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Mike Kojima posted on March 07, 2010 19:00 
The Ultimate guide to Suspension and Handling Part 2, Controlling Body Motion
By Mike Kojima
Previously, we covered the most important aspect of handling, the tires. The next important suspension trick to increase grip is to reduce body motion such as roll under hard cornering, dive under braking and squat under acceleration. In later editions of this series we will get into the technical aspects of chassis dynamics but for now we are covering the basics and will gradually get into the harder to understand parts of the subject.
Check out part one of the series here!
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| This 60's car shows all of the potential bad handling attributes that can be caused by excessive body roll. First the suspension is bottomed on the outside wheels causing a serious loss of traction, then you can easily see the huge amounts of bump and toe steer caused by the large amount of suspension stroking going on. Look at how the tires are pointed in different directions by inches! Next you can see how the camber is so far off, the tires are grinding on their edges. This car is so out of kilter it is in serious danger of rolling. Thank God they don't build them like they used to. |
Contrary to popular belief, body motion does not harm grip during cornering due to weight transfer to the outside wheels in a hard turn. Other things are the major contributors to weight transfer and we will get into that later. You want to reduce body motion because it slows how responsive the car is to inputs from the steering, brakes and accelerator, things that you, the driver use to control the car. Body motion also gives the impression that the car is not handling well, roll, dive, squat and wallowing do not give a feeling that inspires confidence that a high performance car should have; instead these attributes are more appropriate for a boat or an ageing baby boomer’s ride to a long dirt nap. Watch an F-1 car in a turn; it nimbly darts around the corner with hardly any body motion. Now watch an SCCA showroom stock racer, it leans squirms and squeals its way around the track at a much slower pace.
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| This Lamborghini Countach cornering at the limit shows that older exotics were not perfect. Note the extreme turning angle indicating that the front tires are sliding in understeer. This is because the outside front suspension has bottomed out causing the front tire to lose grip. However notice that the tread of the outside front tire's tread is flat on the ground due to the Lambo's more sophisticated suspension geometry than the old 60's car above. |
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| Sorry to use this photo again but here is the Dog II under heavy cornering load. The Dog II is based off of a Nissan Sentra, an Economy sedan with relatively crude suspension, however the suspension geometry has been reworked to optimize it. It also uses pretty sophisticated dampers, sway bars and high rate springs. Look how the body roll is under control and the camber is keeping the tires tread flat, even though they are distorted under side load. By looking at the tire steering angle and attitude, you can tell that the car is well balanced without excessive understeer. The distortion shows how hard the tire is being used. This little Sentra is pulling much more G's than the Lamborghini above. Surprisingly if someone would be willing to spend the money, the Dog II's suspension is pretty streetable. |
Sunday, March 07, 2010 11:43 PM
good article Mike. I love suspennsion geometry stuff. kinda fun to think about. It also helps me understand whats happening while I'm driving. In turn making me a better driver.
Monday, March 08, 2010 1:58 AM
I'm liking this article series. I'm wanting to know more about shock and spring tuning. Also what makes certain adjustable shocks good and others junk.
Monday, March 08, 2010 1:23 PM
I'm a bit confused... with double wishbone suspensions that gain negative camber in a roll, wouldn't we want at least a little body roll? For that kind of suspension, do you tune it to have some roll while minimizing bump/toe steer?
Monday, March 08, 2010 1:45 PM
Theoretically you would not want much if any roll but the suspension would not work well for absorbing bumps, hence the development of active suspension for F1 and other venues before it got banned. So no, you don't tune for roll, roll is the byproduct of having suspension.
Monday, March 08, 2010 3:44 PM
So is there a perfect design? Or do all designs and geometries have their pros and cons and you just have to compromise to find the best middle ground? Are even F1 teams with multi-million dollar budgets having to throw in some compromise somewhere too?
Monday, March 08, 2010 4:04 PM
You should start a school so people like me could pay you to teach us this shit!
Monday, March 08, 2010 4:30 PM
There is no perfect suspension design. All of them have compromises. The unequal length A arm is probably the best. I am not a fan of most multi--links.
Tuesday, March 09, 2010 6:14 AM
Hey Jason, while you're waiting for the more detailed explanation of dampers and what makes a good adjustable damper and what makes a bad one, you could read something I wrote to get the basics: http://www.sr20-forum.com/suspension/24698-opinions-wanted-those-agx-road-magnet-setup.html#post319188 Hey Mike, while I have you, you should shed some light on this (non suspension related) if you can. Tunerlifestyletv is not really doing their job. http://www.sr20-forum.com/general-sr20/28761-tunerlifestyletv-interviewing-mike-kojima-post-your-questions.html
Tuesday, March 09, 2010 8:46 AM
They are supposed to interview me soon. That what I know. As for the P10 I don't have one! All of my cars started off as Nissan dollar cars and they never gave me a P10. The P10 is better but there are few shells and few parts avalible and everything would need to be custom made. Our project P10 does quite well and hold the FWD SR20 lap record at Willow Springs. Anyone who knows me knows I don't care for autocross, I think its boring.
Wednesday, March 10, 2010 7:46 PM
a well put together article mike.really learn alot.this site is the best on the net right now.
Wednesday, March 10, 2010 10:26 PM
I have a hard determining front & rear bump steer in my Z32. The front adjustable upper control arms, tension rods, TEIN suspension, & rear upper control arms, traction arms can have a large potential to make things worse if adjusted improperly. I realize an alignment rack would be ideal however straight labor time on a rack can get pricey pretty quick. Four hours can blow by before you realize it. What would be a cost effective way to measure bump-steer, and also perhaps try to explain to readers what tools we can use (make or buy) at home to measure camber, caster, toe, etc....? (talking ballpark figures, just enough to drive around without toasting tires to the alignment shop for a final check). A lot of choices (mostly bad ones) can be made with what type of alignment strategy you use. I get so many different answers on what to do it gives me a headache. I know there isn't a one all great alignment spec, however a street, track, or weekend warrior spec would probably be easier to explain. If you could Mike can you please include some example alignment specs of your project vehicles to give readers some perspective on the difference between different setups for track and street use. Perhaps some tips on what changes to make first and last would be helpful. An example might look like. 1) establish street, track, or weekend warrior type setup 2) determine correct spring rate(s). 2) establish proper ride height 4) etc....... 5) etc.......
Wednesday, March 10, 2010 11:04 PM
Alignment specs are always in our applicable project vehicles. What you wish is coming in this series. To measure bump steer you can simply measure toe in several places in the suspension stroke. I use a gage especially made for it but you could do it with toe plates.
 
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