learning about my car :)

[2013kAB]

a couple weeks ago i did a beginners driving school at road america. 3 "drills" sessions, 3 classroom sessions and 1 "track" session on their kart track. my car is 2013 gt with 3.55 gears, LSD though not torsen, 18x8 factory wheels and wilwood fnsl6r front brakes with slotted rotors. pirelli all-seasons. nothing else changed. ended up with some ebc greenstuff pads in the front, factory rear pads and rbf600 fluid changed two weeks before the school.

this was the 1st time i ever pushed the mustang hard. for the year .5 that i owned it, and two track days (one in the rain), i feared rear wheel spin in any situation where the throttle was involved. well, the TD in the rain worried me. i guess that was the situation where it seemed like any throttle with the car even slightly turning it would break loose.

according to my factory accelerometer, i did 1.03g braking, .90 turning right, .88 left and .62 accelaration. as opposed to my 1st track day .66 brake, .78 right, .72 left and .37 accel. (with factory brakes up front at that time)

boy did i learn a lot. 1st this car is darn powerful in stock form. 2nd, the car is setup from the factory for the safety of understeer. but it's not a horrible understeer or at least it doesn't onset too fast and there's nothing you can do about it. another thing i learned is that you really have to at the right rpm level and mash the throttle to get the back end to kick out but it's easy to get it under control - i was fearing it would be like driving on ice and once it started you couldn't stop it. just a easy lift and steering correction and it snapped back into place.

another thing i learned was about weight transfer. wow did i learn that. on the kart track there was a strait burst up a little rise then down and hairpin to the right. i actually did enough laps that each time through that down/right i experimented with braking - first brake then turn, next brake deeper and start turning. finally i rode the brakes hard as i could all the way to apex. i could feel just how much more traction there was from being down hill and heavy nose dive. it was quite the experience.

so question: i have the soft factory suspension with lots of travel. does a stiffer suspension mean less weight transfer overall, or does it just mean a longer time for the weight to transfer?

everything in the classroom was great too, just about everything that is said in these forums for beginners, or that was said between runs at the two track days i did was repeated. ha, it's really starting to sink in.

other than that, perhaps the best thing i learned is, i really don't see myself changing anything on my car suspension wise until i get to be a better and smoother driver of this car. it does a lot and i'm just not there. that said, the whole possibility of burning off my factory brakes is why i did the wilwoods. which, at least for the drills and kart-track (akin to auto-x) held up really well!

another question: my factory brakes, the pedal got real mushy after only a few corners at my track day. i could push the pedal down a lot further than when everything was cold. as i went on, i could feel the brakes not grabbing as fast and not slowing me down as much. so - fluid and pads right? (this is not yet my question) with the wilwoods, greenstuffs and rbf600 and the drills we went through plus the laps on the kart track, i could definitely feel like i could push the pedal down a little more as things got hotter. with the pads, i think it was almost the same as "cold" throughout, meaning i felt like i still had the same amount of braking available and i could hit the abs every corner right up to the end. so... my question then is this: even though you have better fluid like rbf600 and even though you have better pads (higher temp) do even race pads and fluids feel softer as you work them hard?

finally in case anyone is new and wondering, geez do an auto-x or driving school so you can push your car and drive like an idiot and learn it safely! before doing track days where there's a higher chance of danger. plus, there's WAY too much performance in a stock mustang for the street to handle you'd get arrested for sure or worse kill someone.

 

[Dubstep Shep]

As far as stiffness of suspension and how weight transfers, you would need a pretty sophisticated analysis.

The way I always look at these things is to imagine what the two extremes would look like.

If your suspension was really, really, really stiff, and you had really good traction you would transfer ALL of your weight to the front on braking almost instantly. There's no absorption of the weight transfer. Usually a really stuff suspension isn't great for grip though because stiffer springs produce a much higher stress level when subjected to an impact. It's a lot like why drag racers use tires with flexible sidewalls.

A really, really, really soft suspension wouldn't transfer the weight as quickly because it would displace further before reaching the same force as a "stiffer" spring that has a higher spring rate. It's slower to respond to any forces because of the increased travel.

The problem with too soft a suspension is the car will roll from side to side or front to back and move the center of gravity around. Hence sway bars and so forth.

It's all about balance. You want a soft enough suspension with enough travel to absorb the impact from any bumps, but you also want to minimize the time it takes to reach maximum weight transfer by using a stiffer suspension with less travel.

To answer your question simply, off the shelf stiffer springs are almost always an improvement over the factory springs in terms of performance.

I hope that helps some.

 

[Sky Render]

To answer your question simply, off the shelf stiffer springs are almost always an improvement over the factory springs in terms of performance.

I hope that helps some.

Gonna have to slightly disagree there. A lot of lowering springs are "too low and too soft." In other words, they lower the car without being stiff enough to make up for the lost suspension travel, and you end up riding the bump stops. Steeda Sports and Ultralites are good choices for "lowering springs" that don't lower your car too much and are stiff enough to not ride around on the bump stops.

Now, OP, what are your goals with the car? What is it doing or not doing that needs to be "fixed"? And are you sure that its "problems" are not driver-induced?

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[Dubstep Shep]

Gonna have to slightly disagree there. A lot of lowering springs are "too low and too soft." In other words, they lower the car without being stiff enough to make up for the lost suspension travel, and you end up riding the bump stops. Steeda Sports and Ultralites are good choices for "lowering springs" that don't lower your car too much and are stiff enough to not ride around on the bump stops.

Agreed. Too soft and short a spring is bad. You need a higher spring rate with any lowering spring in proportion to how much lower it is

 

[2013kAB]

there are several roads around town that just plain suck to the extreme and if i did not do proper lowering, i'd be on the bump stops several times a day i'm sure.

i may have given a conflicting message above, on the one hand i ask about stiffer suspension and on the other i said i really didn't feel the need to change anything.

i think the bottom line is, the car feels floaty around town, i think on rough roads it feels particularly floaty when turning.

i think i can live with stock suspension. i think realistically, at my low level of experience driving fast and experience with this car, i most likely wouldn't benefit from any suspension changes. and by benefit i mean suddenly shave 5+ seconds off my times. and i'm not even keeping track of my times we'll see in a year or two.


so dubstep, sounds like there is a time factor in transferring weight front/back/side/side and also "keeping the ball" from bouncing around too erratically when talking about smoothness. by "keeping the ball" i mean to think of it in terms of an accelerometer and keeping the dot in the middle or smoothly moving different directions.

so stiffer spring might get the weight transferred to the front under hard braking faster/quicker than a softer spring. is there as much weight transfer with a stiff suspension setup? would a 100lb spring allow more weight up front since it squats more and tilts the cg further forward?

as to my other question about brakes - basically it boiled down to: do even high performance brake systems "mush" a little after everything is heated up compared to when things are cooler or lets say not overheated?

 

[Dubstep Shep]

You hinted on how stiffer springs mean less body roll and less displacement of the CG. To an extent that will cause the weight to transfer differently. The higher your CG, the more weight that will transfer to the front under braking. So stiffer springs will actually lower the overall weight transfer there. They will get to that level of weight transfer much quicker than softer springs. You're limited by the amount of traction on your wheels though. The braking causes the CG to move, causing a weight shift, cause more grip on the front tires and less on the rear. It's all pretty friggin complex.

 

[2013kAB]

yeah it is!

 

[Sky Render]

Get some better dampers.

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[csamsh]

On race pads getting soft: yes they do. I did a track day today on new XP20's (front), new rotors, new XP10's (rear), and a fresh bleed of RBF600. My brakes were mush a lot sooner than they normally are. My guess is my damaged ducting needs to be replaced...it's been on there for a year and has holes and bends all over it!

Moral of the story...the faster you go, the better tires you get, more seat time..etc. etc. etc...you'll push harder, more heat, etc, and even the best pads in the world can be mush.

See: Terry Fair, turn 10A, Road Atlanta