RIDE HEIGHT EFFECT ON SUSPENSION GEOMETRY
05-02-2004, 01:35 AM
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RIDE HEIGHT EFFECT ON SUSPENSION GEOMETRY
I’m bringing my car into a Corvette specialist Monday morning to (hopefully) take care of my bad handling. I’ve already attended to the steering system—no improvement there—and I’m hoping that the trailing arm bushings, (rusted) shims and cockeyed rear toe are the source of my problems. It’s gonna cost me plenty either way. I will actually be very happy if the work gets my handling back to where it was before I did all those things to improve my handling!
The threads on suspension geometry and bump-steer are a bit beyond my mechanical acumen. What I’m wondering is if the increased post-mod ride height (c. 1.5” f/r) is at all responsible for my car’s wandering at highway speeds. That is, would this change the suspension geometry to the extent that it alters handling that was previously acceptable? If so, I will have the shop tackle the front springs and rear spring bolts to get me back near stock. Doing custom relocation work is not an option at this juncture. Replacing my “Smart Struts” is not in the cards for now. Will it make any difference reconfiguring the settings via cam vs. rotating rods, or is it the same camber change either way.
By the way, thanks to N, RVR, UKP, TV, G and others who responded to my postings. Previous, related suspension related exchange below:
Corvette Forum: SO MANY MODS, SUCH BAD HANDLING (is technology passing our sharks by?)
Posted by: Runner81 at 7:30 PM 2/7/2004
Trying to figure out where I went wrong and what my next step should be. Or if
the fact that our suspensions were designed in the 50s is too much to overcome.
Lots of variables in my case. I’ve had my ‘81 six years, and am pretty sure it
was more stable at highway and higher speeds before the mods. It’s an automatic
that had the factory fiberglass monospring. In the first couple years, I
installed KYB gas shocks (the rear ones valved by VBP for the glass spring) and
the small factory (FE7) anti-sway bar (7/16”). There was a noticeable handling
improvement. With new rubber (Goodrich T/A 255s), I had the car up to Lime Rock
a couple of times, was comfortable with its handling at the limits, and held my
own against newer, “more advanced” iron.
Of course, like all Forum members, I wanted a lot more of a good thing, and
proceeded to have the following done over the next few years:
- VBP 460lb. front springs
- VBP 330lb. rear monospring
- Bilstein gas shocks all around
- VBP Smart Struts
- Ball joints and bushings replaced
- Computer alignment as close to advanced street specs as possible
I’m not sure where, when or how I went wrong, but the car now handles like a
boat on anything but flat, glassy-smooth road. At highway speeds, any dips,
however gradual, make it a challenge to keep in the lane. A vague, disconnected
jounce follows whenever the suspension compresses, causing the car to wander.
It’s just not enjoyable to drive at speed - forget about even considering 80+ on
any highway with the slightest bends or dips.
Do any of the following sound like possible causes?
- the ride height was way high after the mods (c. 1.5” all around) and I had the
front springs cut, effectively increasing their rate and changing the “ideal”
proportion between VBP’s GT front and rear springs.
- The height was a bit lopsided, so I had bit more of one coil cut than the
other. I also may have adjusted the longer spring bolts disproportionately to
compensate in back.
- My trailing arm shims are rusted/seized, so I’m unable to adjust the rear toe
to ideal specs (alignment guy tells me the rear of the car is basically rotated
very slightly to one side while all 4 wheels point straight down the road).
- The front caster is higher than the specs call for, but this wasn’t
necessarily unitentional. The book “How To Make Your Car Handle Better” says the
higher the caster, the better the car will track, but at the cost of steering
effort. With P/S, this obviously wasn’t a consideration.
- Also alignment-related: first time in the shop after the mods, they adjusted,
adjusted and adjusted, but kept getting further away from the desired specs.
Turned out their computer was way off calibration. I had to bring my car back
after they recalibrated. I can verify that they tweaked the car as close to my
specs as possible, at least according to their equipment. Still, I wonder…
- Finally, fact is, every year car suspensions get more sophisticated. The
average new car rides smoothly and stays comfortably in lane at 100 mph, not to
even mention C-5s, Porsches, BMWs and the like. Is technology slowly passing our
sharks by? Our rear suspension was designed in the late 50s, and the front was
put together from Chevy parts already in existence. Have I gotten so used to
driving newer cars over the years that it’s dulling my senses, and my Vette only
“seems” to handle like a ‘63 Bonneville?
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: MN-Brent at 8:02 PM 2/7/2004
1)Could it be that your body shims were shot, making the ride height adjustment
setup the chassis uneven to the road?
2)How old are the tires now? Internal belts could be giving way.
3)Rear trailing arm bushings and differential mounts OK?
4)Front sway bar mismatch to FE7 rear and condition of front OEM sway bar
bushings?
I would be concerned about having to make offset changes on one side to
compensate for even ride height.
My guess for a fix is;
1)be sure all rear bushings are updated (trailing arm, diff mounts, sway bar,
spring ends),
2)check condition and update the body mount bushings if required (when in doubt,
swap em out)
3)install new front coils (or even out the existing coil count)
4)re-adjust ride height front and rear
5)re-align.
What a pain. Sounds like you already done lots. I think its all about obtaining
a neutral feel and one bad part can upset this effort.
Brent...
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: DaveL82 at 8:52 PM 2/7/2004
check the idler arm for excessive play. Can cause car to change track when under
suspension compression.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: Turbo-Jet at 8:58 PM 2/7/2004
sounds like you want the ride of a touring car and the handling of a racecar.
you may have to compromise on some of your alignment specs or wheel rates.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: norvalwilhelm at 9:18 PM 2/7/2004
I’m not sure where, when or how I went wrong, but the car now handles like a
boat on anything but flat, glassy-smooth road. At highway speeds, any dips,
however gradual, make it a challenge to keep in the lane. A vague, disconnected
jounce follows whenever the suspension compresses, causing the car to wander.
ItÂ’s just not enjoyable to drive at speed - forget about even considering 80+
on any highway with the slightest bends or dips.
You are not new here but have you been following some of my posts on bump
steer???
This is how bump steer works. The front wheels have a mind of their own. Every
dip or bump causes a steering input that doesn't come from the steering wheel.
Just installing the 460 pound springs really increases the bump steer problem.
I once tested a stock C3 and got 2.25 inches of bump steer. That car was
uncontrollable.
My bump is gone and at 100 mph it will match my wife's new Bonneville SSEI
supercharged for smoothness.
All C3's suffer from bump steer, most just install the 460/550 springs and
declare the problem solved, Why not just weld the suspension solid and it will
solve the problem, might ride like a tank but hey no bump steer.
I set my specs at minus .75 camber and 5 degrees positive caster. Toe in or
out?? Still don't know which is better/correct.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Turbo-Jet)
Posted by: motown 71 at 9:21 PM 2/7/2004
WOW ! OK Now I'm concerned.......
I have my suspension out now for the ball joints rod ends bushings springs...
Had it apart for a while now whlie doing other things, nice with all that space,
I am now praying it all goes back together and "acts" nicely !!!
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: mrvette at 10:05 PM 2/7/2004
Runner, is the search was working on this site, you could find all the vast
amount of discussions among Norval, Pete79L82, and Me, and a few others....
wide ranging all over the front and rear setups on stock sharks....
thing is obvioulsly they designed way back in the stone age....well maybe a few
years above Roman Charriots, but only a few.....
so anyway, the camber changes in the front are not desirable, newer tires and
rims being larger make the sidewalls more responsive to the input to your
steering....I think that steering valve is the main source of the 'problems' in
most sharks with a 'few' mods done,.....your car is about the same as mine
really....EXCEPT....I have replaced that entire what I consider to be antequated
old drag link and recirculating ball type input....
having converted my car to rack/pinon steering, I found the thing much better on
the high speed highway wander problem....and also found that taking off the
5/8-3/4 inch rear sway bar, along with reducing the 1/25 inch front bar down to
the lower performance stock size those two changes greatly improved the ride
quality at very little if any decrease in handling...MY opinion....not track
tested....
but the primary differance between our cars is I have 275/50/17 in rear, and
255/50/17 in front....large as I can get.....the MOST differance I found some
years ago was in the tires, the rest of this is just tuning....
HOWEVER, when I did my rack/pin conversion, I found I had the inner tie rod ends
too low, so with suggension from Pete there I finally raised them , and the
handling, bump steer did greatly improve...
several things to look at, the frame is number ONE, the rear suspension is
number two...that means the differential also, as well as the T-arm bushings in
the frame....number 3 is the frame again....
wonder if your car has been hit...that can explain a LOT on frames and body
leaning....look close...
tell you what, I had what I consider a way premature lower ball joint
failure...you may want to look there again....
then again, Norval has a suggestion of increasing the height of the
spindles...to change the reaction of the suspension to pull the top of the tire
IN on loading/force which plants a radial tire more in tune with the tread
requirements, but would roll an old bias tire right off the rim....
the more we tinker with these cars, the more demanding they become...my
experience anyway....and it's a huge start with TIRES.....
learning a LOT....
GENE
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: redvetracr at 10:10 PM 2/7/2004
It looks like your telling us your rear toe is off, WAY OFF, if everything is
"shifted to one side" your car is going down the street (or track) sideways.
First on my list would be trailing arm bushings, shims and a correct alignment
(and while your there EVERY other piece of rubber in the car).
...redvetracr
[Modified by redvetracr, 4:11 PM 2/7/2004]
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (redvetracr)
Posted by: redvetracr at 10:14 PM 2/7/2004
PS: I have yet to see a fast Corvette vintage racer with a fiberglass rear
spring.
PS:ll if you want C-5 or Porsche handling you need to buy a C-5 or a Porsche.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: turtlevette at 11:17 PM 2/7/2004
1)you definitely DONT want to preload the rear spring unevenly at the rear to
make up for an apparent body height difference from side to side. I did that
years ago and the first time i took it out i knew it was wrong.
2)BFG tires may look cool but they are CRAP. Let me repeat that CRAP. If you
want to run the roadcourses you need a better tire. Those BFGs have no material
in the sidewalls and handle like you are riding on Jello. The Eagle GTs may be
better, i run the firestones and they are ok. Pirelli makes the scorpion tire
with black sidewall (yuck) but its supposed to be a handling tire. You might
want to think about 17" tires if you are serious.
3)Remove the smart strut bracket and put the stock back in or at least adjust it
to the uppermost position that puts it back in stock location. You want more
negative camber as you lean into a turn not less.
4)Forget factory alignment specs and give yourself more negative camber all
around and a little more toe in. Toe in reduces the wandering feel on worn
roads. Caster is uesless other than it helps little ole ladies return the wheel
to straight up after going around a corner at low speed.
5)Make sure the rear is as low as practical. These new fiberglass springs can
cause the thing to ride like a 4X4 in the back. You are right in that you want
to keep the car low, providing a lower center of gravity. Pretty basic.
6) C3 are always going to be a little edgy and there's nothing you can do about
that. I would argue it takes a lot more skill to flog a C3 around a road course
than any new car. My instructor drove mine around the course and it scared him
because he was used to rack and pinion precision and such. He signed my solo
license because he thought i handled the car so well.
[Modified by turtlevette, 6:18 PM 2/7/2004]
7) if the front end feels light at speed you might have a damaged or improperly
installed air dam. Maybe there is something better that could be installed.
8) we need to get a C3 handling discussion sticky or subsection going. There is
the autocross and roadrace sect, but those guys don't wanna talk C3s. I need
info on how to get my pig faster too. There are people here with the knowlege to
help us like norval and redvetteracer but it seems like these very usefull
threads get lost in all the noise.
[Modified by turtlevette, 6:38 PM 2/7/2004]
[Modified by turtlevette, 6:41 PM 2/7/2004]
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (norvalwilhelm)
Posted by: Darrell's 68 at 11:45 PM 2/7/2004
Norvalwilhelm, how do you have your C3 suspension set up? What spring rates,
type of rear spring, sway bar sizes, tires/rims, etc are you using that give you
the least amount of bump steer and 100mph smoothness? I
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Darrell's 68)
Posted by: norvalwilhelm at 11:59 PM 2/7/2004
Norvalwilhelm, how do you have your C3 suspension set up? What spring rates,
type of rear spring, sway bar sizes, tires/rims, etc are you using that give you
the least amount of bump steer and 100mph smoothness? I
I am running coil overs all around this year. Last year I ran a steel 140 pound
spring on the back and morosso 280 pound springs on the front along with the
stock sway bar on the front and no rear sway bar.
Bump steer is not affected by springs but by the proper slope of the tie rods
and the correct length of tie rod.
I believe in soft springs to follow the contour of the road and eliminate bump
steer through modification. I finally eliminated bump steer. I originally
started at over 2 inches , worked it down to 5/16 of an inch then down to under
.010 over 7 inches of travel.
I am using pro shock all around, different rating of coarse, 250 pound rear
spring because of their location/ further up the trailing arm, 350 pound fronts.
I still have the 15 inch tires, 255 front and 305 rear.
I plan on switching to 18 or even 20 but the price of tires is rediculous. $700
plus per 20 inch tire vs my $85 BFG 305"s.
Tires are consumable and I usually sell the old every 2nd year and start fresh.
My big improvement in steering came from a totally rebuilt box and eliminating
the bump steer.
To achieve less then .010 bump I had to drop my outer tie rod 1.830 inches. This
involves welding an extension on the steering arm, no spacer could stand this
much spacing so it must be welded for stability.
I also had to increase my tie rods by about 3 inches and this involved a new
center link.
Double click to enlarge
Just an overall shot of the gage needed to accurately measure bump steer
Double click to enlarge
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Darrell's 68)
Posted by: Dk Met Grn 80 L82 at 12:18 AM 2/8/2004
I have been going through my car replacing all the rubber under the car. I did
all the front last year, great ride/handling improvement. In the fall I changed
the rear spring, rear sway bushings, and the power steering control valve at the
same time. Noticably poor handling after the changes. Not sure which one caused
the problem, but I am guessing the rear spring. Rear spring also created ride
height problem. Lowered the car by using 8" bolts, now 29" fender height, still
1" too high. Plan to order a composite spring next week but not sure if the TRW
340 or VB 300 would be better. After I get set on a final spring I am hoping
another alignment will improve handling back to where it was.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: ndirishr1 at 12:40 AM 2/8/2004
I totally redid the bottom end of my '68 a couple of years ago. It was still
mostly stock and badly won and handled like a top heavy boat load of jello. I
used pretty much the same parts you described with poly graphite bushings. It
handles much better now but it'll never handle like a C4 or C5. I thought about
switching to the front C4 type suspension package but decided to stay more
stock. That's an option though.
The threads on suspension geometry and bump-steer are a bit beyond my mechanical acumen. What I’m wondering is if the increased post-mod ride height (c. 1.5” f/r) is at all responsible for my car’s wandering at highway speeds. That is, would this change the suspension geometry to the extent that it alters handling that was previously acceptable? If so, I will have the shop tackle the front springs and rear spring bolts to get me back near stock. Doing custom relocation work is not an option at this juncture. Replacing my “Smart Struts” is not in the cards for now. Will it make any difference reconfiguring the settings via cam vs. rotating rods, or is it the same camber change either way.
By the way, thanks to N, RVR, UKP, TV, G and others who responded to my postings. Previous, related suspension related exchange below:
Corvette Forum: SO MANY MODS, SUCH BAD HANDLING (is technology passing our sharks by?)
Posted by: Runner81 at 7:30 PM 2/7/2004
Trying to figure out where I went wrong and what my next step should be. Or if
the fact that our suspensions were designed in the 50s is too much to overcome.
Lots of variables in my case. I’ve had my ‘81 six years, and am pretty sure it
was more stable at highway and higher speeds before the mods. It’s an automatic
that had the factory fiberglass monospring. In the first couple years, I
installed KYB gas shocks (the rear ones valved by VBP for the glass spring) and
the small factory (FE7) anti-sway bar (7/16”). There was a noticeable handling
improvement. With new rubber (Goodrich T/A 255s), I had the car up to Lime Rock
a couple of times, was comfortable with its handling at the limits, and held my
own against newer, “more advanced” iron.
Of course, like all Forum members, I wanted a lot more of a good thing, and
proceeded to have the following done over the next few years:
- VBP 460lb. front springs
- VBP 330lb. rear monospring
- Bilstein gas shocks all around
- VBP Smart Struts
- Ball joints and bushings replaced
- Computer alignment as close to advanced street specs as possible
I’m not sure where, when or how I went wrong, but the car now handles like a
boat on anything but flat, glassy-smooth road. At highway speeds, any dips,
however gradual, make it a challenge to keep in the lane. A vague, disconnected
jounce follows whenever the suspension compresses, causing the car to wander.
It’s just not enjoyable to drive at speed - forget about even considering 80+ on
any highway with the slightest bends or dips.
Do any of the following sound like possible causes?
- the ride height was way high after the mods (c. 1.5” all around) and I had the
front springs cut, effectively increasing their rate and changing the “ideal”
proportion between VBP’s GT front and rear springs.
- The height was a bit lopsided, so I had bit more of one coil cut than the
other. I also may have adjusted the longer spring bolts disproportionately to
compensate in back.
- My trailing arm shims are rusted/seized, so I’m unable to adjust the rear toe
to ideal specs (alignment guy tells me the rear of the car is basically rotated
very slightly to one side while all 4 wheels point straight down the road).
- The front caster is higher than the specs call for, but this wasn’t
necessarily unitentional. The book “How To Make Your Car Handle Better” says the
higher the caster, the better the car will track, but at the cost of steering
effort. With P/S, this obviously wasn’t a consideration.
- Also alignment-related: first time in the shop after the mods, they adjusted,
adjusted and adjusted, but kept getting further away from the desired specs.
Turned out their computer was way off calibration. I had to bring my car back
after they recalibrated. I can verify that they tweaked the car as close to my
specs as possible, at least according to their equipment. Still, I wonder…
- Finally, fact is, every year car suspensions get more sophisticated. The
average new car rides smoothly and stays comfortably in lane at 100 mph, not to
even mention C-5s, Porsches, BMWs and the like. Is technology slowly passing our
sharks by? Our rear suspension was designed in the late 50s, and the front was
put together from Chevy parts already in existence. Have I gotten so used to
driving newer cars over the years that it’s dulling my senses, and my Vette only
“seems” to handle like a ‘63 Bonneville?
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: MN-Brent at 8:02 PM 2/7/2004
1)Could it be that your body shims were shot, making the ride height adjustment
setup the chassis uneven to the road?
2)How old are the tires now? Internal belts could be giving way.
3)Rear trailing arm bushings and differential mounts OK?
4)Front sway bar mismatch to FE7 rear and condition of front OEM sway bar
bushings?
I would be concerned about having to make offset changes on one side to
compensate for even ride height.
My guess for a fix is;
1)be sure all rear bushings are updated (trailing arm, diff mounts, sway bar,
spring ends),
2)check condition and update the body mount bushings if required (when in doubt,
swap em out)
3)install new front coils (or even out the existing coil count)
4)re-adjust ride height front and rear
5)re-align.
What a pain. Sounds like you already done lots. I think its all about obtaining
a neutral feel and one bad part can upset this effort.
Brent...
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: DaveL82 at 8:52 PM 2/7/2004
check the idler arm for excessive play. Can cause car to change track when under
suspension compression.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: Turbo-Jet at 8:58 PM 2/7/2004
sounds like you want the ride of a touring car and the handling of a racecar.
you may have to compromise on some of your alignment specs or wheel rates.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: norvalwilhelm at 9:18 PM 2/7/2004
I’m not sure where, when or how I went wrong, but the car now handles like a
boat on anything but flat, glassy-smooth road. At highway speeds, any dips,
however gradual, make it a challenge to keep in the lane. A vague, disconnected
jounce follows whenever the suspension compresses, causing the car to wander.
ItÂ’s just not enjoyable to drive at speed - forget about even considering 80+
on any highway with the slightest bends or dips.
You are not new here but have you been following some of my posts on bump
steer???
This is how bump steer works. The front wheels have a mind of their own. Every
dip or bump causes a steering input that doesn't come from the steering wheel.
Just installing the 460 pound springs really increases the bump steer problem.
I once tested a stock C3 and got 2.25 inches of bump steer. That car was
uncontrollable.
My bump is gone and at 100 mph it will match my wife's new Bonneville SSEI
supercharged for smoothness.
All C3's suffer from bump steer, most just install the 460/550 springs and
declare the problem solved, Why not just weld the suspension solid and it will
solve the problem, might ride like a tank but hey no bump steer.
I set my specs at minus .75 camber and 5 degrees positive caster. Toe in or
out?? Still don't know which is better/correct.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Turbo-Jet)
Posted by: motown 71 at 9:21 PM 2/7/2004
WOW ! OK Now I'm concerned.......
I have my suspension out now for the ball joints rod ends bushings springs...
Had it apart for a while now whlie doing other things, nice with all that space,
I am now praying it all goes back together and "acts" nicely !!!
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: mrvette at 10:05 PM 2/7/2004
Runner, is the search was working on this site, you could find all the vast
amount of discussions among Norval, Pete79L82, and Me, and a few others....
wide ranging all over the front and rear setups on stock sharks....
thing is obvioulsly they designed way back in the stone age....well maybe a few
years above Roman Charriots, but only a few.....
so anyway, the camber changes in the front are not desirable, newer tires and
rims being larger make the sidewalls more responsive to the input to your
steering....I think that steering valve is the main source of the 'problems' in
most sharks with a 'few' mods done,.....your car is about the same as mine
really....EXCEPT....I have replaced that entire what I consider to be antequated
old drag link and recirculating ball type input....
having converted my car to rack/pinon steering, I found the thing much better on
the high speed highway wander problem....and also found that taking off the
5/8-3/4 inch rear sway bar, along with reducing the 1/25 inch front bar down to
the lower performance stock size those two changes greatly improved the ride
quality at very little if any decrease in handling...MY opinion....not track
tested....
but the primary differance between our cars is I have 275/50/17 in rear, and
255/50/17 in front....large as I can get.....the MOST differance I found some
years ago was in the tires, the rest of this is just tuning....
HOWEVER, when I did my rack/pin conversion, I found I had the inner tie rod ends
too low, so with suggension from Pete there I finally raised them , and the
handling, bump steer did greatly improve...
several things to look at, the frame is number ONE, the rear suspension is
number two...that means the differential also, as well as the T-arm bushings in
the frame....number 3 is the frame again....
wonder if your car has been hit...that can explain a LOT on frames and body
leaning....look close...
tell you what, I had what I consider a way premature lower ball joint
failure...you may want to look there again....
then again, Norval has a suggestion of increasing the height of the
spindles...to change the reaction of the suspension to pull the top of the tire
IN on loading/force which plants a radial tire more in tune with the tread
requirements, but would roll an old bias tire right off the rim....
the more we tinker with these cars, the more demanding they become...my
experience anyway....and it's a huge start with TIRES.....
learning a LOT....
GENE
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: redvetracr at 10:10 PM 2/7/2004
It looks like your telling us your rear toe is off, WAY OFF, if everything is
"shifted to one side" your car is going down the street (or track) sideways.
First on my list would be trailing arm bushings, shims and a correct alignment
(and while your there EVERY other piece of rubber in the car).
...redvetracr
[Modified by redvetracr, 4:11 PM 2/7/2004]
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (redvetracr)
Posted by: redvetracr at 10:14 PM 2/7/2004
PS: I have yet to see a fast Corvette vintage racer with a fiberglass rear
spring.
PS:ll if you want C-5 or Porsche handling you need to buy a C-5 or a Porsche.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: turtlevette at 11:17 PM 2/7/2004
1)you definitely DONT want to preload the rear spring unevenly at the rear to
make up for an apparent body height difference from side to side. I did that
years ago and the first time i took it out i knew it was wrong.
2)BFG tires may look cool but they are CRAP. Let me repeat that CRAP. If you
want to run the roadcourses you need a better tire. Those BFGs have no material
in the sidewalls and handle like you are riding on Jello. The Eagle GTs may be
better, i run the firestones and they are ok. Pirelli makes the scorpion tire
with black sidewall (yuck) but its supposed to be a handling tire. You might
want to think about 17" tires if you are serious.
3)Remove the smart strut bracket and put the stock back in or at least adjust it
to the uppermost position that puts it back in stock location. You want more
negative camber as you lean into a turn not less.
4)Forget factory alignment specs and give yourself more negative camber all
around and a little more toe in. Toe in reduces the wandering feel on worn
roads. Caster is uesless other than it helps little ole ladies return the wheel
to straight up after going around a corner at low speed.
5)Make sure the rear is as low as practical. These new fiberglass springs can
cause the thing to ride like a 4X4 in the back. You are right in that you want
to keep the car low, providing a lower center of gravity. Pretty basic.
6) C3 are always going to be a little edgy and there's nothing you can do about
that. I would argue it takes a lot more skill to flog a C3 around a road course
than any new car. My instructor drove mine around the course and it scared him
because he was used to rack and pinion precision and such. He signed my solo
license because he thought i handled the car so well.
[Modified by turtlevette, 6:18 PM 2/7/2004]
7) if the front end feels light at speed you might have a damaged or improperly
installed air dam. Maybe there is something better that could be installed.
8) we need to get a C3 handling discussion sticky or subsection going. There is
the autocross and roadrace sect, but those guys don't wanna talk C3s. I need
info on how to get my pig faster too. There are people here with the knowlege to
help us like norval and redvetteracer but it seems like these very usefull
threads get lost in all the noise.
[Modified by turtlevette, 6:38 PM 2/7/2004]
[Modified by turtlevette, 6:41 PM 2/7/2004]
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (norvalwilhelm)
Posted by: Darrell's 68 at 11:45 PM 2/7/2004
Norvalwilhelm, how do you have your C3 suspension set up? What spring rates,
type of rear spring, sway bar sizes, tires/rims, etc are you using that give you
the least amount of bump steer and 100mph smoothness? I
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Darrell's 68)
Posted by: norvalwilhelm at 11:59 PM 2/7/2004
Norvalwilhelm, how do you have your C3 suspension set up? What spring rates,
type of rear spring, sway bar sizes, tires/rims, etc are you using that give you
the least amount of bump steer and 100mph smoothness? I
I am running coil overs all around this year. Last year I ran a steel 140 pound
spring on the back and morosso 280 pound springs on the front along with the
stock sway bar on the front and no rear sway bar.
Bump steer is not affected by springs but by the proper slope of the tie rods
and the correct length of tie rod.
I believe in soft springs to follow the contour of the road and eliminate bump
steer through modification. I finally eliminated bump steer. I originally
started at over 2 inches , worked it down to 5/16 of an inch then down to under
.010 over 7 inches of travel.
I am using pro shock all around, different rating of coarse, 250 pound rear
spring because of their location/ further up the trailing arm, 350 pound fronts.
I still have the 15 inch tires, 255 front and 305 rear.
I plan on switching to 18 or even 20 but the price of tires is rediculous. $700
plus per 20 inch tire vs my $85 BFG 305"s.
Tires are consumable and I usually sell the old every 2nd year and start fresh.
My big improvement in steering came from a totally rebuilt box and eliminating
the bump steer.
To achieve less then .010 bump I had to drop my outer tie rod 1.830 inches. This
involves welding an extension on the steering arm, no spacer could stand this
much spacing so it must be welded for stability.
I also had to increase my tie rods by about 3 inches and this involved a new
center link.
Double click to enlarge
Just an overall shot of the gage needed to accurately measure bump steer
Double click to enlarge
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Darrell's 68)
Posted by: Dk Met Grn 80 L82 at 12:18 AM 2/8/2004
I have been going through my car replacing all the rubber under the car. I did
all the front last year, great ride/handling improvement. In the fall I changed
the rear spring, rear sway bushings, and the power steering control valve at the
same time. Noticably poor handling after the changes. Not sure which one caused
the problem, but I am guessing the rear spring. Rear spring also created ride
height problem. Lowered the car by using 8" bolts, now 29" fender height, still
1" too high. Plan to order a composite spring next week but not sure if the TRW
340 or VB 300 would be better. After I get set on a final spring I am hoping
another alignment will improve handling back to where it was.
Post Title: Re: SO MANY MODS, SUCH BAD HANDLING (Runner81)
Posted by: ndirishr1 at 12:40 AM 2/8/2004
I totally redid the bottom end of my '68 a couple of years ago. It was still
mostly stock and badly won and handled like a top heavy boat load of jello. I
used pretty much the same parts you described with poly graphite bushings. It
handles much better now but it'll never handle like a C4 or C5. I thought about
switching to the front C4 type suspension package but decided to stay more
stock. That's an option though.
05-02-2004, 02:07 AM
#2
Melting Slicks
Re: RIDE HEIGHT EFFECT ON SUSPENSION GEOMETRY (Runner81)
Started reading your post and got a headache :crazy: They really need to fix that weird 'A' thing when you paste from Word.
If the rear is out of alingment you will feel it a lot more than if the front was out. I guess the solution is to find a good honest shop that work with you.
Good luck
If the rear is out of alingment you will feel it a lot more than if the front was out. I guess the solution is to find a good honest shop that work with you.
Good luck
