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Rank: Driver's Permit
 1 user liked this post.
#1 Posted : Tuesday, January 8, 2019 1:55:01 PM(UTC)
Like most of you, l fell for the accepted method of using the max plus min times weight distribution formula to set a 'base', then saving the base and adjusting from there. I felt like the guy on 'A beautiful mind' with all the numbers l had scrawled down, punching away at a calculator. I realized there was a better way. Easier, and imo better. Before l explain my process, l'll put out a disclaimer. I wasn't good at math in school, so my terminology might be off a bit, but the math is on point. I'm going to use a 60/40 as an example throughout this post, and will be referring to this number that l get by dividing, in this case 60÷40 as my fw number. This number is 1.5 for a 60/40, 1.38 for a 58/42, and so on. Back to the 60/40. You set your springs at 300/200, 600/400, or 1200/800. You'll notice that if you set your front at 600, you divide 600 by 1.5, you get 400. Multiply 400 by 1.5 you get 600. This works with any combination of spring stiffness. I stick to multiples of my weight distribution, but you can pick any random stiffness that feels right, divide or multiply by your fw number (1.5 in this case) to get your other number. This works for any weight distribution as long as you get your fw number by dividing your front or highest percentage by your lowest. On rear engine, you'll divide your back by your front. Highest number, divided by your lowest. A 60/40 is still 1.5 regardless of where your weight is. So your springs are set. Hypothetically at 600/400 although l like a 300/200 for dirt circuit racing. I like running even damp, so my rebound damp sets at 6 and 4. Not gonna get into bump, as it's a personal preference. Mine is 66pct, but that's irrelevant to this discussion. On some GRC's or legendary cars, mostly bajas, the springs don't go to 600, and the damp doesn't go below 3, so you do end up with springs at 300/200 and double the damp, but there's flexibility. That's the beauty of this method, there's no setting a base, then adjusting a few percent. You set it where you want. Where it feels right, divide or multiply by your fw number, and it's set. As l said, in my experience evening rebound damp with your springs 'feels right', but doubling it in some cases is the next best. For example, a dirt trail car that l want at 300/200 spring stiffness, a 3/2 damp just doesn't grip on pavement. So l do run a 6/4 damp on a 300/200 spring, but l try to avoid that. If you're with me so far, and buying in, l've also experimented with going 10 pct of your total weight. The springs felt amazing, but l didn't like rounding up or down, on my damp. 5.454 almost sent me over the edge. Oh, AR bars. I made a post explaining my reasoning. All things even, your front is 'softer" bc of the extra weight, so when you soften the rear, you're essentially neutral. I run an even 10 on dirt, and 20 on pavement. But if you do want oversteer, set your first number, again divide or multiply by your fw number, and there you go. Btw, refer to my other post if you get those odd decimal numbers on your AR and spring scales. There's a simple way to get rid of them, and get them to match up again. Thanks for reading. I hope at least a few of ya'll try it. You'll never set a base tune or add a max plus min times weight distribution plus min, again. Just typing that blasted formula made me cringe a bit.
Rank: Driver's License
#2 Posted : Friday, January 11, 2019 8:04:23 AM(UTC)
Good stuff, in this post and elsewhere. Thanks for sharing. I've added your calcs to my spreadsheet, and run a few comparisons.

I'm testing on tarmac right now, but I'll include some dirt as I progress. I adjusted your alignment formula to halve the rear camber (I've never run >1.5 negative rear, but I'll test that as well), and am not using the differential numbers. I also halved rear toe out.

Sometimes I modified spring /rebound by 1.5 rather than 2, but always keeping the ratio between front/rear and rebound/damp.

This yields cars that have similar lap times to my existing tunes, but in a couple of cases significant improvements - I trimmed a half second off my bone shaker tune on a 50-second track with a little tweaking. The rear toe out really helps turn-in and power-on oversteer.

And this is certainly an easier method, although I'd like to factor the power or power:weight ratio into both suspension stiffness and gear ratios. I'm also setting diff balance manually per-car. Mostly 65-70 rear, but some outliers.

Anyway, appreciate you posting more detail as you progress, and I'll do the same. I'm starting to have a decent dataset, so perhaps I'll figure out how to correlate power:weight and such back to settings that work and derive a formula.

Random side note: best power to weight ratio of actually useful A-class cars is not the boneshaker. It's the Ford raptor.