Saidgta

Hi, is there any relation between Adding spacer(or changing Rims Offset) and Bump response to steering wheel?

Bill Verburg

Yes, a spacer cause the scrub radius to go up as does using a wheel w an lower numerical ET,
higher numerical ET causes s/r to go down

any ABS car needs to keep the s/r in the zero to negative side

here's an example a 993 has a stock s/r of -10, change the ET from 54 to 51 say and the s/r goes up by 3mm to -7,

The closer the s/r is to zero, either on the plus or minus side the less feedback at the steering wheel. Other factors particularly caster also affect this.

An example of a car w/ lots of s/r is 911s through '89 which are esteemed for the feedback that they give through the steering wheel, My description is that it feels alive in your hands as you drive. s/r for these w/7ET23.3 heels is 52.4,

Brian C in Az

Bill,
As scrub radius increased, there is less feedback at the wheel due to the fact the tire is scrubbing and doesn't have as much grip. The greater the positive scrub radius, the less effort to turn the wheel and the less feed back to the steering wheel.

Scrub radius also affects braking performance. Increasing scrub radius can make a car less stable under maximum braking.
ABS prefers a more negative number for scrub radius as you approach 0 and positive scrub radius values, it affects the ABS system.

While not an exhaustive explanation, the basics are here: https://en.wikipedia.org/wiki/Scrub_radius