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

I don't know why this doesn't register with me but as the question says what is it? Wider track, better geometry, compliance,damping?

Here is the background my old Datsun has about the same power to weight ratio as a 1.6 spec Miata. My car is 1762lbs with me in it and the 1200cc motor 80rwhp & 99.6 with the 1500cc motor. My car is between 9-12 seconds a lap slower than said spec Miata, some of this is aerodynamics but clearly it's suspension. Also note I'm running on 0 tread wear Hoosier.

I get that it's everything I mentioned but it still doesn't sink in despite the fact I'm well versed in how suspension works.

All this causes me to want to bolt Miata suspension on my Datsun. What's really funny is the open wheel car I autocross is vintage legal but I continue to vintage race the Datsun with its crude leaf spring rear suspension and generic MacPhearson strut front suspension. 

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

Dampers too. Tires don't work well when they aren't touching the ground.

I quit wanting to design my own suspension when I realized that I can model static geometry, but I cant model dynamic transients,

Not only “what is the suspension geometry doing when going around a corner in a trail braking situation with a given brake bias,?” But also where and how are the forces being handled by the chassis for a best case scenario for the most circumstances. Nope...my string computer does not go there.

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. 

I think a big part is that with computers you can really optimize a suspension for toe, camber etc throughout the expected travel.  The big improvements seemed to start in the 90s.  You see some pretty primitive goofy things in the Japanese cars that were designed in the 80s like the S13 240SX and the R32 GT-R that were improved in later gens.  Dampers too have gotten so much better, with some production cars coming with pretty fancy dampers but even the aftermarket getting really good.  Spec Miatas now (or are about to?) run a Penske damper that I'm sure makes most stock older dampers look like a hood strut on a toy car.  

I’d guess there is a bit of difference in transmissions as well.   Is your Datsun a 4 speed?   SM cars have a really good 5 speed and the engine revs out to 7,300ish rpm.  That means a pretty good amount of flexibility in the power output.  

As far as the suspension difference.   Camber through the suspension travel is likely better in the double wishbone Miata setup than your strut setup.   Center of gravity?  I imagine the Mazda COG is lower than the Datsun by several inches.

In reply to Tom1200 :

From a practical standpoint I can tell you that with my STS-lite prepped 90 Miata, I can toss it around an (obviously empty) intersection on the street at way higher speeds than seem prudent, and it will just stick - regardless of how deep the tire ruts, or how big expansion joints I cross are.

I can also tell you from autox that when I do finally find the limits, there’s no drama. In fact, when the back end broke loose I just rolled in more throttle. That happened twice & they were my 2 fastest runs by a significant margin. 

One other question is how much tire do you have? 

The SM runs a 205 in race spec

But the miata does have 130-Ish hp on tap which will also be a factor. 

Tire technology has advanced beyond most people's comprehension.  Also dampers are so much better, and spring rates are better, suspensions are allowed to travel now.  So much....

I've always wanted to see Lightning Lap times for older cars on good modern rubber.  Imagine C5 Z06 lap times on the latest Michelin tires that are on the GT350 instead of what was available 15 years ago.....  The imagine that same C5 Z06 with stickier tires and better dampers, even the C6 Z06 dampers are a huge upgrade and that's 5 years of tech. 

First, not really an answer to your question, but I would think the lower max hp and worse aero is a pretty significant factor in top end speeds.  A 9-12 second per lap delta indicates far lower top speed.  So, your similar power to weight may yield similar acceleration potential, but you'll lose out big time on top speed due to lack of power.  Actually, I'm guessing the miata with fairly stock engine tune will have way better area under the curve for power and torque, so probably accelerates better even with similar power to weight ratio (at peak hp).

And, if you're car is like my first gen rx7, the miata will have far better and more accessible braking potential too.

Second, a (not very technical) answer to your question, the double a-arm suspension at all four corners will do a much better job of maintaining the contact patch than Mac struts up front or a stick axle out back.  Couple that with likely lower center of gravity and better roll control, and it's not really a fair fight.  I have direct experience with this in my rx7, although it has better aero than miata's, so I tend to pull away from spec miata's on the straights and give it all back and them some in the braking zones and corners.

One final thought (and a broad generalization)- typically to make mac struts or stick axles work for race applications, suspension travel is limited to keep the geometry issues in check, which reduces compliance in the suspension and can sacrifice grip.  Basically, the old adage that "any suspension will work as long as you don't let it".

Having driven a 1.6 miata on R-comps if not a spec miata, i think you are way better off with your v8 idea than trying to make the power you have catch a miata. You seem to enjoy the drama of driving the car the way it is. If it was as quick around a track as a 1.6 miata on R-comps it would probably drive more like one too, and... i dont know if you'd still like it at that point. For me it was the 'easiest' autocross lap i've ever taken, take that as you will. I'm sure it gets more interesting at higher speeds, but at autox speeds it  just felt like an electric kart, with so much grip and so little power that the only thing you as the driver could really do was screw it up by trying to make it interesting instead of just serenely and efficiently steering it around a misshapen circle and looking at what number that generated when you finish the lap. If you put a v8 in your datsun and it was still 1 second slower than a spec miata you'd have the time of your life chasing one, whereas if you made it up with grip i have a strong suspicion you would find the car less fun.

Everything has improved. Suspension design, aerodynamics, chassis stiffness, dampers, wider/stickier tires, etc.

hp/lb may be similar between your car and a spec miata but what about tq/lb?

Gearing?

with the same Power to Weight raito's the More Powerful car will achive more Speed Sooner,

  Bonniville Cars are Extreamly heavy, it May Take a Moment Longer but they go Really Fast.

"More horsepower makes better drivers of us all." - Stroker Ace

Tires.

Every new car that comes out claims an increase in torsional stiffness of 50% or more. That means that compared to a car from the 70's, a modern car is like 35,000 times stiffer, which allows the suspension to work better. 

I would say in order it's:

1. Stickier tires

2. Wider tires

3. Better geometry

4. Stiffer chassis

5. Better damping

So, all, remember that this is a modern comparison. Which means tires are equal enough. 

And he mentioned that the power to weight is comparable. At least close enough to not be a huge part of the 8 seconds. 

So it comes more down to the chassis and the geometry. And the geometry was intended for totally different tires. 

First this was a question I know the answer too but I'm still surprised/impressed/amazed at how subtle improvements add up in such a big way.

@Vigo, you would be very correct I do revel in the drama of flogging a car with less than optimal suspension design, I quite enjoy the 4 wheel drifty goodness of the old car. I also love flogging Miatas but that's because you can get away with things in them that you can't in so many other cars. Also analysis of putting a V8 in the car is the exact reasoning my fabricator gave for doing it...........scary.

Some addition bits of info; the Hoosier folks told me to stick with the Vintage TDR versus the R7 as the additional weight of the radial would likely mean slower lap times for my underpowered car. My car also has a 5 speed trans and on most tracks I only use 3rd and 4th. The 80whp motor has a very flat curve making power from 5000-8200 but the 99whp motor starts to drop off significantly below 6500rpm (1.2 hp for every 100 rpm).

A further parallel is the 180-200whp Datsun 510s & 2002s run slightly faster to slightly slower than SM but they are all a couple of seconds slower than Super Miatas. A couple of the cars are driven by SCCA national Champs. A 200whp Datsun is 3 seconds slower than a 140whp Miata, even with an SCCA National Champ behind the wheel of the Datsun.

I think it's a matter of refined suspension kinematics. As Nohome said, not just the wheel paths but behavior under load. In the case of the NA/NB Miata, there are different bushing durometers in different locations to give some rear steer capability. The later Miatas (NC and ND) have various rear steer behaviors brought about by the multi-link suspension - interestingly, they work in almost exactly opposite ways. But there's a much better understanding of how to control the contact patch, especially compared to a McPherson strut (no camber gain and all sorts of stiction problems under load) and a leaf spring (they don't just flex up and down).

Chassis rigidity is a factor as well. If the chassis is deforming, it's a big undamped spring and it allows the suspension geometry to move all over the place.

I think we can take damping out of the equation. For one, I've not been impressed with the damping on a bunch of modern cars compared to cars that are 20 years older. Heck, I can bolt what are almost exactly the same shocks on an NA and an ND Miata and the ND will generate significantly more grip. Let's also assume dampers in good condition and not a set of shagged out shocks or the cheapest parts store replacement.

As you get higher in the speak range, don't forget that power to weight isn't the only concern for speed on the straights.  Power to drag starts to become a significant concern.  So even if you have the same drag as a Miata and the same power to weight, you have worse power to drag.  Low speed acceleration would be just as good, but it'll taper off more at higher speeds than the Miata would.  

sevenracer said:

First, not really an answer to your question, but I would think the lower max hp and worse aero is a pretty significant factor in top end speeds.  A 9-12 second per lap delta indicates far lower top speed.  So, your similar power to weight may yield similar acceleration potential, but you'll lose out big time on top speed due to lack of power.  Actually, I'm guessing the miata with fairly stock engine tune will have way better area under the curve for power and torque, so probably accelerates better even with similar power to weight ratio (at peak hp).

And, if you're car is like my first gen rx7, the miata will have far better and more accessible braking potential too.

That sounds exactly right...hp matters when you're talking about top speed not just hp/lb and top speed changes lap times quite a bit on most tracks.  So do aerodynamics. With those differences I'm not sure how you even talk about suspension/traction differences?  Maybe compare split times through corners?  Speed gun at the corner apex?  autocross times on?  Lap times on a real track won't work though I'm sure of that.

....says the person who's unwilling to give up on an older car ;)

You look at times through a certain section of the track, you look at mid-corner speeds, you look at time from corner entry to corner exit. 

Aero is definitely a factor with speed, as the need for power goes up with the square (or is it the cube?) of speed. Spec Miatas are not aerodynamic, but they're a lot better than an old Datsun. And yes, brakes are important although on single lap speed it's more a factor of the tire's traction - you can't brake harder than your tires will let you. Heat management comes into play later.

We had a two-day Miata autocross at our shop last week. The NDs were absolutely destroying the NAs, and on an autox it's about grip and not power.

How are modern strut based cars so good?  (Ignoring special strut varieants like the FoRS and CTR) Kinematic and geometry issues seem to be baked in.

Not necessarily. You can still do a lot with bushings, for example. I know there's been a lot of work on magic knuckle designs.