Ok…here we go. This first section will be an intro into my tuning theories, my simple math, and finishing with suspension calculations that will have you ready to tune your own by the end of the post.
Tuning will forever be a learning process. You try new combinations, spring rates, damp…you always think it could be just a little better. For that reason, l’m going to avoid absolutes. l’ll be giving you the math, and my process of accounting for weight distribution. The math, and physics, l feel are perfect, but what you base your starting numbers on are left completely up to you. This suspension section will be based on off road builds. I’ll be using total weight percentage for my spring rate. I’ll make suggestions on how to apply this method to stiffer springs, but again, the range that you like will be left to your own preference.
The math:
I was a terrible math student. I am terrible at explaining math, but l’ll be making it easy to digest for this thread. But please, keep the remarks about my way of explaining it to yourselves. It works. First, you probably already know that weight distribution is crucial in tuning. This simple division will help get you the correct balance every time. You divide your highest number by your lowest.
Example:
On a 60 front, 40 rear you get: 60÷40=1.5.
58 front, 42 rear you get: 58÷42=1.38
This simple math will always give you the proper spread for you weight distribution. Simply start with the higher of your two settings, divide by this number. We’ll call it your weight ratio for this post. Once your first number is set, divide by your weight ratio, and there you go.
Example:
A 60/40 split with front springs that l’ve determined a front spring rate of 600.
600÷1.5=400.
Front spring: 600
Rear spring: 400
Determining spring rate:
This is essentially up to you. It should be based on something, though. It can be as simple as 560/440 for a 56/44 split, or as complicated as researching ‘Hooke’s Law’ and diving into spring rates, wheel rates, frequency, and so on. The method l use because it gives me a consistent feel across all my cars, and it’s easier for later calculations such as ride height, AR bars, and aero. I simply go a given % of my total weight. For rally cars, l go 15%. For road going cars you will need to experiment, but 20% seems like a good starting point. When l say 15%, that’s my center, so there’s an extra bit of math to use this as center instead of your top or bottom numbers. This isn’t completely necessary, you can simply use 15% or whatever pct you choose as your actual number. I just like the range that 15 to center comes out to. That’s the beauty of this method. There’s an amazing amount of flexibilIity, though there are settings that need to correspond. Btw, l’m using nice round numbers for my examples…why? because l’m lazy, doing it in my head, and because l’m terrible at math.
Example: total weight 3000 lbs on a 60/40 split
3000 x .15=450
To get 15 pct as center:
450 x 2=900
900 x .60=540
You’ll always multiply by your FW number. Here it’s .60, for a 58/42 it’s .58.
Once your top number is set do the math using your weight ratio.
540 ÷ 1.5= 360
Spring rate: 540/360
Again, this is just my technique. Where you start is up to you. Whether you use a pct technique for spring rate at all is totally up to you. I’m just making sure you’re the right distance apart.
Ar bars:
This is a lot of feel, theory, and tbh maybes, but l carry my body weight percentage theory to my AR bar settings. Again, on my rally cars, l’ll be using 15 as my center. Imo, the 1 to 65 numbers of the scale represents spring/weight ratio. So on a 60/40 split, my ar settings are 18 rear, 12 front. Notice they add up to 30. If l do 10% like my raptor tunes they add up to 20…every time. You’re about to see why. The math on that 60/40 split, with 15 pct s/w ratio. It’s the same as figuring springs.
Example: for 15 pct, double that to 30.
for 10 pct, double to 20
15x2=30
30x.60=18
18 rear Ar
You can get the front a couple of different ways. Since you know it adds back to 30.
30-18=12
Or:
18÷1.5=12
Again, however you decide your rate, this is only a suggestion, and me telling you how l set my rates. I will highly suggest that your ar settings be based on spring/weight ratio, though. I’ve done a lot of testing at the dunes, and on the lake, and l’m very confident that your AR bars should represent the percentage of your body weight that your springs support. If your springs are supporting 25 pct of your total weight. The sway bars should represent that. This is of course, lmo.
Damp:
Do what feels right. You should have the tools by now to make sure you have the distance between, correct. Personally, l set my rebound in the middle. If it’s a 60/40, my rebound is at 6 and 4. 58/42? 5.8/4.2. I set my bump at .66 pct. Boom. That’s it.
Ride Height:
Like Ar bars, once your spring to weight ratio is determined and set, you’ll need to set your ride height as such. Simply take the max height and multiply what’s not accounted for in your springs…ok, l didn’t explain that well. If you are at 10 pct spring/weight ratio, you multiply your max height by 90 pct. 15 pct s/w ratio, multiply by 85 pct.
Example: 10 inch max ride height. 10 pct s/w ratio
10x.90=9
Ride height is 9.
Even the slider and you’re done.
That was horrible. I’m sure l missed, or was unclear on things. I felt myself rushing. Sorry. I hope you guys get the idea. Stay tuned. Let me know if there are any questions. I’m covering alignment, brakes, and differential in the next post. The differential section will lead into the third and hopefully last, more advanced custom gearsets, and making sure your transmission and differential gears are working together, perfectly.