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Corner balance: Preload versus shock height adjustment

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Old 03-06-2017, 04:54 PM
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They could cancel each other out but the effect isn't always the same. From my experience I was able to use both adjustments to get the exact balance and ride height we wanted.
Old 03-06-2017, 10:11 PM
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Originally Posted by thomsbrain
OK, thanks for the input guys. That confirms my thoughts. The context of my question was in regards to the well-documented Ohlins DFV rear and their need for additional preload. I had previously run the necessary preload to center the piston travel at static ride height, which of course is a lot of preload, but I had sufficient shock length adjustment to compensate and ahieve desired ride height. I had a corner balance guy freak out at all the preload and insist it would ruin the corner balance, even though he had headroom on the shock length to adjust corner balance that way and the preload was matched across the axle. He ended up setting it back to "stock" preload and then corner balancing with the shock adjusters from there. I don't have scales of my own to "prove" that the preload wasn't going to screw anything up. This was in the times before SakeBomb came along and added some professional backup to my previously unpopular assertion that the Ohlins rear need a lot of preload unless you get shortened bodies (like SakeBomb now sells).

I'm going to take my existing corner balanced settings and add back my threads of preload and remove equal threads of shock length with the assumption that static corner balance will be unchanged and I'll get back to the correct preload for these Ohlins rears. My corner balance feels great on smooth pavement but big bumps get into the bump stops all the time on the Ohlins at "stock" preload and that can do some unpleasant stuff if you hit them mid-corner.
The point of the SakeBomb lower cups is to either allow you to run preload while still lowering the car, or to run very high spring rates and still lower the car. The shortened bodies simply allow you to lower the car with pre-load, not a substitute for pre-load. Just wanted to be clear.
Old 03-07-2017, 02:51 AM
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Originally Posted by thomsbrain
OK, thanks for the input guys. That confirms my thoughts. The context of my question was in regards to the well-documented Ohlins DFV rear and their need for additional preload. I had previously run the necessary preload to center the piston travel at static ride height, which of course is a lot of preload, but I had sufficient shock length adjustment to compensate and ahieve desired ride height. I had a corner balance guy freak out at all the preload and insist it would ruin the corner balance, even though he had headroom on the shock length to adjust corner balance that way and the preload was matched across the axle. He ended up setting it back to "stock" preload and then corner balancing with the shock adjusters from there. I don't have scales of my own to "prove" that the preload wasn't going to screw anything up. This was in the times before SakeBomb came along and added some professional backup to my previously unpopular assertion that the Ohlins rear need a lot of preload unless you get shortened bodies (like SakeBomb now sells).

I'm going to take my existing corner balanced settings and add back my threads of preload and remove equal threads of shock length with the assumption that static corner balance will be unchanged and I'll get back to the correct preload for these Ohlins rears. My corner balance feels great on smooth pavement but big bumps get into the bump stops all the time on the Ohlins at "stock" preload and that can do some unpleasant stuff if you hit them mid-corner.
To me the car should have been put on the scales first to see where you are. When I did the setup on a 944 we did not have the shock travel limitations of the Ohlins. On that car we set the shock length for ride height, hit the scales then changed preload as needed. If the preload changed the ride height, we went back to the length adjuster as needed. We were able to get the corner weights correct and the ride height in the owners desiered range. Also what corners you decide to adjust, and how much each wheel is adjusted makes a difference.

Knowing what I do about the limitations of the Ohlins, it's all about compromise. To me The limited bump travel trumps using only preload to get the perfect corner balance. Your corner balance guy should understand you were running more preload for static bump travel. Depending on the weights he could have changed preload to the front, or use the length adjusters as needed. However you have a very good reason to run extra preload because of the short shock travel. I would have started the process by giving him some boundaries on rear preload. Say 8-12mm is the ok range. Once outside that, find another way to balance the car.
Old 03-07-2017, 09:10 AM
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Originally Posted by SakeBomb Garage
The point of the SakeBomb lower cups is to either allow you to run preload while still lowering the car, or to run very high spring rates and still lower the car. The shortened bodies simply allow you to lower the car with pre-load, not a substitute for pre-load. Just wanted to be clear.
Thanks for clarifying; what I wrote wasn't phrased properly.
Old 03-07-2017, 05:09 PM
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I've been meaning to take the time to jump in here but I'm just getting to it now. I'll share my overall process when it comes to setting up a car (once I know what spring rates etc)

First you set your static bump-stop clearance to ensure no fender contact is possible using pre-load or helper springs depending on total available stroke and spring rate. Essentially you are determining the available compression & rebound stroke. Then you set your ride you set the ride height using the lower mount adjustment.

The pre-load is used to set the bump-stop clearance and should not be adjusted during a corner balance. The point of a corner balance essentially is to adjust for the tolerances of the chassis and suspension. Unless you find your wheel weights are significantly different than expected you shouldn't adjust the pre-load.

For anyone who is interested we offer custom race alignment and corner balance services services out of our Santa Clara, CA facility.

-Greg @ SBG
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