So what is it exactly about modern suspension that makes for faster lap times.

I don't think there is much difference. You can look at a few E production runoff grids and see a bunch of forty year old Triumphs and Datsuns with very competitive lap times. I think it is a case of more attention and development time spent on extracting the maximum from a new car. Not too many people left who can get the most out of an old swing arm Roto flex Triumph.

bearmtnmartin said:

 Not too many people left who can get the most out of an old swing arm Roto flex Triumph.

Which raises another good point, modern cars have had their scary/dangerous handling characteristics designed out of them, so they are easier to drive fast. Think early 911. Great handling car for it's time, but will absolutely bite you if you don't drive it the right way. That kind of car doesn't exist in new car showrooms anymore.

I was attempting to rule out magic knuckles for strut based cars, because plenty of cars with massive handling prowess don't have them eg. Porsche, M cars, Camaro, Mustang, etc.

Have we got to a point where solid and polyuranthane bushings may actually harm performance for some cars?

Tom1200 said:

So what is it exactly about modern suspension that makes for faster lap times?

NOHOME said:

Modern car designers on the other hand, make it their business to know where every force is for as many situations as they and their computers can dream up, This means that the chassis in a new car is going to be composed in more situations than either the home built or classic chassis could ever be. 

Exactly.  There's no substitute for the rigorous, methodical testing with computer-controlled rigs that OEMs and top race teams conduct.

In reply to Snrub :

Yeah, I have been amazed by the performance of the recent crop of MacStrut cars. It seems like they shouldn't be as fast as they are given their weight and "rudimentary" design. But I remember Andy Hollis saying something about not believing what the internet says about MacStruts, they're not as bad as the conventional wisdome suggests.

Snrub said:

Have we got to a point where solid and polyuranthane bushings may actually harm performance for some cars?

It's kind of always been that way for some cars. The 4-link rear suspension in the Fox body had a lot of bind inherent to it's design, which the factory made up for with soft rubber bushings. Replacing those with hard bushings just made the bind worse.

Snrub said:

I was attempting to rule out magic knuckles for strut based cars, because plenty of cars with massive handling prowess don't have them eg. Porsche, M cars, Camaro, Mustang, etc.

Have we got to a point where solid and polyuranthane bushings may actually harm performance for some cars?

Your examples are cars that are usually RWD in their ultimate form. M cars are moving away from them, but I'll bet there's some magic fairy dust in those knuckle designs. Front suspensions are a pain in the butt as it is, and it's worse when they're asked to drag the car around as well as stop it and turn it.

Solid/poly bushings have changed Miata handling for the last 30 years.

nderwater said:

Tom1200 said:

So what is it exactly about modern suspension that makes for faster lap times?

NOHOME said:

Modern car designers on the other hand, make it their business to know where every force is for as many situations as they and their computers can dream up, This means that the chassis in a new car is going to be composed in more situations than either the home built or classic chassis could ever be. 

Exactly.  There's no substitute for the rigorous, methodical testing with computer-controlled rigs that OEMs and top race teams conduct.

That plus all the simulations that get run before any parts get made! The rigs are mostly there to confirm the simulations.

I suspect the Datsun has a higher CG than the Miata causing it to lean more which upsets the geometry.

Might have a narrower track as well which would mean more lateral weight transfer (compounded by a higher CG).  

If its a track car I am a big fan of just setting the suspension as stiff as it can go and dialing it in with alignment. 

As for your old car tire diameter also has a big effect. easier to setup suspension when you have a smear of a tire and not 58 inches of sidewall. 

Tires are 20.6 x 6 x 13 and the track width is 52" (stock track width is 48.8").

No doubt the CG is higher even with the car being 4.5" lower than stock.

wearymicrobe said:

If its a track car I am a big fan of just setting the suspension as stiff as it can go and dialing it in with alignment. 

The "any suspension will work if you don't let it" technique :)

When I started developing suspension for the Targa Newfoundland, we found that chasing travel and letting the suspension moved led to faster times. It was a bit of a revelation and it's the reason our stuff works like it does. Interesting note - both John Horseman (Gulf Racing) and Mark Donahue (raced Camaros or something) mention discovering major handling problems that were related to a lack of travel as the car had gradually evolved lower and lower with bigger and bigger tires. It's not highlighted in their books but it's part of a big stepping stone in the performance of the car in both cases.

wearymicrobe said:

If its a track car I am a big fan of just setting the suspension as stiff as it can go and dialing it in with alignment. 

 

As for your old car tire diameter also has a big effect. easier to setup suspension when you have a smear of a tire and not 58 inches of sidewall. 

For cars with lots of aero, this is why they are setup that way a car moving around tends to ruin the aero work the engineers did.  For cars with little to no aero, this isn't ideal.

Older cars also tend to have little Ackermann. You say that's not suspension, that's steering, but if the car steers better the suspension works better as well.

Keith Tanner said:

wearymicrobe said:

If its a track car I am a big fan of just setting the suspension as stiff as it can go and dialing it in with alignment. 

The "any suspension will work if you don't let it" technique :)

When I started developing suspension for the Targa Newfoundland, we found that chasing travel and letting the suspension moved led to faster times. It was a bit of a revelation and it's the reason our stuff works like it does. Interesting note - both John Horseman (Gulf Racing) and Mark Donahue (raced Camaros or something) mention discovering major handling problems that were related to a lack of travel as the car had gradually evolved lower and lower with bigger and bigger tires. It's not highlighted in their books but it's part of a big stepping stone in the performance of the car in both cases.

Totally agree and with modern stuff its totally the way to go but if its older then 1965 and I am trying to go fast on a budget I just lower the car the most I can go but the rubber I want on it and deal with being slightly slower then having a 100% setup that moves. Also when the car has aero, I have never mastered driving a car consistently as it moves in and out of aero at speeds with any real travel. 1-2 inches I am ok with any more then that and its gets hard for me at least to know what it is doing in a corner.

Tom_Spangler said:

I'm by no means an expert, but AFAIK, it's geometry, specifically relating to controlling the contact patch throughout suspension travel. Especially camber.

Camber is overrated as a geometry problem.

The real issue is proper control of what is known as roll center (but kind of isn't), anti-squat and anti-dive, and bumpsteer.

Keith Tanner said:

wearymicrobe said:

If its a track car I am a big fan of just setting the suspension as stiff as it can go and dialing it in with alignment. 

The "any suspension will work if you don't let it" technique :)

When I started developing suspension for the Targa Newfoundland, we found that chasing travel and letting the suspension moved led to faster times. It was a bit of a revelation and it's the reason our stuff works like it does. Interesting note - both John Horseman (Gulf Racing) and Mark Donahue (raced Camaros or something) mention discovering major handling problems that were related to a lack of travel as the car had gradually evolved lower and lower with bigger and bigger tires. It's not highlighted in their books but it's part of a big stepping stone in the performance of the car in both cases.

And this ties in with my last comment... a suspension with stable roll centers (let's call them that) and other geometrical things, that don't do massive swings over the suspension travel (or worse, "change signs" going from positive to negative or vice versa - hello swing axle rear suspension) allow you you have a suspension that is permitted to move as necessary to follow the road.  Suspensions that have bad habits need to be kept in check, and this also keeps the tires from following the road, which hurts grip.

One of the handling issues that I am fighting with my RX-7 is that the extremely short control arms used with the FC front suspension cause the suspension to fall into a hole, metaphorically, when bump travel goes too far in a corner, and the suspension just sort of stays sucked up.  The instant roll center for the outside front gets to be about 10 feet underground.  I'm band-aiding it with stiffer springs and shocks to keep it out of that area, but the real fix is to be raising the roll center so there is no hole to fall into in the first place.  The REAL fix would be longer control arms, which would keep the roll center from wandering around like a horny dog, but that isn't possible with a rack and pinion system.

So I'll throw some more things out there.

I set the lap record for the class with my old D-sports racer that car was very wide, I think around 72" with a 69" track width. The key to is was a narrow chassis with extremely wide/long suspension arms. People said the extra width and subsequent frontal area would cause the car to be slow but it was obviously quite the opposite. Additionally the car did not have any anti-sway bars & it had very complaint relatively long suspension travel. It was one of the few open wheelers I've raced that allowed you to pound over the kerbs.

On the opposite end of the spectrum is my F500; the rules limit the maximum width to 55", the track width is probably only 50" it only has about 1/2" of bump travel, while have about 1 1/2" of useful droop, uses bump stops for springs and in effect has friction dampers. Despite all that F500 cars will turn lap times equal to and often slightly faster than Formula Fords.

Keith Tanner said:

Aero is definitely a factor with speed, as the need for power goes up with the square (or is it the cube?) of speed.

Road load varies with the square, power with the cube.

In reply to Knurled. :

IMHO, you are saying the same thing. It’s about geometry and how it interacts with the car and the tire surface. Having bad roll center control is bad just as is a camber curve that does not keep the tire on the surface. 

One thing we need to remember is that suspension theory has changed a lot over the last 60 years, and combine that with tire tech, and you see the likelihood of major changes in how cars are designed. 

Now we have really good dynamic models that work with really good tire models all working with a good surface model. And all of those models are PC capable. 

I think a large part of it is scrub radius/KPI and Caster angle. Many older vehicles have really large scrub radius with many modern vehicles having low or 0 scrub.   KPI would tend to be high on old vehicles which drove positive camber in cornering and older strut designs didn't dial in the caster required to make this better.

Look at cars like the 350/370Z with it's 2 lower ball joints to have a very low effective scrub radius and the multilink suspension designs that allow for much more linear control over the entire vertical and rotational travel of the tire.  

Tom1200 said:

I set the lap record for the class with my old D-sports racer that car was very wide, I think around 72" with a 69" track width. The key to is was a narrow chassis with extremely wide/long suspension arms. People said the extra width and subsequent frontal area would cause the car to be slow but it was obviously quite the opposite. Additionally the car did not have any anti-sway bars & it had very complaint relatively long suspension travel. It was one of the few open wheelers I've raced that allowed you to pound over the kerbs.

That wide track means less weight transfer and thus more grip in the corners, all else being equal. The lack of anti-sway bars is a tuning choice, you need to run stiffer springs for a given amount of roll stiffness and that will change the chassis behavior in a bunch of different ways. A wider track will mean less roll - again, all else being equal.

Compliant, long travel is a wonderful thing once you've experienced it 

Keith Tanner said:

Tom1200 said:

I set the lap record for the class with my old D-sports racer that car was very wide, I think around 72" with a 69" track width. The key to is was a narrow chassis with extremely wide/long suspension arms. People said the extra width and subsequent frontal area would cause the car to be slow but it was obviously quite the opposite. Additionally the car did not have any anti-sway bars & it had very complaint relatively long suspension travel. It was one of the few open wheelers I've raced that allowed you to pound over the kerbs.

That wide track means less weight transfer and thus more grip in the corners, all else being equal. The lack of anti-sway bars is a tuning choice, you need to run stiffer springs for a given amount of roll stiffness and that will change the chassis behavior in a bunch of different ways. A wider track will mean less roll - again, all else being equal.

Compliant, long travel is a wonderful thing once you've experienced it 

Correct. I learned this years ago when Sam McDonald setup my sportbike for track days. 

I have a feeling you probably know who Sam, Norm, and Lucy are. (K&N)

alfadriver said:

In reply to Knurled. :

IMHO, you are saying the same thing. It’s about geometry and how it interacts with the car and the tire surface. Having bad roll center control is bad just as is a camber curve that does not keep the tire on the surface. 

"Camber curve" simplifies it too much, I think.  For example, twin I-beam Ford trucks had one hell of a camber curve.

Roll center height/stability is more important, IMO.   In fact I can't think of a suspension that gains camber as fast as the chassis rolls that wouldn't have all sorts of worse habits.