Staggered Phone Dials
04-02-2002, 12:53 PM
#1
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Staggered Phone Dials
Has anyone ever run a 23.3mm offset 15" Phone Dial on the front, and a 10.3mm offset 16" early Turbo Phone Dial on the rear? I have an 83, and I've found a set of the rare 23.3mm offset Phone Dials from early 1985 which will fit without spacers, and I'm thinking about picking up two of the 16x8 rear Phone Dials from an 86 Turbo.
Since this is a manual steering car, I can continue to run my 205/55-15 tires in the front, thus preserving steering feel and effort, and could then step up to a much wider (and increase my available tire selection!) rear tire for grip.
Any thoughts to share on this?
Since this is a manual steering car, I can continue to run my 205/55-15 tires in the front, thus preserving steering feel and effort, and could then step up to a much wider (and increase my available tire selection!) rear tire for grip.
Any thoughts to share on this?
04-02-2002, 01:39 PM
#2
Done With Sidepatch
Rennlist Member
Rennlist Member
Why do you want to run 15" in the front and 16" in the rear? Common sense dictates you pick the set of four from the '86 951 which allows you to run 205s on the front...I would avoid mixing 15" and 16" on the same car if for no other reason than it would look real wonky not to mention handling concerns...
04-02-2002, 01:52 PM
#3
Race Director
There is no such thing as a 10.3mm offset Turbo PhoneDial. The 944FAQ is completely incorrect in the wheels table on Chp.14 about the Turbo wheels. I wouldn't use it because it'll end up confusing you more than helping. ALL the '86 951 wheels had 23.3mm offset, including the optional Fuchs.
04-02-2002, 01:54 PM
#4
Nordschleife Master
Well I think you could do it, not to say that you should, but you could.
You have to think about how this would effect the handling on the car. The larger series tires in the front and smaller in back would essentially change the spring rates on the car. Soft in the front and harder in the back. And this could make the back of the car a bit more tail happy, but if you put wider tires back there you could combat that a bit. It could be interesting to try and set the car up that way. But I think your best bet is to find a good set of 15inch or 16inch wheels, not a combo of the two.
Best of luck....
You have to think about how this would effect the handling on the car. The larger series tires in the front and smaller in back would essentially change the spring rates on the car. Soft in the front and harder in the back. And this could make the back of the car a bit more tail happy, but if you put wider tires back there you could combat that a bit. It could be interesting to try and set the car up that way. But I think your best bet is to find a good set of 15inch or 16inch wheels, not a combo of the two.
Best of luck....
04-02-2002, 03:01 PM
#5
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
1. Ok, assuming that wider is better, and running spacers is bad, the 16x8 rear turbo wheel will sit farther out in the wheel arch, thus widening the car's track (stability).
2. A 205/55-15 is a little shorter than the stock 215/60-15, but the Kumho tire is actually 4mm wider than 215. I am putting a larger contact patch (.4" wider than a 215/60) on the road, with a slightly shorter sidewall. My speedo gearing is off by less than 5% this way and I get excellent transient response from the tires.
3. A 225/50-16 in a Kumho is nearly 230mm wide (9.1" wide, 8" on the ground), and is virtually the exact same height as a 215/60-15. There are MANY more tires available (although I'll probably stick with the Kumhos for a better match). The side wall will be almost exactly the same size as the front tire, with the overall height being about 24.9" to the front tire's 24.1. I can go as far as running a 245/45-16, and get a 24.6" tall tire that's 9.6" wide with 9.1" hitting the ground!
I LIKE the look of the deep dish phone dials, but I already have 4 15" tires on my cookies so that's mainly why I want to run them in the front. Plus, I don't think I've ever seen this done before, except on race cars. While I don't have a ton of power from my car, the rear still gets a little squirrely when I leave a corner while hard on the gas.
If I find I don't like the feel of the larger tires later, I can always sell them!
Eric
2. A 205/55-15 is a little shorter than the stock 215/60-15, but the Kumho tire is actually 4mm wider than 215. I am putting a larger contact patch (.4" wider than a 215/60) on the road, with a slightly shorter sidewall. My speedo gearing is off by less than 5% this way and I get excellent transient response from the tires.
3. A 225/50-16 in a Kumho is nearly 230mm wide (9.1" wide, 8" on the ground), and is virtually the exact same height as a 215/60-15. There are MANY more tires available (although I'll probably stick with the Kumhos for a better match). The side wall will be almost exactly the same size as the front tire, with the overall height being about 24.9" to the front tire's 24.1. I can go as far as running a 245/45-16, and get a 24.6" tall tire that's 9.6" wide with 9.1" hitting the ground!
I LIKE the look of the deep dish phone dials, but I already have 4 15" tires on my cookies so that's mainly why I want to run them in the front. Plus, I don't think I've ever seen this done before, except on race cars. While I don't have a ton of power from my car, the rear still gets a little squirrely when I leave a corner while hard on the gas.
If I find I don't like the feel of the larger tires later, I can always sell them!
Eric
04-02-2002, 03:17 PM
#6
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Honda uses this same approach on the Acura NSX. A lighter, narrower tire in the front and a larger rim/wider tire in the rear. Both have virtually the same sidewall height. I know that the NSX has a slightly higher rear-weight bias, so maybe that factors into their thinking...
Eric
Eric
04-02-2002, 03:35 PM
#7
Burning Brakes
Join Date: Feb 2002
Location: Seattle, WA
Posts: 903
Likes: 0
Received 0 Likes
on
0 Posts
Not to come down on you too hard, but I don't think you're going to out-think and re-engineer something that's been around for almost 20 years, and that thousands of people have raced, driven, and tweaked.
Find a set of nice 16" wheels that you like, and go with that. There are lots of cars that mix sizes (NSX, lambo, I think lotus, maybe some other exotics) front to back, but they're designed to be that way, and I'm sure someone had their reasons. Comparing yourt 944 to these cars is just a big mistake. Dragsters use really tiny little front wheels too, doesn't mean it'll do you any good.
[quote] ". Ok, assuming that wider is better, and running spacers is bad, the 16x8 rear turbo wheel will sit farther out in the wheel arch, thus widening the car's track (stability)."
<hr></blockquote>
Bigger/Wider/Longer isn't always better, contrary to popular culture.
Find a set of nice 16" wheels that you like, and go with that. There are lots of cars that mix sizes (NSX, lambo, I think lotus, maybe some other exotics) front to back, but they're designed to be that way, and I'm sure someone had their reasons. Comparing yourt 944 to these cars is just a big mistake. Dragsters use really tiny little front wheels too, doesn't mean it'll do you any good.
[quote] ". Ok, assuming that wider is better, and running spacers is bad, the 16x8 rear turbo wheel will sit farther out in the wheel arch, thus widening the car's track (stability)."
<hr></blockquote>
Bigger/Wider/Longer isn't always better, contrary to popular culture.
Trending Topics
04-02-2002, 03:44 PM
#8
Race Director
1. Wider is better, but you to make significant changes like +1-4" for a noticeable change. Also check your back wheel, Porsche used a rear spacer on your car as stock equipment.
2. Contact patch area is the same regardless of tire size. Wider tires just change the contact patch into a wide rectangular shape instead of a short square one.
3. A 245/45-16 will give you significantly better grip than a 205/55-15. One is because of the width of the contact patch (#2 above) and the other because of diameter; larger-diameter tires stick better because of less deflection in the tread contact area (from circular to flat).
All these changes will exacerbate the stock understeering characteristic of your car. I'd just use those 15" Cookie Cutters until all the tires are worn out. Then upgrade to a full set of 16x7/8" Turbo wheels with one size larger tires 225/50-16 & 245/45-16. This is the usual upgrade for 944NA cars and provides a nice bump in performance.
2. Contact patch area is the same regardless of tire size. Wider tires just change the contact patch into a wide rectangular shape instead of a short square one.
3. A 245/45-16 will give you significantly better grip than a 205/55-15. One is because of the width of the contact patch (#2 above) and the other because of diameter; larger-diameter tires stick better because of less deflection in the tread contact area (from circular to flat).
All these changes will exacerbate the stock understeering characteristic of your car. I'd just use those 15" Cookie Cutters until all the tires are worn out. Then upgrade to a full set of 16x7/8" Turbo wheels with one size larger tires 225/50-16 & 245/45-16. This is the usual upgrade for 944NA cars and provides a nice bump in performance.
04-02-2002, 05:38 PM
#9
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Offset equal, a 15x7 and a 16x8, mounted on each side of the car will equal a 1" wider track (+.5 wider on left and right sides of the car), correct?
If I use a similar DIAMETER tire, then the deflection angle is the same, therefore it is ONLY the wider contact patch of the tire which increases lateral grip, correct? Contact patch cannot remain the same for different width tires.
A Porsche bulletin from 1984 or 85 indicated that an additional 8mm spacer could be used on each side in the rear to widen the track. That would be about 1/2 inch. Alldata has the bulletin available, but I don't remember the number. It does not indicate whether longer studs would be needed, but I think that they would be necessary.
BTW-a 50/50 balanced car will not understeer in a full-throttle exit. I believe that it should "drift"; the "push" of the front tires countered by an equal slip angle of the rear tires (the back sliding slightly, not stepped out in a power slide) as torque is applied, exceeding the available grip of the tires. There's a term for this in one of my "How to drive a sports car" books, but I can't remember it right now. I rarely get to drive this car this way, but it definitely does not "understeer" like my previous VW Sciroccos, GTI and Jetta GLI did.
BTW-my car is equipped w/ front and rear anti-sway bars, the addition of the rear seeming to really help the car "rotate".
Eric
If I use a similar DIAMETER tire, then the deflection angle is the same, therefore it is ONLY the wider contact patch of the tire which increases lateral grip, correct? Contact patch cannot remain the same for different width tires.
A Porsche bulletin from 1984 or 85 indicated that an additional 8mm spacer could be used on each side in the rear to widen the track. That would be about 1/2 inch. Alldata has the bulletin available, but I don't remember the number. It does not indicate whether longer studs would be needed, but I think that they would be necessary.
BTW-a 50/50 balanced car will not understeer in a full-throttle exit. I believe that it should "drift"; the "push" of the front tires countered by an equal slip angle of the rear tires (the back sliding slightly, not stepped out in a power slide) as torque is applied, exceeding the available grip of the tires. There's a term for this in one of my "How to drive a sports car" books, but I can't remember it right now. I rarely get to drive this car this way, but it definitely does not "understeer" like my previous VW Sciroccos, GTI and Jetta GLI did.
BTW-my car is equipped w/ front and rear anti-sway bars, the addition of the rear seeming to really help the car "rotate".
Eric
04-02-2002, 07:07 PM
#10
Burning Brakes
Join Date: Feb 2002
Location: Seattle, WA
Posts: 903
Likes: 0
Received 0 Likes
on
0 Posts
Call it what you want, but it's still understeer. There's more to the equation than just the weight balance.
Most 944 drivers seem to agree that the cars will understeer, and that there are a variety of different ways that you can compensate and adjust so that it doesn't (sway bars, etc.) Danno is correct (IMHO) in saying that what you're planning won't help.
Most 944 drivers seem to agree that the cars will understeer, and that there are a variety of different ways that you can compensate and adjust so that it doesn't (sway bars, etc.) Danno is correct (IMHO) in saying that what you're planning won't help.
04-02-2002, 08:51 PM
#11
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
IMHO-Most 944 drivers are then driving their sports cars like the family saloon, plowing through the corner too fast instead of braking first and hard, getting the car to "take a set" just before the turn, then hard on the gas at or near the apex, allowing the car to drift as it powers out, fighting for grip. Its very easy to get into a turn too fast in one of these cars. I think they're very smooth, BUT this is the only one I've driven and I say MINE doesn't understeer, it drifts beautifully (1st and 2nd gear corners) backend sliding slightly but under perfect throttle control.
For MY car, I need more rear grip when accelerating. If I can get the back to hook up, THEN I might have a problem with understeer.
1983 944, manual steering, front Koni adjustables, rear KYB (because my rear Konis died) Sway-a-just, front and rear factory bars, front and rear factory springs, K&N air filter.
Planned upgrades: New front rotors, Metal Master pads, Earls stainless lines, GT racing front fairing w/ foglight elimination, Momo Rookie or T-2000 seat, bored-out throttle body, Turbo fuel pump, adj fuel pressure regulator. Get more air/fuel in= get more power out!
Eric
For MY car, I need more rear grip when accelerating. If I can get the back to hook up, THEN I might have a problem with understeer.
1983 944, manual steering, front Koni adjustables, rear KYB (because my rear Konis died) Sway-a-just, front and rear factory bars, front and rear factory springs, K&N air filter.
Planned upgrades: New front rotors, Metal Master pads, Earls stainless lines, GT racing front fairing w/ foglight elimination, Momo Rookie or T-2000 seat, bored-out throttle body, Turbo fuel pump, adj fuel pressure regulator. Get more air/fuel in= get more power out!
Eric
04-02-2002, 08:54 PM
#12
Race Director
"If I use a similar DIAMETER tire, then the deflection angle is the same, therefore it is ONLY the wider contact patch of the tire which increases lateral grip, correct?"
Yes... sort of.
"Contact patch cannot remain the same for different width tires."
While the contact patch shape has to change with different width tires, the contact path area remains the same with the same pressure. Check out Bernoulli's equations to determine how many square-inches touches the ground based upon air-pressure. For example, assuming a loaded car at 3200lbs with perfectly even weight distribution, you'll have 800lbs on each wheel. Using hot 40psi (lbs/sq-in) in each tire would give you 800lb/40lb/sq-in = 20 square-inches of contact area.
At the same pressure and contact-patch area, the stock 215mm tire has about a 7-inch wide tread, so the contact patch is 20sq-in/7" = 2.9" long x 7" wide. A 245/45-16 tire with 9-inch wide tread (squarer sidewalls) will have a contact patch of 20sq-in/9" = 2.2" long x 9" wide. The longer contact-patch of the 215mm tire (assuming similar diameter) means that the center of the contact-patch has been deflected upwards more than the 245mm tire for the same flat surface area. That means the 215mm tire will experience more tread deflection & squirm and generate more heat; both not conducive to cornering-grip.
Speaking of cornering-grip, it's not the vertical weight load on the wheels that determine whether a car will understeer or oversteer, it's how the lateral weight transfer is apportioned between the outside front & rear wheels under cornering. Under cornering, you'll have a lateral weight transfer to the outside tires (around 700-1000lbs):
Depending upon how you've set up and tuned your suspension, you can divide this weight evenly between the front & rear wheels, or have more going to the front (understeer) or more going to the rear (oversteer):
There are laws of physics involved in vehicle dynamics that cannot be questioned or changed. All that we can do is understand the interactions and design our cars around these rules to provide the behavior that we desire.
"There's a term for this in one of my "How to drive a sports car" books, but I can't remember it right now."
If you can't remember the name of a book, how can you possibly remember the concepts within? I recommend reading at least the following list to really get a cursory understanding of vehicle dynamics:<ol type="1">[*]"How To Make Your Car Handle" By Fred Phun[*]"Fundamentals of Vehicle Dynamics" By Thomas D. Gillespie[*]"Race Car Vehicle Dynamics" By William F. Milliken, Douglas L. Milliken[*]"Tires, Suspension and Handling" By John C. Dixon[*]"Engineer To Win" by Carroll Smith[*]"Tune to Win" by Carroll Smith[*]"Drive to Win" by Carroll Smith[/list=a]
Only by understanding the "whys" of the mechanics behind the vehicle can one possibly hope to master the "hows" of the driving tactics presented in those "how to drive" books...
Yes... sort of.
"Contact patch cannot remain the same for different width tires."
While the contact patch shape has to change with different width tires, the contact path area remains the same with the same pressure. Check out Bernoulli's equations to determine how many square-inches touches the ground based upon air-pressure. For example, assuming a loaded car at 3200lbs with perfectly even weight distribution, you'll have 800lbs on each wheel. Using hot 40psi (lbs/sq-in) in each tire would give you 800lb/40lb/sq-in = 20 square-inches of contact area.
At the same pressure and contact-patch area, the stock 215mm tire has about a 7-inch wide tread, so the contact patch is 20sq-in/7" = 2.9" long x 7" wide. A 245/45-16 tire with 9-inch wide tread (squarer sidewalls) will have a contact patch of 20sq-in/9" = 2.2" long x 9" wide. The longer contact-patch of the 215mm tire (assuming similar diameter) means that the center of the contact-patch has been deflected upwards more than the 245mm tire for the same flat surface area. That means the 215mm tire will experience more tread deflection & squirm and generate more heat; both not conducive to cornering-grip.
Speaking of cornering-grip, it's not the vertical weight load on the wheels that determine whether a car will understeer or oversteer, it's how the lateral weight transfer is apportioned between the outside front & rear wheels under cornering. Under cornering, you'll have a lateral weight transfer to the outside tires (around 700-1000lbs):
Depending upon how you've set up and tuned your suspension, you can divide this weight evenly between the front & rear wheels, or have more going to the front (understeer) or more going to the rear (oversteer):
There are laws of physics involved in vehicle dynamics that cannot be questioned or changed. All that we can do is understand the interactions and design our cars around these rules to provide the behavior that we desire.
"There's a term for this in one of my "How to drive a sports car" books, but I can't remember it right now."
If you can't remember the name of a book, how can you possibly remember the concepts within? I recommend reading at least the following list to really get a cursory understanding of vehicle dynamics:<ol type="1">[*]"How To Make Your Car Handle" By Fred Phun[*]"Fundamentals of Vehicle Dynamics" By Thomas D. Gillespie[*]"Race Car Vehicle Dynamics" By William F. Milliken, Douglas L. Milliken[*]"Tires, Suspension and Handling" By John C. Dixon[*]"Engineer To Win" by Carroll Smith[*]"Tune to Win" by Carroll Smith[*]"Drive to Win" by Carroll Smith[/list=a]
Only by understanding the "whys" of the mechanics behind the vehicle can one possibly hope to master the "hows" of the driving tactics presented in those "how to drive" books...
04-02-2002, 09:05 PM
#13
Race Director
"For MY car, I need more rear grip when accelerating. If I can get the back to hook up, THEN I might have a problem with understeer."
Uh, you need a limited-slip diff... And get some sticky tires like Yokohama A032Rs, Kumho V700 or Victoracers, Hoosiers, etc.
BTW - Does anyone have a suspicion that 'Porschemunkey' is actually 'Craig944' in yet another alias?
Uh, you need a limited-slip diff... And get some sticky tires like Yokohama A032Rs, Kumho V700 or Victoracers, Hoosiers, etc.
BTW - Does anyone have a suspicion that 'Porschemunkey' is actually 'Craig944' in yet another alias?
04-02-2002, 10:04 PM
#14
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
I'm not Craig, don't know him and don't care, but I am very stubborn...
With your theory, a 2600 lb, evenly-balanced car (like my 83 944) theoretically places 650 lbs per tire STATIC. At 32 psi (daily pressure) I see a contact patch of approximately 20.31 inches STATIC (car at rest, not moving). As I increase tire psi, the contact patch will shrink in size (width). In a corner, weight will transfer to the outside tires and, using your formula, as lbs of vertical pressure increase on each tire, so will the deflection change slightly, causing a wider tire patch. The 245 tire, because it is a LONG stripe, narrow across the tire's tread, will deform less, creating more available grip, thus the car will understeer because of the front/rear imbalance. This would explain a 951 with equal tire psi front/rear, but staggered tire sizes understeering at an auto-x.
This example works great until you combine acceleration into the mix... weight will transfer, upon acceleration, to the outside rear tire, causing increased deformation. Perhaps this is why Porsche specifies two different tire pressure, one for front and one for rear, with rear being less?
Acceleration will change both inertial force on the vehicle, and front/rear, side-to-side lbs per tire, hence changing tire tread deflection and causing the tire patch to "squirm" as it folds upwards in the middle. This would explain 951s still understeering with the rear psi dropped because as cornering forces increase, the narrower front tire will still *always* deform more, for a given diameter.
This explains why, for my balanced tire 205/55-15 tires, the rear, on smooth acceleration, the force transferring to the rear tires causes increased lbs/tire in the outside one, thus deforming the tread more, allowing the car to "slide the back", rather than understeering.
I cannot just bolt on 245/45-16s and ride off into the sunset happy as a clam... I can, however, bolt on a 245/45-16 and be happy that I've got a bad-a$$ looking tire on the rear that fills out the wheel arch more than the spindly little 205/55s do! I will auto-x on the Cookies while searching for used hoosiers and kumho R-compound rubber to buy cheap!
Do I pass the test?
The one and only Porschemunkey!
aka Eric Eikenberry
With your theory, a 2600 lb, evenly-balanced car (like my 83 944) theoretically places 650 lbs per tire STATIC. At 32 psi (daily pressure) I see a contact patch of approximately 20.31 inches STATIC (car at rest, not moving). As I increase tire psi, the contact patch will shrink in size (width). In a corner, weight will transfer to the outside tires and, using your formula, as lbs of vertical pressure increase on each tire, so will the deflection change slightly, causing a wider tire patch. The 245 tire, because it is a LONG stripe, narrow across the tire's tread, will deform less, creating more available grip, thus the car will understeer because of the front/rear imbalance. This would explain a 951 with equal tire psi front/rear, but staggered tire sizes understeering at an auto-x.
This example works great until you combine acceleration into the mix... weight will transfer, upon acceleration, to the outside rear tire, causing increased deformation. Perhaps this is why Porsche specifies two different tire pressure, one for front and one for rear, with rear being less?
Acceleration will change both inertial force on the vehicle, and front/rear, side-to-side lbs per tire, hence changing tire tread deflection and causing the tire patch to "squirm" as it folds upwards in the middle. This would explain 951s still understeering with the rear psi dropped because as cornering forces increase, the narrower front tire will still *always* deform more, for a given diameter.
This explains why, for my balanced tire 205/55-15 tires, the rear, on smooth acceleration, the force transferring to the rear tires causes increased lbs/tire in the outside one, thus deforming the tread more, allowing the car to "slide the back", rather than understeering.
I cannot just bolt on 245/45-16s and ride off into the sunset happy as a clam... I can, however, bolt on a 245/45-16 and be happy that I've got a bad-a$$ looking tire on the rear that fills out the wheel arch more than the spindly little 205/55s do! I will auto-x on the Cookies while searching for used hoosiers and kumho R-compound rubber to buy cheap!
Do I pass the test?
The one and only Porschemunkey!
aka Eric Eikenberry
04-02-2002, 10:08 PM
#15
Track Day
Thread Starter
Join Date: Mar 2002
Location: California
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
BTW-you can search for me on the web if you don't believe my identity. You'll find my website at:
<a href="http://users.i10net.com/eeiken" target="_blank">http://users.i10net.com/eeiken</a>
ALL original lightning photography by me! Some of it might even be good. Haha!
Oh, none of the books you named are the one I have... its something like "Performance and Sports Car Driving" by some former World Champion driver or another. The name excapes me right now but its sold virtually everywhere!
P-munkey
<a href="http://users.i10net.com/eeiken" target="_blank">http://users.i10net.com/eeiken</a>
ALL original lightning photography by me! Some of it might even be good. Haha!
Oh, none of the books you named are the one I have... its something like "Performance and Sports Car Driving" by some former World Champion driver or another. The name excapes me right now but its sold virtually everywhere!
P-munkey