Seefo

Hi all,

We are building an SC300 to race (road race) In chumpcar/WRL and possibly in NASA PT. As part of that, I took some measurements of suspension (motion rato, sway bar, corner weights, etc). to put together and calculate our roll stiffness and front roll couple (FRC). I am not sure a lot of people will find this relevant, but I wanted to share it anyway to help anyone else interested and/or get feedback from everyone. A lot of these terms are generic, plenty of google descriptions available (Total Roll stiffness, Front Roll Couple, Spring Natural Frequency, etc.). I posted some links with information at the bottom of the spreadsheet that would be good starting points if you are curious.

This spreadsheet could help you figure out your "gixxer_drew" setup for example.

The motion ratios I calculated are:

Front Shock: .619
Front Sway Bar: .752
Rear Shock: .721
Rear Sway: .535

How To use it:
-The blue section covers springs. The first two columns are the front and rear spring rate. Put your new spring rates in those columns (Highlighted in black). Then look at your "T Roll stiffness" and "FRC" (Highlighted in Red). these are the values you compare with a different setup.


-You can see the Natural Frequency of your springs here. These are affected by corner weights which are located in the upper blue section. I am assuming the car has a equal weight distribution on both sides, which is not really a bad assumption. Our car as 51% left/right and 50% cross weight.


-The Orange section covers sway bars. These can be a bit more complicated since most of the sway bars I find are tubular. In that case you need the sway bar thickness,wall thickness, and arm length. I haven't found the wall thickness for most sway bars, so you are on your own there. Arm length is usually the same as OEM, but sometimes they are different.

Limitations:
-The sway bar measurements, particularly bar length may not be accurate.
-The sway bars on these cars are not straight so each bend will have some bending deflection and will affect the overall stiffness. I don't take these into account, but I am planning to fix that at a later date.
-Lastly, as I mentioned above, sway bar wall thickness has not been measured and is based off an old thread I found on the thickness of the supra sway bars, it may not be correct. I am waiting on a spare so I can drill and measure it.
-Motion ratio inaccuracy can have a drastic effect, I measured them 3 times at a minimum of 60mm of motion so I think they are pretty close, but .01-.02 mistake front and rear is not minor. (so .59 and .74 would definitely be a big difference in the balance). You can see my measurements in the red section underneath the actual spreadsheet.

Realistically, this spreadsheet should be used based on a good before setup, rather than for absolute measurements. In other words, I suggest you plug in some numbers that you liked before, then increase the spring rate/sway bar to compare a new setup you want to try. Lastly, as a general rule for RWD cars you want the car to understeer naturally that way you can trail brake and will have some extra grip mid corner to roll into the throttle. There are some general rules for FRC bias, but they need to be adjusted for testing. We are aiming for about 60-63% FRC at the moment, once we find a suitable setup I will post it.

flash9

Seefo,

This is GREAT Stuff!

Just curious, are the motion ratios, corner weights, and unsprung weights for a stock SC300?
No mater what this is way better than I could do without this spread sheet.

I am thinking of going with the following setup for a nice improvement (without going too harsh) over my 90K OEM suspension.
This will give me a very comfortable Front Bounce Frequency of 1.50Hz and a Rear of 1.52Hz for a Bounce Frequency Ratio of 1.012.
The Front Roll Couple (FRC) will be 61.7% which is right in the middle of the sweet spot of 60-63%.

BTW - Where are you located in North Carolina?

Seefo

Unsprung weight is an estimate off a few parts measurements. Corner weights are bound to change depending on your car. Options/mods/etc, will have an effect on it.

Corner weights are estimates, on a race weight of of 3100 lbs with driver and full tank of gas. I have no clue what the corner weights are for a stock SC300, but its going to be about 700 lbs (overall) heavier if you include a driver. I don't remember the numbers, but our completely stripped car had a weight distribution of (approx.):
52% left
51% cross
54% front

I am in Raleigh, NC btw. Was hoping the spreadsheet would spark some interest and maybe fill in some of the estimates. Unfortunately, I am a bit busy with the car prep (and life), so getting accurate measurements for unsprung weight (or sway bars...) haven't been high on my list. I will say the motion ratios where confirmed by some of the other forums, so I am pretty sure they are accurate.

flash9

Thank you again. I want back and looked on your spreadsheet and you had the car weighing 3,100lbs, and then I remembered I had a spec sheet on the 1998 Lexus SC300. It lists the vehicle weight as 3,560lbs and if you estimate the driver and passenger as about 290lbs. Assuming the front to rear weight bias as about 54% to 46%. This does change the desired spring rates a fair bit, but nothing crazy.

• Front Spring Rate of ~550lbs gives a BF of 1.47Hz
• Rear Spring Rate of ~350lbs/ft give a BF of 1.50Hz
• Bounce Frequency Ratio of 1.02
• Front Roll Couple (FRC) will be 60.5%

Good luck with your racing and I would love to see the car some time.

RXRodger

iTrader: (2)

purpose. Not very far along other than stripping the car and cage going in next week. I appreciate this info, suspension was next on my list to research and buy parts for. Will use this info to make a stab at the set up and will pass along what I find out. At least it won't be a total guess like I was sort of thinking which was throw on some cheap non adjustable damper coilovers with 14/8 spring rates and see what happens.

Seefo

Definitely, where do you live? Its not licensed anymore, so your best bet would be to come out to a track event or one of the races!


And yea, any information in this line is greatly appreciated. the spreadsheet is public so don't hesitate to change/correct/add things!

flash9

Seefo - I wanted you to know I finally got around to putting together my Bilstein/Hyperco Coilovers, and your Suspension Spreedsheet was very helpful.
I know you do not past much here so, I did not know if you would see it. but none-the-less, here is a link to my write-up.

Custom Bilstein / Coilover Suspension

Thank you again.

NCpilot

Seefo,
I am a Chump racer in Raleigh NC as well. We currently race a 1MZ swapped Mr2 but are in the process of building a SC300. Good info on the suspension...not sure what way we are going to go with the rules as is. What races are you planning to participate in for 2017?

John

Seefo

Not sure at this point. We have talked about doing races other than the VIR ones, but unfortunately we got hit pretty hard in the march race and spent most of our yearly budget rebuilding the car. Since we qualified for the chumpionship, we are going that in about 2 weekends.

I think the plan discussed so far is we are going to run VIR with chump, possibly AMP with WRL, and CMP with lemons. Good luck on your build! going to be tough for us in 2017 since we have no points now and a lot of the competitive cars are getting points back.

RXRodger

iTrader: (2)

Yes it will get much tougher next year, but the SC is still a good car out of the box if you get the weight to a minimum. We are going to go all in for Barber in 2 weeks and hopefully podium since it gets much tougher next year.

NCpilot

Seefo,
I am hoping some of the free items loosen up a few ponies and I think we are planning on taking the 40pt hit for coilovers. Our swapped car is fast, but not reliable and that is what we are looking at more than out right speed.

Right now we are planning Road Atlanta, VIR South (with MR2), VIR August and maybe Sebring...

I might come up to VIR in December on Sunday. What is your team name?

Seefo

CYA Racing. SC300 is plenty reliable. 40 points probably won't be worth it for coil-overs.

GOod luck. what is your team name?

RXRodger

iTrader: (2)

Agreed on coilovers not being worth 40 points.

Our team is Burningham Too Racing. The team still runs a 944 under the original name Burningham Racing. We will run Barber in 2 weeks, we may run Chump at Road Atlanta in February or we may wait until the following weekend and run the same place with AER.

NCpilot

Seefo,
Didn't make it up to the race due to work obligations but was keeping up with scoring. Saw something happened to you on Sunday or late Sat. When you get a chance post up a race report! We just picked up our tranny this morning to convert our car to 5-speed! Still shooting for Feb Road Atlanta.

John

Seefo

John,

I made a new thread with the race report.

Not a lot of discussion on the spreadsheet, but just wanted to keep the thread clean-ish in case anyone is reading this info.