Spring rates and body roll ?? - Page 2 - Alfa Romeo Bulletin Board & Forums
 9Likes
Reply
 
LinkBack Thread Tools Display Modes
post #16 of 50 (permalink) Old 11-25-2015, 10:44 PM
Registered User
 
Alleggerita's Avatar
 
Join Date: Sep 2005
Location: BC
Posts: 2,158
Wrong. Knuckle risers raise the roll-center at the front and sliding block lowers roll center at the rear. This, among many other effects on geometry changes the slope of the roll axis, changing under/oversteer balance. It also alters roll couple. Front is more resistant to roll, rear is less resistant to roll. Knuckle risers decrease distance between RC and CG, allowing softer springs in the front. Additional effect of knuckle risers is altered camber curve which results in increased negative camber on bump, widen front track slightly, etc.

Quote:
Originally Posted by hagen111 View Post
Isn't the following true....GTA knuckle risers lower the RC on front suspension, and as the car sits high up the lower RC and relative high center of gravity, cause the car to roll and press hard on the springs. Also the sliding block lower RC, and will therefore make the car push much harder on the springs, also on the front. Hence the car will lift the inner wheel on the front.

Spring rates are defined by RC and CG. Ideally you want to as low as possible on the spring rate, hence you want to raise the RC a bit and lower the car a bit, so both RC and CG come closer together which will allow for using lower springrate, without more roll.
Alleggerita is online now  
Sponsored Links
Advertisement
 
post #17 of 50 (permalink) Old 11-25-2015, 11:15 PM
Senior Member
Platinum Subscriber
 
Join Date: Jul 2005
Location: Utrecht - Netherlands
Posts: 248
Quote:
Originally Posted by Alleggerita View Post
Wrong. Knuckle risers raise the roll-center at the front and sliding block lowers roll center at the rear. This, among many other effects on geometry changes the slope of the roll axis, changing under/oversteer balance. It also alters roll couple. Front is more resistant to roll, rear is less resistant to roll. Knuckle risers decrease distance between RC and CG, allowing softer springs in the front. Additional effect of knuckle risers is altered camber curve which results in increased negative camber on bump, widen front track slightly, etc.
You are so right. Made a quick drawing on a newspaper to see the RC indeed gets raised by Knuckle risers.
hagen111 is offline  
post #18 of 50 (permalink) Old 11-26-2015, 06:00 AM
Registered User
 
Mound Dawg's Avatar
 
Join Date: Jun 2008
Location: Running through the ruins, all directions wrong.
Posts: 1,875
Garage
Knuckle risers and sliding block axles are verboten in U2TC racing as they weren't homologated until after 1966 so we're not allowed those.

The roll centres were horribly mis-matched in these early cars, the later 1750 onwards cars had different uprights which effectively include the knuckle riser so the roll centre is higher on these which evens it out a bit but it's still not good, the rear centre is still too high compared to the front. This is why sliding blocks or Watts linkages have such a big effect on lap times.

Same is true of the transaxle cars, even with the Watts link the roll centres are still mis-matched. Richard Banks told me that when they were racing the Alfetta GT in the British Touring Car Championship back in the 1970s they found 2 seconds a lap by cutting the Watts link pin off the top of the axle and welding it back onto the bottom of the axle!


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

We're gonna make you an Alfa you can't refuse.
Mound Dawg is offline  
Sponsored Links
Advertisement
 
post #19 of 50 (permalink) Old 12-01-2015, 11:35 PM
Registered User
 
Join Date: May 2013
Posts: 17
The knuckle risers might change the roll centre up or down but I think it was done more for tyre wear than anything else.

To get a decent lap time with my Giulia race car, I need to dial in about 2 degrees negative camber. I do not have the luxury of stiffer springs so my car rolls a bit, not as much as the older GTA's though. When the inner wheel lifts up the negative camber becomes more because the upper arm pulls it in without the knuckle risers. It goes below horizontal, decreasing its length, pulling in the upper part of the spindle. Add the body roll to the negative camber and you get about 5 to 8 degrees negative camber on the inside wheel and it only runs on the inner edge of the tyre. On our local circuit there are more right hand corners than left and the right front wears on the inner edge.

If you add the knuckle riser it lifts the upper arm to be pointing down from the wheel towards the body. As the inside wheel then lifts, the arms then "lengthens" decreasing the camber. This in effect can actually change the camber to positive or very little and thereby decreases tyre wear especially the inner edge that gets dragged along, in the slide, if the inner wheel is not completely off the ground. In the early days of the GTA they use to slide around on the tyres available and also have a lot of body roll.

Just my 2 cents worth to add to the discussion.
Alfanutsmurph is offline  
post #20 of 50 (permalink) Old 12-02-2015, 03:49 AM
Registered User
 
Join Date: Jul 2015
Posts: 266
Quote:
Originally Posted by Alleggerita View Post
Wrong. Knuckle risers raise the roll-center at the front and sliding block lowers roll center at the rear. This, among many other effects on geometry changes the slope of the roll axis, changing under/oversteer balance. It also alters roll couple. Front is more resistant to roll, rear is less resistant to roll. Knuckle risers decrease distance between RC and CG, allowing softer springs in the front. Additional effect of knuckle risers is altered camber curve which results in increased negative camber on bump, widen front track slightly, etc.


Nice explanation, that was the true purpose of introducing “slittone” on the rear, and “rialzi” on the front of GTA. Risers changed static camber and allowed the perpendicularity (relative) of the wheel in cornering, while sliding block preserved both tires on the track (obviously working in calculated synergy)
ARGTAReg is offline  
post #21 of 50 (permalink) Old 12-02-2015, 05:07 AM
Registered User
 
Alistair Muir's Avatar
 
Join Date: Mar 2015
Location: Chester, England
Posts: 489
Alfa Romeo's introduction last line in there 1968 performance options catalogue. "it's a collection of items if interest for race car owners only" yea right! There a lot of comments about ride heights, usually after someone gets it home for the first time and wonders about it...then starts asking how to lower front again..

http://www.veloce.se/pdf_filer/Prest...g_gta_1968.pdf

Past 1990 164 V6 in NZ

Last edited by Alistair Muir; 12-02-2015 at 05:20 AM.
Alistair Muir is offline  
post #22 of 50 (permalink) Old 12-02-2015, 09:47 AM Thread Starter
PSk
Registered User
 
Join Date: May 2003
Location: Tauranga New Zealand
Posts: 11,303
Send a message via AIM to PSk Send a message via Yahoo to PSk
Quote:
Originally Posted by Alfanutsmurph View Post
The knuckle risers might change the roll centre up or down but I think it was done more for tyre wear than anything else.

To get a decent lap time with my Giulia race car, I need to dial in about 2 degrees negative camber. I do not have the luxury of stiffer springs so my car rolls a bit, not as much as the older GTA's though. When the inner wheel lifts up the negative camber becomes more because the upper arm pulls it in without the knuckle risers. It goes below horizontal, decreasing its length, pulling in the upper part of the spindle. Add the body roll to the negative camber and you get about 5 to 8 degrees negative camber on the inside wheel and it only runs on the inner edge of the tyre. On our local circuit there are more right hand corners than left and the right front wears on the inner edge.

If you add the knuckle riser it lifts the upper arm to be pointing down from the wheel towards the body. As the inside wheel then lifts, the arms then "lengthens" decreasing the camber. This in effect can actually change the camber to positive or very little and thereby decreases tyre wear especially the inner edge that gets dragged along, in the slide, if the inner wheel is not completely off the ground. In the early days of the GTA they use to slide around on the tyres available and also have a lot of body roll.

Just my 2 cents worth to add to the discussion.
Nobody cares what the inside wheel is doing, only the outside wheel that is doing the cornering work.
Pete

'71 1750 Series 2 GTV:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
156 Series 1 v6 ... and remember it's all just opinions
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
PSk is offline  
post #23 of 50 (permalink) Old 12-03-2015, 06:19 AM
Registered User
 
Mound Dawg's Avatar
 
Join Date: Jun 2008
Location: Running through the ruins, all directions wrong.
Posts: 1,875
Garage
In an ideal world no, you want all four wheels on the ground. This is why a 250 cc go-kart will always set a faster lap time than a 250 cc motorbike with the same engine.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

We're gonna make you an Alfa you can't refuse.
Mound Dawg is offline  
post #24 of 50 (permalink) Old 12-03-2015, 09:47 AM Thread Starter
PSk
Registered User
 
Join Date: May 2003
Location: Tauranga New Zealand
Posts: 11,303
Send a message via AIM to PSk Send a message via Yahoo to PSk
Quote:
Originally Posted by Mound Dawg View Post
In an ideal world no, you want all four wheels on the ground. This is why a 250 cc go-kart will always set a faster lap time than a 250 cc motorbike with the same engine.
Cornering speed is all about tyre contact patch but the load is on the outside wheel, so sorry don't agree that you need to worry about the inside wheel or keep it on the ground.

A car, or go-kart, setup properly has a considerably larger outside wheel contact patch than any motorcycle because that wheel stays closer to vertical than the motorcycle and therefore more of the tread surface is in contact with the ground. Plus lower CoG and roll centres, etc. ... a motorcycle does not stand a chance.

If you picked a single corner and put the skinniest low grip wheel on the inside front of a car and timed it through that corner it would be very similar in time to when it had its normal wheel on that inside front of the car. After all look at a F1 car; often that wheel is bouncing over a kerb or has ridiculous negative camber ... but the designers don't care, 99% of the work is being done by the outside front wheel.

BTW: Have a look at your recent GTA/GTV racing photos and the inside wheel is either off the ground or very close to it and doing little, but the outside tyre is trying to be pulled off the rim .
Pete

'71 1750 Series 2 GTV:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
156 Series 1 v6 ... and remember it's all just opinions
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
PSk is offline  
post #25 of 50 (permalink) Old 12-03-2015, 12:12 PM
Registered User
 
Sketchl's Avatar
 
Join Date: Apr 2012
Location: Sydney, Australia
Posts: 663
Garage
Ciao Pete,

Not sure how much racing you do but there are a few stages to a corner where the inside wheel plays a major part in cornering. Firstly under braking and then the initial turn in when all the weight is on the front end and your trying to reach the apex of the corner. Obviously once you have lined up the apex and you're then under full power the weight will transfer to the outside front and inside wheel will play a role in any oversteer!

Saluti
Sergio
Attached Images
 

1966 Giulia Sprint GT Veloce - slightly modified!
Sketchl is offline  
post #26 of 50 (permalink) Old 12-04-2015, 12:22 AM Thread Starter
PSk
Registered User
 
Join Date: May 2003
Location: Tauranga New Zealand
Posts: 11,303
Send a message via AIM to PSk Send a message via Yahoo to PSk
Quote:
Originally Posted by Sketchl View Post
... there are a few stages to a corner where the inside wheel plays a major part in cornering. Firstly under braking and then the initial turn in when all the weight is on the front end and your trying to reach the apex of the corner. Obviously once you have lined up the apex and you're then under full power the weight will transfer to the outside front and inside wheel will play a role in any oversteer!

Saluti
Sergio
True regarding braking but once cornering, ie. you have turned in, it is all about the outside wheel whether on full power or not.

Note in your excellent photo that the inside front wheel is close to off the ground and unloading. The amount of grip that wheel is providing compared to the outside front wheel is very, very low.

Maybe we are having a misscommunication??
Pete
ps: I have not raced for 20 years, but nothing has changed. The tyre with the most load on it does the most work.

Guys this is why we race with negative camber and often lots of caster angle. If the inside wheel was more important we would race with positive camber like they used to back in the beam axle days so the inside wheel maximised it's contact patch during cornering ... we don't because there is little load on that tyre and therefore pointless.

Look at the F1 photo below. That inside wheel has a ridiculous amount of negative camber during this corner, but they don't care because the outside wheel is the important one and has the maximised contact patch under load.
Attached Images
 

'71 1750 Series 2 GTV:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
156 Series 1 v6 ... and remember it's all just opinions
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Last edited by PSk; 12-04-2015 at 12:58 AM.
PSk is offline  
post #27 of 50 (permalink) Old 12-04-2015, 01:32 AM
Registered User
 
Join Date: May 2013
Posts: 17
Quote:
Originally Posted by PSk View Post
Nobody cares what the inside wheel is doing, only the outside wheel that is doing the cornering work.
Pete
It is not what the inside front tyre is contributing to the handling or cornering ability, I was talking about tyre wear.

The right front tyre on a predominantly right hand corner circuit would wear the inside edge down to the canvas in a short time if you have excessive negative camber on the front wheels. Yes you can let down the tyre pressure and have a good contact patch etc. etc.

As I said: "Add the body roll to the negative camber and you get about 5 to 8 degrees negative camber on the inside wheel and it only runs on the inner edge of the tyre." When you are in a four wheel drift and that inside front wheel is on the road it gets worn down quickly on the inside edge. I have thrown away a few slicks with usable rubber on 90% of the surface except the inside edge of the tyre being worn down to the canvas. I learnt to rotate race tyres the hard way.

A lot of the races in the bygone days were long distance 3 hour 6 hour or 9 hour type races and tyre wear played a huge part.
Alfanutsmurph is offline  
post #28 of 50 (permalink) Old 12-04-2015, 01:24 PM Thread Starter
PSk
Registered User
 
Join Date: May 2003
Location: Tauranga New Zealand
Posts: 11,303
Send a message via AIM to PSk Send a message via Yahoo to PSk
Quote:
Originally Posted by Alfanutsmurph View Post
It is not what the inside front tyre is contributing to the handling or cornering ability, I was talking about tyre wear.
Yes.
Quote:
The right front tyre on a predominantly right hand corner circuit would wear the inside edge down to the canvas in a short time if you have excessive negative camber on the front wheels. Yes you can let down the tyre pressure and have a good contact patch etc. etc.
As heat causes tyre wear and the inside tyre is unloaded and therefore not producing as much heat, wouldn't that wear you are talking about have been caused by the excessive negative camber on the straights? Surely on the straights with more load there would be more heat on that inside edge than on right hand corners?

Maybe ...
Quote:
A lot of the races in the bygone days were long distance 3 hour 6 hour or 9 hour type races and tyre wear played a huge part.
True.
Pete

'71 1750 Series 2 GTV:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
156 Series 1 v6 ... and remember it's all just opinions
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
PSk is offline  
post #29 of 50 (permalink) Old 12-04-2015, 02:54 PM
Registered User
 
Join Date: May 2013
Posts: 17
Quote:
Originally Posted by PSk View Post
As heat causes tyre wear and the inside tyre is unloaded and therefore not producing as much heat, wouldn't that wear you are talking about have been caused by the excessive negative camber on the straights? Surely on the straights with more load there would be more heat on that inside edge than on right hand corners?
Then the inside edges of both tyres would wear down.

I have 2 degrees negative camber on both the front wheels of my Giulia. The right front wears down quicker on a predominantly right hand corner circuit i.e. the predominantly inside front tyre. Another racer on the same circuit with a 1750 GTV has also noticed the right front tyre wears the inside edge down to canvas first.

Maybe you will understand a picture better.
Attached Images
 
Alfanutsmurph is offline  
post #30 of 50 (permalink) Old 12-04-2015, 08:37 PM Thread Starter
PSk
Registered User
 
Join Date: May 2003
Location: Tauranga New Zealand
Posts: 11,303
Send a message via AIM to PSk Send a message via Yahoo to PSk
I did understand what you are saying but yep that is a good picture too.

How does the other front tyre wear? evenly? Because of the mainly right hand corners you would expect that the left front tyre would wear a lot (on the outside edge) and if evenly then potentially the inside of that tyre is being worn on the straights also, or the camber is perfect for the corners to wear evenly.

Do you have a circuit map that you can point me to? as are they really, really long right hand corners, ie. close to an oval?

At the moment yes I can see that only the inside of the inside tyre is on the ground but I cannot understand how it could possibly be producing enough heat to cause excessive wear due to the light loading. But I'm always learning and while I never experienced this myself I have never raced a 105 series.
Pete

'71 1750 Series 2 GTV:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
156 Series 1 v6 ... and remember it's all just opinions
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
PSk is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome