Car Analogy

Measuring is error prone. There is parallax. There is angle you hold the tape at. There is miscounting hash marks. There is squinting...

Counting turns has none of these faults. And precision is less important than consistency. 11.33333 turns aren't necessary. 11 will do fine. But getting exactly 11 on each side is what counting turns does that measuring is less likely to achieve.

B serious

^Yes. Resolution is another advantage of turn-counting.

Any dummy can remember and obtain dot position accuracy within let's say 1/8 turn. Which translates into a measurment accuracy of +/-0.19 mm...or 0.007" on a 1.5mm thread pitch.

Even if you're within a 1/4 turn of dot position, that's pretty COT dang accurate.

Chibo

This is outside the scope of this thread, but shouldn't the preload be adjusted from the base installed preload once installed to level out sag individually? I guess I'm curious why installed preload measurements are the commonly traded thing when a sag number (and thereby position in the damper travel / distance to bumpstop) is actually what you're aiming for and will vary based on each corner and individual car based on mods (changing corner weights). Unless this stuff somehow works differently than motorcycles or the installed preload specified by companies / people is just to put the average car 'in the ballpark', I guess.

B serious

Sure. For cars, a spring will sag a tiny bit after its been on the car a while. But not much...unless its a complete POS spring.

You still cannot set initial preload while the shock is installed.

A car has 800 bushings that all bind up and hold the shock/spring from fully extending. As well as sway bars. A motorcycle doesn't.

Removing the shocks from the chassis is still the best way to set initial (base) preload. Regardless if the spring is pre-sagged or not. You can ACCOUNT for sag by putting a few mm more preload on a brand new spring. But its a guess.

Cars don't settle much because the spring takes a set. Bushings not being clocked properly will cause a HUGE ride height delta, however. So when people talk about how their car took time to "settle" after a spring install...most of that settling comes from their bushings slowly tearing from being non-clocked.

Some springs (rare cases) take like a 1/4" set. But...honestly, my used Ohlins Eibachs probably went from 200mm to like 199mm after they took a set. The set is negligible AF in that case. Teins come pre-set. So do Swifts and some other brands.

There is a small issue with setting 0 preload as your initial. And that is that the rubber mount on top of the spring takes like a 1/8" (~2-3mm) set. I think that's why Ohlins and lots of other companies recommend a ~2mm preload.

Chibo

Oh, yeah, there with you on the initial preload. The clocking on the bushings makes sense too. Sway bar is why you set your ride heights with the swaybar disconnected then use your adjustable endlinks.

When I say sag I mean extended length of the damper versus installed on the car with car weight, not actual spring sag.

B serious

Not sure I follow. What's the advantage/purpose of setting preload with the weight of the car on the ground?

Theoretically, it sets absolute position. The car weighs different weights at different corners, etc.

But...its hard to do (its easy on a motorcycle). And you can always adjust first and then measure free travel with the car on the ground later...and just touch it up.

Chibo

Adjusting the preload is how you change where the damper sits in its stroke at rest, so you'd set your set your installed preload specified by the manufacturer / tuner before you install them, install them, get the car settled, then measure where you are in the stroke from fully extended (this is your sag number) to see if you need to add or remove preload to change where you are in the stroke.

edit: Your edit got what I was getting at

B serious

Yep. Determining the right amount of preload requires knowing where the bumpstop sits at static height. Its only one factor...but its necessary.

I hope nobody is blindly dialing in preload...lol

Car Analogy

Setting preload based on 'sag' is a motorcycle specific thing, simply because final vehicle weight is so dependent on the rider. Yo fat a$$ as a huge impact on how much weight is applied to each 'shock'. Much more so than with a car.

With cars, my 750 lb corner weight isn't going to have that much different sag from your 800, or the other guys 700. So its much easier to just say with this coilover using this spring, start with this much oreload.

For all you non bikers out there, you set sag by putting a tie wrap on the fork tube, so that when you carefully sit on the bike, you have a high mark of how much the suspension compressed. You keep setting preload until the amount of sag is where you want it (there are rules of thumb that for this type of riding, use this much sag, etc). The goal of sag is to have appropriate range of bump travel at normal ride height. To balance compression travel vs rebound travel.

We do the same with cars, its just that stating a specific preload amount is a sufficient starting point.

Chibo

I kinda figured it was due to not being that much different, but if you think about it, these things are measured in small mm increments. I guess after mathing it out a bit 50-60lbs on a 10kg/mm / 560lb/in spring is only about 3mm so a non-issue unless you're comparing a full weight 2900lb street car to something like a 2200lb track car.