Robinhood150

Over the couple years that I've been on the boards I've repeatedly run into some common misconceptions regarding coil spacers, tbar cranking, and preloading. For instance, a lot of people incorrectly think that adding spacers or cranking tbars add preload.

To dispell these myths I've put together an article that discusses basic suspension component functions and how simple modifications effect the system. Keep in mind that this is a basic look at suspension systems and there are many more things going on than I have explained. Also, this article focuses on coilover suspension but the theory transfers over to any coil sprung suspension and to torsion bars.

I welcome any comments, questions or suggestions you may have. Enjoy.

http://www.robinhood4x4.com/suspension1.htm

Bob_98SR5

steve,

this is the most shameless plagarism of my original work. i hope you can live with yourself.
















(nice going steve! EXCELLENT stuff. this should be stickied, IMHO).

Bob

Robinhood150

Hey, I briefly mentioned you at the bottom of the last page in really small print. Besides, you'll never be able to prove it...

amusement

transalper

I do not want to get into a debate about this, but i have been adjusting preload on motorcycles for years by using the adjustment nuts, just like on the SAWs. Increasing the preload by compressing the spring within the shock reduces the sag and raises the bike. Here's a pic from Ohlins that contradicts your definition of preload adjustment:

Are motorcycle shock manufacturers using the term differently than the automobile industry?

Robinhood150

Yeah, I've noticed that about motorcycles. I think they're just using that term because it's an easy term to use for the general public and it gets the point across. However, it is a misnomer.

Robinhood150

Here's a better reason why it's called "preload adjustment."

Preload adjustment in the motorcycle world needs to be understood correctly so you don't missapply it here. You increase the ride height in anticipation of a heavier rider. The rider is the extra pre-load, the motorcycle does not gain weight. We call it a preload adjustment because we are compensating for the anticipated weight but it is important to distinguish between a larger person on a motorcycle and a truck that has not gained any weight and therefore preload.

I guess it's not really a misnomer.

And there's a good discussion going on at 4x4wire if all this is still confusing.

TDiddy

Steve,

Its mertzTr, not Er.

Hey, why are the numbers 9 and 5 offset in Bob's username? It looks like something an old typewriter would do.

Robinhood150

Why you gotta be all different? Just pick an easy name like Pdiddy or somethin'.

Yeah, I typed out the whole article with my trusty typewriter and scanned in the pages. If you look really close, you'll see the pictures are actually done in ascii.

cruizin01

Steve thanks for that info. That cleared up some of the muddy water I had about "preload"

Not to go OT here but how does shock length affect the preload? Or do all systems used on toyotas use the same max. extend shock?

Flygtenstein

Good show on the write up.

There is a difference in effect between the two sorts of spacers out of the coilover versus in.

Regarding cranking the torsion bars, it is good to be clear on what all the words mean and such, but the end result is that ride and travel suffer.

The discussion of spacers would create preload on an in the coilover spacer if the coils were progressive, right?

You are an engineer IIRC, so I will bow to your knowledge on this, just wanted to ask for that clarity.

Robinhood150

Shock length doesn't affect the preload at all unless you are riding around fully extended or fully compressed everywhere you go. That certainly does not make for a comfy ride.

hmmm...just thought of something though...to elaborate on my explanation further it's not the shock length per se, but rather the physical travel limits of the suspension, be it the bumpstops, shock travel, or ball joint limits.

So let's imagine you do ride around with the travel always fully extended. When you add a spacer under this condition, then the spring IS compressed more than normal and thus the preload increases.

cruizin01

Thats exactly why Ive always been confused. Im pretty sure that my setup sets at the top of the shock for most of the ride. It seems to me that I compressed the coil so much to get the shock nut on that the weight of the truck isn't enough to compress the coil enough to let the shock "travel: Im sure I just dont understand part of the physics so just call me stupid if its appropriate.

BruceTS

Actually, many auto manufacturers do preload their springs, you can see this when you remove your stock coilover assy on your 4Runner. Where you'll need a spring compressor to dissassemble the unit.

Say your running SAW's on the front of your 4Runner, the springs are 650lb(a popular set-up). You can easily teardown your shock assembly without a spring compressor. Now you decide you want to run lighter springs, say 550. The problem is, if you get the same uncompressed length of springs as the 650, they will need to be compressed much further, to maintain the same ride height. Ideally you want to run as much spring as possible on your assembly and still allow for full compression. To offset this you buy longer springs, but now they won't fit unless you use a spring compressor for assembly, this would be considered preloading, but the overall initial load on the springs will be the same, reguardless of what weight spring is being used. The difference will be in the compressability of the springs, the lighter springs will compress easier. As for longevity of your springs the larger the diameter and more coils you can get away with, the longer they will last. this is due to the torsional effect the springs are put under. With larger coils the twisting is spread over a greater area.

cruizin01

too...much...info....brain...cant...process....CRA SH!!!

So what would the effect be of using say 10" 650lb spring vs. a 12" 550lb spring. Wouldn't you be able to get the same lift but have more movement of the spring (up and down) resulting in a better ride? Or do the lighter springs just get compressed alot more resulting in the same ride? I hope I dont sound REALLY Stupid. I just want to understand the best I can.

BruceTS

Real simple a 650lb spring compresses 1" for ever 650lb, it takes 1300 lbs to compress 2" etc. etc. now with a 550lb spring it will compress aprox 2.36" with 1300lbs, but the difference is the amount of weight needed to compress the next 1" of spring, it only takes 550lbs. By preloading the spring .36", you can achieve the same ride height as the heavier spring with the same loaded spring length.

cruizin01

You cheater you edited it....Trying to confuse the crap out of me..no wonder I couldn't figure that sentence out..lol

Ok it makes a little more sense to me still muddy but I dont think there is a clear answer.

BruceTS

Sorry about the edit job, forgot to proof read before posting. I'm trying to make it as clear as possible. Maybe I should have used a lighter spring in my example.

650 inch pound spring, takes 650 pounds to compress each 1" of spring, 1300 pounds to compress 2", 1950 pounds to compress 3" and 2600 pounds to compress 4".

550 inch pound spring, takes 550 pounds to compress 1". 1100 for 2", 1650 for 3", 2200 for 4" and 2750 for 5"

now it the total weight on that wheel was 2600 pounds, then with the 650 inch pound spring it would compress 4" whereas with a 550 inch pound spring would compress almost 5". But to compress an additional 1" of travel it would take another 650 pounds of force compared to 550 pounds of force with the lighter spring. I hope this clears the muddy water..............

cruizin01

That part makes total sense to me. The part I dont get is say my coil is 650lb. and I have to compress it 3 inches to get it on the shock. Does it take 2600 lbs to compress the spring 1 more inch or is it still going to move 1 inch for every 650lbs that gets put on it?

jruz

But combined with the angle of the dangle of the rest of the IFS components they do (?) create preload...? Obviously these types of lifts cannot exist with the rest of the components (A-arms, balljoints, etc.), so in all fairness, they do increase this...?

I agree with your reasoning, just not quite with the conclusion...

Jim