yomomspimp06

I thought the Star was only for series 2. I'll have to look back at the pdf later

kbrewmr2

he may be running a custom base class, which would be especially smart for RX8s as they don't make power without spending alot of points - thus a custom reclass ends up working out in our favor typically.

cwatson

iTrader: (1)

Which is why the target numbers for the new setup came from two years of track testing experience with old setups on the same car with the same tires and a similar alignment. Do you have wheel load data that confirms that 'spreadsheet' LLTDs are rearward of reality? I suspected it went the other way, with real LLTDs nearer 50%.

Arca_ex

iTrader: (10)

Yep that's correct.

I'll be on a dyno reclass. Mandatory due to street porting. Notice how I don't have to take any points for engine mods or weight reduction.

Also another thing to keep in mind is that I'm trying to modify the car so I can grow with it in terms of power. My long term goal for this car is to compete in TT2 at 2800lbs minimum competition weight and 350WHP. My options are naturally aspirated 20b or 13b-REW single turbo. I'm leaning towards the 20b. This is years down the road though.

TeamRX8

iTrader: (25)

you're making some significant changes, such as ride height. How did you account for this in the setup calculation?

maybe you can explain how some people are running 900-1100# front and 350-450# rear rates with a very high rate front bar ....

blu3dragon

iTrader: (1)

That was with a 14 inch ride height, front alignment: -2.2 camber, 4.5 caster (so max possible static camber), 0 toe; rear alignment -2.1 camber, 0.04 toe in. The shocks are also shorter than stock (so bump stops will engage at a lower height), and they are valved to be about equivalent in both compression and rebound to avoid any jacking effect. 425 lbs front springs, 375 lbs rear springs, 28.5/6.35mm front bar with a 15mm longer than stock arm, stock rear bar on/off.

The FRC was calculated using the FCM miata spreadsheet here:

FRC_NC.xls

with the following settings:
https://www.rx8club.com/attachments/...n_calcs-v2-png

I since tried a 13.5 inch ride height and found I needed a higher % of FRC. I ended up with the front bar set to full stiff (15mm shorter arm than medium) and the rx8 rear bar. I did not have the car aligned after adjusting from 14->13.5 inch ride height. At that height, front camber seemed closer to ideal, rear was probably slightly too much per my tire temp measurements taken back in the paddock (so maybe not that accurate).

I must admit, I had to go and look up what LLTD is, and I am still not sure I fully understand its relationship to FRC, but it seems like that should be close to 50% for a neutral balance taking everything affecting tire grip into account, while FRC may be some way off that due to the effect of roll heights and other variables.

I would be surprised if you are not engaging the bump stops in the corners... You can get different bump stops from FCM:Fat Cat Motorsports - Koni products - Miata 06+, RX-8 04+
You can also get spacers to adjust the relative front to rear bump stop engagement points to fine tune things.

Given what you are looking for, I have to say I think you should figure out a way to justify paying the extra for full coilovers & custom valved shocks to match your spring rates. Maybe skip one or two weekends at the track? The FCM coils I have cost ~2300 + 75 shipping + any tax due to your state and IMO are worth the investment. I really could not fault the way the car drove at my last track event. The valving and quality of the FCM shocks is also such that you can go stiffer and still have a decent ride. I am at a ride frequency of ~2.0Hz, daily driving (~20k miles/year) and OK with it. I was at a slightly lower ride frequency on my Civic with koni sport shocks and not OK... I think you should be able to go with ~1.8Hz and still have a good degree of comfort.

Feel free to PM me for more info or impressions on my setup. I enjoy talking about this stuff and would be interested to learn more.

cwatson

iTrader: (1)

I looked at translating the roll centers in the same direction of the ride height change along with lowering the center of gravity. Your point is exactly why I'll be measuring the pickup points. Do you have more complete information on the car? Ride height, bars, springs, sprung mass, unsprung mass, and corner-radii/speed estimates would be a good start. Any information on more setups will help me validate or invalidate the calculations.

I get the following for your setups, not including bump stops:
Sprung mass natural frequency incl tires: 1.74/1.89Hz F/R

Stock roll center height, front bar 15mm soft:
w/ stock rear bar: FRC = 66.9%F, LLTD = 62.6%F
no bar: FRC = 74.2%F, LLTD = 68.6%F

front bar 15mm stiff:
w/ stock rear bar: FRC = 71.7%F, LLTD = 66.7%F
no bar: FRC = 78.3%F, LLTD = 72.1%F

Lower roll centers 1'':
w/ stock rear bar: FRC = 71.7%F, LLTD = 67.8%F
no bar: FRC = 78.3%F, LLTD = 73.6%F

Your experience would suggest my 62.5%F LLTD target will result in minor oversteer (as team suspected) with the higher ride rates, camber, and lowered car. I was planning to target your alignment almost identically. Your experience needing a higher FRC with the lower height may suggest the front roll center is moving further from the sprung roll axis than the rear for a given height change. What apex speeds do you normally see? I'm looking at around 45-70 mid-corner on the local tracks.

The definition for FRC is the same as LLTD in Millikens' RCVD. I'm using FRC as front roll stiffness distribution from the springs and bars. The LLTD calculation includes the unsprung mass and the roll centers. I presume the FCM calculator is using FRC per my definition because it has no inputs for roll centers and because changes in the unsprung masses don't change the FRC value.

Neutral LLTD is forward of cg because the rear tires need grip to generate thrust to overcome the drag from rolling resistance, air drag, and the backward component of the turned wheels' cornering force. I am working to integrate these factors now...the devil is in the differential modeling.

Got a great deal on the Konis so I am moving forward with this route. It's funny - the guy next to me at work almost convinced me to go with the coilovers using the same reasoning. Unfortunately, the track budget is fixed so that $1750 is going to building a new Chump Car this winter. The only non-consumable I've bought for the '8 is the bars, mostly to help tire wear. I have the philosophy that seat time is more valuable than any mod. However, I flat-lined (many laps within 0.5s) on my last couple of track weekends. The TTD record-holder at my local track took the car out for a session and didn't think it had anything left without addressing the damping issues (braking stability and turn-in consistency).

I feel the need to take some measurements before deciding how to handle the bump stops. They'll definitely be an issue for me if you're running stiffer springs, shorter shocks, and a similar ride height. The info and offerings at FCM both look very good. Thanks for the link.

etzilon

I typically overthink everything.. You guys overdid me good.

TeamRX8

iTrader: (25)

try looking beyond the obvious ....






.

blu3dragon

iTrader: (1)

Haha, well understanding how things work is part of the fun for me. I am actually tempted to go buy a copy of Millikens' RCVD now... I am quite happy to accept that I am the guy staring at the cone in front of the car when it comes to vehicle dynamics, but at least I have my eyes open

cwatson

iTrader: (1)

RCVD is a comprehensive reference on most factors that come in to play when designing and setting up performance cars. There are other resources that handle the specifics better, but RCVD will give you a great overview.

I am going through this exercise is to understand how well these methods can predict a setup or change when applied to street cars. Race cars are nicer to deal with when you have all the car parameters, suspension kinematics, dynamics, more complete instrumentation, and testing time to validate.

etzilon

I wanted to thank Zelse for the useful information on his blog.

Chasing a bit more camber with factory control arm bushings, I found his post about "worn out" camber bolts. Got them replaced and, at the same ride height than previously, I can hit -2.6 degrees in the front (much more than that on the right side.. pity I don't run oval tracks). That's a -0.5 degree increase! I mean decrease!

kbrewmr2

I need to start a petition to switch what negative and positive camber is labelled - top of tire in is GOOD, why is it NEGATIVE

*pullshairout*

I'll be chasing you in a street car with a street alignment with street tires and street brakes. Don't blow my doors off too bad, heh!

etzilon

It might rain and I'm a sissy in the rain... Regardless, Texas World Speedway, here we go!!

etzilon

blu3dragon

iTrader: (1)

Good to know, thanks!

Arca_ex

iTrader: (10)

Hmm... I'm really torn between two clutch setups.

5.5" QuarterMaster V-Drive Twin Disk (5.6lbs) with 4.75lbs flywheel.
7.25" QuarterMaster V-Drive Twin Disk (?.?lbs) with 4.40lbs flywheel.

Only $110 bucks more for the 5.5" setup. But I want to be able to drive the car to car shows every once in awhile and local track events. I have no idea what the difference in driveability is between the two, but it just needs to be better than "impossible" for me to be comfortable with it. Obviously the 5.5" will fare better on track.

The hardest part for me has been finding any reviews on these in similar applications, how much the 7.25" unit weighs, what is the difference in service times for the clutches and what their torque ratings are.

Obviously they can hold way more torque than any Renesis can put out but I'm more concerned if I try to use this with a 20b way down the road.

TeamRX8

iTrader: (25)

I saved a bunch ordering my Tilton clutch through Summit Racing. Nobody else was within several hundred dollar$, received it direct drop-shipped within a week. The big difference between 7.5 and 5.5 is the MOI is substantially lower than the total weight. This will vary some by manufacturer though. OE is 225mm, or about 9"

According to the people I spoke to, carbon-carbon has the best driveability, life, and overall value, but at a high initial entry cost. I really wanted to go there, but it was just too tight.

The Renesis can't exceed the TQ rating of a single 5.5" disc. 2-disc is recommended for longer disc life.

.

TeamRX8

iTrader: (25)

It was posted on this forum long before the blog ...

Arca_ex

iTrader: (10)

How much was the Tilton? The Quartermasters I'm looking at are $650 for the 5.5" and $540 for the 7.25". Also did you need to switch to a hydraulic throwout bearing?

TeamRX8

iTrader: (25)

you don't need a hydraulic throwout bearing, but you do need a throwout bearing with a radiused contact face, the one from Mazdatrix is $150, but seems like a very high quality part

Tilton has all their weights, MOI's, & part #s listed, pick the one you want and specify a 1"-23 spline hub

The Mazdatrix flywheel is a step-type, you will need this too.

The one I bought cost a lot more than anything you listed. Not the most expensive one they sell, nor the cheapest.


.

MagnusRacing

iTrader: (2)

I run a 5.5" twin disc tilton. I do drive the car on the street and at rallys. It takes some practice to get used to the quick engagement but it is by no means undrivable. Really not even all that bad once you get used to it.

Three years, many races and about 3000 street/rally miles on the clutch and it's still in great shape. I've just been using the stock throw out bearing.

TeamRX8

iTrader: (25)

The one advantage of a hydraulic throwout is that you can resize the clutch master to slow down the engagement throw distance for more engagement control. You have to make sure not to have too much engagement throw on these small clutches. It may mean adding a pedal stop. Won't know for sure until mine goes in.

the OE bearing gets sloppy fast. You won't feel it in use until it is on the verge of destroying itself. It requires hand/visual inspection before then. That said, 3k miles is not much use on one

Arca_ex

iTrader: (10)

Thank you guys both for your input, going to go with the 5.5". I've heard a lot of good things about both Tilton and Quartermaster, I'm going with the quartermaster. I think this unit will be able to hold a 20b at 350WHP okay, which is what I'm going for to max out in TT2 later. Or I might aim for 400WHP and take out a ton of weight for TT1, then I might need to look at their triple plate but I'll worry about it when I get there. The other thing that I factored in was that I don't see any replacement flywheel inserts for the 7.25" either. I'll probably purchase a rebuild kit for the clutch and a flywheel insert shortly after to keep in the spare parts box for when I need them.

TeamRX8

iTrader: (25)

Missed that its for a 20B. Would recommend 3-disc for 5.5"