Ohlins DFV Coilover Kit
09-20-2016, 07:40 PM
#131
I have no idea why you would set preload with shocks in the car. The bushings will give you artificial spring compression.
lets say you set the shock to 2mm preload outside of the car. Then you install them. The bushings will compress the spring a bit. So...now you're at 10mm preload. If you back off to 2mm again...you'll lose shock travel. Then you have to add preload to compensate for the preload you just lost. The bushing bind will change for each wheel. You'll be adding swaybar bind because you're only adjusting one shock at a time. Once you've completely gone insane from the constantly changing preloads, you will just say "f#&k it" and drive as is.
The moral is
Always set preload outside of the car, on the bench.
The question is, "How much preload?"
Well....
With Öhlins' 2mm setting:
I set my preload to 2mm OUTSIDE of the car. Meaning a 198mm spring length with the shock fully extended. Once the car is on the ground, the spring length is 159mm, as seen below.
-The shock starts with 2.125" of travel before bumpstop (so I'm told).
-At my 198mm spring length, PRELOADED OUTSIDE OF THE CAR, the shock is fully extended. Any compression in the shock will lead to spring compression. So the shock and spring travel as one. Yes? Yes.
-My spring ends up at 159mm at static ride height...full weight of the car on the ground.
- [198mm - 159mm] = 39mm. 39mm = 1.53".
- 2.125" - 1.53" = 0.595" (rounded up to 0.6" for us hillbillies) of shock travel left before touching bumpstop.
II like my car low, y0. So I set the bottom bracket 10mm lower than Öhlins suggested. Don't panic or call police. I stayed within their (+/-) 15mm zone.
Remember...I got 0.6" of clear travel by following Öhlins' recs. So...the rumor tthat the rear suspension is useless at Öhlins' recs is wrong.
Do you want 1" of shock travel before bumpstop? Try about 12-13mm of TOTAL preload. On a bench. Before installing.
Don't take my word for it. Try it. Measure afterward. Lmk.
Don't like math? Wanna see the travel? Do the initial install of ONE shock on each axle sans boot. Then you can SEE where the bumpstops are and make out how much room you have/need/want/desire/crave/pine/bloodlust for. Write down your measurement. Remove, replace the boot, mimic the measurement on the other side.
**To set preload, make sure the tophat center nut is fully tightened first!!!!
Remember. Adding preload may add bump travel. But will rob extension travel. It will also change spring reaction and require more work from the damper. So...don't go absolutely crazy and add 20 feet of it.
lets say you set the shock to 2mm preload outside of the car. Then you install them. The bushings will compress the spring a bit. So...now you're at 10mm preload. If you back off to 2mm again...you'll lose shock travel. Then you have to add preload to compensate for the preload you just lost. The bushing bind will change for each wheel. You'll be adding swaybar bind because you're only adjusting one shock at a time. Once you've completely gone insane from the constantly changing preloads, you will just say "f#&k it" and drive as is.
The moral is
Always set preload outside of the car, on the bench.
The question is, "How much preload?"
Well....
With Öhlins' 2mm setting:
I set my preload to 2mm OUTSIDE of the car. Meaning a 198mm spring length with the shock fully extended. Once the car is on the ground, the spring length is 159mm, as seen below.
-The shock starts with 2.125" of travel before bumpstop (so I'm told).
-At my 198mm spring length, PRELOADED OUTSIDE OF THE CAR, the shock is fully extended. Any compression in the shock will lead to spring compression. So the shock and spring travel as one. Yes? Yes.
-My spring ends up at 159mm at static ride height...full weight of the car on the ground.
- [198mm - 159mm] = 39mm. 39mm = 1.53".
- 2.125" - 1.53" = 0.595" (rounded up to 0.6" for us hillbillies) of shock travel left before touching bumpstop.
II like my car low, y0. So I set the bottom bracket 10mm lower than Öhlins suggested. Don't panic or call police. I stayed within their (+/-) 15mm zone.
Remember...I got 0.6" of clear travel by following Öhlins' recs. So...the rumor tthat the rear suspension is useless at Öhlins' recs is wrong.
Do you want 1" of shock travel before bumpstop? Try about 12-13mm of TOTAL preload. On a bench. Before installing.
Don't take my word for it. Try it. Measure afterward. Lmk.
Don't like math? Wanna see the travel? Do the initial install of ONE shock on each axle sans boot. Then you can SEE where the bumpstops are and make out how much room you have/need/want/desire/crave/pine/bloodlust for. Write down your measurement. Remove, replace the boot, mimic the measurement on the other side.
**To set preload, make sure the tophat center nut is fully tightened first!!!!
Remember. Adding preload may add bump travel. But will rob extension travel. It will also change spring reaction and require more work from the damper. So...don't go absolutely crazy and add 20 feet of it.
09-20-2016, 07:48 PM
#132
Some things:
-When you clock bushings properly, you will create MORE bushing bind with the car lifted up.
-You need to clock bushings by tightening them at ride height. You are NOT preloading bushings by doing this. You are clocking them.
People confuse bushing clocking and spring preload by calling them both "preload". You preload SPRINGS. You clock BUSHINGS.
-Its crazy to think that if you add 1200LB of force into a 450LB spring via wheel rate/motion ratio...that the spring will compress (1200/450) = 2.7".
Why? Because the car weighs like 600LB at the shock tower. Not 1200LB...and not infinity. The spring will compress til it can lift the car's 600LB sprung corner weight. Then it will move the chassis away. This is a simple example...discounting the COS of the shock angle. With the COS factored in, you actually put like 680LB into the spring at the shock tower weight of 600LB.
Do the wheel rate math in reverse. Then look at the above logic.
-When you clock bushings properly, you will create MORE bushing bind with the car lifted up.
-You need to clock bushings by tightening them at ride height. You are NOT preloading bushings by doing this. You are clocking them.
People confuse bushing clocking and spring preload by calling them both "preload". You preload SPRINGS. You clock BUSHINGS.
-Its crazy to think that if you add 1200LB of force into a 450LB spring via wheel rate/motion ratio...that the spring will compress (1200/450) = 2.7".
Why? Because the car weighs like 600LB at the shock tower. Not 1200LB...and not infinity. The spring will compress til it can lift the car's 600LB sprung corner weight. Then it will move the chassis away. This is a simple example...discounting the COS of the shock angle. With the COS factored in, you actually put like 680LB into the spring at the shock tower weight of 600LB.
Do the wheel rate math in reverse. Then look at the above logic.
09-20-2016, 07:48 PM
#133
Thanks B for the response , was trying to make sense of it all but couldn't figure out all the math like the 1.7 inches of travel at rest from the OP.
Sounds like we should stick to the 2mm and avoid all the preload binding you mentioned, thanks again for the info, sometimes reading more doesn't clear things up very much
Sounds like we should stick to the 2mm and avoid all the preload binding you mentioned, thanks again for the info, sometimes reading more doesn't clear things up very much
09-20-2016, 08:00 PM
#134
No problem.
Cliff's notes:
-Set spring preload outside of the car. Always.
-Then install the shocks to the car.
-Then clock the bushings by compressing the suspension and tightening the bushings at ride height (completely different than spring preload...you're just doing this so you dont tear the bushings).
Guidelines:
-2mm spring preload will leave you with about 0.55 to 0.6" of shock travel. My car is like 120-140LB lighter than stock. I got 0.6".
-About 17mm of TOTAL preload will give you about 1" of clear travel before bumpstop contact on a stock weight, empty S2000. **this is via my math. So its likely correct...but LMK, someone.
If you ever need to change preload, it is best to remove the shock assy from the car and re-set it.
Cliff's notes:
-Set spring preload outside of the car. Always.
-Then install the shocks to the car.
-Then clock the bushings by compressing the suspension and tightening the bushings at ride height (completely different than spring preload...you're just doing this so you dont tear the bushings).
Guidelines:
-2mm spring preload will leave you with about 0.55 to 0.6" of shock travel. My car is like 120-140LB lighter than stock. I got 0.6".
-About 17mm of TOTAL preload will give you about 1" of clear travel before bumpstop contact on a stock weight, empty S2000. **this is via my math. So its likely correct...but LMK, someone.
If you ever need to change preload, it is best to remove the shock assy from the car and re-set it.
09-20-2016, 08:08 PM
#136
Good stuff. 
Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.
No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
09-20-2016, 08:09 PM
#137
09-20-2016, 08:13 PM
#138
Good stuff. Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.
No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
And you can make preload adjustments (after doing the initial settings on a bench) with shocks installed...if you can keep a count of the spring lengths.
09-20-2016, 08:16 PM
#139
Originally Posted by andrewhake' timestamp='1474430894' post='24066570
Good stuff. Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.
No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
And you can make preload adjustments (after doing the initial settings on a bench) with shocks installed...if you can keep a count of the spring lengths.
09-20-2016, 08:24 PM
#140
Originally Posted by B serious' timestamp='1474431217' post='24066574
[quote name='andrewhake' timestamp='1474430894' post='24066570']
Good stuff. Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.
No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
Good stuff.
Yes you definitely don't want to set measured spring pre-load with the shocks on the car. I think that's where a lot of confusion comes from. The suspension arms themselves being limited to how much they can travel due to the bushings will "preload" the spring as you have mentioned. The amount this happens will vary car to car, if a car has sphericals for example this could be much less.No reason to think that you can make small adjustments to the preload once they are on the car, just keeping in mind that one rotation of a spring perch will adjust 1.5mm, you shouldn't be measuring the compressed spring length as a baseline though, and you should know your unloaded spring preload length.
And you can make preload adjustments (after doing the initial settings on a bench) with shocks installed...if you can keep a count of the spring lengths.
[/quote]
thanks bud!I want to try 1" of clear travel. BUT won't make any changes til late October before putting the car away. I would like to touch a 1.44.xx lap at Gingerman with the car exactly as it sits lol. I'm at 1.45. Must...touch. I'm used to the car and I like it. So I don't wanna screw with it til after this next track day.
In late October, I'll try different lengths/preloads and take more pics for peoples' info.