procomp
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| posted on 14/9/06 at 07:46 AM |
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Hi but if it will pull 3-4 cars lenght on thoes whithou it of the line and 2-3 lenghts out of the tighter corners it has got to be worth using.
The only time it has ever caused me any problems under braking was at pembrey whilst braking for the hairpin at turn 1 but given the speed caried
down to that corner and the fact it is a hairpin it is about as bad as it gets and that just neded the damper going up 1 click to controle the axle
tramp.
cheers matt
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Syd Bridge
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| posted on 14/9/06 at 08:51 AM |
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Some words of caution;
In roll or one wheel bump or droop, unequal length or non-parallel trailing arms WILL impart a large torque reaction into the axle housing,
trying to tear the mounts off the casing.
Best to angle both trailing arms up and keep them parallel. This also alleviates the suspension locking at a certain point, which I suspect is
what is giving some of the benefits being discussed here.
Cheers,
Syd. 
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Steve Morten
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| posted on 14/9/06 at 03:55 PM |
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Your right syd. You have to build a bit of compliance into the bushes so don't use rose joints. Anyway most race cars don't have a lot of
suspension travel.
The other thing you have to be carefull of if you have top and bottom arms angled the same, is that, as you roll, say on a right hand turn then the
left rear wheel will move back slightly and the right will move forward slightly thus steering the back of the car out as in oversteer. Thus is great
for us Autotesters but I don't think it would be good at speed. It tell's you how to conteract this in this article I posted earlier:
http://www.afcoracing.com/tech_pages/4link.shtml
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procomp
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| posted on 14/9/06 at 06:21 PM |
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Hi compliance in the bushes is also the secret to getting it all to work nicely.
cheers matt
sorry for short reply in a big rush.
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Syd Bridge
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| posted on 14/9/06 at 07:38 PM |
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And how many locost racers are utilising a rotating trailing arm mount (bird cage type thing) on the diff casing??
Compliant bushes just spread the load, but can't stop the forces acting. ie They soften the effect of the twisting, but don't stop it.
The article mentioned above states that arms shorter than 17" are not effective, because of the high longitudinal movements with rotation. Where
does all this sit with a Locost with 12" arm lengths?
And lastly, none of this works with wishbones, no matter how much some may want you to think otherwise. All you end up doing is buggering up perfectly
good(?) geometry.
Cheers,
Syd.
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Steve Morten
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| posted on 15/9/06 at 01:36 PM |
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Hi Syd,
I guess the reason they go on about birdcage is because they are talking about oval track racing so they are going to need more suspension movement
than in a seven.
The twisting effect on a live back axle is there whether you angle the arms up or not. The shorter the arms the more the twisting. Maybe thats why
they prefer longer then 17" arms. Anyway my axle hasn't broken yet, and thats after 2 years about 50 events and 2 drivers. In fact I guess
the twisting effect acts like a rear anti roll bar?
All I did when first trying mine was to add more mounting holes at the front. I put 3 holes in at 3, 5, and 9 degrees. If it didn't work I could
always move them back.
As for independant rear & wishbones I agree I don't see how you can biuld anti-squat in.
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C10CoryM
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| posted on 18/9/06 at 04:02 PM |
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Sorry for the delayed response.
Obviously anti squat has its place in racing. How much, and what compromises you are willing to take depends on your car and type of racing.
Drag racing it is one of the primary concerns. Second only to a straight launch. Autocross and low speed road racing where it's more about
traction than exit speed it is still a high priority consideration.
High speed road racing or open road events where speeds rarely reach below 70mph......... there is much more important things to worry about.
With loose surface racing, I have no idea. Never really played like that although it does seem fun  . I would guess it has no real effect until
you sweep the track down to the hard pan.
In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle (pinion trying to turn up on
acceleration). This is why you generally end up with a setup like the first diagram I posted. The top link pulls straight back on the chassis (no
effect) and the lower link is pushed forward and up on the chassis.
The Afco article is talking about a 4 link with birdcages. You still need something to control pinion angle. They generally run a pull or push
bar
( http://www.racepartsoutlet.com/PartDetail.cfm/ID/3531 )
which is a "torque link" from axle to chassis. This uncoupled link is where they get most of their antisquat from. Angle it down and when
the pinion rotates it lifts the chassis up. Brake hop can become an issue of course which is why they sometimes add yet another uncoupled link to
control pinion angle on braking. Did I mention the oval track guys are well known for uncoupling forces and adding links?
So in the article posted using birdcages, the only antisquat you are getting is from the forward thrust of the tires which if the links are angled up
in front will try to lift the chassis as well. You wont see much more than 25% antisquat that way.
This is also how it works with a SLA IRS system. Yes Syd, it does work. Whether you opt to use it or not is your choice, but it definitely does
work.
If you take your upper and lower A-arms and angle the fronts upwards you get the same lifting effect when the wheels/hubs thrust forward. See attached
pic. Sorry for the lousy doodle but I'm too lazy to do a nice one
Are there more important things to worry about? Yes, but if you are drag racing or doing low speed road racing (probably what most locosts are doing)
and you need more traction I would opt for some antisquat.
With 4links its so easy to give yourself the adjustablility so why not? Adjustable length links and a couple more holes in your brakects is all you
need. Then you can play around and tune to suit each situation. I like versatilty in my toys.
Cheers.
 
Rescued attachment antisquat.JPG
"Our watchword evermore shall be: The Maple Leaf Forever!"
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3GEComponents
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| posted on 18/9/06 at 08:14 PM |
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Could mountain bike makers Ellsworth's instant centre suspension be adapted to work for anti squat?
They use it to control chain torque to prevent the suspension from bobbing when peddaling.
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C10CoryM
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| posted on 18/9/06 at 09:24 PM |
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quote:
Originally posted by jroberts
Could mountain bike makers Ellsworth's instant centre suspension be adapted to work for anti squat?
They use it to control chain torque to prevent the suspension from bobbing when peddaling.
Dunno, I have a Kona hardtail because Im way too lazy to XC a full suspension bike .
I suppose you could angle the lower link up a little but look out for brake hop. I would guess that braking is considered far more important. God
knows when Im at the mountains I use brakes far more than I need traction . Also I'd guess the downward push of the pedal would be stronger
than any upward force gained via antisquat. Since we are on the topic, I think I'll go riding.
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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Steve Morten
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| posted on 19/9/06 at 10:52 AM |
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Hi C10CoryM,
Your post is explains a lot to me thanks.
This bit especially:
"In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle (pinion trying to turn up on
acceleration). This is why you generally end up with a setup like the first diagram I posted. The top link pulls straight back on the chassis (no
effect) and the lower link is pushed forward and up on the chassis. "
I didn't realise the top link pulls all the time on accelaration. I thought it was just initially as the drive kicked in?
That might explain why some of the Irish autotesters are mounting the shocks forward of the axle rather then on top?
So if you have both links pointing up, then does the top link counteract by pulling the axle up, against the bottom link pushing the axle down into
the ground? and would you get more traction by pointing the top link down?
Stephen.
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C10CoryM
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| posted on 19/9/06 at 06:17 PM |
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Firstly I should be more careful with what I type.
"In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle"
In some cases depending on axle pivot location (leverage) and a few other factors you may actually get more antisquat from the forward thrust. I
don't think it is very common, but it is possible.
Anytime the tires are trying to accelerate the vehicle there will be torque trying to lift the front of the pinion. How much force depends on how
much acceleration there is. At 100mph in a locost there will be very little, but it will still be there. At 10mph in a 1000hp camaro with
slicks...... lots.
The autotesters may be moving there shocks for any number of reasons. Reduced wheel hop on acceleration would be my guess.
So we understand that there are two types of antisquat. One from the forward thrust of the axle (lets call this Jacking Anti Squat), and one from
the torque of the axle (Torque Anti Squat).
Lets start with JAS (and yes I am inventing abbreviations  )
4link suspension can be thought of as a swing arm. If you draw a line through your upper and lower link pivots in Side View you get your Instant
Center where the lines cross. This is also your Swing Arm length. This is the point where your rear axle pivots on while moving.
Due to the weight transfer/ height of CG if you draw a line from the rear tire and ground point to the CG height and front axle point you get whats
called the "100% line".
If your IC is below that line you get less than 100% AS. If above, more than 100%.
So with this, you can calculate what percent JAS your car has. I will let you draw out some examples of different link angles on your own and see
where the AS ends up.
So now lets look at the TAS which is simplest to think of as a torque arm with no other pinion angle control (say a 3 link or a 4link with
birdcages).
So when you step on the gas the big blue arm is trying to lift in front due to the torque of the differential. The front of the arm is fastened to
the sprung mass (chassis) The shorter the arm, the less leverage the arm uses against the differential and the further away from the CG (more
leverage). Now go back to the swing arm length/height of the 4link. This is your torque arm and is what acts on the CG to reduce AS. The shorter
it is, and the further away from the CG the more AS you will gain.
Ok, so that's looking at the two AS as uncoupled forces. Now if you try and think about how a 4link locost with solid axle brackets it gets
really complicated really fast. Now that the two forces are coupled they fight each other, and help each other. To be honest, I don't think I
could reliably calculate out the forces involved. You can see why un-coupling the AS from the swing arm is so popular.
It allows you to have your SA exactly how you want it, while being able to tune the AS accordingly.
After all that, I want to say again that everything is a compromise. Short SA have some major flaws, specifically wheel hop on braking.
Not going to re-read that so I hope I have done OK .
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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procomp
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| posted on 20/9/06 at 07:28 AM |
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Hi that sounds like a perfect description of what i also belive to be true about antisquat.
The only thing i would add further is that to get this lot working in a locost type setup is that it needs a lot of playing with the dampers on the
rear to get the best controle of the axle movment and espesialy when you start to get towards the point of wheel hop under braking.
I knew this would be an interesting debate.
cheers matt
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