Thou tire is a factor, but actually base gt86 will be on the same time as ND with it's 16x6.5 205/55/16 tire (not primacy hp, Yokohama Db 205s)........Cuz that 16inch base tire/wheel along makes 86 roughly 1 sec faster.

You would think so. But surprisingly, the Miata's CoG is only half an inch higher than the 86 (C&D measured 18.0 and 18.5, no I don't have the links handy). The 86 is also a bit wider, so the difference in "aspect ratio" works out to something like 5%. The body roll is mainly due to spring and sway bar choices. In Japan, some of the trim levels don't even come with a rear sway bar.

And the ND has enormous amounts of suspension travel. The body roll is by design, and definitely intended to improve the ride quality. But I agree, it means transitions are going to be slower, and it will punish non-smooth inputs.

^^

Yep agreed, body roll is generally never a positive. It's just a byproduct of suspension compliance at a given CG height & track width.

There are very few scenarios at the track where you'd want to prolong weight transfer, and that's really at the far extremes.

The point I continue to not agree on is that these types of comparisons are biased because Mazda offers the option from the factory of Brembo's, LSD, etc and Subaru/Toyota and (in the US/Europe) the comparisons are done with the stock tires. It is what it is.

It could very well be that the Miata has too much body roll, but the point that stiff always equals better is what I was trying to make. It is simply not true. Some bodyroll can result in adding more mechanical grip which can be a good thing. In the case of the Miata it does seem some as simple as a better sway bar could really improve the car.

I read somewhere that the tires for the Toyota 86 is not standard across all areas in Australia, and that the lower trims for the car in parts of the world sometimes don't have Torsen Limited-Slip Differential (such as the automatic 86 GT in Australia).

Hate to nitpick, but it's not the body roll that's adding grip in that scenario, it's the suspension compliance.

Body roll is an effect of weight transfer, it doesn't affect weight transfer. It definitely has poaitivrs and negatives. I know I've replied this to you before and somehow you never belive me, so I will try to spell it out a bit more.

So first off, you are correct that more compliant suspension ie lower spring rates gives more mechanical traction. More body roll is an effect of having more compliant suspension if you don't control it with sway bars.

But with double a arms, body roll has a benefit of giving you better camber curves. If you look at all the posts on the miata forums, the miata gains more than 1:1 camber for body motion, which is a very good thing. You want as little camber for braking and acceleration, and the appropriate camber for cornering. You want all four tires to be at like 5 degree camber with respect to the ground, which means negative camber for the outside compressing tire and positive camber for the inside extensing tire.

If you deal with a constant radius circle, you actually get maximum lateral grip with the softest springs possible and body roll to maximize the work of the unequal length a arms.

Now the negative to rolling around a lot is it takes longer in transitions and drivers don't like it. In autox where you have lots of transitions, sway bars usually take of tons of time wheras they usually do nothing or hurt on road racing. Drivers, especially amateur drivers really don't like it because it takes time to load up the weight so you have to be purposeful and have finesse when putting in driving input. That's why amateur drivers usually like super stiff front sways, because that responds to driver input faster. Also why amateur drivers like super stiff compression on the shocks. It will turn in quicker but your maximum traction suffers. What drivers like is not always faster.

You say but race cars don't roll much! But they do. The missing part of the equation is the ride height. Lower cog is super important, and the point at which the losses of too stiff suspension and loss of suspension camber control overtakes the gain of lower cog is about 2-3" of bump travel. But now in the era of aero, the benefit of aero overtakes any suspension and the best ride height in our aero era is basically as low as rules will allow.

If you look at videos and pictures of race cars, you will see the roll as much as their ride height will allow until their front splitter would hit the ground. If you look at f1 cars from the pre aero like 1950s you will see they have 2-3" of bump travel and roll the maximum possible.

So where does that leave the mx-5 and fr-s? So because both are street cars, they both have about 5" of bump travel for clearance and cargo purposes. Mazda, as it is usually focused on road racing, set up a suspension for road courses. So it has soft springs and big roll to take advantage of the double a arms and the huge ride height since it has to have it anyways. So people complain about the roll but drivers like pobst can turn out good numbers. It however will hurt the car on autox

The fr-s were designed for driver feel and not for time. The McPhearson fronts basically get nothing from roll so they have a super flat car with no roll and high low speed compression damping that drivers love.

Side note the reason why hp is more important than than torque and hp/weight ratio on high speeds is that air resistance is like subtracting a net jp from the car. So at 80mph its like -50 hp from the car. -50 hp out of 170 to 120hp is significabtly worse than 150hp.

Also the miata has to run w top down on road courses and its cod is terrible compared to a hard top.

I didn't quote the long post, but you're still basically looking at it backwards. The reason that the dynamic camber curve of double-wishbone suspension is advantageous is that it compensates for the positive camber induced by body roll.

Not just that, but body roll introduces its own weight transfer and reduces total overall grip. Also the more body roll you have, the longer your weight transfer takes.

Again I'll state this simply. There are no performance advantages to body roll. You want suspension compliance for grip over surface irregularities, but not the body roll that comes with it. Body roll is just the negative byproduct of building in suspension compliance. Thankfully it's possible to reduce body roll without affecting suspension compliance by lowering CG height, adjusting roll center, etc.

You'll never hear of a race car engineer trying to build in as much body roll as possible on a chassis. If they did, you'd see race cars tipping over everywhere. The whole concept is frankly a bit absurd.

Did you even read what I wrote? Do NOT use common sense to talk about vehicle dynamics. I explained every single one of the objections you brought up. Please explain why it is not valid. Please do some real reading on vehicle dynamics.

Sorry I am typing on phone so there are typos and I can't format this point by point but I'll go point by point

Uneven length a arms more than compensates for body motion. For each degree of body roll compression, the miata suspension gains more than 1 degree of camber. This is very good as tires want 0 camber in a straight line and like 5 degrees of camber in curves (-5 on outside and +5 on inside). There is no way to achieve this with McPhearson. I can't find the nd numbers but the na/NB miata get about 5 degrees of camber for 3 degrees of roll. So if you roll the cars 3 degrees you end up with -2 degrees on the outside and +2 degrees on the inside. If you have a macphearson you will get more like 2 degrees per 3 degrees of roll so you will end up with +1 on the outside and -1 on the inside, which is bad. So w a miata if you run -1.5 static you get -3.5 and +0.5. W a macphearson you'd run more like 3 and end up w -2 and -4 which is not as great and also a static -3.

Roll angle does not affect total weight transfer in any meaningful way. The fundamental equation for total weight transfer (lateral acceleration x cg height x weight/track width) does not include roll. If you want to talk about instantaneous vs geometric cg centers, the effects are trivial. The fact that you think roll affects weight transfer makes me think you havent read up on vehicle dynamics as that is one of the most common incorrect assumptions that all books and instructors take time showing how it is wrong.

Soft springs more roll and lower compression damping all affects how long transitions takes. And yes it is bad, but there are tradeoffs for each.

You think about suspension completely backwards. You don't tweak roll with cog and compliance. Compliance is limited by cog. You need as soft as springs as possible, but you need to not bottom out. So with 2" bump travel you end up w 2.5 wheel rates and a super stiff ride. This causes you to have not too much roll. If you still need to reduce roll to not scrape you use roll bars.

That is why race cars don't maximize for roll. You have a low cog and low bump travel and low clearance. They roll as much as possible given those constraints.

Street cars have different constraints as they have way more bump wtravel than is ideal because of practicality concerns. Because of that they can roll more than you see race cars do. and if you have double a arms it helps

Roll angle is trivial to decrease. Just throw in bigger anti roll bars. There isva reason most road racers don't really care for it too much and a lot pull out oem roll bars and why autoxers put in huge ones.

I know you hate me and think I some sort of troll, but you really should believe I've done my reading.

Whoa I think you need to step back and relax, you're taking this way too personally. I don't hate you and it doesn't matter whether you're a troll or not. Just debating facts here.

I'm surprised in all of your reading you haven't come across explanations of how body roll adds weight transfer. There are plenty of materials out there that explain it. In fact, your formula citing to CG height states it right there, you just don't realize it yet. If you think through the effect of body roll on CG, you'll see it.

http://www.autozine.org/technical_sc.../body_roll.jpg


As for the camber curve on the Miata being greater than the degree of body roll, of course. You have to take into consideration at what angle the tire is reacting the way the suspension engineer wants (temps, grip, wear), as well as deformation of the tire. None of that changes the accuracy of what I said.

No offense, but I'm not going to touch your statement that "compliance is limited by COG". Your statements about CG height and swaybars are kind of missing what I was saying. It's more than I want to address right now.

At the end of the day, if you want so hotly to believe that body roll is a good thing for handling and somehow adds grip, that's fine by me. It doesn't really matter what you or I believe, so let's just agree here to disagree.

Jeez.

To body roll or not... that is the question...

This thread has gotten way too technical. I kind of like it.