Mech33

I'll wait patiently for your measurements and updated model. Looking forward to it.

Leong72

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.

ML///

Thanks for that review and information. Your information helped me understand that there is only one way to install these links.

ExMB

986 / 987 cars did not have a multi link rear suspensi9n. They had MacPherson struts just like the 981.

jphughan

"New" could simply mean "revised and updated", like "the new 911". There was a 911 model before the "new" one.

ExMB

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.

jphughan

D'oh! Completely spaced on the significance of the X when I read that.

JD-Motorsports

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.

Mech33

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.

JD-Motorsports

Good question. In a perfect world and how we did it at KPAX racing, was to have the car level on jack stands, wheels off, precision toe plate bolted to the hub and springs removed. Using the shock position sensors, we could find ride height and set up our dial indicators. Zero the indicators at ride height, then measure inch of bump and inch of droop. Document, adjust either the inner or outside pickups with bumpsteer shims. Usually would take at least .030"of an inch movement to change the curve. That is the way I was taught and measured bumpsteer ... But at my current place of employment we do not have this equipment available. So, for this exercise I did it all on the alignment rack using the Hunter alignment heads to provide the measurements. Set the static toe at ride height, accurately raised and lowered the rear end 1" in each direction. Documented the results. So while there are more variables and room for error , I have confidence that the above method illustrates that the offset bushings are shifting the bumpsteer curve into a more optimal zone. Is it as accurate as I would like? No. But it is what it is!

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.

Leong72

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.

Mech33

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)?

Leong72

Seems that way but the last 944 that I passed is the quickest 944 in the country and although I got past him in the straight he was all over me thru the infield that lap and only slightly further back the next lap. He was on slicks. I was trying.... Maybe it doesn't look it because the suspension is more composed? All the clips from the first video are from a trackday on 9 June when we had good weather and a full day with consistent track conditions. The car was in same spec apart from the toe links. I only did one 1.12.8 that day and the rest of the times were in the 1.13's, hence my comment that today wasn't too bad. I only got three flying laps in the previous session and the three I got on video. Rest of the day was wet. Also, because of poor weather I didn't bother with tyre pressures and was running road pressures all day... The rears got up to 39psi by the end of session.

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.

JD-Motorsports

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.

Mech33

My eye is definitely not a calibrated instrument! Thanks for sharing the data. Do you have steering angle data from those exact same runs you could overlay and share?