New for 2021, Verkline is pleased to announce the release of the Verkline Suspension Upgrade Package for the A90/A91 Toyota Supra & G Series BMW Z4. Fixing some well documented handling issues as well as dramatically improving performance on the road, track and strip!
These issues are well documented with the complaints of Nurburgring Taxi wizards Apex Nurburgring, complaining of the issues the excessive Bump-Steer creates in the GR Supra. Checkout the video below whereby Misha explains some of the problems and Verkline's owner, Albert walks you through the products.
For those wanting to delve a little deeper, here's the story:
Toyota Supra A90/A91 and BMW Z4 G29 was originally designed to provide the best driving experience for normal street use and easy factory tail-happy handling to encourage the driver to have some fun and go a little bit sideways from time to time during everyday use. The case is that when we are starting to look in that car for performance, that tail-happy behaviours are starting to be for us problems with instability.
The main cause for that is the rear end bump steer. In simple words bump steer is telling us how the toe is changing, more or less through the suspension travel. In stock Supra, bump steer is quite significant. For example, during alignment you can set your rear toe to 0,11° toe in (black center dot on graph below). This is using stock camber values.
Under hard acceleration your rear end is going down, around 40mm (even more on lowered cars and cars with more power and grip!). Then due to bump steer your toe is changing to about 0,3° toe in (blue left dot on graph below). On the other hand under hard braking Your rear suspension is going up, again around 40mm. This time it will give You about -0,1° toe out
(yellow right dot on graph below).
As You can see, the Supra/Z4 bump steer has a significant impact on the toe during driving. During alignment you will set your wheels to be toe in, however during driving and with the factory Bump-Steer setup, you may be driving with rear toe out which is causing the rear end to be very lively. In daily low speeds it is not so bad, but on track usage or highways it could be the cause of dangerous situations.
Another issue with that suspension (5 link especially) is that it has a lot of interdependencies between its properties. It makes it very complicated to modify its setup without deterioration of its kinematics. On the graph below You can find an example of how a change of camber (new alignment setup) by 0,5°, which is common for people to go to do with track setups with semi-slicks, this can increase bump steer even more (green line - 0,5° increased camber, red line - stock camber setup). Therefore, increasing camber can actually make bump-steer WORSE!
If we would look again at an example of hard braking and rebound of rear suspension by 40mm, we are getting about -0,2° of toe out (pink dot on graph above) instead of -0,1° for stock setup (yellow dot on graph above).
In some cases like going fast over a crest You can have up to 80mm of rebound which in that case would give as much as -0,5° of toe out per wheel. This is -1° of total toe out! Such big change into toe out for a driving which is not experienced or waiting for it to happen may end in a loss of control.
That is why to reduce these problems we have created 3 suspension setup presets (Track, Street, Drag) to provide the best possible performance out of the box, for every type of driver.
These developed by us 3 suspension setups consist of our basic alignment and ride height suggestions, and what is the most important, predefined lengths of every arm, to provide proper kinematics for every designated use of car.
On the graph below You can find a comparison of 2 previous shown bump steer curves (red and green lines) with a curve of our Street setup preset (yellow line).
As You can see the bump steer curve of our setup provides much reduced bump steer to prevent toe out through all suspension travel. This will give You a stable handling without unpredictable dangerous situations, which were caused by sudden transitions from toe in to toe out.
As a summarising, VERKLINE goal in preparing that 3 setup presets is to improve stock Supra A9x/Z4 G29 and additionally prevent all issues which would occur due to modifying e.g. camber or ride height to fit the car to a designated use.
The Verkline parts are available separately, as a complete bundle or some smaller bundles to help you some money. Take a look at the below product links for specific product information.
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