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how low is too low?

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frankenstang57

frankenstang57

Jedi Warrior
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/ubbthreads/images/graemlins/tongue.gifQuestion for you guys about my Spitfire. I'm planning on using the car for racing only and was wondering how low I can drop it. I figured with addition of the V-8 the front end would sit a bit lower. Well, I was wrong. With all the lightening and the set back of the motor, the front end is way high. I was thinking about chopping down the springs a bit to bring it down. My question is, how far the car can come down before suffering any negative affects? Any suggetsions? Thanx! /ubbthreads/images/graemlins/tongue.gif
 
All I can say is: DON'T CHOP THE SPRINGS! By doing that, you keep the same spring rates, but the springs are now shorter so they will bottom out much faster. A much better alternative is to buy shorter springs
 
There is no absolute answer. It depends on track surface conditions, suspension travel, vehicle weight, ratio of sprung to unsprung weight, driver technique, tire flex, aerodynamic loads, yada, yada, yada...

As a minimum I would hope that no part of the car touches down before the suspension hits the bump stops.


PC.
 
[ QUOTE ]
All I can say is: DON'T CHOP THE SPRINGS! By doing that, you keep the same spring rates, but the springs are now shorter so they will bottom out much faster. A much better alternative is to buy shorter springs

[/ QUOTE ]
Actually when you chop (shorten) the spring, the rate of the remaining spring increases. View the spring as a torsion bar which it actually is. Just coiled up.The shorter the bar for a given diameter, the stiffer the bar.

The static height will be lower & the rebound travel greater. More rebound travel may not be desirable & you may want to decrease the rebound travel. Otherwise, the short spring may get dislocated when the suspension is at full rebound. This is of no concern if the static height is already way above stock.
D
 
Actually, you can chop the springs get a stiffer rate. If there are 10 coils, and one coils is cut off, the spring rate will be about 1/10 (10%) stiffer...if all else is equal (and that's a big "if"). [edit: Dave, you beat me to it!]

But PC is correct too...there is no hard and fast answer and you will have to test, test, test.
I dropped my car down until the front sway bar mount was *lightly* kissing the road at one of the bumpiest sections of Pocono. After fitting slightly new dampers, I discovered that the sway bar wasn't even coming close due to better dampening....so I dropped it a bit more.
Really, it depends on spring rate, dampening rate, the bumps on the track surface and a host of other things.
Just for reference, my Sprite has 2.75" of static ground clearance at the closest point (front sway bar mount) and the other Sprite I race has around 4"

One of the most important things to remember with dropping a car is that the front steering geometry needs to corrected afterwards. Otherwise, the car will have horrible bump-steer and the toe-out-on-turns will be all messed up.
Many of these "lowered, slammed tuner cars" have pathetic steering and are very "darty". Most probably have poorer handling than if they were at the correct ride height.
 
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...Many of these "lowered, slammed tuner cars" have pathetic steering and are very "darty". Most probably have poorer handling than if they were at the correct ride height.

[/ QUOTE ]Yeah, but they compensate for the altered geometry by adding Eibach stickers. /ubbthreads/images/graemlins/wink.gif


PC.
/ubbthreads/images/graemlins/hammer.gif
 
[ QUOTE ]
[ QUOTE ]
...Many of these "lowered, slammed tuner cars" have pathetic steering and are very "darty". Most probably have poorer handling than if they were at the correct ride height.

[/ QUOTE ]Yeah, but they compensate for the altered geometry by adding Eibach stickers. /ubbthreads/images/graemlins/wink.gif


PC.
/ubbthreads/images/graemlins/hammer.gif

[/ QUOTE ]

That geniuinly made me laugh out loud. I've heard that Greddy stickers can add as much as 10 horsepower each, though.
 
[ QUOTE ]
Actually when you chop (shorten) the spring, the rate of the remaining spring increases. View the spring as a torsion bar which it actually is. Just coiled up.The shorter the bar for a given diameter, the stiffer the bar.

D

[/ QUOTE ]

Dave and Aeronca, I believe you becaue you're very knowledgable, but I don't understand how cutting a spring could make it stiffer. If we use your torsion bar example, it seems like cutting it shorter would make it harder to bend, but only because you have less leverage than with a longer bar. So the mechanical advantage changes, but not the stiffness. /ubbthreads/images/graemlins/confused.gif
 
Webb,

Look at it this way,

Let's say you had one spring 10" long with ten coils and the spring rate is one hundred pounds per inch.

Squeezing it one inch squeezes each coils 0.1" and since they are all end-to-end (in series) that means each one must exert 100 pounds of force. So therefore each individual coil's spring rate is 100 pounds per 0.1".

Now cut it in half. You have five coils.

By squeezing the half-spring one inch you are now squeezing each coil 0.2".

Since each coil's rate is 100 pounds per 0.1" you now must exert 200 pounds of force to squeeze each coil 0.2".

You are therefore exerting 200 pounds per inch on the cut spring, twice the spring rate, twice as stiff.


PC.
 
Hi Webb,
Harder to twist, not harder to bend. The coil spring wire actually twists to give it spring. It doesn't bend sideways. Not real obvious from looking at it I guess.

I'm trying to think of a good analogy. Adapt a 3/8" drive socket extension, say 12" long, to a 1/2" drive long handled breaker bar. Clamp the free end of the extension in a vise & exert enough pressure on the handle to twist the extension slightly. Use a torque wrench instead of the breaker bar if it helps. You will probably have to eyeball the amount of twist in the extension.

Now do the same with a 4" extension instead of the 12". Which of the two extensions is the easiest to twist the same amount? The long one. Same with torsion bars, same with coil springs which are in fact a form of coiled torsion bars. Maybe you can just use the analogy without the hardware.

Aside: Stretching a coil spring will make it longer & increase the preload, but it won't increase the actual spring rate. Stretching it & then cutting it back to original length will increase the spring rate.
D
 
/ubbthreads/images/graemlins/laugh.gif I've got one of those K&N 100hp stickers on my Kia, but it's only good for 50 because I stuck it on the airbox under the hood. I gues I should have stuck it to the back window! /ubbthreads/images/graemlins/grin.gif I'm more concerned with geometry than spring rate. You guys are right about chopping the springs will increase the rates a bit. Upping the rate wouldn't necesarilly a bad thing, but I'm only talking about a coil. I know from setting up my Mustang, there comes a point where it is too far. I was thinking I would be OK as long as I keep the control arms parallel to the ground. The car will be used for auto-x. /ubbthreads/images/graemlins/tongue.gif
 
Actually you could probably go a bit lower. Dropping the front will reduce the camber or even maybe make it a bit negative. Good for traction when pushing it hard.
D
 
PC,
That makes sense, thanks. I always have to have some sort of real world example for things to make sense. I'm a visual person, so either seeing it or being able to visualize it in my brain is always a good thing.
 
It doesn't really matter much how low it goes...where is he going to race a V-8 powered Spit???? Wherever, it won't be competitive with the "real" modifieds so why urge him on??
 
[ QUOTE ]
It doesn't really matter much how low it goes...where is he going to race a V-8 powered Spit???? Wherever, it won't be competitive with the "real" modifieds so why urge him on??

[/ QUOTE ]
Where is he going to race it? Here; https://www.grassrootsmotorsports.com/challenge.php Why build it? https://community.webshots.com/album/180188045Biemlk Competetive? heck yes. It worked for Carol Shelby. If it weren't for me the car would be a cube headin' for China. Nice response. /ubbthreads/images/graemlins/nonod.gif
 
As long as we are talking about low... I lowered my Midget two weeks ago by dropping the spring perches. I used extra long bolts and 2" spacers. That two inches became about 4" of lowering due to geometry. It looked AWESOME but with stock spring rates it bottomed out on the tow-hooks up front and put a nice flat-spot on my exhaust pipe. Although it only cost about $20 from the Depot for the hardware and was infinitely adjustable, I decided I needed stiffer springs if it was going to be that low. I noticed that Minimania.com had spridget competition springs on sale for $99 for ALL spring rates (they offer 320, 400, 420 and 520 pounders for spridgets). I decided to go with the 520# springs even though my car is a street-daily-driver. I wasn't sure that 520# might be too stiff and the ride might be harsh on the road but it turns out they were perfect. They lowered the car about 3" and I ditched the spacers. That gave me back an inch, it still looks wicked and now I don't bottom out anywhere not to mention the increased handling and the ride actually is very little bumpier. Understeer and dive are a thing of the past for me! Definitely worth while and every penny! /ubbthreads/images/graemlins/yesnod.gif
 
Does anyone have any links where I can read up on suspension geometry? After the talk about lowering cars, that's something I don't know about. I know what bump-toe in and toe out are, etc, but not much about the "geometry" of suspension.

Thanks in advance.
 
I bought a book a few years back called "Tune to Win" by Caroll Smith (ISBN: 0879380713) and it was EXCELLENT for learning more about suspension geometry, weight transfer, camber, the effect of the coefficent of friction on acceleration, turning, stopping, tire deflection. The book even has cut-outs on the last couple pages that you can cut out and tack together to see how the suspension moves and how small changes effect the geometry. I bought this book before installing the "negative camber and wedge" kit on my Mustang which relocates the A-arm to correct the backwards camber curve. Plus it has an absolutely spectacular picture of an F1 car in a corner at about 5g... the wheel looks like it is going to tear right out of the tire!! Check at your local library if you don't want to buy it, otherwise, I got my copy and barnes and noble. They have the book online here. The book covers other aspects of building/driving a high-performance vehicle. Who knows what other techniques you'll find to employ! Highly recomended! /ubbthreads/images/graemlins/yesnod.gif Have fun!!
 
/ubbthreads/images/graemlins/tongue.gifThat Korman chart is pretty handy. I think the biggest concern would be the relation between the angles of the tierods in regard to the ground. I think I may install spacers under the rack to keep them parallel to the ground. As far as lowering the car without expensive coil overs, I'm going to cut the spring mounts off the frame and move them up 2" or so. I can then adjust it up or down by installing shims. I can move the lower mounts down an inch or so pretty easily as well. Thanx for the inputs. /ubbthreads/images/graemlins/tongue.gif
 
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