One of the most common questions from beginning, and even seasoned, autocrossers [and track racers] deals with how tire selections, tire pressures, spring rates, camber angles, sway bars, etc... affect handling. This thread is here to hopefully give the basics, and then answer questions if any remain.
First, a bit of terminology: Camber is the measure of how much "lean" a tire has compared with the ground, when viewed from the front or the rear. It is typically measured in degrees, through the center line of the tire tread, or by the angle that the carrier hub is held.
Spring rates are how "stiff" a spring is. For you physics type people it's really just the spring constant, and refers to how much weight [force] is needed to compress or stretch the spring a given unit from it's equilibrium position. For example, a 600lb spring needs 600lbs of weight to compress the spring one inch.
Sway bars are put on a car to reduce body roll. The way this is accomplished is by joining both sides of the suspension for the front or rear of the car together by the sway bar so that as one side is compressed, the opposite side is [theorhetically] compressed the same amount, which means that the front [or rear] suspension corners stay at the same level. Of course no material can be completely resistant to twist, so swaybars are made of steel, and their stiffness is guaged by it's main section diameter.
Tire pressures are measured in pounds of pressure per square inch [psi], and can directly affect the shape and stiffness of a tire, which will be discussed later.
Tire compounds are measured on an arbitrary scale of hardness, normally with a durometer. A super simple way to describe how a given value can be represented in a tire, a value of 40 would be a very soft tire that you could leave an impression in with your fingernail with very little effort, while a value of 100 would be the hardness of your kitchen counter. For the vast majority of tire consumers, these compounds are simplified into categories speed ratings, tread wear ratings, and temperature resistance.
Caster is similar to camber, but refers to the axis of rotation [and it's variation in degrees fore to aft] that the hub carrier is held when the car's wheels are turned. Caster can have a dramatic effect on the weight transfer of a car's chassis when entering a turn, but since this is largely un-adjustible even with camber plates on most FWD cars, it will not be discussed.
Toe-in/out refers to the amount that the tires in the front or rear set with their leading edges pointing towards, or away from each other, respectively.
Damping rates refer to the shock or strut's ability to control the oscillations of the spring. There is no real defined scale other than a very high rate prevents the spring from moving much, and the highest rate would prevent any movement, whereas a very low rate would allow the spring almost free movement without resistance.
Ok, now that everyone should know what I'm talking about, lets get down to business.
For starters, we will be dealing mainly with FWD cars, this being a Honda enthusiast site, and the vast majority of Hondas being FWD. The inherent handling of a stock Honda is that they understeer, badly. This is due to a high percentage of the weight being over the nose, which is to say that the rear tires don't normally have enough grip to force the front tires in the directions they are pointed. The other inherent handling trait is that Hondas exhibit lift-throttle oversteer, which again deals with the heavy amount of weight being over the nose, and the ability of the engine to slow the front wheels without affecting rear wheel momentum; result, the rear tries to pass the front. So what do we end up with? A car that doesn't want to turn in, but as soon as you lift off the throttle, tries to swap ends on you.
While this sort of behavior is quite driveable, it's usually not the comfortable way to drive at the limit, which is to say that it's also no the fastest way. In my opinion, if a driver isn't comfortable with thier car, they won't be driving it to it's fullest potential. The general preference for drivers is to have a car that has good on-throttle turn in, with a slight bit of oversteer when off-throttle, but tucks the rear in nicely when back on the throttle again. At no point during a turn should the car be twitchy, slow in response to inputs, or unpredictable. This is commonly referred to as neutral handling, although different drivers have different opinions as to what is neutral.
Great, we know what we're after, how do we get there?
For starters, most people try to make sure the suspension has as little slop or other variables that can play havok with handling as possible. This includes installing strut tower braces, lower tie bars, polyurethane bushings, spherical bearings, heim joints, and of course, making sure the unibody is straight and true before doing any modifications.
Ok, your suspension is only going to move in the directions you want, now what?
Most people like to get springs and shocks and worry about sway bars later, however, these items should ideally be paired and installed at the same time to get the greatest benefit [**disclaimer: any time you make handling changes to your car, you should practice EXTREME caution when learning the new limits to your car**]. Typically the goal is to reduce body roll and force the suspension to make greater use of the tires. This means higher spring rates and higher damping rates on all four corners of the car typically, and also means that you would need a heavier sway bar in order to force the car into cornering flat with the stronger springs. Spring rates are going to vary from application to application, however most find that heavier spring rates in cause the car to rotate easier in corners, so that is something to keep in mind. Additionally, sway bar thicknesses and availabilities are going to vary from car to car, but it should be noted that if the sway bar is thicker than necessary, the car will exhibit more "jittery" behavior over uneven bumps [track curbing, potholes, etc.].
Ok, your suspension now moves only how you want it to, corners flat, and forces the tires to do more work since the car is no longer unloading as much weight off of the inside of the car, now it's time to look at your link to the road: your tires.
Your handling is only going to be as good as your tires, so it's time to evaluate what you can live with. The ideal tire would be one that is as soft as a gumball, that never overheats, and wears like iron. Like I said, that would be the ideal tire because it doesn't exsist. Instead, it's time to make some compromise choices. For those on a budget, a tire that offers excellent grip and doesn't wear out very fast means that they are normally prone to overheating, which eliminates them as the best choice for high speed, tight corner courses, but could make them an excellent 35 second per run autox tire. Still on a budget, if you're looking for a tire that has excellent grip and doesn't overheat, you can kiss durability goodbye, this is because these types of tires normally cool theirselves off by shedding rubber from the tread area, sticky race slicks come to mind in this area. And finally, if you want a tire that doesn't overheat and will run forever, well then... don't expect the greatest grip, it just isn't doable with tires nearly as hard as stones.
Alright, suspension is done, and you have your tires picked out, time to go kick tail right? Not so fast. All of your new parts and handling just means you spent a bunch of money, which doesn't earn you competition wins unless you know how to tune them for greatest effect.
Certain tracks and courses like different settings. If you were on a rough track with poor grip, for example, you might want a softer spring rate to cope with the bumps, and you may want a slightly softer damping rate so that the tire can spend as much possible time on the ground. On the other hand, a fast, smooth track would allow you to run a higher spring rate with a higher damping rate, which means your tires will likely never get a rest from being buried in the pavement. Obviously most people can't change spring rates at the course to cope with the conditions, especially those on a budget. What you can do, however, is to start with a middle-range spring rate, which can be quite versatile, and adjust the handling characteristics with some adjustible damping rate shocks or struts.
So you're all tuned in the suspension, what can you do to make sure the tires will do their part?
First things first, you need to know how the tires are wearing. Ideally, you want the outside front tire to use it's entire treadwidth evenly in the hardest high speed corner on the course. This will insure that you never roll the tire over on the sidewall which can unload all the grip you'd built up to that point, which also means that the car will only use as much tread as needed in all the lesser speed corners, which helps reduce your rolling resistance in a corner. To accomplish this will take some experimentation. The best tools to use for this are chalk [or white shoe polish] and a tire pyrometer [if you can afford it, otherwise trust the calibrated touch/sight method]. If your camber is set correctly, you'll use up to the edge of the tread, but not over, and if your tire pressures are correct, you'll have an even temperature across the tire. Adjust both camber and pressures until all is well.
Ok, pressures are set, suspension is set, and the car still doesn't feel right.
It happens. What you have to decide is what specifically don't you like about what the car is doing, and what is going to be your plan to go about changing it for the better.
These kinds of complaints and solutions are going to vary widely from person to person, but the one thing that should absolutely be kept in mind is to only change one item at a time between tests if you change more than one thing at a time, how will you know what change had what effect? This leads into another point I'd like to stress on everyone: keep a detailed notebook of changes and effects. This notebook should include important information such as tire pressures, which tires you're using [if you change], what the track conditions are, what the weather is like, and biggie: what the car was doing. This is going to help you find a setup that works for any situation before you ever put the car out on course, which will save you time when you need to start tweaking for your particular event.
If there is anything I missed that you'd like to hear about, please mention it, and if there's anything you'd like a clarification on, please quote it.
-Harry
AIM: NDcissive
CRX and Pre '92 Civic, Engine Tech and Tuning, & Track and Autocross Forum Mod
One thing I never understood is why the Japan FF road racers and gymkhana folk run spring/shock suspension setups that are OPPOSITE to those of us US folk. Higher spring rates in front/lower rates in rear, ESPECIALLY in gymkhana. One would think this would contribute to huge understeer.
Then again, running super high rates in the rear make the car prone to dive bombing and becoming squiggly under hard braking.
Originally posted by Shingoblade-GSR One thing I never understood is why the Japan FF road racers and gymkhana folk run spring/shock suspension setups that are OPPOSITE to those of us US folk. Higher spring rates in front/lower rates in rear, ESPECIALLY in gymkhana. One would think this would contribute to huge understeer.
Then again, running super high rates in the rear make the car prone to dive bombing and becoming squiggly under hard braking.
Any thoughts on this?
Ok, this is a classic example of regional preference. Here in the US, drivers are taught on the basis of threshold braking. That is, we brake in a straight line before turn-in. What this does with the higher rear spring rates is forces more weight over the front tires for more positive turn in, while allowing for a lot of rotation in the rear, until power is applied at the apex, effectively planting the rear tires again.
In Japan, trail braking rules supreme. Drivers will drive into a corner as fast as possible, hit the brakes VERY late, and stay on them until they're ready to hit the power again. By driving in such a manner, they're getting almost the same effective weight transfer that US drivers are, which means they're getting about the same handling, but their corner entry speed is usually much higher, at the expense of a little corner exit speed, which is focused on here in the US. You may also notice that drifting is also much bigger in Japan than here, and so higher front spring rates play a huge role in that, but more for the reason of guaranteeing steering control with the car sideways, while allowing the car to remain sideways; which is difficult at best with a US prepped car once you apply the power again.
In addition to what Harry said, some Japanese race cars run skinnier tires on the back to encourage rotation without transferring too much weight away from the front.
Originally posted by 1stGenCRXer Caster is similar to camber, but refers to the axis of rotation [and it's variation in degrees fore to aft] that the hub carrier is held when the car's wheels are turned. Caster can have a dramatic effect on the weight transfer of a car's chassis when entering a turn, but since this is largely un-adjustable even with camber plates on most FWD cars, it will not be discussed.
On mine it's adjustable , so if you don't mind I would like to discuss it. I know that more positive caster helps high speed stability and allows the steering wheel to return faster, but I was unaware of the weight transfer issue. If you don't mind, could you please explain the effects that caster has on weight transfer?
TIA,
Andrew
'98 DX Sedan
Sus. Tech. springs
Extemely Conservative Mode-
Frnt:
-0.1*(L), +0.2*(R) Camber (3/10 Split to compensate for road crown here in Idaho)
+1.8* Caster
+0.05* Toe
Originally posted by forcedinduction If you don't mind, could you please explain the effects that caster has on weight transfer?
Alright.
The easiest way to think about how caster works is to imagine a wheel and how it moves during steering, or, you can illustrate with a roll of tape on your desk.
Using the tape example, use a rubber band or something sufficient to hold a pencil through the centerline of the roll of tape, orienting the roll like the tire and wheel would be. Now, during steering we all know that the wheel will turn left or right about it's steering axis, and this can be demonstrated by holding the pencil perpendicular to the table and twisting. Now, if we tilt the pencil back towards us and turn the wheel, what happens?
Can't really tell can you? Do the same thing, and this time, hold the pencil with your other hand and hold the tape slightly above the table surface. What you should notice is that when you turn outboard, the wheel "digs in" to the table, and when you turn inboard to the pencil, it seems to lift slightly. Any time the contact patch of the tire changes it's "distance" up or down, it tries to carry or lose more weight. When the tape tries to "dig in" it's effectively trying to carry more weight, which is what you want for cornering, more inside weight for stability, especially since the natural tendency is for items of mass to travel to the outside radius.
Now, if you do the same observations but this time tilting the pencil away from you, you'll notice that when the tape turns outboard, it tries to lift from the table.
This isn't an entirely bad thing. The idea is for the inside to be forced to carry more weight by raising it's height, which will then catch the weight of the outside wheel as the front tries to re-establish an equilibrium. This normally means the outside tire takes a lot of abuse on corner entry, and that corner entry is a bit more squimish.
This isn't entirely the front tire's fault though. What I haven't mentioned is the weight transfer effect to the rear wheels.
Now, in an ideal chassis, the frame is absolutely rigid, and as we all know, if you lift on one corner, the weight has to be carried by another corner. This is where cross-weight comes into play in the grand scheme of cornering weight transfer.
I hope I didn't go through that too quick, any other questions?
Originally posted by 1stGenCRXer
(Refering to positive caster):When the tape tries to "dig in" it's effectively trying to carry more weight, which is what you want for cornering, more inside weight for stability...
&
Originally posted by 1stGenCRXer
(Refering to negative caster):...you'll notice that when the tape turns outboard, it tries to lift from the table. This isn't an entirely bad thing. The idea is for the inside to be forced to carry more weight by raising it's height, which will then catch the weight of the outside wheel as the front tries to re-establish an equilibrium. This normally means the outside tire takes a lot of abuse on corner entry, and that corner entry is a bit more squimish.
You say that neither one is entirely bad, but you make it sound like that one would prefer more a more positive caster angle than a negative one, correct? Also, at what point does too much positive caster hurt a FWD car? I've seen most FWD cars to have a stock spec of about +2-2.5* while other RWD cars like the 240SX and Porsche 914 are blessed with as much as +6-7*!
Thanks,
Andrew
P.S. I liked your visual with the tape and pencil, very creative.
For starters, we will be dealing mainly with FWD cars, this being a Honda enthusiast site, and the vast majority of Hondas being FWD. The inherent handling of a stock Honda is that they oversteer, badly. This is due to a high percentage of the weight being over the nose, which is to say that the rear tires don't normally have enough grip to force the front tires in the directions they are pointed. The other inherent handling trait is that Hondas exhibit lift-throttle oversteer, which again deals with the heavy amount of weight being over the nose, and the ability of the engine to slow the front wheels without affecting rear wheel momentum; result, the rear tries to pass the front. So what do we end up with? A car that doesn't want to turn in, but as soon as you lift off the throttle, tries to swap ends on you.
I found an error
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You say that neither one is entirely bad, but you make it sound like that one would prefer more a more positive caster angle than a negative one, correct? Also, at what point does too much positive caster hurt a FWD car?
Originally posted by forcedinduction You say that neither one is entirely bad, but you make it sound like that one would prefer more a more positive caster angle than a negative one, correct? Also, at what point does too much positive caster hurt a FWD car? I've seen most FWD cars to have a stock spec of about +2-2.5* while other RWD cars like the 240SX and Porsche 914 are blessed with as much as +6-7*!
Ok, neither is really preferred over the other, besides the weight transfer advantage, caster helps to return the steering wheel to center naturally when you exit a corner. No matter whether the caster is positive or negative, there will still be a tendency for the steering to return to center, although probably marginally moreso with positive caster.
Now, the reason for so much rear caster on a rear wheel drive is because the chassis can use it more. The power is delivered at the rear wheels, so the more cross weight you can get to the wheel, the harder you're going to force the tire to work in your favor. Obviously this has some limits, but that's the basic principle. On a FWD car, obviously the power is not delivered at the rear wheels, so you really only need to get enough weight transfer to keep the rear of the car predictable. It's all about weight transfer and cross-weights for corner entry.
Originally posted by 1stGenCRXer Now, the reason for so much rear caster on a rear wheel drive is because ...
The numbers I was talking about are off the front of the car, not the rear.
So if I understand you correctly, the MORE caster you have (more being greater than 0 weather it be positive or negative) the MORE weight transfer you will have (theoretically speaking of course)? Sorry for dragging it out, but I would really like to understand this concept. Thank you for taking the time to explain it to me.
Originally posted by forcedinduction The numbers I was talking about are off the front of the car, not the rear.
Right, caster only makes an effect if the wheels are being used for steering anyways.
So if I understand you correctly, the MORE caster you have (more being greater than 0 weather it be positive or negative) the MORE weight transfer you will have (theoretically speaking of course)?
yes. Theorhetically speaking
Sorry for dragging it out, but I would really like to understand this concept. Thank you for taking the time to explain it to me.
-Andrew
It's all good, it takes a little bit to get it all, and I understand that.
For lowered cars, is it safe to assume that some type of adjustable camber plate is being used? Or better still, what is a typical ride height that would not require camber plates?
The buffer safe zone for most Hondas are 1.5-2.0" where you do not need a camber kit. ONe thing that will affect wear too is toe. Too much drop and if I remember right your car will toe in, that will cause tire wear just as bad as bad camber.
I've been dropped 2" for over a year and my tires have worn nicely. But I also autocross on them frequently scrubbing the outsides too.
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I notice that in my 4dr 93 civic that if I'm cruising down a gravel road at 80km/h+ my ass end becomes QUITE loose and I have learned howto drive with it doing that. Its not the coolest feeling, but I can live with it for now.
how much should i lower my car?
i know nothing about camber ive only heard that u must put some sort of camber kit if u drop more than 2 inches.. i was thinking of dropping 1.75 inches.. is this a good amount to get alot of downforce and be able to hug the corners?
Lowering a car has no direct affect on downforce unless the underside of your car is channeled to make best use of the air that travels under it.
What it does do is change the center of gravity on the car so that the forces on the tires become more parallel to the contact patch.
That said, camber kits for lowered cars are largely needed so that you don't get uneven wear characteristics on the tread.
The amount you should lower your car depends on your car, spring rates, tires, and road surface. For an average street car, 1.5"-1.75" is fine, but if you don't get a good set of shocks, and don't balance your spring rates accordingly, your handling could actually get worse.
-Harry
AIM: NDcissive
CRX and Pre '92 Civic, Engine Tech and Tuning, & Track and Autocross Forum Mod
i plan to get really good springs and shocks and a good suspension setup
upon asking around.. ive been recommended many things and here is my plan for my setup on my 98 civic cx h/b.. please let me know what u think:
with my gs-r swap ill be getting a LSD tranny
custom ground control springs
koni yellow shocks
energy suspension polyurethane bushings
front and rear sway bar upgrades (any help here? i dont know much)
front and rear upper strut tower bars (neuspeed?)
front and rear lower tie bars (recommendations?)
crossbar
lower the car (im not sure to what height... what u recommend?)
15" konig helium wheels
falken azenis tires
i would like to build the car to handle very well at the track so i can destroy this prelude around here that is known for being fast on the track..
let me know what u think and if u have any concerns, critiques..
thanks
As we veteran racers always say the best money spent is on schooling - whether it be an HPDE (High Performance Driving Education) or Evolution School (autocross).
Spend $1000 on suspension mods and you might gain .5-1 second on a 30 second course. Spend $225 on an Evolution School and you can drop 4-10 seconds off the same course. Schooling is much more cost effective than spending money on mods.
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Originally posted by 1stGenCRXer Ok, this is a classic example of regional preference. Here in the US, drivers are taught on the basis of threshold braking. That is, we brake in a straight line before turn-in....In Japan, trail braking rules supreme. Drivers will drive into a corner as fast as possible, hit the brakes VERY late, and stay on them until they're ready to hit the power again.
Playing a bit of catch up on the threads, and noticed this.
Are you sure you don't know trailbraking USDM drivers?
I know:
* NASA instructors who teach FF trailbraking techniques to upper level Group 2 drivers, and Group 3 drivers who ask them along.
*Some very successful Honda Challenge drivers (including the H1 and H2 champions in '02), who trail brake as a matter of course.
Having observed the Spoon Sports #96 car up close, and having talked to Ichisima about the differences between USDM and JDM racing setups, the biggest difference physically seems to be that the JDM drivers run more extreme camber settings (negative) on the front, and have bigger swaybars on the back of the car.
When everything's said and done, the JDM and USDM cars appear to have the same handling dynamics, but they achieve it differently.
The USDM way is cheaper, which is a consideration for students.
A couple of years ago, I bought Spoon springs (heavy front) for my ITR, without really telling anybody I was doing it or consulting anybody.
They were a little upset w/me because simply buying the springs, and knowing the purpose I had in mind, they felt this was detrimental and they'd be getting bad publicity for it. It really didn't do what I wanted, and in getting suggestions for sorting it out correctly, AJ Racing (Spoon distributor for North America) advised me that -2.5 negative camber on the front would be a part of the solution.
I'm now on revalved Koni Yellows, 400# springs front, 500# springs rear, and the car's a delight to drive on street or track. Swaybars OEM. It fits perfectly into NASA Group 3 but it can still be driven to and from the track in complete comfort.
I have heard the comment about JDM-exclusive trailbraking before, and I'm not really sure where that comes from. Perhaps it has to do w/all the videos we get from them, which videos have a little screen focused on the pedal activity.
I think that most of the people who watch those tapes are not at a developmental stage where they'd be considering trailbraking in an FF car, and they're not at a stage of development that their instructors are comfortable talking to them about it. So they continue to believe that it's a JDM characteristic.
I watched the RealTime DC2 cars in the only World Challenge race I've seen at VIR Full, and those guys were definitely trailbraking.... Definitely. LOL...
Personally, with my setup, I trailbrake a little, but it's not extreme, since I'm out there to have fun and fully intend to drive the car home and not spin out in front of the Cobra I just passed on the straight.
Example I can think of is Summit Turn 5.
If your lap times are faster, you can get by some very fast cars between Turn 4 and Turn 5, but you'll be faced with having to slow down from 110 to 45 very quickly. An ITR will be borderline ABS even on good R compounds w/that manoeuvre, and you'll have to trailbrake into the turn to control it.
If you time it right, you're on the gas again right when you get to the apex and the Cobra or Porsche driver is mentally scratching his head wondering how you did that.
As the years go by, it seems that more and more USDM racing outfits are using the JDM heavy nose setup but with heavier bars in the rear and radical camber up front to make up for it. Although I'm not at the stage of development where I'd want to start over w/a different suspension, I know there's got to be something to it. I believe that Jason Franza, the ECHC H2 champion in '03 has a heavy nose setup.
That refers to the DC2 people. I've noticed that all the DC5 and EP3 people seem to agree on heavy spring rears. Even the Mugen Street setup (on my daily driver EP3) is heavy springs on the rear.
George, I know how to trail brake, and maybe my definition of trail braking differs a bit from yours.
To me, you're describing when a late braking manuever turns into a necessary trail braking situation. Most ECHC guys I've seen fall into this category, but the majority of their braking occurs with the wheels as straight as possible.
When I trail brake, braking doesn't even begin until AFTER turn-in. Sure, the driver has to lift off the gas a little earlier, but actual braking doesn't start until you've already started your initial turn. Most FF cars suffer an aburpt trip to the gravel trying this .
The additional camber in the front plays a big role in how much you can get away with trail braking, in any car, because of weight transfer. As you turn in, the tire starts flattening, and then once you apply the brakes, the forward outside corner really dives down and takes a lot of weight. A tire nearing zero camber is going to roll over and send you again, to the gravel. Of course, to get the greatest benefit from this without excessive body roll, you need some stiff springs, and you can get away with lighter springs in the rear for rotation under braking.
I've had a chance to talk with drivers from around the world from my living room [internet is great that way], and in my travels been able to talk with regional drivers. There's lots of ways to be fast, but it's all about comfort.
-Harry
AIM: NDcissive
CRX and Pre '92 Civic, Engine Tech and Tuning, & Track and Autocross Forum Mod
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, so if you don't mind I would like to discuss it. I know that more positive caster helps high speed stability and allows the steering wheel to return faster, but I was unaware of the weight transfer issue. If you don't mind, could you please explain the effects that caster has on weight transfer?
Take your time!
1stGenCRXer
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