East Tennessee Region SCCA

no.. larger

JB,

By uncalibrated eyeball, it looks like there's a lot of vertical suspension travel. What's the motion ratio of the front springs, i.e. what's the actual wheel rate?

the whole range used in the video is appx 1.75 inches.... I dont know if less would be good... (?)

NO less would be bad, a certain amount of travel is needed or you hit the stops hard and unload the suspension....

I think DeWitt is asking why John isn't running stiffer springs, which isn't the same thing as travel.

700 thinking about going stiffer.. but not sure the dampers would handle much more.

It looks fairly controlled to me.. no sharp movements nor po=going...

would be interesting to see JY or Randys cars motions from a similar angle

NO less would be bad, a certain amount of travel is needed or you hit the stops hard and unload the suspension....

I think DeWitt is asking why John isn't running stiffer springs, which isn't the same thing as travel.

Well, yes, more or less. You can see from the video that JB is barely, if at all, touching the bump stop at full compression. Putting in a stiffer spring at the same ride height would reduce travel and be even further away from the stop at full compression. Or you could lower the car some more if that doesn't move to a bad part of the camber gain curve or add bump steer.

the whole range used in the video is appx 1.75 inches.... I dont know if less would be good... (?)

It depends on the quality of your suspension geometry, but generally less is better until the tires won't stay planted. Of course you could stand a higher spring rate at zMax than you could at Bristol because zMax is pretty smooth. As I remember, BFG's don't like camber change relative to the ground in roll. With a lowered McPherson strut suspension like mine you need a lot of spring and bar to minimize roll. Increased front roll stiffness can actually increase grip enough to at least partially make up for the increased weight transfer to the front wheels and make the car be able to go faster.

The motion ratio for my car is pretty close to 1. My mechanic runs 600 lbs/inch front springs in his NASA American Iron S197 Mustang, which gives a wheel rate of about 540 lbs/in and the bar probably adds another 400 lbs/in or so. I've dropped back to 475 lbs/inch front springs from 550 because I thought it was a bit too harsh. If I heard correctly, however, Loughlin was running 700 lbs/in front springs in his S550 Mustang at zMax with, I think, similar front suspension geometry to mine.

700 thinking about going stiffer.. but not sure the dampers would handle much more.

Can you put in a bigger anti-roll bar?

I see the Challenger has an SLA suspension so the motion ratio is going to be significantly less than 1. Since the wheel rate is the spring rate times the square of the motion ratio, the wheel rate is going to be a lot less than 700 lbs/inch. Here's a link to a short article about calculating spring rates:

http://www.worksevo.com/Spring_Rates_1.pdf

My calculated front suspension frequency is 2.1Hz with 475 lbs/inch springs. With 700 lbs/inch springs, it would be 2.6Hz. For a car with almost no aero, that's about the upper practical limit. I don't think I'd want to drive it on the street every day, though. My guess would be that to get your ride frequency above 2 Hz, you're going to need a lot stiffer springs and shocks.

Kinetic wrote: ↑Mon Apr 02, 2018 11:00 pm Here is my fastest run from the Charlotte Match Tour during the first round of the underdog challenge Saturday.

https://youtu.be/Bm7nLTZVcPg

That's really good.

x2... definitely liked the finish slalom. The mid engine cars are so much fun in elements like that.

Sent from my SM-G930P using Tapatalk

Yeah, Adam Norton and I talked about how much fun that course would have been in our Spyders.

Dewitt... your right.. I did only hit the bump stops once..maybe.. but, thats also one of the smoothest lots we will ever run on..maybe short of Wilmington. I actually softened up the front bar a hole.. and the turn in was a tad better.
My next area of attention is the upper arm bushing change.. and attempt to cut the castor in half.. Its actual current castor is 9.5.. I want to get near 6.5 degrees.

MARKP wrote: ↑Tue Apr 03, 2018 10:12 pm x2... definitely liked the finish slalom. The mid engine cars are so much fun in elements like that.

Sent from my SM-G930P using Tapatalk

yes! even in the big Dodge, that finish salom was fun.. to see how early you could maash it to the floor!

that shit leading up to the finish salom.....

going out was fun... coming back was one of the worst examples of "flowing: I have ever done on a National course.

9.5 degrees caster!!!!