professor, did a quick internet search and found your answer on the tamiyaclub.com website. Here is a link -
http://www.tamiyaclub.com/forum/inde...d-info-please/
Basically you need to go with a longer ball connector/stud on the steering knuckle. According to the post you need Tamiya part number 19805825.
Check out this picture and you will see the longer ball stud which is a brass piece
https://www.tamiyausa.com/product/it...oduct-id=92231
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Bump steer is usually caused when the steering turnbuckles change at a different rate/angle when compared to the front a-arms. Adjusting the height of the ball stud on the steering knuckle should help alleviate/lessen the excessive bump steer.