body separation

what is body separation and is it a good or bad thing?

It is suspension separation , it is caused by the instant center location in relation to weight distribution of the car. The balance of power and weight distribution of the car is set unless you move weight or change power level so we move the instant center to try and make the car work right. Some cars like a lot of separation and some don't it depends on the power, ic and weight distribution of the car.

Shock extension valving is another part of the picture that can also have an effect on the total amount of suspension separation happening at/during the initial hit. Depending on how "good" a set of rear shocks might be (age, total adjustment range, dampening capabilities) they can in effect "mask/change/override" (to some degree) the expected actions of a given I/C placement.

So a shock with the extension valving set really tight can in effect help make a relatively short/high (violent) I/C setting act less violent & calmer separating less at the initial hit than expected. And a looser shock extension setting can in effect help make a longer/lower (lazier) I/C placement hit harder & separate more than expected at the initial hit.

Thanks to modern highly adjustable shocks, racers have a biger adjustment window to work with these days. Some people like to use a violent I/C placement calmed back down with tight shock extension settings. Some like a lazy I/C placement that they "wake-up" with looser shock extension settings. And some choose a middle of the road setting for both I/C placement & shock settings. All three methods can be made to work good, it's really more of a personal preference/personal experience thing than anything.


Engine torque & I/C placement generates the given amount of leverage for separation, shock valving controls the speed (over a period of time) at which that leverage is applied/released. It's a balancing game.

so separation is the extension of the front struts on launch? is the compression of the rear also?

Larry Williams wrote:so separation is the extension of the front struts on launch? is the compression of the rear also?

No,

Body/suspension separation refers to the very first action (initial hit) the rear housing/rims takes, separating away from the chassis & planting the sidewalls down into the track surface. This first inital action might be very big (leafspring car) or very, very small (Pro Mod type car).

Seperation is the extension of the rear shocks. The fronts should always extend on launch. The rears can extend, compress or barely move at all at the hit. Just depend on the set-up.

Dave, you treed me!

wouldn't a lot of rear compression unload the tires?

BigDave65 wrote:......Dave, you treed me!

On a side note, the squatting rear suspension action during the recovery period some cars exhibit (after the first initial hit separation action) is sometimes not actually really the rear suspension it's self "squatting" (moving back up-into the car). Sometimes it's actually just the rims getting closer & closer to the track surface (and the body just following along) as the sidewall is wound-up tight. But viewed at full speed the human eye/brain can't tell the difference between the two. Only video slowed down lets you get a good look at the difference between sidewall squat vs suspension squat.


A data logger is the ultimate tool to see exactly how much total rear suspension separation and squat (or neither) might actually be happening at the shocks. Slo-mo video is great, but it can't compare to actual data taken at the shocks.

Larry Williams wrote:wouldn't a lot of rear compression unload the tires?

It really all depends on the total combo.

During the recovery period of the launch where the rear shocks are more likely to see some compression, a stiffer compression setting might help the already planted sidewall/tread surface stay planted longer. But on the other hand a stiffer compression setting might also unload the slicks too much on a wheelie bar car.

A stiffer rear compression setting might also hurt down track by making the slicks spin a little as they "skip over" bumps in the track instead of allowing them to follow the track surface more closely.

Slo-Mo video is your friend when chassis tuning. I used to spend hours watching vids of my own and other cars. You see things that scare you sometimes . I can't seem to get anyone to film nowdays.

i'd like "whitelightning"from the other forum to read this,he'd shit,then tell all you what it realy is and how f***ed up your cars are.

Cool40 maybe you should put a link to this thread over there!

cool40 wrote:i'd like "whitelightning"from the other forum to read this,he'd shit,then tell all you what it realy is and how f***ed up your cars are.

I just visited that thread. I missed it when it started. All I can say is WOW! I hope no one followed his advice. I quote "Body deperation is bad!" I guess he's never seen an old leaf spring Mopar stocker leave the line.

lghting94 wrote:Cool40 maybe you should put a link to this thread over there!

by god!

now we can share! http://www.460ford.com/forum/showthread.php?p=983373&posted=1#post983373

cool40 wrote:now we can share! http://www.460ford.com/forum/showthread.php?p=983373&posted=1#post983373

I completely missed that older thread, I thought you were referring to the newer one about anti-squat/percentage of rise.

All the references to Dave Morgan's chassis book are fine, but sometimes some people put the book a little too high up-on a pedestal. His book can be a great resource, especially for the beginner, but it isn't 100% right 100% of the time. And Dave's stuff isn't the only reading out there, there's Bickel's stuff, and even the ancient Alston ring-binder book is worth a read (if you can find it). One down side to Dave's book for the beginner is it can be a little too "math-ish" & technobabble at times for readers who aren't into geometry.

But to be honest sometimes all the so called "correct" chassis book math does get thrown out the window anyway when enough power is thrown at some cars. Real world track test results trump "book theory" results every time.

BigDave65 wrote:.........I can't seem to get anyone to film nowdays.

Dave if you tow the car to the staging lanes, would it be possible to talk the person driving the golf cart/4 wheeler into also doing the filming?

I drive mine to staging Dave. I know from experience it's aggravating for a crew guy to help me and fool with a camera. My mom used to film all the time, but she can't make it as often anymore. I pretty much have my car where I want it. On a decent track I'm 1.17 60's and they won't hardly vary more than .01-.015 all day, it's just as consistent as you'd ever want. Even with body seperation in the car! But it's cool to have the good races on film. I've been lucky enough to have quite a few wins on video, and a few screw ups too.

DILLIGASDAVE wrote:

cool40 wrote:now we can share! http://www.460ford.com/forum/showthread.php?p=983373&posted=1#post983373

I completely missed that older thread, I thought you were referring to the newer one about anti-squat/percentage of rise.

All the references to Dave Morgan's chassis book are fine, but sometimes some people put the book a little too high up-on a pedestal. His book can be a great resource, especially for the beginner, but it isn't 100% right 100% of the time. And Dave's stuff isn't the only reading out there, there's Bickel's stuff, and even the ancient Alston ring-binder book is worth a read (if you can find it). One down side to Dave's book for the beginner is it can be a little too "math-ish" & technobabble at times for readers who aren't into geometry.

But to be honest sometimes all the so called "correct" chassis book math does get thrown out the window anyway when enough power is thrown at some cars. Real world track test results trump "book theory" results every time.

I started out with the Alston Chassis Manual. I probably read that thing about 15 times before it started making sense. It is a bit dated but a lot of good solid info is in there. By the time I applied the info to the car I had at that time (which was the red/white '69 Mustang 2x3 car) It just became a hooking beast. The proverbial "hooking in a mudhole". The slicker the track was the bigger advantage I had.

I also have the Rick Jones book. It has some good info, but a lot of it leans more toward the Pro Stock level car. Some of the things just don't apply to a 8-900 hp bracket car.

what i could'nt understand about that other thread was.............wtf are they looking in "the book"to find out about a mud/sand truck?i know some of the basic shit will be the same but damn it's like put'n mud tires on a moped.