Weight Reduction Thread

[wilazn]

Guys, if you're over 200lbs with +30% body fat you can afford to lose some weight by making healthier food choices. If you're like me and over 200lbs with 10% body fat, you're probably focused on gaining weight, not losing it.

Lmao

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[Victor Newman]

My weight reduction so far:

1) replaced stock grille with lighter RS grille
2) removed two supercharger / engine covers
3) removed floor mats
4) removed owner's manual from glove box
5) cleaned out storage compartments and just left necessities in there
6) removed spare tire, jack, tools, and added two cans of fix-a-flat and full tire repair kit
7) not sure how the Stoptech BBK compares with the stock brakes, but that is a change

Next up is a lightweight battery. Looking to get a Braille 9.5 lb. battery to remove the (as far as I've researched) 50 lb. stock battery.

My clutch isn't going to last much longer, so I'm going to go with a light flywheel / clutch combo

That'll probably be it for a while, until going with lighter wheels

[firstars]

Mine is down to 3,781 lbs with a little under a half tank. No spare, no rear seats. Could be worse I suppose. Im loaded up DSG prestige model so starting out with highest curb weight.

[shadycrew31]

So what did his car end up weighing?


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No one will ever know.

[Victor Newman]

Mine is down to 3,781 lbs with a little under a half tank. No spare, no rear seats. Could be worse I suppose. Im loaded up DSG prestige model so starting out with highest curb weight.

Thanks, that's a lot of good info there. I was wondering about the balance front-to-back. That gives me some info to run numbers on

Can you lay out the items that you have removed or switched out that would have a weight impact?

[firstars]

Thanks, that's a lot of good info there. I was wondering about the balance front-to-back. That gives me some info to run numbers on

Can you lay out the items that you have removed or switched out that would have a weight impact?

Remove rear seat and seatback (over 70lbs), Vorsteiner VFF 106 19x9.5 et35 (under 21 lbs), RE71R tires, Brembo Club Racing 355 BBK (I have weight somewhere), H&R RSS+ coilovers (definitely lighter than OEM ADS shocks), no spare, no rubber mats, no tool kit, milltek exhaust (didnt weight but might actually be more than OEM since its valved)

[Victor Newman]

Remove rear seat and seatback (over 70lbs), Vorsteiner VFF 106 19x9.5 et35 (under 21 lbs), RE71R tires, Brembo Club Racing 355 BBK (I have weight somewhere), H&R RSS+ coilovers (definitely lighter than OEM ADS shocks), no spare, no rubber mats, no tool kit, milltek exhaust (didnt weight but might actually be more than OEM since its valved)

So stock battery, right?

Since I haven't weighed my car that specifically, I'm going to be playing around with your weight balance numbers to see what adding weight back to the trunk (spare / jack) or replacing the stock battery with a lightweight battery would do to the static weight at the wheels, and by how much the CG would move forward. I want to compare that to front / rear weight balance and total weight on the front axle versus rear axle. There are definitely more "ideal" places to remove weight - like the front end of our cars, but I'd like to know whether removing weight in the rear would have any negative effect. I don't think so, but would be good to get some objectivity behind it.

After removing my spare and jack, I felt like turn-in was better due to not having to accelerate that weight in the tail. The front felt the same - still heavy steering, but at least the rear wasn't pulling to the outside too.

[Victor Newman]

A couple of quick rough numbers.

Rear axle to center of battery and spare tire is 20". Say you removed 100 lb. from that point between the spare, battery, jack, tools, etc. (100 lb. just as an example). The static load is 100 lb. on the 20" cantilever generates 118 lb. on the rear axle with an uplift of 18 lb. on the front axle.

So by removing the 100 lb.:

1) you're removing 100 lb. from the total weight, and decreasing moment of inertia (CG moves forward by a very small margin)
2) rear axle weight decreases by 118 lb.
3) front axle weight increases by 18 lb.

If firstars removed an additional 50 lb. from the rear, it would end up being:

Front axle weight: 2202 lb.
Rear axle weight: 1529 lb.
Distribution: 59% / 41%
Total weight lost: 1.3%

...........i think

And wouldn't that reduce understeer? If the front tires see more weight, but the actual mass at the front doesn't change, you don't have to accelerate it laterally at the front end. So basically, you've got more front end traction, but with the same mass to accelerate laterally.

And while the rear tires have less weight on them, they would lose grip sooner, but again, you don't have that rear mass to accelerate laterally, either. Moment of inertia decreases, and the car is lighter overall for braking and acceleration. But i could be wrong.

[Jay@JXB]

Here are all the wheel/tire setups I've weighed:

18 x 9.5 et45 Enkei RPF1 with new 235/40/18 Nokian Hakkapelitta R2: 41.82 lb



19 x 9.5 et40 AG M510 with some worn down all seasons: 52.25 lb



Stock rotors with 255/35/19 RE71Rs almost completely bald: 49.36 lb



Some Tire Rack crap Advanti Racing 18 x 8 et35 with 245/40/18 Dunlop WinterMaxx: 49.10 lb



So...get RPF1s, they're the shit.


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[Victor Newman]

by removing 100 lb from the point where the center of the spare sits, moment of inertia is reduced by about 4,750 lb ft^2 for whatever that is worth, relatively.

so it looks like there is an advantage in multiple areas to removing weight out of the rear. reducing that rear mass should allow the sport diff to rotate it easier as well

[jachien]

by removing 100 lb from the point where the center of the spare sits, moment of inertia is reduced by about 4,750 lb ft^2 for whatever that is worth, relatively.

so it looks like there is an advantage in multiple areas to removing weight out of the rear. reducing that rear mass should allow the sport diff to rotate it easier as well

How did you obtain that number for the moment of inertia? there should be various moments depending on distances over which they will be 'rotating' about, ie: roll axis, cg, etc...

[AudiTFSI3o3]

so to the guys who are counting "weight saving" by swapping grilles, are you serious? that's like, < 1 lb, right?

[shadycrew31]

so to the guys who are counting "weight saving" by swapping grilles, are you serious? that's like, < 1 lb, right?

Next we will talk about shaving body hair off, several crucial lbs there for some of us.

Personally I use these lightweight socks from under armor, every ounce counts.

[Victor Newman]

How did you obtain that number for the moment of inertia? there should be various moments depending on distances over which they will be 'rotating' about, ie: roll axis, cg, etc...

just static from the center of gravity

inertia is just the point mass multiplied by the squared distance from the CG - it shouldn't change. The tires are exerting external forces on the car, which will change, but inertia of the vehicle itself should stay the same I would think

[Victor Newman]

Next we will talk about shaving body hair off, several crucial lbs there for some of us.

Personally I use these lightweight socks from under armor, every ounce counts.

You laugh, but on top of shaving less than one pound from the front by switching grilles, I have shaved my pubes and don't wear any socks at all. Threw them all out so that my house also has weight reduction

[shadycrew31]

You laugh, but on top of shaving less than one pound from the front by switching grilles, I have shaved my pubes and don't wear any socks at all. Threw them all out so that my house also has weight reduction

You are well on your way to success!

[Victor Newman]

You are well on your way to success!

Obviously a pound here and there isn't going to make a difference, but if you can get away with losing the spare, jack, tools, and going with a lightweight battery, you can really help this car rotate better. It's not going to be some killer race car, but it could be more fun to drive and have a lighter feel. Thinking through it and running some quick numbers was just to see how it actually affects the front-to-rear balance of the car. Others have suggested that removing weight from the rear of the car would hurt balance, but it turns out that it doesn't.

Of course a spare is better than a couple cans of fix-a-flat and a tire repair kit, and the battery in our car is sized for our Canadian friends and we never have to worry about not having enough cranking amps in an AWD car intended to be used in winter. But I'm willing to risk plugging or patching a flat, and since my car is garaged and NC winters are mild, I don't need a battery quite that stout. I can feel an improvement in steering with the spare and tools removed, and I'm looking to get more of that by shedding another 40 lb. with a $190 lightweight battery. Some Vorsteiners that are lighter would be next.

Switching grilles, removing little covers or floormats isn't going to make a difference - it's just for fun.

[vwblackb5]

Mine is down to 3,781 lbs with a little under a half tank. No spare, no rear seats. Could be worse I suppose. Im loaded up DSG prestige model so starting out with highest curb weight.

Are you on coils or springs only? Wondering if -2 negative camber F/R and L/R correct post alignment?


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[shadycrew31]

Obviously a pound here and there isn't going to make a difference, but if you can get away with losing the spare, jack, tools, and going with a lightweight battery, you can really help this car rotate better. It's not going to be some killer race car, but it could be more fun to drive and have a lighter feel. Thinking through it and running some quick numbers was just to see how it actually affects the front-to-rear balance of the car. Others have suggested that removing weight from the rear of the car would hurt balance, but it turns out that it doesn't.

Of course a spare is better than a couple cans of fix-a-flat and a tire repair kit, and the battery in our car is sized for our Canadian friends and we never have to worry about not having enough cranking amps in an AWD car intended to be used in winter. But I'm willing to risk plugging or patching a flat, and since my car is garaged and NC winters are mild, I don't need a battery quite that stout. I can feel an improvement in steering with the spare and tools removed, and I'm looking to get more of that by shedding another 40 lb. with a $190 lightweight battery. Some Vorsteiners that are lighter would be next.

Switching grilles, removing little covers or floormats isn't going to make a difference - it's just for fun.

I found that I saved 200 lbs by not being in the car. HUGE Savings.

Sidenote, what $190 battery are you speaking of, I didn't know there was a lighter battery in that price range.

[Victor Newman]

I found that I saved 200 lbs by not being in the car. HUGE Savings.

Sidenote, what $190 battery are you speaking of, I didn't know there was a lighter battery in that price range.

Braille

https://www.braillebattery.com/index...ightweight_agm

I'm looking at the B129

[eurotic]

I can feel an improvement in steering with the spare and tools removed

Well that just emphasizes how out of tune I am with my car. Hell I've autocrossed with a passenger and couldn't say there was an appreciable difference in handling without him there. I bet that if I had someone secretly adding or removing ballast from my car between runs I don't think I'd ever be able to tell unless it was a lot of weight. Or maybe I just haven't paid enough attention.

[Jay@JXB]

Braille

https://www.braillebattery.com/index...ightweight_agm

I'm looking at the B129

Let me know how that works out for you I definitely want to go down that road but I'm afraid of the stupid Audiisms that may occur.


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[AudiTFSI3o3]

next we will talk about shaving body hair off, several crucial lbs there for some of us.

Personally i use these lightweight socks from under armor, every ounce counts.

you laugh, but on top of shaving less than one pound from the front by switching grilles, i have shaved my pubes and don't wear any socks at all. Threw them all out so that my house also has weight reduction

gahahahaha

[Victor Newman]

Let me know how that works out for you I definitely want to go down that road but I'm afraid of the stupid Audiisms that may occur.


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Yea, me too, but I'm going to give it a try

[Oloung1]

If firstars removed an additional 50 lb. from the rear, it would end up being:

Front axle weight: 2202 lb.
Rear axle weight: 1529 lb.
Distribution: 59% / 41%
Total weight lost: 1.3%

...........i think

And wouldn't that reduce understeer? If the front tires see more weight, but the actual mass at the front doesn't change, you don't have to accelerate it laterally at the front end. So basically, you've got more front end traction, but with the same mass to accelerate laterally.

And while the rear tires have less weight on them, they would lose grip sooner, but again, you don't have that rear mass to accelerate laterally, either. Moment of inertia decreases, and the car is lighter overall for braking and acceleration. But i could be wrong.

im following you with your example but im not certain that in this scenario weight reduction = added benefits of added downforce. our chassis is nose heavy to begin with, increasing the weight ratio to the front sounds like more chances of the car pushing in corners.

maybe some engineers or racers on board can give us insight on what is the optimal weight distribution on our cars for tracking?

[firstars]

Gotta remember too there are other things you can do to combat under steer besides weight distribution (although that is a major factor) here are some of the things I run to combat understeer and get the car more neutral: run wider front track than rear (et34/37), bump up compression on front shocks, run more camber, raise rear ride height, raise front tire pressure, run stiffer rear sway bar.

Then the best part is once you are patient and let the car turn in the sports diff rotates the car wonderfully and masks any inherit to understeer.

All experimentation I've worked with over the last year. There is also aero, adjustable control arms, and reducing front weight (carbon fiber hood?)

[shadycrew31]

Braille

https://www.braillebattery.com/index...ightweight_agm

I'm looking at the B129

Oh me and braille dont get along. Too many explosions for me!

[Victor Newman]

im following you with your example but im not certain that in this scenario weight reduction = added benefits of added downforce. our chassis is nose heavy to begin with, increasing the weight ratio to the front sounds like more chances of the car pushing in corners.

maybe some engineers or racers on board can give us insight on what is the optimal weight distribution on our cars for tracking?

There is a difference between weight in the front end of the car, and pressure on the front tires. In this case, the weight in the front end of the car that has to be accelerated laterally stays the same. If a weight is cantilevered over the rear axle, it creates an uplift force on the front tires, reducing the pressure on the front tires, it doesn't decrease the weight in the front of the car. For example, the engine weight stays the same in both cases. What is different is that you're simply putting more pressure on the front tires, increasing grip and postponing understeer.

So before rear weight reduction, you have the same weight in the front end to accelerate laterally, but less pressure on the front tires for grip. After rear weight reduction, the uplift in the front tires from the rear cantilever goes away. Weight in the front end stays the same, but the front tires have more pressure on them for more grip.

Now, from the example, it's only 18 lbs. added to front tire grip for every 100 lbs. removed from the rear, so effectively no change, especially relative to what firstars posted about managing the throttle correctly to not induce understeer. The example is just to put numbers behind the idea that removing weight from the rear does not negatively affect the balance of the car. And I'm really using "weight" loosely when talking about mass for lateral acceleration to make it easier to follow the example.

As a separate factor from above, the real "feel" of lightness comes from, I think, the reduction in the moment of inertia. Because the CG is farther forward for the S4, (approximately 46.5" behind the front axle in firstars' case) removing rear weight is very beneficial because of its distance from the CG, which is squared.

[Victor Newman]

Well that just emphasizes how out of tune I am with my car. Hell I've autocrossed with a passenger and couldn't say there was an appreciable difference in handling without him there. I bet that if I had someone secretly adding or removing ballast from my car between runs I don't think I'd ever be able to tell unless it was a lot of weight. Or maybe I just haven't paid enough attention.

Well, your passenger is near the center of gravity

[Jay@JXB]

Yea, me too, but I'm going to give it a try

Did you end up trying this?


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[Jay@JXB]

Cross-posting this. Rear seat pan, seat back, and center buckle anchors weigh a total of 86 lbs.

If anyone knows how to remove the rear retractors PLMK I don't want to screw up the order of operations with all the trim. They appear to be beneath the rear deck trim which is held in place by screws, clips, and the c-pillar trim.





Car is getting lighter! This is with 1/8 tank of gas spare, tools, back seats removed. Plus a 30 lb trailer hitch.




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[Jay@JXB]

RSS+ weigh a whopping 20 lbs less than PSS10! Haven't weighed my stock suspension yet; I'm assuming PSS10 is just really heavy judging by the number and width of the coils.






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[whiped]

C pillar just pops off. Be careful as there are airbags under there.

There is a pretty high chance the clips will be left behind, using a fork was the best way I found to remove them.

Here is an unrelated DIY that will help: http://www.audiworld.com/forums/s4-b...guide-2790664/

[MagillaGorilla]

I got a bullet proof plan.

Step 1: Don't buy a large AWD luxury sedan.

[MS203]

I got a bullet proof plan.

Step 1: Don't buy a large AWD luxury sedan.
Step 2: ???
Step 3: Profit

Lol.

In all seriousness, for those with modified suspensions, aftermarket wheels and tires... do you really need to run a spare?? Is anyone not? My car is pretty slammed currently on coilovers. I have about a half-finger gap on all wheel wells. My setup is perfect at the moment with zero rubbing. It dawned on me the other day that my spare may not even bolt up properly, given the cars much lower ride height. I could be totally wrong, but when I envision the spare being put on I picture a sketchy and lopsided/tilted ride home. I can't imagine how a donut would work given my current stance and fitment.

I really want to just remove the spare and its tools, which would shave off a decent amount of weight. The only problem is my commute M-F is 50 miles each way on the highway, thinking of just doing it anyway. Flatbeds aren't so bad, right?

[Jay@JXB]

I got a bullet proof plan.

Step 1: Don't buy a large AWD luxury sedan.

Building for Street Modified class in autocross. I firmly believe I will trophy at nationals with this car before this is over.


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[Jay@JXB]

C pillar just pops off. Be careful as there are airbags under there.

There is a pretty high chance the clips will be left behind, using a fork was the best way I found to remove them.

Here is an unrelated DIY that will help: http://www.audiworld.com/forums/s4-b...guide-2790664/

Awesome that's exactly what I was looking for!


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[Victor Newman]

Did you end up trying this?


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Haven't yet, but it'll be soon. Braille and CR15 are next for me. Will post up in this thread when I do

[doughboy17]

Carbs are the enemy.

[fitzydude]

Anyone tried adding fiber to their diet?