CuriousGeorge

Hey B preloading 12 mm on the rear compresses the spring , will the ride be more firm due to the amount of preload? I will right but not bad enough to make it uncomfortable or unsettle the chassis over rough roads or bumps?


Also does corner balance shops adjust preload and right height or just ride height for those coilover set up that have both adjustments?

B serious

Yep...preload to any amount, by definition, will crush the spring. I think you already know this...but for anyone that isn't clear on it...

What I meant by preload is crushing the spring by some amount.

12mm preload is defined:
(Fully extended spring length) - 12mm = preloaded length.

In the case of the factory Öhlins springs,
200 - 12 = 188.

I haven't ever used 12mm of preload. I'm not sure how it will ride. I was just saying it *should* give you 1" of clear space (travel before touching bumpstop).

It shouldn't be harsh. 12mm isn't ridiculous. But...if it is, you can change it.

My suggestion would be to finalize your ride settings before getting it corner balanced.

Then drive it 500-1K miles so you can make changes if need be, and/or make changes in order to account for spring sag.

Then get it corner balanced. Then aligned.

Don't do it all at once.

I would assume they'll just change the bottom perch without adjusting preload unless they run out of bottom bracket travel.

FWIW, my car is not corner balanced. I could do it myself. But...I'd rather have a sandwich or something. Opinions will vary.

CuriousGeorge

Thanks B , going thru the OP post I see he went with 0.6 inch preload in the rear which is about 15mm, so not too far off from the 12 mm I have loaded now, wish I can knock the lower collar and set the height too on the bench

B serious

Put a long extension (or big screw driver) through the lower shock mounting point.

Prop the shock up by resting the tophat (NOT the adjuster knob) on a box or something.

That way you can hold on to it. Set your preload first. then knock the bottom adjuster loose. Make sure you're turning it the right way. CCW if you're looking down from the top of the shock.

CuriousGeorge

Ok I'll give that a try tonight, also did you do 2mm preload up front? Seems to be the consensus , it's the rear that was weird since the calculations dont match the actuals like your pictures show, so thanks for all the responses for the set up.

Looks like it's on pretty tight , will adjust it on the car

Final adjustments are

Front springs:198mm
Height adjustable collar: 103

Rear springs: 186mm (12mm preload)
Height adjustable collar: 15 mm (39mm due to preload - 12 mm - 12mm) since OP said the front end dropped another 12mm hopefully this evens out for a 1.5inch drop all the way around?

Does that look right?

B serious

No problem. My calculations more or less matched my rear suspension compression. The fault in the originally posted logic is that a 600LB object can cause 1200LB worth of spring compression at static. Its why none of the OP's calculations panned out.

Its hard to measure the front compression. So I'm not sure what it is.

I used 2mm preload all around. I set the preload exactly as Öhlins spec'd. I wanted to get a base reading/feel. The reason being...if I was unhappy with the car at 2mm, I'd go change something. The only thing that's different from Öhlins' spec is my bottom bracket height. I wanted the car low because I am a simpleton.

2mm or 12mm or 5mm or 1mm is as good of a place to start as any, I guess. Start at 12 for the rear since you already have it adjusted. Don't like it? Its got threads on it...so infinite possibility.

When changing things, change ONE thing at a time.

Get it set how you like it. As long as it keeps working for you, you won't need to change it until you find something better (if ever).

I bought a lifetime alignment for many reasons. I can change heights and angles whenever I want.

I didn't bother with corner balancing at this point. If, at some point, I become smitten with how the car rides and is set up...after trying a few different ride configurations...and I need to shave another few 10ths off...I'll corner balance it.

The shock bodies are threaded so you can experiment with different configurations. The way I see it...it'd be a waste to never try anything new to see if it could be better. Or you may as well have gotten lowering springs for like $2200 less.

Pimpo

Preloading the spring should not change the ride harshness as long as you are not compressing more than the corner weight (and you are not)

This is because even without preload, the spring would compress more than what you are. Someone correct me if I'm wrong.

B serious

That's basically correct. But...you can run out of droop travel even if you're not preloading past corner weight.

example:
500Lb spring. Preloaded 1". Put a 600LB corner on it. It will compress the spring only 0.2" further.

600/500 = 1.2".
1.2" - 1 = 0.2".

If you hit a bump(s) that requires more than 0.2" of rebound (you will), the car will ride like shit.

On THIS application, though...at 12mm, he will theoretically still have 1.13" of total droop. Should be fine.

CuriousGeorge

Hi B, I do like your ride height and if you did 10mm shorter all the way around then below should be my measurements and if not I can adjust from there as you said

Preload 2mm OUTSIDE Car
Front spring length: 198mm
Height adjustable collar: 93mm (manual stated stock position @2mm preload is 103mm - 10mm for addition .5 inches of lowering)

Preload 14mm OUTSIDE Car
Rear spring length: 186mm
Height adjustable collar: 15 mm (Ended up at 39mm - 14mm preload = 25 mm - 10mm for additional drop)

Or

Height adjustable collar: 17mm (39mm - 12 mm preload = 27 mm which is back to manufacture gap - 10mm more for additional gap)


Does that look right?
This post has been edited by CuriousGeorge: Today, 04:08 PM

B serious

To mimic my height, your fronts should be fine.

For the rears.....with 12mm of spring preload, your "gap" in the below pic should be 15MM.

You turned the spring collar up 10mm from where mine is. You shorten the bottom bracket the corresponding 10mm. Gap ends up at 15mm again.

You're just moving everything 10mm up from mine together.

Notes:
-That SHOULD work.
-...if you can get that much out of the bottom bracket. I don't think you can :'(