creizlein

Just out of curiosity and with the intention to look for feedback and comments, What are the pros and cons between using the same spring rate on both Axels Vs using stiffer spring rate in the front and lower on the rear?
I have seen some people which choose to use lets say 10kg/mm or 8kg/mm on both axles while others like 10kg/mm on front and 6kg/mm on real, a 60/40 difference per say, but not sure what would be best?
Having in mind this is going to be a street car with occasional drag/race track usage everynow and then, but mostly just daily driver.

Please bear in mind that i am not asking what is the best spring rate to use, as that topic has been discussed on several thread, but instead asking what are the pros/cons of use the same on both or stiffer in front?

KoRn_vIRuZ

In a very simplified way, the stiffer the rear is relative to the front, the more the car will oversteer. Conversely, the stiffer the front is relative to the rear, the more the car will understeer.

Also note the influence of weight. Since an FF car has most of its weight in front, using springs with the same rate on all 4 corners does not make for neutral handling, it promotes oversteer. Which may me exactly what you want, or not. It depends.

This is ignoring the sway bars, of course. In practice they add to the spring rate under cornering and you can change the balance of the car using them instead of the wheel springs.

If you don't understand what is happening here I'd recommend you either study up and do the math (it's not that hard) or go with spring rates pre-determined by the manufacturer to be suitable for your vehicle. Hopefully their engineers did the math.

B serious

iTrader: (1)

pros and cons depend on the chassis and what the intended use is.

There's no ONE right combination of spring rates (as evidenced from the countless discussions of spring rates that you've mentioned).

Different cars and chassis' have different MR's resulting in different wheel rates. Different dynamics. Different weight distributions. Etc etc. So different spring rates will affect their behaviour in different ways.

creizlein

Appreciate your feedback KoRn_vIRuZ, good one!

the use as described in the thread itself, and the chassis wasnt, my bad, its a Civic Ek4 4dr, (like the '99 Si but 4dr jdm, not sold in the us as is)

Tyson

They're not relative. Your front suspension is not connected to your rear.

You tune them differently if you're smart.

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Croc NZ

As a matter of illustration, in New Zealand our FWD Toyota Corollas used suspension settings designed by Chris Amon, a Formula 1 driver for Ferrari in the early 1970s. In many parts of the world Corollas were horrible, understeering and unresponsive. But here they were an absolute delight to drive.

Here are the figures for my 1995 one - still my daily driver:
MacPherson struts all round, so spring stiffness is almost the same as wheel stiffness.
Front springs: 120 lb/in (2.1 kg.mm)
Rear springs: 120 lb/in (2.1 kg.mm)
Front bar - adds the equivalent of 30 lb/in in roll (0.5 kg.mm)
Rear bar - adds the equivalent of 75 lb/in in roll (1.3 kg.mm)

Note - the front bar is 24 mm, the rear bar is 16 mm. You will note that the bars themselves are very different in size, and that a 24 mm bar is 10 times more difficult to twist than a 16 mm bar. Yet the 16 mm rear bar provides over double the roll resistance of the 34 mm front one. This is a classic example of how the geometry of the bar and the way it is connected to the suspension determines its effectiveness...

Summary: Roll resistance (that's 1/2" up one side, 1/2" down the other)
Front: 150 lb/in of roll (2.7 kg.mm)
Rear: 190 lb/in of roll (3.4 kg.mm)

So it is significantly stiffer in the rear.

Of course this is a road car, relatively softly sprung. But it's a typical FWD car, much heavier in the front than the rear. It handles impeccably, understeer is absolutely minimal.

By far the most critical factor in transition behaviour - things like turn-in, reaction to throttle and bumps - are the dampers (shock absorbers).

Snap oversteer is caused not by too much rear stiffness, it will be a tyre issue, lack of available suspension movement, or poor damping.

To cope with race tyres and their increased grip, the suspension spring and bar rates must be increased. That's obvious. But what so many people completely forget is that the car must still be able to negotiate bumps, and that the stiffer springing MUST be controlled by equivalently stiffer rebound rates in the dampers. If your front-heavy FWD car is wanting to swap ends, don't blame the springs. (Race tyres don't work cold, and it's hard to get heat into the rear tyres, but that's a separate issue. Likewise, when using treaded tyres, brand-new ones have much less grip than well-worn ones. But very old tyres have tread rubber that has gone hard. Snow tyres on the front but summer tyres on the rear are not a great idea in snow. Nor the other way around in summer, or a half-flat rear tyre.)

Your suspension must have sufficient useable travel, both up and down, so that it copes with any bumps that may be encountered under maximum acceleration, braking, and cornering conditions. And very stiff springs on the light rear of a FWD car will mean that there is far too little available suspension movement. The whole idea of suspension is to keep wheels on the ground, not to bounce them into the air! So there is a definite limit to how stiff the rear springs can be. Any increase in roll stiffness on top of that must be made using an anti-roll bar. But above all it must be damped properly. Shock absorbers are the most vital part of the whole process. Stiff springs will overload shock absorbers that worked fine for softer springs, and make transitions sudden and unpredictable.

Any suspension that is double or more the wheel stiffness of my example is going to have very poor travel. You end up using the tyre as the spring, and the shock absorber has no control over that at all. (Remember, stiffness at the wheel is the spring stiffness multiplied by the motion ratio squared. Motion ratios in Hondas vary - e.g. Integra DC5/RSX front is about .95, rear 0.5, so, in this case, the rear wheel stiffness is one-quarter of the spring stiffness whereas the MacPherson front is virtually the same as the spring.)

A well-set-up FWD car will have front roll stiffness that prevents too much body roll, but no more than that, with rear roll stiffness so that during maximum cornering, the outside wheel is taking all of the weight of the rear of the car. Lifting the inside rear wheel a little does no harm, but if it's excessive it's an indication that the front is too soft, or the front roll centre is too low.