Spacers and Track width

[DarkSunrise]

Originally Posted by renfield90

You're missing my point, which is that saying extra track width won't help stability contravenes basic physics. It probably won't fix the OP's problem but this is an error of fact.

Yeah it's theoretically correct that increased track width will decrease load transfer (and increase grip). I just thought it was odd seeing SSF there, but I can see why you would bring it up as an example.

[wparsons]

Originally Posted by renfield90

While I agree that the OP should change the fundamentals in his setup first if he has a handling condition he doesn't like, I fundamentally and strongly disagree with this. In fact, the formula for Static Stability Factor uses track width as one of the inputs (the other being CG height).

There's a reason every major racing series has very strict limits on track width with big penalties for going over.

Rollover stability, sure. But making it less twitchy, no chance it's going to do a damn thing. You need to change the grip balance between front and rear to do that, and spacing out the wheels isn't going to accomplish that.

You'll have a bigger change from the change it has to the roll center than actually moving the contact patches out 20mm per side.

[tnle]

Originally Posted by DarkSunrise

OP, if you like the car's balance in low speed corners and only want to increase high speed stability, I would think a rear diffuser (and possibly a wing) would be the way to do it.

Definitely an idea in the books. Will consider it once a proper lightweight front splitter is developed.

Keep the ideas coming guys

[gramicci101]

Originally Posted by tnle

Definitely an idea in the books. Will consider it once a proper lightweight front splitter is developed.

Keep the ideas coming guys

Look into the FT-86 SpeedFactory front splitter and the Driveway Labs rear diffuser.

I do have spacers on my car (20mm front/25mm rear), but I only did that to fill out the wheelwells a little better, because the stock wheels by themselves look really sucked in. An extra 50mm of track width (3% increase) doesn't make a huge difference in stability.

[ddeflyer]

Originally Posted by tnle

Track - Winton Motor Raceway
Turn 5 to 6
130km/h give or take 5km/h (AD08Rs - 32PSI Hot) - high speed sweeper is just the name given to it
Dances - as in tail is in and out and I have to do micro corrections through it

I have 7 clicks down from the front and 5 from the rear because I like the over steer characteristics, I'm well aware this plays a factor in how it "dances" but the current settings suits the track

Experience level of the track - 5 with the 86
**I've driven a 34 GTR (400kg heavier) with less development time going through that same turn more stable and faster (yes I know these are 2 completely different cars)

Car Mods (in short)
UEL Headers (4 to 1) & Overpipe 2.5'
OFT Stage 2 UEL E85
Perrin Oil Cooler

Shockworks Coilovers (6f / 5r) - camber 3.4 front - 2.7 rear
Cusco Front Sway 20mm
Cusco Rear Sway 16mm
Cusco Rear Lateral Link - Lower Control Arms
Cusco Rear Lateral Link - Toe Arms
Cusco 4.556 Final Gears + Solid Pinion Spacer

Volk Racing TE37SL 18 x 9.5 +45
Yokohama Advan Neova AD08R - 255 35 18

Essex AP Racing Endurance Competition Brake Kit
Project Mu RC09 Club Racer (F1102) - Front / Rear

What is the basis for that tire pressure? I've only used AD08Rs on 18 inch rims (225/40R18), but my experience on that size (including through pyrometer readings) was that AD08Rs wanted more pressure than that.

[tnle]

Originally Posted by ddeflyer

What is the basis for that tire pressure? I've only used AD08Rs on 18 inch rims (225/40R18), but my experience on that size (including through pyrometer readings) was that AD08Rs wanted more pressure than that.

Was advised by the Yokohama tire technician to stay between 32-34 hot.
I'll shuffle in between those numbers, based on a number of variables of the day.

And only whip out the pyrometer to record variances in the temperature of my tire... if I honestly thought my camber settings were off and I could tweak out more grip in future adjustments.

[mistressmotorsports]

To answer the original question, adding equal spacers all the way around will not do a ton for high speed balance. There may be some steady state change based on the new motion ratios front to rear, but I don't know what the baseline MRs are, so I can't calculate the new ones immediately (I bet Mike C has them memorized.)

To help in general with high speed stability, therer are may possible answers. Some of them depend on knowing whether the issue is transient, speed dependent, or constant. Some suggestions are:
Stiffer front or softer rear sway bar
Stiffer front of softer rear spring rates
Lower tire pressures in back/higher in front
shock adjustments (for transient response changes only)
Alignment corrections - especially rear toe
more rear aero (affects high speed more than low, obviously)
wider rear track only (softens effective rear spring rate - see spring suggestion)
Bigger tires on rear
etc.

So, depending on the exact issue, there are different possible answers. In general, though, just adding spacers may not get you what you are looking for. Or, it might make a difference if just in ther rear, but you may not be happy with other changes that occur as a result.

Sorry for a very inexact answer, but we would need to know a little more to make further suggestions.

[OkieSnuffBox]

Originally Posted by tnle

I had one of my mates check the endurance kit template behind his rpf1 17 x 9 +35, he said they do not clear the barrels

Are you doing endurance racing or track days?

If you're doing track days, ducting the stock stuff and using proper pads will be fine. Although I do advocate the better pedal feel from fixed calipers and typically increased longevity of pads, due to much less taper wear, and typically increased thermal capacity.

If you track a lot a BKK will save money in the long run.

Sorry for the OT regarding the wheels.

[wparsons]

Originally Posted by tnle

130km/h give or take 5km/h (AD08Rs - 32PSI Hot) - high speed sweeper is just the name given to it
Dances - as in tail is in and out and I have to do micro corrections through it

I have 7 clicks down from the front and 5 from the rear because I like the over steer characteristics, I'm well aware this plays a factor in how it "dances" but the current settings suits the track

Missed this before...

You have it set up loose because it suits the track, but don't like that it behaves like a loose car at high speeds??

IMO, there are 3 solutions

1) Back off slightly at that corner if you aren't comfortable being that close to the limit at those speeds

2) Accept that a loose car is going to be loose and power through it, you haven't stuffed it yet so you're obviously handling it pretty well

3) Add aero to the rear to give more rear grip at high speed without changing how it handles at lower speeds.

Changing anything but aero is going to change how it drives at all speeds, so if you're only concerned at higher speeds then I would start with a good diffuser.

[Racecomp Engineering]

Drive smoother or add some rear toe-in.

A rear wing or diffuser may "help" too but takes a bit more set-up to get things right.

- Andy

[ApexEight]

Originally Posted by Racecomp Engineering

Drive smoother or add some rear toe-in.

A rear wing or diffuser may "help" too but takes a bit more set-up to get things right.

- Andy

Rear toe-in will help rearend stability in a sweeper? I thought that was for straight-line stability.

Sorry for the thread necro. Interesting thread though.