Worth a switch from P to K FRPP springs?

Hi Guys,

I recently ordered some of the Vorshlag caster/camber plates and i'm wondering if it is worth swapping springs while i've got the struts pulled out.

I'm running mostly HPDEs and have done a few time trials now as well - obvious addiction.

Current Suspension Mods: FRPP Adjustable shocks/struts (similar tokico d-specs), Cortex Watts link, Strano adjustable end links, '13 GT500 brembo take offs.

I've got street tires/wheels that are 20" 255F/295R 35R20 that fill up the wheel wells nicely on the FRPP "P" springs but when I put on my race wheels/tires (Apex EC-7 with 295/35R18 all the way around) we are back to 4x4 land with enough room between the fenders and tires to fit another mustang.

Not going to lie, 90% of the motivation for this swap would be cosmetic and i'm not even sure how much difference I will see going from the 1" drop of the P springs to the 1.5" drop on the K springs. I really don't want to add spring swap to my list of HPDE track prep (currently just doing pads and wheels/tires) so any additional lower springs still need to clear my 20" street wheels. I 'think' the 1.5" K springs should still clear from what I've researched.

The question is: if not for the cosmetic benefit, would there be any tangible handling benefit to moving from P springs to K springs with my setup? I know dropping CG is always helpful but this is not a huge drop so it may be immaterial. I don't mind the $180 for the springs but if there is nothing but looks to be gained then i'll keep my money. I also don't want to end up with the scope creep of required bump steer kit, LCA relocation, etc. if I go too low, though i'm not even sure 'how low' is 'too low' that those items become necessary.

Thanks for any advice!

Austin

Nutter281 said:

The question is: if not for the cosmetic benefit, would there be any tangible handling benefit to moving from P springs to K springs with my setup? I know dropping CG is always helpful but this is not a huge drop so it may be immaterial. I don't mind the $180 for the springs but if there is nothing but looks to be gained then i'll keep my money. I also don't want to end up with the scope creep of required bump steer kit, LCA relocation, etc. if I go too low, though i'm not even sure 'how low' is 'too low' that those items become necessary.


Austin

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Just a note on the scope creep...personally I wouldn't worry about the front geometry correction. The rear LCA's provide a nice tangible benefit though.

What are the rates of the P vs. K?

Good question. I am having a hard time tracking down the spring rate on the "P" springs. From Steeda's website they only show 1 rate for the "K" springs but they are still progressive so they should be showing a range...

For the "K" Spring:
Spring Rate
Front: 228 lb/in.
Rear: 199.5 lb/in.

Will keep digging for the p springs. Maybe Steeda just lists the maximum rate?

On that line of thinking - would I be better off, yet, to switch gears to a linear rate instead of the progressives?


Austin

Practically anything linear would be better than a progressive spring for track use.

Spring rates pulled from trackmustangsonline:

Mustang GT (2011+) Stock: Ft 122 lbs./in Rr 154 lbs./in * Source, Maximum Motorsports
Brembo Stock: Ft 131 lbs. /in. Rr 167 lbs./in
Boss Stock: Ft 148 lbs./in. Rr 185 lbs./in
Boss LS Stock: Ft 137 lbs./in. Rr 191 lbs./in
Eibach Pro-Kit: Ft 159 lbs./in Rr 193 lbs./in * Source, Maximum Motorsports
FRPP K Springs: Ft. 188 lbs./in Rr 221 lbs./in *Vorshlag Tested
FRPP P Springs: Ft. 204 lbs./in Rr. 165 lbs./in *Vorshlag Tested
Steeda Competition: Ft 225 lbs./in. Rr 185 lbs./in
Steeda Sports: Ft 200 lbs./in. Rr 175 lbs./in
Steeda Boss Springs: Ft 225 lbs./in. Rr 195 lbs./in
Steeda Ultra-lite: Ft. 195 lbs./in. Rr. 175 lbs./in
Eibach Pro street Coilover: FT. 225 lbs./in Rr. 90-200 lbs./in * Eibach Spec sheet
Eibach Pro R1: Ft 225 lbs./in Rr 250lbs./in * Eibach Spec sheet
H&R RSS Clubsport: Ft 630 lbs./in Rr 515 lbs./in * H&R Spec sheet
302S: Ft 600lbs./in Rr 350lbs./in * Official Ford 302S manual
Suspension Techniques/KW V1/2/3: Ft. 342lbs./in Rr 200lbs./in * KW confirmed. Rates are @ static load/ride height

Awesome data Champale, thank you!

So I'm going to ask the annoying question, anyone know how much spring rate I can run on FRPP adjustable shocks/struts before I've exceeded the damping capabilities with too much spring rate?

Thanks,
Austin

FRPP P Springs: Ft 204 lbs./in Rr 165 lbs./in * Vorshlag Tested

I have ran the MM road and track springs a both Laguna Seca, Button Willow and Sears Point with good results with Koni sports. Might want to look into those as well. I don't have them on the car now. but they worked very well. Better with Billstein's.

Nutter281 said:

I've got street tires/wheels that are 20" 255F/295R 35R20 that fill up the wheel wells nicely on the FRPP "P" springs but when I put on my race wheels/tires (Apex EC-7 with 295/35R18 all the way around) we are back to 4x4 land with enough room between the fenders and tires to fit another mustang.

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No matter what you do with ride height, you're going to have a whole inch more tire to rear fenderwell opening gap with your track tires and about half an inch more up front than you'll have with your street tires.

I'd ignore the appearance consequences at the track because it'll still look different from the way it'll look with your street tires, and the people at the track are going to have a different view than your typical street observers who wouldn't have a clue as to what's going on for a dual-duty street/track car.

Buy springs for an increased rate, and assuming that you're at least generally happy with your car's street appearance, don't crowd that for a mostly irrelevant appearance at the track. If it works and anybody doesn't care for what it looks like, let 'em scratch their head trying to figure it out.


Norm

Hey Nutter281 you are very welcome!

I don't have an answer for you about how much spring rate your Tokicos can handle - I ran P's on my Boss Laguna with the stock dampers and the springs overpowered the rebound damping, even at max stiff. I am pretty sure that Tokico D-specs have a lot more rebound damping, though.

All good feedback - I definitely agree with you Norm that aesthetics are worthless at the track so I really shouldn't chase that too hard.

I am curious how much spring rate I could run though before the FRPP struts lose their damping control.

I'm also curious why, from the data above, the FRPP P springs have higher spring rate in the front and the FRPP K springs have higher spring rate in the back?

Was that possibly mistyped or a deliberate design move by the engineers at FRPP and, if the latter, what would be the conditions that make one or the other ideal? My most recent track outing did land me offroad a couple of times from serious understeer (I'm also fairly novice so driver's mod is obvious must) but I'd love to dial out some of the plow. Would softening the front springs help mitigate some understeer?

Austin

Personally, I would go with new swaybars before going with K's if you are trying to dial out the push.

I believe that I have read the K's are stiffer in back because the suspension travel is shorter so it needs to be stiffer to help prevent bottoming.

If you head over to the website I referenced earlier, you will see that the real fast trackrats used P's for a long time (along with D-specs or Koni Yellows). I can't think of many people using the K's.

Champale said:

I believe that I have read the K's are stiffer in back because the suspension travel is shorter so it needs to be stiffer to help prevent bottoming.

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There is some information over in the flat ride theory thread that states travel is similar front to rear (maybe a little more out back). The stiffer stock rear springs seem to support flat ride calculations. It might be that K springs have a compromise toward maintaining some of the stock flat ride characteristics.

Nutter281 said:

I'm also curious why, from the data above, the FRPP P springs have higher spring rate in the front and the FRPP K springs have higher spring rate in the back?

Was that possibly mistyped or a deliberate design move by the engineers at FRPP and, if the latter, what would be the conditions that make one or the other ideal? My most recent track outing did land me offroad a couple of times from serious understeer (I'm also fairly novice so driver's mod is obvious must) but I'd love to dial out some of the plow. Would softening the front springs help mitigate some understeer?

Austin

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No real idea. Most of the other Ford spring sets have stiffer rates in the back than up front.

Stiffer rear springs would call for less rear sta-bar stiffness and would tend to crutch the fairly low anti-squat % that these cars come with in stock form. This throws the flat ride a little out of whack, which isn't really a problem as long as your shocks & struts are in good shape.


Are you sure that you were completely off the brakes before you got very close to the apex or generating much in the way of cornering g's? Brakes + steering can easily = plow.


Norm

I definitely could have been into the brakes, though, in that particular turn, I typically am already sufficiently slowed from the turn that immediately precedes it. As mentioned, I'm going to take full responsibility for my fair share of ownership on those 3 off track excursions but all 3 of them were plow-induced and I was, at least, 'cognitively aware' that I should not be on the brakes while apexing.

Sounds like I may be better off treating the symptom of plow with sway bar upgrades - which has been on my list. I like the Stranos adjustables for front/rear - anyone have any suggestions?

thanks again!

Austin

I do have Sam's (Hellwig's?) bars in the early combination, which has a lighter rear bar than the later combo offers. I'm at mid-firm front, full firm rear, with a little understeer remaining but not so much that the car can't be steered on the throttle in a long sweeper. NJMP if you care to look at track maps.

Incidentally, my car is still on the OE GT springs, and I've got datalogs showing cornering as high as 1.3x g on MPSS tires.


Norm

Running GT OEM springs?? Seriously impressive dude - i'm over here trying to over-compensate for lack of skill via provision and you're putting down 1.3g with even less to work with.

FWIW, these are the places I went off-roading in my 4x4 with as close to the actual trajectories that MS Paint would allow in the 30 seconds I wanted to spend on the activity:

I'm betting on entry speed being too high, turned in too soon, or too much loud pedal coming off apex. Your understeer is on exit, right? How does entry and mid-corner feel?

Next time you're on track give this a try... Over-slow (slightly) prior to corner entry, start the turn-in at maintenance throttle (not really accelerating, but holding steady speed despite the wheel scrub from the turn), and hold that until the car is absolutely SET at entry. Single (slow, smooth) wheel motion, and feel the car roll. Once it stops rolling (chassis takes a set) start rolling into the gas smoothly and progressively, aiming to feel the outside rear tire really biting, but making sure that the front is still tracking the way you want it to. Your goal with this is to get to WOT at or shortly after apex, after you KNOW that the car is set, and on line. Feed in as much throttle as you can, as early as you can, until the car starts to push wide of apex. As the car starts to push, breathe off the throttle slightly, and watch the car tuck right back onto the line. Welcome to throttle-steering.

It goes without saying that you have got to consistently nail your turn-in point, and consistently hit your apex point. Once you have the "feel" of that move pretty much down, then start to move your braking point back closer to the corner to increase your entry speed until you start to push at turn-in, then back it off a few feet. Again, hit your marks.

Also, try going for a slightly later apex than you think you need, and see how that feels. This approach works well if you tend to have a heavy foot, as I do.

I have comparison data with a buddy (enduro co-driver) in my car, and we turn pretty similar lap times, but it's interesting to see how it gets done. He brakes harder, later than I do, and also carries 1-2mph more speed into the corner, with a slightly earlier apex point, closer to geometric center. I, on the other hand, tend to be on the gas sooner and harder than he is, and I'm normally 2-3mph faster at exit than he is. I give up the time in the braking zone, and make it back up at corner exit. We both destroy tires equally well, but I think I have a slight edge on him with brake pad consumption, while he has slightly better long-stint fuel economy than I do. All this within 500mS of lap time on a 4-mile, 14-turn high-speed track. The moral of the story is that there's more than one way to get it done, and you need to figure out how your driving style works.

One other thing I'm seeing when looking at the track map, is that you're also having problems with transitioning from a right to a left, or vice-versa. Are you letting the chassis neutral-up between direction changes, or are you tossing it side-to-side like a slalom? If you can, pause for a tick when the car gets neutral (after the left, before the right), and then make the second half of the combination. Consciously break the combo into two separate events. Remember that the corner with priority is the one leading to the longest straight, if you have to alter line to make that happen. There's a combination at Mid Ohio that plays hell with you until you get that figured out. Fairly tight mid-speed left hander OVER the crest of a hill, followed by a quick right-hander, that leads to a short straight and a full-throttle left-hand sweeper up another hill. Fun stuff! In this particular case, you sacrifice the exit of the first corner (track out to 2/3 track to allow recovery) to nail the second one, as there is just enough time to let the chassis settle before the final left-hander, which represents a reasonably long straight, even if it is bent and heading up a hill.

We all know that the stock setup pushes fairly badly. That said, it's still a case of "drive what you have," so figure out what you're doing that would cause you to work for Fouroff's Landscaping Service, and fix that first. Your impetus to slap hardware on the car should be driven by lap times or the consistent sense that "X" is forcing you to make adjustments to your driving technique to compensate. Then fix that, and only that.

Darn't Dave and Norm, why do you have to come into this thread and ruin my frivalous ambition to modify my car with your all your sensible wisdom derived from practical application of theory and experience? Do you know how much harder it is to convince my wife to let me buy car parts when 95% of the problem is me??

Nutter281 said:

Darn't Dave and Norm, why do you have to come into this thread and ruin my frivalous ambition to modify my car with your all your sensible wisdom derived from practical application of theory and experience? Do you know how much harder it is to convince my wife to let me buy car parts when 95% of the problem is me??

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Just conveniently omit this discussion when talking with her.


Seriously, though, modifying your car could easily take it further from your preferences (those preferences may well be something you discover later rather than knowing now) unless you discuss your preferences in detail with someone who knows how to set the car up to adhere to your preferences. It's why you are vastly better off gaining experience with the car as it is before you make any changes. You can't know what to change without first knowing why you want to change it, and you can't know why you want to change it until you have experience that tells you how you want the car to behave, and that only comes from experiencing the car as it is and learning what it does that you don't like.

Seeing how the track nuts over on trackmustangsonline really like the P spring setup in general, and seeing how you already have that, I'd stick with that for the time being. You can always change them out later once you've really learned that the car is behaving in a way that demands a change of springs. But you may find, instead, that what you really want is a change of sway bars.


I started off with a bone stock setup (2014 Track Package GT). Found that I hated the harshness of the ride over small sharp bumps, so I changed the dampers to Koni Sports. Then drove on that setup for about a year, and finally learned, firstly, that the car took some time to take a set (this was only noticeable when pitching the car into a corner, though, so I never really saw it until I deliberately did that on the track) and, secondly, that control over the rear was a lot harder to do by removing throttle (you had to come all the way off the throttle to get the tail to come out) than by adding throttle, when I wanted to be able to control it by removing throttle as well. Which is to say, I ended up learning through experience that I wanted a car with a more neutral balance than what the car came with. And since my car is a daily driver and I have to regularly deal with steep driveways and such (a requirement that takes most coilover setups off the table), I chose the most logical combination I could think of: Boss 302 springs (standard 148 lb/in up front, Laguna Seca 191 lb/in in the rear), Laguna Seca rear sway bar, and Laguna Seca panhard bar (I wouldn't have touched the Panhard bar except that the Laguna Seca bushings are stiffer and so should allow for more feel from the rear end, and it was cheap). Of course, it didn't hurt that the springs were about $100 for all four corners.

And now the turn-in responsiveness is much greater than the mild change would suggest, enough so that I don't notice a problem with it anymore even when pitching it into a corner, and the tail is in fact much more lively (enough so that Sam Strano doesn't like it. But I do! ) and controllable.

If I hadn't gained the experience I have, I wouldn't have known to make that change, and more importantly wouldn't be prepared to properly deal with its handling characteristics. It is possible to change these cars in such a way that how they handle will be beyond your initial capabilities to properly control. The best way to learn how to control it is to drive it in an autocross type environment where you can flog the crap out of the car safely. The track environment isn't that kind of environment.

The nice thing about your car the way it is right now is that it is an excellent platform for learning car control. Yours might even be more understeerish than stock. When mine was in stock form, I found that the rear could sometimes threaten to come out when going around a long sweeper and at neutral throttle, which told me that the handling balance was fairly neutral in large-radius corners. If yours never does that, then maybe yours has more understeer than mine did.


There's another way to think about all this, which might simplify things dramatically: you can spend your money on modding the car, or you can spend it on modding the driver. Which is to say, you can either spend the money on changes to the car, or you can spend it on more driving events. Which would you have more fun with? For me, the answer is clear: modding the driver is more fun! Why? Because that is what involves getting out there and driving the car! Put another way, you modify the car to make it more fun to drive, but that is probably a losing proposition if you have to sacrifice driving the car in order to modify it. It's only if you really don't like how the car drives now, or you have enough funds and time that you can modify the car without affecting how often you'll drive it at events, that modifying the car is a winning proposition.


So: unless you have enough experience with the car that you know definitively what behavior you want to change and why, the right answer is to keep driving it, keep learning how to control it at the limit, and ultimately learn what it does that you don't like. Once you know that, you'll be in the right position to change it.

You all make a compelling case - i'm sticking with the P springs for now!

May still do the sway bars though, I think I have already begun to develop some preferences and that is: I'd rather have oversteer than understeer any day of the week.

thanks again guys!

Austin