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How to drive a stiff or compliant car.


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#1 pbukovca

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Posted 13 January 2012 - 04:22

What is the difference in the way a stiff car or a compliant car is driven by the driver ? How can the driver control
a really stiff car on a bumpy track ? Does less stiff mean more grip but less handling so the car might understeer
and the driver have to change his driving style such as corner approach and maybe pick a new apex ?

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#2 cheapracer

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Posted 13 January 2012 - 06:12

pbukovca, your questions are too broad and simply impossible to answer considering the variables - you need to specify some tighter parameters or examples.....

#3 johnny yuma

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Posted 16 January 2012 - 00:39

pbukovca, your questions are too broad and simply impossible to answer considering the variables - you need to specify some tighter parameters or examples.....

Many manufacturers for years created softly sprung cars for understeer as it was thought the average driver was frightened of oversteer and would feel
more in control with understeer.Then most cars became front wheel drive and the understeer had to be tamed a bit.
The only way to get the old understeering beasties around a corner was chucking them at the corner and try to induce a little oversteer on exit.However
if you throw a decent handling RWD newer car into a corner too fast it may oversteer too much (unless electronic devices intervene...)

#4 cheapracer

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Posted 17 January 2012 - 09:25

Many manufacturers for years created softly sprung cars for understeer


Soft or stiff overall has nothing at all to do with under or oversteer although differences in soft and stiff between each end can have some effect.

#5 DaveW

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Posted 18 January 2012 - 09:45

What is the difference in the way a stiff car or a compliant car is driven by the driver ?

In a racing context, a "stiff" car can be run as stiff or as soft as you wish, depending on spring & damper settings & tyres. A "soft" car limits what can be achieved with spring & damper settings.

Generally, when converting a road car for racing, the primary "golden" rules are:

1. Use the roll over cage as the primary car structure to "nail" together the suspension elements. Even then it is usually worth seam welding existing welded joints.
2. Replace all suspension bushings by "proper" structural fittings (including the top mounts).
3. Replace engine mounts, etc. so the power train becomes integral with the spring mass.





#6 NeilR

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Posted 18 January 2012 - 12:20

very good point. I had looked at the question and considered spring rates and roll rates, but not structure.

#7 cheapracer

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Posted 18 January 2012 - 14:45

How can the driver control a really stiff car on a bumpy track ?


In my mind this question relates to suspension stiffness not chassis stiffness.


#8 pugfan

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Posted 18 January 2012 - 21:37

pbukovca, your questions are too broad and simply impossible to answer considering the variables - you need to specify some tighter parameters or examples.....


My first thought when seeing the topic heading was, with the steering wheel and pedals.

#9 Catalina Park

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Posted 19 January 2012 - 06:57

My first thought when seeing the topic heading was, with the steering wheel and pedals.

You have a very vivid imagination. My first thought was, turn the key.

#10 johnny yuma

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Posted 19 January 2012 - 08:00

I see this as a good topic.Why does a car have a suspension? Lets say historically primarily for comfort,then to keep all 4 wheels on the ground.How would a gokart handle on a bumpy track?
You need suspension travel for comfort,but this may lead to body roll ,and handling problems if independent suspension geometry causes positive camber on the weight bearing side during cornering.
Even current high performance versions of mass produced cars get bagged by road testers for having non-compliant ride comfort.That's the price you pay if the car can sit on 240kmh.
If your track car is jittery and unhappy on a surfaced but bumpy racetrack ,perhaps it is merely too hard sprung,inadequately damped,bottoming,or subject to bump steer because the steering/suspension geometry
is wrong by initial design or modified by misadventure.

#11 Kelpiecross

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Posted 20 January 2012 - 04:50

[quote name='johnny yuma' date='Jan 19 2012, 19:00' post='5485385']
I see this as a good topic.Why does a car have a suspension? Lets say historically primarily for comfort,then to keep all 4 wheels on the ground.How would a gokart handle on a bumpy track?

I have wondered why nobody seems to have ever at least tested a suspension-less car for circuit racing. There would still be some "suspension" in the tyres. The whole car could be much lighter and simpler without suspension. The type of car I am thinking of would be something like a simple clubman-style car.


#12 Warpspeed

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Posted 20 January 2012 - 08:20

Something similar to a no suspension vehicle happens when you solidly bottom out onto very hard bump stops at speed.
And nothing good has ever been said about what immediately followed.

The rally guys driving at highs speed on gravel, where yaw direction has absolutely nothing at all to do with vehicle direction, much prefer softer suspensions with plenty of travel.

#13 kikiturbo2

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Posted 20 January 2012 - 10:43

Something similar to a no suspension vehicle happens when you solidly bottom out onto very hard bump stops at speed.
And nothing good has ever been said about what immediately followed.

The rally guys driving at highs speed on gravel, where yaw direction has absolutely nothing at all to do with vehicle direction, much prefer softer suspensions with plenty of travel.


also, on tarmac, even though they run very low, and relatively stiff, they have amazing amount of drop, which they use to soak up the landings..

#14 cheapracer

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Posted 20 January 2012 - 11:26

I have wondered why nobody seems to have ever at least tested a suspension-less car for circuit racing. There would still be some "suspension" in the tyres. The whole car could be much lighter and simpler without suspension. The type of car I am thinking of would be something like a simple clubman-style car.


Williams tried it in testing, look on Youtube for "Gentleman lift your skirts".

F500 racers in the USA have to make do with a 3" rubber bush for suspension, that\s the rules.

#15 24gerrard

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Posted 20 January 2012 - 13:42

Williams tried it in testing, look on Youtube for "Gentleman lift your skirts".

F500 racers in the USA have to make do with a 3" rubber bush for suspension, that\s the rules.


F500 racers have to make do with a three inch rubber Cheapy?

Sorry I had to say it. :rotfl: :rolleyes:

Edited by 24gerrard, 20 January 2012 - 13:43.


#16 Paolo

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Posted 20 January 2012 - 16:49

Superkarts have no suspension, just a flexi chassis and tyre compliance, and they run F3 speeds on real racetracks.
I think the main reason why racecars have suspension nowdays is that rules mandate them.

#17 desmo

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Posted 20 January 2012 - 18:56

Superkarts have no suspension, just a flexi chassis and tyre compliance, and they run F3 speeds on real racetracks.
I think the main reason why racecars have suspension nowdays is that rules mandate them.


Indeed. Why else would there be rules mandating suspension unless the rulemakers considered the idea of suspensionless cars potentially advantageous? Rulemakers aren't in the habit of outlawing ideas with absolutely no potential merit.


#18 carlt

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Posted 20 January 2012 - 20:40

Rulemakers aren't in the habit of outlawing ideas with absolutely no potential merit.



What, like Forum Hosts ? :D :kiss:

#19 Kelpiecross

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Posted 21 January 2012 - 04:46

Williams tried it in testing, look on Youtube for "Gentleman lift your skirts".

F500 racers in the USA have to make do with a 3" rubber bush for suspension, that\s the rules.


Thank you Cheapy - very interesting.

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#20 cheapracer

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Posted 21 January 2012 - 06:44

F500 racers have to make do with a three inch rubber Cheapy?


No, Americans in general.

and happy New Year from China!


#21 Tony Matthews

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Posted 21 January 2012 - 09:37

Xin Nian Kuai Le!

#22 DaveW

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Posted 21 January 2012 - 10:29

Williams tried it in testing, look on Youtube for "Gentleman lift your skirts".

So did Lotus, with dynamic absorbers (mass dampers) fitted to the uprights. The car, tested at Donington, circuited surprising quickly, but absolutely destroyed its tyres.





#23 h4887

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Posted 21 January 2012 - 11:24

Xin Nian Kuai Le!

I'll have that with fried rice :wave:

#24 cheapracer

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Posted 21 January 2012 - 11:36

Xin Nian Kuai Le!


xin = new

nian = year

kuaile = happy

BTW, there is no high case letters in pinyin.


I'll have that with fried rice


or it can mean "cat".


#25 cheapracer

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Posted 21 January 2012 - 11:38

So did Lotus, with dynamic absorbers (mass dampers) fitted to the uprights. The car, tested at Donington, circuited surprising quickly, but absolutely destroyed its tyres.


Thanks Dave, interesting.

We will never know of course the greater majority of various things that teams try in testing.


#26 Engineguy

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Posted 21 January 2012 - 12:00

Superkarts have no suspension, just a flexi chassis and tyre compliance, and they run F3 speeds on real racetracks.
I think the main reason why racecars have suspension nowdays is that rules mandate them.

Firstly, a flexi chassis is suspension. If you double the tube diameter of the longitudnals and crossmembers and I think bumps would become a nightmare.
Secondly, the frame is free to articulate relative to a major portion of the sprung mass, the driver's upper torso and head.
Thirdly, the driver's body is compliant... i.e. the left front wheel may bump 20mm and the driver's upper torso and head may not even move.
In contrast, a car has it's sprung mass move as a solid single unit, even the driver if he's strapped tightly into a racing seat.
That's my view, for what it's worth.

Having said that, if a race track is smooth enough, suspension may not be needed. Stay between the lines though!

P.S. ... Imagine how hard it would be to accurately model the vehicle dynamics of a kart and driver... a flexi frame with no distinct pivot points... and all those independent masses held together by ball joints and tendons... sprung/damped by electronically varible rate muscles, etc. :eek:

Edited by Engineguy, 21 January 2012 - 12:07.


#27 Tony Matthews

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Posted 21 January 2012 - 12:22

Imagine how hard it would be to accurately model the vehicle dynamics of a kart and driver... a flexi frame with no distinct pivot points... and all those independent masses held together by ball joints and tendons... sprung/damped by electronically varible rate muscles, etc. :eek:

Plus a Full English Breakfast with a mind of its own...

#28 Kelpiecross

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Posted 21 January 2012 - 12:46

So did Lotus, with dynamic absorbers (mass dampers) fitted to the uprights. The car, tested at Donington, circuited surprising quickly, but absolutely destroyed its tyres.


If you were going to make a car with no suspension - (dare I say it) - 3 wheels may be better than 4 wheels. On an uneven surface a 4-wheeled car would rock like a table with one short leg. 3 wheels would be like a 3-legged stool - always stable.

#29 Wolf

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Posted 21 January 2012 - 13:38

Didn't Chapman say that any suspension is good, as long as you don't let it move? And more to the point- wasn't that the purpose behind Lotus 88 twin chassis- main chassis with virtually no suspension (presumably for the benefit of ground effects), and inner sprung chassis with driver (I guess so it does not shake his teeth out)?

#30 Engineguy

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Posted 21 January 2012 - 13:58

Didn't Chapman say that any suspension is good, as long as you don't let it move? And more to the point- wasn't that the purpose behind Lotus 88 twin chassis- main chassis with virtually no suspension (presumably for the benefit of ground effects), and inner sprung chassis with driver (I guess so it does not shake his teeth out)?

I'm not sure of the wording, but I think he was not advocationg non-moving suspension. His point, as I recall, was that no matter how crazy the dynamics of a suspesion, you could spring it so stiff that the suspension never travels through those dynamics. If you mount the steering rack at a stupidly inappropriate height, for example, you'll nevertheless see zero bumpsteer if you don't let the suspension travel. Likewise, if your suspension linkage layout causes stupidly inappropriate camber changes throughout its normal travel, you'll never see those camber changes if the suspension is not allowed to move.

Edited by Engineguy, 21 January 2012 - 14:02.


#31 Wolf

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Posted 21 January 2012 - 14:26

I'm not sure of the wording, but I think he was not advocationg non-moving suspension. His point, as I recall, was that no matter how crazy the dynamics of a suspesion, you could spring it so stiff that the suspension never travels through those dynamics. If you mount the steering rack at a stupidly inappropriate height, for example, you'll nevertheless see zero bumpsteer if you don't let the suspension travel. Likewise, if your suspension linkage layout causes stupidly inappropriate camber changes throughout its normal travel, you'll never see those camber changes if the suspension is not allowed to move.


But wasn't the point of Lotus 88 having an unsprung chassis? BTW, I was under the impression he meant it exactly as you interpret it- if it's not moving, kinematics and sprung/unsprung masses, &c don't matter... And I think it's mostly what's happening in F1 even today (what follows is my speculation)- they mandate 13" wheels so they don't have to bother much with regulating brakes (by effectively limiting the space constraints), which results in very high profile tyres, tyres end up doing most of the suspension work so the rest of suspension doesn't have to moove much and they get away with what seems awfully close to equal length parallel wishbones. If rim sizes were to go up to 15", I think many interesting things would happen to car's noses...

#32 Engineguy

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Posted 21 January 2012 - 16:14

But wasn't the point of Lotus 88 having an unsprung chassis?


The 88 in effect had two sprung chassis... the conventional one with all the mass (tub, driver, fuel, engine, transaxle, and most of the inboard portion of the suspension). It was conventionally sprung except for (potentially) being softer... because... no aero downforce was applied to the conventional chassis.

The second "chassis" was just sidepods and the rear wing. it was not attached to the main chassis (at least not rigidly)... it was attached to the outboard end of the suspension arms so all the downforce went directly to the tires. Of course the rules stated, since mid-1960s you can't do that, so there were some little springs (no doubt VERY stiff) involved in the attachment to the suspension so Lotus could claim the 2nd chassis was sprung. Therefore they "cleverly cheated" the requirement that downforce be applied to the sprung chassis. Since the 2nd chassis articulated with the outboard ends of the suspension, the sidepods kept a constant nearly perfect seal to the pavement, the point of the whole exercise. If anything, this was an admission by Chapman that the main mass needs suspension. He could have accomplished the same by a suspension so stiff that it did not move. Some tried that for a year or two, and drivers had vison problems, IIRC.




#33 Tony Matthews

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Posted 21 January 2012 - 16:39

Posted Image
Yet again...

#34 Wolf

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Posted 21 January 2012 - 16:52

Thanks, Tony- marvelous drawing. :up:

Engineguy, I think those vision problems were before 88 (I think it may have been Brabham)- so my assumption was that in light of that Chapman went for softer sprung inner chassis, otherwise could've gotten away with stiffly sprung outside chassis.

#35 Engineguy

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Posted 21 January 2012 - 17:02

Posted Image
Yet again...

Those tire proportions, cockpit location, etc. look so odd today that it looks like you had a momentary lapse of talent when you drew it, though I'm sure that's not the case.

#36 Tony Matthews

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Posted 21 January 2012 - 17:15

The proportions are are right as I could get them, and the forward driving position looks suicidal now... The slightly odd view, although it does show the concept reasonably well, was chosen simply because ACBC did a spidery sketch on lined notepaper as he was explaining the layout to me, and I couldn't see any real reason for changing it, plus I thought he would be more receptive if his view was used. There was a tight deadline, I didn't want any arguments, and there were about four drawings in the sequence (this being the last), plus various other drawings which I have never seen since... A very clever idea.

#37 Magoo

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Posted 21 January 2012 - 19:39

The second "chassis" was just sidepods and the rear wing.


Exactly -- Chapman's reality distortion field at work. The car did not have two chassis. It had two bodies.

#38 cheapracer

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Posted 22 January 2012 - 04:20

The second "chassis" was just sidepods and the rear wing. it was not attached to the main chassis (at least not rigidly)... it was attached to the outboard end of the suspension arms so all the downforce went directly to the tires. Of course the rules stated, since mid-1960s you can't do that, so there were some little springs (no doubt VERY stiff) involved in the attachment to the suspension


Just a correction, I believe the second springs were actually very soft and fully compressed quite quickly with just a small amount of DF. This would have also allowed some droop when skipping kerbs etc.


#39 Lee Nicolle

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Posted 22 January 2012 - 05:06

Many manufacturers for years created softly sprung cars for understeer as it was thought the average driver was frightened of oversteer and would feel
more in control with understeer.Then most cars became front wheel drive and the understeer had to be tamed a bit.
The only way to get the old understeering beasties around a corner was chucking them at the corner and try to induce a little oversteer on exit.However
if you throw a decent handling RWD newer car into a corner too fast it may oversteer too much (unless electronic devices intervene...)

Electronic devices have no place on any car that is to be used in a spirited manner,,, or on the towcar!
And yes I tend to agree that some modern rear drivers are a bit 'loose'. They have to be driven smoother plus the power stteering can emphasise both under and over steer.


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#40 Lee Nicolle

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Posted 22 January 2012 - 05:17

This subject really is far too wide. Lots of modern open wheelers are very stiffly sprung and either go real quick or fall off the road regularly and then get hung up as they have that little suspension.Which may be fine on a hi speed Euro raod course but can be useless on a point and squirt type circuit. Though ar bloody quick until they literally bounce off the road.
One would presume that Lemans style sportys are a lot more forgiving, though have very stiff suspension.And big aero.
Tintops generally need softer suspension as they have a lot more mass and height. Look at a V8 Thupercar, they rock and roll like the family hack,, but are quite fast for such big fat pigs. They droop 2" under brakes and squat even more under power down.

#41 24gerrard

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Posted 22 January 2012 - 10:33

The proportions are are right as I could get them, and the forward driving position looks suicidal now... The slightly odd view, although it does show the concept reasonably well, was chosen simply because ACBC did a spidery sketch on lined notepaper as he was explaining the layout to me, and I couldn't see any real reason for changing it, plus I thought he would be more receptive if his view was used. There was a tight deadline, I didn't want any arguments, and there were about four drawings in the sequence (this being the last), plus various other drawings which I have never seen since... A very clever idea.


Tony Rudd showed me one at my Bushey Transmissions Office which he visited around this time about autoboxes and other things.
It was not this drawing Tony but was probably one of yours.
I might have a copy somewhere, I will take a look.
All fag packets and poor paper in those days.
Tony did ask my opinion on active, for what it is worth I only saw a real use for military vehicles to assist turret stability and things like that.
I could see little use for active or ground effects on road cars.
It is still a huge pity that the 88 did not compete.

Edited by 24gerrard, 22 January 2012 - 10:34.


#42 Magoo

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Posted 22 January 2012 - 15:02

What is the difference in the way a stiff car or a compliant car is driven by the driver ? How can the driver control
a really stiff car on a bumpy track ? Does less stiff mean more grip but less handling so the car might understeer
and the driver have to change his driving style such as corner approach and maybe pick a new apex ?


Getting back to the original topic or as I perceive it anyway... This is as much as anything a matter of driver ability. In general: the better the driver, the stiffer the car he can drive. A car with soft springs/damping gives more and broader input to the driver. Pitch and roll are far more apparent, while the tire's grip curves seem loooonger and more linear. With a stiffer setup, things tend to happen more quickly and with less warning. (This is why we typically go full soft with a rain setup -- so the driver can feel the car on the slick surface.)

So really, the best advice to drivers in managing a stiff setup is to become more talented.

#43 24gerrard

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Posted 22 January 2012 - 21:43

Getting back to the original topic or as I perceive it anyway... This is as much as anything a matter of driver ability. In general: the better the driver, the stiffer the car he can drive. A car with soft springs/damping gives more and broader input to the driver. Pitch and roll are far more apparent, while the tire's grip curves seem loooonger and more linear. With a stiffer setup, things tend to happen more quickly and with less warning. (This is why we typically go full soft with a rain setup -- so the driver can feel the car on the slick surface.)

So really, the best advice to drivers in managing a stiff setup is to become more talented.


Of course one could also say do away with downforce, at least by 50 percent.
Then we could have a meaningful discusion on mechanical handling in F1.

#44 DaveW

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Posted 23 January 2012 - 08:44

Tony did ask my opinion on active, for what it is worth I only saw a real use for military vehicles to assist turret stability and things like that.

That is an interesting story...

I could see little use for active or ground effects on road cars.

Did you ever drive a car fitted with a Lotus Active Suspension, Keith?


Of course one could also say do away with downforce, at least by 50 percent.
Then we could have a meaningful discusion on mechanical handling in F1.

I have sympathy with your views, but history suggests that a design group dominated by aerodynamicists will devote whatever resource it has trying to recover the lost 50 percent. Hence the discussion would not be very meaningful.

Edited by DaveW, 23 January 2012 - 09:36.


#45 DaveW

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Posted 23 January 2012 - 09:01

In general: the better the driver, the stiffer the car he can drive.

That might be true, Magoo, & all drivers prefer a stiff set-up, I think, all things being equal. However, endurance racing suggests that the "better" driver is more content to drive a "softer" car. With a softer set-up he will often be quicker on a single lap & will almost always be quicker over a stint than his less experienced team mate. The conundrum is do you pander to the rookie, costing performance overall, or to experience, risking a DNF?

Edited by DaveW, 23 January 2012 - 09:18.


#46 Fat Boy

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Posted 23 January 2012 - 19:56

That might be true, Magoo, & all drivers prefer a stiff set-up, I think, all things being equal. However, endurance racing suggests that the "better" driver is more content to drive a "softer" car. With a softer set-up he will often be quicker on a single lap & will almost always be quicker over a stint than his less experienced team mate. The conundrum is do you pander to the rookie, costing performance overall, or to experience, risking a DNF?


Spot on, Dave.

I don't particularly agree with the stiffer is better theory. There are places it is correct and places it is not. A soft car will require a driver to be more deliberate and patient with his inputs. It also will tend to have less immediate feedback. If a driver is comfortable with a low-ish level of feedback, soft can be very fast. A stiff car (think racing kart) will have instant and powerful feedback, but it will also tend to be sliding and skipping around a lot. It's one of those things where it 'feels' fast, but the stopwatch may not agree.

You are usually put in a position of compromising between response and grip. Depending on the situation, aero may or may not be an issue as well. What you generally have to do with a rookie is educate him. Look at what Ganassi has done in DP with Pruett and Rojas. Rojas was OK when he started. He's much better now. I promise you they didn't tailor the car around him. The trick for us is to come up with a car that has the most amount of response and grip. Enter DaveW and the world of dampers.


#47 Magoo

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Posted 24 January 2012 - 12:36

That might be true, Magoo, & all drivers prefer a stiff set-up, I think, all things being equal. However, endurance racing suggests that the "better" driver is more content to drive a "softer" car. With a softer set-up he will often be quicker on a single lap & will almost always be quicker over a stint than his less experienced team mate. The conundrum is do you pander to the rookie, costing performance overall, or to experience, risking a DNF?


All I am saying is a better driver can drive a stiffer spring. I was not speaking to driver preference or optimum setup. You kinda changed the subject there. What you say is often true but totally relative. How stiff is too stiff? Well, how high is up?



#48 Fat Boy

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Posted 25 January 2012 - 17:46

How stiff is too stiff?


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#49 DaveW

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Posted 25 January 2012 - 19:03

All I am saying is a better driver can drive a stiffer spring. I was not speaking to driver preference or optimum setup. You kinda changed the subject there. What you say is often true but totally relative.

You are correct, of course. I commented only because I felt that you were in danger of misleading the casual reader. If I continue to assume that "drive" means "drive quickly", then, without going into details like those kindly provided by FB, I would add that a balanced set-up that is too "soft" may (in the limit) consume a set of tyres without actually reaching racing speeds. Alternatively a balanced set-up that is too "stiff" is likely to reach racing speeds quickly to be followed by a reduction in performance, accompanied by rapid tyre consumption. A set-up that is "right" will depend upon the vehicle and track and will often allow the tyres to be multi-stinted. In my view, tyres are a major "totally relative" performance factor and a stop watch will help to decide what is right, as suggested by FB.



#50 MatsNorway

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Posted 25 January 2012 - 21:03

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Is there really a clock manufacturer named after the city i live and work in?

Edited by MatsNorway, 25 January 2012 - 21:03.