carmudgeons.com  

Go Back   carmudgeons.com > Automotive Forums > Car Talk > Perseverators Anonymous

Reply
 
Thread Tools Display Modes
Old 08-14-2017, 11:35 AM   #41
John V
No more BMWs
 
John V's Avatar
 
Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
Quote:
Originally Posted by FC View Post
Well, the news today of the M3 loosing its CF shaft really bothers me.
Why?
John V is offline   Reply With Quote
Old 08-14-2017, 01:49 PM   #42
FC
Solving problems
 
FC's Avatar
 
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,215
Quote:
Originally Posted by John V View Post
Why?
Because they made such a big deal out of it when it was released. Actual improvements aside, they should at the very least lower the price commensurately - especially when they just raised the price on the car.

The car will take a hit on responsiveness and acceleration. How much and if it will noticeable remains to be known, but it's physics.
FC is offline   Reply With Quote
Old 08-14-2017, 02:20 PM   #43
John V
No more BMWs
 
John V's Avatar
 
Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
You will never notice the change.
John V is offline   Reply With Quote
Old 08-14-2017, 07:47 PM   #44
equ
Alphanumeric
 
equ's Avatar
 
Join Date: Aug 2005
Carmudgeonly Ride: 981S, 340i
Posts: 9,580
Rotational inertia should be very small for a driveshaft. Especially the difference between a steel/alloy one vs. carbon, given that there is engine inertia, gears, flywheel, diff, axles, wheels and tires attached. Most of those with a higher radius than the shaft. IIRC, it goes like MR^2, so I'm not even sure why they bothered in the first place.
equ is offline   Reply With Quote
Old 08-15-2017, 07:41 AM   #45
FC
Solving problems
 
FC's Avatar
 
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,215
Quote:
Originally Posted by equ View Post
Rotational inertia should be very small for a driveshaft. Especially the difference between a steel/alloy one vs. carbon, given that there is engine inertia, gears, flywheel, diff, axles, wheels and tires attached. Most of those with a higher radius than the shaft. IIRC, it goes like MR^2, so I'm not even sure why they bothered in the first place.
Every bit helps. Also, the wheels and tires are past the rear differential so their moment of inertia reflected to the engine would lower by that gear ratio. Still far more than the shaft, of course.

Like I said, I am not arguing that it will make much of a difference, just how they are handling it on the customer side. There are actually some benefits in going to steel. But the replacement cost of the CF shaft is something like $2500 vs. a few hundred for the one in steel. To do a swap without adjusting the cost is kinda crappy, again, considering what a big stinking deal they made of it at launch.
FC is offline   Reply With Quote
Old 08-15-2017, 07:53 AM   #46
John V
No more BMWs
 
John V's Avatar
 
Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
Quote:
Originally Posted by equ View Post
Rotational inertia should be very small for a driveshaft. Especially the difference between a steel/alloy one vs. carbon, given that there is engine inertia, gears, flywheel, diff, axles, wheels and tires attached. Most of those with a higher radius than the shaft. IIRC, it goes like MR^2, so I'm not even sure why they bothered in the first place.
Because fanbois.
John V is offline   Reply With Quote
Old 08-15-2017, 08:13 AM   #47
equ
Alphanumeric
 
equ's Avatar
 
Join Date: Aug 2005
Carmudgeonly Ride: 981S, 340i
Posts: 9,580
Mkting for Fanbois for sure (what isn't and of course I'm one too). With morning freshness another physical property comes to mind. Perhaps the steel loads up/stores some undesirable twist while carbon's stress-strain tensor can be 3d designed to avoid whatever you want. Carbon bike frames have some cool properties (though they cannot be repaired).

Sent from my SM-G900V using Tapatalk
equ is offline   Reply With Quote
Old 08-15-2017, 10:59 AM   #48
Plaz
•••••••
 
Join Date: Oct 2003
Carmudgeonly Ride: '11 1M
Location: Churzee
Posts: 17,741
Quote:
Originally Posted by equ View Post
With morning freshness another physical property comes to mind.
Morning wood?
__________________
2011 1M
Plaz is offline   Reply With Quote
Old 08-15-2017, 01:30 PM   #49
John V
No more BMWs
 
John V's Avatar
 
Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
Quote:
Originally Posted by equ View Post
Mkting for Fanbois for sure (what isn't and of course I'm one too). With morning freshness another physical property comes to mind. Perhaps the steel loads up/stores some undesirable twist while carbon's stress-strain tensor can be 3d designed to avoid whatever you want. Carbon bike frames have some cool properties (though they cannot be repaired).

Sent from my SM-G900V using Tapatalk
Given the other areas for slop in the system, I highly doubt this is the motivation.

My guess is the carbon driveshaft was implemented not for rotational inertia but to reduce total vehicle weight. Given the cost and the small amount of weight saved it's no wonder they're getting rid of it.
John V is offline   Reply With Quote
Old 08-15-2017, 02:27 PM   #50
lemming
Western Anomaly
 
lemming's Avatar
 
Join Date: Oct 2003
Carmudgeonly Ride: White Orca
Posts: 16,582
it's hard to describe how wickedly fast (and reasonably soul-less) the current gen M3/M4 is.

the RS3 would just be a nose heavy overboosted pig, in comparison.

*just my opinion.

obviously the RS3 is a huge upgrade over the S3. but the S3 felt chintzy to me.
__________________


lemming is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

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 01:26 PM.


Powered by vBulletin® Version 3.7.1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Forums © 2003-2008, 'Mudgeon Enterprises - Site hosting by AYN & Associates, LLC