KPI/SAI vs Caster vs Scrub Radius/Wheel Offset vs Track Width

[Sky Render]

You don't have to apologize for dubs, yo. Ferrari 458/488, Porsche 991 GT3 (RS has 21" rears!), Nissan GT-R, etc have 20 inch wheels and no one complains about them in the slightest. Mustang world is weird (cheap?) in that regard.

I get tired of the "you have to have 25.5" Lifesaver-sized tires to be trak kool!" stuff.

Look up "moment of inertia," and then come back and talk.

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[mavisky]

I will agree with the others here that for optimum track times you should run a wheel that is as light as possible while fitting as much tire and clearing your brake setup.

That being said, for many of us these cars are dual purpose and there's nothing wrong with making minor sacrifices in the name of good looks. Not many in this thread are at the risk of losing sponsor dollars if their times are a tenth or two off of what they could be with different wheels.

 

[Sky Render]

You do realize this is a thread about extracting the ABSOLUTE MAXIMUM cornering performance out of an S197, right?

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[cbass]

Okay, enough about the wheels, he already said he's planning on changing them and the donks were a bad choice. Back to the tekkkkk.

What impact does lowering our cars on springs have? It has the same basic impact as compression, so the caster is the same, but camber increases? What about kingpin?

 

[Norm Peterson]

That being said, for many of us these cars are dual purpose and there's nothing wrong with making minor sacrifices in the name of good looks. Not many in this thread are at the risk of losing sponsor dollars if their times are a tenth or two off of what they could be with different wheels.

"Good looks" is a pretty arbitrary measure.

But anyway . . . to me, a wheel always looks better when function has driven its specs and its design.

Even for my street driving, I'm not going to compromise away from that to impress anybody whose appearance preferences are different from mine. They'll either understand what I'm going for or they won't, and I'm good with that either way.


Norm

 

[Sky Render]

Okay, enough about the wheels, he already said he's planning on changing them and the donks were a bad choice. Back to the tekkkkk.

What impact does lowering our cars on springs have? It has the same basic impact as compression, so the caster is the same, but camber increases? What about kingpin?

If you're not moving or modifying the top strut mount in any way (i.e. only installing lowering springs and nothing else), you're not really affecting caster or kingpin angle.

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[Norm Peterson]

What impact does lowering our cars on springs have? It has the same basic impact as compression, so the caster is the same, but camber increases? What about kingpin?

Caster probably increases slightly as you lower the car (I suspect that the ball joint moves upward and ahead of the line between the ball joint's static position and the effective pivot location of the top strut mount).

KPI/SAI also increases. It's the included angle that remains fixed (unless you make a camber adjustment at the strut/knuckle joint).


Norm

 

[DevGittinJr]

This video briefly touches on the effects of SAI in relation to caster, scrub, etc.

https://www.youtube.com/watch?v=x0oi9SHJPvg&list=FLDiDv8kZEnmqSAG5zHC4MOg&index=1

 

[barbaro]

Here's a link to Ron Sutton and a couple of ways to get to Mark Ortiz taken from the header to the latest issue of his "Chassis Newsletter".

http://www.ronsuttonracetechnology.com/

Mark Ortiz Automotive is a chassis consulting service primarily serving oval track and road racers. This newsletter is a free service intended to benefit racers and enthusiasts by offering useful insights into chassis engineering and answers to questions. Readers may mail questions to: 155 Wankel Dr., Kannapolis, NC 28083-8200; submit questions by phone at 704-933-8876; or submit questions by e-mail to: [email protected]. Readers are invited to subscribe to this newsletter by e-mail. Just e-mail me and request to be added to the list.


Norm

Norm, when I quoted Ron Sutton with respect to JRI shocks, II was roundly ridiculed as I usually am on this forum even though I've been proven right every single time. And here you are referring to him as a resource. This is a wonderful day of vindication.

 

[barbaro]

This video briefly touches on the effects of SAI in relation to caster, scrub, etc.

https://www.youtube.com/watch?v=x0oi9SHJPvg&list=FLDiDv8kZEnmqSAG5zHC4MOg&index=1

Filip is now finally a member of this forum maybe you can direct your inquiries to him.

 

[Norm Peterson]

Norm, when I quoted Ron Sutton with respect to JRI shocks, II was roundly ridiculed as I usually am on this forum even though I've been proven right every single time. And here you are referring to him as a resource. This is a wonderful day of vindication.

It was never about Ron's credentials, I just know he's dealt with the original topic of this thread. But you do have to understand that even people at his level have their own preferences - and that even these experts don't always agree with each other. That seems to be the nature of the beast.

Sure, he's a resource. As is Mark Ortiz. So was Billy Shope, though his interests were mainly drag racing. That's just off the top of my head.

You get ridiculed because once you've got the bone between your teeth on some choice you've made there's no convincing you that any other solution is anywhere near as good as the one you just chose. Maybe that solution really was the absolute best solution for you, but that hardly makes it a universal truth. Being strident about it and continually claiming to have been proven right isn't helping.


I hope to have some conversations with Filip, I did leave the door open.


Norm

 

[barbaro]

You know Norm, even a broken clock is right twice a day and maybe that's what happened with me.

 

[DevGittinJr]

This is a wonderful day of vindication.

Filip is now finally a member of this forum maybe you can direct your inquiries to him.

It'd be great if Filip chimed in. I'd bet we're all interested in his perspective on both dual purpose and class-regulated setups. Anything he can add to the topic of setting up the front-end geometry would be beneficial.

I hope to have some conversations with Filip, I did leave the door open.

Good things are coming. Good things.