Bumpsteer - 2009 Nissan GT-R Long-Term Road Test

2009 Nissan GT-R Long-Term Road Test

2009 Nissan GT-R: Bumpsteer

July 06, 2009

gg bridge r34.jpg

Our longterm 2009 Nissan GT-R has always had a noted tendency to sniff out cambers. Super-sticky, wide tires plus stiff sidewalls and bushings will do that. There's not much we can do about it.

But how do other manufacturers address the issue? Over the weekend, at a park in San Francisco, I encountered one solution that has a whole bunch of drawbacks.

See, they rent these quadcycles which you can rent to ride around the park. They have truly awful steering in every sense of the word. But these rickety contraptions also manage to have absolutely zero bumpsteer.

quadcycle f34.jpg

They accomplish this feat by having no suspension at all, so the steering geometry remains the same at all times. Barring the loose bearings and slop in the steering, that is.

A lack of wheel travel means the tie rod ends don't shorten or lengthen when the thing crashes over bumps. And this means no bumpsteer.

quadcycle steer.jpg I was curious what made the quadcycle's steering so wretched when the GT-R's is rather excellent, so I started peeking around. Heads up, the rest of this really has nothing to do with the GT-R.

First is the cam that converts your steering inputs into wheel movement.

Due to the physics of the device, the steering is ultra-hyper-quick right around center, and slowest out at the steering stops, which you find when the inside front tire hits your foot.

quadcycle cam.jpg

Quick steering would be fine if there was any--and I mean any--on-center feel. And on-center feel comes in part from caster.

quadcycle caster.jpg Would you guess that this quadcycle has zero caster? Yes, you probably would.

The result of this confluence of bad ideas is steering that is way, way too sensitive to overcorrections around center, and it goes unstable very easily. Gather up any speed and you end up in a steering death spiral, wobbling back and forth as you desparately try to not weave into the path of an oncoming E-class.

You just can't keep the thing pointed straight, which is pretty ironic considering it has no bumpsteer.

Jason Kavanagh, Engineering Editor at 24,661 miles.

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