Kenny Brown Performance cars and coffee

JJ427R said:

He specifies in the videos different springs for different setups such as street, street track, full track? Did you not see that? He actually talked about that quite a bit? That is why he offers those different options for purchase as well. He has become a big believer in the JRZ stuff and he explains that in the videos as well.

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I watched it this morning - don't forget that fb viewing in real time isn't an option for me.

I found this episode to be better and more informative than others I've watched pieces of.

Around 16 minutes in, he gets into it being a real PITA for him to try to fix something when a customer went off on his own for some of it, and I understand that completely. It shouldn't be his problem to solve when it's the customer who changed something without realizing the implications of doing so. Especially if KB isn't keeping all of the engineering data right at his fingertips. I don't blame him a bit.


In some ways, KB's thinking isn't all that much different from my own, but in others (and certainly at the detail level for a few things) it does differ.

KB's philosophy definitely feels more toward "stiff spring/soft bar" than most, that his approach is more about dialing back from race rather than building up from OE street.

400-ish for performance street - I'm really thinking that's where a dual-purpose occasional street/fairly serious HPDE car might end up - is definitely up there, somewhere around 2.0 Hz. Not un-do-able, but you and your passengers had better be able to appreciate a firm ride all the time.


Fun fact - his Koni yellow/H&R Race recommendation really isn't much different from my Koni yellow/BMR GT500 Handling combination. H&R's are about 25% stiffer (I just don't care for the H&R amounts of lowering or the fact that the H&R front and rear springs are both variable-rate).


Norm

Norm Peterson said:

Really? Where are you finding roads good enough to where a 2.5Hz ride frequency is reasonable for street driving?...

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Norm Peterson said:

400-ish for performance street - I'm really thinking that's where a dual-purpose occasional street/fairly serious HPDE car might end up - is definitely up there, somewhere around 2.0 Hz. Not un-do-able, but you and your passengers had better be able to appreciate a firm ride all the time

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Could you please show how you calculate this?

Then, how is that information useful?

Thank you

Vibration frequency of a spring-mass system can be calculated by knowing the stiffness of the spring and the mass that would be vibrating.

The equation looks like 3.13 ÷ sqrt([sprung corner weight] ÷ [wheel rate])

where wheel rate = [spring rate] x [motion ratio]^2.

I'm taking motion ratio as the ratio of spring travel divided by wheel travel here, which would normally be less than 1.0.


There are rough guidelines for ride frequencies vs car use - it's a guideline for evaluating the basic ride vs handling balance of a car. 1.0Hz is soft, 1.2 might be about where a base Mustang is, 1.6 is about where the current GT350 fronts are, and where a certain BMR GT500 part number on a non-GT500 early S197 more or less puts things. H&R race fronts would be up around 1.8 Hz.


Norm

I have a lot of springs and tested them all. S197s are severely undersprung. 400 lb/in springs up front are not stiff on the road by a long shot. But yet again, you're extrapolating way past your knowledge range without any first hand experience. But maybe I should have had a cage and hans to test my 400lb and higher springs.

Racer47 said:

I have a lot of springs and tested them all. S197s are severely undersprung. 400 lb/in springs up front are not stiff on the road by a long shot. But yet again, you're extrapolating way past your knowledge range without any first hand experience. But maybe I should have had a cage and hans to test my 400lb and higher springs.

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Too stiff or not is a subjective opinion based on individual experiences. Your experiences and mine are a bit different.

I think the difference between you and me is that you're building down relative to a dedicated and trailered race car, while I'm looking at the aftermarket spring business as building up from base OE street cars that still see more street miles than track miles.

You're fine with a 2.0 hz street ride, and I'm pretty sure that I'd be OK with it on most streets as well. But I doubt that my wife would appreciate it, and the Mustang-owning neighbor across the street would not be happy at all about that much firmness (he's not a corner-carver type).


Norm

I drive it daily. It's no trailer queen. 400 even 500 rides way better than you may think. I thought we were talking performance not grandma's car.

Racer47 said:

I drive it daily. It's no trailer queen. 400 even 500 rides way better than you may think.

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Like I said, I expect I'd be OK at 400, maybe even 500. That's coilover territory, and aside from that feeling more race car than street car, I can't justify spending as much on one corner of the car as what would get me a full set of Koni yellows or Bilsteins. You wouldn't catch me shopping in the bargain basement for C/O's any more than you'd see Gas-Matic regular shocks in my shopping cart.

I thought we were talking performance not grandma's car.

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We are. But we seem to be coming at it from different directions and with somewhat different targets. FWIW, the grandma in this case has never preferred a lightly damped 1 Hz ride as might be expected.

I'd be much more inclined to chase stiffer springs if the car felt like it was rolling or still nose-diving too far. So far, I'm OK with the car rolling something like 2.5°/g (about half a degree per g of that being due to tire vertical stiffness effects). Maybe the time will come when I'm no longer satisfied with that, maybe it won't. I'll just have to wait, drive, and see, though I'm seeing it being a case of diminishing returns - moving up to 400/350 from where the car is now would only take about a third of a degree per g of roll out of what's there now.


Norm

Norm Peterson said:

Too stiff or not is a subjective opinion based on individual experiences. Your experiences and mine are a bit different.

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I could say the same thing regarding the KB Matrix Brace! I'm still just blown away by how many on here dismiss the effectiveness of that....

JJ427R said:

I could say the same thing regarding the KB Matrix Brace! I'm still just blown away by how many on here dismiss the effectiveness of that....

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We've been through all this before, and the short story here is that the S197 doesn't leave enough missing stiffness on the table for it to do much about, either structurally or handling-wise.

It'd be a somewhat different story with the more flexible-chassis Fox, and such bracing would be more effective yet in a flexi-flyer original-body 1960s chassis. In the S197 it's considerably deeper into the realm of diminishing returns than a 400/350 spring setup would be relative to 260/220.

I am not dismissing its effectiveness with respect to driver confidence. Not at all. If it made everything click for you and got you to that 'a-ha' moment, then it absolutely was a worthwhile mod for you.


Norm

Norm Peterson said:

I am not dismissing its effectiveness with respect to driver confidence. Not at all. If it made everything click for you and got you to that 'a-ha' moment, then it absolutely was a worthwhile mod for you.

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Like you said, it's all subjective opinion...