Good ways to reduce the unsprung weight

[Jb325is]

Yeah from what I understand about your car you're already at the point of diminishing returns--it gets a lot pricier and/or less street friendly from here. If this is your only car, I'd spend the money on seat time.

Yep. If anything, some good coilovers for adjustability. 2450 lb e30 with 200hp and good shocks should be a rocket on the track.

[2mAn]

Yeah from what I understand about your car you're already at the point of diminishing returns--it gets a lot pricier and/or less street friendly from here. If this is your only car, I'd spend the money on seat time.

seat time... good idea. why didnt I think of that (not being sarcastic)

Yep. If anything, some good coilovers for adjustability. 2450 lb e30 with 225whp and good shocks should be a rocket on the track.

ftfy. I think I will focus on making the idiot behind the wheel better and eventually get coilovers.

[Wh33lhop]

What suspension are you running?

[2mAn]

Bilsteins & IE3 Race. Treehouse racings CABs. iX & Vert sways. I think Bilsteins will need to be rebuilt soon or maybe just buy Koni's.... or GC Coils

[Eric]

http://www.akgmotorsport.com/catalog/catalog.php

FK3036

[agent]

it's sprung, but ditch the current battery for a miata battery

honestly going any further than that is just wasting your time man. unless you go extreme with your reductions you might net you a loss of 25-50lbs or so. you might notice the difference, but that's only a reduction of roughly 2% (that's with a generous weight guesstimate of 2500lbs)

At the track this past weekend I had two instructors tell me (in unrelated conversations) that 8 pounds is the equivalent of 1 HP. So trunk tar removal alone means effectively gaining 6 HP.

[jalopi]

6hp... lol

but in all seriousness that's an interesting factoid (if it's true)

after crunching some numbers it makes sense though, my bike, which runs roughly the same 1/4 mile times as a Z06 vette, when compensating for the weight using the 8:1 formula gets you almost exactly the same amount of power

[e30_302]

Reducing unsprung weight does not always equal faster laps. Case in point: I went from a 15x6 wheel to 17x9's, combined extra weight of the wheel/tire was probably 20# per corner. Lap times decreased dramatically due to the extra grip.

[dsm2002]

6hp... lol

I know race engine builder who's motto is: "I never met a hp I didn't like". Therefore 6 likes!

[Hooffenstein HD]

Reducing unsprung weight does not always equal faster laps. Case in point: I went from a 15x6 wheel to 17x9's, combined extra weight of the wheel/tire was probably 20# per corner. Lap times decreased dramatically due to the extra grip.

So you needed more grip. Retain the same amount of grip while reducing unsprung weight and post results.

[Eric]

Good ways to reduce the unsprung weight

I wonder where the crossover point is between spring and u spring weight on the rear subframe.

you could try a small case diff, I think that is about 30lbs lighter. 16x8 enkei rpf1's are sub 15lbs I think.


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[Axxe]

Diff is sprung. Not worth going to a glass diff for weight in quite possibly the best spot to have weight in an E30.

[e30_302]

So you needed more grip. Retain the same amount of grip while reducing unsprung weight and post results.

Not the point. Of course if it was lighter, it would be better. But that would require very expensive new wheels, which I am not interested in buying.

[Wh33lhop]

6hp... lol

but in all seriousness that's an interesting factoid (if it's true)

after crunching some numbers it makes sense though, my bike, which runs roughly the same 1/4 mile times as a Z06 vette, when compensating for the weight using the 8:1 formula gets you almost exactly the same amount of power

That ratio will depend entirely on the power to weight ratio of the vehicle in question. You can check it pretty easily:

Let's apply it to an 325i with boltons weighing 2700lbs and making 180hp

-Baseline 2700#, 180hp, 2700/180 = 15.00lbs per hp
-Remove 8#: 2692#, 180hp; 2692/180 = 14.96lbs per hp, .04 difference from baseline
-Add 1hp: 2700#, 181hp; 2700/181 = 14.92lbs per hp, .08 difference from baseline

So in the case of a bolt-on E30, 8lbs makes about 1/2 the difference 1hp does. So roughly 16lbs is worth 1hp.

If we use a track prepped swapped E30, say 2400lbs and 270hp

-Baseline 2400/270 = 8.889lbs per hp
-Remove 8# = 8.859lbs per hp
-Add 1hp = 8.856lbs per hp

So in this case it's roughly correct. In fact, the 8lbs/1hp rule will be spot-on when your power to weight is 8lbs per hp. Kind of makes sense, huh? :)

[Wh33lhop]

I wonder where the crossover point is between spring and u spring weight on the rear subframe.

you could try a small case diff, I think that is about 30lbs lighter. 16x8 enkei rpf1's are sub 15lbs I think.


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The effect the diff has will depend on how it's mounted. With stock bushings it'll be semi-sprung weight, though it's not unsprung in the way that suspension is; with stiff bushings it'll be fully sprung. Either way I'd advise against removing weight from the rear at the expense of robustness.