scrub radius question

[cparsons]

I was a little surprised to discover that my rear uprights will fit on the front. I was curious how much it would change the track so I checked it out. Well, it widens it alot, maaybe 8" or so, but I would end up with a scrub radius of about 5". How god-awful ugly heavy would that make the front feel, and what would it do to tire wear and suspension? Are there ANY advantages to high scrub radii? I am not considering changing wheel backspace or a-arms or anything. Just thinking of this as optional way to widen front track. It really doesn't need to be wider, just curious.

[Peter Olivola]

As the old saying goes, that all depends. What's your current scrub radius? Keeping in mind that scrub radius has to be slightly negative to achieve neutral effect, it should be easy to extrapolate the different between neutral, your present steering input effort and the result of a five inch scrub radius.

However, that may not be the biggest issue with such a big positive scrub radius. I would be far more concerned with the effect of braking on uneven adhesion surfaces as it would want to twist the steering wheel violently and without any prior indication of which direction.

I was a little surprised to discover that my rear uprights will fit on the front. I was curious how much it would change the track so I checked it out. Well, it widens it alot, maaybe 8" or so, but I would end up with a scrub radius of about 5". How god-awful ugly heavy would that make the front feel, and what would it do to tire wear and suspension? Are there ANY advantages to high scrub radii? I am not considering changing wheel backspace or a-arms or anything. Just thinking of this as optional way to widen front track. It really doesn't need to be wider, just curious.

[ghickman]

Chuck
Assuming you've drawn your uprights up in CAD?....having built my own car and experimented with scrub radius in my opinion you won't be happy with the results you get from that large of a scrub radius.

I went to great pains to get mine as close to zero scrub as possible. Makes the tires happy and leasens the steering effort.

How is the car progressing?? Haven't heard much from you lately.

just my 2 cents worth

Gary Hickman
FB #76

[Brian]

I had a car with close to 5" scrub radius on 10" wheels. It was virtually undriveable, very uncomfortable. Hard to steer, hard to steer in a straight line, darty under braking. Scrub radius can be good to give feedback to the driver, but too much gets old fast. I modified it to 2.5" scrub radius and that was a lot better. A lot of people who probably know more than I ever will think it should be zero with zero KPI too, but all of my cars have at least an inch of scrub radius.

Brian

[cparsons]

Hey Gary, et al. thanks for the input. I had a very rare "I'm in the garage at night during the workweek" and had nothing planned moment so I putzed around. I'll put it back and leave it alone.
Forward progress has been very slow lately BUT I think I have finally muddled most of the way through the stuff I know absolutely nothing about, which means I have 125% more stuff I don't know anything about to muddle through.
And I need to stop changing things just because I can and follow the plan...

[Christopera]

Driven a shifter kart? Given the steering effort required (granted the vast geometry differences) to handle a 380lbs. vehicle i can't imagine the much scrub radius is advisable in a car. Besides, scrub creates big issues with caster angle and weight jacking.