A8 Parts Forum  

Go Back   A8 Parts Forum > A8 D2 > D2 - Axles, Brakes, Suspension and Steering

D2 - Axles, Brakes, Suspension and Steering Brakes, Springs, shocks, steering racks, steering columns, suspension arms, wheel hubs etc.

Reply
 
Thread Tools Display Modes
  #21  
Old 17th July 2020, 12:35 AM
Audifan Audifan is offline
Senior Member
 
Join Date: Feb 2020
Location: America
Posts: 388
Default

Thanks again MikkiJayne but now I'm confused. How is the flat bar mounted as there is no way it will mount flat to the upright as see in this picture Or is the opposite side of the upright flat that's not visible in this picture?

Reply With Quote
  #22  
Old 17th July 2020, 01:26 AM
ainarssems ainarssems is offline
Senior Member
 
Join Date: Aug 2010
Location: Rushden, Northants
Posts: 3,799
Default

Quote:
Originally Posted by Audifan View Post
Thanks again MikkiJayne but now I'm confused. How is the flat bar mounted as there is no way it will mount flat to the upright as see in this picture Or is the opposite side of the upright flat that's not visible in this picture?

Your picture is from different car. Flat bar was on S8 with Brembo brakes. Different brakes and uprights on S8 compared to A8
__________________
Currently 8less
2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D

8 history:
2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
Reply With Quote
  #23  
Old 17th July 2020, 08:54 AM
MikkiJayne MikkiJayne is offline
Senior Member
 
Join Date: Jan 2012
Posts: 5,017
Default

Correct ^

The RS4 setup is on an S8 Brembo upright whereas I am showing the Porsche 18z with the A8 HP2 upright.
Reply With Quote
  #24  
Old 18th July 2020, 12:30 AM
Audifan Audifan is offline
Senior Member
 
Join Date: Feb 2020
Location: America
Posts: 388
Default

Thanks for the clarification as that makes more sense.
Reply With Quote
  #25  
Old 20th July 2020, 02:24 AM
27litres's Avatar
27litres 27litres is offline
Senior Member
 
Join Date: Jan 2014
Location: Belgrave, Australia
Posts: 803
Default

Quote:
Originally Posted by MikkiJayne View Post
the RS6 had 19s.
In the land of Audifan, the C5 RS6 had 18's stock. So assuming they didn't change the brakes, they will fit under 18" wheels.


Quote:
Originally Posted by Stromaluski View Post
If you purely want your car to stop better, you'd actually be WAY better off buying better tires. Your car's limit in how quickly it can stop is purely a function of how much your tires can grip the road.

Using a more simplified example, here's something you can think about. If you can lock up the brakes on your car (assuming the car doesn't have ABS), then having even more clamping force will provide zero benefit at all. You can't make the wheels stop any more if they're already stopped. The same idea would apply even to a car with ABS. The limit of how fast you can slow down is an issue of how much grip your tires can withstand before they lock up on the road surface. Bigger brakes, more clamping force, etc won't change that at all.

Basically a long post to simply say if you want to increase your braking capability... buy better tires.
I like your thinking, but one of the biggest factors for increasing disc size is heat dissipation.
You're right in tyres being a critical factor in how efficient your braking is, and the leverage action of larger discs and calipers, but the larger size disc also provides a critical benefit in heat dissipation.
You alluded to it a bit anyway, so I'm sure you're aware of most of this, but brakes are all about energy management.

When the car is at speed, it has a large amount of momentum which is Potential Energy.
In order to slow the car, you need to convert that energy into another form (conservation of energy).
Cars use brakes to convert all this Potential Energy into Kinetic Energy, in the form of heat.
That heat energy then needs to be added to the surrounding environment through equilibrium as efficiently as possible.

A measure of how effective the brakes are, is how effectively they can shed the heat, which is a measure of exposed surface area.
So:
Ventilated discs are better than solid discs.
Bigger discs are better than smaller discs.
Larger pads are better than smaller pads (within disc coverage limits), and larger/multi piston calipers allow for larger pads and better control.

Then there's the engineering compromises of unsprung mass, physical wheel size, metalurgy, cost etc

But as you said, none of this is any good if your tyres lose grip!
__________________
Cheers

Marty


____________________
Current:
2001 Audi S8 - Brilliant Black with Black interior, C5 RS6 rims (whenever I actually put them on...), Solar Sunroof, Tinted side and rear glass, RNS-D, Grom, Bose, clunky old phone in arm rest!
2002 Audi S8 - Project
Replacement head coming arrived thanks to MJ
Silver with Black interior. All features as the '01, with the 'S' mode auto shifter. Dodgey rear tint (need to find a way to get rid of that).
Family:
2009 Volvo XC90 V8 R Design
- has a louder more obnoxious exhaust than the S8, sounds great! Love this thing - Q7 was double the price, and certainly not double the car!

Sold:
1997 Audi A4
- Hamilton's Club Sport, Achat Grey (will miss the old girl)

Last edited by 27litres; 20th July 2020 at 02:27 AM.
Reply With Quote
  #26  
Old 20th July 2020, 10:13 AM
MikkiJayne MikkiJayne is offline
Senior Member
 
Join Date: Jan 2012
Posts: 5,017
Default

Larger pads you say...



Porsche / Q7 18z pad vs S8 Brembo! These things are huge Tbh I should have figured that out from the size of the caliper but it didn't really register until I had them in my hand.

Btw, cheapest brake pads on the market for a Porsche Cayenne / Audi Q7? £26

For reference, this is the 18z caliper on an S8 Brembo upright - no way this will work:





This is the 18z caliper on the S8 345mm disc - also not going to work



However, the pads fit the D3 360mm disc perfectly. The only challenge then is a 4mm offset in the mounting holes:



I think this might be possible to solve by boring out both the caliper and the upright an additional 1mm and creating an offset bushing to take an M12 12.9 bolt, something like this:



I'd have a plain one in the caliper, and the threaded one in the upright, both knurled slightly to grip the aluminium and not rotate, then they'd hold everything in place nicely. I did this many years ago to get Nissan Skyline 4-pots caliper on my Corrado However with this setup, its a compromise between using M12 12.9 hardware vs OE M14 10.9 hardware or removing sufficient material from the caliper to get M14 hardware in without losing strength.
Attached Thumbnails
Click image for larger version

Name:	IMG_20200718_125729.jpg
Views:	561
Size:	83.8 KB
ID:	23640   Click image for larger version

Name:	IMG_20200718_130608.jpg
Views:	573
Size:	77.2 KB
ID:	23641   Click image for larger version

Name:	IMG_20200718_130622.jpg
Views:	561
Size:	71.9 KB
ID:	23642   Click image for larger version

Name:	IMG_20200718_132921.jpg
Views:	533
Size:	46.1 KB
ID:	23643   Click image for larger version

Name:	IMG_20200718_132109.jpg
Views:	603
Size:	78.3 KB
ID:	23644   Click image for larger version

Name:	offset bushing.JPG
Views:	550
Size:	15.1 KB
ID:	23645  
Reply With Quote
  #27  
Old 20th July 2020, 02:34 PM
Stromaluski's Avatar
Stromaluski Stromaluski is offline
Member
 
Join Date: Apr 2019
Location: Greenville, SC, USA
Posts: 82
Default

Quote:
Originally Posted by 27litres View Post
I like your thinking, but one of the biggest factors for increasing disc size is heat dissipation.
You're right in tyres being a critical factor in how efficient your braking is, and the leverage action of larger discs and calipers, but the larger size disc also provides a critical benefit in heat dissipation.
You alluded to it a bit anyway, so I'm sure you're aware of most of this, but brakes are all about energy management.

When the car is at speed, it has a large amount of momentum which is Potential Energy.
In order to slow the car, you need to convert that energy into another form (conservation of energy).
Cars use brakes to convert all this Potential Energy into Kinetic Energy, in the form of heat.
That heat energy then needs to be added to the surrounding environment through equilibrium as efficiently as possible.

A measure of how effective the brakes are, is how effectively they can shed the heat, which is a measure of exposed surface area.
So:
Ventilated discs are better than solid discs.
Bigger discs are better than smaller discs.
Larger pads are better than smaller pads (within disc coverage limits), and larger/multi piston calipers allow for larger pads and better control.

Then there's the engineering compromises of unsprung mass, physical wheel size, metalurgy, cost etc

But as you said, none of this is any good if your tyres lose grip!
Agree with all of this.
__________________
-Andrew
1967 Bus
1980 Rabbit Pickup
1992 Corrado
2001 S8
2010 Jetta TDI Cup Edition
Reply With Quote
  #28  
Old 20th July 2020, 06:13 PM
Audifan Audifan is offline
Senior Member
 
Join Date: Feb 2020
Location: America
Posts: 388
Default

Lots of great information. Thanks for sharing.
Reply With Quote
  #29  
Old 21st July 2020, 10:50 PM
Audifan Audifan is offline
Senior Member
 
Join Date: Feb 2020
Location: America
Posts: 388
Default

I've gave it some thought and decided to go with C5 RS6 front caliper and discs since it'll be easier for me to mount the calipers. And for the rears I'm going to go with C5 RS6 rear brakes instead of trying to fit 4 piston calipers from a Boxster and custom install a hydraulic e-brake or try to custom install an additional mechanical parking brake setup.

This upgrade is something that I will eventually do and as of right now it looks like I won't be able to get around to piecing it together till next year. So I'm just looking to get as much information about it now.
Reply With Quote
  #30  
Old 22nd July 2020, 12:19 PM
Conan_the_Librarian's Avatar
Conan_the_Librarian Conan_the_Librarian is offline
UberSeniorChiefLibrarian
 
Join Date: Jan 2009
Location: In a library
Posts: 3,860
Default

The only issues you will have with the C5 RS6 rears is the Handbrake cable. You will need the cables from a LWB D2 A8. They are pretty rare. Maybe Audi heritage?
__________________
Conan (the Librarian)

Watch it if you dare

Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.
Reply With Quote
Reply

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. The time now is 10:59 AM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.