Plastic Fantastic 2

[69427]

This is the answer I like best:

If the answer was mid to low speed then one of the following options can be used to solve the understeer:
1) Increase caster angle
2) Increase front toe out
3) Reduce front ride height
4) Check tyre pressures with a gauge to ensure that the tyres are operating within recommended hot temperatures. Increase or decrease pressures accordingly.
5) Check tyre temperatures with a tyre pyrometer and make sure that the temperatures are distributed by between 10 and 15 degrees Celsius between edges with the inside being the hottest. If the inside is too hot then increase positive camber. If the outside is too hot then increase negative camber.

From your description, it sounds like the problem is more acute when the wheels are turned fairly sharply (low speed 180 at the end of a slalom) which would cause me to look at Ackermann. Do you have a situation where you have drastically increasing or decreasing Ackermann as the wheels are turned? This can be partially solved by increasing or decreasing static toe, but may hurt in other areas. I would try to duplicate the turn-in (set the wheel turn angle and ride compression/height) and check the total toe between the front wheels.

Pappy

I agree with your comments. When I first put the C4 suspension under my '69 I had a helluva bad understeer in the tight corners. After a lot of head scratching I relocated the steering rack to increase the Ackerman, and also got rid of the toe-in, and occasionally play with a touch of toe-out.

 

[phantomjock]

Following Pappy's lead -- but I like simple first:

1. Reduce Front Ride height. Not only will it help, overall it will benefit on any long straight. One less thing to change track side.
2. Set more Caster. If need be, go to the max and then back off. Not always an easy adjustment, but will improve tracking. Don't go so far the steering gets too heavy at parking lot speed.
3. You've got to use a pyrometer. Most important thing a crew can do for you is check the tires (right after checking your belts)!​

Ive attached 2 images. I hope all can find them useful. (I claim no credit - just always on the hunt.)

This one (Alignment specs) won't "fit" a C4/C5+ front dimensions:


But, note the variation between street/ax/race, front/rear, and the several sources. What it really shows is the integration of the various parameters that is required. Unfortunately, they all lack some important details; track width F/R, spring rates, cross weight, F/R weight, and rake. Change one, means change another.

The fancy graphic
is one that you can walk through and see where you want to go.

F/R balance/bias is important as it sets the potential for rotation (yaw) up to be stable, consistent - or not. Conservation of momentum and yaw rates. Not just weight, but tire profile, springs, ARB, etc., and what you do with the "stick and rudder!"

Cheers - Jim

 

[SuperBuickGuy]

very helpful.

I've struggled with what alignment specs to use. I need to spend more time here considering what differences (if any) there are between the C3 recommendations and the C5 (which is what the front suspension is)..... so much to learn.

From the Z06 Forum
Here are my recommendations:
Objectives:
- Reduce factory understeer AMAP and get car as neutral as possible.
- Better, later and shorter Braking
- More front grip
- Better Turn IN
- Better Steering Response
- Better Steering Modulation
- Better Rear grip and Acceleration
- Better handling
- Increase corner entry speed, mid-corner speed and higher corner exit speed.
Retain some power oversteer.

ORDER: Lower AMAP, Corner weigh, Corner weight, set Ride Height and Rake (1/2" - 3/4"), Get F/R weight ratio as close to 50/50 as Possible (=< 2%).
MOST IMPORTANT SPEC: Cross Corner Weight % Difference as close to 50/50as possible (=< 1%). Set Camber, then Caster, then Toe.

AutoX Alignment:

FRONT:
Camber = -2.4*
Caster = As much positive as possible without sacrificing Camber
Toe = Toe OUT, 1/16" - 1/8" Each, !/4" Total Toe OUT Max.

REAR:
Camber = -1.5*
Toe = Toe IN, 1.8" - 1/4" Each, 1/2" Total Toe IN Max.

The alignment specs are only a starting point and should be adjusted after proper tire inflation pressures air selected and the tires are "read" using a probe type Pyrometer.

 

[SuperBuickGuy]

then there's this advice.... what kills me is I'm so inexperienced that I've no context to judge.... ah well, it's also fascinating so into the deep end I dive

1. For AutoX you should corner weigh, corner weight, Check the Cross Corner weight % Difference and align the car
- After all mods possible have been done
- after lowering
- with the driver or an equilivant driver weight in the drivers seat
- 1/8 tank of gas, 1/4 max load
-Initially with both the front and rear swaybars disconnected
- and if using adjustable shocks; with the Bump setting set on the next to last SOFT setting and just after the car was driven or 'bounced".
- Align & set ride height with the race wheels and tires on the car
- remove all unnecessary weight from the car, this includes:
- empty the windshield washer tank
- run a minimum level in the coolant overflow tank and run a 70/30 water coolant ratio
- with 1 qt additional oil added for C5 Z06's
- remove everything from the glove box and center console
- remove the floor mats
- remove the tire inflation kit
- remove the OEM Ti exhaust and install a Corsa "Z Series" Titanium Race Exhaust WITHOUT the optional mufflers
- remove the plastic coil covers.

2. When installing allowable mods such as a hand held Fire Extinguisher or Fire Suppression System mount them on the RIGHT side of the car as LOW and as far REARWARD as practicle.
- when installing a 6 point drivers restraint belt such as "clip-in" Hardbar or Brey Krause mounts, install the right side passenger mounts as well but remove passenger belts for AutoX competition.

3. Attatch the sway bars and recheck the Cross Corner Weight % Difference
- Minimally adjust the ride height at each corner to bring the CCW%D as close to 50/50 and within 1%. Should be like 50.5%F/49.5%R
The F/R ratio should be within 2%, say 51.2%F/48.8%R max.
- If you have installed an allowable front sway bar you should have also installed adjustable sway bar end links. These initially should be installed at their shortest adjustment. If you need more rear corner weight to bring the F/R ratio and the CCW%D into spec then you can minimally lengthen each front end link. This effectively preloads the bar and shifts weight to the rear. BE SURE TO INITIALLY ADJUST BOTH SIDES EQUALLY.

4. You could also install a higher rate or higher recurved front spring or a low rate or lower recurved rear spring but this would be disallowed and cheating in SS. It also shows the limitations of the transverse spring .....you can not independantly change a corner's spring rate.

As you can see there are some very limited things you can do in SS to lighten the car and shift weight around.
After all the static weight is shifted as much as possible the left front will still be the heviest corner and the right rear the lightest.
Unfortunetly on the Z06 the only other way in SS to adjust corner weights is by tweaking the ride heights and or adjusting the front sway bar end links if you have installed them.

NOTE: as from the factory the Z06 is pretty close to a 50/50 F/R ratio and a 50/50 CCW%D as possible...but it is possible to get it dead on with a little tweaking.

ABOVE ALL, THE CROSS CORNER WEIGHT % DIFFERENCE IS THE MOST IMPORTANT SPEC.

The advantage of a coil over system is that you CAN adjust individual corner weight INDEPENDANT of Static Ride Height. By simply adjusting the spring collar thus adjusting the ride height on a coil over spring perch you are essentially doing the same thing as you are on an OEM Z06 when you adjust ride height using the spring perch bolts. You are taking the easy way out and in effect defeating the advantage.

The proper way to adjust corner weights in a coil over system is to:
1. Set the Static Ride Height and Rake
2. Corner Weigh the car
3. Corner Weight the car by physically moveing things around to effect the corner weight(s), CCW%D
4. Change each individual corner spring as to appropriate Spring RATE to match each individual Corner Weight*

* NOTE: EACH car is different and actually each corner is different...that is why I do not recommend the purchase of a generic coil over system and especially one built on non-adjustable shocks. You are using someone elses spring setting(s) , which while being close, may not be right for your car ...AND as each coil spring should be tailored to each individual corner; each shock needs to be adjusted to each individual spring (rate) to properly dampen the spring harmonics. Non revalvable shocks can not do this and non adjustablke shocks can't do it properly.
Each coil spring needs to be tuned to the individual corner and each shock needs to be tuned to each individual spring at least in Compression and Rebound (each individually). Shock selection is another topic.

 

[SuperBuickGuy]

Today, you should see numbers from Ackerman. I lost my slide plates, so I have to make due with what's coming today.... don't laugh too hard :crutches:


I'm using 2004 Z06 specs as my search criteria. My wheelbase is 7" shorter (which is why the Ackerman measurement), but the width and range of adjustment are basically Z06 stock ....

for the rear, Camaro suspension, -1.5 camber, zero toe (which is close to stock specs)....

also, I'd love to go to a 295 front tire, but pretty sure I'll rub pretty hard when the suspension is under compression.

 

[mfain]

Today, you should see numbers from Ackerman. I lost my slide plates, so I have to make due with what's coming today.... don't laugh too hard :crutches:


I'm using 2004 Z06 specs as my search criteria. My wheelbase is 7" shorter (which is why the Ackerman measurement), but the width and range of adjustment are basically Z06 stock ....

for the rear, Camaro suspension, -1.5 camber, zero toe (which is close to stock specs)....

also, I'd love to go to a 295 front tire, but pretty sure I'll rub pretty hard when the suspension is under compression.

One question - I know you used C5 front suspension, but when you did the install did you use the "stock" dimensions for all of the suspension pick-up points, especially the rack location (height and fore-aft placement with respect to ends of the steering arms)? As you pointed out, the difference in wheelbase will change Ackermann, and as 69427 points out, moving the rack fore or aft will also allow you to increase or decrease Ackermann. If you put a C5 in a parking lot and turn very sharply at low speed, you will feel the front tires "chatter" on the pavement. This is caused, generally, by incorrect Ackermann with the short turn radius. Basically, the front tires are turned a different amount (dynamic toe caused by the car's Ackermann geometry) and each tire is not turning in an optimum turn radius. By dynamic toe, I mean Ackermann adds or subtracts toe from the static toe-in/out setting as the wheels are turned, depending on the built in or adjusted Ackermann geometry. In your case, you need to turn the wheels as far as you think you are turning on the tight autocross turn and measure the toe. It will be different than the static toe you set. Also effecting the situation is ride height - if you are compressed from braking, you add caster and any bump steer the suspension might have, which will affect the dynamic toe measurement. Sometimes this whole Ackermann thing is a compromise. If you are doing more high speed road course events where the turn angle is not great, then you might accept a little more understeer in the "one" tight corner on the autocross. I would just check your Ackermann (toe with wheels turned) to make sure you are not off the charts. If I can find it, one of the best descriptions of Ackermann effects and adjustment was in the technical section of Tony Woodward's catalog. A word of caution - dirt track guys have a different view of Ackermann requirements than asphalt road course guys. LOL

Edit: Here is the Woodward link. See page 72: http://www.woodwardsteering.com/PDF/tech section guide.pdf

 

[SuperBuickGuy]

Today, you should see numbers from Ackerman. I lost my slide plates, so I have to make due with what's coming today.... don't laugh too hard :crutches:


I'm using 2004 Z06 specs as my search criteria. My wheelbase is 7" shorter (which is why the Ackerman measurement), but the width and range of adjustment are basically Z06 stock ....

for the rear, Camaro suspension, -1.5 camber, zero toe (which is close to stock specs)....

also, I'd love to go to a 295 front tire, but pretty sure I'll rub pretty hard when the suspension is under compression.

One question - I know you used C5 front suspension, but when you did the install did you use the "stock" dimensions for all of the suspension pick-up points, especially the rack location (height and fore-aft placement with respect to ends of the steering arms)? As you pointed out, the difference in wheelbase will change Ackermann, and as 69427 points out, moving the rack fore or aft will also allow you to increase or decrease Ackermann. If you put a C5 in a parking lot and turn very sharply at low speed, you will feel the front tires "chatter" on the pavement. This is caused, generally, by incorrect Ackermann with the short turn radius. Basically, the front tires are turned a different amount (dynamic toe caused by the car's Ackermann geometry) and each tire is not turning in an optimum turn radius. By dynamic toe, I mean Ackermann adds or subtracts toe from the static toe-in/out setting as the wheels are turned, depending on the built in or adjusted Ackermann geometry. In your case, you need to turn the wheels as far as you think you are turning on the tight autocross turn and measure the toe. It will be different than the static toe you set. Also effecting the situation is ride height - if you are compressed from braking, you add caster and any bump steer the suspension might have, which will affect the dynamic toe measurement. Sometimes this whole Ackermann thing is a compromise. If you are doing more high speed road course events where the turn angle is not great, then you might accept a little more understeer in the "one" tight corner on the autocross. I would just check your Ackermann (toe with wheels turned) to make sure you are not off the charts. If I can find it, one of the best descriptions of Ackermann effects and adjustment was in the technical section of Tony Woodward's catalog. A word of caution - dirt track guys have a different view of Ackermann requirements than asphalt road course guys. LOL

Edit: Here is the Woodward link. See page 72: http://www.woodwardsteering.com/PDF/tech section guide.pdf

I used to stock dimensions - I can't remember who sent it, but someone sent me the blueprints of the C5 chassis. I also used the stock, C5 cradle - so all the attachment points: the rack, the lower control arms, the sway bar, are all fixed from where GM put them on the C5. I did build the upper mounts, but I had the blueprint and a friend's C5 to use as reference.... I make mistakes, but I'm fairly confident at where things are in relation to each other on the front (and back too since the only thing fabricated is the upper, coil-over mount).

It doesn't chatter at lock

What did I read when I saw I should turn the left tire 10 degrees and the right tire should be 3 degrees less (or 7 degrees)?

 

[mfain]

What did I read when I saw I should turn the left tire 10 degrees and the right tire should be 3 degrees less (or 7 degrees)?

3 degrees is a lot, but is typical for short track circle racers. Good turn in on tight tracks. That much Ackermann will slow you down on a faster, longer turn radius track. Did you get any measurements yet?

 

[SuperBuickGuy]

What did I read when I saw I should turn the left tire 10 degrees and the right tire should be 3 degrees less (or 7 degrees)?

3 degrees is a lot, but is typical for short track circle racers. Good turn in on tight tracks. That much Ackermann will slow you down on a faster, longer turn radius track. Did you get any measurements yet?

yes, but not the ones we need

First step... measure
for those with my eyesight...
​​​​​​​1/8" toe in, 98" wheelbase


there was a puppy play time.... sorry?

Luigi's brother came for a visit/wrestle, then there was the creek, then a round of baths for all participants

 

[SuperBuickGuy]

any favorites for race software/gps? I suspect I'm going a lot faster then I perceive I am - which, for testing purposes might be good to know...

also, I'll change the toe to out 1/8 and just see what happens.... from what I'm reading, that seems like I might get pretty solid improvement.... I'm waiting on something to check the degree (though at the moment, I may temp something just to get an idea)....

 

[phantomjock]

You mentioned "speed" and not Lap-time. There are several different ways to get both - some not the same solution set. I'll address Speed now.
Do you want:

Something quick and easy, or
Something with growth potential, or
Something that integrates video and data real time, or
Something that provides real-time telemetry, data. and video to the pit?​

Lowest investment for most payback, is probably what we all look for.

I did a deep dive on these a while back and will look for my spread sheet. But I'll offer the following.
If all you want/need is speed information real-time a GPS-speedometer with a HUD would be real-time. Integrate that (internally between the ears) with an Apexpro to get real-time tire-slip and "G-available." You just moved up your data utility, but also your processing. Apexpro is under $500 as I recall. GPS with HUD ~ eBay under $50.
Focus a video camera on your line of sight and include the GPS Speed and Apexpro in the view and you have post processing available. Could be a cheapie - or pick something that has growth potential. AIM, GoPro are maybe the standouts. Something purpose-built and hard mounted to a roll cage beats a phone flying around the cockpit.

More expensive items AIM, MO-TEC, Race-Technology (my favorite), RaceCapture Pro. There are phone apps, and some stand-alone lap-timers. I'll look for the xls file some. Hope I still have it...

BTW - The APEXPRO would be helpful in real-time assessment of the front suspension changes. Hit a corner at the same speed, turn-in point, see the g-available.

Cheers - Jim

 

[phantomjock]

I "melted down" the chart above with the various C3 front settings. Not necessarily a C5+ (I'll look - but if someone has a link that helps). BUT, it shows the range of values for Caster/Toe/Camber -- on a C3.




Your mileage may vary.
Cheers - Jim

Rear numbers as I find some time.

 

[phantomjock]

Data ACQ

Found it!
I'll post later (today?), in a separate thread.
Will pass along here when its up.

May take a bit to bring up to speed

Cheers - Jim

ADDED - Apexpro has a post race processing and "sharing" stuff available- but that app is Apple only - so I don't use it. Their web site has some good videos and heaps of YT. Not a saleman - just use/like.

 

[SuperBuickGuy]

You mentioned "speed" and not Lap-time. There are several different ways to get both - some not the same solution set. I'll address Speed now.
Do you want:

Something quick and easy, or
Something with growth potential, or
Something that integrates video and data real time, or
Something that provides real-time telemetry, data. and video to the pit?​

Lowest investment for most payback, is probably what we all look for.

I did a deep dive on these a while back and will look for my spread sheet. But I'll offer the following.
If all you want/need is speed information real-time a GPS-speedometer with a HUD would be real-time. Integrate that (internally between the ears) with an Apexpro to get real-time tire-slip and "G-available." You just moved up your data utility, but also your processing. Apexpro is under $500 as I recall. GPS with HUD ~ eBay under $50.
Focus a video camera on your line of sight and include the GPS Speed and Apexpro in the view and you have post processing available. Could be a cheapie - or pick something that has growth potential. AIM, GoPro are maybe the standouts. Something purpose-built and hard mounted to a roll cage beats a phone flying around the cockpit.

More expensive items AIM, MO-TEC, Race-Technology (my favorite), RaceCapture Pro. There are phone apps, and some stand-alone lap-timers. I'll look for the xls file some. Hope I still have it...

BTW - The APEXPRO would be helpful in real-time assessment of the front suspension changes. Hit a corner at the same speed, turn-in point, see the g-available.

Cheers - Jim

you reminded me of the other issue I had last weekend... the seats interfere with where I was mounting the go-pro.... need to resolve that issue as well

speed/moment in time - I have no idea how fast I'm going when the front end washes out to understeer (also a bit of a - should have bought different needles on the Dakota Digital, white over black is impossible to comprehend quickly for me). So far, where I'm running I immediately get the raw lap time when I'm done either on the big board or Race Monitor (app).

I also have big plans to get a led RPM indicator on the dash.... but I just found out we may be moving 300 miles - so that may throw a wrench or two into my upgrade plans.....

Apex pro has a 10-12 wait.... in short, I'd wait for SEMA before buying something since this year should be pretty cool with the new stuff coming and 2 years of backlog

I didn't even realize that my Go-pro 9 (black) had the capability.... time to order the race-technology software.... outside of the rpm indicator, that seems to be all I need... cool!

 

[phantomjock]

Good catch - I forgot about the GoPro to RT integration. That developed maybe 2 years or so back - I was a beta tester for a while but dropped out as my unit was incompatible.

I have the spread sheet and a pdf from Frank Whiton (GM engineer) from a few years back. He goes through all the possible integration/application - right down to parts layout. Will load later - maybe in downloads section with a pointer thread.

Cheers - Jim

 

[SuperBuickGuy]

Good catch - I forgot about the GoPro to RT integration. That developed maybe 2 years or so back - I was a beta tester for a while but dropped out as my unit was incompatible.

I have the spread sheet and a pdf from Frank Whiton (GM engineer) from a few years back. He goes through all the possible integration/application - right down to parts layout. Will load later - maybe in downloads section with a pointer thread.

Cheers - Jim

saw your thread, thank you, it will be really cool to have a one-stop shop for that ...

 

[phantomjock]

The 2 documents are loaded now in Electrical & Wiring Downloads.

Cheers - Jim

 

[SuperBuickGuy]

The 2 documents are loaded now in Electrical & Wiring Downloads.

Cheers - Jim

downloaded... the expected outputs from each sensor is gold-level knowledge. It also helps me understand why the 'same' sensor (2 different ones) give wildly different outputs. My temp sensor for the Dakota Digital reads about 10 degrees higher then the Holley sensor. Testing showed that the Holley sensor is right. The sensors are twins... and within 6 inches of each other (either side of the thermostat.) Which could be that one side is running warmer - but the spark plugs on either side read the same....

 

[SuperBuickGuy]

In reading through some of the other great stuff on the downloads, I should expect a 0 degree ackerman right/left on the C5 front suspension. Also has the target ride heights, which is quite helpful.

Wish I could upload the file I have on C5 frame dimensions, but it came from a copyrighted source.... if anyone needs it, however, fair use law says I can send it to you.... just not upload it for general consumption.

 

[phantomjock]

Might reach out to vette427sbc over on the east-coast (NJ?)
I seem to recall he maybe was using SuspensionPro (Performance Trends) for some design, and was also doing a C5 front end. He might have some design ideas that he's been through - Ackerman, bump steer, etc. We are a Community!

Cheers - Jim