Opti

Traum said:

Bear in mind that with only a sway bar upgrade, you've increased the effective spring rate of the car throughout the turn, but you have not changed any of the dampening that the car (the shocks, really) can handle.

What this means is, while a higher spring rate is there to reduce the initial body roll, when that first turn is done and the car tries to regain its neutral body position, that increased spring rate is gonna rebound more energy back than before, and your dampers may not be able to handle (dampen) that increased force because they have not been upgraded. On the street, I don't think this will lead to too big of an issue even if you drive aggressively. But in situations where more aggressive driving is done (eg. autox, track, or anywhere where multiple linked / slalom type turns are involved), the setup might actually bite you more. That's because without any improvement to the dampening, there is more energy involved in the rebound stroke of that first turn. This extra energy adds to the compression stroke of your 2nd turn, and same thing happens with your 2nd turn's rebound stroke and the 3rd turn's compression stroke, etc.

When I was previously autox-ing an otherwise stock NC with just some upgraded MS/Eibach sway bars, this was precisely the problem I ran into when I was doing slaloms. The first turn would feel great because of the stiffer sway bars, but the 2nd turn gets more hairy as the car seems to wobble more. But the 3rd turn, my control of the car would get even more out of shape, and that 3rd turn is usually when I would wipe out, or at least incur some sort of major screw up. It also didn't that help that at the time, I was an autox newbie that didn't know squat about car control...

At any rate, just keep those 2nd, 3rd, and subsequent turns in mind if you have only upgraded the sway bars. The sway bar mod is a great bang for the buck solution to remedy the stock NC's body roll problem. But if the driving becomes too intense, it will reveal itself as the bandaid solution that it is.

-Lik

Doesnt sound right to me but I cant think of a way to explain it.
From personal experience(not miatas) when putting stiffer springs that overpower a stock shock, the car would right like hell, but putting even the stiffest sway bars readily available for a Fbody (37mm and 25mm) on a stock spring shock setup the decrease in ride quality was alsmot neglible. And we have really bad shocks from the factory.

hustler

iTrader: (6)

If both sides of the car go over the same bump, the sway bar provides no change in effective spring-rate aside from drag in the rubbers.

18psi

iTrader: (76)

So then what he's saying would hold true only if mid corner you'd hit a bump/dip with 1 wheel and not the other?

hustler

iTrader: (6)

Right. Sway bars are used for low-shaft-speed velocities, they are the enemy on highspeed (think about curbing on the racetrack). Supposedly this is why some of the Daytona Prototype guys don't run swaybars, some do.

jeff_man

iTrader: (7)

Just from the title of the post i know it's not ture

EErockMiata

You have to keep in mind you are effectively borrowing spring rate from the other side in a corner. In a situation like what hustler describes there is no associated spring rate increase because the leverage point is moving an equal (or very close to equal) amount thus no leveraged spring rate is added.

I have no data to back this up (it wouldn't be hard to find but I'm just lazy) but I would be willing to bet that the spring rate that conditionally added to the non leveraged side would be within damper tolerance (at least considering stock springs on stock billstien dampers)

Joe Perez

iTrader: (8)

Correct, but incomplete.

The stiffest sway-bar will have no effect on "ride quality" in that it does not alter the effective spring rate of the suspension, so long as you are going in a straight line.

However, stiffening the sway bar on one end of the car will have the practical effect of shifting traction away from that end when cornering.

So if you add a stiffer front sway bar, you will decrease traction on the front end while cornering, increasing the understeer of the vehicle. If you increase the stiffness of the rear bar, you will decrease the traction at the rear end, increasing the oversteer of the vehicle.

IMO, most "matched" swaybar kits available for the Miata add far too much stiffness on the rear end relative to the typical front-rear springrate combinations found on these cars. Speaking from personal experience, this is a good way to back your car into a tree at 40 MPH while hot-******* it through the canyons. (Fortunately it was a very small tree.)

A lot of turbo-owning Miata drivers (myself included) run no rear bar at all, or at most, keep the stock rear bar and add a stiffer front.

EErockMiata

which is further proof of why Daytona Prototype's are for low life nascar folks. (although I do catch myself watching the races for some godforsaken reason... I must be self loathing).

ALMS or GTFO!

JasonC SBB

The statement "it will bounce back after the initial roll with big bars and stock shocks" is only true when

1) said bars made the car underdamped in roll

and

2) the roll input velocity is high enough that it is faster than the car's natural frequency in roll (i.e. very fast movement on the steering wheel)


A typical car is much more damped in roll than in heave (up down). It takes a lot to get it from overdamped to underdamped in roll. The main reason is that the radius of gyration in roll (moment of inertia) is a smaller fraction of the roll damping than total mass is, relative to damping, in heave.

The majority of driver roll inputs are slower than a car's natural roll frequency.

The NC with stock shocks and big bars in a slalom violates the above because
1) the shocks are pretty darn underdamped in heave at low shaft speeds with their super soft springs, and thus closer to being underdamped in roll; the big bars they add to supersoft springs puts it over the edge
2) Autox slaloms are exactly a violation of (2) above

JasonC SBB

A qualifier is missing: true as long as bumps and dips are 2-sided, i.e. the bumps and dips are larger than the car. A car with siff bars will be stiff in "warp". (diagonal wheels go up, opposite diagonal wheels go down). Which means they will be stiff on one-sided bumps.

Especially true, and produces a well balanced setup if:
1) your front camber is close to the rear, which does maximize overall total grip at the expense of front inside tire wear under braking
2) you run a reasonable amount of rake which produces enough roll axis inclination (where rear is higher).
3) you run a spring rate combo where the rear bounce frequency is the same as, or slightly higher than the front

JasonC SBB

It's not the shaft velocity that plays a role here. It's the fact that when an inside wheel is bumped up by a curb, the swaybar applies a lifting force to the outside wheel (which is providing more of the cornering traction).

The "optimum" distribution of total roll stiffness, between bars and springs, affects a number of things:
- relative ratio of damping ratios in heave vs. roll
- natural frequency of heave vs. roll
- how much grip increase you get from reduced roll vs. how much the tires are upset on 1-sided bumps a la curbs

Big springs / small bars are stiffer on the freeway where most bumps and dips are bigger than the car (i.e. hit both left and right at the same time) and would have less grip on 2-sided bumps. But the car is upset less on 1-sided bumps.

More total roll stiffness is good for grip on smooth surfaces (more favorable tire camber in cornering), but stiffer reduces grip on bumps.

It's a compromise, and ultimately there seems to be a range that works pretty well for a given road / application. Within that range, driver preference is what matters.

Joe Perez

iTrader: (8)

Yes, I was thinking more of a uniform roadway, but you're spot-on here.

One thing to bear in mind from, a practical standpoint, is that in cars with extremely small amounts of "free" suspension travel (eg: Miatas, especially lowered ones) increasing the spring rate can actually improve ride comfort. Stiffer springs will reduce the tendency of the suspension to "bottom-out" on hard bumps (eg: the shocks travel upwards and come into contact with the bump-stops) at which point the effective spring-rate skyrockets. The stiffest spring is softer than the softest bump-stop.

The real-world applicability of this can hardly be understated.

JasonC SBB

Correct, and then the spring rate for a given ride height that gives the best ride, depends on the type of road / size of the bumps.

hustler

iTrader: (6)

1. You are fully ******* retarded.
2. You know nothing about suspension tuning
3. You are certainly a bottom
4. http://www.eviltwinmotorsports.com/w...ter-2011.2.pdf
5. Nascar suspension tuning is awesome

EErockMiata

JasonC SBB

Mark Ortiz is great. What he said below agrees with what I wrote above about roll typically being overdamped relative to ride, due to the radius of gyration about the roll axis being small: