My brain is on holiday this weekend so rather than think it through I thought I would get someone else to think for me
so here goes: If anti-squat improves traction does anti-dive similarly improve braking?
Hi
My brain is on holiday this weekend so rather than think it through I thought I would get someone else to think for me so here goes:
If anti-squat improves traction does anti-dive similarly improve braking?
as far as i know (which could be wrong)
anti dive is the same kind of thing as anti squat, but for for braking. it stops to front of the car dropping down under braking
Hi, Blakep82 is right, it is where suspension geometry is used to convert the forward dive motion of the body into a vertical movement. The anti
squat is the same on the rear - the suspension geometry converts the squatting of the rear under acceleration into vertical force that raises the
rear.
hope this helps
Steve
So from the above if the body is forced to rise on braking the reaction will be to force the wheels down increasing braking ability.
thats not the way i see it, you cant change the amount of weight on the wheels. All you can do is prevent (reduce) the nose rising or falling and thus maintain better geometry and contact.
thats not totally true...
if a car dives his centre of gravity moves forward..
and thus increases the weight on the front wheels...
while accelerating the weight trasfers to the rear... thats the reason that a FWD cant accelerate as fast as a RWD.....
Tks
Anti-dive is only to be used with caution -- it can cause the suspension to go solid under braking cause wheel patter. It also has major effects on
steering geometry --ie castor and bump steer and toe in
Anti squat is useful in small amounts ---
surely having the front end of the car dive a little must be benificial? as was said previously the weight transfers onto the front wheels, increasing
the grip, increasing braking ability and making the turning better because the front wheels have more grip?
anyone care to enlighten me?
Matt
I didn't say its favourable i only say that it happens...
if the weight transfers it means you loose grip on the rear wheels...
Tks
The question remains - do you stop quicker with anti-dive or without it.
when you brake and you car dives, to a point this is beneficial as you have good contact between the tyre and road (largely also affcted by camber)
but as braking forces cause the front to dive they also lessen the forces on the rear. This decrease in the forces pushing the rear tyres onto the
ground will effectively decrease the effectiveness of the rear brakes (rear wheel lockup). This is more controlable than front wheel lockup but not
ideal in any car.
Britishtrident is right in saying that it is to be used with caution but part of the reason for anti dive is so that the suspension is allowed to
continue to do it's work in absorbing bumps etc during braking rather than the shocks and springs compressing, going solid while the front end
dives and the tyres bounce from bump to bump causing a skid.
regards
Steve
Anti-dive does not change the weight transfer, weight transfer is a function of the location of CoG (vertical and horisontal) in relation to the
wheels. Anti-dive only "carries" a portion of the weight during braking instead of deplacing the springs, similar to anti roll bars only
resisting body roll, not weight transfer to the outside wheel.
Both anti-dive and ARBs have unwanted side effects, so their use/dimensioning should be made with care.
I would personally avoid very much anti-dive.
I don't know all the techy wording for this, but there are two things:
1) Dive shifts weight forwards helping braking (as has already been said)
2) Retaining compliance in the front suspension when braking reduces the tendency to lock wheels. Anti-dive can under some circumstances cause wheel
locking on bumpy surfaces, when no anti-dive leaves wheels able to be properly controlled by dampers etc.
Having dampers that respond differently in two wheel bump to single wheel bump, and even roll, would be an interesting development, but out of our
budgets!!
As has been said already Anti dive dosen't change weight tranfer -- it can't re-write old Newtons laws.
With anti-dive the only difference is that some of the weight transfer is taken by the wishbone pivots not the spring or damper.
Some dive has some advantages --- for example it generates aerodynamic down force
(my way of looking at it)
Lateral weight transfer:
The distance between CoG and rollcenter (RC) determines how much of the weight transfer is taken by the springs (causing roll), and how much is taken
"stiff" by the wishbones. (If the CoG is a distance 1 from the ground and the RC is 1/3 from the ground, 2/3 of the wieght transfer is taken
by the springs, the rest goes stiff trough the wishbones)
The same reasoning can be made for longitudal weight transfer: The % of "anti" determines how much is taken through the stiff suspension
components.
I guess that 100% anti is not good because sudden changes in weight transfer cause sudden load changes on the wheel that can break traction.
Springs/dampers will smooth things out.
Anti-squat first became fashionable in the late 1960s. Jaguar took the plunge introduced a little anti-squat on the on the original Mk1 XJ6 it worked
fairly well. Since them most softly sprung luxury RWD saloons have had anti-squat, and increasingly some anti-dive on this type of vehicle it works
well.
Always with an eye to developments Chapman dictated that the Lotus 72 design were to have generous ammounts of both anti-squat, both were removed
pretty quickly at the drivers request.
Look at modern F1 cars, they pull 3g but can you see any noticeable anti-dive inclination of the front wishbones ?
Anti-dive has a big hidden disadvantage that anti-squat dosen't suffer from ---- it plays havoc with the steering geometry particularly caster,
bump and roll steer.
[Edited on 1/5/07 by britishtrident]
During braking the front tyre contact patch becomes the point through which the braking force is applied which can be represented as a moment about
the C of G plus an applied force that represents the general retardation. In normal suspensions the moment causes the front suspension to dip but as
the retardation forces is along the line of the wishbone pivots there is no other vertical loads applied to the front suspension as a result of the
retardation forces.
For anti dive suspensions the same load is applied to front supspension as a resut of the moment, but the retardation force is now a force that is
applied at an angle to the wishbone pivots and therefore can be resolved into a force along the pivot as well as a force perpendicular to it. This
perpendicular force resists the load that results from the moment. Therefore on an anti dive suspension the load on the front is less and hence at the
extreme allows better braking due to the systems ability to follow the bumps in the road.
Note however that as the frictional force between the tyre and the road is generally related to the applied load, anti dive systems will have less
grip in the same circumstance and therefore more likely to skid.
quote:
Originally posted by dnmalc
Therefore on an anti dive suspension the load on the front is less ...
Johan
what you have in your equation is the load transfer that results from the moment created by the moment about the C of G. If what you have indicated
was all that was concerned there would be no forces acting to prevent the front dipping.
The whole point about an anti dive system is that the wishbones are inclined and when you consider the applied force they produce a counter load .
I said
quote:
Originally posted by Ivan
Hi
My brain is on holiday this weekend so rather than think it through I thought I would get someone else to think for me
If anti-squat improves traction does anti-dive similarly improve braking?
quote:
Originally posted by dnmalc
Johan
what you have in your equation is the load transfer that results from the moment created by the moment about the C of G. If what you have indicated was all that was concerned there would be no forces acting to prevent the front dipping.
The whole point about an anti dive system is that the wishbones are inclined and when you consider the applied force they produce a counter load .
quote:
Originally posted by Johan
What I want to point out is that if you break with a certain retardation this will result in a weight transfer (depending only on wheelbase and CoG hight) that will have to be carried by front wheels contact patches. No antidive can make this weight transfer smaller.
[Edited on 5/5/07 by Johan]
It depends on your camber curves. If you have a lot of camber compensation, as the nose drops, the tires camber in and you end up riding on the edge
of your tires. In that case, yes, in a straight line, anti-dive would help. BUT, if you're in a turn, the effectively stiffened suspension,
it'll cause more understeer. Sorry, there is no black-and-white answer to this.
And regarding some earlier comments, suspension design has nothing to do with weight transfer. The same force moves forwards under braking regardless
of anti-this or that. Oh sure, your CG cants forward maybe 1/8" but that's not going to measurably matter.
Heh heh all this brings me back to the lively anti-squat debates on here!!!
Whatever the science of the matter (all of which I understand and will not argue with! ) I could always get faster starts from a standing start in my
grasser using PRO-squat geometry, not anti-squat!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Anti-squat was great on a dry, flat track, but on anything with
bumps and water on it, pro-squat worked better...................................
Regarding anti-dive:
Am I being stupid (I don't think so!!! ) in my assumption that you are effectively jacking up the front of the car under braking, by transferring
a proportion of the longitudinal force generated by the contact patch and brakes, into a load acting along the control arm/wishbone/tension
strut/compression strut etc etc etc...................................
In which case, you are therefore effectively reducing the load seen by the spring and damper, hence the lack of dive for the same weight
transfer..............................
In which case, how is this good for braking???????????????? We know the overall weight applied to the contact patch does not change, that is dictated
by the weight of the vehicle, the c of g and the deceleration.
Which means that instead of applying all that load through a nice spring and damper combination, you are now applying a percentage of it through a
rigid metal strut with no compliance whatsoever, which means that any undulation in the road surface is MORE likely to cause lockup and skidding as
the load at the contact patch will vary more rapidly and in a less controlled fashion........................
which may well be why F1 don't use lots of anti-squat!!
Don't think so Nat - if you pivoted your wishbones on ballraces (perfect ones of course with no friction) you'd still get anti- dive but
nothing's locking up, it's not moving because the force is perpendicular to the available movement. So the suspension would still work for
bumps :^)
Bob
PS I never considered anti dive or squat for my car - the low CoG does the job nicely, even with very low rate springs!
quote:
Originally posted by NS Dev
...instead of applying all that load through a nice spring and damper combination, you are now applying a percentage of it through a rigid metal strut with no compliance whatsoever, which means that any undulation in the road surface is MORE likely to cause lockup and skidding as the load at the contact patch will vary more rapidly and in a less controlled fashion........................
quote:
Originally posted by kb58 as the nose drops, the tires camber in and you end up riding on the edge of your tires. In that case, yes, in a straight line, anti-dive would help
quote:
Originally posted by sebastiaan...2) weight transfer due to the different rake angle of the vehicle....
Sebastiaan
quote:
Originally posted by kb58...Oh sure, your CG cants forward maybe 1/8" but that's not going to measurably matter.
quote:
Originally posted by Bob C
Don't think so Nat - if you pivoted your wishbones on ballraces (perfect ones of course with no friction) you'd still get anti- dive but nothing's locking up, it's not moving because the force is perpendicular to the available movement. So the suspension would still work for bumps :^)
Bob
PS I never considered anti dive or squat for my car - the low CoG does the job nicely, even with very low rate springs!
Hah - had another look & I guess I did get wrong end of stick. I still don't see a problem though - OK the slanty pivots resolve deceleration
into a vertical jacking force - this force is fixed & continuous, specifically NOT proportional to displacement, therefore will not give rise to
undamped oscillations - it's like fixing a balloon to the front of the car, won't affect it's dynamic behaviour at all, just the ride
height (????)
CHEERS
bOB
quote:
Originally posted by Johan
And regarding
quote:
Originally posted by sebastiaan...2) weight transfer due to the different rake angle of the vehicle....
Sebastiaan
kb58 sums it up for me:
quote:
Originally posted by kb58...Oh sure, your CG cants forward maybe 1/8" but that's not going to measurably matter.