Aftermarket suspension making handling worse?

[wparsons]

Originally Posted by Ubersuber

Which gap?

These figures suggest gains in only some corners.

Whether you get gains from stiffer springs (and lower static ride height) depends on a number of factors.

Note the braking forces remain the same and the peak g is the same, practically speaking. Tire can generate only so much force. Add grip and both sets of times, speeds, g's and braking distances will improve. There is no particular reason why any of the deltas would change.

Interesting that the stock setup gave a higher peak speed...depending on the track that might be aerodynamics but more likely would be acceleration out of the corners which is hindered by too much real roll stiffness, regardless of any "improved" balance in the corner. Exit speed is king especially with low power since you can't gain much at the end of each straight.

If you add grip, but don't change roll stiffness (either through sway bars or spring rates) you'll get more body roll, which gives less than desirable contact patches and can also load the suspension to the point of bottoming out the bump stops just from cornering forces alone. That's when you need more spring rate (and dampening) to control the body motion generated by the higher cornering forces. Keeping the geometry in check is what gives you more grip.

Keep in mind there are two ways to have a higher exit speed... carry more speed through the corner, or be able to accelerate harder from the apex. With the lower power, these cars benefit more from carrying more speed through the whole corner vs blasting away from the apex.

[Ubersuber]

Originally Posted by wparsons

If you add grip, but don't change roll stiffness (either through sway bars or spring rates) you'll get more body roll, which gives less than desirable contact patches and can also load the suspension to the point of bottoming out the bump stops just from cornering forces alone. That's when you need more spring rate (and dampening) to control the body motion generated by the higher cornering forces. Keeping the geometry in check is what gives you more grip.

Keep in mind there are two ways to have a higher exit speed... carry more speed through the corner, or be able to accelerate harder from the apex. With the lower power, these cars benefit more from carrying more speed through the whole corner vs blasting away from the apex.

Well, not necessarily. People tend to think of body roll as bad but that is just a stand in for suspension changes. The body roll per se is not relevant.

You now have your point the right way around though. If you change the spring rates you may improve the grip from the stock tires by speeding up the load transfer effects (misleading called "weight transfer" when no weight is transferred, it is purely an acceleration effect proportional to vehicle weight and height of the cg above the roll axis). If you change the ride height as well (which almost inevitably happens if you fit higher road spring rates but does not happen with stiffer roll bars) then you change the static suspension height which may or may not be beneficial depending upon the actual geometry and the difference in static roll height.

If you add tire grip you may benefit from changing roll rates. Tire grip has no effect on roll rates, that is purely geometry acting on the given effective spring rates. Adding tire grip to stock suspension will always improve total grip. Changing roll rates may or may not improve grip. (Just by the by, hitting those bump stops substantially increases the spring rate and rapidly progressively which actually hurts the handling of this car).

Interestingly, adding tire grip may not happen when fitting bigger tires (as R&T shows in their interesting experiment). By far the most important factor in tire grip is compound. Tread design has importance but mainly by its absence. Tire carcass design is the other huge factor. When you compare the effects of improving tires to those of improving spring rates it is obvious where you should spend your money first (provided the damping is correct which on the stock BRZ so far anyway, it is not really).

[wparsons]

Oh please tell me you're suberman...

Either way, you're totally missing the point. More grip than the stock spring rates can handle will induce too much body movement, which decreases overall grip. This isn't voodoo, it's physics. The reason race cars running slicks (even those without aero) run such high spring rates is to keep the body motion in check, not because they want a jarring ride.

As for body roll not being bad, just look at how much positive camber you'll have on the outside front tire with excessive body roll and try to tell me that's good for grip. A bit of body roll isn't bad, too much severely affects the contact patches in a bad way.

[Dipstik-sportech]

Yes that is suberman

[wparsons]

Originally Posted by Dipstik-sportech

Yes that is suberman

I'm so glad such a successful lawyer decided to slum it with us common folk again

[Ubersuber]

It is important to distinguish the effects of increasing tire grip, which is very easy to effect on this car, and "reducing" body roll which may be a fairly pointless exercise.

Unless you change the suspension geometry then at the limits of the suspension travel the maximum body roll angle remains the same with coilovers or roll bars or new tires because the body roll angle is determined by suspension arcs not by spring rates.

I say again, fitting stiffer springs/rollbars/or bump stops changes the rate at which the body rolls, i.e. the rate at which the camber of the four wheels changes but cannot change the ultimate position of the body, and therefore the ultimate camber angle of the suspension.

This is why fitting grippier tires is the very first thing you do if you want to go faster. Nothing else makes a bigger difference.

It is also why fitting stiffer spring rates in roll does not affect ultimate grip, only tires can do that. Note the difference between the g for stock and the g for coilovers on stock tires in the very interesting and illuminating link posted in this thread. I'd be very interested to know how closely the measurements were controlled but the difference in the recorded measurements would be indiscernible to the driver.

It is true that stiffer springs in roll may well keep the tires at a more favourable camber angle for more of the time, but, then again, maybe not. It aint necessarily so. What is necessarily so is once the car is on its bump stops the camber isn't changing by much regardless of the road spring rates. Therefore, coilovers cannot usefully increase maximum grip by camber control. I am of course disregarding changes in roll rates front to rear which usually has a major effect and does not necessarily mean you need to fit stiffer bars to achieve. Note on the Honda the front bar was simply disconnected....

Spring rates matter in transitions, that's the key to understanding the "need" for improvement. Tires matter for grip.

That leaves aside the huge improvement in damper control the KW will be giving you over stock. Damper control is exceptionally important in controlling the rate at which the wheels change camber

[wparsons]

Will you please just stop spouting off your incorrect dribble? You don't know what you're talking about, and have no real world experience testing different changes. Just stop before you make yourself look dumb again.

Originally Posted by Ubersuber

It is important to distinguish the effects of increasing tire grip, which is very easy to effect on this car, and "reducing" body roll which may be a fairly pointless exercise.

Unless you change the suspension geometry then at the limits of the suspension travel the maximum body roll angle remains the same with coilovers or roll bars or new tires because the body roll angle is determined by suspension arcs not by spring rates.

You're assuming that the reason the body isn't rolling more is because the suspension is fully compressed on the loaded side, which isn't the case with stock tires. Not by a long shot. Ironically, you've also pointed out exactly why stiffer springs DO increase grip more with sticky tires. More grip means more load is being transfered to the outside tires, which means the suspension is being compressed more. This is bad, we want the suspension travel for bumps, not for absorbing cornering forces.

Originally Posted by Ubersuber

I say again, fitting stiffer springs/rollbars/or bump stops changes the rate at which the body rolls, i.e. the rate at which the camber of the four wheels changes but cannot change the ultimate position of the body, and therefore the ultimate camber angle of the suspension.

Spring rates, by definition, can in fact change the body position by controlling motion.

Spring rate controls how much something will move, damper rate controls how fast it will move.

Originally Posted by Ubersuber

This is why fitting grippier tires is the very first thing you do if you want to go faster. Nothing else makes a bigger difference.

Based on the article you keep quoting the V3's alone took off 1.5 seconds, while the tires took off 2.5 seconds. Yes the tires made more difference, but 1.5 seconds is nothing to ignore, that's a VERY significant difference in lap time.

Originally Posted by Ubersuber

It is true that stiffer springs in roll may well keep the tires at a more favourable camber angle for more of the time, but, then again, maybe not. It aint necessarily so. What is necessarily so is once the car is on its bump stops the camber isn't changing by much regardless of the road spring rates.

If a car is bottoming out the bump stops mid corner, the spring rates are way too low. You NEED bump travel mid corner because roads/tracks aren't glass smooth.

Originally Posted by Ubersuber

Note on the Honda the front bar was simply disconnected....

Please don't even try to compare what they did to a FWD car to get it rotating to what works on a well balanced RWD car.

Originally Posted by Ubersuber

That leaves aside the huge improvement in damper control the KW will be giving you over stock. Damper control is exceptionally important in controlling the rate at which the wheels change camber

Shock damping rates control camber now? Here I was thinking the physical geometry of the suspension was what controlled camber (and camber change).

You can't look at tire grip and spring/damper rates independently, they are very closely linked if you want optimal grip. With more grip you transfer more weight to the outside, which compresses the suspension more, eventually you can bottom out the suspension just from cornering loads which is a horribly bad thing to have happen on a track. At this point you need more spring (and damper) rate to preserve bump travel for actual bumps.

It shouldn't be a shock to you that the stock springs/shocks were matched to the stock tires, but as you pile on grip you quickly overwhelm them.

If you throw slicks on a bone stock car, you'll be faster than stock, but you'll roast the outside edges of the tires and be riding the bump stops way too hard. Throw them on the same car with much higher spring/damper rates and it'll be MUCH faster without ruining the outside edge of the tires.

From the article:

In the end, the Civic Si improved its lap time by almost 4.7 seconds, while the FR-S dropped almost 4.3 seconds off its baseline lap time. Both responded extremely well to the upgrade process, and not too surprisingly, the Honda benefited a bit more from them because of its softer OE setup

So the article you keep referencing even says that increased spring rates increase grip.

CC @CSG Mike @Racecomp Engineering

[Racecomp Engineering]

Originally Posted by Ubersuber

I say again, fitting stiffer springs/rollbars/or bump stops changes the rate at which the body rolls, i.e. the rate at which the camber of the four wheels changes but cannot change the ultimate position of the body, and therefore the ultimate camber angle of the suspension.

What?

Two cars that are identical in every way except one has stiffer springs...the one with stiffer springs is going to have less body roll in a given corner at a given speed (and lateral G). I don't think that's something we're going to debate.

If we increase grip with stickier tires and take the same cars through at a higher speed, the softer car may be bottomed out on the outside while the stiffer car is not. Softer car may have its spring rate spike to infinity. Softer car may also have its geometry much more compromised then stiffer car.

This is why we increase spring rates for cars with more grip. With tires that have very little grip, the car isn't going to roll very much because it breaks traction before that happens, so we should use softer rates for more evenly loaded tires. This is why stiffly sprung cars are generally not so great in the rain.

People generally associate dampers for rate of body roll and transitions.

- Andy

[CSG Mike]

Originally Posted by wparsons

If a car is bottoming out the bump stops mid corner, the spring rates are way too low. You NEED bump travel mid corner because roads/tracks aren't glass smooth.

Sometimes, the bump stop is a part of the suspension's design...


Generally speaking, stiffer springs with matched dampers will be better than softer springs with matched dampers on smoother surfaces. For rougher surfaces, softer rates will work better. Think off-roading vs karting, for an extreme example (huge suspension travel, soft rates, vs no suspension, infinite spring rate)

[blackhawkdown]

[Ubersuber]

Interesting variety of expressions of ideas.

Responding with my views to the original poster is yes, you can definitely and easily ruin this car by fitting aftermarket suspension.

Before buying or installing anything you need to decide what you want the car to do.

For my money and after doing a little modest modification I would begin with the better dampers and struts. Given the basic competence of this car right out of the box this is the most worthwhile addition you can make for the money.

I now even think the stock tires would give satisfactory performance if you just upgrade the dampers and struts. No need to go adjustable and no need to go coilovers.

My next upgrade would be better tires but, as I say, I did the tires first and then the rear dampers and I would now do this the other way around. One way of reconsidering the readily apparent deficiencies of the stock tire is to consider how much fun they can be. These are very good tires for the type they are and it is only on a car this well sorted that they seem inadequate. If you are looking to preserve the fun factor but have better handling just fit good dampers and struts.

I bought light wheels partly because I need two sets, I put winters on the stock rims.

There is some internally inconsistent commentary in preceding posts about whether and when the stock suspension rides its bump stops. Well, at the rear the car begins to ride the bump stops very early in the suspension travel. I think this is less than ideal and shorter rear bump stops should work better.

The next upgrade I would choose is a slightly stiffer front roll bar. Depending on how that worked out I might then also fit a larger rear bar, the TRD combination looks about right and other suppliers have similar kits.

Coilovers are about lowering the chassis and that is pretty much pointless for road use. You must use stiffer springs if you lower the car. Stiffer springs aren't going to provide better handling on the road.

One thing to remember about lowering or fitting a higher rate rear roll bar is you will likely need to reverse this process if you add a supercharger. The car is a tad tail happy box stock and would benefit from even more chassis understeer than it already has. If you're trying to get another 60 bhp or so down onto the road the last thing you want is more rear roll stiffness both for traction and handling reasons.

That's about all the ideas I have that respond to the original post. I do recommend anyone thinking of upgrading to check out that link included in one of the posts above. It is very illuminating.

[wparsons]

Originally Posted by CSG Mike

Sometimes, the bump stop is a part of the suspension's design...

I didn't mean brushing the bump stop, I meant fully compressed on the loaded side, as in 0 bump travel left regardless of what you hit.

[Ubersuber]

Originally Posted by wparsons

I didn't mean brushing the bump stop, I meant fully compressed on the loaded side, as in 0 bump travel left regardless of what you hit.

Somebody said he measured the free travel before the rear bump stop is engaged at 1/2 in.

I put a stock rear bump stop in a vice to see its compression progression and it is pretty high rate and progressive as you would expect.

Most of the low spring rate compression of the bump stop is used up in the next half inch of bump stop compression as far as I could see, (of course I did not have a means of measuring the actual compression force required). There are the two "necks" which compress fairly easily and once that is taken up the bump stop behaves much like a solid one would, i.e. not much travel with a lot of force.

From the way this car handles stock it certainly feels like the rear bump stops are fully engaged quite often. The rear spring rate seems to spike with very short compression stroke. Speed humps are a great indicator of this and really illuminate the advantage of using roll bars to control roll angles over using spring rates.

A car doesn't suddenly drive differently on a track than it does on the street, only the expectations of the driver change. If you drive on a track as bumpy as a road you would not want to lower this car, just for example. If you want to drive fast over unfamiliar roads you would want to stay at stock spring rates, for example.

When deciding what to change in your car the single most valuable item is the expertise of the company who is putting your package together. You need to decide what you think you want and contact the suppliers who know what they're doing and get advice. Knowing what you actually want is the key factor. A reputable supplier will save you money by making sure he sells you what you need to get what you want.

Simple example? If your coilover kit does not come with new design specific bump stops you won't be happy with your results. The factory bump stops will be way too long for any lowered setup, at least at the rear.