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Discussion Starter · #1 ·
Hi! I have two questions.

1. My 130i has front end higher than a rear. Rear end is sitting bit low (20-30mm) comparing to front. I put new rear springs but nothing changed. Is it really factory setting? Car has sport suspenion package.
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2. The car really likes the low weight (can feel it when driving full and nearly empty tank). It is much more fun to drive when its lighter. Has anyone ever calculated or reseached options what gives the most bang for the buck for a 130i street car? It's my "backup" car so i drive it around 4000miles per year in a city. So track modifications like plastic doors and back seat delete are not an option. Also spending a fortune is not reasonable thing to do. As far i calculated, even a carbon hood is more bang for buck than new lightweight rims. Another alternative is to gain hp but the main thing to do is go catless headers(?). But i dont like that modification because of the smell and cel. Any clever and tested solutions or i can see them only in my dreams?
 

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Lightweight alloys will be a bigger improvement than it looks on paper, the car will feel much more nimble if you can shave off unsprung weight so I'd do that before butchering the car. After that you're looking at removing sound deadening, rear seats and swapping out panels for lightweight alternatives which I don't think are worth the gains on a street car. You could always just put less petrol in it.
 

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Easiest option: sell it and buy an E81. They're 90kg lighter than the E87 out of the box.

As nivens mentioned, lightweight wheels will make an enormous noticeable difference, far more than you'd think just from the numbers. You can also drop 2kg of unsprung from stock 130i front brakes using two-piece Z4 discs, part number 34116794427.

Other than the above, here's a few rough numbers I stole from elsewhere. Can't speak for their accuracy.
  • Lightweight 17" wheel/tire combo: -25kg (unsprung!!!)
  • Lithium race battery: -20kg (source)
  • Rear seat delete: -20kg (source) - additional -5kg from removing bolsters and side panels
  • Race seats: -20kg per seat (power seats) or -15kg per seat (manual seats) - both compared to Recaro PP at 9kg including rails/mounts
  • Sunroof delete (carbon panel): -15kg (source)
  • Lexan: -13kg (all glass) or -8kg (side/rear glass only) - based on 50% weight of factory glass
  • Carbon hood: -10kg (various different sources)
  • Lightweight stainless exhaust (catted but centre muffler delete): -10kg (citation needed)
  • Carbon roof skin: -6kg (citation needed)
Edited with new info re weights - some of what I'd copied was inaccurate.
 

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I’ve swapped to Bola alloys (FLB) for the reduction in unsprung mass but didn’t realise how much the sunroof option adds to the car. Makes sense when you think about it as it’s a big lump of glass + motor + mechanism (right at the top of the car as well)
 

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I’ve swapped to Bola alloys (FLB) for the reduction in unsprung mass but didn’t realise how much the sunroof option adds to the car
As mentioned it could be inaccurate, I've nicked those numbers from others across the web. 50kg seems unrealistic just for a sunroof delete but that's what was claimed.

Edit: According to these guys, it's more like a 15kg loss. Might have been a typo on my part converting to metric or something, or the original source seriously inflated their weight loss!!

 

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Discussion Starter · #7 ·
First of all thank You all for youre ideas. Selling and replacing it with E81 is not an option as it is more impractical. Also it has a perfect history and the car is top condiotion so it is close to my heart. I do have a sunroof and i like it. So far rims, battery, hood, exhaust and brakes sounds like best option. I do have nice oem sport seats so swaping the seats are questionable but the weight loss amount is very noticeable and i will think about it. I would like to read about unsprung mass more. About lightweight rims and brakes differences compared to oem. Real (bmw) test results? Have anyone made specific tests that accurately confirms the arguments? Any good posts or articles?
 

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Fitting lightweight wheels is basically like removing 4 heavy flywheels from the car, it will feel noticeably nippier around town (less difference at motorway speeds). They’re also easier for the suspension to keep in contact with the road, so expect grip improvements over undulating surfaces also.

If you want to compound the effect, go for lightweight tyres too, they can vary by over a kilo from brand to brand for the exact same size/performance.

Wheels are easily resellable, once you’ve had your fun. If you can find a 2nd had set, they should basically be free over the long term. Win, win.
 

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In case it helps, I posted the comparative weights of the various brake upgrade options a while back. Stock calipers with E89 discs and uprated pads/fluid would be a good minimal-weight, minimal cost setup, closely followed by mlite brakes which give you a multi-pot caliper and larger discs for about 400g over the stock setup, although higher cost.

Weight is for a caliper (including carriers for 130i/335i/M3), brand new OEM discs (two-piece for mlite), and brand new OEM pads. Didn't include the protection plates because they're basically interchangeable. In ascending order:

  • 130i w/ E89 two-piece discs (RealOEM): 15.28kg
  • 130i (actual weight of mine): 16.10kg (vs RealOEM = 16.19kg)
  • Fxx 340mm Brembo (actual weight of mine): 16.52kg (vs RealOEM = 16.57kg)
  • M3 (RealOEM): 17.48kg
  • 135i/BMWP 338mm Brembo (RealOEM): 17.71kg
  • 335i (RealOEM): 18.19kg[/QUOTE}
 

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Easiest option: sell it and buy an E81. They're 90kg lighter than the E87 out of the box.

As nivens mentioned, lightweight wheels will make an enormous noticeable difference, far more than you'd think just from the numbers. You can also drop 2kg of unsprung from stock 130i front brakes using two-piece Z4 discs, part number 34116794427.

Other than the above, here's a few rough numbers I stole from elsewhere. Can't speak for their accuracy.
  • Lightweight 17" wheel/tire combo: -25kg (unsprung!!!)
  • Lithium race battery: -20kg (source)
  • Rear seat delete: -20kg (source) - additional -5kg from removing bolsters and side panels
  • Race seats: -20kg per seat (power seats) or -15kg per seat (manual seats) - both compared to Recaro PP at 9kg including rails/mounts
  • Sunroof delete (carbon panel): -15kg (source)
  • Lexan: -13kg (all glass) or -8kg (side/rear glass only) - based on 50% weight of factory glass
  • Carbon hood: -10kg (various different sources)
  • Lightweight stainless exhaust (catted but centre muffler delete): -10kg (citation needed)
  • Carbon roof skin: -6kg (citation needed)
Edited with new info re weights - some of what I'd copied was inaccurate.
Wow, didn’t know that you can save that much on race battery alone… might be looking at this battery when mine dies
 

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Pretty vague with the prices there but just my rough stab. It's a lot of money 😬🙂
Yep, losing 100kg could easily cost the same amount as the car itself if you wanted to avoid the easy wins like stripping the interior :(

Biginboca on E90post has an epic build thread for his E92 328i 'CSL' which has been through quite aggressive weight loss, most of the parts on that platform are a straight swap onto an E8x so it's worth a read. It's a big one but there's a 'contents' page at the beginning!

 

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Having sampled various cars, the E81/87 have to be fairly heavily insulated with sound proofing etc too I think.

If you remove the seats and dash and carpets, I bet there is about 20kg of sound proofing/padding all around the bulkhead and under the seats that you could remove... and bonus is you get some nice noise coming from the engine/gearbox etc that way too.
 
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