78 replies to this topic

[meb58]

Do we like anti-dive or anti-squat?

Aside from my own driving observations, anti dive/squat seem to ruin the purity of weight transfer between body and spring/damper. I think I understand anti is a program goal when comfort is a concern/priority, but from a pure racing perspective this type of geometry seems to corrupt handling and feel.

[gruntguru]

Do we like anti-dive or anti-squat?

Aside from my own driving observations, anti dive/squat seem to ruin the purity of weight transfer between body and spring/damper. I think I understand anti is a program goal when comfort is a concern/priority, but from a pure racing perspective this type of geometry seems to corrupt handling and feel.

Dive and squat (pitching) is detrimental to ground effects.

[Greg Locock]

There are circumstances in which antiX can be useful, for instance drag racers use it to maximise rearward load transfer at takeoff, paying the price later on when the thrust has dropped off a bit. A reasonably powerful road car with no antisquat might be a rather inelegant thing to drive, but we used to have a 'thing' about zero pitch changes during gear changes, our new IRS doesn't allow that and I can't say that anybody who didn't know ever noticed the difference.

Antidive seems to offer little benefit for road cars, other than those with high CGs or very soft suspensions. The springs are usually enough to keep the pitch angles under control.

[meb58]

I understand the two examples Greg, thanks.

gruntguru,

...but wouldn't a pure race car - ground effects as well - handle poorly with anti? Don't anti-dive/squat limit (bad word but I have no other) initial weight transfer? The feeling I get upon initial turn-in is vague steering followed by fairly quick tire loading - off throttle. I can get around this by keeping on the throttle but there are times when I need to feather the throttle and the feeling is a little disconnected...vague. Mark A. helped me thru a little of this...if I remember softer front springs was but one bit of advice but to my novice brain this might perpetuate the duration of anti-dive?

EDIT: for a frame of reference, I installed a much stiffer bushing in the LCA and although it does not change geometry, side view RC at rest, it does resist dive compared with the stock bushing.

Funny how we learn something new and try to apply it to the very first scenario that seems to fit. The Brawn team were having trouble getting heat into their tires...too much anti I mused...don't take this seriously.

Edited by meb58, 23 June 2009 - 12:40.

[DOF_power]

Do we like anti-dive or anti-squat?

Aside from my own driving observations, anti dive/squat seem to ruin the purity of weight transfer between body and spring/damper. I think I understand anti is a program goal when comfort is a concern/priority, but from a pure racing perspective this type of geometry seems to corrupt handling and feel.

The active ride cars had advanced active suspensions with reduced dive, squat and roll to 0. They could even make the car roll into a corner like a motorcycle.

It control directly and/or indirectly a lot of things, like the camber, caster, toe, ride height to each corner, rake angle, cross-weight, center of pressure, center of gravity, underbody downforce and wings AoA, it peeled the drag on the straight and increased downforce on the corners.

http://www.youtube.c...feature=related

[Greg Locock]

The active ride cars had advanced active suspensions with reduced dive, squat and roll to 0. They could even make the car roll into a corner like a motorcycle.

You keep mentioning that. The only drivers who liked it were Volvo evaluators, as it gives improved ride comfort for passengers (less head toss).

[murpia]

Don't anti-dive/squat limit (bad word but I have no other) initial weight transfer?

I would have thought they would increase the (rate of) initial weight (load) transfer, as there is less requirement for the sprung mass to move before contact patch vertical force can change (either transiently through damper velocity or quasi-statically through spring compression).

However I fully accept that you might not be able to actually 'feel' it, and therefore make use of it...

Regards, Ian

[meb58]

I was making an uneducated assumption about weight transfer...I assume that weight does not transfer - momentarily and based on decel Gs - which is why I get that vague feeling. My thinking, which may be wrong, is if this were not so I wouldn't get that vague feeling along with a little initial understeer.

Also, if I draw the geometry in sideview I can see how some folks might use the word 'locked out' to describe what happens in anti-dive. I think this term is probably wrong but unfortunately helps one to see this action in his mind's eye. 'locked out' probably propigates some really bad notions about anti-dive...

[DOF_power]

You keep mentioning that. The only drivers who liked it were Volvo evaluators, as it gives improved ride comfort for passengers (less head toss).

And the only driver who liked the early mid-engined cars was Rosemeyer.
So your point would be ?!

[Greg Locock]

And the only driver who liked the early mid-engined cars was Rosemeyer.
So your point would be ?!

My point is that it offers no performance benefit in its own right according to performance oriented drivers, and therefore, like many of your over aggressively stated opinions is irrelevant to the rational discussion in progress.

meb - antidive does lock suspensions up. It is not a bad notion at all.

[murpia]

meb - antidive does lock suspensions up. It is not a bad notion at all.

I've often wondered if this effect largely goes away with flexure joint suspension. It must mainly be down to joint friction in the first place.

Regards, Ian

[Greg Locock]

I've often wondered if this effect largely goes away with flexure joint suspension. It must mainly be down to joint friction in the first place.

Let's take a simple double wishbone. Parallel body end mounts in side view. The suspension is free. Turn the top wishbone by 90 degrees about the Y axis. The suspension is now locked. In between those two extremities there must be a sliding scale of behaviour, accommodated by moving the flexure points along their hinge lines (ie axial thrust on rubber bushes, shear on flex joints).

[DOF_power]

My point is that it offers no performance benefit in its own right according to performance oriented drivers, and therefore, like many of your over aggressively stated opinions is irrelevant to the rational discussion in progress.

meb - antidive does lock suspensions up. It is not a bad notion at all.

What this B* with no performance benefit.
The active suspensions gave those cars an estimated 2 to 3 extra seconds per lap.

You must be confusing efficient implementation of the technology with the technology efficiency.


Who are these performance orientated drivers ?!

[meb58]

Greg, murpia

I think you described what I am feeling and what is happening...the geometry hasn't changed per se with the addition of the motorsport bushing, but the stock bushing allow a little more movement...if I were to guess I would say that under braking - keeping in mind the the front portion of the LCA is fastened via a ball joint - the rear portion of this arm raises a bit when compared to the motorsport bushing.

The LCA is a wishbone...the front inner portion is attached via a ball joint, the rear is a stud that moves freely within an oil-filled bushing(stock) and the third point of restraint is the outer ball joint.

Regarding friction...this arm moves in a fairly peculiar way and friction does show up at the extremes of travel. The front of the LCA has to rotate over the face of a ball joint - the actual pivot being in the center of the ball joitn I believe. As the LCA goes thru this motion, the rear stud moves in and out of the rear bushing while changing axis slightly. If I weren't such a moron working with computers I would include a little video of this movement. I still prefer a pencil.

I cannot imagine the differences between the two are more than a few degrees but the location of the side view RC is perhaps influential.

Edited by meb58, 25 June 2009 - 12:38.

[murpia]

Let's take a simple double wishbone. Parallel body end mounts in side view. The suspension is free. Turn the top wishbone by 90 degrees about the Y axis. The suspension is now locked. In between those two extremities there must be a sliding scale of behaviour, accommodated by moving the flexure points along their hinge lines (ie axial thrust on rubber bushes, shear on flex joints).

Agreed, but I'm not 100% convinced that this is the cause of the 'harsh' / 'dead' feel effect attributed by many to anti-dive geometry.

Consider instead a 2CV style trailing (well leading really) arm front suspension. We are taught by many sources that a double wishbone suspension may be reduced to a side view instant centre (i.e. a equivalent single leading arm) when designing 'anti' properties.

I see no locking effect as you describe above in this scenario.

If we want to design our 2CV for 100% anti-dive (consider a hypothetical 2CV with front brakes only, outboard, to simplify the analysis), we just need to place our single trailing arm pivot on the line connecting the contact patch to the centre of gravity. At least this is what my memory of the maths and diagrams in several sources tells me to do. Any braking force induced moment at the centre of gravity is matched by the anti-dive moment.

We DO have wheel movement forward in bump, which I understand is an issue for many applications. But probably not for racecars on smooth circuits.

I still strongly believe that much of the anti-anti (!) anecdotal preference is down to suspension friction. The same goes for high roll centres, but that's a different argument...

Regards, Ian

[meb58]

murpia,

When you write 'friction' do you literally mean any kind of friction that slows the operation of spring and dampers - pure weigth transfer if you will? ...excluding anti-dive geometry? Written another way, if we had rod ends at every joint there would be very little friction...nothing that road going fare would care about anyway...

I know nothing about 2CV trailing arm set ups so this question may seem odd here...if we have 100% anti-dive in any scenario wouldn't the need for suspension be eliminated? Wouldn't we essentially have an invisible stick as suspension with zero weight transfer?

[murpia]

When you write 'friction' do you literally mean any kind of friction that slows the operation of spring and dampers - pure weigth transfer if you will? ...excluding anti-dive geometry? Written another way, if we had rod ends at every joint there would be very little friction...nothing that road going fare would care about anyway...

By friction I do mean friction in the spherical joints of the suspension, whether rod ends or staked spherical joints.

They may seem free in the paddock but put several kN of force through them under braking and they are anything but free... The benefit of flexures is measureable on both the K&C rig and the 4/7 post rig... The prime design purpose of spherical joints is precise positional control (i.e. no slop). There are low-friction designs out there using ball elements between the spherical and the housing. They are bigger, heavier and costlier, and therefore underused in racecars...

I know nothing about 2CV trailing arm set ups so this question may seem odd here...if we have 100% anti-dive in any scenario wouldn' the need for suspension be eliminated? Wouldn't we essentially have an invisible stick as suspension with zero weight transfer?

Don't confuse 100% anti dive with zero load transfer. That can only be achieved with a centre of gravity at ground level. 100% anti-dive just transfers the same load through the linkages instead of the springs.

I suggest you have a read of Gillespie, it has a good 'conventional' treatment of antis.

Regards, Ian

[Greg Locock]

Yes, I think if you wanted to replace the suspension by a stick with one end pointing at the cg, and the other at the CP, and a spring, you'd have a suspension of sorts, with 100% a/d. You could consider some rear suspensions to be little more than that.

Ian, I'm not convinced that friction is the sole bad guy, simply because rubber bushes don't have much friction, they have damping but that ain't the same thing.

DOF_power, I meant that there was no improvement in handling performance by leaning the car into the turn. Do try and keep up old chap. The evaluators were the usual suspects, Becker, Wright, Miles etc from Lotus, plus the Michelin guys, plus the Volvo ones.

[NRoshier]

I was under the impression that the percentage of anti is only fixed in steady state. When the car is moving all over the place then the kinematic effects are much harder to predict...or am I barking up the wrong tree?

[Greg Locock]

I was under the impression that the percentage of anti is only fixed in steady state. When the car is moving all over the place then the kinematic effects are much harder to predict...or am I barking up the wrong tree?

Yes it moves around a lot as the geometry changes, rather like the roll centres. Just like roll centres, it is telling you something, and directional changes are helpful,(I want more, I want less) but not worth going to the barricades for specific quantities. If your cg is relatively low it matter less and less.

I suppose, like rch, it will give more initial bite, but since that is in advance of the pitching of the car there may be some funny business, ie it might need you to come off the pedal and back on.

[Lukin]

I always consider anti-dive (and anti-squat) to be another way of supporting the car rather than spring, damper etc. Realistically you need *something* to stop the car smashing into the ground. I figure that the characteristics of the tracks (track grip, bumps etc) affect the ability of the car to deal with disturbances and as that varies the amount of geometric and elastic changes.

I wrote something on another forum a while back, I will just steal it from there...

"As most people have pointed out, anti-dive dictates how much longitudinal load transfer goes through the sprung mass and how much goes through the spring and how much through the suspension links. The way I look at it, the transmission through the springs occurs at the wheel rate (2-4 Hz) while the transmission through the suspension links occurs at a higher rate (8-12 Hz) so any disturbance (bumps) will cause greater change in the grip at the contact patch.

The next point is why do we care about anti-dive and pitching? I've found drivers are real sensitive to pitch under brakes, so we do what we can to reduce it. Not always the amount, but the rate of pitch as someone alluded to. Excluding the loss of driver confidence it can create, too much pitch can increase rear locking and entry oversteer off the brake.

If the track was perfectly smooth you could run a lot of anti-dive for braking support and a soft front spring for front grip and performance over the kerbs.

Most tracks aren't smooth, so the more anti-dive we run, the more prone the car is to locking the inside front and pushing wide on corner entry as the load on the inside front tyre is varying too much over the bumps and disturbances in the road. Off course anti-dive effects the corner entry phase, unless of course you are off the brakes before you start to turn!

So with that in mind you take anti-dive off for bumpy circuits and give the car more front spring (if inside front locking and understeer is a drama over bumps, adding front bar won't be the fix as it will introduce co-dependance between the front tyres you don't really want). This comes back to transmission frequencies, it's better to have disturbances at 2 Hz than 10 Hz if your the tyre!

This hurts the roll distribution front to rear but overall you need to get the car to the corner (without the front tyre on fire and with the car on line) so you take what you can get. It's not perfect but it never is.

If you talk to drivers, they feel it as harsh and say that the more anti-dive you run, the harder it is to unlock a front lock up and you lose feel/compliance as you release the brake and reach full steering lock to the apex."

[murpia]

I was under the impression that the percentage of anti is only fixed in steady state. When the car is moving all over the place then the kinematic effects are much harder to predict...or am I barking up the wrong tree?

Yes, I think you are correct. Once the sprung mass CoG moves relative to the unsprung masses, or you introduce roll, then the percentage of anti is no longer fixed and probably different side to side. Percent antis are like the kinematic roll centre height, easy to quote and draw but of dubious value once the vehicle starts moving around much.

Nobody ever seems to complain about high roll centres deadening the car mid corner or locking up the suspension under high lateral loads. So, I have a suspicion that humans are less able to feel longitudinal g than lateral g or yaw rate, at least when sitting on a seat like in a racecar. They rely on cues such as vehicle pitch to assess braking grip. Maybe if there was some kind of longitudinal force feedback through brake pedal, like there can be for lateral force through the steering, then large amounts of anti-dive would be more acceptable?

Regards, Ian

[Greg Locock]

Yes, I think you are correct. Once the sprung mass CoG moves relative to the unsprung masses, or you introduce roll, then the percentage of anti is no longer fixed and probably different side to side. Percent antis are like the kinematic roll centre height, easy to quote and draw but of dubious value once the vehicle starts moving around much.

Nobody ever seems to complain about high roll centres deadening the car mid corner or locking up the suspension under high lateral loads. So, I have a suspicion that humans are less able to feel longitudinal g than lateral g or yaw rate, at least when sitting on a seat like in a racecar. They rely on cues such as vehicle pitch to assess braking grip. Maybe if there was some kind of longitudinal force feedback through brake pedal, like there can be for lateral force through the steering, then large amounts of anti-dive would be more acceptable?

Nice point, but most cars have low RCH/track, so perhaps we haven't really explored the envelope.

[cheapracer]

I always consider anti-dive (and anti-squat) to be another way of supporting the car rather than spring, damper etc. Realistically you need *something* to stop the car smashing into the ground. I figure that the characteristics of the tracks (track grip, bumps etc) affect the ability of the car to deal with disturbances and as that varies the amount of geometric and elastic changes.

I wrote something on another forum a while back, I will just steal it from there...

"As most people have pointed out, anti-dive dictates how much longitudinal load transfer goes through the sprung mass and how much goes through the spring and how much through the suspension links. The way I look at it, the transmission through the springs occurs at the wheel rate (2-4 Hz) while the transmission through the suspension links occurs at a higher rate (8-12 Hz) so any disturbance (bumps) will cause greater change in the grip at the contact patch.

The next point is why do we care about anti-dive and pitching? I've found drivers are real sensitive to pitch under brakes, so we do what we can to reduce it. Not always the amount, but the rate of pitch as someone alluded to. Excluding the loss of driver confidence it can create, too much pitch can increase rear locking and entry oversteer off the brake.

If the track was perfectly smooth you could run a lot of anti-dive for braking support and a soft front spring for front grip and performance over the kerbs.

Most tracks aren't smooth, so the more anti-dive we run, the more prone the car is to locking the inside front and pushing wide on corner entry as the load on the inside front tyre is varying too much over the bumps and disturbances in the road. Off course anti-dive effects the corner entry phase, unless of course you are off the brakes before you start to turn!

So with that in mind you take anti-dive off for bumpy circuits and give the car more front spring (if inside front locking and understeer is a drama over bumps, adding front bar won't be the fix as it will introduce co-dependance between the front tyres you don't really want). This comes back to transmission frequencies, it's better to have disturbances at 2 Hz than 10 Hz if your the tyre!

This hurts the roll distribution front to rear but overall you need to get the car to the corner (without the front tyre on fire and with the car on line) so you take what you can get. It's not perfect but it never is.

If you talk to drivers, they feel it as harsh and say that the more anti-dive you run, the harder it is to unlock a front lock up and you lose feel/compliance as you release the brake and reach full steering lock to the apex."

Great post Lukin

[NRoshier]

From Lukin's interesting post I wonder if the race drivers he is used to (assuming this is based on his work) are more sensitive to pitch as they are driving at speed, heavily strapped into a race seat?
Is there a transition period between the anti being active and then not active?

[meb58]

Greg,

Post #20, your second sentence, bingo!

Greg, Lukin, NRochier,

I try to enter a turn in the classic manner, slow in fast out. However, depending on the type of turn - radius and speed - I may keep my foot on the brake pedal for a moment to help with rotation. Pedal force is always decreasing in this instance. In other circumstances I may use a drop throttle technique - somewhat abrupt but in control. Either of these techniques produce that vague feeling, like driving on ice for a few fractions of a second - I don't mean that the car slides just that steering on ice is creepy, vague.

So I am assuming that anti-dive does work even off brakes under some circumstance(?) but for sure under braking in a straight line. And wouldn't the anit-dive effect be differnt side to side as the car pitches since the side view RCs are not connected?

This is the only portion of my track driving experince that literally spooks me and so, I enter turns much slower than I should. I may need to soften the front springs a hair...or play with rebound damping.

Great stuff here!!!

Edited by meb58, 26 June 2009 - 12:40.

[cheapracer]

So I am assuming that anti-dive does work even off brakes under some circumstance(?) but for sure under braking in a straight line.

Your not only thinking anti D works just on braking are you? When you turn the front wheels the anti D (if any) comes into play as the car (literally) tries to ride over the resistance offered.

[Lukin]

They rely on cues such as vehicle pitch to assess braking grip. Maybe if there was some kind of longitudinal force feedback through brake pedal, like there can be for lateral force through the steering, then large amounts of anti-dive would be more acceptable?

For pure braking, the most common sensor is the nose. If you smell tyre smoke, release the brake!

[Lukin]

I try to enter a turn in the classic manner, slow in fast out. However, depending on the type of turn - radius and speed - I may keep my foot on the brake pedal for a moment to help with rotation. Pedal force is always decreasing in this instance. In other circumstances I may use a drop throttle technique - somewhat abrupt but in control. Either of these techniques produce that vague feeling, like driving on ice for a few fractions of a second - I don't mean that the car slides just that steering on ice is creepy, vague.

So I am assuming that anti-dive does work even off brakes under some circumstance(?) but for sure under braking in a straight line. And wouldn't the anit-dive effect be differnt side to side as the car pitches since the side view RCs are not connected?

This is the only portion of my track driving experince that literally spooks me and so, I enter turns much slower than I should. I may need to soften the front springs a hair...or play with rebound damping.

The anti-dive would be different side side, but unless your running 5 lb/in springs the amount of travel and the next change in IC shouldn't be huge. Anti-dive squat works any time there is a non-zero longitudinal acceleration. Same as RCH effects the lateral load transfer characteristics. So realistically it works all the time unless your crusing (which I sincerely hope your not).

So what exactly do you feel? Talk us through the corners from the time you hit the brake to the time you get to full throttle for any variety of corners. Also what sort of car and approximate stiffness?

[phantom II]

C4 Corvettes( 84 to 96) had the most anti-dive and squat that I have ever seen. They retained the 'E Type' rear suspension from the C3 but it was beautifully made from forged aluminum parts, including the drive shaft. The side shaft was the upper link. I owned a 86(First Vette with ABS), 88, 90, 92, 93 ZR1, and a 95. The geometry changed twice and the anti dive was reduced in 86.
Late braking traditionally loaded the suspension which caused binding in roll when the turn was initiated. Once the braking was done, the suspension unloaded and performed much better in a steady state turn but the transition was tricky. Ask any NSX driver. Vette handling was always good on smooth courses during all those years, but by 96, it was outstanding. I think chassis flex was part of the suspension geometry. The most noticeable feature was the constant pitch which was comforting and predictible. It took the C5 about 3 years to match the 96 GS Corvette 's handling. People still race those old 87-88 light weight Challenge Vettes.
The C6 has much reduced anti-dive and squat and pitch changes are noticeable and late braking is always accompanied by an abrupt, though well damped, pitch change with no adverse effects. The C6 ZR1 is a vast improvement over the 06 Z06 and they say the new Grand Sport is even better. All to do with spring rates and damping. They all retain composite transverse leaf springs.
My roadster has zerosanti- dive and squat, low CG and low RCs, no ARBs, zero Ackerman and scrub, 1800lbs and 450 hp and it seems to work very well but I assist the geometry with my left foot on the brake.

[meb58]

Lukin,

Greg's #20 points to some of the equation but as well, phantom II's Late braking paragraph.

The car is an 05 JCW Mini. The mini is very easy to control...too easy perhaps since it can nearly be placed and replaced at speed. That's another story. The suspension package is thru BMW and the rates are not advertised, but I suspect they are in the 250 - 280 lb/in or 5 - 5.5kg/mm range with front and rear rates being nearly the same. This car weighs 2,563 lbs with a half tank and I weigh about 170 lbs.

As phantom II wrote, the car does bind or lock up under any trail braking - which I prefer not to use but occasionally do. Those occasions are while try to protect my corner so I have to go deep.

I also use very subtle on and off throttle positions to point the car thru some turns as a way of balancing the chassis and this works with 63% of the weight over the front drive axle.

These two examples seem to invoke anti-dive like a switch each time weight is thrown - a relative term - on the front axle. Again, I cannot say that grip is diminished, just that, and I am changing terms again, some of those tinlgy messages I expect to feel about tire loading and saturation suddenly disappear. It is creepy. There is no bind in the swaybar endlinks or other suspension components...that I know of...

Once on the throttle all is fine. I cannot say I would be any faster if the fidelity of the experince were improved, just that I might be less suspicous of what's next, if that makes any sense. I am begining to feel a little embarrassed about the level of detail discussed...at some point one might suggest, "listen you weenie, just go drive the car." And one wouldn't be wrong...

Edited by meb58, 26 June 2009 - 15:43.

[GrpB]

I think you could put front anti dive and rear anti lift into the same category of having to balance the reduced ability to deal with bumps (due to precession) with their ability to control pitch, with front anti lift and rear anti squat as pitch control without the negative effects in bump because of recession. Depending of course on the drive configuration or track specific requirements. I think that subjectively lots of geometric anti-dive can feel funny because the pitch rate of change (subjective assessment of) is not as consistent when controlled by geometry and suspension member/joint stiffness, as compared to pitch change controlled by spring/damper. Specially if you're braking in a straight line with little pitch, and then as you turn in it pitches and rolls on to the front outer because of a relatively soft spring rate. Nothing is free.

I think if I could, I would choose to minimze the use of precession based anti-dive for pitch if I really wanted to keep spring rates down but still maintain good subjective feel on the front, and would rather use something like anti-pitch torsion bars which coupled the sides together (LF-LR, RF-RR) to control pitch based on relative heights (cog, anti-X geometries) and wheelbase. Those would be really heavy though, probably would be better to use push/pull rods with spring/damper/linkage between them, like a monoshock front but coupling front/rear instead of side/side. This must already have been done before for something like off road racing where you want both good performance over bumps but still want to control pitch because of high cog and relatively soft spring rates, perhaps the performance increase is minimal with respect to the complexity or perhaps not so durable.

[gruntguru]

and would rather use something like anti-pitch torsion bars which coupled the sides together (LF-LR, RF-RR) to control pitch based on relative heights (cog, anti-X geometries) and wheelbase.

Third spring front and rear will produce a similar effect.

[meb58]

gruntguru,

You lost me...

[gruntguru]

gruntguru,

You lost me...

Third spring on the front is the invers of an ARB - it resists simultaneous bump on both front wheels thus providing a non-geometry form of anti dive.

Ditto for anti squat with third spring on the rear.

[murpia]

Third spring on the front is the invers of an ARB - it resists simultaneous bump on both front wheels thus providing a non-geometry form of anti dive.

Ditto for anti squat with third spring on the rear.

One criticism levelled against anti-dive is 'harshness over braking bumps'.

I would be very interested to know if anyone has compared anti-dive to a 3rd spring arrangement, for similar levels of front ride height compensation under braking.

Which was 'harsher'?

Regards, Ian

[Greg Locock]

One criticism levelled against anti-dive is 'harshness over braking bumps'.

I would be very interested to know if anyone has compared anti-dive to a 3rd spring arrangement, for similar levels of front ride height compensation under braking.

Which was 'harsher'?

Regards, Ian

A 3 spring system is basically like fitting stiffer road springs for pitch control. The main reason I experimented with mechanical a/d two years ago was to reduce impact harshness, which is not really affected overmuch by the road springs, the transmission path is via the bushes. So if I was designing a system that was stiff in pitch, but not harsh, I'd use stiff springs and no a/d. I'd also pay a lot of money for the bushes that control recession compliance at the wheel centre.

[gruntguru]

A 3 spring system is basically like fitting stiffer road springs for pitch control. The main reason I experimented with mechanical a/d two years ago was to reduce impact harshness, which is not really affected overmuch by the road springs, the transmission path is via the bushes. So if I was designing a system that was stiff in pitch, but not harsh, I'd use stiff springs and no a/d. I'd also pay a lot of money for the bushes that control recession compliance at the wheel centre.

The benefit of the third spring is softer wheel rates for a given level of pitch control. Of course the compromise is reduced roll stiffness.

[Petervl]

A 3 spring system is basically like fitting stiffer road springs for pitch control. The main reason I experimented with mechanical a/d two years ago was to reduce impact harshness, which is not really affected overmuch by the road springs, the transmission path is via the bushes. So if I was designing a system that was stiff in pitch, but not harsh, I'd use stiff springs and no a/d. I'd also pay a lot of money for the bushes that control recession compliance at the wheel centre.

What kind of suspension was this? I would say that the load path for a bump is more favorable for an anti geometry than a (3rd) spring, therefor I would think a anti geometry gives more tire compliance during bumps compared to stiff springs, I could be wrong though.

Edited by Petervl, 01 July 2009 - 11:39.

[Tony Matthews]

I thought this was an interesting system - I confess I can't remember where it originated, may have been Lola.

[murpia]

The benefit of the third spring is softer wheel rates for a given level of pitch control. Of course the compromise is reduced roll stiffness.

Actually I'd argue the complete opposite:

The benefit of the 3rd spring is a greater level of pitch control for equal wheel rates and no change in roll stiffness. Much like adding anti-dive and leaving the springs the same, hence my query.

What you do with the improved pitch control is a separate issue: lowering the ride height is the obvious choice for improved performance.

Also, I ought to avoid weasel words like 'harshness' and go straight to performance metrics:

I would be very interested to know if anyone has compared anti-dive to a 3rd spring arrangement, for similar levels of front ride height compensation under braking.

Which was faster, or had the lowest contact patch load fluctuations?

Regards, Ian

[meb58]

I am one of the uninitiated and so, that drawing gave me a headache ...and I draw for a living. I don't see the thrird spring, sorry...

Is there a more rudimentary way of describing the third spring?

Greg,

You seem to write replys that hit my thinking/queries spot on. I am keen to eliminate anti-dive, or in the least, reduce what has been added by the motorsport bushing so that I can use heavier springs. It was suggested I use softer springs but that direction seems all wrong to me.

[Tony Matthews]

I am one of the uninitiated and so, that drawing gave me a headache ...and I draw for a living. I don't see the thrird spring, sorry...

In the middle, where it says 'Optional third spring/bump rubber'. It is not a classic three-spring set-up, but came to light when I was searching for such an illustration.

[DaveW]

I thought this was an interesting system - I confess I can't remember where it originated, may have been Lola.

Tony, looks very like one version of an F3000 front, but I never saw the "optional 3rd". Neither do I recall the F3K rocker having such a large rising rate. Lola's F1 attempt, perhaps? A weakness of the layout is the high loads carried by the drop link sphericals.

[gruntguru]

Actually I'd argue the complete opposite:

???? You haven't argued the complete opposite at all. You have described the same thing with a stiffer setup.

Your quote
"The benefit of the 3rd spring is a greater level of pitch control for equal wheel rates and no change in roll stiffness. Much like adding anti-dive and leaving the springs the same, hence my query."

My quote
"The benefit of the third spring is softer wheel rates for a given level of pitch control."

Edited by gruntguru, 01 July 2009 - 22:54.

[gruntguru]

A weakness of the layout is the high loads carried by the drop link sphericals.

The drop links are only carrying ARB loads (+ 3rd spring if fitted) and only at about 1/2 the rate in the pushrods, so I wouldn't consider them highly loaded.

Can someone enlighten me - doesn't an ARB + 3rd spring (with the same wheel-rates) add up to the same thing as stiffer spring rates - therefore why use both?

[phantom II]

The 3rd spring is for aero loads.

The drop links are only carrying ARB loads (+ 3rd spring if fitted) and only at about 1/2 the rate in the pushrods, so I wouldn't consider them highly loaded.

Can someone enlighten me - doesn't an ARB + 3rd spring (with the same wheel-rates) add up to the same thing as stiffer spring rates - therefore why use both?

[phantom II]

Talking about LT5s, did you know Kimble? Was he any good as a artist? This drawing is in Dave McLellan's, "Corvette From the Inside".



Edit: Oops, wrong thread.

I thought this was an interesting system - I confess I can't remember where it originated, may have been Lola.

Edited by phantom II, 01 July 2009 - 23:28.

[gruntguru]

The 3rd spring is for aero loads.

If your saying there is a need on that particular car to readily add or remove the third spring - OK.

My question relates to a permanent installation - doesn't ARB+3rd spring add up to more wheel rate which could be acchieved with stiffer springs+(ARB or 3rd spring but not both)

Edited by gruntguru, 01 July 2009 - 23:41.

[phantom II]

That would be for ARBs in roll and 3rd spring in pitch, not both. Kakkenen wouldn't have been able to drive over the curbs so easily as he did with stiffer springs. 3rd springs are rising rates so that at low speed, the wheel rate is not effected that much.

If your saying there is a need on that particular car to readily add or remove the third spring - OK.

My question relates to a permanent installation - doesn't ARB+3rd spring add up to more wheel rate which could be acchieved with stiffer springs+(ARB or 3rd spring)