TPC or Tarrett toe links?
#31
I should be able to measure on a GT4 next weekend. If you're interested in a better simulation sooner than that, I'm happy to re-run it any time with provided measurements.
After a more detailed look, I'd be inclined to agree - 25 mm was just a nice number that made a visible difference in the geometry. I'll definitely update that when I improve the rest of the dimensions.
After a more detailed look, I'd be inclined to agree - 25 mm was just a nice number that made a visible difference in the geometry. I'll definitely update that when I improve the rest of the dimensions.
#32
Instructor
Jeff installed my TPC Offset toe links yesterday, took some photos and wrote this report detailing the resultant toe compared to the stock bushings. Looking forward to the next trackday on 31 July.
Cayman GT4 rear bump-steer
Suspension / Set-up specs:
Factory Ride Height @ 110 mm front and 130 mm rear.
Approx. -3 deg. Front Camber using 29mm shims
Approx. -2.5 deg. Rear Camber using 16mm shims
Tarett Solid LCA mono ***** front and rear
Tarett solid caster bushing in front LCA’s
Tarett front tie rod with Bump-steer correction
1mm (8’) toe out per wheel on front axle
1.5mm (10’) toe in per wheel on rear axle
*TPC racing rear toe arms with Bump-steer correction*
Bump-steer results with symmetrical bushings on inner rear toe arm.
1” of compression = 0.15’ (2mm) toed in by .5mm
0 – Ride Height = 0.10’ (1.5mm) static toe
1” of droop = 0.05’ (.7mm) toed out by .8mm
Under compression, the rear wheels would toe in by up to .5mm at 1’’ of travel.
As the suspension unloads, (droop), the wheels would toe out by up to .7mm.
With the new MacPherson rear suspension in the 981 platform, the chassis is more sensitive to rear bump-steer than the 9X7 / 9X6 Multi-link cars. This is most notable under braking during corner entry. The rear can feel nervous and dance around due to the rear wheels moving towards toe out. The rear toe arms with bump-steer correction bushings help reduce this effect.
Bump-steer results with TPC racing rear toe arms
1” of compression = 0.13’ (1.7mm) toed in by .2mm
0 – Ride Height = 0.10’ (1.5mm) static toe
1” of droop = 0.08’ (1.2mm) toed out by .3mm
The bump-steer curve is better. As the suspension moves throughout its travel, the static toe setting is maintained better. There is still room for improvement, but the design of the inner pick up on the toe arm does not lend itself to more adjustment. The bushings are as offset as possible without running into clearance issues with the sub-frame.
The bump-steer numbers will probably vary from chassis to chassis due to suspension geometry differences. But the offset bushings should push the bump-steer curve in the right direction regardless.
Suspension / Set-up specs:
Factory Ride Height @ 110 mm front and 130 mm rear.
Approx. -3 deg. Front Camber using 29mm shims
Approx. -2.5 deg. Rear Camber using 16mm shims
Tarett Solid LCA mono ***** front and rear
Tarett solid caster bushing in front LCA’s
Tarett front tie rod with Bump-steer correction
1mm (8’) toe out per wheel on front axle
1.5mm (10’) toe in per wheel on rear axle
*TPC racing rear toe arms with Bump-steer correction*
Bump-steer results with symmetrical bushings on inner rear toe arm.
1” of compression = 0.15’ (2mm) toed in by .5mm
0 – Ride Height = 0.10’ (1.5mm) static toe
1” of droop = 0.05’ (.7mm) toed out by .8mm
Under compression, the rear wheels would toe in by up to .5mm at 1’’ of travel.
As the suspension unloads, (droop), the wheels would toe out by up to .7mm.
With the new MacPherson rear suspension in the 981 platform, the chassis is more sensitive to rear bump-steer than the 9X7 / 9X6 Multi-link cars. This is most notable under braking during corner entry. The rear can feel nervous and dance around due to the rear wheels moving towards toe out. The rear toe arms with bump-steer correction bushings help reduce this effect.
Bump-steer results with TPC racing rear toe arms
1” of compression = 0.13’ (1.7mm) toed in by .2mm
0 – Ride Height = 0.10’ (1.5mm) static toe
1” of droop = 0.08’ (1.2mm) toed out by .3mm
The bump-steer curve is better. As the suspension moves throughout its travel, the static toe setting is maintained better. There is still room for improvement, but the design of the inner pick up on the toe arm does not lend itself to more adjustment. The bushings are as offset as possible without running into clearance issues with the sub-frame.
The bump-steer numbers will probably vary from chassis to chassis due to suspension geometry differences. But the offset bushings should push the bump-steer curve in the right direction regardless.
#34
.......With the new MacPherson rear suspension in the 981 platform, the chassis is more sensitive to rear bump-steer than the 9X7 / 9X6 Multi-link cars. .......
#35
Drifting
#36
You have to take the whole sentence and not just part of it. X denotes a variable of choosing, allowing it to be 996 / 997 / 986 / 987. Two of these are multi link and two are not; apples and oranges.
#37
Drifting
#38
My mistake on the blanket statement of 9x6 & 9x7 cars. The point I was trying to make is the 981 and more so the GT4 appear to have a rear bump-steer curve that is less than ideal. Something we have not seen in other models, Strut or Multi link. It is also worth noting that the 981 is the first rear suspension (in the mid-engine model range) to feature the outer joint fixed on a horizontal plane opposed to the more common vertical plane. Maybe there is something to this, maybe not? In any event, it appears that with the OEM bushings on the inner pickup (centered), the arm is too short. In compression it has the effect of toeing in the wheel, and in droop it toes out. The offset bushing lengthen the arm and correct this geometry. From my measurements it looks like you could lengthen the arm a little further, but the inner pickup is just about as forward as possible. The next mod would be to come up with a method to use bump-steer shims on the outside tie rod joint. But, that might be picking the black out of the pepper so to speak. There reaches a point were the chassis and or driver become numb to the minute changes in toe. This current mod very well could put the chassis in this zone.
I have full confidence having been Randy Pobst's car chief during the 2012 and 2013 Volvo S60 years in PWC, that if he and Mike put their heads together and tuned / developed this product that it works, and works well. Randy was always very particular on how his car was setup for corner entry. He has very little tolerance for a car that is entry loose and flat out wont drive the car at the limit until he is confident in the car on entry.
I have full confidence having been Randy Pobst's car chief during the 2012 and 2013 Volvo S60 years in PWC, that if he and Mike put their heads together and tuned / developed this product that it works, and works well. Randy was always very particular on how his car was setup for corner entry. He has very little tolerance for a car that is entry loose and flat out wont drive the car at the limit until he is confident in the car on entry.
Last edited by JD-Motorsports; 07-23-2016 at 12:00 AM.
#39
Awesome, thanks for sharing these measurements. How confident are you in the toe measurement under compression / droop? These should be easy to corroborate with a simple suspension model. Looking forward to an updated analysis from PLC.
#40
In regards to a suspension model computer generated output. I would like to see the inputs and how they arrive at their results. I would think to do this one would need to probe the entire corner assembly with a Faro arm or something similar. Input all those data points, then run a simulation.
Last edited by JD-Motorsports; 07-31-2016 at 06:29 AM.
#41
Instructor
So, first trackday with the TPC Offset rear toe links today. Unfortunately a very wet start, hail during scrutineering and showers for the first three sessions. Only two short sessions on a reasonably dry track. On the second one I had the Gopro and vbox sport on - hadn’t bothered up till then due to weather.
In my opinion these toe links make a very significant difference if you’re experiencing corner entry oversteer in the GT4. This may or may not be an issue for you depending on your alignment and driving style. (My specs on a post above).
The rear has lost that nervous feeling where it may slide, at the point where you’re coming off the brakes and turning in. Previously I was having to concentrate on balancing the car delicately with the steering, i.e. applying a little opposite lock just to keep things in check - now I’m more confident that the car won’t snap into an oversteer situation, and even under extreme provocation, shown on the last lap in the video, it was easy to control. I think you can see in the video, that I’m not having to apply as much correction with the steering wheel as previously. Given the poor conditions on the day my best time of 1.13.05, was pretty good, IMO - my best time ever is 1.12.58. One unexpected benefit was at Turn 3 where I feel more confident in applying power thru this off cambered turn.
The first video is a few short clips from turns 1,2 and 6 that show the typical situation before. The video isn’t intended to show actual oversteer, but just the need to be ready to apply opposite lock as the rear gets nervous and starts to step out.
This video is from today with the offset rear toe links. Even under extreme provocation at turn 6 towards the end, the car has lost that tendency to oversteer and is much more predictable and forgiving. I think that with more time and better conditions it will be faster also, due to increased confidence. Needless to say I'm happy with mine and will be keeping them on.
In my opinion these toe links make a very significant difference if you’re experiencing corner entry oversteer in the GT4. This may or may not be an issue for you depending on your alignment and driving style. (My specs on a post above).
The rear has lost that nervous feeling where it may slide, at the point where you’re coming off the brakes and turning in. Previously I was having to concentrate on balancing the car delicately with the steering, i.e. applying a little opposite lock just to keep things in check - now I’m more confident that the car won’t snap into an oversteer situation, and even under extreme provocation, shown on the last lap in the video, it was easy to control. I think you can see in the video, that I’m not having to apply as much correction with the steering wheel as previously. Given the poor conditions on the day my best time of 1.13.05, was pretty good, IMO - my best time ever is 1.12.58. One unexpected benefit was at Turn 3 where I feel more confident in applying power thru this off cambered turn.
The first video is a few short clips from turns 1,2 and 6 that show the typical situation before. The video isn’t intended to show actual oversteer, but just the need to be ready to apply opposite lock as the rear gets nervous and starts to step out.
This video is from today with the offset rear toe links. Even under extreme provocation at turn 6 towards the end, the car has lost that tendency to oversteer and is much more predictable and forgiving. I think that with more time and better conditions it will be faster also, due to increased confidence. Needless to say I'm happy with mine and will be keeping them on.
Last edited by Leong72; 07-31-2016 at 04:04 PM.
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QShip (10-30-2020)
#42
Great post. To my skeptical eye, it looks like you aren't pushing it as hard in the 2nd video with TPC (tire squeal is much more rare and limited), and in those that had significant tire squeal, there was still some opposite lock needed, though subjectively perhaps not as much.
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
So, first trackday with the Tarett Offset rear toe links today. Unfortunately a very wet start, hail during scrutineering and showers for the first three sessions. Only two short sessions on a reasonably dry track. On the second one I had the Gopro and vbox sport on - hadn’t bothered up till then due to weather.
In my opinion these toe links make a very significant difference if you’re experiencing corner entry oversteer in the GT4. This may or may not be an issue for you depending on your alignment and driving style. (My specs on a post above).
The rear has lost that nervous feeling where it may slide, at the point where you’re coming off the brakes and turning in. Previously I was having to concentrate on balancing the car delicately with the steering, i.e. applying a little opposite lock just to keep things in check - now I’m more confident that the car won’t snap into an oversteer situation, and even under extreme provocation, shown on the last lap in the video, it was easy to control. I think you can see in the video, that I’m not having to apply as much correction with the steering wheel as previously. Given the poor conditions on the day my best time of 1.13.05, was pretty good, IMO - my best time ever is 1.12.58. One unexpected benefit was at Turn 3 where I feel more confident in applying power thru this off cambered turn.
The first video is a few short clips from turns 1,2 and 6 that show the typical situation before. The video isn’t intended to show actual oversteer, but just the need to be ready to apply opposite lock as the rear gets nervous and starts to step out.
Pre Offset Rear toe links - YouTube
This video is from today with the offset rear toe links. Even under extreme provocation at turn 6 towards the end, the car has lost that tendency to oversteer and is much more predictable and forgiving. I think that with more time and better conditions it will be faster also, due to increased confidence. Needless to say I'm happy with mine and will be keeping them on.
My Movie - YouTube
In my opinion these toe links make a very significant difference if you’re experiencing corner entry oversteer in the GT4. This may or may not be an issue for you depending on your alignment and driving style. (My specs on a post above).
The rear has lost that nervous feeling where it may slide, at the point where you’re coming off the brakes and turning in. Previously I was having to concentrate on balancing the car delicately with the steering, i.e. applying a little opposite lock just to keep things in check - now I’m more confident that the car won’t snap into an oversteer situation, and even under extreme provocation, shown on the last lap in the video, it was easy to control. I think you can see in the video, that I’m not having to apply as much correction with the steering wheel as previously. Given the poor conditions on the day my best time of 1.13.05, was pretty good, IMO - my best time ever is 1.12.58. One unexpected benefit was at Turn 3 where I feel more confident in applying power thru this off cambered turn.
The first video is a few short clips from turns 1,2 and 6 that show the typical situation before. The video isn’t intended to show actual oversteer, but just the need to be ready to apply opposite lock as the rear gets nervous and starts to step out.
Pre Offset Rear toe links - YouTube
This video is from today with the offset rear toe links. Even under extreme provocation at turn 6 towards the end, the car has lost that tendency to oversteer and is much more predictable and forgiving. I think that with more time and better conditions it will be faster also, due to increased confidence. Needless to say I'm happy with mine and will be keeping them on.
My Movie - YouTube
#43
Instructor
Great post. To my skeptical eye, it looks like you aren't pushing it as hard in the 2nd video with TPC (tire squeal is much more rare and limited), and in those that had significant tire squeal, there was still some opposite lock needed, though subjectively perhaps not as much.
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
No, it didn't make the car understeer, certainly nothing like the understeer I had before adjusting sway bars etc. I think the toe links just make the car's balance ie understeer/oversteer balance the same whether the suspension is loaded or unloaded. More predictable.
#44
Great post. To my skeptical eye, it looks like you aren't pushing it as hard in the 2nd video with TPC (tire squeal is much more rare and limited), and in those that had significant tire squeal, there was still some opposite lock needed, though subjectively perhaps not as much.
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
Do you feel like the reduced entry oversteer also made the car feel less maneuverable (understeery)?
#45
Your sceptical eye needs calibrating my friend! For the lap in question, when overlaid with the PB lap of 1.12.8, he was able to carry more speed on entry for 3 out of 6 corners. I am confident with more laps, we will be able to improve the entries for all 6 corners and still get good exits...WIN-WIN.