Spring Preload for Autocrossing

[Project S13]

Hey guys, I autocross a `91 240SX hatchback in STS.Among the suspension work are tein he coilovers. These are 8kg front 6kg rear. They have seperate adjustment for ride height and spring preload but so far I have not adjusted spring preload.

I've read some suspension books and have an idea of what preloading the spring is, but not so great an idea of what it functionally *does* when driving at an autocross. Could someone please give me an idea of the reason for preloading springs and it's effect on the handling?

Then I can decide whether or not to use spring preload. BTW this is not my daily driver so I have room to experiment without worrying about ride quality. Thanks for reading.

[McRussellPants]

don't bother, it will make your suspension effectively stiffer and you'll lose droop travel.

Both not good things when pimping around in a parking lot.

[Project S13]

If that is all it does then I certainly agree. At some locations the HE coilovers are already a little to stiff; sometimes skipping over the surface slightly and upsetting the balance of the car.

Is there no other benefit of preloading? I thought perhaps it would help the shocks react better to becoming unweighted when going over a bump such as in the above example. Though if it worked like that the added stiffness would cause more skipping.

[McRussellPants]

It skips because your closer to the droop stop on the shock so it will unload quicker.

I cant think of the reasons why you preload now since I'm tired as hell.

[nismofly]

it increases suspension travel without increasing ride height iirc

but you can also lift the wheel gti style if you have too much

[ArticDragon192]

I put 5mm of preload on my flexes to stiffen them up a bit and have immediate response from the springs instead of waiting for the springs to load when they are not loaded or when they have 0 preload. IMO, 5mm of shock travel is enough of a sacrifice. I've taken corners pretty hard and have not felt, heard, or seen any negative effects of the 5mm less of travel.

[Red coupe]

I would not mess with preload with out a set of scales.you would probably just end up making the corner weights all screwy.

[naed240sx]

I put 5mm of preload on my flexes to stiffen them up a bit and have immediate response from the springs instead of waiting for the springs to load when they are not loaded or when they have 0 preload. IMO, 5mm of shock travel is enough of a sacrifice. I've taken corners pretty hard and have not felt, heard, or seen any negative effects of the 5mm less of travel.

Preloading won't really make them much more responsive. You don't have to wait for the springs to load, because they are loaded as soon as you lower the car off of your jack.

[Project S13]

Preloading won't really make them much more responsive. You don't have to wait for the springs to load, because they are loaded as soon as you lower the car off of your jack.

So was I partially correct in my suspicion that preloading would help if the car became unweighted while driving, such as coming up over a hill at high speed and the springs unload the weight of the car, or when skipping over a bump in a course? Might help to preload the springs for a course with many ups and downs .

Also I don't think I'll be messing with my spring preload sounds like it's too much hassle for what I'll be doing. Though I do need to corner weight the car at some point.

[naed240sx]

So was I partially correct in my suspicion that preloading would help if the car became unweighted while driving, such as coming up over a hill at high speed and the springs unload the weight of the car, or when skipping over a bump in a course? Might help to preload the springs for a course with many ups and downs .

Also I don't think I'll be messing with my spring preload sounds like it's too much hassle for what I'll be doing. Though I do need to corner weight the car at some point.

From what I have heard, the biggest benefit of preloading is being able to corner balance your car. Since I don't have access to scales, I don't use any.

[InsanityInc]

Preload only changes the rate if your springs are progressive. If they're linear, then they're linear. Compressing them won't change the rate (unless of course you compress them to full bind). That's what linear means.

[ArticDragon192]

It won't change the rate, but there's a force already if you compress the spring,

[C-Kwik]

Teh only time preload would actually have an effect on stiffness at static ride height would be if you precompressed the spring so much that it's compressed length is shorter than the length of the spring would normally be under just the weight of the car.

Keep in mind that a car's weight will remain constant(assuming same fluid levels). A spring compresses under load. The more load you put on it, the more it compresses. Lets just assume we have a car with 500 lbs at each corner. With a 100 lb/inch spring, each spring would compress 5 inches. Now lets just say you precompress the spring in the strut assemblies by 2 inches. The spring will have a 'preload' of 2 inches and will be puching on the spring perches with 200 hundred pounds of force. As you start putting load onto the spring, the spring will remain at teh preload height until they see more than 200 pounds. Then it will compress another 3 inches as you put the remainder of the weight on the springs. Ultimately, the spring will still have a total compressed height of 5 inches. this means that the actual ride characteristics will not change except that you know have 2 inches less rebound travel from normal ride height.

Now lets pretend you preload the spring 7 inches. This means the springs will be providing 700 pounds of resistance to teh spring perches. When you lower the 500 lbs of weight onto the springs, the resistance will not be exceeded so the suspension will not compress at all from that point. Essentially, unless you hit a bump or corner with a load that exceeds 200 lbs for a given spring, that spring will not compress. And since it's not compressing under static weight, the suspension is effetively riding at full extention. The tires will be unable to maintain contact when you get small dips in the road. This is not a good thing.

Now I will say that I'v enever actually seen the term preload used in suspension spak before. None of my references mention it. I am making assumptions as to what you are descriing as I can not think of what else it can possible be. But if we are describing the same thing, then you really only need enough preload to keep the spring from moving within or falling out of the spring perches under full extension. You should be much more concerned with the vehicle's cross-weight.

[McRussellPants]

Teh only time preload would actually have an effect on stiffness at static ride height would be if you precompressed the spring so much that it's compressed length is shorter than the length of the spring would normally be under just the weight of the car.

Keep in mind that a car's weight will remain constant(assuming same fluid levels). A spring compresses under load. The more load you put on it, the more it compresses. Lets just assume we have a car with 500 lbs at each corner. With a 100 lb/inch spring, each spring would compress 5 inches. Now lets just say you precompress the spring in the strut assemblies by 2 inches. The spring will have a 'preload' of 2 inches and will be puching on the spring perches with 200 hundred pounds of force. As you start putting load onto the spring, the spring will remain at teh preload height until they see more than 200 pounds. Then it will compress another 3 inches as you put the remainder of the weight on the springs. Ultimately, the spring will still have a total compressed height of 5 inches. this means that the actual ride characteristics will not change except that you know have 2 inches less rebound travel from normal ride height.

Now lets pretend you preload the spring 7 inches. This means the springs will be providing 700 pounds of resistance to teh spring perches. When you lower the 500 lbs of weight onto the springs, the resistance will not be exceeded so the suspension will not compress at all from that point. Essentially, unless you hit a bump or corner with a load that exceeds 200 lbs for a given spring, that spring will not compress. And since it's not compressing under static weight, the suspension is effetively riding at full extention. The tires will be unable to maintain contact when you get small dips in the road. This is not a good thing.

Now I will say that I'v enever actually seen the term preload used in suspension spak before. None of my references mention it. I am making assumptions as to what you are descriing as I can not think of what else it can possible be. But if we are describing the same thing, then you really only need enough preload to keep the spring from moving within or falling out of the spring perches under full extension. You should be much more concerned with the vehicle's cross-weight.

Exactly.

[Project S13]

Good info, guys. Thanks for sharing the knowledge.

[Onizuka]

You probably wont lose any suspension travel by adding preload if you keep it sane, you tend to hit the bumpstops on the shock before you encounter any coil binding with coilovers.

Supposedly you can tune preload to make your car transition faster and in general be more sensitive to driver inputs. Just dont ask me how to do it

[C-Kwik]

You probably wont lose any suspension travel by adding preload if you keep it sane, you tend to hit the bumpstops on the shock before you encounter any coil binding with coilovers.

Supposedly you can tune preload to make your car transition faster and in general be more sensitive to driver inputs. Just dont ask me how to do it

The resistance a spring gives is constant to a given weight. If you are trying to get more resistance, then you need to get a stiffer spring. The only exception is if you precompress the spring within the assembly to a point beyond the normal rideheight for the given spring and weight of the vehicle. But it will have the negative effects I stated in my previous post.

And the lost suspension travel we are talking about is in rebound, not compression. Having enough rebound travel is important. Preloading too much will effective reduce the rebound travel.