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Old 07-24-2007, 01:50 PM   #1
oldsxtc

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Default G-body Suspension

I'm Looking To Put A Whole New Suspension In My G-body
I'm Making A Corner Carver Not A Quarter Miler
I Got A 79 Supreme With A 455, A 200 R4, Posi With A 4:11 ( The Extra Gear Will Keep My Hiway Rpm's Down) I'm Puuting On 17's
(30-31in.tire) And Dropping It 2 Inches (maybe, I Haven't Decided Yet)

I'm Looking For Recomendations On The Brand Name Of The Suspension Parts And Setup To Use For Example Air Bags Or Not Coil Over Or Not Rack And Pinoin Or Parralelogram, Etc..

I Know I Want Da La Lum Bushing Instead Of Polygraphite ( Less Binding)

Any Input, Ideas, Or Experiences Let Me Know

Last edited by oldsxtc : 07-24-2007 at 03:09 PM.
 
Old 07-24-2007, 02:06 PM   #2
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http://www.umiperformance.com/gbody

they are one of our sponsors..check them out.
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Old 07-24-2007, 03:51 PM   #3
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If you want to get serious about G-body handling, you gotta get the front roll center upwards by changing the front geometry. You can do this with taller spindles or tall ball joints. Tall spindles (like the B-body setups) help this out, but increase the bumpsteer of the car (BAD!).

With raising the roll center, the car will tend to roll a lot less, and you can put a reasonably rated spring on the car so the ride quality will not suffer as much. Some people will throw some extremely stiff springs on the car to prevent the roll, but it just masks the underlying poor geometry and drops the ride quality down the toilet.

Pretty much the best G-body suspension parts come from Savitske... their website is www.scandc.com.

I plan to run their stage 2 front kit with adjustable tubular upper arms, and tall upper and lower ball joints. The kit will drop the car 0.75" in the front... combined with an Eibach 1" drop spring, the car will sit very nicely in the front.

I would run Eibach springs and Bilstein shocks on all 4 corners. If you want to cheap out on the springs, some Moog 5660's for front and 5409/5413's for the rear.

For the rear suspension, DON'T USE POLY IN THE FOUR LINK (it binds). Anybody who suggests it is either a straight line guy or doesn't actually push the car handling-wise. I've felt my 4 link bind with Camaro 1LE bushings bind and snap oversteer, and its wicked. Savitske's sells some killer rear trailing arms (Currietracs), but they are pricey. Depending what kind of NVH you can tolerate, you might want to run a spherical bearing/rod end.

While you are at it, consider upgrading the brakes. With 17" wheels, you can put on a newer LS1 camaro 12" brake setup on all 4 corners for a very reasonable price.

Is all this costly? yes. But it will definitely make the car ride and drive like a totally different machine. This is basically the buildup I am going to be putting on my car this fall.

Don't waste your time with rack and pinion on the G-body. You'll blow a ton of money on the swap. Get a good F41 box out of a 3rd gen IROC, get it adjusted right, and your steering feel will improve a ton. Coilovers are nice, but also pricey. I might eventually put a QA1 kit on my car in front with adjustable shocks in the rear.
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Last edited by 83hurstguy : 07-24-2007 at 03:53 PM.
 
Old 07-24-2007, 04:56 PM   #4
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Great post Luke. Hey Eaton has that posi for you.
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Old 07-24-2007, 05:43 PM   #5
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I second the SC&C recommendation. I have their stage II kit with the Pro-lite lightweight adjustable upper control arms, HOWE tall modular ball joints and del-a-lum bushings in the lower control arms.

For the rear, Marcus with SC&C recommended the Edelbrock double adjustable upper control arms with the Spherical bearing on the frame side and poly bushing on the rear end side along with the Currie-Trac lower control arms with spherical bushings and poly.

For what its worth, you probably don't want the del-a-lum bushings in the rear suspension considering their basically just a solid bushing with a delrin washer.

Give Marcus a call at SC&C and he'll help explain a lot of what will help make the G-body handle really well. He's a great guy to talk with. Their company test car is a 442 Olds G-body that they've developed a lot of these pieces from, including the 3 link rear suspension everyone is so eagerly awaiting, including me.
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Old 07-24-2007, 06:24 PM   #6
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You'll also want to stiffen the body mounts if you haven't already. I put a set of Energy Suspension red urethane mounts in my '80. Made a big difference in the body roll.

I can't say much for suspension, I haven't dove into that part yet.
 
Old 07-24-2007, 06:33 PM   #7
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Quote:
Originally Posted by Vern View Post
Great post Luke. Hey Eaton has that posi for you.
Thanks! I'm definitely going to be looking for an Eaton soon. I don't have the energy to yank the rear end just yet.
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Old 07-24-2007, 06:36 PM   #8
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Just out of curiosity what would you say is inexpensive for the 12" 1LE parts Luke? I'd probably need different spindles huh? I'm spooked about getting into bumpsteer issues so I'd like to avoid changing spindles until I read what's a foolproof replacement. Rather than hijack this thread is there somewhere you frequent that discusses the 12" upgrade you can direct me to? I searched here but came up empty.
Thanks!
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Old 07-24-2007, 06:52 PM   #9
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Quote:
Originally Posted by 83hurstguy View Post
If you want to get serious about G-body handling, you gotta get the front roll center upwards by changing the front geometry. You can do this with taller spindles or tall ball joints. Tall spindles (like the B-body setups) help this out, but increase the bumpsteer of the car (BAD!).

With raising the roll center, the car will tend to roll a lot less, and you can put a reasonably rated spring on the car so the ride quality will not suffer as much. Some people will throw some extremely stiff springs on the car to prevent the roll, but it just masks the underlying poor geometry and drops the ride quality down the toilet.

Pretty much the best G-body suspension parts come from Savitske... their website is www.scandc.com.

I plan to run their stage 2 front kit with adjustable tubular upper arms, and tall upper and lower ball joints. The kit will drop the car 0.75" in the front... combined with an Eibach 1" drop spring, the car will sit very nicely in the front.

I would run Eibach springs and Bilstein shocks on all 4 corners. If you want to cheap out on the springs, some Moog 5660's for front and 5409/5413's for the rear.

For the rear suspension, DON'T USE POLY IN THE FOUR LINK (it binds). Anybody who suggests it is either a straight line guy or doesn't actually push the car handling-wise. I've felt my 4 link bind with Camaro 1LE bushings bind and snap oversteer, and its wicked. Savitske's sells some killer rear trailing arms (Currietracs), but they are pricey. Depending what kind of NVH you can tolerate, you might want to run a spherical bearing/rod end.


While you are at it, consider upgrading the brakes. With 17" wheels, you can put on a newer LS1 camaro 12" brake setup on all 4 corners for a very reasonable price.

Is all this costly? yes. But it will definitely make the car ride and drive like a totally different machine. This is basically the buildup I am going to be putting on my car this fall.

Don't waste your time with rack and pinion on the G-body. You'll blow a ton of money on the swap. Get a good F41 box out of a 3rd gen IROC, get it adjusted right, and your steering feel will improve a ton. Coilovers are nice, but also pricey. I might eventually put a QA1 kit on my car in front with adjustable shocks in the rear.
can you explain the front roll center better i thought if you raised it you rolled more
nvh what is this?
f41 adjusted right?? do you mean turn ratio? if so what's good?

Last edited by oldsxtc : 07-24-2007 at 06:54 PM.
 
Old 07-24-2007, 06:56 PM   #10
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Quote:
Originally Posted by 7T2Z28 View Post
You'll also want to stiffen the body mounts if you haven't already. I put a set of Energy Suspension red urethane mounts in my '80. Made a big difference in the body roll.

I can't say much for suspension, I haven't dove into that part yet.
i'm in the process now but thanks for the heads up
 
Old 07-24-2007, 07:32 PM   #11
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Quote:
Originally Posted by oldsxtc View Post
nvh what is this?
Noise/Vibration/Harshness
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Old 07-24-2007, 08:03 PM   #12
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Quote:
Originally Posted by 84 H/O View Post
Just out of curiosity what would you say is inexpensive for the 12" 1LE parts Luke? I'd probably need different spindles huh? I'm spooked about getting into bumpsteer issues so I'd like to avoid changing spindles until I read what's a foolproof replacement. Rather than hijack this thread is there somewhere you frequent that discusses the 12" upgrade you can direct me to? I searched here but came up empty.
Thanks!
I'll have to do some digging for the 1LE upgrade info. Check montecarloss.com. I'm headed to bed in a few, I'll look for some info tomorrow.

You use B-body spindles, 1LE rotors, and B-body calipers (or rare, expensive 1LE calipers) for the 12" brake swap. The spindles are taller, and move the steering arm mount in the wrong direction, making the bumpsteer worse.

What you CAN do is either use Baer tracker tie rod ends or drop the tie rod mounting point on the center drag link to tune out the bumpsteer. Here is one method of doing so: http://jeffd.50megs.com/bump_steer_mods_page.htm

Note that the spindle swap also bumps the track width of the front wheels out by .25" or so... I don't remember the exact number. You will also need a shorter upper control arm with the B-body spindle swap. UB machine makes an affordable tubular upper arm... or you can do as 2quik2see on this site did and modify the upper arm on your own.

For these reason, I will be running the Savitske tall ball joint with aluminum adjustable arms. No alignment shims, stock G-body spindle, no bumpsteer, and the roll center moved to a much better location.

Quote:
Originally Posted by oldsxtc View Post
can you explain the front roll center better i thought if you raised it you rolled more
nvh what is this?
f41 adjusted right?? do you mean turn ratio? if so what's good?
The roll center is a virtual point that the front of the car "rolls" around. Roll center height is a design concept that is chosen based on many tradeoffs (as everything is in suspension). If the roll center is too high, above ground, you get a force vector pointed upwards during roll, causing jacking. If its too far underground, the car will have a large roll moment (roll moment is the distance between the center of mass of the car and the roll center), causing the car to roll much more. The roll center is visualized from a front view of the car.

If you draw the front suspension, you use lines to extend the A-arms on one side of the car until they converge to a point (this is the instant center for that half of the suspension). From each of these instant center points, you draw a line from that to the same side tire contact patch. Where the two lines intersect, you have the front roll center. Here is a picture...



The stock G-body front roll center is like 4.5" or so under ground. The SC&C stage 2 kit moves it quite a bit closer to ground level.

Here's one definition: http://en.wikipedia.org/wiki/Roll_center If you google search "suspension roll center" or "roll center" you'll find much more information.

Like Andrew said, NVH is noise, vibration, harshness. Basically ride quality of the car. High priority in new street cars, very low priority in a race car. Its up to each individual car modder how high of a priority NVH is to him or her.

F41 is the GM RPO code for firm ride and handling suspension. This will be a box with a 12.7:1 ratio, and either 2.25 or 2.5 turns lock to lock (the f-body boxes are 2.25 IIRC, the G-body boxes are 2.5).

Clear as mud? lol. Suspension is definitely confusing at first.
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Old 07-24-2007, 10:50 PM   #13
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With all this tech info I really have nothing to add but to use eibach instead of moog. I've used both and will never again consider the moogs for anything but stock replacements. Bilsteins get thumbs up to, Koni also makes adj shocks for the g-body but I dont think many people have used them.
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Old 07-25-2007, 04:17 AM   #14
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Quote:
Originally Posted by 83hurstguy View Post
I'll have to do some digging for the 1LE upgrade info. Check montecarloss.com. I'm headed to bed in a few, I'll look for some info tomorrow.

You use B-body spindles, 1LE rotors, and B-body calipers (or rare, expensive 1LE calipers) for the 12" brake swap. The spindles are taller, and move the steering arm mount in the wrong direction, making the bumpsteer worse.

What you CAN do is either use Baer tracker tie rod ends or drop the tie rod mounting point on the center drag link to tune out the bumpsteer. Here is one method of doing so: http://jeffd.50megs.com/bump_steer_mods_page.htm

Note that the spindle swap also bumps the track width of the front wheels out by .25" or so... I don't remember the exact number. You will also need a shorter upper control arm with the B-body spindle swap. UB machine makes an affordable tubular upper arm... or you can do as 2quik2see on this site did and modify the upper arm on your own.

For these reason, I will be running the Savitske tall ball joint with aluminum adjustable arms. No alignment shims, stock G-body spindle, no bumpsteer, and the roll center moved to a much better location.



The roll center is a virtual point that the front of the car "rolls" around. Roll center height is a design concept that is chosen based on many tradeoffs (as everything is in suspension). If the roll center is too high, above ground, you get a force vector pointed upwards during roll, causing jacking. If its too far underground, the car will have a large roll moment (roll moment is the distance between the center of mass of the car and the roll center), causing the car to roll much more. The roll center is visualized from a front view of the car.

If you draw the front suspension, you use lines to extend the A-arms on one side of the car until they converge to a point (this is the instant center for that half of the suspension). From each of these instant center points, you draw a line from that to the same side tire contact patch. Where the two lines intersect, you have the front roll center. Here is a picture...



The stock G-body front roll center is like 4.5" or so under ground. The SC&C stage 2 kit moves it quite a bit closer to ground level.

Here's one definition: http://en.wikipedia.org/wiki/Roll_center If you google search "suspension roll center" or "roll center" you'll find much more information.

Like Andrew said, NVH is noise, vibration, harshness. Basically ride quality of the car. High priority in new street cars, very low priority in a race car. Its up to each individual car modder how high of a priority NVH is to him or her.

F41 is the GM RPO code for firm ride and handling suspension. This will be a box with a 12.7:1 ratio, and either 2.25 or 2.5 turns lock to lock (the f-body boxes are 2.25 IIRC, the G-body boxes are 2.5).

Clear as mud? lol. Suspension is definitely confusing at first.
ok i'm following you but you bring more ?'s to mind
what affect does the tire height (say 15" compared to 17")have on the roll center?
will the set-up you speak of change wanting a slight negative camber? or is that factored into the design of this set-up?

what affect does this have on the cars center of gravity? i.e. where does it move c.o.g. to? if i'm correct doesn't it lower it and bring it forward slightly?

I've been told that i need 4" backspacing on a 17" tire in order to have a 60's up front it seems to me that sends to much weight too far outboard of the centerline of the rim on hard turns already (could be wrong i'm not sure)
will this setup make it worse or compensate becuase of the new geometry?
or am i offbase? does that make sense?

if the c.o.g. is moved forward even though it's lowered won't it add more
g-force to the outside wheel on turns thus adding even more stress to the outside of the already offset centerline of the rim? if this is true it seems i'm
gonna seriously stress the metal possibly snapping something turning too hard and shifting all that weight? or am i way offbase?

i know that's a lot of ?'s but i live near the blueridge mtns. and i'm dying to take some winding roads to the limit but i don't want to introduce me or my car to the bottom of a ravine so i intend on getting it right the first time not going with a trial by error (or death)

thanks in advance
 
Old 07-25-2007, 04:32 AM   #15
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Are you talking about a 60 series tire?? Why are you using such a tall tire with the 17" rims?

If you run a 245/45ZR17 tire up front on a 17x8" rim with 4.5" backspacing, it will fit fine. Overall tire height is 25.68" tall and I believe stock, a g-body was around 26" which is generally what I try to stay close too.

In the past I've run the above wheel and tire, only with a 4" backspace and had issues with the tires hitting the inside of the front fenders on large dips/bumps in the road and that was at stock ride height. With the 4.5" backspace it should pull the wheel/tire inboard more and fix that problem, although you may run into frame/sway bar interference on tight turns.

On the rear I've run the same 17x8's with 4" backspacing and 255/45ZR17 tires and they fit perfectly.

Quote:
Originally Posted by oldsxtc View Post
I've been told that i need 4" backspacing on a 17" tire in order to have a 60's up front it seems to me that sends to much weight too far outboard of the centerline of the rim on hard turns already (
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Old 07-25-2007, 04:50 AM   #16
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Quote:
Originally Posted by 83hurstguy View Post

For these reason, I will be running the Savitske tall ball joint with aluminum adjustable arms. No alignment shims, stock G-body spindle, no bumpsteer, and the roll center moved to a much better location.
And just to clarify a little here, the stock spindle, if you keep it, needs modified then to run the LS1 or C5 front brakes.

Here's a picture of my spindles, the one on the left is modified for the C5/LS1 calipers, the one on the right is stock:



Essentially, you cut off the original caliper "ears" and then enlarge two of the original dust shield bolt holes. Then you buy a conversion bracket for either the LS1 or C5 brakes (which ever your using) and it bolts to the spindles at those locations.

But, something I found out is that the C5 brakes don't fit behind a 17" TTII wheel. So I had to use a special bracket made to adapt the C5 calipers to the LS1 12" rotor (thanks to Luke for finding that )

Figured I'd throw some of that in there in case you were wanting the big brakes also.




Quote:
The stock G-body front roll center is like 4.5" or so under ground. The SC&C stage 2 kit moves it quite a bit closer to ground level.
Here's what SC&C had on their website for comparison of a stock G-body, Stage I kit and Stage II kit:







They are only showing the stock roll center at 1.07. I'm not an engineer so a lot of this stuff is over my head. lol




Quote:
F41 is the GM RPO code for firm ride and handling suspension. This will be a box with a 12.7:1 ratio, and either 2.25 or 2.5 turns lock to lock (the f-body boxes are 2.25 IIRC, the G-body boxes are 2.5).
Check out Mike's Monte's for gear boxes. He's on Ebay a lot but sells stuff through is website also I believe. I just bought a rebuilt F41 box from him and its really nice. It was only around $140 I believe.
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Old 07-25-2007, 05:56 AM   #17
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so, I had an huge response just ready to post, and my work computer froze I can't waste any more time right now, so I'll try to get it done again later this morning. I'll get to your questions then, oldsxtc.

Thanks for the brake info, Andrew. This thread will be getting stickied down in the tech section after its all done...

In regards to the plots from Savitske, note that the suspension data is in 1" of dive (noted on the top of the chart) and appears to be turning. Also, seeing those numbers makes me wonder if they are for one of their "stage" kits... either way, the roll center has migrated from where it would be at stock ride height.
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Old 07-25-2007, 06:03 AM   #18
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Quote:
Originally Posted by BigBlockOlds View Post
Are you talking about a 60 series tire?? Why are you using such a tall tire with the 17" rims?

If you run a 245/45ZR17 tire up front on a 17x8" rim with 4.5" backspacing, it will fit fine. Overall tire height is 25.68" tall and I believe stock, a g-body was around 26" which is generally what I try to stay close too.

In the past I've run the above wheel and tire, only with a 4" backspace and had issues with the tires hitting the inside of the front fenders on large dips/bumps in the road and that was at stock ride height. With the 4.5" backspace it should pull the wheel/tire inboard more and fix that problem, although you may run into frame/sway bar interference on tight turns.

On the rear I've run the same 17x8's with 4" backspacing and 255/45ZR17 tires and they fit perfectly.
i haven't put on 17's yet i'm researching right now
at the moment i have 60 series on 15's and i have frame rub o tight right hand turn but its minimal wouldn't 45 series increase this and wouldn't 45's be way too big on the front ?
 
Old 07-25-2007, 10:09 AM   #19
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A 45 series tire just means that the sidewall height is 45% of the width of the tire.
So the width combined with the aspect ratio will determine how tall the tire is.

Example:

245/60R14

Section width: 9.64"
Overall diameter: 25.57"
Sidewall height: 5.78"

245/45R17

Section width: 9.64"
Overall diameter: 25.68"
Sidewall height: 4.34"

So the overall diameter only changed by .11" even though the rim size grew
3" because the aspect ratio was descreased to 45.

Another thing to remember is that for every one inch (I believe) of rim width that you change from what the tire manufacturer lists their tire as being measured on, the section width will increase/descrease by .40".

Also you can gain clearance around suspension components by going to the larger rim a lot of the time which can help things out.

Hope I explained that somewhat decent.

Check out http://www.1010tires.com/TireSizeCalculator.asp and plug in different size tires to see their effects
I also use www.tirerack.com to get a lot of the manufactuer specs on a tire to plug in and compare.

Quote:
Originally Posted by oldsxtc View Post
i haven't put on 17's yet i'm researching right now
at the moment i have 60 series on 15's and i have frame rub o tight right hand turn but its minimal wouldn't 45 series increase this and wouldn't 45's be way too big on the front ?
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Old 07-25-2007, 10:10 AM   #20
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Quote:
Originally Posted by 83hurstguy View Post
In regards to the plots from Savitske, note that the suspension data is in 1" of dive (noted on the top of the chart) and appears to be turning.
After I posted those plots I saw the 1" dive note and wondered if that is what caused the different numbers. Thanks.
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Old 07-25-2007, 10:26 AM   #21
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For a really great kinda basic setup, I can heartily recommend the Hotchkis kit. I have upper and lower rear control arms, braces, front and rear sway bars, and 1 1/2" lowering springs, all from Hotchkis, and the difference in the roll, handling, and ride is astounding. My '85 Cutlass now handles VERY well, and doesn't ride harshly at all. (though I see from previous posts on this thread there's a LOT more to consider! ) I will be getting the Hotchkis tubular front control arms installed this winter, which require the larger spindles and B-body rotors and calipers.
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Old 07-25-2007, 10:46 AM   #22
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Quote:
Originally Posted by BigBlockOlds View Post
A 45 series tire just means that the sidewall height is 45% of the width of the tire.
So the width combined with the aspect ratio will determine how tall the tire is.

Example:

245/60R14

Section width: 9.64"
Overall diameter: 25.57"
Sidewall height: 5.78"

245/45R17

Section width: 9.64"
Overall diameter: 25.68"
Sidewall height: 4.34"

So the overall diameter only changed by .11" even though the rim size grew
3" because the aspect ratio was descreased to 45.

Another thing to remember is that for every one inch (I believe) of rim width that you change from what the tire manufacturer lists their tire as being measured on, the section width will increase/descrease by .40".

Also you can gain clearance around suspension components by going to the larger rim a lot of the time which can help things out.

Hope I explained that somewhat decent.

Check out http://www.1010tires.com/TireSizeCalculator.asp and plug in different size tires to see their effects
I also use www.tirerack.com to get a lot of the manufactuer specs on a tire to plug in and compare.
thanks for the info and web link it was very helpful
 
Old 07-25-2007, 01:27 PM   #23
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Quote:
Originally Posted by 83hurstguy's edited response View Post
Pretty much the best G-body suspension parts come from Savitske... their website is www.scandc.com.

I plan to run their stage 2 front kit with adjustable tubular upper arms, and tall upper and lower ball joints. The kit will drop the car 0.75" in the front... combined with an Eibach 1" drop spring, the car will sit very nicely in the front.

For the rear suspension, DON'T USE POLY IN THE FOUR LINK (it binds). Anybody who suggests it is either a straight line guy or doesn't actually push the car handling-wise. I've felt my 4 link bind with Camaro 1LE bushings bind and snap oversteer, and its wicked. Savitske's sells some killer rear trailing arms (Currietracs), but they are pricey. Depending what kind of NVH you can tolerate, you might want to run a spherical bearing/rod end.
well, i run SC&C's stage 2 "plus" package on my 71 el camino, not a g-body but at least i can testify to the quality of the products, especially on the bumpsteer reduction. on the old stock suspension, driving over certain poor quality, uneven and potholed streets day in day out, would require me to grab the steering wheel and "correct" very much to stay in a straight line, but with the adjustable front UCAs now, i can drive over those same garbage roads, barely with a pinky on the wheel, and still go straight. and DO plan ahead for the drop ball joints, if you go with em. the drop made my large 245/60/15s rub in the front and i had to go with smaller tires.

as for poly bushings, well I guess i must be a straight line guy then i now have poly bushings on nearly every location possible in the rear, and it doesn't bother me, it's just noisy sometimes, but it peforms much better than stock. but how much of that is the overall improved suspension parts, and how much is the bushings, is hard for me to tell
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Old 07-26-2007, 05:45 AM   #24
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ok i'm following you but you bring more ?'s to mind
what affect does the tire height (say 15" compared to 17")have on the roll center?
will the set-up you speak of change wanting a slight negative camber? or is that factored into the design of this set-up?

what affect does this have on the cars center of gravity? i.e. where does it move c.o.g. to? if i'm correct doesn't it lower it and bring it forward slightly?
ok, back to my response from yesterday. sorry for the delay.

You'll still want negative static camber and positive caster. The shorter upper arm/taller spindle also provides a better camber curve... that is, as the wheel moves in bump, the camber should ideally be more negative. With the SC&C adjustable arms, you'll be able to add more caster easily to the front alignment settings.

Overall tire/wheel combo height will affect roll center, but it will also raise the center of mass of the car at the same time (unless you go about lowering the ride height, in which case roll center will change again as well). So raising the car will probably come with more negative handling effects than actual gains.

The only time COG/COM moves is if you change the ride height of the car or the actual weight distribution of the car. Not sure where you got the assumption the the COM is moving forward with the new suspension. It will not be. The Stage 2 kit lowers the car, so that lowers the COM... with another 1" drop from the springs you have a pretty good COM drop. We'll get to the relationship of COM and roll center again in a sec.


Quote:
Originally Posted by oldsxtc View Post
I've been told that i need 4" backspacing on a 17" tire in order to have a 60's up front it seems to me that sends to much weight too far outboard of the centerline of the rim on hard turns already (could be wrong i'm not sure)
will this setup make it worse or compensate becuase of the new geometry?
or am i offbase? does that make sense?
Don't worry about the rim, it will be fine. Scrub radius will change from stock slightly, as the center of the rim is moving further outboard. The scrub radius affects steering feel... it is defined as the contact patch defined between the angle of the kingpin (where it would intersect the ground) and the centerline of the wheel. A whole other discussion, lol... don't worry about it for now.

Quote:
Originally Posted by oldsxtc View Post
if the c.o.g. is moved forward even though it's lowered won't it add more
g-force to the outside wheel on turns thus adding even more stress to the outside of the already offset centerline of the rim? if this is true it seems i'm
gonna seriously stress the metal possibly snapping something turning too hard and shifting all that weight? or am i way offbase?
COM shouldn't be moved forward at all. Look at your car from the front. Imagine that the roll center exists right at ground level in the center of the car. Also imagine that the COM of the front of the car exists right between the front suspension, somewhere in the middle of the engine. All lateral force acts on the COM. However, the car wants to "roll" around the roll center, located at ground level.

Essentially, imagine a line connecting the roll center and the COM. This line is known as the "roll moment". Its kind of like a torque. The longer the line connecting the two points is, the greater the roll moment is, and the harder the car wants to roll in turns (and the greater the weight transfer across the front wheels). Just like breaking a bolt loose, the longer bar provides more torque to turn the bolt.

Remember that a stock G-body roll center is several inches below ground, and the COM is pretty high (at least compared to a sports car). Essentially, by lowering the car, you lower the COM. With a taller spindle height, you raise the roll center. You are reducing the roll moment in the front suspension, which in turn affects weight transfer. Lateral load transfer decreases the overall lateral grip of the car.
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Old 07-26-2007, 07:42 AM   #25
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i went to auto school back in '90 and went into mechanics wich eventually led into truck driving, i was essentially a parts swapper so i forgot all this stuff
but as i read your response it all (well most) came back to me like a refresher course
thanks for all your time
 
 


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