BMW M3 Forum (E90 E92)

BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   M3Post - BMW M3 Forum > E90/E92 M3 Technical Topics > Suspension | Brakes | Chassis
 
INDustry distribution
Post Reply
 
Thread Tools Search this Thread
      12-05-2013, 05:50 PM   #243
Craigy
Sporty Puristic 6
Craigy's Avatar
22
Rep
379
Posts

Drives: '09 M3
Join Date: Jun 2013
Location: Louisiana

iTrader: (0)

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...
Appreciate 0
      12-05-2013, 07:51 PM   #244
klammer
Brigadier General
48
Rep
3,246
Posts

Drives: 11 spc gry m3 e90, 07 X5
Join Date: Jan 2010
Location: chicago

iTrader: (0)

Quote:
Originally Posted by Craigy View Post
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...
__________________
mods: akra evo, dinan 3.45 diff, ess akra tune, dinan stg.3, Alcon bbk, HRE P40
Appreciate 0
      12-12-2013, 05:59 PM   #245
oldmanstyle
Private First Class
21
Rep
168
Posts

Drives: M3
Join Date: Feb 2010
Location: USA

iTrader: (0)

Quote:
Originally Posted by Craigy View Post
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.
Appreciate 0
      12-13-2013, 05:57 PM   #246
Ant Man
Major
United Kingdom
26
Rep
1,096
Posts

Drives: E92 M3 Santorini Competition
Join Date: Jun 2008
Location: East Anglia

iTrader: (1)

Quote:
Originally Posted by oldmanstyle View Post
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.
Appreciate 0
      01-01-2014, 08:42 PM   #247
klammer
Brigadier General
48
Rep
3,246
Posts

Drives: 11 spc gry m3 e90, 07 X5
Join Date: Jan 2010
Location: chicago

iTrader: (0)

Quote:
Originally Posted by oldmanstyle View Post
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
__________________
mods: akra evo, dinan 3.45 diff, ess akra tune, dinan stg.3, Alcon bbk, HRE P40
Appreciate 0
      06-08-2014, 09:47 PM   #248
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

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
__________________

Last edited by Richbot; 06-16-2014 at 05:52 PM.
Appreciate 0
      08-31-2014, 07:07 AM   #249
TheSnail
Private First Class
TheSnail's Avatar
6
Rep
102
Posts

Drives: 2012 Alpine White M3
Join Date: Aug 2014
Location: Marietta

iTrader: (1)

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)
__________________
MS Intake, MS Pulley, Akrapovic GT4, Akrapovic Slipon, BPM Tune, KW-V3.
Appreciate 0
      10-08-2014, 04:55 PM   #250
Groundpilot
Banned
Groundpilot's Avatar
United_States
473
Rep
1,714
Posts

Drives: 135I DCT , e92 M3 DCT, Audi A6
Join Date: Mar 2010
Location: long island,ny

iTrader: (0)

Send a message via ICQ to 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?
Appreciate 0
      10-08-2014, 09:24 PM   #251
bigjae1976
Major General
bigjae1976's Avatar
205
Rep
6,339
Posts

Drives: 11 E90 M3 Individual
Join Date: Mar 2006
Location: Wichita, KS

iTrader: (14)

Garage List
2004 BMW M3  [4.50]
2011 BMW E90 M3  [5.00]
2013 BMW 328i  [5.00]
Quote:
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.
__________________
2015 F34 328iX GT Glacier Silver
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red
Appreciate 0
      06-10-2016, 08:25 PM   #252
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

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
__________________
Appreciate 1
      06-10-2016, 08:31 PM   #253
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

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.
__________________

Last edited by Richbot; 06-10-2016 at 08:44 PM.
Appreciate 2
      06-10-2016, 10:27 PM   #254
Hujan
Brigadier General
Hujan's Avatar
United_States
182
Rep
3,332
Posts

Drives: 2013 E92 M3
Join Date: Apr 2013
Location: San Diego, CA

iTrader: (14)

Quote:
Originally Posted by Richbot View Post
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.
__________________
E92 M3: MRF Velaforza | Brembo GT | KW Clubsport | BBS E88 | Recaro Sportsters
Appreciate 0
      06-11-2016, 02:28 AM   #255
roastbeef
Brigadier General
roastbeef's Avatar
United_States
574
Rep
3,447
Posts

Drives: E92 M3
Join Date: Nov 2010
Location: Orange County, CA

iTrader: (1)

Quote:
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?
__________________
Appreciate 0
      06-11-2016, 04:52 PM   #256
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

Quote:
Originally Posted by roastbeef View Post
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.
__________________

Last edited by Richbot; 06-11-2016 at 04:58 PM.
Appreciate 1
      06-12-2016, 09:04 PM   #257
roastbeef
Brigadier General
roastbeef's Avatar
United_States
574
Rep
3,447
Posts

Drives: E92 M3
Join Date: Nov 2010
Location: Orange County, CA

iTrader: (1)

Quote:
Originally Posted by Richbot View Post
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.
__________________
Appreciate 0
      06-13-2016, 08:41 AM   #258
jakob66
Private First Class
jakob66's Avatar
United_States
42
Rep
152
Posts

Drives: M3 white, long list
Join Date: Apr 2014
Location: TN

iTrader: (2)

Quote:
Originally Posted by Richbot View Post
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
__________________
ST-60 w. XR1 / BPM tune / KW shocks / Solid subframe / Recaro Racer XL / 6p bolt-in cage / RD sway F&R / 295/315/30 / M24 Oil Cooler / CSF radiator / GT4 splitter / GT-250 / JP aero stage2
Appreciate 0
      06-13-2016, 01:14 PM   #259
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

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
__________________

Last edited by Richbot; 06-13-2016 at 01:52 PM.
Appreciate 1
      06-22-2016, 08:21 AM   #260
Ant Man
Major
United Kingdom
26
Rep
1,096
Posts

Drives: E92 M3 Santorini Competition
Join Date: Jun 2008
Location: East Anglia

iTrader: (1)

Quote:
Originally Posted by Richbot View Post
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
Appreciate 0
      06-23-2016, 02:48 PM   #261
Richbot
Colonel
191
Rep
2,732
Posts

Drives: Jerez Black E90
Join Date: Sep 2007
Location: STL

iTrader: (2)

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.
__________________
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 09:45 PM.




m3post
m3post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST