wat are some other books you would recommend buying that are focused around suspension and shit
The only books I both currently own and can sensibly reccomend to people when it comes to explaining suspension systems understandably is that Carroll Smith series. It's a good thing Won't Be Beat convinced me to buy it last year too, cause the other books I have are eather too elementary or are like physics textbooks (which will put you to sleep). Besides, the Smith books are between $15 and $25 each. Some of my other books cost me $80+.
PS: If you finish any good driving/automotive engineering book and you feel that you need more info on something, they will almost always have a list of reccomended reading at the end of it. You won't have any problems finding more info.
wait, wtf was taht, not only was this thread revived from over a month ago, but it was revived with the most useless comment ive ever seen in my life hahahahaha, good wrk
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subaru wrx?!?, wtf am i doin here...
If you are cornering at the limit, the tyres cannot take any more stress without breaking traction.
Now in drifting, that's often what you want at the right time, and I guess the "opposite" of heel-n-toe is the clutch-kicking technique which allows the engine to temporarily rev much higher and then snatch the driven wheels causing them to get too much force applied; therefore they break free and off you go on a drift that either works or slams you into a power pole.
Anyway, traditionally HnT is a technique to control the shock on the tires when DOWNSHIFTING - eg going from 3rd to 2nd gears as you slow for a corner.
Upshifting is generally easy - if you time it just right, you get off the gas, in with the clutch and move the stick. While the gears are snicking into place the engine revs have dropped a few thousand and if it's all done well, the clutch will pick up at a perfectly matched revs for the new gear. Upshifting is pretty easy to get rev-matching happening, and you know you've done it right when you cannot feel any shock thru the car as the clutch engages.
Downshifting requires skill. If you pick up 2nd gear from 3rd, then at the same speed (eg 60mph) the engine revs might need to be 4000 in 3rd, but 6500 in 2nd gear as you collect it. If you haven't "blipped" the gas to make the engine speed up, and if you let the clutch out rapidly, the engine will grab the drive train and rip the driven wheels out of contact with the road.
If you are at the limits of traction already then you will either start a skid in a straight line, or at corner entry the car will jump around without "settling" into it's cornering stance, of if you are mid-corner and you rip the driven wheels out of traction, you'll either bum out backwards in a RWD car, or understeer into the other side of the road in a FWD car, or just temporarily skid offline even in a 4WD and that equally slow although not as devastating unless you run out of road.
No matter whether the car is FWD, RWD or 4WD, causing a shock when you are at the limit will take you off the perfect line, which means you lose the race or crash out. The easiest way to compensate for this is to simply enter the corner slower than the car can achieve, so that the shock doesn't add up to too much stress on the tyres. Once again, you lose the race but at least you don't break anything precious like your skull or the car.
as for lowered suspension: that's ultimately about improving the "contact patch" of the tyres during hard cornering. As the car rolls over, the tyres are also tilted, and when the tyre is tilted, it's contact patch goes from a nice square region to a smaller triangle. The traction available from the tyre is directly related to the size of that little contact patch, so if your car leans over and you lose 20% contact patch, then that's how much cornering force you loose too.
If you can make it so that you only lose 10% contact patch, then you can go around corners quicker. One way is to artificially introduce a negative tilt to the tyres using "negative camber" which means to tilt the top of the tyres in. Then, when the car leans, the negative camber helps to reduce the loss of contact patch.
There is a limit to how much negative camber you can apply, so even in hard-core racing classes, they'll probably be only using a few degrees at most. This also works together with stiffer suspension and lower centre of gravity from the car.
Having a car at normal hight, gives a certain rolling force. If you lower the car 3 inches, the weight of the car acts lower and closer to the tyres, so it tilts the car less. Apart from that, a soft car sitting high will slop around on the end of it's suspension, and that will also "shock" the tyres and cause them to lose traction temporarily.
When a car is lowered it will normally also get stiffer suspension. The stiffer springs also resist tilt, and that means the tyre contact patch is improved during cornering.
If you lower too much and get suspension that is too stiff, and then you try to corner hard on the street, you'll find that any bump and ripple in the road will slap the tyres much harder, and once again that causes shocks which rips the tyres off the ground, and you lose traction.
A seriously stiff and lowered car can often corner really badly on a medium quality road. The suspension must be set for the surface you will be using the most. Sometimes a softer setup on the street will smoke a car with a really stiff setup. However, put both of those cars on a beautifully smooth race track, and the stiffer car will be a clear winner if the driver is competent and the setup is good.
Back to drift: heal and toe is a general purpose skill, which will be useful in drift when you need it to maintain a steady slide, or you can deliberately violate the heel-n-toe rule to initiate a drift. This also puts big stresses on the transmission of the car so don't expect your car to survive for a long time if you keep hitting it like that.
__________________ I'd rather beSideways
1975 Datsun 180B - thrashed 'n' thrown around
1992 N14 Pulsar SSS - worn into the ground wasting HSV's through the corners - Enjoy your retirement my friend 2002 Aus. S15 200SX GT (a.k.a. Silvia) - standard (until funds allow)
as for lowered suspension: that's ultimately about improving the "contact patch" of the tyres during hard cornering. As the car rolls over, the tyres are also tilted, and when the tyre is tilted, it's contact patch goes from a nice square region to a smaller triangle. The traction available from the tyre is directly related to the size of that little contact patch, so if your car leans over and you lose 20% contact patch, then that's how much cornering force you loose too.
If you can make it so that you only lose 10% contact patch, then you can go around corners quicker. One way is to artificially introduce a negative tilt to the tyres using "negative camber" which means to tilt the top of the tyres in. Then, when the car leans, the negative camber helps to reduce the loss of contact patch.
There is a limit to how much negative camber you can apply, so even in hard-core racing classes, they'll probably be only using a few degrees at most. This also works together with stiffer suspension and lower centre of gravity from the car.
Having a car at normal hight, gives a certain rolling force. If you lower the car 3 inches, the weight of the car acts lower and closer to the tyres, so it tilts the car less. Apart from that, a soft car sitting high will slop around on the end of it's suspension, and that will also "shock" the tyres and cause them to lose traction temporarily.
When a car is lowered it will normally also get stiffer suspension. The stiffer springs also resist tilt, and that means the tyre contact patch is improved during cornering.
If you lower too much and get suspension that is too stiff, and then you try to corner hard on the street, you'll find that any bump and ripple in the road will slap the tyres much harder, and once again that causes shocks which rips the tyres off the ground, and you lose traction.
A seriously stiff and lowered car can often corner really badly on a medium quality road. The suspension must be set for the surface you will be using the most. Sometimes a softer setup on the street will smoke a car with a really stiff setup. However, put both of those cars on a beautifully smooth race track, and the stiffer car will be a clear winner if the driver is competent and the setup is good.
The heel & toe stuff is pretty much correct. The suspension stuff above is a bit off.
Lowering your car does not directly affect the contact patch of the tyres. When you lower your car, what you are actually (primarily) doing is decreasing the height of the center of gravity. This means that the amount of lateral load (left to right, rear to front, etc) transferred is reduced, which results in less load on the "loaded" tyres (the outside tyres when cornering, the rear tyres when accelerating, and the front tyres when braking) because less load is transferred away from the "less loaded" tyres.
I know people get confused when I try to explain stuff like this, so let me present an example using diagrams (ASCII art!). Say you have a car which has the following load distribution at rest. The "I" in the center is the car (the top and bottom being the axles and the vertical bars on the corners being where the wheels attach to the hubs), and the numbers on the corners represent the amount of load on the tyre at that corner (assuming 4 tyres):
Now say the driver lowers the ride height of the car a reasonable amount (not enough to cause bottoming out, CV joint wear, or any other undesirable side effects that we all have to watch out for when doing this for our cars). For the purpose of this example, I'll just say 1".
So what's the advantage to all of this? Well, the less load on any one tyre, the less work that tyre is doing, and the less it's being stressed. But more importantly, the less load gets transferred away from the tyres on the inside, so they do more work when they aren't loaded. The final result? A slightly higher overall traction limit due to the better distribution of loads, a car that's easier to control because it responds better to sudden load transfers, and in the case of front wheel drive cars, better acceleration (take the above example and think about what happens when the load moves from the front to the rear).
Controlling the car's roll is a different story.
The car doesn't necessarily roll around the center of gravity (it usually doesn't). The car rolls around the roll center of the car, which is a different point and should be somewhere within the car's chassis. When the suspension geometry changes, the roll center usually changes as well. How much lowering the chassis changes the roll center height depends on the suspension geometry of the car, and the original roll center of the car. With a current generation Ford Mustang, for example, putting inexpensive lowering springs puts the roll center height at the front of the car at ground level or lower (which is not good, because now not only is the chassis rolling around the roll center, so are the front axles and wheels). On a Toyota MR-2 Spyder, lowering the ride height 1 inch reportedly has little to no effect on the location of the roll center on either end of the vehicle. There are numerous ways to change the location of the roll center, but the roll center cannot be too low or too high.
Controlling the total amount of body roll also depends on the stiffness of the springs. Rather intuitively, stiffer springs help limit the total amount of body roll a car produces. The downside is that as with any sort of spring adjustment, using too stiff a spring means that the car skips/skates across the track, due to camber changes, rough pavement, or just an uneven road surface.
Controlling the speed at which the roll sets in is the damper's job. Specifically, the rebound adjustment knob on your damper is what you're going to adjust to change this. Dampers cannot limit the total amount of body roll that a car produces, only how quickly it sets in.
The heel & toe stuff is pretty much correct. The suspension stuff above is a bit off.
(BIG SNIP)
Lowering your car does not directly affect the contact patch of the tyres.
I just wanted to correct and clarify that.
Yeah - fair call. I was thinking more of the body roll which does also tilt the suspension and therefore the tyres. If you look at photo's of any standard car cornering at it's limit you'll see the outside wheels are close to 10 degrees past vertical in the worst case.
But the change in the load transfer is also very significant as you point out.
And the more load put onto a tire, the worse it's "efficiency" becomes. Eg a tyre with 500lb weight may offer 500lb side resistance, but put the weight to 1000lb and it's side resistance will only be maybe 750lb, so ultimately a heavier load will not be able to corner as efficiently for the same tyre.
not applicable to drifting 'cos you are supposed to be sliding right ;-)
__________________ I'd rather beSideways
1975 Datsun 180B - thrashed 'n' thrown around
1992 N14 Pulsar SSS - worn into the ground wasting HSV's through the corners - Enjoy your retirement my friend 2002 Aus. S15 200SX GT (a.k.a. Silvia) - standard (until funds allow)
Yeah - fair call. I was thinking more of the body roll which does also tilt the suspension and therefore the tyres. If you look at photo's of any standard car cornering at it's limit you'll see the outside wheels are close to 10 degrees past vertical in the worst case.
But the change in the load transfer is also very significant as you point out.
And the more load put onto a tire, the worse it's "efficiency" becomes. Eg a tyre with 500lb weight may offer 500lb side resistance, but put the weight to 1000lb and it's side resistance will only be maybe 750lb, so ultimately a heavier load will not be able to corner as efficiently for the same tyre.
Nope. That isn't correct either. Remember, tyres are made of rubber. Rubber generates more friction, internal and with other surfaces, during deformation and while it is being moved against a surface. Take a look at a traction-load graph, and you'll see that the tyres will generate more grip with increased load until it gets to a certain point, at which it tapers off, then drops. Also note that the load mentioned above is downward load, and despite intuition, it does not have anything to do directly with horizontal forces pushing the car out (the "imaginary" "centrifugal" force that everyone loves to talk about in high school physics).
What you're thinking about is how much sidewall flex affects cornering. That's a different problem. When you get up to a certain point, that sort of thing is not a serious concern.
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Captain Slow.
Last edited by ReVerm : Jul 20th, 2004 at 07:59 AM.
Reason: Retracting unecessarily harsh words
Nope. That isn't correct either. Remember, tyres are made of rubber. Rubber generates more friction, internal and with other surfaces, during deformation and while it is being moved against a surface. Take a look at a traction-load graph, and you'll see that the tyres will generate more grip with increased load until it gets to a certain point, at which it tapers off, then drops. Also note that the load mentioned above is downward load, and despite intuition, it does not have anything to do directly with horizontal forces pushing the car out (the "imaginary" "centrifugal" force that everyone loves to talk about in high school physics).
What you're thinking about is how much sidewall flex affects cornering. That's a different problem. When you get up to a certain point, that sort of thing is not a serious concern.
Please don't look at street cars and guess when it comes to stuff like this. Someone might take your advice the wrong way and injure themselves.
Sorry, that's not a guess but I'll have to dig out my books to back it up. It's due to all sorts of things - side wall deformation, stresses in the rubber itself and other points, but put tyre X on a 1000kg vehicle and you might pull 1G cornering. Therefore the force vector is at 45 degrees.
Also remember I'm talking about percentage efficiency - cornering force vs downforce. If you think of the angle of the total force vector then that's a good indicator of the efficiency. I think you thought I was talking about absolute force, and yeah, that would make me very wrong.
Add weight to the vehicle to 1500kg and test. The extra downforce from the weight should theoretically cause a corresponding increase in allowable sideforce to match (just as you learned in highschool physics). eg drag a weight across a carpet - the more you push down the more you have to drag before it will break traction and slide. Theoretically it should be proprotional.
But it doesn't. For a practical tyre it's ability to handle side force will drop, and so the 1500kg test vehicle, being otherwise identical, will only corner at maybe 0.95G. The efficiency of the tyre has dropped due to increased load.
All the efficiency curves I've ever seen are a decreasing curve - starting at zero downforce allowing the highest cornering percentage, and getting lower percentage as the downforce rises. The curve gets steadily steeper (ie worse) the more weight (downforce) applied.
Very hard to draw in ascii art but this ain't bad:
That's a crap drawing but it's fairly close. Efficiency is the Y axis and downforce is the X axis.
Efficiency measured in percentage - if you like, the multiplier that will tell you how much side force it can handle as a factor of downforce.
If I was talking absolute forces, the theory I stated would be that if you increase the downforce from 1000 to 1500, the max side force would change from 1000 to 800 - WRONG.
In percentage terms: 1000 => 1500 results in 1000 => 1350
efficiencies:
1000/1000 = 100%
1350/1500 = 90%
Total cornering force still increases, but according to the law of diminishing returns.
__________________ I'd rather beSideways
1975 Datsun 180B - thrashed 'n' thrown around
1992 N14 Pulsar SSS - worn into the ground wasting HSV's through the corners - Enjoy your retirement my friend 2002 Aus. S15 200SX GT (a.k.a. Silvia) - standard (until funds allow)
OK - that's really dodgy, but it mostly shows the idea. I can't get the stray spaces out of it.
Y axis PERCENTAGE efficiency
X axis downforce
__________________ I'd rather beSideways
1975 Datsun 180B - thrashed 'n' thrown around
1992 N14 Pulsar SSS - worn into the ground wasting HSV's through the corners - Enjoy your retirement my friend 2002 Aus. S15 200SX GT (a.k.a. Silvia) - standard (until funds allow)
Ah, now I understand what you meant. It is rather simplified, but I'm sure you did that because it really is impractical to go into every detail on a forum post.
I apolegize if the previous post sounded a bit harsh. I certainly was confused about what you were talking about (I thought you were just regurgitating simple tyre theory stuff when you were actually contributing to the thread). Sorry.
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