science behind adjustable anti roll bar drop links

science behind adjustable anti roll bar drop links

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StreetDragster

Original Poster:

1,513 posts

217 months

Wednesday 13th August 2014
quotequote all
Hi all,

I'm trying to understand the benefits of using adjustable length anti roll bar drop links.

I have a car that's lowered by 30mm for track use, concensus seems to be that this requires adjustable drop links, but i don't understand why.

The roll bar is free to rotate on its mounts, the standard do links are identical in length on both sides, so surely the bar rotates a little in its mounts to match the new lower arm position when lowered.

What are the implications of the anti roll bar ' tails ' not being horizontal by ~30mm at the tips?

It's £120 plus vat and delivery for four adjustable do links vs £20 for pattern parts all in

Thanks
Matt

spitfire4v8

3,990 posts

180 months

Wednesday 13th August 2014
quotequote all
Imagine if you lowered or raised the car so far that the anti roll bar became vertical? How much roll stiffness do you think it would add then?
In reality, try it with your original drop links and see what happens, then change them and see what happens. then decide what you prefer..

stevieturbo

17,229 posts

246 months

Thursday 14th August 2014
quotequote all
StreetDragster said:
Hi all,

I'm trying to understand the benefits of using adjustable length anti roll bar drop links.

I have a car that's lowered by 30mm for track use, concensus seems to be that this requires adjustable drop links, but i don't understand why.

The roll bar is free to rotate on its mounts, the standard do links are identical in length on both sides, so surely the bar rotates a little in its mounts to match the new lower arm position when lowered.

What are the implications of the anti roll bar ' tails ' not being horizontal by ~30mm at the tips?

It's £120 plus vat and delivery for four adjustable do links vs £20 for pattern parts all in

Thanks
Matt
Might help if you specify what "track use" means. Track can mean different things to different people.

And what vehicle, and whether front or rear etc etc

Post is wayyy too vague to even consider an answer. And as far as adjustable, are you just meaning length, or position on the bar ?

RC Developments

83 posts

123 months

Saturday 23rd August 2014
quotequote all
Adjustable drop links are used to help keep zero pre-load on the anti roll bar. The roll bar should be fitted with the car on the ground "not always easy!" using the drop links to take up any difference in the mounting point height.

Pumajay

1,051 posts

203 months

Thursday 28th August 2014
quotequote all
I presume he means length, Ive seen these advertised, Ive got a Ford Puma track car and ive considered buying them for the front of my car but im unsure of what benefits they will offer, if at all any?


Chirpsean

55 posts

132 months

Saturday 30th August 2014
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Pumajay said:
I presume he means length, Ive seen these advertised, Ive got a Ford Puma track car and ive considered buying them for the front of my car but im unsure of what benefits they will offer, if at all any?
Two main reasons for adjustable links. One, as stated above is to ensure that there is zero preload on the bar when the car is sat naturally at ride height with no roll and the second is so you can ensure the bar doesn't foul on the body/chassis if the vehicle is lowered.

PhillipM

6,515 posts

188 months

Saturday 6th September 2014
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The third is to make sure you don't run out of joint angle when running different ride heights/suspension travel to what the originals were designed to take.

StreetDragster

Original Poster:

1,513 posts

217 months

Saturday 29th April 2017
quotequote all
Thread resurrection!

At the weekend I had some driving instruction, as part of this the instructor drove both mine and my friends cars back to back and commented that my friends car was much less understeery than mine and that I'm probably driving around this tendency.

This was quite unexpected in the paddock as our cars are very similar in build, except for brands of parts.

Mine -
Mazda RX8
Koni adjustable dampers 50/50 setting front/rear with tein springs
Racing beat anti roll bars front and rear with adjustable drop links
Ad08r tyres
Urethane bushes throughout
Parallel toe front/rear
1.5 negative front camber, 2 rear

His -
Bilstein dampers and springs, none adjustable I think
Whiteline front anti roll bar, standard rear, standard links
Ad08r tyres
Some rubber some urethane bushes
Same settings


I setup my anti roll bars weight on wheels for horizontal anti roll bar with minimal proload.
I now want to adjust them to try and dial our a bit of the understeer.
Firstly, tighten the rear of soften the front?
Secondly, can someone confirm if it's shorter links for softer anti roll bar?

Roll bars are not adjustable in attachment points to the drop links
Track use is hard driving in this case on Anglesey, instructor with us all day so we were pushing it
Both front and rear links are adjustable in length only

Thanks
Matt



Edited by StreetDragster on Saturday 29th April 22:58

GreenV8S

30,150 posts

283 months

Sunday 30th April 2017
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StreetDragster said:
Secondly, can someone confirm if it's shorter links for softer anti roll bar?
No, it won't do that.

To increase the stiffness of a given bar you need to reduce the leverage of the drop links relative to the bar and/or increase it relative relative to the suspension. Adjustable anti-roll bars often include a blade which can be twisted to alter its effective stiffness in the direction of load.

Do you know the effective roll stiffness of the two vehicles? The anti-roll bar is only one of many things affecting the understeer/oversteer balance so you have many other options to alter the handling. Obviously this is a well researched subject and there are loads of books covering the theory and practice.

Mr2Mike

20,143 posts

254 months

Sunday 30th April 2017
quotequote all
StreetDragster said:
Thread resurrection!

Mine -
Mazda RX8
Koni adjustable dampers 50/50 setting front/rear with tein springs
What are the spring rates like compared to your mate's car? Tein appear to specialise in suspension kits that have all the compliance of a block of steel.

Also is there any difference in the diameter of the front anti-roll bars?

Are you running the same tyre brand and sizes?

E-bmw

9,105 posts

151 months

Sunday 30th April 2017
quotequote all
OP.

As you are probably gathering by now there are approximately 6,975,363 settings/parts that can affect what you are thinking may be caused by just one of them.

HustleRussell

24,602 posts

159 months

Sunday 30th April 2017
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Sounds like it wants setting up from scratch starting with ride height and rake and going through it from there.

StreetDragster

Original Poster:

1,513 posts

217 months

Monday 1st May 2017
quotequote all
Thanks for all replies so far, some research required.

I'm well aware that this may be a complicated issue, race teams don't employ numerous people with college degrees in this stuff because its easy. And I certainly don't have a degree it in either.

However, you have to start learning somewhere and this is the first time I will be trying to change the cars handling with a desired output without 'just' buying parts with a brand name on them.

I have front castor, front and rear toe, front and rear camber, front and rear drop link length, and front and rear damper rebound.

I guess I'm asking, of these adjustable parts, is there any which I could start to adjust to try and dial this understeer out a bit.

Thanks
Matt

StreetDragster

Original Poster:

1,513 posts

217 months

Monday 1st May 2017
quotequote all
Mr2Mike said:
StreetDragster said:
Thread resurrection!

Mine -
Mazda RX8
Koni adjustable dampers 50/50 setting front/rear with tein springs
What are the spring rates like compared to your mate's car? Tein appear to specialise in suspension kits that have all the compliance of a block of steel.

Also is there any difference in the diameter of the front anti-roll bars?

Are you running the same tyre brand and sizes?
Same tyre brands, and sizes on both cars
I'll have to check the anti roll bars and get some specs on the springs

Thanks
Matt

PaulKemp

979 posts

144 months

Monday 1st May 2017
quotequote all
This is a rather simple list but gives you an option of trying a few things before laying and cash out

To reduce oversteer
Therefore increase understeer

Increase front spring rate
Decrease rear spring rate
Stiffen front damper
Soften rear damper
Increase rear tyre width
Decrease front tyre width
Increase rear tyre pressure
Decrease front tyre pressure
More positive front camber
More negative rear camber
Stiffer front anti-roll bar
Softer rear anti-roll bar
More weight to the front
Less weight to the rear

To reduce understeer
Therefore increase oversteer

Decrease front spring rate
Increase rear spring rate
Soften front damper
Stiffen rear damper
Decrease rear tyre width
Increase front tyre width
Decrease rear tyre pressure
Increase front tyre pressure
More negative front camber
More positive rear camber
Soften front anti-roll bar
Stiffen rear anti-roll bar
Less weight to the front
More weight to the rear

Unhinged

56 posts

125 months

Tuesday 9th May 2017
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I suspect that maybe your Koni shocks have too much rebound on the front axle - try softening and see if grip returns.
The Bilstein shocks are monutube and will more than likely give more grip than the twin tube konis.
More caster can dial out understeer - worth a try.
Tein are one of the only manufacturers I've found to make Street suspension that is good on the Street - but a lot of Japanese imports arrive here with Racing spec stuff unsuited to our roads.
The Tein springs you have are soft 196lb in front 140lb in rear, the Eibach spring (i've calculated the rate based on spring dimensions so not 100% correct) is 162lb in front but on the rear it's progressive. So his softer front rate will create less understeer on turn in, then as the car loads up the rear spring rate will increase, initial rate would again be softer than Tein.

With roll bar sizes in mm it would be possible to see how that effects the weight transfer. One thing you might be doing is hitting the bumpstop on the front if the understeer is worse on corner exit.


StreetDragster

Original Poster:

1,513 posts

217 months

Wednesday 10th May 2017
quotequote all
Thanks everyone for the help, really beneficial, especially unhinged.

I'm on Rockingham this weekend, I have taken two psi out of the rear tyres and softened up the front dampers a little, see how it goes, wish me luck.

Thanks
Matt

CarsOrBikes

1,135 posts

183 months

Thursday 11th May 2017
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OP just try and set the rear arb in the centre of it's arc with the car on the ground, if you need adjustable links to do this get them, adjust them to the same length or so both end drop right in place assuming the car is on properly level ground.

As for later post, at Rockingham just for fun you could, with higher front spring rates, leave other settings, and remove one front drop link, just to see the easy effects of no front bar.

Someone said roll bars aren't adjustable but they are, my rear for example in it's lowest setting of three holes is 208% stiffer than standard, I have it there now but will be moving it up for Anglesey next time, but may also run the disconnected front bar beforehand as my front spring is a little stronger vs ideal.

All is down to preference for your own style perhaps, don't change too much at once, and make notes.