Home  
Site Partners: SpotterGuides Veloce Books  
Related Sites: Your Link Here  

Go Back   TenTenths Motorsport Forum > Racing Talk > Racing Technology

Reply
 
Thread Tools Display Modes
Old 26 Jan 2006, 20:41 (Ref:1509672)   #1
rcr286
Rookie
 
Join Date: Jan 2006
United States
Washington State
Posts: 33
rcr286 should be qualifying in the top 10 on the grid
Weight Transfer Equations - Anti Roll Bars

I have been working on a simple tool to calculate baseline suspension setups and I would like information on anti roll bar rate calculations. Each time I search, I find a new equation!

Does anyone here have real life experience with anti roll bar production or design? What is the "industry" standard? (I am looking for both solid and hollow bars)

Thanks in advance.
rcr286 is offline  
Quote
Old 27 Jan 2006, 10:13 (Ref:1509999)   #2
JohnD
Veteran
 
JohnD's Avatar
 
Join Date: Sep 2003
Location:
North West UK
Posts: 1,073
JohnD should be qualifying in the top 5 on the gridJohnD should be qualifying in the top 5 on the grid
Ric(?),
Have you read Alan Staniforth's "Sourcebook" or "Competition Car Suspension" book?
He makes the point that each change in design produces a new answer, but that this iterative method will not focus down on the 'right' answer.
While it's good to understand what your suspension is doing, in the end you have to make a subjective choice.
John
JohnD is offline  
Quote
Old 27 Jan 2006, 13:25 (Ref:1510114)   #3
TEAM78
Racer
 
Join Date: Oct 2005
United Kingdom
Posts: 234
TEAM78 has a lot of promise if they can keep it on the circuit!
how are you currently calculating it?
TEAM78 is offline  
__________________
If you want to make a million pounds in motorsport start with ten million pounds
Quote
Old 30 Jan 2006, 09:08 (Ref:1511703)   #4
ubrben
Veteran
 
Join Date: Jun 2005
United Kingdom
Birmingham
Posts: 508
ubrben has a lot of promise if they can keep it on the circuit!
Quote:
Originally Posted by JohnD
Ric(?),
Have you read Alan Staniforth's "Sourcebook" or "Competition Car Suspension" book?
He makes the point that each change in design produces a new answer, but that this iterative method will not focus down on the 'right' answer.
While it's good to understand what your suspension is doing, in the end you have to make a subjective choice.
John
There isn't a "right answer" but to say the choice is subjective is not really correct.

What you're doing is making an educated choice.

For weight transfer I'd use Milliken or the OptimumG spreadsheet that Lukin posted on this forum a while back.

Ben
ubrben is offline  
Quote
Old 31 Jan 2006, 16:30 (Ref:1512813)   #5
rcr286
Rookie
 
Join Date: Jan 2006
United States
Washington State
Posts: 33
rcr286 should be qualifying in the top 10 on the grid
Thanks Ben...you just took the fun out of my project!

This .xls is VERY similar to what I am building for myself. Actually, this saves me a lot of time. It is not like I was 'bored' and decided to build this to pass the time. As you said, this enables us to make an educated choice. Nothing is really absolute until you test it on the track, and that is only absolute until the next development or theory comes along. So for the 'moment', I will 'roll' with this.

-Roger
rcr286 is offline  
Quote
Old 31 Jan 2006, 17:20 (Ref:1512864)   #6
phoenix
Veteran
 
phoenix's Avatar
 
Join Date: Jul 2005
European Union
Posts: 1,981
phoenix should be qualifying in the top 5 on the gridphoenix should be qualifying in the top 5 on the grid
I too have come across more than one formula, but I have found that they all work out to within a couple of percent of each other. As Pilbeam make successful cars, I prefer to use Mike Pilbeam's formula. I also aim to have the lever arms at 90 degrees to the bar axes, that eliminating the variable that angled lever arms have on stiffness.

I can let you have a little spreadsheet that calculates roll stiffness for solid or tubular bars of any dimension and will give figures for lbs/degree and lbs/inch deflection.

As you probably know, you will need to have dimensions for the proposed bar including width, diameter, bore (if a tube) and the length of the 'lever arms'.

If you know the roll stiffness offered by the springs, you can then estimate sensible targets for the stiffness required for the bars 1) to give the total roll resistance you require and 2) to give the weight tranfer you require.

As steel tends to come in stock sizes, it is then a question of playing with diamters, bores, lengths and lever arms lengths to match your requirements, not forgetting where the bar connects to the suspension as this is likely to introduce a motion ratio with respect to wheel travel:bar travel. This motion ratio can be helpful in the design for getting the desired finished roll resistance, however.
phoenix is offline  
Quote
Old 31 Jan 2006, 20:53 (Ref:1513009)   #7
breezeblock
Rookie
 
Join Date: Dec 2005
Scotland
stirlingshire
Posts: 79
breezeblock should be qualifying in the top 10 on the grid
how much stiffer is a tube over a solid bar is it worth changing to tube for the weight loss
breezeblock is offline  
Quote
Old 31 Jan 2006, 21:24 (Ref:1513041)   #8
GordonG
Racer
 
Join Date: May 2004
Posts: 155
GordonG should be qualifying in the top 10 on the grid
Torsional stiffness of a bar is proportional to D**4 (Diameter to the power of 4). Torsional stiffness of a tube is proportional to OD**4-ID**4. Play with some numbers in those calculations and you find that you need a tube only very slightly larger in OD than a bar to get the same stiffness.

G
GordonG is offline  
Quote
Old 1 Feb 2006, 01:35 (Ref:1513166)   #9
TEAM78
Racer
 
Join Date: Oct 2005
United Kingdom
Posts: 234
TEAM78 has a lot of promise if they can keep it on the circuit!
Quote:
Originally Posted by breezeblock
how much stiffer is a tube over a solid bar is it worth changing to tube for the weight loss
Tube isnt stiffer than solid??? the tubular bar is making more efficient use of the material used in the ARB,
Chasing the ideal tube sizes can get very expensive and time consuming, well it was for me anyway, I saved over 1.5kg out my bar by going tube on a saloon car. it depends how serious your formula is, If its F1 then yes, if its a track day car, er no, put it this way I think you will find it very hard to feel the difference.
Also note with tubular bars the production accuracy means the Internal diameter (ID) can vary so beware!
Best to experimentally test the tubular ARB once you have made it to verify the torsional stiffness, do it for solid bars as well if you fancy it

For weight transfer Calcs, Ive used various ones, from Milliken, Optimum G etc. . they all give an answer to within 0.25kg! which is pretty dam good so just use one you feel good with,
TEAM78 is offline  
__________________
If you want to make a million pounds in motorsport start with ten million pounds
Quote
Old 1 Feb 2006, 16:26 (Ref:1513600)   #10
rcr286
Rookie
 
Join Date: Jan 2006
United States
Washington State
Posts: 33
rcr286 should be qualifying in the top 10 on the grid
Thank you very much guys, you have been very helpful.

Phoenix, I would like to see the sheet that you use. I believe that my email is available for you to send personal mail. I will take anything I can get. Most of the formulas really are very similar, but the constant (usually Modulus of Elasticity) can vary greatly. With this being said though, I have not seen a difference of only a couple of percent between equations. I guess that is why I am investigating a more definative answer.

I discovered another sheet a while ago while playing Live for Speed. Whenever I play an new video game that allows you to set up cars, I immediately enter a setup that I know works on the car and try it out. Then I enter a completely goofy setup and see if changes are predicatable. This is one of the only games that actually has a grasp on these dynamics. Unfortunately, this and Grand Prix Legends both suffer from crappy tire physics. Anyways, this sheet (download from http://forum.rscnet.org/showthread.php?t=157180 ) has some pretty cool macros and makes it very easy to use and read. It is very similar to the Magic Number, but more graphical...for those visual learners like me. It is very basic, but it is a great foundation for a potentially powerful tool.

Thanks again,

Roger
rcr286 is offline  
Quote
Old 3 Feb 2006, 09:27 (Ref:1514651)   #11
idol
Rookie
 
Join Date: Feb 2006
Posts: 2
idol should be qualifying in the top 10 on the grid
Have a look at this program http://www.bevenyoung.com.au/suswin.htm (free demo version) the help file has a section on Technical and implementation notes with a page on arb calculations. The "constant" E depends on the material used and its treatment.
idol is offline  
Quote
Old 3 Feb 2006, 20:25 (Ref:1515077)   #12
Goran Malmberg
Registered User
Racer
 
Join Date: Mar 2004
Sweden
Stockholm Sweden
Posts: 319
Goran Malmberg should be qualifying in the top 10 on the grid
If the car has the same TW as WB we shuld not need any rollbars. The car shuld roll the same deflection as it pitch at the same G-force. So, when the car got a narrower TW than WB, the deflection is going to become greater sideways than in pitch. To get back to the same as the "square" car we must add rollbars of the same dignity as the TW is less than the WB. This is what is the basic balance between the springs and rollbars.

Another thing is to find the motion ratio to calculate the wheelrate from the springrate. AND, the rollbar wheelrate from the rollbar rate. This is no easy task. Moost literature Talk only about the leverage of the A-arm and the mounting place of the spring-rollbar at the A-arm. This is fare from accurate. Scrub distance and upper A-arm angle has a great influence on tha calculation and make this quite complex. In short we could say that a very camber compensative suspension is very dependent on scrub distance for Mr.

Goran Malmberg
Goran Malmberg is offline  
Quote
Old 3 Feb 2006, 21:26 (Ref:1515103)   #13
TEAM78
Racer
 
Join Date: Oct 2005
United Kingdom
Posts: 234
TEAM78 has a lot of promise if they can keep it on the circuit!
Quote:
Originally Posted by Goran Malmberg
I In short we could say that a very camber compensative suspension is very dependent on scrub distance for Mr.
Goran Malmberg
Can you tell us more please Goran, how is a camber compensative suspension dependent upon scrub distance?
im currently in the middle of evaluating camber compensation for a rear suspension on a FS car, I currently have roll camber at 0.4, any more than this sticks the RC up over 2" and provides silly angles on the wishbones, which I really dont want as it will cause undue loadings on everything. There isnt much literature on full camber compensation, and some colleges use it as a bloody buzz word round ere which is annoying as im not that keen on it really hence hope to disprove em.
TEAM78 is offline  
__________________
If you want to make a million pounds in motorsport start with ten million pounds
Quote
Old 4 Feb 2006, 11:53 (Ref:1515382)   #14
Goran Malmberg
Registered User
Racer
 
Join Date: Mar 2004
Sweden
Stockholm Sweden
Posts: 319
Goran Malmberg should be qualifying in the top 10 on the grid
I should use the word "cambergain" is place for "cabercompensation". Neither is "scrub" a proper word to use since it includes the angle of SAI . However, this means that we must concider taking SAI under cocideration even for the rear uppright.

To explain things properly I should need to use a drawing, so I stay with a principal explanation.

As the upper A-arm is at an angle, closer to ground mounting on the car while the lower A-arm is horizontal and longer, the upper spindle balljoint is moving up and in to the car during bump. If the lower spindle balljoint is located at the centre load line of the tire, the tire contact patch will remain at the same height distance to the balljoint, (only a slight movements sideways).

Now, if we draw a vertical line from the lower balljoint to ground, and the configuration is such that we got a distance here to the centre of wheel load line, we is having a lever distance making the contact patch not only moving sideways but also vertically. This distance is not really to be
confused with scrub, since SAI angle is not a vertical line.

So, under bump the wheel is travelling a longer distace than the lower balljoint. And it does so in an increasing rate, progressively reversd to what we likes it to do. If for example the upper A-arm has a static angle of 15 dgr and the "scrub" distance is 150 mm the effect will becom very influencial. A 50% reduction in wheelrate is no fantasy in an extreem case.

We can either use zero scrub OR a horizontal upper A-arm, both action brings the motion ratio back to only depend on the coilover mounting (angle) location on the lower A-arm. Of course we can compensate this by using a higher rate spring , but we still have to deal with the progression in Mr. The best is zero scrub when using exsessive camber copensation.

Compare this to what a slight change in rollbar will do to balance, and it becomes appearent how easy we will get lost in balance if the mentioned things is not taken under cocideration. Long parallel A-arms as used in F1 or le Mans racing prototypes does NOT suffer from these sort of behaviour.

This are things coming from my own studying of my half scale axle model. I must also add that ther might be error in my observation .
Regards
Goran Malmberg
Goran Malmberg is offline  
Quote
Old 4 Feb 2006, 12:02 (Ref:1515387)   #15
Goran Malmberg
Registered User
Racer
 
Join Date: Mar 2004
Sweden
Stockholm Sweden
Posts: 319
Goran Malmberg should be qualifying in the top 10 on the grid
Oh, I must add, that it is apparent that the same goes for both front and rear suspension. So, then we must also see to the scrub of the rear suspension even as the rear wheel dosnt steer....

Goran Malmberg
Goran Malmberg is offline  
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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Roll couple or roll centre??? HELP!!!!!! jonners Racing Technology 66 30 Dec 2006 02:48
Anti roll bar FilW Racing Technology 3 27 Apr 2006 12:31
Adjustable "Blade Type" Anti-Roll Bars Design Questions rabieng Racing Technology 5 5 Mar 2006 13:06
Anti Roll Bar Graham K Racing Technology 26 2 Feb 2006 11:07
Roll-Bars & Sportscars bobdrummond Sportscar & GT Racing 8 12 Apr 2002 15:18


All times are GMT. The time now is 13:58.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
Original Website Copyright © 1998-2003 Craig Antil. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2004-2021 Royalridge Computing. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2021-2022 Grant MacDonald. All Rights Reserved.