how do I tame body roll? (track)
05-01-2014, 12:22 AM
#17
Rennlist Member
What a great question(s)!
We read, "My car now has:
*Bilstein HD lowered to RS+10 (ROW-10)
*M030 springs
*stock M033 sway bars
*R compound tires"
***IMHO, the best value for DOT 100 tires has got to be the Nitto NT-01, not as fast as Hoosiers but last 2X, and you can drive to the track with them, supposedly.
The "Rub" that never goes away. The more you modify the car to optimize track performance, the worse it will be on the street. You must be prepared to make compromises. If you are willing...take advice from Bill V and others. Better yet, find a pal with a track modified 993, drive it a bit, see if you like it.
In the past year I drove a pal's 993, on the track, lowered but not slammed, with Bilstein HD's and perhaps sway bars, not too certain there. It was a dream to drive, very predictable, no snap oversteer, minimal understeer....were I you, I'd live with a little body roll...although "anti-roll" bars will help a bit, don't expect miracles. If the price is right at ?????, just buy them: One of these days they will be unavailable. Note you may need 993 RS drop links...expensive, and sometimes hard to find. I use Tarrett Engineering adjustable drop links, very nicer and 100% reliable.
I have the 993 RS sway bars on my car...love them. I seldom change the rear setting, the front setting stays right in the middle of the 5 settings. I have also "invested" substantial sums in the suspension, the 2 way adjustable Motion Control Suspension (MCS) the H&R front #700 and rear #900 springs/tenders, a package developed for me by Steve Weiner....don't regret it for a minute...at the same rime added 993 RS wheel carriers and GT2 tie rods. The cars is "street legal"....but, the ride in no way approximates my pal's 993 with the Bilstein HDs. Keep in mind that a full on track suspension can get close to $10,000, ouch!
Be careful what you wish for....just call Steve Weiner. He has a consulting service that is worth every penny....and finally, if you have $10,000 in loose change in your pocket, talk to Steve about a set of close ratio gears, 3rd - 6th, transforms the car, like night and day. While driving, street or track, you are never very far from the 993 engine's sweet spot, torque galore is always available.
*Bilstein HD lowered to RS+10 (ROW-10)
*M030 springs
*stock M033 sway bars
*R compound tires"
***IMHO, the best value for DOT 100 tires has got to be the Nitto NT-01, not as fast as Hoosiers but last 2X, and you can drive to the track with them, supposedly.
The "Rub" that never goes away. The more you modify the car to optimize track performance, the worse it will be on the street. You must be prepared to make compromises. If you are willing...take advice from Bill V and others. Better yet, find a pal with a track modified 993, drive it a bit, see if you like it.
In the past year I drove a pal's 993, on the track, lowered but not slammed, with Bilstein HD's and perhaps sway bars, not too certain there. It was a dream to drive, very predictable, no snap oversteer, minimal understeer....were I you, I'd live with a little body roll...although "anti-roll" bars will help a bit, don't expect miracles. If the price is right at ?????, just buy them: One of these days they will be unavailable. Note you may need 993 RS drop links...expensive, and sometimes hard to find. I use Tarrett Engineering adjustable drop links, very nicer and 100% reliable.
I have the 993 RS sway bars on my car...love them. I seldom change the rear setting, the front setting stays right in the middle of the 5 settings. I have also "invested" substantial sums in the suspension, the 2 way adjustable Motion Control Suspension (MCS) the H&R front #700 and rear #900 springs/tenders, a package developed for me by Steve Weiner....don't regret it for a minute...at the same rime added 993 RS wheel carriers and GT2 tie rods. The cars is "street legal"....but, the ride in no way approximates my pal's 993 with the Bilstein HDs. Keep in mind that a full on track suspension can get close to $10,000, ouch!
Be careful what you wish for....just call Steve Weiner. He has a consulting service that is worth every penny....and finally, if you have $10,000 in loose change in your pocket, talk to Steve about a set of close ratio gears, 3rd - 6th, transforms the car, like night and day. While driving, street or track, you are never very far from the 993 engine's sweet spot, torque galore is always available.
05-01-2014, 08:18 AM
#18
Race Car
Thread Starter
Thanks for all the replies. Martin, I agree with you on the nittos. I switched to them from Hoosiers 2 track weekend ago. I'm faster on them according to Harry's Laptimer. I suppose it's because they are so predictable, I have more confidence and can get closer to the limit. They also still have grip when just over the limit. A buddy got video of me doing a Top Gear style drift through turn 1 at Sebring accidentally at 90 MPH a couple weeks ago...
As for the topic at hand. Sebring is my home track. It's rough... This conversation has confirmed that I should just live with it. I need soft suspension for the rough track, and the rough streets I live in. I really couldn't have it any stiffer for daily. The seats I have don't help. They are great for the track, but not so much for street duty.
As for the topic at hand. Sebring is my home track. It's rough... This conversation has confirmed that I should just live with it. I need soft suspension for the rough track, and the rough streets I live in. I really couldn't have it any stiffer for daily. The seats I have don't help. They are great for the track, but not so much for street duty.
05-01-2014, 10:56 AM
#19
Rennlist Member
Look at all the money you have saved....
"This conversation has confirmed that I should just live with it. I need soft suspension for the rough track, and the rough streets I live in. I really couldn't have it any stiffer for daily. The seats I have don't help. They are great for the track, but not so much for street duty."
Let me broach heresy here, 17" VS 18" tires/wheels. In general the 17" tires will have a higher/taller sidewall, making the car a little more accommodating on rough tracks and streets. The only thing you loose is a little width, that is if you go 245 from and 275 rear, 235 front works great on 7" from wheels...the 275 are good on a 9" rear wheel. And the bonus, 17" tires are cheaper. In contrast, on 18" tires, the rear width on 285/30/18 Hoosiers is a mere 10mm wider per side than the 275s (I did this math in my head)
The 275 Nittos will b e a little taller ....but in your case that's a good thing. I have two (2) sets of O-Z Allegritta wheels, in 18"....wish I had 17"....but getting 8" and 10" wide wheels in 17" is very pricy.
Cheap wheels that work: Tire Rack has their Cup IV wheels, 7 1/2 " wide front and 9" wide rear. They are a little heavy....their web site has the weight, but they work. Os your would expect they are made in Chin, but have JIC approval. I have had several sets in the past....got 18" wheel fever and sold them. Also note you can get Hankook Z 214 tires in 17", C50 road racing compound. These tires kick major butt, as quick as Hoosiers, but cheap at about $1,000 a set.
I was being totally serious on the close ratio transmission. What an incredible upgrade, and if you ever sell your car to purchase another 993, you'll get some (maybe all) of your "investment" money back with a close ratio transmission. If you do install a close ratio tranny, driving on the street will be ever so much more fun, and on the track....you are always in the power range, no long tall 3rd gear anymore.
Off to work I go.
Let me broach heresy here, 17" VS 18" tires/wheels. In general the 17" tires will have a higher/taller sidewall, making the car a little more accommodating on rough tracks and streets. The only thing you loose is a little width, that is if you go 245 from and 275 rear, 235 front works great on 7" from wheels...the 275 are good on a 9" rear wheel. And the bonus, 17" tires are cheaper. In contrast, on 18" tires, the rear width on 285/30/18 Hoosiers is a mere 10mm wider per side than the 275s (I did this math in my head)
The 275 Nittos will b e a little taller ....but in your case that's a good thing. I have two (2) sets of O-Z Allegritta wheels, in 18"....wish I had 17"....but getting 8" and 10" wide wheels in 17" is very pricy.Cheap wheels that work: Tire Rack has their Cup IV wheels, 7 1/2 " wide front and 9" wide rear. They are a little heavy....their web site has the weight, but they work. Os your would expect they are made in Chin, but have JIC approval. I have had several sets in the past....got 18" wheel fever and sold them. Also note you can get Hankook Z 214 tires in 17", C50 road racing compound. These tires kick major butt, as quick as Hoosiers, but cheap at about $1,000 a set.
I was being totally serious on the close ratio transmission. What an incredible upgrade, and if you ever sell your car to purchase another 993, you'll get some (maybe all) of your "investment" money back with a close ratio transmission. If you do install a close ratio tranny, driving on the street will be ever so much more fun, and on the track....you are always in the power range, no long tall 3rd gear anymore.
Off to work I go.
05-01-2014, 01:49 PM
#20
Rennlist Member
Actually, the amount lateral weight transfer during chassis corner motion is a function of the ratio of center of gravity (CG) height to track width (distance between wheels viewed from ends of car) and the coefficient of friction (CF) of tires, not the ratio of front to rear roll stiffness.
Thus the higher the CF of tire (stickier) the greater the potential load transfer during cornering and thus more body roll. Multiplying the CF times cars weight = the total potential load transfer. With race tires CF can be as high as 1.5 and with street tires as low as 0.85 or so.
Theoretically if the CG were at ground level there is no weight transfer and no roll and if the Roll center and CG are at the same level there is weight transfer but no roll.
Widening the track width and lowering the CG have the same effect on lateral weight transfer, but due to the track width being wider than the CG is high, it takes a lot more track widening for the same effect.
The axial roll force is a function of the distance the roll center of the suspension (a virtual migrating axis in service) is from the CG and can be positive or negative. This means a set of suspension links could be set up with no roll at all or so the roll of the car's top is inward rather than outward relative to the corner's center (imagine a pendulum swinging on a stick where the pivot point could be moved from the very top tip toward the swinging mass and the motion of the stick)
Spring rates control the amount of suspension deflection for a given amount of weight transfer and the stiffer the spring the less roll, but given linear spring rates, weight transfer is the same at any given rate.
Anti roll bars are torsion bar springs that operate in response to the body roll and are connected to the chassis which is in itself another "torsion bar" which has a spring rate to the anti roll bar at the rear thus, there can be control of front to rear weight transfer ratio in a corner altering the corner weighting and the basic balance of chassis at that weight load transfer. Games can be played here with only one anti-roll bar and spring rates front to rear, etc. but most Porsche have two bars keeping spring rate and roll bar rate less connected. Chassis torsional stiffness (high spring rate) comes into play and the stiffer the better - hence the roll cage is more than a safety device.
So, in my opinion, I think the simplest thing is to buy a set of larger diameter anti-roll bars and install them over an afternoon and go out and have some fun.
Thus the higher the CF of tire (stickier) the greater the potential load transfer during cornering and thus more body roll. Multiplying the CF times cars weight = the total potential load transfer. With race tires CF can be as high as 1.5 and with street tires as low as 0.85 or so.
Theoretically if the CG were at ground level there is no weight transfer and no roll and if the Roll center and CG are at the same level there is weight transfer but no roll.
Widening the track width and lowering the CG have the same effect on lateral weight transfer, but due to the track width being wider than the CG is high, it takes a lot more track widening for the same effect.
The axial roll force is a function of the distance the roll center of the suspension (a virtual migrating axis in service) is from the CG and can be positive or negative. This means a set of suspension links could be set up with no roll at all or so the roll of the car's top is inward rather than outward relative to the corner's center (imagine a pendulum swinging on a stick where the pivot point could be moved from the very top tip toward the swinging mass and the motion of the stick)
Spring rates control the amount of suspension deflection for a given amount of weight transfer and the stiffer the spring the less roll, but given linear spring rates, weight transfer is the same at any given rate.
Anti roll bars are torsion bar springs that operate in response to the body roll and are connected to the chassis which is in itself another "torsion bar" which has a spring rate to the anti roll bar at the rear thus, there can be control of front to rear weight transfer ratio in a corner altering the corner weighting and the basic balance of chassis at that weight load transfer. Games can be played here with only one anti-roll bar and spring rates front to rear, etc. but most Porsche have two bars keeping spring rate and roll bar rate less connected. Chassis torsional stiffness (high spring rate) comes into play and the stiffer the better - hence the roll cage is more than a safety device.
So, in my opinion, I think the simplest thing is to buy a set of larger diameter anti-roll bars and install them over an afternoon and go out and have some fun.
05-01-2014, 02:08 PM
#21
Rennlist Member
If you have read through Cup Car's post, you now know the physics in the most basic terms...God bless Cup Car for his insight.
His closing advice is the "take away": "So, in my opinion, I think the simplest thing is to buy a set of larger diameter anti-roll bars and install them over an afternoon and go out and have some fun."
Note...the non-adjustable M030 RoW 22mm front bars use standard drop links, cheap and available too. The 993 RS bars have their own drop links, and not cheap and may be difficult to source.
For the rear bar you can install RoW 993 Turbo bar at 21mm. It can be drilled for adjustability. Both from and rear RoW bars use standard drop links.
If you can get the 993 RS bars cheap enough, they are adjustable, 5 point front, 3 point rear, and are 23mm in diameter front, 20mm in diameter rear. Price out the 993 RS drop links too...perhaps you can use standard/stock drop links on the 993 RS bar, but sort of doubt it.
And finally, non-Porsche anti-roll bars can be a pain in the ***. Some are difficult to fit, and others are simply too thick...stick with Porsche, you'll be happy you did.
His closing advice is the "take away": "So, in my opinion, I think the simplest thing is to buy a set of larger diameter anti-roll bars and install them over an afternoon and go out and have some fun."
Note...the non-adjustable M030 RoW 22mm front bars use standard drop links, cheap and available too. The 993 RS bars have their own drop links, and not cheap and may be difficult to source.
For the rear bar you can install RoW 993 Turbo bar at 21mm. It can be drilled for adjustability. Both from and rear RoW bars use standard drop links.
If you can get the 993 RS bars cheap enough, they are adjustable, 5 point front, 3 point rear, and are 23mm in diameter front, 20mm in diameter rear. Price out the 993 RS drop links too...perhaps you can use standard/stock drop links on the 993 RS bar, but sort of doubt it.
And finally, non-Porsche anti-roll bars can be a pain in the ***. Some are difficult to fit, and others are simply too thick...stick with Porsche, you'll be happy you did.
05-01-2014, 02:23 PM
#22
Rennlist Member
Join Date: Sep 2008
Location: Flyoverland - Central, Ohio
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Rats, should have gotten you out in my 993 @ Sebring
@FalconDriver, rats, should have gotten you out in my car when @ Sebring so you could feel the 800 lbs and RS bits. For a DD, and some of the roads I trailered over in FL, that would be enough to lose fillings :-) even with shocks on soft max.
Link to RS Tribute DE car details
Thanks again for the hospitality and the hot laps.
Link to RS Tribute DE car details
Thanks again for the hospitality and the hot laps.
05-01-2014, 02:33 PM
#23
Rennlist Member
...Note...the non-adjustable M030 RoW 22mm front bars use standard drop links, cheap and available too. The 993 RS bars have their own drop links, and not cheap and may be difficult to source.
For the rear bar you can install RoW 993 Turbo bar at 21mm. It can be drilled for adjustability. Both from and rear RoW bars use standard drop links.
If you can get the 993 RS bars cheap enough, they are adjustable, 5 point front, 3 point rear, and are 23mm in diameter front, 20mm in diameter rear. Price out the 993 RS drop links too...perhaps you can use standard/stock drop links on the 993 RS bar, but sort of doubt it.
And finally, non-Porsche anti-roll bars can be a pain in the ***. Some are difficult to fit, and others are simply too thick...stick with Porsche, you'll be happy you did.
For the rear bar you can install RoW 993 Turbo bar at 21mm. It can be drilled for adjustability. Both from and rear RoW bars use standard drop links.
If you can get the 993 RS bars cheap enough, they are adjustable, 5 point front, 3 point rear, and are 23mm in diameter front, 20mm in diameter rear. Price out the 993 RS drop links too...perhaps you can use standard/stock drop links on the 993 RS bar, but sort of doubt it.
And finally, non-Porsche anti-roll bars can be a pain in the ***. Some are difficult to fit, and others are simply too thick...stick with Porsche, you'll be happy you did.
05-01-2014, 03:01 PM
#24
Rennlist Member
Cupcar,
I should have explained a bit better, but in my mind vehicle geometry is essentially fixed, how will varying front to rear roll stiffness ratio not alter his weight transfer? When altering the relative stiffness of the wheel pairs, the car has no choice but to move the load to the alternate axle and re-distrute the dynamic weight... Since he's not gonna see any gross changes in his center of gravity, vehicle weight, or his track width, the most effective way to distribute the weight of the car evenly across the front and rear axles would be to stiffen the opposite wheel pairs. Ex, in steady state cornering loads, increasing roll stiffness at the rear wheels will increase weight transfer at the rear wheels, while decreasing it at the front. Net weight transfer from side to side for a given turn and grip levels WILL STILL BE THE SAME (and nearly always is without large changes in vehicle geometry, weight, or cornering force) but by varying your f/r stiffness ratio you can adjust the relative weight transfer between the two axles.
Am I off point on this?
I should have explained a bit better, but in my mind vehicle geometry is essentially fixed, how will varying front to rear roll stiffness ratio not alter his weight transfer? When altering the relative stiffness of the wheel pairs, the car has no choice but to move the load to the alternate axle and re-distrute the dynamic weight... Since he's not gonna see any gross changes in his center of gravity, vehicle weight, or his track width, the most effective way to distribute the weight of the car evenly across the front and rear axles would be to stiffen the opposite wheel pairs. Ex, in steady state cornering loads, increasing roll stiffness at the rear wheels will increase weight transfer at the rear wheels, while decreasing it at the front. Net weight transfer from side to side for a given turn and grip levels WILL STILL BE THE SAME (and nearly always is without large changes in vehicle geometry, weight, or cornering force) but by varying your f/r stiffness ratio you can adjust the relative weight transfer between the two axles.
Am I off point on this?
05-01-2014, 03:11 PM
#25
Rennlist Member
Cupcar,
I should have explained a bit better, but in my mind vehicle geometry is essentially fixed, how will varying front to rear roll stiffness ratio not alter his weight transfer? When altering the relative stiffness of the wheel pairs, the car has no choice but to move the load to the alternate axle and re-distrute the dynamic weight... Since he's not gonna see any gross changes in his center of gravity, vehicle weight, or his track width, the most effective way to distribute the weight of the car evenly across the front and rear axles would be to stiffen the opposite wheel pairs. Ex, in steady state cornering loads, increasing roll stiffness at the rear wheels will increase weight transfer at the rear wheels, while decreasing it at the front. Net weight transfer from side to side for a given turn and grip levels WILL STILL BE THE SAME (and nearly always is without large changes in vehicle geometry, weight, or cornering force) but by varying your f/r stiffness ratio you can adjust the relative weight transfer between the two axles.
Am I off point on this?
I should have explained a bit better, but in my mind vehicle geometry is essentially fixed, how will varying front to rear roll stiffness ratio not alter his weight transfer? When altering the relative stiffness of the wheel pairs, the car has no choice but to move the load to the alternate axle and re-distrute the dynamic weight... Since he's not gonna see any gross changes in his center of gravity, vehicle weight, or his track width, the most effective way to distribute the weight of the car evenly across the front and rear axles would be to stiffen the opposite wheel pairs. Ex, in steady state cornering loads, increasing roll stiffness at the rear wheels will increase weight transfer at the rear wheels, while decreasing it at the front. Net weight transfer from side to side for a given turn and grip levels WILL STILL BE THE SAME (and nearly always is without large changes in vehicle geometry, weight, or cornering force) but by varying your f/r stiffness ratio you can adjust the relative weight transfer between the two axles.
Am I off point on this?
05-01-2014, 03:17 PM
#26
Rennlist Member
One thing here the basic vehicle geometry which controls weight transfer is the CG height relation to track for lateral (cornering) and wheelbase for longitudinal (braking) weight transfer.
If one welded the suspension together and drove the car there would be no pitch in braking and no roll in corners, but the totals of weight transfer would be the same during these maneuvers.
Think "Go-kart"
If one welded the suspension together and drove the car there would be no pitch in braking and no roll in corners, but the totals of weight transfer would be the same during these maneuvers.
Think "Go-kart"
Last edited by Cupcar; 05-01-2014 at 03:48 PM.
