1969 Torino

[SBDave]

This discussion, those wheels, I like all of what's going on here!
...and I have nothing to contribute.
Carry on!

[Ron Sutton]

Originally Posted by 67goatman455

Whew! i never thought i would see so many informative posts in a row in this thread!

I have so many noob questions, that i'm pretty lost but ill sit back and keep reading. Hopefully ill catch on. looks like i need to change my mind set, I too planned on throwing the biggest freaking tire on the back i could, and make do with what i could up front. I will be quite disappointed on the track if i do that, i see!

Yes, Scott, you would be constantly fighting a push condition. And that's no fun.

[Sieg]

Originally Posted by DaleTx

Rob... I just checked the track width on my first gen Camaro and it measures 60-7/8" in the front, and 60-1/8' in the rear. The overall width of my tires are 10.35" in front and 10.91"in rear. I measured the track width from the center of the tread to center of tread.

This is great info here on wheel and tire sizing.

Ron - Here's my track width data:

Measured outer sidewall to sidewall front and rear. Tire width is sidewall to sidewall. Nitto NT-05's IIRCC - Dale's running Nitto NT-01 255/40/17, 275/40/17.

Front: 69.0625" 245/40/18 tire on 8" rim measures 9.5"
Centerline Track = 59.5625"

Rear: 70.875" 275/40/18 tire on 9.5" rim measures 10.875"
Centerline Track = 60.00"

[Ron Sutton]

Originally Posted by Sieg

Ron - Here's my track width data:

Measured outer sidewall to sidewall front and rear. Tire width is sidewall to sidewall. Nitto NT-05's IIRCC - Dale's running Nitto NT-01 255/40/17, 275/40/17.

Front: 69.0625" 245/40/18 tire on 8" rim measures 9.5"
Centerline Track = 59.5625"

Rear: 70.875" 275/40/18 tire on 9.5" rim measures 10.875"
Centerline Track = 60.00"

Hi Sieg,

Your rear TW is 7/16" wider than the front, so that will contribute a very small amount to freeing up your car in the corners.

The 12% wider tires in the rear will contribute a larger amount to tightening up your car in the corners.

Both of those items are just two pieces of the bigger puzzle.

If ... your front geometry is like most PT cars with the KPI/Caster split favoring the KPI significantly ... that would contribute the largest amount to the car's handling being unbalanced & tight/pushy on tight corners ... until the front geometry is corrected or the rear suspension tuned to reduce grip to free the car up.

On the other hand, if you're not running track days with tight corners or AutoX, it may not matter. I surely don't know your car or situation, so I don't want to make any unfounded assumptions.

...

[Sieg]

Ron,

I meant Rob - as he requested my data in a PM...........

But Ron, thank you very much

I have a spare stock subframe sitting in the garage that I plan to do on a budget somewhat "Smokey" style and this information greatly helps the quest.

My current setup is somewhat goofy as I feel it handles much better than it should, but I've yet to get it to the track and exploit the short-comings. FWIW my only road course experience is on two wheels.

Again thank you for sharing this information, it is very much appreciated.

[Ron Sutton]

Originally Posted by Sieg

Ron,

I meant Rob - as he requested my data in a PM...........
Oops! No worries.

But Ron, thank you very much
You're welcome.

I have a spare stock subframe sitting in the garage that I plan to do on a budget somewhat "Smokey" style and this information greatly helps the quest.
Hmmm. Where are you located? I have some ideas, but would need to show you in person on the clip.

My current setup is somewhat goofy as I feel it handles much better than it should,
Well that's cool.

but I've yet to get it to the track and exploit the short-comings. FWIW my only road course experience is on two wheels.
Cool. I love bikes but only raced motocross as a kid, never road courses. I'm sure it's a thrill.

Again thank you for sharing this information, it is very much appreciated.

Take care.

...

[Sieg]

Originally Posted by Ron Sutton

Take care.

...

I'm located in Springfield, OR.......near nothing.

[carbuff]

Wow... Ask what I thought was a pretty simple question, and I got an amazingly detailed answer! Thank you for taking the time to explain all of that! I've read it twice, and I'm still absorbing it, but your explanation made sense and was very well presented!

I think the next thing I need to figure out is what scrub radius I actually have now. It sounds like that would be one of the next big factors in the equation...

Thanx again!

[carbuff]

On the subject of caster, I do have another question...

I've heard that changing the amount of caster has an impact on the 'feel' of the steering. I've also heard that caster is often used in a street alignment to offset the irregularities that we may experience when driving down the road.

Can you touch on either or both of those, particular how either would relate to the KPI / SAI as you explained them above? Is there a crossover point, for example, on how increasing / decreasing the caster will affect the steering 'feel'? I ask partly because if that's true, I wonder if you can hit a point where we might 'overwork' the steering rack we are using? In other words, I would guess that if we make a change to the caster that causes us to have to use more force to turn the wheels, are we possibly putting more pressure on the rack, and risk damaging it?

I'm thinking out loud with that question, so perhaps it's irrelevant... But in my case, since I'm using a Ford rack that was likely never built to take much abuse, I wonder if that can become a problem?

[Ron Sutton]

Hi Bryan,

On the subject of caster, I do have another question...

I've heard that changing the amount of caster has an impact on the 'feel' of the steering.
More caster increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less caster decrease this feel.

More scrub radius increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less scrub radius decrease this feel.

Since reducing scrub radius is good for turning ability ... but takes away the feel ... and adding caster also helps the turning ability ... and returns the feel ... these are two good tuning changes to do together. .

I've also heard that caster is often used in a street alignment to offset the irregularities that we may experience when driving down the road.
What your referring to is factory passenger car settings to help the car drive straight on roads that are crowned. Some mechanics like to put a little more caster in the RF wheel to offset this ... others prefer to add a little static camber in the RF to achieve this.

I'm a race car designer & crew chief, focused on track cars, so we don't do this on road course or AutoX cars ... just oval track cars.

Can you touch on either or both of those, particular how either would relate to the KPI / SAI as you explained them above? Is there a crossover point, for example, on how increasing / decreasing the caster will affect the steering 'feel'? I ask partly because if that's true, I wonder if you can hit a point where we might 'overwork' the steering rack we are using? In other words, I would guess that if we make a change to the caster that causes us to have to use more force to turn the wheels, are we possibly putting more pressure on the rack, and risk damaging it?
That question reminds me of a guy one time buying a large duration, high lift, "mean" aggressive inverted flank ramp roller cam to build optimum power in his 434" SBC ... and then asking how the fuel mileage would be?

Yes, almost anything you do to make your front end grip more & turn better, is going to put more load on the steering box. Wider tires, grippier tires, wheels with the width wider than the tread width, low profile tires, faster steering ratios, more caster, more camber, bigger sway bars, springs & shocks to provide grip, etc, etc, etc.

About the only thing that will help the car turn better & not increase the load on the steering box is reducing scrub radius.

I'm thinking out loud with that question, so perhaps it's irrelevant... But in my case, since I'm using a Ford rack that was likely never built to take much abuse, I wonder if that can become a problem?[/QUOTE]
That's smart thinking. If you build a mean handling machine & utilize a small, moderate duty steering box, you could have issues.

What R&P do you have ?

.