Suspension experts! ANY way to reduce bumpsteer WITHOUT going 993 evo uprights?
02-17-2016, 08:53 PM
#16
Nordschleife Master
If you study the pics in Spyrex's build thread you can see that his shop is running the balljoints top mounted. If you study some of the suspension pics on the Patrick Motorsports site they do it too.
Patrick Motorsports never answered my email messages on the topic. Maybe Spyerx's builder would comment on it? Or maybe 9M or Steve Weiner have some feedback.
It's too bad Geoffrey (consolidated race car thread) isn't active anymore because I remember reading his old threads where he did exactly what nick mentioned. Removed the spring and measured camber and toe curves in order to minimize bump steer using tie-rod mount spacing and by controlling the suspension travel via spring rates.
Patrick Motorsports never answered my email messages on the topic. Maybe Spyerx's builder would comment on it? Or maybe 9M or Steve Weiner have some feedback.
It's too bad Geoffrey (consolidated race car thread) isn't active anymore because I remember reading his old threads where he did exactly what nick mentioned. Removed the spring and measured camber and toe curves in order to minimize bump steer using tie-rod mount spacing and by controlling the suspension travel via spring rates.
02-18-2016, 05:47 AM
#18
I'd be interested to know your chassis set up/alignment if you are willing to share, also what dif are you using? My car is having the uprights fitted now along with linear springs and moton shocks. My previous set up with cup shocks and rs progressive springs was awful regarding bump steer on a bumpy back road but bearable on a track when you can drive committed and the track surface is smoother. Is the bump steer on your car ok on the street or is it stiff enough to not come into effect, if so how does it drive on a rougher country road?
Set up is;
Front:
Ride height RS -25mm
Camber - 2.75 deg
Maximum caster
5 min toe out
RS anti roll bar - 1 off full stiff
Spring rate 340LB
Damper - KW clubsport
Brakes - 993Turbo calipers with 964 Turbo discs Pagid yellow pads
Front Strut brace
Rear:
Ride height RS -20mm
Camber -3.0 deg
10 min toe out
RS anti roll bar - Full stiff
Spring rate 685LB
Brakes - 993C2 with 964RS discs, pagid yellow pads
RS engine mounts
RSR engine support bracket
Tyres: cup 2
The set up guys amongst you will note that the front camber settings compared to the rear will create an imblance. The reasoning is that with the bigger brakes and forward bias will cause the abs to trigger initially under heavy braking due to the reduced contact patch. We had a similar problem when we were setting up the 996 GT3RS. You can modify your braking technique to drive aound it but its not preffereable. I drive the car completely on its nose. Drop it under initial braking and hold it down with a trail all the way into the apex on medium and tight corners. The brake set up make it easy to trim. Holding the nose down also redresses the imbalance between front and rear camber.
On the track,the car is very quick. The set up is quite sharp but very quick on the track. On the road - provining you are not looking to be driving at 9-10/10ths - its absolutely fine but again its sharp.
Diff is currently the standard factory option. This is fine while the tyres are offering full grip but as the performance trails off there is a slight nervousness but the car will always take full throttle on the apex. Ultimately I will replace the diff with a 60:40 guards or GT diff with plenty of pre load.
Thats it. The 911's that ive raced always require a similar driving style to achieve maximum speed (i have no experience with long hood, torsion bar cars so I cannot comment here). This set up is specifically designed to compliment that driving style and it works very well. If you want to work around the inherant bumpsteer in the 964 front geometry, this is a solution BUT it will only work for you if you are happy with the stiffness of the chassis and competent at driving at threashold.
02-18-2016, 07:56 AM
#19
Here is some in car from the first test. Subsiquently added another .5 degree of neg camber front and rear. You can see that im either on the brake (trailing) or the throttle. Full throttle always at apex. It is quite a digital driving style. The rear is nice and stable under braking. No understeer issues.
02-18-2016, 08:58 AM
#20
Oh so that's you then, seen the video on YouTube! The web is a small place. You sure can hustle that 964 along at a good rate. Your car looks really confidence inspiring, or maybe that's just your skill!
Glad to hear you get along with the standard lsd in the car as that's what I've got and everyone says they're sh1te on the track! Thanks for sharing your set up, I'm going to use it as a starting point when my suspension/uprights go on next week. I see your caster is set at max, what top mounts are you using?
Glad to hear you get along with the standard lsd in the car as that's what I've got and everyone says they're sh1te on the track! Thanks for sharing your set up, I'm going to use it as a starting point when my suspension/uprights go on next week. I see your caster is set at max, what top mounts are you using?
02-18-2016, 09:11 AM
#21
The KW Clubsport dampers have a top mount option so I just added those to the order. It a well priced piece of kit as it shares the valving and internals of the race damper so the damping control is actually very good. I've mainly been used to working with teams running high end dampers like JRZ or Moton etc but i have to say I am plesantly surprised at the quality of these dampers.
02-18-2016, 10:39 AM
#22
Both Spyrex and Geoffrey use 993RS wheel carriers w/ o/s tie rods ends.
Spyrex doe have the top mount ball joints(Geoffrey does not), at first glance this would appear to make the arc difference between the suspension and steering deviate more from stock. It has the effect of pushing the A-arm down further, both is absolute terms and relative to the steering arm, for any given ride height.
all 964 have a lot of front bias, the best bias is seen w/ the 2 piston rears, worst is stock 4/4, w/ the RS type BBK only slightly better.
anything that can be done to increase the efficiency of the rear brakes is a +. It's virtually impossible to get too much rear bias on a 911 using oe components.
Spyrex doe have the top mount ball joints(Geoffrey does not), at first glance this would appear to make the arc difference between the suspension and steering deviate more from stock. It has the effect of pushing the A-arm down further, both is absolute terms and relative to the steering arm, for any given ride height.
all 964 have a lot of front bias, the best bias is seen w/ the 2 piston rears, worst is stock 4/4, w/ the RS type BBK only slightly better.
anything that can be done to increase the efficiency of the rear brakes is a +. It's virtually impossible to get too much rear bias on a 911 using oe components.
02-18-2016, 10:55 AM
#23
The bias thing is interesting. Speaking from a racing driver's point of view, if I could adjust the bias of my 964 manully from inside the car, I'd be winding a fair bit more to the front. Obviously in the wet id go rearward but as a guide i'd set my bias forward until the fronts lock then back just a tad and thats my starting point. As the race progressed and tyre wear became a factor, id be ajusting the bias. Also, if there were some big stops and tight hairpins, i may also adjust during the lap on a sprint race. Certainly from my point of view, the bias on my 964 is still too far rearward.
Ive always found brake bias a subjective issue. My experience of racing 911's is mainly Carrera Cup and GT endurance. To be competitive in these series you need to drive a 911 on its nose. Almost all of the time during a lap is found in the braking one to apex since everyone is flat on the apex.
Ive always found brake bias a subjective issue. My experience of racing 911's is mainly Carrera Cup and GT endurance. To be competitive in these series you need to drive a 911 on its nose. Almost all of the time during a lap is found in the braking one to apex since everyone is flat on the apex.
02-18-2016, 06:03 PM
#24
The bias thing is interesting. Speaking from a racing driver's point of view, if I could adjust the bias of my 964 manully from inside the car, I'd be winding a fair bit more to the front. Obviously in the wet id go rearward but as a guide i'd set my bias forward until the fronts lock then back just a tad and thats my starting point. As the race progressed and tyre wear became a factor, id be ajusting the bias. Also, if there were some big stops and tight hairpins, i may also adjust during the lap on a sprint race. Certainly from my point of view, the bias on my 964 is still too far rearward.
Ive always found brake bias a subjective issue. My experience of racing 911's is mainly Carrera Cup and GT endurance. To be competitive in these series you need to drive a 911 on its nose. Almost all of the time during a lap is found in the braking one to apex since everyone is flat on the apex.
Ive always found brake bias a subjective issue. My experience of racing 911's is mainly Carrera Cup and GT endurance. To be competitive in these series you need to drive a 911 on its nose. Almost all of the time during a lap is found in the braking one to apex since everyone is flat on the apex.
The whole point of braking most of the time is to slow as much as possible in as short a time as possible. Yes, there is the trail braking segment at the end but ignoring that for the time being, the main objective is the most Δv in the least Δt while keeping the brake fluid from boiling and the other components from over heating and the tires from sliding too much.
To do that you need to maximize usable brake torque at each wheel.
Generally the front wheels can utilize more brake torque that the rears due to the effect on weight transfer.
Generally you want the fronts to slide just a fraction before the rears.
bias requirements change all the time on the same circuit so w/o adjustable bias you aim for the safest worst case bias
just for example a late RSR based on a 997 will have 4545nm of front brake torque and from 2423 to 3607nm in back at `60# pedal pressure. Bias ratio works out to 1.875 on the high end and 1.260 on the low end and 1.613 in what they call the neutral position.
Getting back to 964 @ 70 bar line pressure
a stock 4/4 964 will have 1974nm/1139nm for a bias of 1.734 w/o any p/v and 3.210 w/ the stock p/v
a 4/2 964 will have 1974nm/1309nm bias of 1.508w/o p/v and 2.793 w/ p/v
a 964RS/Cup will have 2381nm/1390nm bias 1.713 w/o/pv and 3.072 w/ Note that for racing the Cups removed the p/v
a 964 w/ 993RS/tt front and 993 rear will have 2306nm/1391nm for a bias of 1.659w/ p/v and 3.072 w/o
early 911 say 2.7RS has 1444nm/969nm for 1.491 bias never had a p/v
993RS/Cup 2306nm/1618nm 1.426 bias w/o p/v and 2.64 w/ p/v, I have both of my cars set up w/ these brakes w/o p/v
Why use lower more rear bias
1) to get each end working as much as possible, safely
2) to distribute thermal and mechanical loads more broadly
3) for the greatest Δv in the least Δt
Things that help a car to utilize more rear bias
1) lower
2) stiffer
3) more effective lsd
Things that reduce the amount of brake torque that a tire can use
1) more camber
2) more toe
3) narrower tire
4) narrower wheel
5) taller side wall
6) more rotating mass
7) poor corner balance
8) open diff
02-18-2016, 06:44 PM
#25
Rennlist Member
Personally I like the science behind this stuff but I'm not an expert. Being a firm believer in "do it once and do it right" i go with what is recommended by those i trust. I'm very happy with how the chassis has been setup and the car behaves. Can it work w/o the Evo uprights? Sure. Optimal? Maybe not... but when you're going all in... might as well finish the job.
Rancie you are hustling that car for sure! Looks like a fun track.
Rancie you are hustling that car for sure! Looks like a fun track.
02-19-2016, 09:57 PM
#26
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Rancie - if your at (ride height) frt RS -25mm and rear RS - 20mm. How much upward suspension travel do you have front and rear. Do you have tire scrub on the upper interior / exterior fenders??
02-20-2016, 03:50 AM
#27
You'd be giving up a lot of performance.
The whole point of braking most of the time is to slow as much as possible in as short a time as possible. Yes, there is the trail braking segment at the end but ignoring that for the time being, the main objective is the most Δv in the least Δt while keeping the brake fluid from boiling and the other components from over heating and the tires from sliding too much.
To do that you need to maximize usable brake torque at each wheel.
Generally the front wheels can utilize more brake torque that the rears due to the effect on weight transfer.
Generally you want the fronts to slide just a fraction before the rears.
bias requirements change all the time on the same circuit so w/o adjustable bias you aim for the safest worst case bias
just for example a late RSR based on a 997 will have 4545nm of front brake torque and from 2423 to 3607nm in back at `60# pedal pressure. Bias ratio works out to 1.875 on the high end and 1.260 on the low end and 1.613 in what they call the neutral position.
Getting back to 964 @ 70 bar line pressure
a stock 4/4 964 will have 1974nm/1139nm for a bias of 1.734 w/o any p/v and 3.210 w/ the stock p/v
a 4/2 964 will have 1974nm/1309nm bias of 1.508w/o p/v and 2.793 w/ p/v
a 964RS/Cup will have 2381nm/1390nm bias 1.713 w/o/pv and 3.072 w/ Note that for racing the Cups removed the p/v
a 964 w/ 993RS/tt front and 993 rear will have 2306nm/1391nm for a bias of 1.659w/ p/v and 3.072 w/o
early 911 say 2.7RS has 1444nm/969nm for 1.491 bias never had a p/v
993RS/Cup 2306nm/1618nm 1.426 bias w/o p/v and 2.64 w/ p/v, I have both of my cars set up w/ these brakes w/o p/v
Why use lower more rear bias
1) to get each end working as much as possible, safely
2) to distribute thermal and mechanical loads more broadly
3) for the greatest Δv in the least Δt
Things that help a car to utilize more rear bias
1) lower
2) stiffer
3) more effective lsd
Things that reduce the amount of brake torque that a tire can use
1) more camber
2) more toe
3) narrower tire
4) narrower wheel
5) taller side wall
6) more rotating mass
7) poor corner balance
8) open diff
The whole point of braking most of the time is to slow as much as possible in as short a time as possible. Yes, there is the trail braking segment at the end but ignoring that for the time being, the main objective is the most Δv in the least Δt while keeping the brake fluid from boiling and the other components from over heating and the tires from sliding too much.
To do that you need to maximize usable brake torque at each wheel.
Generally the front wheels can utilize more brake torque that the rears due to the effect on weight transfer.
Generally you want the fronts to slide just a fraction before the rears.
bias requirements change all the time on the same circuit so w/o adjustable bias you aim for the safest worst case bias
just for example a late RSR based on a 997 will have 4545nm of front brake torque and from 2423 to 3607nm in back at `60# pedal pressure. Bias ratio works out to 1.875 on the high end and 1.260 on the low end and 1.613 in what they call the neutral position.
Getting back to 964 @ 70 bar line pressure
a stock 4/4 964 will have 1974nm/1139nm for a bias of 1.734 w/o any p/v and 3.210 w/ the stock p/v
a 4/2 964 will have 1974nm/1309nm bias of 1.508w/o p/v and 2.793 w/ p/v
a 964RS/Cup will have 2381nm/1390nm bias 1.713 w/o/pv and 3.072 w/ Note that for racing the Cups removed the p/v
a 964 w/ 993RS/tt front and 993 rear will have 2306nm/1391nm for a bias of 1.659w/ p/v and 3.072 w/o
early 911 say 2.7RS has 1444nm/969nm for 1.491 bias never had a p/v
993RS/Cup 2306nm/1618nm 1.426 bias w/o p/v and 2.64 w/ p/v, I have both of my cars set up w/ these brakes w/o p/v
Why use lower more rear bias
1) to get each end working as much as possible, safely
2) to distribute thermal and mechanical loads more broadly
3) for the greatest Δv in the least Δt
Things that help a car to utilize more rear bias
1) lower
2) stiffer
3) more effective lsd
Things that reduce the amount of brake torque that a tire can use
1) more camber
2) more toe
3) narrower tire
4) narrower wheel
5) taller side wall
6) more rotating mass
7) poor corner balance
8) open diff
I have not measured the suspension travel but have never experienced 'bottoming' on poor road surfaces. No tyre scrub anywhere except a slight amount on the front inner arches under full lock.
02-20-2016, 04:35 AM
#28
You'd be giving up a lot of performance.
The whole point of braking most of the time is to slow as much as possible in as short a time as possible. Yes, there is the trail braking segment at the end but ignoring that for the time being, the main objective is the most Δv in the least Δt while keeping the brake fluid from boiling and the other components from over heating and the tires from sliding too much.
To do that you need to maximize usable brake torque at each wheel.
Generally the front wheels can utilize more brake torque that the rears due to the effect on weight transfer.
Generally you want the fronts to slide just a fraction before the rears.
bias requirements change all the time on the same circuit so w/o adjustable bias you aim for the safest worst case bias
just for example a late RSR based on a 997 will have 4545nm of front brake torque and from 2423 to 3607nm in back at `60# pedal pressure. Bias ratio works out to 1.875 on the high end and 1.260 on the low end and 1.613 in what they call the neutral position.
Getting back to 964 @ 70 bar line pressure
a stock 4/4 964 will have 1974nm/1139nm for a bias of 1.734 w/o any p/v and 3.210 w/ the stock p/v
a 4/2 964 will have 1974nm/1309nm bias of 1.508w/o p/v and 2.793 w/ p/v
a 964RS/Cup will have 2381nm/1390nm bias 1.713 w/o/pv and 3.072 w/ Note that for racing the Cups removed the p/v
a 964 w/ 993RS/tt front and 993 rear will have 2306nm/1391nm for a bias of 1.659w/ p/v and 3.072 w/o
early 911 say 2.7RS has 1444nm/969nm for 1.491 bias never had a p/v
993RS/Cup 2306nm/1618nm 1.426 bias w/o p/v and 2.64 w/ p/v, I have both of my cars set up w/ these brakes w/o p/v
Why use lower more rear bias
1) to get each end working as much as possible, safely
2) to distribute thermal and mechanical loads more broadly
3) for the greatest Δv in the least Δt
Things that help a car to utilize more rear bias
1) lower
2) stiffer
3) more effective lsd
Things that reduce the amount of brake torque that a tire can use
1) more camber
2) more toe
3) narrower tire
4) narrower wheel
5) taller side wall
6) more rotating mass
7) poor corner balance
8) open diff
The whole point of braking most of the time is to slow as much as possible in as short a time as possible. Yes, there is the trail braking segment at the end but ignoring that for the time being, the main objective is the most Δv in the least Δt while keeping the brake fluid from boiling and the other components from over heating and the tires from sliding too much.
To do that you need to maximize usable brake torque at each wheel.
Generally the front wheels can utilize more brake torque that the rears due to the effect on weight transfer.
Generally you want the fronts to slide just a fraction before the rears.
bias requirements change all the time on the same circuit so w/o adjustable bias you aim for the safest worst case bias
just for example a late RSR based on a 997 will have 4545nm of front brake torque and from 2423 to 3607nm in back at `60# pedal pressure. Bias ratio works out to 1.875 on the high end and 1.260 on the low end and 1.613 in what they call the neutral position.
Getting back to 964 @ 70 bar line pressure
a stock 4/4 964 will have 1974nm/1139nm for a bias of 1.734 w/o any p/v and 3.210 w/ the stock p/v
a 4/2 964 will have 1974nm/1309nm bias of 1.508w/o p/v and 2.793 w/ p/v
a 964RS/Cup will have 2381nm/1390nm bias 1.713 w/o/pv and 3.072 w/ Note that for racing the Cups removed the p/v
a 964 w/ 993RS/tt front and 993 rear will have 2306nm/1391nm for a bias of 1.659w/ p/v and 3.072 w/o
early 911 say 2.7RS has 1444nm/969nm for 1.491 bias never had a p/v
993RS/Cup 2306nm/1618nm 1.426 bias w/o p/v and 2.64 w/ p/v, I have both of my cars set up w/ these brakes w/o p/v
Why use lower more rear bias
1) to get each end working as much as possible, safely
2) to distribute thermal and mechanical loads more broadly
3) for the greatest Δv in the least Δt
Things that help a car to utilize more rear bias
1) lower
2) stiffer
3) more effective lsd
Things that reduce the amount of brake torque that a tire can use
1) more camber
2) more toe
3) narrower tire
4) narrower wheel
5) taller side wall
6) more rotating mass
7) poor corner balance
8) open diff
What a great and interesting post. I agree, there is a trade off in ultimate braking performance by pushing the bias forward. The upside is the ability to carry a much harder trail into apex after turn in. Using the above video as an example. At 35 seconds and 3.03 is the braking zone at the end of the back straight at Snetterton. With my set up, I can brake very late here and carry a heavy trail all the way to the final apex of the complex holding the nose down and settling the car nicely for full throttle at apex. If I had more rear bias, I could stop quicker in a straight line but I would need to brake earlier as the rearward bias would not allow me to carry such a heavy trail after turn in. I would therefore be settling the car to apex on a trail throttle which would lose me time. Also the diff would be open so the car would not be as nicely settled by apex and therefore full throttle would come a little later. Effectively I visualise a braking zone which always extends all the way to apex. Effectively curved. It requires the ability to be able to competently drive to threshold with spare capacity as you are constantly balancing the car against rotational and lateral threshold. The rear of the car always the end that needs managing as there is no understeer because the nose is always held down. A decent diff is essential as is a forward brake bias to prevent the rears from locking throwing the car into terminal oversteer.
That's how the boys at the sharp end of the grid in Carrera Cup would drive a 911. It's not an easy technique to master but it's very quick. It's helped me to to championship wins and several lap records in contemporary 911's. To give perspective, in a 997 cup you would approach the above corner in 6th gear at about 160mph. Employing a normal mid/front engined technique required braking at 120 meters. Employing the technique described above, it is possible to begin braking at 75meters. Our motec data showed a gain of 4/10's on the complex with approx 70% braking pressure applied at turn in, 20% immediately prior to apex And 90% throttle at apex. Initially, the brain does not accept that it is possible which leads to a frightening few seconds but it is and once you dial yourself into the concept it's fine. I have 2 lap records at Snetterton applying this technique.
Anyway, I hope that I haven't bored you all too much with this protracted post and that it may have shed a little light on why my set up allows me to run my little 964 on stock uprights.
I will say that in an ideal world I would fit 993 evo uprights, it makes life easier and gives more set up options - although I'd still have essentially the same set up - but it was my wish to keep my car as stock as possible.
01-18-2017, 02:50 PM
#29
Rennlist Member
Elephant Racing Bump Steer Correcting Tie Rod Kit
Has anyone tried this?
Any comment or thought?
http://www.elephantracing.com/suspen...ods.htm#prod_3
Has anyone tried this?
Any comment or thought?
http://www.elephantracing.com/suspen...ods.htm#prod_3
01-18-2017, 08:34 PM
#30
Three Wheelin'
I've been wondering just how those Elephant bits manage to change the geometry significantly enough to appreciable reduce the bump steer. Nothing unique about them that I can see. And no mention to what degree they reduce the bump steer. They won't get rid of it entirely. This screams of marketing junk. Especially for the outrageous price tag.
I've been searching for an off-the-shelf solution for the inners that use a normal spherical joint instead of our odd rubber bushing versions. The problem is finding a m14 left-hand thread on the turnbuckle side of the inner. If there are outer tie rods available with a normal female thread, and that match the cone shape, then finding a spherical inner is easy. None of that alters the bump geometry though.
I've been searching for an off-the-shelf solution for the inners that use a normal spherical joint instead of our odd rubber bushing versions. The problem is finding a m14 left-hand thread on the turnbuckle side of the inner. If there are outer tie rods available with a normal female thread, and that match the cone shape, then finding a spherical inner is easy. None of that alters the bump geometry though.