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      05-17-2016, 05:40 AM   #1
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GTS has a wider front track?

Reading through the GTS Technical Training doc, I noticed a table that specifies that the GTS has a wider front track by 17mm compared to the the base M4. Further, it is also specified that the GTS wheels have the same offset as the base M4 (ET29 front and ET40 rear), meaning that the wider track would not come from the wheels. Before anyone jumps in about the 0.5" wider wheels from the GTS, note that they do not contribute to a wider track since track is measured from the tire center line. The GTS does seem to have a "flusher" look than the base car IMO. A wider track by 17mm plus the 0.5" wider wheels would push the front wheel face out by ~15mm.

If all this info is correct, that would mean that the GTS' front suspension has been modified extensively enough to provide that wider track. Interesting.
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      05-17-2016, 06:40 AM   #2
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Hmm, but doesn't the chart also appear to claim that the standard M4 has Pilot Sport Cup 2 tires?
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      05-17-2016, 07:27 AM   #3
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Quote:
Originally Posted by mkoesel View Post
Hmm, but doesn't the chart also appear to claim that the standard M4 has Pilot Sport Cup 2 tires?
I know. So many typos and unclear info in BMW documentation, it is sometimes difficult to figure what is correct. That is why I did not formulate my post as an absolute certainty. But I believe it is something worthwhile exploring...
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      05-18-2016, 08:57 AM   #4
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Hmmmmm. The official press release that is available on BMW's press website states that the track width is indeed different.

Civic M4
Track, front/rear: (mm) 1579/1603
M4 GTS
Track, front/rear: (mm) 1596/1604

Had a brief look at ETK and I see no changes (... all I see is racist faces. *2Pac's voice* ) in any suspension components. Everything has the same part number.


*DUN-DUN-DUUUN*

This has nothing to do with the front track, but der ETK says that the rear GTS wheel has an ET42 offset...

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      05-18-2016, 09:02 AM   #5
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Quote:
Originally Posted by swagon View Post
Hmmmmm. The official press release that is available on BMW's press website states that the track width is indeed different.

Civic M4
Track, front/rear: (mm) 1579/1603
M4 GTS
Track, front/rear: (mm) 1596/1604

Had a brief look at ETK and I see no changes (... all I see is racist faces. *2Pac's voice* ) in any suspension components. Everything has the same part number.


*DUN-DUN-DUUUN*

This has nothing to do with the front track, but der ETK says that the rear GTS wheel has an ET42 offset...

Hmmmm,

A 2mm increase in rear wheel offset would reduce the rear track by 4mm. All the more confusing...

Albeit we are talking very small numbers here. Could the increased factory camber be the source of the increase the track?
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      05-18-2016, 03:49 PM   #6
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Quote:
Originally Posted by CanAutM3 View Post
Hmmmm,

A 2mm increase in rear wheel offset would reduce the rear track by 4mm. All the more confusing...

Albeit we are talking very small numbers here. Could the increased factory camber be the source of the increase the track?
Didn't I read somewhere that the front hub has been modified/is new on the GTS to allow for more camber?

On a 17" rim, a camber increase of 1 degree equals roughly a 10mm increase at the bottom of the rim, or a 10mm decrease at the top of the rim (if that makes sense). Ie, to increase camber by ca 1 degree you have to either tilt the top of the rim inward by 10mm (which is what a camber plate at the top srut mount does). Or extend the bottom of the rim outward by 10mm (which is what an adjustable lower control arm does). I have just played with camber settings on my old Ford Sierra RS Cosworth with 17" rims, which is why I have these measurements at hand

Here the camber change is less than 1 degree (?) and the increase in track by 17mm seems very plausible to be explained by the increase in negative camber. Especially since the top strut mount probably is similar and the increased camber comes from a changed hub which basically tilts the wheel more inwards at the top and extends it further outward at the bottom.

I feel my English is a bit lacking in trying to explain my thoughts here, but I hope it makes some sense...

PS. Is the rear camber also increased compared with the std M4? If it's a small change in camber, that could also explain the combination of a higher offset and similar track.
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      05-18-2016, 04:31 PM   #7
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Quote:
Originally Posted by Boss330 View Post
Didn't I read somewhere that the front hub has been modified/is new on the GTS to allow for more camber?

On a 17" rim, a camber increase of 1 degree equals roughly a 10mm increase at the bottom of the rim, or a 10mm decrease at the top of the rim (if that makes sense). Ie, to increase camber by ca 1 degree you have to either tilt the top of the rim inward by 10mm (which is what a camber plate at the top srut mount does). Or extend the bottom of the rim outward by 10mm (which is what an adjustable lower control arm does). I have just played with camber settings on my old Ford Sierra RS Cosworth with 17" rims, which is why I have these measurements at hand

Here the camber change is less than 1 degree (?) and the increase in track by 17mm seems very plausible to be explained by the increase in negative camber. Especially since the top strut mount probably is similar and the increased camber comes from a changed hub which basically tilts the wheel more inwards at the top and extends it further outward at the bottom.

I feel my English is a bit lacking in trying to explain my thoughts here, but I hope it makes some sense...

PS. Is the rear camber also increased compared with the std M4? If it's a small change in camber, that could also explain the combination of a higher offset and similar track.
IIRC, it is the opposite. Front camber is same as the base car while rear is increased.

The GTS front camber spec is the same as the base car at -1.45 deg. So the camber does not really explain the wider front track IMO.

In the rear, the camber is 0.2deg more at -2.0deg for the GTS instead of -1.8deg for the base car. So I believe the camber could explain the 1mm wider track despite the offsets that should make the track 4mm narrower.

PS: Your English is perfectly fine
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      05-27-2016, 04:32 AM   #8
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The lead technical engineer did confirm to me the car is wider than a atandard M4
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      05-27-2016, 01:21 PM   #9
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Doesn't look like a standard m4 spindle to me.
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      05-27-2016, 10:17 PM   #10
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The carrier is a different, GTS specif P/N.

M4 Assembly:
Name:  M4Upright.jpg
Views: 1958
Size:  170.7 KB


GTS Assembly:
Name:  M4GTS_Upright.jpg
Views: 1783
Size:  190.0 KB
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      06-17-2016, 12:12 PM   #11
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FTFY:

Quote:
Originally Posted by jml View Post
The carrier is a different, GTS specif P/N.

GTS Assembly:
Attachment 1430737


M4 Assembly:
Attachment 1430738
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      06-17-2016, 12:41 PM   #12
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It's about the billet spindle
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      06-18-2016, 01:11 PM   #13
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Dream Car = my M3 with M4 GTS suspension geometry.

I'm guessing a decreased front wheel offset won't be able produce the same handling benefits that the GTS-specific front carrier is able to produce...... Probably would screw up how the camber angle changes when corning as well as the scrub radius.

If some third party (like Vorshlag) replicated the GTS front carriers, I would buy them.

Last edited by Celestion; 06-18-2016 at 01:19 PM..
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