Questions about ride height: wheel gaps and rake angle?
06-02-2009, 11:16 AM
#17
Rennlist Member
Thread Starter
Even if I set my ride heights equal (e.g. 92/92, or 107/107, etc) I'd only have around -0.5 degrees rake. So I don't see how people get -1 degree rake...
I think I'll shoot for RS-5 front / RS+5 rear, for a rake around 0 to -0.2 deg, and call it a day.
06-02-2009, 11:56 AM
#18
Burning Brakes
I'll have my shop take some measurements and report.
My car sits HIGH for a track car. Part of the issue is that I'm using a 245/40/18 tire in the front. (serves several purposes)
However, the car sits too high to use a real/purposeful splitter. I use the diveplanes to help set the front down a bit but I'm more concerned about trying to balance out the rear wing's effect. (trying to counter the wheelie effect)
I totally agree that air getting under the car is not good for aero but I don't think my car is the most aerodynamic in the first place (it's a c2s). I've been told that when I pass people on the straight the air coming off the car feels like a semi passing you.
My car sits HIGH for a track car. Part of the issue is that I'm using a 245/40/18 tire in the front. (serves several purposes)
However, the car sits too high to use a real/purposeful splitter. I use the diveplanes to help set the front down a bit but I'm more concerned about trying to balance out the rear wing's effect. (trying to counter the wheelie effect)
I totally agree that air getting under the car is not good for aero but I don't think my car is the most aerodynamic in the first place (it's a c2s). I've been told that when I pass people on the straight the air coming off the car feels like a semi passing you.
06-02-2009, 03:09 PM
#19
I'll have my shop take some measurements and report.
My car sits HIGH for a track car. Part of the issue is that I'm using a 245/40/18 tire in the front. (serves several purposes)
However, the car sits too high to use a real/purposeful splitter. I use the diveplanes to help set the front down a bit but I'm more concerned about trying to balance out the rear wing's effect. (trying to counter the wheelie effect)
I totally agree that air getting under the car is not good for aero but I don't think my car is the most aerodynamic in the first place (it's a c2s). I've been told that when I pass people on the straight the air coming off the car feels like a semi passing you.
My car sits HIGH for a track car. Part of the issue is that I'm using a 245/40/18 tire in the front. (serves several purposes)
However, the car sits too high to use a real/purposeful splitter. I use the diveplanes to help set the front down a bit but I'm more concerned about trying to balance out the rear wing's effect. (trying to counter the wheelie effect)
I totally agree that air getting under the car is not good for aero but I don't think my car is the most aerodynamic in the first place (it's a c2s). I've been told that when I pass people on the straight the air coming off the car feels like a semi passing you.
BTW keeping the tires inside the fenders is another aero aid.
The aero on a 993 is what it is, but it can be improved to an extent by setup.
06-02-2009, 03:33 PM
#20
RL Technical Advisor
Your car would really benefit from a proper splitter to balance the downforce from your rear wing.
06-02-2009, 04:33 PM
#21
Burning Brakes
Steve - I can and do appreciate your feedback. You were responsible for assisting me in my setup on this car a few years ago, although the communication was handled by a vendor.
I have stuck with the same set up since I purchased NEW several years ago: Moton clubsport, HR springs 450/700, and GT2 sways. I've since upgraded all of the suspension components to monoball/heim and included uprights and tie rods. Next logical step was aero since I had the stock C2S wing. I didn't want to put a wing on the car without having something to balance out the front and *I* was responsible for the logic that the splitter wouldn't help as much since I'm way off the ground.
I would be interested in learning what recommendations you might have for this? I'll try and illustrate where I am right now.
I cannot argue with what *can* fit under the front fender but I can argue that what I have works for me. The car scoots around VIR as any on RL who is familiar with the car can attest. That is not to say that I can't go faster and have a desire to do so.
I have a 245/40/18 tire in the front. My rationale is this: I like a softer front (more tire) for feel, I needed more tire for grip to balance out push in the car, and I found that 235 rubber was getting too hot and greasy. I've had nothing but terrific experiences with the 245/40 tire other than it's tall and can affect aero as it relates to this conversation.
My car does look funny since my front appears higher than the rear. See below:
I get tremendous feel with this setup. I added diveplanes to the car when I bought the wing to attempt to balance out the downforce. I do feel it helps - but the biggest factor this set up has had on my driving is confidence. Really screams at high-speed.
As you can see in the below picture my tires are not nearly as wide as many think. They are tall. you can see here that the tire does not come out past the fender until the car is turned a good ways (this is turn 1 at VIR). You can also notice that the diveplanes do help to push air above the exposed tire.
So I guess my question is what's next? There are a number of front end clips that I could install but not sure about this for a few reasons (#1, I have a front-mount oil cooler that sits behind the front grill, and #2 I'd have to add more body to the car in terms of skirts and what-not in order to maximize the effect??)
Maybe I'm just stuck and need to add power.
I have stuck with the same set up since I purchased NEW several years ago: Moton clubsport, HR springs 450/700, and GT2 sways. I've since upgraded all of the suspension components to monoball/heim and included uprights and tie rods. Next logical step was aero since I had the stock C2S wing. I didn't want to put a wing on the car without having something to balance out the front and *I* was responsible for the logic that the splitter wouldn't help as much since I'm way off the ground.
I would be interested in learning what recommendations you might have for this? I'll try and illustrate where I am right now.
I cannot argue with what *can* fit under the front fender but I can argue that what I have works for me. The car scoots around VIR as any on RL who is familiar with the car can attest. That is not to say that I can't go faster and have a desire to do so.
I have a 245/40/18 tire in the front. My rationale is this: I like a softer front (more tire) for feel, I needed more tire for grip to balance out push in the car, and I found that 235 rubber was getting too hot and greasy. I've had nothing but terrific experiences with the 245/40 tire other than it's tall and can affect aero as it relates to this conversation.
My car does look funny since my front appears higher than the rear. See below:
I get tremendous feel with this setup. I added diveplanes to the car when I bought the wing to attempt to balance out the downforce. I do feel it helps - but the biggest factor this set up has had on my driving is confidence. Really screams at high-speed.
As you can see in the below picture my tires are not nearly as wide as many think. They are tall. you can see here that the tire does not come out past the fender until the car is turned a good ways (this is turn 1 at VIR). You can also notice that the diveplanes do help to push air above the exposed tire.
So I guess my question is what's next? There are a number of front end clips that I could install but not sure about this for a few reasons (#1, I have a front-mount oil cooler that sits behind the front grill, and #2 I'd have to add more body to the car in terms of skirts and what-not in order to maximize the effect??)
Maybe I'm just stuck and need to add power.
06-02-2009, 06:38 PM
#22
Are you running Hoosiers?
If so why not try a 245/35 x18 front, the tire is 1" shorter than 245/40 and will drop the front end ~ .5" all by itself, the additiaonal tire clearance will allow the ssupension to be setup more advantageously too.
If so why not try a 245/35 x18 front, the tire is 1" shorter than 245/40 and will drop the front end ~ .5" all by itself, the additiaonal tire clearance will allow the ssupension to be setup more advantageously too.
06-02-2009, 10:36 PM
#23
RL Technical Advisor
If it were my own car, I'd be building and fitting a splitter to the front valence to balance the car. That does wonders to improve front end grip and balance what your rear wing is currently doing,.....
I usually add a Gurney flap to the rear wing's blade, but that shouldn't happen until the splitter is fitted.
I usually add a Gurney flap to the rear wing's blade, but that shouldn't happen until the splitter is fitted.
06-03-2009, 03:14 PM
#24
Burning Brakes
Bill, I've considered using a 35 A/R tire but I'm already hitting the inside body with this tire at full lock.
BTW, it's interesting to note that the left side will touch the body when turned to full lock right, but the right wheel won't touch the body when turned full lock left. Must have something to do with the body offset (steering wheel is a good example).
Steve, I'll consider fabbing some sort of splitter for the front of the car. I have an extra bumper that I've been toying around with while installing the oil cooler. I should be able to test this a bit more.
Gurney flap is something I did not consider and I am aware they make quite a difference. I appreciate everybody's input.
BTW, it's interesting to note that the left side will touch the body when turned to full lock right, but the right wheel won't touch the body when turned full lock left. Must have something to do with the body offset (steering wheel is a good example).
Steve, I'll consider fabbing some sort of splitter for the front of the car. I have an extra bumper that I've been toying around with while installing the oil cooler. I should be able to test this a bit more.
Gurney flap is something I did not consider and I am aware they make quite a difference. I appreciate everybody's input.
06-03-2009, 03:30 PM
#25
Bill, I've considered using a 35 A/R tire but I'm already hitting the inside body with this tire at full lock.
BTW, it's interesting to note that the left side will touch the body when turned to full lock right, but the right wheel won't touch the body when turned full lock left. Must have something to do with the body offset (steering wheel is a good example).
...
BTW, it's interesting to note that the left side will touch the body when turned to full lock right, but the right wheel won't touch the body when turned full lock left. Must have something to do with the body offset (steering wheel is a good example).
...
there are supposed to be steering stops to limit the range of motion of the steering rack, but hitting the inner wall a tad at full lock is not a big deal
06-03-2009, 06:29 PM
#26
Rennlist Member
Are you saying that people intentionally deviate from the target specs (but within the tolerance range) in order to get 1 degree of downward rake? If so, I have to wonder who started that, since Porsche made no such recommendation AFAIK.
p.s. No, I didn't see that on Pelican, but I did see it in my workshop manuals.
p.s. No, I didn't see that on Pelican, but I did see it in my workshop manuals.
ride height from P car suggested pads =
Front = 123
Rear = 115
I run 235 - 40 X 18 fronts with no issues, but am craving trying 245's.
maybe 245 X 35's?
cheers
06-03-2009, 07:58 PM
#28
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Only trouble is I dont have aeromaps for the 993. Center of pressure location on X axis would be great to know.
06-04-2009, 04:18 PM
#30
Burning Brakes
I've already removed the liner so it's actually touching the body on full lock.
Spacers and a roll would clear it though. Hmm....
