etzilon

In case you guys weren't following the races:
PTC - 1st place - Dennis Holloway
PTD - 4th place - John Magnuson
PTD - 9th place - Lee Papageorge

Great racing on Sunday!

MagnusRacing

iTrader: (2)

Thanks! I think I actually had 3rd place... but who knows... there was some confusion when the class leader broke down the last lap.

Was a really fun race. I was leading for a bit but then had an odd problem that slowed me. Half way through the race I ran over some gators at the exit of a turn and it shook the rear view mirror off. As it was the stock rear view mirror it still had some wiring attached to it and was hanging suspended in the middle of the cabin at about shifter height. No matter what I tried or how I yanked I could not rip it out of the way or secure it. It kept swinging about the cabin and hitting me. On hard rights it would get jammed in front of the shifter and block my shifts to 3rd and I'd have to smack it out of the way and try shifting again. My rearward visibilty was a bit impaired as well as you could imagine. It was almost funny. I kept trying different ways to secure it but there was no real solution. Needless to say this was distracting enough that it killed my pace a bit.

Overall it was a great time. 3rd (or 4th) in PTD and 2nd in TTD. Car ran flawlessly the whole weekend. I was a one man team but literally all I had to do to the car all week was add oil, check air pressure and change tires. Nothing else.

We'll see where it is next year... they have not committed to Miller again at this point. I think they have a better turn out at Mid Ohio since almost nobody from the Midwest or East Coast will travel to Utah.

It seems the hot ticket is PT these days is a light weight highly modified miata that gets back tons of points for running skinny tires. I hope Greg closes this loop hole. There was a miata running like that that was 2-3 seconds a lap faster than anyone else.

TeamRX8

iTrader: (25)

wow

etzilon

Incredible. Talk about unknown unknowns.


It was an exciting race from this side of the camera. Congrats again.

kbrewmr2

hell there were even alot of CA people that didn't go to Miller, and that location was soley to throw SoCal and NorCal a bone after it being at Mid-O for so many years. 2014 and beyond hasn't even been hinted at from mgmt. I haven't been able to dig up any credible rumors either so who knows at this point...

That is certianly some adversity to drive through especially in a big race like Nats. Great work!

etzilon

Link to the PT race: SpeedcastTV

cwatson

iTrader: (1)

What do you guys recommend as the minimum fender lip to wheel center height for acceptable roll center migration? The springs that come in the ride rate I want (~1.5Hz, dual duty car) will drop the car ~1.1'' in the back and ~1.75'' in the front. I'm combining these with Koni Yellows, so that may be up to another 1/2'' drop over the stock Tokicos. It's hard to tell what the final height will be because my current shocks are blown and the front is preloaded up. I assume I can raise the car about 1/2''-1'' via bushing preload if need be, but that obviously has an effect on bushing wear and rates.

Current camber is around ~-1.5 to -2.0 all around and wear/heating is unacceptable. The car does have big bars (est 1.5-2.0 deg/g total including bushings). The LCA adjusters are seized but near maxed out. The UCA is offset all the way in to the chassis (and then some) already, so there's nothing to be had there. I'm hoping to get -2.5 to -3 all around.

Thanks,
Chris

TeamRX8

iTrader: (25)

About 13.5" in the front. You should be able to get about -2.5 deg in the front with the OE adjusters. If you want more then you should consider offset bushings. Maybe another 1/4" lower if you need just another tenth or two.

Arca_ex

iTrader: (10)

Just don't try to raise the ride height via bushing preload, all it will do is fight the shocks and springs constantly.

cwatson

iTrader: (1)

Thanks. The UCA is already offset and the LCA is seized.

Do you have a rough value for the rear as well? The front is currently 15'', so it's going to be tricky to keep 13.5'' with ~2'' expected drop from the springs and shocks. Has anyone heard of a spring spacer for this car? Something between the perch and first coil...

-Chris

yomomspimp06

PTd finish was awesome.

TeamRX8

iTrader: (25)

depending on the spring/bar combination & balance you may want the rear to be anywhere from level to the front up to 1/2" higher. Generally speaking the more rake the chassis has the looser the handling will be

blu3dragon

iTrader: (1)

My s2 sport had a front ride height of 15 inches stock so you are at around stock height right now.

13 inches is going to be very low. I found 13.5 (front and rear) to work well on track, and get the needed camber without any aftermarket bushings, but it is a little low to get over the speed bumps in my work car park, or up my driveway. 14 inches worked well on the street, but not quite enough camber on track. I'm now at 13.75 and it is good enough on the street. Will see how it does on track in a few weeks.

Have you ruled out coilovers? I know it is likely to be significantly more expensive than shocks + springs, but I am really liking my fatcat setup. With that, you can pick your spring rates and ride height front and rear and get shocks specifically valved to match them. I'm pretty sure you could go up to 1.8hz and still be comfortable on the street. I am at around 2Hz and still drive the car every day. I would not want to go any stiffer than my current rates, but at the same time, I am not regretting those spring rates and at lower speeds I think it is actually more comfortable than stock. It is over freeway dips and rises where you feel the higher spring rates.

cwatson

iTrader: (1)

The rear sits at 13.75'' right now, so I presume the stock shocks are blown. 13.5'' sounds pretty reasonable.

I was originally looking for coilovers but decided the $750 koni+spring combo would give me rates, camber, and level of adjustability that I wanted for the time being. The impression I got was that the coilovers would be $2300-$3000 to guarantee the equivalent performance of Konis with well-matched springs. That said, the adjustability may be worth the added cost in the future.

Does anyone know the perch to perch distance at a given ride height? I had the springs tested and am looking at 1.5/1.7Hz F/R (330/320lb/in) at 1g vertical. I know the spring length, but don't have a conversion to ride height.

-Chris

blu3dragon

iTrader: (1)

Yep, stock rear ride height was ~15 to 15.25 inches for me.
I can try to get some perch to perch measurements off my car, but probably not for a few days.
With $2300-$3000 you should get better than koni performance. IMO, the koni's work very well at stock spring rates, but less well the further you get from those.

TeamRX8

iTrader: (25)

The OE ride height info encompasses a range and is listed in the service manual

just changing from the OE high pressure monotube shocks to Koni low pressure shocks (or no pressure for custom valving & other changes) will drop the car quite a bit all else being equal

this may not be what's in the current service manual, the attached are from a very early internet manual that had a lot of errors which were later corrected

cwatson

iTrader: (1)

See attached. Target is with 3300 lbm total, 330/315 springs, 0.7/0.2 damping ratio low/high speed. Rear shocks are biased 2:1 rebound:compression for both high and low speed. Fronts are 1.5:1 LS and 2:1 HS. The increased front biasing under compression should help control pitch acceleration under braking, where longitudinal accelerations are highest. Note the stock front biases even more towards compression than the target design. It looks like the fronts are well matched for trackside tuning and the rears will have to be adjusted to ~75% hard to start. I can add stock rear curves if anyone has dyno data. The other curves are from FCM.

Team, I saw the charts you posted in the alignment thread. Very helpful to judge camber gain from a given ride height change.

Has anyone measured the pickup points? I can do it when installing the shocks if it might help everyone out.

TeamRX8

iTrader: (25)

The amount of camber change isn't linear. It starts increasing more and more as the suspension pivots upward. There isn't just a sweet spot relative to suspension roll centers, but also suspension camber change too.

IMO your proposed setup will have oversteer issues.

cwatson

iTrader: (1)

I am also suspicious it will oversteer based on the spring stiffnesses without a bar adjustment. However, the springs are only responsible for ~20%/~40% F/R of the roll stiffness. This is not considering bushings, which I believe will affect the bar more based on mounting locations and its higher stiffness.

The car currently has slight understeer mid corner and okay on corner exit. The car is very loose on braking and trail braking and pushes at turn in. I suspect this has something to do with blown rear shocks.

These numbers do not take into account bushing or chassis stiffness. Assuming the bushing/chassis stiffness contribution is even front to rear, the FRC and LLTD will tend towards 50% from the values below, tending towards oversteer:

FRC = Front roll couple = roll stiffness distribution of bars/springs %F
LLTD = Lateral load transfer distribution %F

Stock (push, believe from poor camber with too much roll):
FRC = 69.6%F, LLTD = 65.3%F
Stock with drilled rear bar (neutral mid-corner balance)
FRC: 66.5%F, LLTD = 62.7%F

Current setup (progress tech):
FRC = 69.3%F, LLTD = 65.0%F

Proposed springs with stock ride height,roll centers, and same bar settings:
FRC = 65.2%F, LLTD = 61.6%F
Drop height 1.5'':
FRC = 65.2%F, LLTD = 61.2%F
Drop roll centers 0.5'':
FRC = 65.2%F, LLTD = 61.6%F
Adjust bars max understeer:
FRC = 71.0%F, LLTD = 66.5%F
Adjust bars max oversteer:
FRC = 62.6%F, LLTD = 59.4%F

So, assuming the under/oversteer line is somewhere around 62.5%F LLTD with the current alignment for these calculations, I should be okay by adjusting the bars. These numbers are sensitive to roll center heights, so I'll probably take the time to measure pickup points when doing the shock install.

TeamRX8

iTrader: (25)

there are a lot of factors besides number crunching, hope it works out like you expect it to

Arca_ex

iTrader: (10)

Well, just sent in measurements from my car to Brooks Motorsport Composites to start drawing up a wing. Should be ridiculous.

blu3dragon

iTrader: (1)

Looks like you have done some research on this one... I don't think the suspension bushings are going to have a huge effect, but are you accounting for bump stop stiffness and engagement points?

Also, be aware that the koni adjustments are not linear, and may not even respond the same shock to shock. That means lots of playing around on each corner, or setting them on a dyno if you want to hit a pre-calculated value.

I have posted some FRC numbers from my car using the FCM calculator in the sway bar options thread (under s1 susp & brakes). I have found balance to change slightly based on ride height (I suspect due to not having enough front camber at higher ride heights to compensate for the greater roll angles).

Whatever you go with I would expect you can balance it using different sway bars or settings.
^There is quite a range of adjustment available if you are prepared to swap bars.

cwatson

iTrader: (1)

Agreed, but numbers are what we have to work with in the absence of experience or free testing time. I'm mostly looking for A-B comparisons based on the other setups I have tried. The calculations definitely need more detail if I'm getting a front LLTD of 62.5% for neutral handling on a ~50/50 car with the same tires on all four corners!

Camber with the lower height is definitely going to muddy the waters. The tires are currently wearing in a way that calls for a flip at 30-50% of their life.

Shock matching over the adjustment range is a very real concern that I don't have a plan to address. We have a dyno at work but I don't know how to operate it or if we can use it for personal stuff. I believe the konis are dynod for QC before leaving the factory, but it would be nice to see some data on the actual variation. I also understand to stay away from the extreme ends of the adjustment range.

I would like to stay off the bump stops if possible. I imagine they will be hard to avoid with the anticipated ride height and spring stiffness. I'm currently looking at just under 1 deg/g without the bushings. I believe the bushings will bring that number close to 2 deg/g based on the difference between my estimation of the stock setup and the real stock roll gradient (3.4 deg/g) as measured by Car & Driver. Steady state cornering on flat ground should therefore only require about 1'' of travel on either side. I'm working on getting some better information as to the magnitude of bumps/curbs (anyone have some Az data?) on a typical track. If the bump stops look unavoidable, I'll take some quick stiffness measurements using a scale and zip-tie the shafts to check for interference.

I still have the stock sways with drilled adjustment holes, in case this setup goes too far in one direction. The rear can be swapped at lunch or maybe between sessions. The front requires a little more finesse.

Measuring the pickup points will give us some better information about roll center movement under roll/heave/swb.

Do you have the bar/spring/height parameters that correspond to these setups? I'd like to work out the LLTD to see how that compares to my estimates.

TeamRX8

iTrader: (25)

until you actually start testing it's all just going on and on about guesses. Nothing personal mind you, just that once you start testing then you have a feasible reference point from which to start make some meaningful decisions & discussions on where you are vs. where you need to be.

In my experience, based on the calculation system you're using, the LLTD is low in relationship to *reality*, which is what generated my oversteer hunch. But you will only find out what's what once you start actually doing something more than shuffling paper. Without real world data results the preliminary calculated guesses and long ramblings regarding them doesn't serve any useful purpose. The numbers out are only as accurate as the numbers in and how the calculating system is handling them (pun intended).

Arca_ex

iTrader: (10)

Well I think I landed on what configuration I'm going to use for TTC... little less aero, little more tire.

Keep in mind I'm also trying to stay competitive in a Time Attack series that I will have another tune for where the only real rules are DOT tires and 15.0 or above power to weight, so there will be a couple compromises in TT but I think I should still be able to win. I don't ever really plan on going to nationals so if I can win regionally then that's cool.

TT-D* Base Class Aiming for 200-210WHP then I will ask for a weight.

+7 for one * in base class
+10 Tire Compound (Hoosier R6)
+7 Tire Width (275/35R17 on 17x10" RPF1)
+3 Shocks
+2 Springs
+2 Sway Bars
+3 Splitter
+4 Rear Wing

that's 38 out of 39 points. The last one I can use to either cut up the rear bumper or put on vortex generators, either of which will probably yield negligible gains...