Modifying Bilstein Shocks

[Hyper4mance2k]

Originally Posted by Shankenstein

I ran across a couple video serieses (produced recently), and wanted to share.

The first set is not really professional-grade... but it's the same guy who wrote the DIY for ClubLexus (mentioned before). He walks you through the tools and procedures needed to rebuild BC Racing shocks. This is with Bilstein guts.

Thank you. The information in his videos are invaluable!

[wootwoot]

Originally Posted by Shankenstein

It's good to analyze grip level vs effective wheel rate.

Dimensions: From stock, you're increasing the contact patch by 9% (7.5" to 8.2").

Compound: The compound is designed for more grip, and based on C/D's test (LINK to PDF), it's probably ~20% more grip.

You may see lateral forces ~30% more than stock, so a good set of lowering springs would be sufficient for your current setup.

For 400 lb/in springs, that's 3x stiffer up front and 2x stiffer in the rear (for a Toyota FR-S). They will be stiff, but dampers will determine if this is back-breaking or buttery smooth. Either way, your sway bars and bump stops will be less relevant (a good thing, in my opinion).

If this is a daily driver (with lots of potholes and hopping curbs)... this may not be ideal. For "street" tires (Direzza, RS3, RE71R, Rivals up to 245 width) with bolt-on power levels (200-250 hp), this is a fine choice. If you're pushing 300+ rwhp and R-compounds, you'll want more.

TL;DR - 400 lbs/in springs will be stiff... but it's OK with your current setup and will be future-proof for upgrades to tires and power. Once you transform into a track monster, a revalve and new springs are in order.

Thank you. That's about the best explanation I've heard on the subject.

[Shankenstein]

Originally Posted by Hyper4mance2k

Thank you. The information in his videos are invaluable!

I was really confused about how to disassemble an inverted shock, and seeing the Mini Cooper setup helps demystify it.

I'm still not 100% clear on the process of de-pressurizing and re-pressurizing the gas behind the separator piston. It looks like the system is designed not to need pressurization. Once the separator piston makes the seal, the gas behind it gets compressed 10-15x (150 - 220 psi). This is the right range for shocks anyways... so it may not need to be "filled" in the traditional sense. Obviously, nitrogen (or atleast dry shop air) would be used.

[strat61caster]

Originally Posted by Shankenstein

I was really confused about how to disassemble an inverted shock, and seeing the Mini Cooper setup helps demystify it.

I'm still not 100% clear on the process of de-pressurizing and re-pressurizing the gas behind the separator piston. It looks like the system is designed not to need pressurization. Once the separator piston makes the seal, the gas behind it gets compressed 10-15x (150 - 220 psi). This is the right range for shocks anyways... so it may not need to be "filled" in the traditional sense. Obviously, nitrogen (or atleast dry shop air) would be used.

Many dampers actually have a Schrader valve to adjust the gas pressure as a tuning device essentially skewing the damper curve up or down the dyno, once above the 20lbs or so to prevent cavitation under fast movements.

Here's a Bilstein off road damper with a valve:

http://offroadwarehouse.com/i-116352...-hardware.html

I assume the sealed dampers that are built for most automotive applications are done as you describe in the factory but many people that modify the dampers add the Schrader valve.

Hopefully this Miata net post will link properly:
http://forum.miata.net/vb/showthread.php?t=185685

Edit: here's a link for Bilstein revalve manual for their racing customers, from what I've heard Bilstein uses the same guts across their line. Last set of links on the page, wont cover the disassembly but the receiver prices should be similar.

http://www.bilsteinus.com/downloads/...t-information/

[Kostamojen]

Small update with the Swift front springs I'm running on my B14's:

Last week I decided to lower the front a little more because it was a solid .5" higher than the rears and higher than it was with the stock B14 springs. The ride/handling was extremely good with it at that height surprisingly but it didn't look right.

Now that ive lowered it about half an inch or around 3 of the groves on the collar ofthe coilover, the ride has gotten noticeably worse. I feel a lot of bump steer now and it might actually be hitting bumpstops on turns.

As a result, ill probably have to try raising the rears and raising the fronts. But I might also have to run camber plates up front that help lower the car, that might be the solution to improving B14's im general since they are not double adjustable and having plenty of bump travel may be critical.

[JoeHK]

Thanks for the update... Sad to hear they ride much worse, my car on stock bilstein springs is all the way down in the front & i'd like to keep it that way... So unless your problem could be fixed with other spring specs, this doesn't seem an interesting option :/


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[strat61caster]

Originally Posted by Kostamojen

Small update with the Swift front springs I'm running on my B14's:

Last week I decided to lower the front a little more because it was a solid .5" higher than the rears and higher than it was with the stock B14 springs. The ride/handling was extremely good with it at that height surprisingly but it didn't look right.

Now that ive lowered it about half an inch or around 3 of the groves on the collar ofthe coilover, the ride has gotten noticeably worse. I feel a lot of bump steer now and it might actually be hitting bumpstops on turns.

As a result, ill probably have to try raising the rears and raising the fronts. But I might also have to run camber plates up front that help lower the car, that might be the solution to improving B14's im general since they are not double adjustable and having plenty of bump travel may be critical.

If it is solely you riding on the bumpstops causing these problems (not a geometry change, parts change, or installation error), shaving 10-15mm off of the bumpstop Bilstein supplied should allow you to keep your desired ride height and be as comfortable as they were before at +0.5" (~12.7mm) without sacrificing safety.

@Shankenstein linked the most relevant video earlier, a how to in the following post, the Fatcat motorsports series #3/7, 8th video down:
http://www.ft86club.com/forums/showp...4&postcount=85

Fatcat also has a series on measuring wheel travel to see if you have any clearance issues which you can do before (to see if you're close and might be uncomfortable cutting the stop) and after you cut the stop. Basically you install the strut/damper without the spring and jack the suspension assembly up with and without the tire to see what kind of clearance you have 'fully bottomed out'. That's the entire purpose of the bumpstop, prevent the damper, wheel/tire, and moving suspension arms from making hard contact with something they shouldn't. If you can jack up the corner with enough weight to start lifting the chassis off the jackstands and all your suspension pieces clear than you're safe.

[Kostamojen]

Originally Posted by JoeHK

Thanks for the update... Sad to hear they ride much worse, my car on stock bilstein springs is all the way down in the front & i'd like to keep it that way... So unless your problem could be fixed with other spring specs, this doesn't seem an interesting option :/


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Still rides WAY better than with the stock springs.

Originally Posted by strat61caster

If it is solely you riding on the bumpstops causing these problems (not a geometry change, parts change, or installation error), shaving 10-15mm off of the bumpstop Bilstein supplied should allow you to keep your desired ride height and be as comfortable as they were before at +0.5" (~12.7mm) without sacrificing safety.

@Shankenstein linked the most relevant video earlier, a how to in the following post, the Fatcat motorsports series #3/7, 8th video down:
http://www.ft86club.com/forums/showp...4&postcount=85

Fatcat also has a series on measuring wheel travel to see if you have any clearance issues which you can do before (to see if you're close and might be uncomfortable cutting the stop) and after you cut the stop. Basically you install the strut/damper without the spring and jack the suspension assembly up with and without the tire to see what kind of clearance you have 'fully bottomed out'. That's the entire purpose of the bumpstop, prevent the damper, wheel/tire, and moving suspension arms from making hard contact with something they shouldn't. If you can jack up the corner with enough weight to start lifting the chassis off the jackstands and all your suspension pieces clear than you're safe.

You do realize the front shocks are inverted and have no external bumpstops, right?

[strat61caster]

Originally Posted by Kostamojen

You do realize the front shocks are inverted and have no external bumpstops, right?

[ame="https://www.youtube.com/watch?v=RU-p0qTNVIY"]How Shocks Work - Access Bilstein strut internal bump stop (3/7), v2.30 - YouTube[/ame]

[Kostamojen]

Originally Posted by strat61caster

Ya, I'm really not interesting in disassembling the shock... But that is a huge ass bumpstop. I'm sure I'll ruin something if I try to do that.

[JoeHK]

Originally Posted by Kostamojen

Still rides WAY better than with the stock springs.

Oooh okay, i thought you meant it was also worse than with the stock progressive springs thanks for clarifying!


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[Ro_Ja]

I've only had a passenger a few times, but when I took my coworker to lunch today, I noticed the extra weight actually improved the ride quality of the B14s pretty significantly (and it also felt like there was an improvement in handling too, but not sure if placebo effect or not). I also notice a difference depending on how full the gas tank is, but nowhere near the difference the extra person makes. Anyone else notice this? What would the technical description of the issue be? And is it able to be solved by changing the spring rate?

[Kostamojen]

Originally Posted by Ro_Ja

I've only had a passenger a few times, but when I took my coworker to lunch today, I noticed the extra weight actually improved the ride quality of the B14s pretty significantly (and it also felt like there was an improvement in handling too, but not sure if placebo effect or not). I also notice a difference depending on how full the gas tank is, but nowhere near the difference the extra person makes. Anyone else notice this? What would the technical description of the issue be? And is it able to be solved by changing the spring rate?

It is possible the extra weight compresses the progressive springs slightly so that the spring rate is past the soft side and closer to the stiffer side.

[JoeHK]

Originally Posted by Kostamojen

Last week I decided to lower the front a little more because it was a solid .5" higher than the rears and higher than it was with the stock B14 springs. The ride/handling was extremely good with it at that height surprisingly but it didn't look right.

I was just thinking of this...

Yesterday i put my summer wheels back on, 18x9,5 ET44 with 255/35/18 tires.
The problem i had was that if i lowered the front Bilsteins all the way down, the tires hit the spring. So now i've put 4mm spacers on there, but sometimes when driving in/out of parking spots and simultaneously cornering the front wheels still rub on something, i think it's still the springs... When driving (and hard cornering/ full lock) it completely goes away, it's only when the car has been parked for a while and i have to leave )

So if i convert to linear springs, lets say same specs as the ones you have installed, will my car raise 12mm (0,5inch)??
Cause honestly i like the way it looks how it sits now, but if it raises 1cm with different springs i can't lower it any more to compensate...

Any tips on what i could do lol?
(i'm an absolute noob when it comes to coilovers so that's why i prefer asking here instead of impulse buying different parts or just switching my coilovers to lets say KW V1's )

Greetz