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

Go Back   BMW M3 and BMW M4 Forum > BMW F80 M3 / F82 M4 Forum > BMW M4 GTS Discussions

Post Reply
 
Thread Tools Search this Thread
      03-15-2021, 05:00 PM   #1
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

Spring rates with gt4 aero kit

I recently added gt4 bumper, splitter, brake ducts, and spoiler. First track event was this last weekend at road Atlanta with the new aero. I’m now having a ton of rubbing. I actually bottomed out enough to brake the backing on the drivers side headlight at turn 10. I have the compression bumped up 4 clicks above recommended track setting. I’m running pirelli dh scrubs 305 front 315 rear on the apex 10” and 11”. Camber is around 3.5 front. I didn’t have any issues with rubbing before the aero was added. Anyone go up to higher spring rates?
Attached Images
 
Appreciate 3
irunalot1515.50
Gomeler500.00
FormulaMMM3662.50
      03-15-2021, 05:21 PM   #2
4play
First Lieutenant
415
Rep
366
Posts

Drives: 2016 M4 GTS
Join Date: Sep 2012
Location: Atlanta

iTrader: (0)

Nice, what kind of laptimes were you running?

You probably have an extra 200 lbs of front downforce vs. the stock GTS coming into 10a at 160+. Definitely need higher front spring rates, though I can't say exactly what. But would probably go for a 50% increase minimum.
Appreciate 0
      03-15-2021, 05:25 PM   #3
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

I wasn’t pushing too hard because of the rubbing which was unsettling. I was down around 1:38.
Appreciate 0
      03-15-2021, 06:25 PM   #4
Lienrocs
Captain
Lienrocs's Avatar
701
Rep
867
Posts

Drives: E92 M3, M4 GTS, HP4
Join Date: May 2017
Location: Austin

iTrader: (3)

Are you on the standard KW's? Also, do you have any pictures of the front splitter install process? I'm considering going full GT4 aero on my GTS as well.

Edit, not trying to derail the thread. Just curious about the whole set up.
Appreciate 2
      03-16-2021, 09:38 AM   #5
SYT_Shadow
///M Powered for Life
SYT_Shadow's Avatar
11421
Rep
10,296
Posts

Drives: E90M/E92M/M4GTS/M4GT4/X5M
Join Date: Sep 2010
Location: Greenwich, CT

iTrader: (2)

That looks so hot! Damn!

For sure you need stiffer spring rates all around. Likely 850 front and 1200 rear for GTS aero and higher for the GT4 aero!

Last edited by SYT_Shadow; 03-16-2021 at 11:30 AM..
Appreciate 0
      03-16-2021, 10:57 AM   #6
Lienrocs
Captain
Lienrocs's Avatar
701
Rep
867
Posts

Drives: E92 M3, M4 GTS, HP4
Join Date: May 2017
Location: Austin

iTrader: (3)

Quote:
Originally Posted by SYT_Shadow View Post
That looks so hot! Damn!

For sure you need stiffer spring rates all around. Likely 850 front and 1200 rear
I think the issue you're going to run in to is the softest rear rate you can select for a GT4 is 150 NM (856 in/lb). Seeing as you're effectively running a GT4 Racecar you'll need around a 1400-1600 pound rear spring (standard divorced set up) to get a similar motion ratio. The problem with a spring that stiff is they don't make them that long so you will have almost zero droop travel. On top of that, I'm not sure the stock dampers can handle that big of a spring rate change with the stock valving. Your best bet is to probably go to a true coilover in the back so you can get the correct spring rate/length/amount of travel and go to a damper that is more capable of handling the spring rate increase.

Edit: but my god does your car look good.
Appreciate 2
SYT_Shadow11421.00
redrumm3417.00
      03-16-2021, 11:02 PM   #7
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

Quote:
Originally Posted by Lienrocs View Post
I think the issue you're going to run in to is the softest rear rate you can select for a GT4 is 150 NM (856 in/lb). Seeing as you're effectively running a GT4 Racecar you'll need around a 1400-1600 pound rear spring (standard divorced set up) to get a similar motion ratio. The problem with a spring that stiff is they don't make them that long so you will have almost zero droop travel. On top of that, I'm not sure the stock dampers can handle that big of a spring rate change with the stock valving. Your best bet is to probably go to a true coilover in the back so you can get the correct spring rate/length/amount of travel and go to a damper that is more capable of handling the spring rate increase.

Edit: but my god does your car look good.
Thanks!

I was talking with bimmerworld tech that recommended going to mcs 3 way. This is what they recommended below.
Attached Images
  

Last edited by Docall; 03-16-2021 at 11:05 PM.. Reason: Add pics
Appreciate 4
irunalot1515.50
Lienrocs701.00
      03-16-2021, 11:37 PM   #8
FaRKle!
Brigadier General
3995
Rep
3,531
Posts

Drives: 328d Wagon, M2 Comp, i4 eD35
Join Date: Sep 2016
Location: Bay Area, CA

iTrader: (4)

Garage List
Did Bimmerworld go over the amount of downforce with you and how much that affects the ride frequencies/damping needs with those spring rates? If I was about to spend ~$9k on parts I'd want to spend some time with someone who'll REALLY do the homework and calculations/modelling to see that it's actually what I want.
__________________
-328d Wagon Build Log (with helpful reference links)
-My YouTube Channel for some of the best DIYs and in depth information

Please don't PM me for suspension recommendations unless interested in paid private consultations.
Appreciate 0
      03-17-2021, 07:15 AM   #9
coryf
Private
48
Rep
58
Posts

Drives: 2016 M4 GTS
Join Date: Aug 2015
Location: charleston sc

iTrader: (0)

Wow that looks good! Maybe try some packers to reduce the compression travel. If its only touching under braking into 10a, it might be worth a try to keep it simple.

Also, where did you source the GT4 parts? Original motorsport or replica like from the place in England?
Appreciate 0
      03-17-2021, 08:30 AM   #10
SYT_Shadow
///M Powered for Life
SYT_Shadow's Avatar
11421
Rep
10,296
Posts

Drives: E90M/E92M/M4GTS/M4GT4/X5M
Join Date: Sep 2010
Location: Greenwich, CT

iTrader: (2)

Quote:
Originally Posted by FaRKle! View Post
Did Bimmerworld go over the amount of downforce with you and how much that affects the ride frequencies/damping needs with those spring rates? If I was about to spend ~$9k on parts I'd want to spend some time with someone who'll REALLY do the homework and calculations/modelling to see that it's actually what I want.
Remember Bimmerworld has 3 M4 GT4s... they may know a thing or two about setting them up and what is the right setup
Appreciate 3
irunalot1515.50
sly1types426.50
      03-17-2021, 09:16 AM   #11
Lienrocs
Captain
Lienrocs's Avatar
701
Rep
867
Posts

Drives: E92 M3, M4 GTS, HP4
Join Date: May 2017
Location: Austin

iTrader: (3)

Quote:
Originally Posted by Docall View Post
Quote:
Originally Posted by Lienrocs View Post
I think the issue you're going to run in to is the softest rear rate you can select for a GT4 is 150 NM (856 in/lb). Seeing as you're effectively running a GT4 Racecar you'll need around a 1400-1600 pound rear spring (standard divorced set up) to get a similar motion ratio. The problem with a spring that stiff is they don't make them that long so you will have almost zero droop travel. On top of that, I'm not sure the stock dampers can handle that big of a spring rate change with the stock valving. Your best bet is to probably go to a true coilover in the back so you can get the correct spring rate/length/amount of travel and go to a damper that is more capable of handling the spring rate increase.

Edit: but my god does your car look good.
Thanks!

I was talking with bimmerworld tech that recommended going to mcs 3 way. This is what they recommended below.
I'm running those same spring rates (900/800) on my car (Ohlins TTX). That's probably going to to work with the rear wing at the minimum AOA. But it's all conjecture at this point from me.

Is your car still street driven? If it isn't I'd go straight for the minimum GT4 spring rates and take the guess work out of that part of the equation. Even with super stiff springs, though, the MCS dampers are super good at street driving. I have a set on my E92 (800 pound front, 1100 pound rear) and it's easily daily drivable. GT4 spring rates won't be that comfortably but, dare I say it, the car won't be absolutely miserable for the odd street outing either.
Appreciate 0
      03-17-2021, 10:58 AM   #12
FaRKle!
Brigadier General
3995
Rep
3,531
Posts

Drives: 328d Wagon, M2 Comp, i4 eD35
Join Date: Sep 2016
Location: Bay Area, CA

iTrader: (4)

Garage List
Quote:
Originally Posted by SYT_Shadow View Post
Remember Bimmerworld has 3 M4 GT4s... they may know a thing or two about setting them up and what is the right setup
That's called "argument to authority." Does Bimmerworld run their GT4s on the street like Docall? Do they have the exact same driving profile? Nope.

When it's your dollars on the line you should "trust but verify."
__________________
-328d Wagon Build Log (with helpful reference links)
-My YouTube Channel for some of the best DIYs and in depth information

Please don't PM me for suspension recommendations unless interested in paid private consultations.
Appreciate 1
      03-17-2021, 11:08 AM   #13
SYT_Shadow
///M Powered for Life
SYT_Shadow's Avatar
11421
Rep
10,296
Posts

Drives: E90M/E92M/M4GTS/M4GT4/X5M
Join Date: Sep 2010
Location: Greenwich, CT

iTrader: (2)

Quote:
Originally Posted by FaRKle! View Post
That's called "argument to authority." Does Bimmerworld run their GT4s on the street like Docall? Do they have the exact same driving profile? Nope.

When it's your dollars on the line you should "trust but verify."
For sure they don't have the exact same driving profile, just as sure as it is likelier than not that their feedback is excellent.

I also took logic class in high school. It doesn't change than unless one has infinite time and resources, going to one of the teams that run and setup these cars is a smart choice and likely drops you off in the sweet spot of performance.

From wiki:
An argument from authority (argumentum ab auctoritate), also called an appeal to authority, or argumentum ad verecundiam, is a form of argument in which the opinion of an authority on a topic is used as evidence to support an argument.[1] Some consider that it is used in a cogent form if all sides of a discussion agree on the reliability of the authority in the given context,[2][3] and others consider it to always be a fallacy to cite an authority on the discussed topic as the primary means of supporting an argument.[4]

Do we all agree that a company that runs 3 M4 GT4 cars has a good idea of how to set these up for track driving?
Do we all agree that premium suspensions can take high spring rates but still be reasonably compliant on the street?

If you think OP should work with Turner instead I won't challenge that, but to act like people who run that aero package professionally don't have an advantage in knowledge is ridiculous

Last edited by SYT_Shadow; 04-27-2021 at 11:09 AM..
Appreciate 3
FormulaMMM3662.50
irunalot1515.50
      03-17-2021, 11:10 AM   #14
SYT_Shadow
///M Powered for Life
SYT_Shadow's Avatar
11421
Rep
10,296
Posts

Drives: E90M/E92M/M4GTS/M4GT4/X5M
Join Date: Sep 2010
Location: Greenwich, CT

iTrader: (2)

Quote:
Originally Posted by Lienrocs View Post
I'm running those same spring rates (900/800) on my car (Ohlins TTX). That's probably going to to work with the rear wing at the minimum AOA. But it's all conjecture at this point from me.

Is your car still street driven? If it isn't I'd go straight for the minimum GT4 spring rates and take the guess work out of that part of the equation. Even with super stiff springs, though, the MCS dampers are super good at street driving. I have a set on my E92 (800 pound front, 1100 pound rear) and it's easily daily drivable. GT4 spring rates won't be that comfortably but, dare I say it, the car won't be absolutely miserable for the odd street outing either.
To Lienrocs comment, I have a CS with 3W MCS and 800/700 rates, it rides quite well. I was recently driving a M440 and thought that was uncomfortable
Appreciate 1
sly1types426.50
      03-17-2021, 11:34 AM   #15
FormulaMMM
Brigadier General
FormulaMMM's Avatar
United_States
3663
Rep
3,422
Posts

Drives: E90 M3
Join Date: Oct 2011
Location: Midwest

iTrader: (2)

Quote:
Originally Posted by SYT_Shadow View Post
Do we all agree that a company that runs 3 M4 GT4 cars has a good idea of how to set these up for track driving?
Do we all agree that premium suspensions can take high spring rates but still be reasonably compliant on the street?

If you think OP should work with Turner instead I won't challenge that, but to act like people who run that aero package professionally don't have an advantage in knowledge is ridiculous
As I was watching this unfold live my first thought was, these dudes have no idea what the hell they're doing.



Actually, what I was thinking is why don't I just ship my GTS to one or the other with the goal of finding 3 seconds/lap.

Interested in where these GT4 parts are being sourced...
__________________
M4 GTS, GT3, C63 S | E90 M3s, E39 M5

Appreciate 3
SYT_Shadow11421.00
irunalot1515.50
      03-17-2021, 12:05 PM   #16
SYT_Shadow
///M Powered for Life
SYT_Shadow's Avatar
11421
Rep
10,296
Posts

Drives: E90M/E92M/M4GTS/M4GT4/X5M
Join Date: Sep 2010
Location: Greenwich, CT

iTrader: (2)

Quote:
Originally Posted by FormulaMMM View Post
As I was watching this unfold live my first thought was, these dudes have no idea what the hell they're doing.

Actually, what I was thinking is why don't I just ship my GTS to one or the other with the goal of finding 3 seconds/lap.

Interested in where these GT4 parts are being sourced...
That was such an awesome race finish!
Appreciate 1
FormulaMMM3662.50
      03-17-2021, 12:26 PM   #17
FaRKle!
Brigadier General
3995
Rep
3,531
Posts

Drives: 328d Wagon, M2 Comp, i4 eD35
Join Date: Sep 2016
Location: Bay Area, CA

iTrader: (4)

Garage List
Quote:
Originally Posted by SYT_Shadow View Post
If you think OP should work with Turner instead I won't challenge that, but to act like people who run that aero package professionally don't have an advantage in knowledge is ridiculous
You're putting words into my mouth. I never said they didn't have an advantage in knowledge, I said he should see the "homework" himself and understand how they came to the conclusion/recommendation. Bimmerworld is more than capable of doing that and IMO when you're spending $9k with them, it's not unreasonable to ask.

Can we agree that making sure the design intent/priorities of their recommendation follows OP's needs is the right thing to do?
Can we agree that seeing the data/calc to justify their recommendation is a good thing?
__________________
-328d Wagon Build Log (with helpful reference links)
-My YouTube Channel for some of the best DIYs and in depth information

Please don't PM me for suspension recommendations unless interested in paid private consultations.
Appreciate 0
      03-17-2021, 05:47 PM   #18
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

Quote:
Originally Posted by Lienrocs View Post
I'm running those same spring rates (900/800) on my car (Ohlins TTX). That's probably going to to work with the rear wing at the minimum AOA. But it's all conjecture at this point from me.

Is your car still street driven? If it isn't I'd go straight for the minimum GT4 spring rates and take the guess work out of that part of the equation. Even with super stiff springs, though, the MCS dampers are super good at street driving. I have a set on my E92 (800 pound front, 1100 pound rear) and it's easily daily drivable. GT4 spring rates won't be that comfortably but, dare I say it, the car won't be absolutely miserable for the odd street outing either.
I really do not plan on street driving it anymore with that splitter. So going stiffer won’t be an issue.
Appreciate 1
      03-17-2021, 05:50 PM   #19
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

I will also be following up with bimmerworld to ask why they chose those rates. I do appreciate all the input.
Appreciate 1
Lienrocs701.00
      03-17-2021, 06:42 PM   #20
Lienrocs
Captain
Lienrocs's Avatar
701
Rep
867
Posts

Drives: E92 M3, M4 GTS, HP4
Join Date: May 2017
Location: Austin

iTrader: (3)

Quote:
Originally Posted by Docall View Post
Quote:
Originally Posted by Lienrocs View Post
I'm running those same spring rates (900/800) on my car (Ohlins TTX). That's probably going to to work with the rear wing at the minimum AOA. But it's all conjecture at this point from me.

Is your car still street driven? If it isn't I'd go straight for the minimum GT4 spring rates and take the guess work out of that part of the equation. Even with super stiff springs, though, the MCS dampers are super good at street driving. I have a set on my E92 (800 pound front, 1100 pound rear) and it's easily daily drivable. GT4 spring rates won't be that comfortably but, dare I say it, the car won't be absolutely miserable for the odd street outing either.
I really do not plan on street driving it anymore with that splitter. So going stiffer won’t be an issue.
Sent you a pm.
Appreciate 0
      03-18-2021, 08:36 PM   #21
Docall
Private
87
Rep
58
Posts

Drives: 2015 m4, 2009 Audi s5
Join Date: May 2019
Location: USA

iTrader: (0)

Quote:
Originally Posted by coryf View Post
Wow that looks good! Maybe try some packers to reduce the compression travel. If its only touching under braking into 10a, it might be worth a try to keep it simple.

Also, where did you source the GT4 parts? Original motorsport or replica like from the place in England?
I sourced the splitter and spoiler from apmotorsports in England. Bumper, inlets, and brake ducts from bimmerworld.
Appreciate 1
Lienrocs701.00
      04-26-2021, 11:37 AM   #22
sly1types
Captain
427
Rep
934
Posts

Drives: F80M3 and E46M3
Join Date: Apr 2007
Location: KC

iTrader: (0)

Quote:
Originally Posted by Docall View Post
Thanks!

I was talking with bimmerworld tech that recommended going to mcs 3 way. This is what they recommended below.
I would also add rear canister disconnects, otherwise i'm not sure how you will get them in the trunk. I have 2Way Remotes with 700/600 and its pretty flat in the corners, but im not on slicks or aero.
__________________
F80 M3-DCT MaxPSI CH, BM3 with F80 Paul E85 and Custom Rom track tune MCS 2Way Remotes
Signature SV104
E46 M3
F85 X5M
https://www.instagram.com/fastmacm3/
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



All times are GMT -5. The time now is 05:17 PM.




f80post
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
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