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 Post subject: Offset Hub Center Line
PostPosted: January 11, 2017, 12:41 pm 
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So the solstice Upright has a hub that offset from the center line of the ball joints. How will this affect the cars handling?? It looks like it just decreases the mechanical trial a bit. So is it even an issue?? I'm also not sure if the caster angle is still taken through the ball joints or not with this type of upright. Thoughts?


See pic of the current layout


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caster.JPG
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PostPosted: January 11, 2017, 12:57 pm 
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It's the correct way to control mechanical trail. Nothing to worry about.

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PostPosted: January 12, 2017, 8:08 am 
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If the offset is nothing to worry about, why did GM make the upright with an offset?

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PostPosted: January 12, 2017, 8:17 am 
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The offset allows more caster (and it benefits) without excess mechanical trail. The Solstice uses 8* caster, but it "feels" like a lot less


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PostPosted: January 12, 2017, 10:32 am 
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What are the benefits of increased caster angle once acceptable return to center steering is achieved?

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PostPosted: January 12, 2017, 11:02 am 
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glenbinegar wrote:
What are the benefits of increased caster angle once acceptable return to center steering is achieved?

Greater camber gain when the wheel is turned. This can get you better front end cornering grip in a suspension design that doesn't have a lot of camber gain due to roll, without reducing braking grip by having a bunch of static camber


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PostPosted: January 12, 2017, 2:37 pm 
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Bent Wrench wrote:
If the offset is nothing to worry about, why did GM make the upright with an offset?


It's the right way to design trail versus compromising caster.

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PostPosted: January 12, 2017, 5:05 pm 
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Posthumane, so there is an advantage (in large caster angles) for a Mcpherson strut front suspension or one with equal length upper and lower control arms. These are not popular suspension configurations for most of us, at least those planning to build their own suspension system with built in camber gain. Hoping this response isn't tactless, just trying to see the whole picture.

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PostPosted: January 12, 2017, 6:44 pm 
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Mo, in the Solstice picture above I think the trail has been increased, not decreased. It isn't drawn to show what you want to see though. The line thru the axle pin should be vertical. not inclined like the caster line. Then you would see the offset adds to the trail. Or maybe I'm seeing your diagram wrong...

I am skeptical of using large amounts of caster. In your diagram you show 9 degrees, which I would consider to be a high value. The problem is you need to turn the steering wheel a lot to generate camber this way. Once you do this you are already out of a performance area, unless you are turning very tight circles.

For an easy example look at Andrew Moore's avatar below. You can see his car is cornering, but the front wheels are nearly straight ahead. It is in a balanced drift. If he turned the wheels more, they would cause more drag. The vector of force they produce is not pointed to the center of the turning circle but behind it which slows you down.

A further subtlety here is that when the front wheels are at much of an angle the back tires produce less cornering force too. You can only generate so much slip angle before the tire starts to slide instead of slip. If the front wheels are at their limit, the back wheels cannot also be at their slip angle limit, unless it's a very tight turn. If you race in a parking lot, castor for camber probably works - but the faster you are going the less help it will be, so not so good for road racing....

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PostPosted: January 12, 2017, 9:00 pm 
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horizenjob wrote:
Mo, in the Solstice picture above I think the trail has been increased, not decreased. It isn't drawn to show what you want to see though. The line thru the axle pin should be vertical. not inclined like the caster line. Then you would see the offset adds to the trail. Or maybe I'm seeing your diagram wrong...

I am skeptical of using large amounts of caster. In your diagram you show 9 degrees, which I would consider to be a high value. The problem is you need to turn the steering wheel a lot to generate camber this way. Once you do this you are already out of a performance area, unless you are turning very tight circles.

For an easy example look at Andrew Moore's avatar below. You can see his car is cornering, but the front wheels are nearly straight ahead. It is in a balanced drift. If he turned the wheels more, they would cause more drag. The vector of force they produce is not pointed to the center of the turning circle but behind it which slows you down.

A further subtlety here is that when the front wheels are at much of an angle the back tires produce less cornering force too. You can only generate so much slip angle before the tire starts to slide instead of slip. If the front wheels are at their limit, the back wheels cannot also be at their slip angle limit, unless it's a very tight turn. If you race in a parking lot, castor for camber probably works - but the faster you are going the less help it will be, so not so good for road racing....


That was an exaggeration to show it better. My car only has 5deg of caster and this car will probably have the same statically.

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