a LOT of ways to get 50/50 balance that will behave very differently on the road.

For example a 25/25/25/25 distribution will have a very different rotational inertia than 10/40/40/10. Or 40/10/10/40. I think you get the idea.

[tahdizzle]

Originally Posted by jvincent

No real opinion here, but I wanted to chime in with a comment about weight distribution that has annoyed me for a while.

From a physics point of view, splitting the car into equal halves isn't really that meaningful for weight distribution IMHO. There are a LOT of ways to get 50/50 balance that will behave very differently on the road.

For example a 25/25/25/25 distribution will have a very different rotational inertia than 10/40/40/10. Or 40/10/10/40. I think you get the idea.

Agreed. But no one said a 50/50 split was ideal in all scenarios.

Weigh distrubution and alignments all need to be tuned for your needs and driving style.

[brz7400]

glad to know someone else keeps the spare in!
i thought i was the only one that autocrossed with the spare in.

every time i take out the spare, the rear becomes too loose and i lack the skills to control it properly.
it's also why i am scared to change the exhaust for weight savings...
and keep the gas tank filled anywhere more like 1/3~2/3.

i'm looking at lightweight wheels as my next allowed mod, since a nice young man asked me to drive his brz at a practice event a month ago and i immediately noticed the car accelerated off the start line much quicker than mine.
but then he also had the spare tire removed for additional weight savings and i ended up spinning his car on the first sweeper.

so i'll agree that both matters.
if i was a better driver, i would run without spare and low gas tank and muffler delete and lightweight wheels.
but for me, i'll have to stick to keeping the spare in, plenty of gas, regular muffler and hope to pick up some speed through lightweight wheels.

[jvincent]

On the topic of keeping the spare in, the groups that run events at the track near me require you to take the spare/jack/etc out of the car for safety reasons.

I figured that would be the case for everyone.

[D K]

I'm actually blown away how much more front bias our car has...

[rice_classic]

Originally Posted by glamcem

Please see above

Quit denying your addiction and where it's taking you... Takin' out interior bits, thinking of relocating the battery, buying R-comps for a street car... Just stop monkeying with the FRS and embrace the inevitable already.

Go buy a damn racecar.

Resistance if futile.

[bimmer635csi]

I'd say weight reduction first, then weight balance second because:

1) When the car accelerates, weight shifts to the back anyway, balancing out the small imbalance (which is the opposite under braking, but that should be a lower percentage of a lap time)

2) You can tune to the small imbalance with springs, air pressure, sway bars, driving style, etc. You can not tune less weight (or more power) in the car as easily.

3) A lot of classes have minimum weights, so if you can get below the minimum, then you can place ballast where you need it to tune the car.

Forgive me if this seems basic, but the OP's question did also.

[renfield90]

Removing weight will, by the simple laws of physics, make the car faster. You will go, stop, and turn faster. Period.

The same cannot be strictly said for weight distribution unless you're racing in Formula 1 and the fancy computer spits out the perfect weight and alignment settings for the exact track you're on. (I'm treating weight distribution strictly from the perspective of the weight on each tire; a more complex discussion involving where the mass is located and the resulting moments of inertia is probably beyond the scope of this thread.)

Ideally, your car will have some sort of adjustable ride height so you can tune the weight distribution a little bit. This is the key; your weight distribution is a tool you can use to tune the handling of your car, and it's a small tool at that. Your shock settings will have a greater impact on the balance of the car than your weight distribution.

The raw weight of your car is an impediment to your performance. It is NOT a tool. Don't use it as such.