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Mike Kojima posted on June 08, 2010 15:25 
The Ultimate Guide to Suspension and Handling Part 3: Balance the chassis
By Mike Kojima
Check out part one of the series here!
Check out part two of the series here!
Now that you have reduced body motion and improved steering response, we can work on the next major area of improvement, improving chassis balance. The goal for most of us is to have a car with neutral balance. Neutral balance, where all four tires slide the same amount, is the fastest way around a corner most of the time. This way the total maximum grip of each tire is being used. It might seem odd but experienced drifters prefer a neutrally balanced car because it allows them to have many control options for setting the car sideways. For example I set up Dai Yoshihara's Team Falken S13 in about the same way I would if it was a Time Attack car.
Unfortunately for the enthusiast, most cars are tuned to understeer from the factory. Understeer occurs when the front tires slide before the rears at the limit of grip. Manufacturers do this because it is the easiest handling mode for the average driver to control. Understeer is not efficient for extracting maximum lateral acceleration because the car will use the front tires excessively while the traction contribution of the rear tires is wasted. It’s also the slowest and most boring way around a corner. Bottom line? Understeer sucks.
If we go too far in the quest to eliminate understeer through chassis tuning we will inevitably create oversteer. Oversteer occurs when, at the limit, the rear tires slide before the fronts. Drifters work at controlling and driving in a state of continuous oversteer, raising it into an artform. A fast autocross car is often set to oversteer as are most rally cars. Any sort of race car that is driven mostly in very tight corners will probably be faster if it tends to have a bit of oversteer. Due to consumer advocate Ralph Nader's highly publicized campaign against General Motors and the rear engined Corvair in the 60's which resulted in huge lawsuits against automakers, the entire automotive industry is adverse to producing a car with anything close to oversteer. When an oversteering car exceeds its limits, it "spins out" which lawyers like to make sound especially heinous. However this simply means that an understeeing car will plow off the road nose first and an oversteering car will go tail first. You are gonna crash either way!
Tuesday, June 08, 2010 6:42 PM
with more articles like this, i can relocate my SCC rags into proper display cases instead of strewn about for quick reference.. its articles like this that sets you particular group of motorheads apart from the droves of overly surface-deep outfits. ill be looking forward to future installments.
Tuesday, June 08, 2010 7:00 PM
I love technical articles like this. While I have read and understand the information above before, it is always nice to have a refresher, as well as a place to refer less knowledgeable friends to. It's hard to find information like this in one place, especially in forums! Keep them coming guys. I'm a sponge ready to absorb.
Wednesday, June 09, 2010 10:55 AM
Hmmm Good To Know.
Wednesday, June 09, 2010 1:27 PM
I found the tire pressure section really interesting, I know about the extremes from back in the day when I used to "tune" my golf cart (I worked with what I had), but I thought it's really interesting pressures have an inverse effect inside that tuning envelope. I guess it makes sense, higher air pressure stiffens the sidewall, affecting the performance of the tire.
Thursday, June 10, 2010 10:36 AM
You say that moving the sway bar endlink mounting point further inward relative to the plane the bar operates on increases stiffness of the bar. However, in order to calculate the torsion rate of a sway bar you multiply the perpindicular distance of the bar by it's length. (specifically it's perpindicular length squared by a constant). So, really on a adjustable bar, lengthening the sway bar (moving the link out further) makes it stiffer and have a higher rate, not the other way around. Glad you guys are doing these articles. Not that I haven't found all these sorts of things out myself, but it's very easy to direct other people who I know here. And it's always fun to read up on these things. you never know, you may learn something new!
Thursday, June 10, 2010 11:27 AM
Great read!! It's nice to read articles written by someone who knows what they are talking about then some random guys on car forums.
Friday, June 11, 2010 10:33 AM
Low enough tire pressures can make for an unpredictable car, too. I had the pressures on the Rx-7 set at ~30psi while I was playing around with it a bit, and if I cornered hard enough it felt like the sidewall of the outside front tire was folding over and popping back as steering went back to center, which made the front end of the car dart in the opposite direction. Tire was a 205/60-13 Sumitomo HTR on a stock (6? 6.5? inch wide) wheel.
Friday, June 11, 2010 12:05 PM
Tomo, moving the end link away from the plane of the bar makes its softer not stiffer. The bar is a rod in torsion and moving it away increases the moment arm that twists the bar softening it, not stiffening it.
Saturday, June 12, 2010 10:07 AM
Good article Mike, keep them coming, also some really straightforward points but as you see in comments there isn't 100% agreement or understanding on all the variables at play here.
Sunday, June 13, 2010 6:32 AM
Your series of articles on handling was a good read Mike, it ranges from the basics to stuff that can get tedious. Just recently, i realized who you were when i watched a video of JRod interviewing you and the team. I was wondering from a practicality stand point of a chassis and suspension engineer that works in the FD industry: when setting up a car, such as Dai's S13, do you guys calculate things like the roll rate, roll stiffness (spring rate, motion ratio, roll bar stiffness, tire stiffness), sprung vs unsprung weight, and geometric vs elastic weight transfer? Or do you guys purely rely on driving input of how the vehicle feels?
Sunday, June 13, 2010 9:23 PM
In the beginning we do all of that, I have an excel spreadsheet that calculates all of that and more, we consider the ride frequency and under/oversteer gradient as well although I don't really tune for that in drifting as I don't think its that important unless the numbers are really out of whack. This is because a cars wheelbase and track width are so variable in drifting depending on the slip angle. It is more important in grip driving though and for a road racer I do tune around frequency matching. Believe it or not I set up Dai's car like it would be set for grip driving and his car would be a killer road racer if it were harder sprung with aero. So different springs, a real wing and diffuser with a splitter and a flat bottom, look out time attack. Once we calculate the basic set up in testing we fine tune it relying on driver feedback, tire temps and eyeballing. KW's Chris Marion and I are pretty good at looking at how a car is driving and knowing what it needs. The suspension is one of the great secrets of Dai's car and what allows him to pull away from cars with 100-200 more hp than him in drift. If you look at photos on Motor Mavens and Drifting.com, you will see photos of Dai's car nearly pulling the wheels off the ground in drift like a world of outlaws sprinter. In some shots he's three wheeling.
Wednesday, February 15, 2012 4:19 PM
Thank you mr. Kojima for sharing this stuff. It's not easy to find such detailed infos from a reliable source on the internet. There's one thing I don't understand, though: after looking at some graphs on race car vehicle dynamics book (p. 26-29), i understand that slip angle decreases with load, while here you say that greater load means greater slip angle.. who do I have to believe? :-) Thank you
 
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