Aero Issue?
02-17-2011, 10:45 PM
#1
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Aero Issue?
Turn 2 at Brainerd used to be a 115 mph corner in my '97 M3 (lightly modified). In my RX-8 with KW3s, -2 camber and slight toe-in all the way around and r-comp tires, it feels vaguely unstable at that speed. Everywhere else it corners better than the M3 and tire wear on the track is even front to rear (supporting the balanced idea). Is it technique, suspension or aero?
In the M3, I braked slightly, turned and got on the gas immediatly for the long, late apex sweeper. It took a set and went to the apex and the outside of the track accelerating all the way.
Tried the same technique with the RX-8. It did not feel settled. This is a corner I don't push too hard. If you go sideways off, you will roll. So I spent the day (325 miles on the track) going slower and never figuring it out.
I don't want to add camber to the rear - it will understeer too much on every other corner. (the KW3s already added understeer because the increase in spring rate in front is much greater than the rear. I am running stock sways.
Ideas? Thanks.
In the M3, I braked slightly, turned and got on the gas immediatly for the long, late apex sweeper. It took a set and went to the apex and the outside of the track accelerating all the way.
Tried the same technique with the RX-8. It did not feel settled. This is a corner I don't push too hard. If you go sideways off, you will roll. So I spent the day (325 miles on the track) going slower and never figuring it out.
I don't want to add camber to the rear - it will understeer too much on every other corner. (the KW3s already added understeer because the increase in spring rate in front is much greater than the rear. I am running stock sways.
Ideas? Thanks.
Last edited by ganseg; 02-18-2011 at 11:05 PM.
02-17-2011, 11:38 PM
#2
Is there still a berm on the outside of that corner? I would think you shouldn't have to lift at all. It has the radius as Turn 1, it just doesn't have the banking to help you out.
I suspect your getting air trapped under the car causing the rear end to lift. You need to either get an airdam/spoiler for the front or lower it to get the air up and around the car rather than underneath.
Brainard should still be covered with snow. When is the first track day? 2 months?
I suspect your getting air trapped under the car causing the rear end to lift. You need to either get an airdam/spoiler for the front or lower it to get the air up and around the car rather than underneath.
Brainard should still be covered with snow. When is the first track day? 2 months?
02-17-2011, 11:47 PM
#3
Here some shock tunning info taken from http://www.ozebiz.com.au/racetech/th...hocktune1.html
CORNERING PHASE DEFINITIONS
PHASE 1: Increasing braking + increasing steeringThis phase is the first part of a fast decreasing radius turn. This phase will not occur at all if maximum braking is achieved before turning in. Since weight is being transferred both forward and outboard, the outside front damper moves in the bump direction. Also, the inside rear damper moves in rebound. The other two dampers do not move as much or as rapidly, so their effects are minimal. For our purposes, we will consider the inside front and outside rear dampers to have a fixed position during phase 1.
Oversteering. Increase Outside Front Compression and reduce Outside rear rebound
Understeering: Reduce Outside front Compression and Increase Outside Rear rebound.
PHASE 2: Decreasing braking + increasing steering
This is the turn in phase of a slow corner. This phase may or may not occur depending on the type of turn and driving technique. Weight is being transferred outboard and aft, so the outboard rear damper moves in bump and the inside front damper moves in rebound. The other two
dampers are considered to be stationary.
Oversteering: Increase Inside Front rebound and reduce Outside rear compression.
Understeering: Decrease Inside Front rebound and Increase Outside rear compression.
PHASE 3A: Increasing steering at constant throttle
This phase can be a course correction, a slalom turn in, or a turn entry taken at full throttle. Weight is being transferred outboard, so both outside dampers travel in bump and both inside dampers travel in rebound.
Oversteering: Increase Outside Front Compression and Inside Front Rebound. Decrease Outside rear Compression and Inside Rear Rebound.
Understeering: Decrease Outside Front Compression and Inside Front Rebound. Increase Outside rear Compression and Inside Rear Rebound.
PHASE 3B: Decreasing steering at constant throttle
This is the opposite of phase 3A. During a slalom, this phase occurs while the steering is changing away from the current cornering direction. As soon as the lateral acceleration passes through zero, the car reverts to phase 3A. This is part of why so many spins occur in slaloms.
Oversteering: Decrease Outside Front Compression and Inside Front Rebound. Increase Outside rear Compression and Inside Rear Rebound.
Understeering: Increase Outside Front Compression and Inside Front Rebound. Decrease Outside rear Compression and Inside Rear Rebound.
PHASE 4: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and aft, so the outside front moves in rebound and the inside rear moves in bump. The other two dampers are considered stationary.
Oversteering: Decrease Outside Front Rebound and Increase Inside rear Compression.
Understeering: Increase Outside Front Rebound and Decrease Inside rear Compression.
CORNERING PHASE DEFINITIONS
PHASE 1: Increasing braking + increasing steeringThis phase is the first part of a fast decreasing radius turn. This phase will not occur at all if maximum braking is achieved before turning in. Since weight is being transferred both forward and outboard, the outside front damper moves in the bump direction. Also, the inside rear damper moves in rebound. The other two dampers do not move as much or as rapidly, so their effects are minimal. For our purposes, we will consider the inside front and outside rear dampers to have a fixed position during phase 1.
Oversteering. Increase Outside Front Compression and reduce Outside rear rebound
Understeering: Reduce Outside front Compression and Increase Outside Rear rebound.
PHASE 2: Decreasing braking + increasing steering
This is the turn in phase of a slow corner. This phase may or may not occur depending on the type of turn and driving technique. Weight is being transferred outboard and aft, so the outboard rear damper moves in bump and the inside front damper moves in rebound. The other two
dampers are considered to be stationary.
Oversteering: Increase Inside Front rebound and reduce Outside rear compression.
Understeering: Decrease Inside Front rebound and Increase Outside rear compression.
PHASE 3A: Increasing steering at constant throttle
This phase can be a course correction, a slalom turn in, or a turn entry taken at full throttle. Weight is being transferred outboard, so both outside dampers travel in bump and both inside dampers travel in rebound.
Oversteering: Increase Outside Front Compression and Inside Front Rebound. Decrease Outside rear Compression and Inside Rear Rebound.
Understeering: Decrease Outside Front Compression and Inside Front Rebound. Increase Outside rear Compression and Inside Rear Rebound.
PHASE 3B: Decreasing steering at constant throttle
This is the opposite of phase 3A. During a slalom, this phase occurs while the steering is changing away from the current cornering direction. As soon as the lateral acceleration passes through zero, the car reverts to phase 3A. This is part of why so many spins occur in slaloms.
Oversteering: Decrease Outside Front Compression and Inside Front Rebound. Increase Outside rear Compression and Inside Rear Rebound.
Understeering: Increase Outside Front Compression and Inside Front Rebound. Decrease Outside rear Compression and Inside Rear Rebound.
PHASE 4: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and aft, so the outside front moves in rebound and the inside rear moves in bump. The other two dampers are considered stationary.
Oversteering: Decrease Outside Front Rebound and Increase Inside rear Compression.
Understeering: Increase Outside Front Rebound and Decrease Inside rear Compression.
Last edited by Highway8; 02-18-2011 at 12:07 AM.
02-18-2011, 09:39 AM
#4
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You guys are great!
Al - you been at Brainerd? Then you know exactly what I am talking about! There is no berm along the outside, but you are right, you don't lift except before turn in. I am at 120/125 before turn in and am tentatively looking knock off 5 to 10 mph by turn in. The event I am going to is May 13, 14 and 15. (just found out it will be on the Competition course, but turn 2 is the same either way) I do it every year and never seen snow, but the temps are often in the 30s in the morning.
My big goal is to improve my driving with the improved neutrality of the RX-8 over the M3. But, I won't risk losing it on this corner. Therefore I am interested in a car fix to get rid of the apparent instability. I am not closed minded however to a technique change.
In every other corner I have increased my speed and think I can increase further. Even though this car doesn't pull as hard as the M3, I reduced my lap times on my first day with it - says a lot about the RX-8's cornering!
Regarding the suspension, I can change dampening in both ways. I can also lower it more (I followed the 1" drop guideline). Finally, I am really cheap so I don't want to buy more than I have too.
I haven't seen the ozebiz stuff before so it was good - but "I think" I need to be on the gas way early in this corner. In the M3, the car would take a set right after turn in with the gas and it would be steady state from there to the apex to turn out. I would only do even throttle when I missed my turn in (whether too early or too late I would have to lessen the throttle to be on the track at turn out).
This corner is the most important on the track because you are over 110 mph for a long way. But is also the most dangerous on the track so I hold a little back.
Al - you been at Brainerd? Then you know exactly what I am talking about! There is no berm along the outside, but you are right, you don't lift except before turn in. I am at 120/125 before turn in and am tentatively looking knock off 5 to 10 mph by turn in. The event I am going to is May 13, 14 and 15. (just found out it will be on the Competition course, but turn 2 is the same either way) I do it every year and never seen snow, but the temps are often in the 30s in the morning.
My big goal is to improve my driving with the improved neutrality of the RX-8 over the M3. But, I won't risk losing it on this corner. Therefore I am interested in a car fix to get rid of the apparent instability. I am not closed minded however to a technique change.
In every other corner I have increased my speed and think I can increase further. Even though this car doesn't pull as hard as the M3, I reduced my lap times on my first day with it - says a lot about the RX-8's cornering!
Regarding the suspension, I can change dampening in both ways. I can also lower it more (I followed the 1" drop guideline). Finally, I am really cheap so I don't want to buy more than I have too.
I haven't seen the ozebiz stuff before so it was good - but "I think" I need to be on the gas way early in this corner. In the M3, the car would take a set right after turn in with the gas and it would be steady state from there to the apex to turn out. I would only do even throttle when I missed my turn in (whether too early or too late I would have to lessen the throttle to be on the track at turn out).
This corner is the most important on the track because you are over 110 mph for a long way. But is also the most dangerous on the track so I hold a little back.
02-18-2011, 10:01 AM
#5
I would suggest you corner balance the car. Here is a good article.
http://grassrootsmotorsports.com/art...orner-weights/
Upgrading the sway might help too, I recommend an adj set like the Progress Tech or Agency Power. Both allow you even more fine tunning of the suspension.
Series 2 rx8's improved the cars aero and one of the things they did was to install some underpaneling. The most important piece was the engine under panel. You might consider getting the beat rush aluminum underpanel. It should help reduce front end lift at highspeed.
In order to improve Driver technique you need to properly gather and analyze track data. I use an in car camara and the racechrono touchscreen pro with obd2 logger. http://racechronosystems.com/lap_timers.shtml
and/or hire a pro coach or have a more experianced driver ride along.
http://grassrootsmotorsports.com/art...orner-weights/
Upgrading the sway might help too, I recommend an adj set like the Progress Tech or Agency Power. Both allow you even more fine tunning of the suspension.
Series 2 rx8's improved the cars aero and one of the things they did was to install some underpaneling. The most important piece was the engine under panel. You might consider getting the beat rush aluminum underpanel. It should help reduce front end lift at highspeed.
In order to improve Driver technique you need to properly gather and analyze track data. I use an in car camara and the racechrono touchscreen pro with obd2 logger. http://racechronosystems.com/lap_timers.shtml
and/or hire a pro coach or have a more experianced driver ride along.
02-18-2011, 10:09 AM
#6
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I have been eyeing the Kami group buy - only $112 for the underpanel. Just trying to decide if it would make a material improvement. I haven't seen the S2 underpanel - is the Beatrush similar in how far it goes back? does the S2 try to vent air from the engine compartment?
02-18-2011, 10:14 AM
#7
I have yet to drive Brainard. I have worked corners 2 & 5. I know the track layout. BIR turn 2 is like Road Americas turn 11. It takes ***** to go flat out and I finally worked my way to that point in my RX7. At RA, I would exit turn 10 at 90 mph, grab another gear and go. Turn 11 was over 1/4 mile away and was to hairy to look at the spedo.
Like I said, I think your getting rear end lift at high speeds from air getting under the car. I have experienced this, with the RX8, on the expressway. It was fine at 125, but it was feeling funny at 135 and I backed it down. I have since lowered the car, but have yet to get back to the track.
Like I said, I think your getting rear end lift at high speeds from air getting under the car. I have experienced this, with the RX8, on the expressway. It was fine at 125, but it was feeling funny at 135 and I backed it down. I have since lowered the car, but have yet to get back to the track.
02-18-2011, 10:19 AM
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Did anyone ever lose it in 2? Someone did when I was there two years ago.
Come with me in May! What do you think about a rear defuser? (again being cheap I only want to buy one thing - I don't mind if it looks funny without side skirts - maybe I could take it off for the street.)
Come with me in May! What do you think about a rear defuser? (again being cheap I only want to buy one thing - I don't mind if it looks funny without side skirts - maybe I could take it off for the street.)
02-18-2011, 10:29 AM
#9
The beatrush panel for $112 is a great deal. I think it is a better piece then mazda put on the S2. It goes from the plastic underpanel back to the aluminum cross memeber.
Serieously, first step is to corner balance the car. If you want to add a little rake (rear end higher) that could help reduce rear end lift. Excessivly lowering the car might help with highspeed lift, but it hurts the suspension geometry and overall I think it would hurt your lap times. A .5-1" drop is a good compromise.
A rear diffuser like the mazdapseed piece might help at highspeeds.
Serieously, first step is to corner balance the car. If you want to add a little rake (rear end higher) that could help reduce rear end lift. Excessivly lowering the car might help with highspeed lift, but it hurts the suspension geometry and overall I think it would hurt your lap times. A .5-1" drop is a good compromise.
A rear diffuser like the mazdapseed piece might help at highspeeds.
02-18-2011, 10:31 AM
#10
Did anyone ever lose it in 2? Someone did when I was there two years ago.
Come with me in May! What do you think about a rear defuser? (again being cheap I only want to buy one thing - I don't mind if it looks funny without side skirts - maybe I could take it off for the street.)
Come with me in May! What do you think about a rear defuser? (again being cheap I only want to buy one thing - I don't mind if it looks funny without side skirts - maybe I could take it off for the street.)
BIR is a 10 hr drive for me. My ex's sister lives in Mankato, so one weekend we took them up to the track. Lowering your ride height and/or installing a lip may be the most cost effective way to attempt to solve the problem.
02-18-2011, 12:54 PM
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The GRM article was very good. I was surprised, though, by this: "The only way to change the static weight distribution percentages is to physically move weight around in the car. Jacking weight will not alter the left side or the rear percentages.
I had assumed that lowering the front or rear relative to the other would effect the front to rear weights and how the weight would transition to the front or rear under braking or acelleration.
I had assumed that lowering the front or rear relative to the other would effect the front to rear weights and how the weight would transition to the front or rear under braking or acelleration.
02-18-2011, 01:12 PM
#12
The GRM article was very good. I was surprised, though, by this: "The only way to change the static weight distribution percentages is to physically move weight around in the car. Jacking weight will not alter the left side or the rear percentages.
I had assumed that lowering the front or rear relative to the other would effect the front to rear weights and how the weight would transition to the front or rear under braking or acelleration.
I had assumed that lowering the front or rear relative to the other would effect the front to rear weights and how the weight would transition to the front or rear under braking or acelleration.
Knowing the actual corner weights will allow me to better focus my efforts when it comes to weight reduction.
02-18-2011, 01:16 PM
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What kind of group is going up in May? I was thinking about signing up for another performance school in May. I've been looking for a mazda speed rear diffuser also but can't find any anywhere. I've also looked into this front lip, but I would be very worried about driving it anywhere since it seems like it would hang down quite low in the front. 
02-18-2011, 01:33 PM
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I've also thought about trying to build my own front splitter. I'm just not sure how far the splitter needs to come back beneith the car and if you have to cut any vents in the bottom to allow airflow for the engine bay. Those things go beyond my knowledge.
02-18-2011, 02:23 PM
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That front lip is pretty flimsy, unless your do some custom bracing for it, it will flop up and down just by your hand moving it. I've also broke 2 driving around with it on. I've since switched to a re-amemiya replica thats much more sturdy and i've had good result with it on track, feels much more planted up front but i think you would need something in the back also to balance it out
02-18-2011, 02:26 PM
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Is the mazda speed rear wing worthwhile for actually race track applications? I'm pretty sure that it's adjustable, but I'm not sure if it sits high enough to catch enough air to cause downforce.
The reason I ask about the mazda speed wing is because it's legal for stx in autocross.
The reason I ask about the mazda speed wing is because it's legal for stx in autocross.
Last edited by Pstone; 02-18-2011 at 02:31 PM.
02-18-2011, 03:13 PM
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Is the mazda speed rear wing worthwhile for actually race track applications? I'm pretty sure that it's adjustable, but I'm not sure if it sits high enough to catch enough air to cause downforce.
The reason I ask about the mazda speed wing is because it's legal for stx in autocross.
The reason I ask about the mazda speed wing is because it's legal for stx in autocross.
How much down force is an unknown though...
02-18-2011, 03:33 PM
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02-18-2011, 04:30 PM
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Registration hasn't opened - it should within a week. If you plan to go out of state for an event - check this out: http://dougrippiemotorsportsopenhouse.eventbrite.com/. Last year they had a great deal on Brainerd and Autobahn together
Last edited by ganseg; 02-18-2011 at 04:36 PM.
02-18-2011, 10:19 PM
#22
dont bother with the expense of a mazdaspeed wing. if you go with a wing get a real one.
At those speeds and the standard GT package you have--you are getting over one inch of lift in the front and about the same in the rear.
You do need aero changes. And remember when aero changes are being done--its not one big thing usually--its a bunch of little things.
I would start with a non flex front splitter, removing the rear tire air diffusers/dams, getting the 09 fronts (about 2 inches longer) and the motor guard wouldnt be bad. remove the windshield wiper for track.
If you add downforce, then you are going to increase resistance and your straight a way speeds may go down some.
Once you get over 125mph with the stock S1 body style--your eyes open a little wider.
Wait til you get to 140 :0
At those speeds and the standard GT package you have--you are getting over one inch of lift in the front and about the same in the rear.
You do need aero changes. And remember when aero changes are being done--its not one big thing usually--its a bunch of little things.
I would start with a non flex front splitter, removing the rear tire air diffusers/dams, getting the 09 fronts (about 2 inches longer) and the motor guard wouldnt be bad. remove the windshield wiper for track.
If you add downforce, then you are going to increase resistance and your straight a way speeds may go down some.
Once you get over 125mph with the stock S1 body style--your eyes open a little wider.
Wait til you get to 140 :0
02-18-2011, 10:34 PM
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...You do need aero changes. And remember when aero changes are being done--its not one big thing usually--its a bunch of little things.
I would start with a non flex front splitter, removing the rear tire air diffusers/dams, getting the 09 fronts (about 2 inches longer) and the motor guard wouldnt be bad. remove the windshield wiper for track.
If you add downforce, then you are going to increase resistance and your straight a way speeds may go down some.
Once you get over 125mph with the stock S1 body style--your eyes open a little wider.
Wait til you get to 140 :0
I would start with a non flex front splitter, removing the rear tire air diffusers/dams, getting the 09 fronts (about 2 inches longer) and the motor guard wouldnt be bad. remove the windshield wiper for track.
If you add downforce, then you are going to increase resistance and your straight a way speeds may go down some.
Once you get over 125mph with the stock S1 body style--your eyes open a little wider.
Wait til you get to 140 :0
I still want your car!
Last edited by ganseg; 02-18-2011 at 11:06 PM.
02-19-2011, 01:34 AM
#25
Look at my signature and some of the topics I have talked about in the last 6-9 months and you will see that I am 100% in favor of aero improvements, front splitter/rear wing ect.
However, just because reducing lift and adding DF will help or possible solve the problem doent mean there isn't room to improve simply by making other changes. There is a reason the OP has KW V3 coilovers. Adjusting the corner balance and shocks may help or fix the problem and really is the first place to start. Many time go fast parts will mask the underlining chassis setup or driver issue.
However, just because reducing lift and adding DF will help or possible solve the problem doent mean there isn't room to improve simply by making other changes. There is a reason the OP has KW V3 coilovers. Adjusting the corner balance and shocks may help or fix the problem and really is the first place to start. Many time go fast parts will mask the underlining chassis setup or driver issue.
Last edited by Highway8; 02-19-2011 at 08:15 AM.