Weight savings cost/benefit benchmarks

[Craigy]

Don't be so surrious.

He's just picking on you since you're coming in, telling someone they're wrong, and not providing any actual input as to a correct answer.

Frankly I buy the "it understeers because there's a couple hundred less pounds in the back" answer. Makes sense to me. Unless you want to tell us the correct answer...

[klammer]

Originally Posted by Craigy

Don't be so surrious.

He's just picking on you since you're coming in, telling someone they're wrong, and not providing any actual input as to a correct answer.

Frankly I buy the "it understeers because there's a couple hundred less pounds in the back" answer. Makes sense to me. Unless you want to tell us the correct answer...

[oldmanstyle]

Originally Posted by Craigy

Don't be so surrious.

He's just picking on you since you're coming in, telling someone they're wrong, and not providing any actual input as to a correct answer.

Frankly I buy the "it understeers because there's a couple hundred less pounds in the back" answer. Makes sense to me. Unless you want to tell us the correct answer...

I wouldn't say I didn't provide ANY actual input to a correct answer, but you're right I didn't completely spell it out. Of course we could have elaborated on that and had some discussion, but the conversation took a different turn...

So we have the car going around corner. The centrifugal force acts on the car, but it's the tires that provide traction for the car and determine where it's going (understeer/neutral/oversteer). Each tire has a limited amount of grip that can go to braking, accelerating, cornering, or a combination of those forces. These traction forces are developed by the friction between the tire and the pavement, and the magnitude of a friction force is dependent on the mass of the object pushing down on the friction surface (among other variables). For example, if you slid a small wooden block over a sheet of sandpaper by just pushing it from behind, then it will slide somewhat easily. If you put a 5 lb weight on the block, then it will take more force to slide it over the surface because the frictional force has increased due to the increase of the mass of the wooden block pushing down on the friction surface.

So getting back to the car, when mass is removed from the rear, it takes away from the magnitude of the traction force that the tire can provide through friction. With the rear tires having less traction available to them because of the loss of mass pushing down on them, they will lose traction earlier. This situation is made worse when entering a corner because the rear tire also has the acceleration force to deal with to go along with the cornering force (since we should be on the throttle through a corner). So it will exceed its available traction sooner than before, meaning the tail of the car has less grip and will swing out more easily, aka oversteer.

Aside from the technical explanation, I'm experiencing this exact problem in my track car that has had extensive lightweight mods in the back seat/trunk, but limited lightweight mods towards the front of the car.

[Ant Man]

Originally Posted by oldmanstyle

I wouldn't say I didn't provide ANY actual input to a correct answer, but you're right I didn't completely spell it out. Of course we could have elaborated on that and had some discussion, but the conversation took a different turn...

So we have the car going around corner. The centrifugal force acts on the car, but it's the tires that provide traction for the car and determine where it's going (understeer/neutral/oversteer). Each tire has a limited amount of grip that can go to braking, accelerating, cornering, or a combination of those forces. These traction forces are developed by the friction between the tire and the pavement, and the magnitude of a friction force is dependent on the mass of the object pushing down on the friction surface (among other variables). For example, if you slid a small wooden block over a sheet of sandpaper by just pushing it from behind, then it will slide somewhat easily. If you put a 5 lb weight on the block, then it will take more force to slide it over the surface because the frictional force has increased due to the increase of the mass of the wooden block pushing down on the friction surface.

So getting back to the car, when mass is removed from the rear, it takes away from the magnitude of the traction force that the tire can provide through friction. With the rear tires having less traction available to them because of the loss of mass pushing down on them, they will lose traction earlier. This situation is made worse when entering a corner because the rear tire also has the acceleration force to deal with to go along with the cornering force (since we should be on the throttle through a corner). So it will exceed its available traction sooner than before, meaning the tail of the car has less grip and will swing out more easily, aka oversteer.

Aside from the technical explanation, I'm experiencing this exact problem in my track car that has had extensive lightweight mods in the back seat/trunk, but limited lightweight mods towards the front of the car.

Exactly and very well written. Hence in my first post where I couldn't understand why removing weight from the rear would increase understeer, quite the reverse. In my mind (rightly or wrongly) I used the simple analogy of downforce and running less rear wing. Less weight in effect pushing the rear into the tarmac and hence less grip. Less grip on the rear = more oversteer.

[klammer]

Originally Posted by oldmanstyle

I wouldn't say I didn't provide ANY actual input to a correct answer, but you're right I didn't completely spell it out. Of course we could have elaborated on that and had some discussion, but the conversation took a different turn...

So we have the car going around corner. The centrifugal force acts on the car, but it's the tires that provide traction for the car and determine where it's going (understeer/neutral/oversteer). Each tire has a limited amount of grip that can go to braking, accelerating, cornering, or a combination of those forces. These traction forces are developed by the friction between the tire and the pavement, and the magnitude of a friction force is dependent on the mass of the object pushing down on the friction surface (among other variables). For example, if you slid a small wooden block over a sheet of sandpaper by just pushing it from behind, then it will slide somewhat easily. If you put a 5 lb weight on the block, then it will take more force to slide it over the surface because the frictional force has increased due to the increase of the mass of the wooden block pushing down on the friction surface.

So getting back to the car, when mass is removed from the rear, it takes away from the magnitude of the traction force that the tire can provide through friction. With the rear tires having less traction available to them because of the loss of mass pushing down on them, they will lose traction earlier. This situation is made worse when entering a corner because the rear tire also has the acceleration force to deal with to go along with the cornering force (since we should be on the throttle through a corner). So it will exceed its available traction sooner than before, meaning the tail of the car has less grip and will swing out more easily, aka oversteer.

Aside from the technical explanation, I'm experiencing this exact problem in my track car that has had extensive lightweight mods in the back seat/trunk, but limited lightweight mods towards the front of the car.

an actual explanation...and what kind of track car? and where do you run? btw, this conversation has gone exactly where I wanted

[Richbot]

The regular Stoptech stuff is in the first page, but I only see the ST60 non-Trophy setup listed so here's what I just did (finally):

Stoptech Trophy Sport 355mmx35mm ST40 front kit

Stock caliper/line/bracket with worn pads: 14lb
STR40 Trophy Sport caliper, bracket, pads, line: 10lb

Stock worn front rotor: 21.5lb (about 0.26lb of cast iron disappears from the rotor from new to used, based on 28.4mm minimum thickness, 30mm new thickness, 50mm swept area and a quick calculation of the mass of an annular cylinder, basically negligible change in mass from wear)
Stoptech 355x35mm front rotor/hat: 20lb

Total weight lost: approx. 5.5lb per corner, 11 total

[TheSnail]

Might I add, that coilovers or at least the KW V3 I just installed yesterday weight slightly more. All of people think you can drop 15-20lbs with some coilovers, but on this car, the OEM struts are very light. The OEM fronts are cast aluminum unlike most steel struts/shocks.

KW V3

Fronts are 1.5lbs heavier a piece.
Rears are 0.5 heavier a piece.

This is going from a OEM base model suspension to KW V3 (Part #: 35220067)

[Groundpilot]

Has anyone removed a front passinger seat just for track days?
Its about 62 pounds of a dead weight, and its a free way to add lightness.
Will removing just a front passenger seat trigger some warning lights and disable air bags?

[bigjae1976]

Originally Posted by Groundpilot

Has anyone removed a front passinger seat just for track days?
Its about 62 pounds of a dead weight, and its a free way to add lightness.
Will removing just a front passenger seat trigger some warning lights and disable air bags?

You'll get an airbag light unless you get a sensor emulator.

[Richbot]

Low profile USB dual charging cigarette lighter thingie: 11 grams
Crappy one from the airport: 15 grams

Weight savings: 0.0088lb
Cost: $4.50 with free prime shipping!
Cost/lb: $511.36/lb

[Richbot]

A few people are running them long term now and have done it but I haven't seen it in this thread

Voltphreaks VPH900 battery: 7lb
Custom Mounting plate and aluminum strap battery restraint system including titanium fasteners: 2lb (rounding up)
Stock battery: 60lb with stock bolt-down bracket

Weight savings: 51lb

Battery cost: $1100 (mine was nib never installed so I got it for less secondhand)
Bracket cost: $25 because I used ti fasteners I had lying around

Cost/lb: $22.05/lb

One of the most economical weighs to lose weight for sure. And based on my personal experience this battery has none of the issues of lead acid tiny batteries on this car.

[Hujan]

Originally Posted by Richbot

A few people are running them long term now and have done it but I haven't seen it in this thread

Voltphreaks VPH900 battery: 7lb
Custom Mounting plate and aluminum strap battery restraint system including titanium fasteners: 2lb (rounding up)
Stock battery: 60lb with stock bolt-down bracket

Weight savings: 51lb

Battery cost: $1100 (mine was nib never installed so I got it for less secondhand)
Bracket cost: $25 because I used ti fasteners I had lying around

Cost/lb: $22.05/lb

One of the most economical weighs to lose weight for sure. And based on my personal experience this battery has none of the issues of lead acid tiny batteries on this car.

Glad it worked out for you, Richbot! My loss is your gain.

[roastbeef]

Originally Posted by Richbot

A few people are running them long term now and have done it but I haven't seen it in this thread

Voltphreaks VPH900 battery: 7lb
Custom Mounting plate and aluminum strap battery restraint system including titanium fasteners: 2lb (rounding up)
Stock battery: 60lb with stock bolt-down bracket

Weight savings: 51lb

Battery cost: $1100 (mine was nib never installed so I got it for less secondhand)
Bracket cost: $25 because I used ti fasteners I had lying around

Cost/lb: $22.05/lb

One of the most economical weighs to lose weight for sure. And based on my personal experience this battery has none of the issues of lead acid tiny batteries on this car.

Do you daily drive your car? Trickle charger?

[Richbot]

Originally Posted by roastbeef

Do you daily drive your car? Trickle charger?

It's a daily. The stock battery wouldn't be happy after sitting for more than a week without a charger. I always used a battery tender if it was going to sit for more than 5 days or so. This battery so far has sat for 3 days with no issues starting afterwards and if anything the starter seems to getting all the juice it is asking for right away whereas the stock battery seemed to discharge more slowly during startup even if it was just on the tender.

This particular lifepo setup has an automatic shutoff that will stop it from draining enough to cause a no start. Was never impressed with the stock battery so I guess I don't see how it could get much worse. I'm planning on letting it sit without using a tender and drive it normally and just see how it goes so I can learn the limits of what it can handle. Will be interesting to see what it does when the weather turns colder.

[roastbeef]

Originally Posted by Richbot

It's a daily. The stock battery wouldn't be happy after sitting for more than a week without a charger. I always used a battery tender if it was going to sit for more than 5 days or so. This battery so far has sat for 3 days with no issues starting afterwards and if anything the starter seems to getting all the juice it is asking for right away whereas the stock battery seemed to discharge more slowly during startup even if it was just on the tender.

This particular lifepo setup has an automatic shutoff that will stop it from draining enough to cause a no start. Was never impressed with the stock battery so I guess I don't see how it could get much worse. I'm planning on letting it sit without using a tender and drive it normally and just see how it goes so I can learn the limits of what it can handle. Will be interesting to see what it does when the weather turns colder.

interesting. so it sounds like it is designed to be a lightweight oem replacement. i like that it has the auto shutoff.
as of now, i don't drive my car for sometimes two weeks. oem original battery from 2011. maybe i'm rolling the dice, but i expect to have to replace it soon anyways. if i go the same route as the battery you have, i'll run a trickle charger.

[jakob66]

Originally Posted by Richbot

A few people are running them long term now and have done it but I haven't seen it in this thread

Voltphreaks VPH900 battery: 7lb
Custom Mounting plate and aluminum strap battery restraint system including titanium fasteners: 2lb (rounding up)
Stock battery: 60lb with stock bolt-down bracket

Weight savings: 51lb

Battery cost: $1100 (mine was nib never installed so I got it for less secondhand)
Bracket cost: $25 because I used ti fasteners I had lying around

Cost/lb: $22.05/lb

One of the most economical weighs to lose weight for sure. And based on my personal experience this battery has none of the issues of lead acid tiny batteries on this car.

Richbot
Did you corner weight your car afterwards? My car is stripped (3575lbs with driver) and I actually need at least a 55ah battery in the right rear to get to 50.4% cross balance. The difference of weight loss is noticeable but the 'bad' cross weight unfortunately too.
Thanks

[Richbot]

I happen to have my own set of scales for racecar setup and weighed the car before and after. The battery made about 0.1% difference in cross weight to the worse. I sold my MCS doubles and I'm using OEM dampers and ZCP springs so I don't have any way to influence cross weight, but a .1% difference would be very easy to tune out with a few turns of the spring adjusters at each corner if I had them

The battery weight is outside the wheelbase, nearly 18" off the ground and pretty far from the CG, not a good place to carry extra weight if you don't have to because it has an exaggerated influence on the ability of the car to change directions quickly. If you have to put ballast way back there to get the car to cross correctly something else is going on. I would rather put some ballast plates in the rear passenger footwell, it's below the CG height and helps bring the polar moment down. But since you're not trying to make your car heavier I get it

People talk about the battery location on BMW's as if it's evidence of good engineering and it is, to a point, I mean it's better to have the battery in back than hanging out over the front wheels, and better to have it in back than a fuel tank that could take a crash and throw fuel everywhere, plus variable fuel weight affects handling less as the tank runs dry if it's low and centrally located, but if you could ignore safety you would probably want that huge battery located under the rear passenger-side seat. Unfortunately there's a fuel tank there.

Think about this, the battery is the single heaviest component on the car barring front seats, maybe engine block, the chassis itself and the front and rear subframes, and IIRC the aluminum front subframe might even be lighter bare. So it's like the second-lowest hanging fruit behind seats and exhaust for weight loss on this car without just removing parts. Unless you want to start adding speed holes. IMO, most of the objections to losing weight off the rear of the car can be solved by pointing at the GT350R (53% front), Z28 (53% front) and other fast FR sedan cars. If car too light in rear, add bigass rear tires, amke sure you add front tires too, and if you're serious about going quicker 'round corners, a wing. Don't throw bags of cement in back in pursuit of perfect weight distribution because as soon as you turn the steering wheel those pretty numbers on the scale readout mean zip

But like I said, my car is a street car. I just want the car to go faster from 0-legal, and if losing weight off the rear makes the handling more "interesting" at legal speeds, great

[Ant Man]

Originally Posted by Richbot

It's a daily. The stock battery wouldn't be happy after sitting for more than a week without a charger. I always used a battery tender if it was going to sit for more than 5 days or so. This battery so far has sat for 3 days with no issues starting afterwards and if anything the starter seems to getting all the juice it is asking for right away whereas the stock battery seemed to discharge more slowly during startup even if it was just on the tender.

This particular lifepo setup has an automatic shutoff that will stop it from draining enough to cause a no start. Was never impressed with the stock battery so I guess I don't see how it could get much worse. I'm planning on letting it sit without using a tender and drive it normally and just see how it goes so I can learn the limits of what it can handle. Will be interesting to see what it does when the weather turns colder.

I'd be very interested in your additional feedback on learning how long the VPH900 battery will last without charging. I definitely want to install a lightweight battery.

The difference would like running with a near empty tank compared to a full one.

Probably best to start another specific thread if you can pls.

Cheers

[Richbot]

There's a Voltphreaks-specific thread in the DIY section I'll post there with any updates I have once the battery has actually been put through its paces.

[Richbot]

Coil covers
free/save money if you break one during a spark plug change: 1.4 lb

[Richbot]

Remove aluminum door trim pieces - 1.9lb free (E90M)

Switch from sycamore anthracite to aluminum dash trim - 0.5 lb. - maybe net positive?$ ironically the sycamore veneer main dash trim is a pretty hefty piece of cast aluminum so it's quite a bit heavier than the plastic backed brushed aluminum dash piece

[Richbot]

For those who have cold weather package and don't like the headlight washers:

Remove 10' of 1/2" OD rubber washer fluid hose and various fittings and clips:

-2.0 lb off the nose

Have to cap the line at the reservoir and code out the headlight washers with Carly or similar, so it may not be free if you're paying somebody to code. Also, $0.50 for a 1/2" rubber vacuum cap

$/lb: $0.25+