flash9

Here is my write-up on putting together an updated suspension for my 1998 Lexus SC300.

I have had good luck with Bilstein HD shocks on some of my other cars and really wanted to put these on my 90,000 mile 1998 Lexus SC300. At first it appeared I was out of luck since Bilstein does not list any shocks for the SC300. After doing a little research I learned that Toyota basically used the Supra suspension on the first and second generation Lexus SC cars. There is a great write-up on the Supra Forums website of using the MKIV Supra Bilstein shocks on his Lexus SC. The guy who wrote the original post (gixxer_drew) in 2007 did a great job of laying out everything someone needed to do to assemble these coilovers. But, I became discouraged as I got to the last few pages of these posts since some people were reporting that Bilstein had changed the shock body and piston lengths. Basically they were reporting that at OEM ride heights, the springs would go loose at full suspension unload (basically when jacking up the car) if no helper spring were used. Also, with the reported longer shock bodies, the shocks were riding on the bump stops, which defeats the purpose of having a good quality shock like the Bilstein HD.

After being assured by one of the Bilstein engineers that they had not changed these shock in any way, I decided to go ahead with the project with off the shelf AK1243 and AK1242 shocks.

A little (or actually a lot) of background before we begin.

I have two Mazda Miata’s that I have installed the following coilover suspensions:

• Bilstein NB (2nd Generation Miata) Shocks
• AllStar 7” Coilover sleeves
• Hypercoil Springs with spring rates applicable to both the ‘91 and ‘01 Miata’s
• Honda Bump stops
• OEM NB Mazda Miata Shock Mounts

These coilovers have been a huge improvement over the OEM Miata coilover suspension. On neither of these setups I did not go wild with the Spring Rates because the Bilstein HD shocks are not valved for really high spring rates. Since Bilstein HD shocks have digressive valving, which allow for a high level of control without being harsh when increasing the spring rates by up to 100% over the OEM Miata’s spring rates.

I sized the spring rates using a very nice online spreadsheet created by Shaikh at Fat Cat Motorsports.

I strongly suggest anyone wanting to consider assembling their own coilovers, from off the shelf parts, step through Shaikh’s Miata Tutorial.

• Mazda Miata Spring and Sway bar Sizing Tutorial
• You can find some of his other
  Online Suspension Calculators Here
  • Then Click: Education > Resources > Tech Info > Online Suspension Calculator

The tutorial does a great job stepping through the proper way to size, front and rear springs, as well as sway bars. This goes into how changing one suspension component impacts the handling characteristics of a car.

I was wishing I had the equivalent suspension spreadsheet for the Lexus SC300. I was very fortunate to stumble upon this post about a Lexus SC300 Suspension Spreadsheet by Seefo.

After looking at his spreadsheet, I realized that the some of the values needed to be updated for a typical street car vs the race car that Seefo was building. The biggest change that needed to be updated was the weight of the car. His spreadsheet had the total weight as 3100lbs, and a SC300 with a driver and a passenger is closer to 3,850lbs. NOTE: I believe the SC400 would weight about 100lbs more.

I have attached my revised version of Seefo’s SC300 Suspension Spreadsheet v2 which has been updated for a more typical SC300 that is driven on average USA roads.

I did take the car values from Shaikh’s Mazda Miata Suspension Calculator Spreadsheet and put them into the SC300 Suspension Spreadsheet V2, and both spreadsheets came back with nearly the same values.

In upgrading my SC300’s suspension, I was looking to basically keep the ~14” ride height, while tightening up the handling without compromising the ride quality too much. So let’s take a look at how I intend to do that.

One of the things to remember when using the SC300 Suspension Spreadsheet v2, is there are some assumptions that needed to be made, and what you really want to look at are the changes from a known setup. In my case, my car still had its original shocks and springs, thus the known setup for my car. Below is a summary of the differences between the OEM coilovers and my assembled coilovers.

NOTE: My setup is in Maroon text in the SC300 Suspension Spreadsheet V2 (Row 22).

Just a few comments on the changes I have made to my SC300 suspension. As the Bounce Frequency goes up the ride quality will decrease, but the car will transfer the weigh more quickly, which can improve the handling of the car. Values between 0.9 and 1.3 tend to be on the more luxury side, while values in the 1.4 to 1.7 tend to be on the sporty side. Once you get over 1.9 the ride quality begins to get harsh and jarring for the driver (and passengers) on typical roads in the USA. At higher Bounce Frequencies typical road imperfections can actually make the car loose grip and traction. I prefer for the Front and Rear Bounce Frequencies to be about the same, so a Bounce Frequency Ratio close to 1.0 is desirable. Roll Stiffness is an indication of how much body roll the car will have when cornering. The best way to increase the body roll stiffness (ie decrease the body roll) is to increase the sway bars, but obviously increasing the coilover spring rates will also increase the cars roll stiffness. In my case, I wanted to try to keep my OEM sway bays. What you really want to look out for is the Front Roll Couple (often shortened to FRC) value! If this value gets much less than 60% the car will understeer and not want to turn in and plow through the corners. If the value gets much more than 63% the car will have a tendency to oversteer and the rear can break loose and the car will want to spin. So, it is my understanding for a rear wheel drive car you want to try to keep the FRC between 60% and 63%. One important note, is if the car is lowered too far with the Bilstein shocks, it will begin to ride on it bump stops and all of these calculations go out the window!

So here are the items I purchased to assemble my coilovers.

• (2) Bilstein HD AK1243 – Front
• (2) Bilstein HD AK1242 – Rear
  • NOTE: When ordering the shocks, I paid $10 per shock to have Bilstein CA cut a new snap ring grove 7” down the shock body. This allowed the 7” Coilover Sleeves to fit without doing any cutting of the sleeves.
• (2) Hypercoil 8B0525 - 525lb/in - 8" Long Hypercoil Springs 2.5"ID Front
• (2) Hypercoil 10B0325 - 325lb/in - 10" Long Hypercoil Springs 2.5"ID Rear
• (4) Allstar ALL64143 - 2”ID - 7" long Coilover Sleeves Kits
  • Note: I replaced the setscrew with ½” length, or you could cut it shorter if you would like. This makes adjusting with the optional spanner wrench much easier.
• (2) Energy Suspension 4.6103G - Mustang Bump Stops NOTE: Sold as a PAIR
  • Note: It took a fair amount of grinding to the diameter to squeeze these into the Allstar Coilover tops.
• (2) Moog K160129 – Front Shock Mount
• (2) Moog K90292 – Rear Shock Mount

I have been extremely happy with my setup and as long as you do not feel the need to slam your car these Spring Rates are a wonderful improvement over OEM.

I do want to say that gixxer_drew from the Supra Forum did a great job with his coilover write-up, but I personally do not like any of the suggested spring rates combinations listed in the first post. In my opinion all have too large of a difference between the Front and Rear Bounce Frequencies, thus resulting in too large of a Bounce Frequency Ratio (BFR), assuming the SC300 Suspension Spreadsheet v2 are correct.

• 650/500 has a BFR of 1.120
  • Potential better combination 650/400 has a BFR of 1.001
• 600/325 has a BFR of 0.940
  • Potential better combination 600/375 has a BFR of 1.009
• 500/250 has a BFR of 0.903
  • Potential better combination 500/300 has a BFR of 0.989

I have had one problem with an unusual clunking sound from the rear suspension that I believe I have figured out and I will write-up that in a different post.

t2d2

iTrader: (8)

Bookmarked for sure! It's a strong post when I have to break it up into multiple sittings.

TXMAG

iTrader: (1)

I'd actually like to see what your ride height looks like if you could take some pictures (head on of the wheel as well as down the side at a bit of an angle). If you do this can you please list wheel size, offset, and tire size too?

Clear

Great write up!!
I'd also like to see where your car sits.

I was literally just reading about gixxer_drew today and came to the suspension thread to ask a question about this setup vs an off the shelf coil over setup. Seems like fate that I do this

Are there any coilovers in the $1000 - $1500 that compare to or out perform this Bilstein setup? Like Fortune Auto or BC (I realize Bilstein is in another league with KW and Ohlins, but this is a relatively old setup, circa. 2007), or do you think those are made with a more stance approach in mind? I want a moderate drop, but, I want to improve the handling, the ride height that RedPheonix achieved seems perfect to me. Also if someone with coilovers with dampening setting could chime in on how useful it is to have adjustable dampening and such, that'd be great. I don't know much about what to look for in coilovers, and what I do know seems to be from the stance guys

All in all I really want to build this setup, seems perfect!


Here's RedPheonix's car with the Bilstein setup:
All Credits to RedPheonix, got it off the gixxer_drew suspension thread.

TXMAG

iTrader: (1)

There is nothing available off the shelf sub $2000 (exclude used/sale items) that will give you as good of a ride, or last as long as the Bilstein setup. In that price range you're looking at Asian made shocks which just aren't on the same quality level as their European counterparts. The best sub-$1500 coilover from what I've seen is probably the HKS Hipermax IV GT. It is at least made entirely in Japan where QA is usually top notch.

If you truly want to improve handling the Gixxer_drew setup is still the budget king for this chassis. But only if you drop it no more than an inch or so past stock. Once you get too low, regardless of coilover choice, you throw the suspension geometry completely out of whack. Lowering a car by 2"-3" does not make it handle better if it's not done as part of a completely thought out suspension setup. Most of the time guys just lower it for aesthetic reasons and not performance ones.

As for dampening, it's useful if it works properly. In my experience low cost coilovers have dampening settings that can be way out of whack. I've seen shock dynos where the softest setting is actually harder than the hardest setting. In my mind, this goes back to QA issues with budget Asian market coilovers - The quality is wildly inconsistent. That's why I said if I was going to use a low-cost option I'd pick something from Japan, e.g. HKS.

flash9

This setup has been on my car for about nine months, so everything has settled.
This weekend I went ahead the dropped the spring seat as low as I could on both the front and rear coil-over sleeves without having the springs go loose.
The proper way to measure suspension height is from the fender wall to the center of the tire rim.


This way it does not matter the rim or tire size.
At it lowest setting the suspension has the following measurements:

• Front: 13.000"
• Rear: 13.500"

I was asked to Profile and Side Angle so here they are:







My rims are OEM Lexus and the tires: Hankook Ventus S1 noble2 - 225/55ZR16

I forgot to measure the location of the rear spring seat so, I am still working on getting the rear suspension height back to being correct.
I plan to do this this afternoon. I will adjust it and take some update photos.
I just finished fixing the rear settings, so here is a current setup photo.

I am currently riding 0.25" lower than OEM the front, and about 0.125" lower than OEM in the rear.

• Front: 14.125"
• Rear: 13.875"

People need to remember suspensions need to be able to travel to do their jobs and slammed suspension can not do this.

flash9

If you really want to lower your ride height the H&R Toyota Supra (Part Number 29966-1) was designed to lower the Toyota Supra by 1.0in to 2.5in, so this would drop a Lexus SC a fair bit.

Here was H&R’s description of these shocks and springs:

H&R coil-overs are engineered for street use. Unlike traditional twin-tube shock absorbers, H&R coil-overs feature a state of the art mono-tube gas shock construction. Combined with the knowledge and skill of H&R's suspension engineers, the use of this state of the art technology results in the best suspension product that you can buy for your vehicle. H&R is the originator of the true coil-over system for the street and continues to lead the market with an extensive line of applications. Each shock is tuned with a progressive rate spring that is engineered from its inception to work with the shocks valving, creating a finely tuned suspension system. H&R coil-overs are the suspension answer for everybody, from daily drivers to the serious tuner.

Features:

• Unrivaled comfort, performance.
• Lowering range of 1.0 to 2.5 inches on average.
• Fully threaded shock body for adjustable vehicle lowering.
• Awesome handling and ride comfort.

From what I was able to find out, the H&R’s are not actually Bilstein Shocks, but they are made in Germany and potentially might use Bilstein innards. They are high quality shocks with very good digressive valving qualities. The supplied Spring Rates are actually very well matched to the Lexus SC300. This was just much lower ride height then I wanted to take my Lexus SC300.You will need to either reuse your shock mounts and bump stops or purchase new ones, because these coilovers do not include these parts.

Here is the problem, for some reason H&R stopped selling these in the USA, but H&R Germany is still selling these, and I was able to find them for about 1,000 Euros including shipping by doing a little searching on ebay and other sites. These coilovers include; threaded shock bodies with height adjustable lower spring mounts. They include 515lb/ft Front Springs, and 285lb/ft Rear Springs. As far as I can tell they do not include the Bump Stops or the Shock Mounts.

NOTE 1: You can see how the H&R supplied springs perform in the updated Lexus SC300 Suspension Spreadsheet V2 (Row 25).

NOTE 2: You will still find websites here in the USA listing these as “In Stock”, but trust me, none of them have them available. These businesses are just order takers, and then would have had these dropped shipped from H&R USA, and they no longer have any to ship.

TXMAG

iTrader: (1)

Nice find. I was actually looking for these at one point. I think I remember reading somewhere that this setup pretty much copied the Gixxer_drew setup just with better lowering capability. I thought I also remembered reading that they did use a Bilstein setup. In any event, I'd give these a shot if I could find them.

flash9

Available from German ebay Seller: CarTurningPoint for ~$1,150 including shipping.
Of couse if a shock fails good luck getting it replaced under warranty.

Clear

I think I'm sold on the gixxer_drew setup, my suspension needs a complete refresh, so I'm excited to get everything together to make this happen. I might go with 300lb in the rear and 500lb in the front.

Also, any additional info on this?

Seefo

Glad to see you post you results flash. I would suggest you host your spreadsheet online so its easier to find/see. Another data point, our car has settled in at about 1100/~525 springs. Its pretty good setup that we are all happy with it. It used to have a lot of understeer, but it turned out a bit of that was due to some alignment woes we had. Now its good enough that most of us don't want to change it, but I would really like to try a slightly stiffer rear....

Last thing I am finding is we are very close to ride height limited by the shocks, but for the most part its so low that the car is a pain to get up/down my driveway or even on the trailer, so not sure anyone would really want that for a street car... We measure our ride height from the pinch welds to the ground and its somewhere around ~4.75-5". I need to go back and measure it if someone is interested. You can fit a finger or two between the tire and wheel arch, depending on which corner you are at.


We had a rear suspension clunk due to the top hat nut not being all the way down. You need to make sure the nut takes the whole tophat assembly all the way to that small metal seat, otherwise it will slide up and down as weight shifts.

flash9

I am not 100% sure this was what was causing the clunking, but it has gone away since I made this change.
Where the top of the springs sit on this top spring seat, there is a split that is about an 3/4" wide.



I really do not like this part of the suspension and would eventually like to replace it with something that looks like this.



I just need to find someone who can make it for me.
It could be turned from one piece of material or three circles could be cut out of 3/8" shock and welded together.

That being said, I was getting the clunking on the rear passenger side when driving over uneven roads or speed bumps at lower speeds. At this location the shock spring was sitting such that the end of the springs tip was right in the 3/4" gap and I think it was making the noise. I have gone to each corner and now have the top spring seat slots facing out and the ends of the springs facing it towards the car.

You can see what I am talking about in the image below.



It has only been about 200 miles since I make the change but the clunking is gone for now.

flash9

Just to remind everyone the SC300 Suspension Spreadsheet v2 is attached at the bottom of my 1st post.
For me, if I click on hyperlink it asks me if I want to download the file.
Please let me know if that is not working to others?

Clear

Quick question, where did you order the shocks from? I called Bilstien CA, but they said they don't like modifying their product and were not very helpful, also I'm aware that Bilstein CA does not sell directly to the public.

flash9

I purchased mine from AJUSA and I would be happy to share my Point-Of-Contact from both Bilstein USA and who I worked with from AJUSA in a Private Message.

(2) Bilstein HD AK1243 – Front - $98.40 each
(2) Bilstein HD AK1242 – Rear - $98.40 each