the natural frequncy of a spring mass system is Squareroot(K/M) where k is the spring constant and M is the mass involved. If the spring constant ratio front to rear differe greatly from the mass ratio, the same bump will make the front "bounce" and a different frequency (speed) than the rear. No matter what else, this can't be good!

Now dampening out the "ring" in one or so oscillations makes this less of a problem, but still, if the spring rates are a lot off this, then you'll end up with the front and rear doing very, very different things over the vary same bump.

I private conversations with some track guys, I'm finding some very fast drivers with rates in front about 1.5x what's out back. But this is very, very different than many are running.

But when I looked at my Ledas, and I see 250 up front, and 325 - 350 out back, I really wonder where those rates came from! They don't make any sense at all, and I'm not surprised that I (and TonyB) had a buch of bottoming problems with these springs. Just to friggin soft!

But this is a new world to me, so I'll have to unlearn my physics, and learn more suspension tuning!

Matt

 

See, a 250 spring is heavier than stock, but no bottoming with the stock setup...due to more travel (?) and or better dampening (?).

My Megans came with 285# springs up front and 335# springs in the rear. If I adjusted the dampers equally front to rear, the car would pogo a bit over undualtions. If I turned the damping up 1 notch in the rear, the pogoing went away...counter to my expectations.

So, what I wrote someplace else was, dampers have a way of really complicating any set up...in fact the basics can be absolutely perfect - springs, bars, ride height etc, but if the damping is off, it's all off.

There are programs that illustrate front to rear damping cycles with given springs matched to a car's natural frequency, and, intended use. I ain't got one

 

Leda special wind fronts and Hypercoil rears... 325 lb/in... This is our standard 'Softcore' setup.

 

FWIW, my previous Acura Type R had linear rate front springs and progressive rate rear springs and that was a very nice car to push around as a stocker. Once past the progressive stage, the rears were said to be the same rate as the front...but every discussion I've ever had about how progressive rate springs work has had as many descriptions...

The Type R was very neutral in most situations. It lacked some of the Mini's fast steering and a little feel - was typically honda light - but was more than capable. I trucker didn't know to mass cannot occupy the same space. And, Acura produced only so many and I was otta luck for a new one, hence the 99 Si...the year Acura skipped a production run. The Si ain't no Type R, but I'm off topic.

 

You can't always directly compare front and rear spring rates, because motion ratios may change what the wheel is actually seeing.

In the case of the Mini, it seems like the springs more or less act directly on the wheel both front and rear, so I don't think there is a much motion ratio to speak of

Natural frequency is only defined for linear systems. Most dampers have different compression and rebound damping, so that's going to give very non-linear behavior. And if you have a damper like that paired with a progressive rate spring, you might as well forget about any frequency analysis

Give in to the dark side: Suspension tuning is black magic unless you have a supercomputer, some expensive software, and a heck of a lot sweet measurement tools.


Michael - I didn't know you had a Type-R. What a sweet car! I love those things. My buddy used to have one, which he let me autocross a lot back in the day. Perhaps interestingly, perhaps not, I've done ~50-100 autocross runs in a Type-R, but never driven one 50 feet on a public road

 

We'll soon have local access to a shock dyno and some new coilovers to play with, along with full rebuild capabilities and upgrading said units to triple adjustables with a remote reservoir... I am really looking forward to playing even more.

 

Hey Roger!!!

The mini's front LCA motion ratio can change a lot with offset, and I learned a few days ago that the rear will not change measurably. So you are correct as I pointed a few replys above; working from a 40mm offset, if we were to add 15mm spacers up front we would need to increase the spring rate by 10%.

I will add this, I'm beginning to feel like I need to be schooled all over again. The suspension engineers who are responsible for really good handling road cars, and, F1 cars deserve a raise

 

Haha, I think the device engineers that make such sweet chips deserve a raise