Scrub radius impact on handling

[CTX-SLPR]

Howdy,

Since I have the pleasure of redesigning my front suspension on my '64 Riviera, I can design for whatever offset wheel I want. However since I do want to make an effort to maximize the handling and comfort of the suspension, how important is scrub radius? I'm basing most of the design off of the C5/6 Corvette and using the same upright. Is keeping the same 54-56mm offset critical to the handling and/or bearing life?
How much thought about scrub radius actually goes into most people's wheel selection?
How much impact does say moving the kingpin axis 1in inboard make?



Thanks,

[exwestracer]

There's a LOT to that simple question. Basically, longer scrub radius magnifies whatever motion the hub flange goes through as you steer. Caster "jacking" increases, and the tire physically moves further fore and aft in the wheel well, which can cause clearance issues. In extreme cases (yours isn't), heavy braking can cause some "torque steer" from the increased leverage against the steering knuckle.

Look at your proposed change as a percentage of tire width. If you change the scrub radius 1" on a 10" tire, it won't have as dramatic an effect (depending on static caster) as moving it 1" on a 6" tire. If the steering axis line moves OFF the tread surface, you are really getting into a lot of scrub at that point...

[CTX-SLPR]

Ray,

Anything has to be better than the stock set up with very very low 3 3/8in backspacing. Reason I ask is the C5/6 has a front wheel offset of 54-56mm but I am not wild about any of the wheels nor can I fit a 9.5in wheel on the front. I do however like more than a few BMW wheels which tend to run in the 20-40mm offset range depending on the chassis they came off of. Shooting for an 18x8 in the front and either the same or an 18x9 on the rear. I'm guessing you recommend getting as close to the original offset as possible?

Thanks,

[CTX-SLPR]

Ok, doing some math (good gravey I love math!) and according to my modeling I can get away with a wider tire just by drastically moving the kingpin axis inside of the wheel. Using a simple excell model of the lower control arm and tire I found that even keeping the track width the same I pick up a few more degrees of steering angle before the tire hits the frame with a 245/45R18 tire. Now I can't say that my math is 100% but I think it's a fair approximation.

What happens when you get very close to 0 scrub radius? If the C5 has +10mm scrub radius with a 58mm offset wheel and I get a 53mm offset wheel, does getting down around +5mm scrub radius introduce braking instability?

Thanks,