so, between reading alot of information on here and other sites it seems that actually softening the front spring rates help increase alittle oversteer, which I would think make the car more neutral with stock suspension. so my question, what is the spring rate of the COOPER sport springs. and the stock cooper s springs? im talking about the front.

now question two.. putting less tire pressure in the front tires help reduce power understeer for fwd cars correct? so would putting less tire pressure up front and more in the rear also create more oversteer? if so whats the drawbacks?

-thanks!

 

.. hmm ok, easier question.. are the cooper sport front springs softer or exactly the same as the cooper springs?

 

The tire presure thing is a debated subject...but a classical approach is if you remove psi from the rear the car will understeer less. But the actual values are very important because these, along with the huge variation in tires, make a big difference. Some folks like to add a lot more psi to the rear to invoke oversteer and this will work too...but the two extremes work in different ways and when the beck end comes around, it will do so in different ways. I imagine that higher psi will work better in an AtuoX event and less will be better on a road course or on the street. Suspension tuning will also affect this nature.

to a point, less psi can aid mechanical grip, just like a soft spring can aid mechanical grip. What you give up is control and herein lay the balance you must try to achieve. Control is important, but so is grip...balance, control and grip, a classical war raged (yes, raged in my case) between car and driver.

...too much understeer...install a larger rear bar and leave the springs alone...take small steps.

 

rear sway, is the easy way out from understeer.. but as others have said a poor way to tune the suspension. so with that Im trying to figure out HOW to tune the suspension in the best way possible where EVERYTHING is nuetral.. Ive been told I cant have it all but id love to try haha. as far as the tire pressure goes, thanks that helps. but still leaves me alittle blank other than now I know less pressure prevokes less understeer.. yet so does more pressure...

so basically this tells me either to leave tire pressure in the middle and work elsewhere... or there actually is a better army in one of them.

what are the downsides and upsides of lower rear pressure?

once again thanks alot!

ps. I already have springs, and sway. but im building my ideas for a stock cooper

 

In theory, more psi will build very narrow slip angles, and as well, stiffen the tire's sidewall. A norrow slip angle builds cornering force quickly to saturation...it will let go very quickly. And since the side wall is not flexing, there is little warning. This may not be bad in an autoX arena since the forces acting on the car are typically far less than on a road course; a car traveling at 30-40mph have less force than one traveling at 100-125mph.

A tire with less air will do the exact opposite; it will build cornering forces slowly and telegraph saturation with warning.

Saturation is a term used to describe a tire at its max lateral grip. It can be shown as a sin wave or curve. When the tire exceeds saturation, it reverses sin. It looks just like a horse power curve in character. As the curve reaches the peak, that is saturation...when it begins to drop off, that indicates a loss of grip. If the curve drop steeply, the tire losses grip quickly. If the curve drops off slowly over time, you get warning. I personally feel this character in a car defines how easy it is to probe limits safely and consistently. Tires can make a difference, but it's the package really.

The tire with more air might in theory build higher cornering forces, but saturation may be a knife edge that is very hard to dance...spiky if you will. This can be beneficial in an autoX event where you want a tire that is extremely controllable and perhaps a little spiky. That trait is somewhat easier to control at lower speeds.

I would begin with 35psi in the front and 32 psi in the rear - cold - and give it a run. Keep track of the hot tire temps too...32psi may allow enough sidewall deflection to cause the tire temps, and therefore psi, to grow a lot more than anticipated.

The rear swaybar is not the easy way out by the way. Swaybars should be used for fine tuning, but not a cure-all, as you correctly wrote. I wouldn't hesitate, unless you already have one. Just keep in mind that a bigger rear bar will increase wheel rate which may require you to add more air...it gets complicated. The tire psi thingy works for one set of conditions. Change those and you have to begin new tire temp testing.

In the end, you may find that a setup that is easy to predict is the fastest because you can be consistent. However, that setup may not provide the highest lateral grip or the idealized balance. Understeer and tire slip feedback are as important as control.

 

wow thanks alot! that was about the best explained Ive heard thus far so now, does that basically mean in short that more pressure will make the car loose saturation faster/easier, which now I can see why it would be better for autocross where that would be a key tool in handling at low speeds. where at highspeeds it would almost be too easy to loose all traction at anygiven time in a corner? or like you said on a knifes edge.

ok, question 2. the front tires.. I know putting alot of pressure in the front can create alot of power understeer (not really a problem in my justacooper)
but is that why you would recommend more psi in the front? because it is easier to handle alittle bit more spikey saturation?

and thanks for your time!
justin

 

A front driver is the reverse of a mid engine car...literally the reverse of all 9 series Porsches. With engine in front of the axle's centerline and most of the mass up front, more psi in front will give you more control. This is all relative, but there are also a few dozen other considerations that affect weight transfer and the contact patch.

I try to keep my hot psi 1-2 psi less in back, no more...sort of hard to do for daily driving; 39 degress when I drive to work and near 80 degrees during the day. The track is an easier place to play if you can get your temps quickly after a run...most of the time they cool too much to be race team accurate.

 

i was going threw the exact same problem you are having. I wasnt going to put the biggest baddest sway i could find on (the h sport race), and then trhe more i studied the more it looked like a rear sway was not the way to go. That said, a friend of mini loaned me his hsport sport rear sway. I can go faster around corners now than before, which is what i was after. I was affraid that the rear sway would give me oversteer, but not necesarily make me faster on the corners. I am extremely satisfied, and am going to buy a rear sway, whenever he wants this one back, lol. The tune your suspension by staying away from sway, you would need fully adjustable coilovers, and a bunch of diffrent spring rates to test out. Also, try going toe out in the front, i did that, and took my rear seat out, and my car would rotate whenever i wanted it to, but not until i told it to. Came around fast and predictable. This was on runflats. Like i said before, i was in the antisway once i studied more, but now feel that they are indeed the best bet for instant improvement.

Hope this helps

Beecher

 

The best way to describe a well set up car with a proper swaybar; the faster you drive thru a turn, the harder the car corners...so the swaybar comes on-;ine if you will, with more steering angle and more speed. You will know when too much is too much; the back end steps out under power or you have a snap oversteer condition with drop throttle - ffot abruptly off the gas.

Obviously handling is much more complicated than my description, and in fact way above my experience, but that's how I like it to be. And Don's shop gave me a great street alignment to go with my bar setup.

 

I gotta say, since switching tire pressure to 35 front and 42 rear, the car with stock S suspension and bar oversteers much better. I'm learning to drive the FWD still, my car is a 330i and the mini is my wife's.

Anyway, I did 35/45 in my BMW and it is AWESOME for anything under 40 mph. However, on a tight off ramp I used to enter at 80 and then gun it to exit at 105 I now get WAY too much oversteer, and SNAP scary oversteer (thank god for DSC) if I lift the throttle mid-corner.

I was going to get the Hsport 19mm but think I'll hold off and do the USS first.

I'm amazed at how hard it corners and how neutral it is with the tire adjustments. Still, gotta learn how to apply throttle through turns.. doesn't work the same lol.

Oh yeah, forgot to mention that with the higher pressure, like meb said, the tires break away faster and with less warning at the limits. I want to fix this through chassis tweaks and let some air out.

 

well, Im not staying away from the sway or anything, im just trying to deepen my understanding of it all. I have a 22mm rear sway, cooper s sport front sway, koni lowering springs, sway endlinks, and m7 uss. my car rotates fine, and all. but Id love to fine tune things if you know what I mean haha. this question was more designed for my friend's cooper s that we are building the handling on. kind of a sleeper suspension set up is what we are going for