When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Can you remove the brake rotor dust shields?
It seems to me that if you remove them it would allow a lot more air to circulate around the rotors and prevent them from heating as much.
I get knockback after high G corners, but it's half a pump to get to my brakes. It happens after several laps once the assembly is at full temperature. My theory is that I'm developing bearing play when the hub heats up. I've also had to drill my bearing caps to keep them from popping off on track . . . so I know they are getting hot.
I'm limited to stock components by vintage racing rules. So I need to just improve/work-around what I have. Getting cooling air to the hub is important.
I think you are on to something there hornetball! I'll run the numbers: Steel expands about .06% in length per 100 degrees. So the space between your two wheel bearings that you so carefully blueprinted to .001" or so would grow as it heats up. Let's say it is 2 inches distance. And we are talking only 400 degrees F temp at the spindle under the bearing, which is not an unreasonable expectation. Your 2 inches of space would swell larger by .06% or .0012" for every 100 degrees! For a total of .0048" looser at 400 degrees. And that is at the bearing itself, which would basically be tripled at the rotor edge, for a grand total of .014" rotor wobble!?!?! There goes your carefully set .003" rotor wobble or whatever you started with. No wonder the rotor is pushing the pistons and the pads around!
And if you are melting grease you may be getting temps twice that high. They do make temp paste / paint that you paint on the spindle to estimate how hot it is getting. Maybe you can cool it down some. https://www.mcmaster.com/temperature-indicating-paint/
Back to the Camber Curve graph for a Typical "Performance Suspension" setup:
For the best handling, all 4 tires need to be loaded equally, and stay flat at all times, and not roll over.
For a performance handling car setup change #1 is always to lower the front end.
The first benefit of this is to lower the center of gravity, so the weight remains a little more balanced right/left in a turn. Less weight transfers. How much less? Using my dynamic suspension analysis spreadsheet (post #1) the car transfers 1031 lb in a 1G corner. And only 969 lb if you lower the car 1" That is 62 lb less. Every little bit helps. So the lightly loaded inside tire works a little bit harder than before. Duntov built in an easy 1-1/5" drop into the front suspension geometry.
The first issue with this is you used to have 2.5" until you hit the bump stop, now you only have 1.5" ( in a 1G turn or on the brakes) So you probably need to trim the bump stop on the lower a -arm, or use stiffer springs, or both.
Stiffer front springs are the usual 2nd change. The first benefit here is to keep the car off the bump stops on the brakes, therefore the car is not suddenly "upset"
With a typical 550# front spring upgrade, the nose will only drop 0.7" on the 1G brakes, vs 1.7"
The 2nd advantage is the car settles quicker and takes a "set" quicker on the brakes, so they work better, sooner.
The 3rd advantage is there is now less camber change. Using the curve above you can see that the front end gains about 1.7 neg camber with stock springs and only 0.7 degrees with heavier springs. This is great for braking, the front tires stay flatter and the brakes stop harder.
The same thing happens in a turn at 1G. You gain less positive camber. With stock springs and bars, the car rolls 3 degrees or 1.5" on each side. You lose 3 degrees with body roll, and gain 1.5 back due to the camber curve. Even if you start with zero camber, you will wind up with 1.5 degree positive camber in the corner, not good for cornering.
With stiffer springs and sway bars (change #3) there is much less roll. (The stiff bars contribute about half of the roll stiffness) With the roll cut in half to 0.7" so is the pos camber, now only 0.6 positive.
This is the 4th advantage: the car takes a set in a turn in half the time, so the "transitions" are quicker. It feels like it has quicker reflexes now.
The above positive camber readings in a turn can be compensated for by just adding negative camber into your static camber setting. 1.5 degree for one car and 0.6 degree for the other.
This is the 5th advantage for the stiffer car, the 0.6 degree static camber setting allows for much better braking than the other softer car.
The next change (#4) is adding more positive caster. The 1st advantage here is the car tracks straighter at speed, it is less twitchy.
The 2nd advantage is you can actually feel what the tires are doing better, the steering becomes slightly firmer, as you are literally lifting the car very slightly when you turn the wheel. If you have power steering you can easily handle 4-5-6 degrees positive caster and it will feel great. With manual steering you are probably stuck with around 2 degrees before the steering gets too heavy and too tiring.
The third and hidden advantage to increased positive caster is that it increases the camber curve. You get a greater increase in negative camber than the stock curve shown above. I'll try to calculate it later.
The other way to increase the camber curve (change #5) is to use a 3/4" taller upper ball joint. Jason said it added another 1 degree of negative camber on his car.
The ultimate goal is to run as close to 0.6 negative static camber as possible to get the best possible braking, and still get as close to 0.5 negative camber in the turn as possible to get maximum cornering. And to get both at the same time with the same suspension setup. If you can find that secret combo, you will beat the guys with 3.5 degree negative camber settings.
The 6th typical change is more rigid a-arm suspension bushings. Rubber bushings may be the cause of almost another 0.5 degree positive camber in a turn. There is another hidden advantage in there due to less toe-in changes.
Another change (#7) that really helps keep the tires flat in a turn is to run as wide of a wheel as possible. I ran some test with exactly the same set of 245/45 tires, with 9.5" of tread, and went up 1.5" in wheel width from a 8" to a 9.5" wide wheel, and the required tuning changes were many. The tires needed less air pressure by 8 psi,(32 to 24#) less static camber by 0.7-0.9 degree, the tire still rolled over less onto the sidewall, tire temps were much more even, I had more square inches of tire on the road, and my G readings in turns jumped from 1.05 to about 1.15G. And the wheels were the only part I changed. The suspension settings were optimized both before and after, it just worked better after.
The other advantage to the wider wheels was it cut about 2" of movement out of the steering wheel. The response became like a surgeons scalpel afterwards, I could use 1/4" movements of the steering wheel and get a reaction.
This stock front suspension geometry is really not that hard to "fix" and make this car into a really excellent performer!
Can you remove the brake rotor dust shields?
It seems to me that if you remove them it would allow a lot more air to circulate around the rotors and prevent them from heating as much.
They also trap heat in when you stop. I got rid of mine 30 years ago when I was thinking about possible rotor warpage and worthless weight.
Instead of removing the dust covers for my mainly street car, I modified them to accept cooling ducts. I haven't had any brake cooling related issues since I added these. I welded on exhaust tubing to direct cooling air to the center of the rotor. The cooling ducts are smaller than ideal due to packing concerns - I didn't want them to be noticeable unless someone was really looking for them.
Tonight's analysis. I had downloaded a free trial of "Suspension Analyzer". And I discovered it had some sample data in it that would make for some very interesting comparisons. It is always good to analyze the "competition" and see if any lessons can be applied. Here are some notes I made:
I plugged in several variations of a C3 suspension. And then compared it to a 2001 C 5 Corvette, a Winston Cup Car designed for 1.5 mile ovals, and a Nascar Touring car designed for 1/2 mile ovals.
Observations:
Our C3 has a very low CG and is comparable to several V8 racing cars. There is not much to be gained there. Duntov suggests lowering the C3 1-1.25" for racing use. THat drops the CG to 3.25".
All 3 of the other cars run much more Positive Caster. (5-9 degrees) We can mod our cars with tubular a-arms or offset a arm shafts and increase that from 2 to about 5-6.
All 3 of the other cars have a much higher roll stiffness (in ft lb / degree). We can add stiffer springs and sway bars and get close to that. Even the Massively stiff 1.25" Van Steel front bar coupled with the 3/4" rear bar may not be too much in a racing environment. Less roll is usually better. The C4 rolls much less than all others. Well the C4 does have a very unique spring setup that would greatly increase the roll rate. And I do have incomplete data on the 2 race cars.
The VBP dual mount spring sort of duplicates the C4 setup and should result in very little roll. That is really a whole different suspension package.
The Camber Gain curve of both the Nascar cars is 40-50% more than our C3s .95 degree/inch. We can approach those levels by lowering the car, increasing caster, and using a 3/4" taller ball joint. If my math is correct that may allow us to run as little as 0.6 neg static camber, and still prevent the wheel from going very positive in a corner. That would be terrific news for both braking and turning. I will test a 3/4" taller ball joint later for possible use on my car.
Lowering the front of the car 1-1.5" increases the camber gain by moving it to a steeper part of the curve.
Changing our C3 from 2 to 5 positive caster did add a little Camber Gain to the Camber Curve, but that effect was very small.
Most interestingly our C3 has much more front anti-dive othan all 3 of the other cars. Even more than 2 dedicated race cars. Anti-Dive is due to the 3" downward tilt of the upper a-arm. It prevents the front from dropping as much on the brakes, but it also mechanically binds up the suspension. The race cars would only less anti-dive if it was faster and felt better to the driver.
During anti-dive, the front suspension would "bind-up" on the brakes and not be very responsive to bumps, the tire would tend to "skip". But the front end would not drop very much. The race cars must have tested it both ways and determined 50% was plenty, and faster, due to bumps.
Also as the driver transitioned off the brakes, and rolled into the turn, the left front suspension would drop lower as the car turned. Requiring shock movement, response time, etc. I went to great lengths on my Pro-Solo car adjusting the dive and the roll rate to keep that left front tire planted (loaded) while down 1" on the brakes and then just slowly transition to the turn without that tire moving up/down at all. It made trail-braking very controllable.
It would be possible to reduce the anti-dive on our C3s. It would require moving the a arm studs vertically. Going from a 3.0" difference to a 2.0" difference should drop the anti dive by a third, from 80% to 50% and may indeed make the car more controllable during trail braking or braking on the bumps. We do have enough suspension movement room to allow a little bit more droop on the brakes. But welding is required. The dirt track cars make this characteristic adjustable on their cars, with slots and slugs, and use it as a driver tuning aid, depending on how bumpy the track is. If you move only the inside of the upper a-arm it is possible to change that and effect almost no other suspension geometry.. I am not sure I want to go that far. Maybe if I were to seriously Solo this car. But there may be someone here who would want to experiment with it.
1. 2001 is a C5, not a C4.
2. The C2 suspension was designed for bias ply tires that don't need as much static negative camber to prevent rollover in the turns. C3 changed a few numbers but is still somewhat saddled with the original design intent. Fortunately for me, we run bias plies in vintage racing.
I found the bias ply tires lift the inside edge easier, breakaway more slowly and have large drift angles. Even adding more camber would not keep them flat or give me even tire temps. Car was slower. I was not impressed. Hoosiers, they were supposed to be terrific. Plus they really slowed the steering response of the car down. I had to learn to drive all over again. Frustrating time for me. But hey you gotta experiment.
I agree the C2/C3 suspension was designed for bias ply tires. It was also designed for only 6" wide tires. Basically camber was less important to the design team. With the almost twice as wide performance tires now in Vogue (10-11"), combined with the stiff inner tread surface, controlling the camber in the middle of the turn becomes much more important than it did with bias tires. When these wide radials "lift an edge" performance drops off precipitously, not slowly. So the camber has to be "just right". I feel that is the main reason we need to pay so much more attention to camber, on this old frame, than what it was designed for, even if we have to "massage" the geometry a little, just to get the wide tires to work to their best.
Tonight's Analysis.
I made some more measurements for the Suspension Analyzer program.
Was able to graph the improvements in the Front Camber curve with incremental changes.
All four scenarios begin with a 0.5 negative camber setting.
Light blue line is stock springs bars. 2 degree caster. Car rolls 3 degrees and has 1.25 positive camber in a corner.
Red line adds F41 springs & heavy sway bars. Lowers car 1" and Car only rolls 1.5 degrees and has 0.4 positive camber in a corner.
Green Line: Changing upper A-Arms allows 5 degrees positive caster. Cornering camber is 0.25 positive.
Purple Line: Added 3/4" taller upper ball joint. Cornering camber now virtually zero underload. Goes from 0.5 negative static camber setting to zero in a corner..
Would you consider adding the Howe +0.9" extended ball joint to your camber gain chart?
I am also interested in how lowering the inner pivot point of the upper control arm effects camber gain.
How much lower would be beneficial 1/8 , 3/16 , 1/4 ?
How does it interact with extended spindle length?
I very much appreciate the efforts to share your experience, suspension calculations and charts with the forum.
I can do that! I have 2 days left on my 10 "trial" period of this amazing software. It is Suspension Analyzer by Performance Trends. I would like to keep it, but it is $500. Over my budget. It's more of a professional level suspension designer software than home hobbiest. It computes in 3D too, it is no joke!
Spoiler alert! ......working on the C3 rear suspension now......
In addition to the mods in post #113 above, I added a 0.9" tall upper Ball joint which tilted the a arm more.
Then I dropped the inner a arm pivot point by 5/8"
This combo increased the negative camber gain to -1.58 degree per degree roll.
The car finally has negative camber in a 1G turn, while only beginning with 0.5 degree static camber.
Remember the completely stock car wound up at 1.5 degree positive camber in the same turn.
Now is dropping the inner a arm pivot point 5/8"easy? Heck no. But it sure works for Camber.
But when you change geometry there are always tradeoffs.
In this case the front roll center being raised significantly from 3.5" to 7" now.
What that does is change the way the front rolls and transfers weight. The car's CG is 16.5" so the lever or roll moment is normally 13". That would drop to 9.5" and significantly change the handling balance of the car. The front will feel stiffer and it will roll less. It is a significant 27% change in roll moment. It should oversteer much more than before. The springs and sway bars and handling balance will need to be re-tuned. It may be too much of a change. Normal recommendations for a front RCH are 15-30% of the CG. That would be 5" tops. And this RCH is way over that. I would proceed with due caution.
Thank you for charting more data with the longer ball joint and lower inner pivot point.
It looks like a lower control arm inner pivot adds more camber gain than raising the ball joint.
A Moog offset upper shaft is limited to dropping the arm 1/8" to 3/16" max without welding.
I wonder if less than 5/8" has a proportionately less improvement in camber gain.
Moving it back 1/4" for more caster is no problem.
How much were you lowering the Camaro pivot?
Awhile back I posted about making a 7068 aluminum upper shaft and no one wanted to share their info.
I would like to use a removable insert for adjustability, but without a CNC mill that would be a lot of work.
An educated guess on where to put a simple hole is much easier to fabricate.
With the material I have a 1/4" or 5/16" drop would be about max.
Unfortunately 7068 has gotten hard to find in larger sizes.
Thank you again.
I see you added more to your reply while I was typing.
My instinct was for a smaller change in pivot height.
The more you learn the more complicated it gets and the less I Know.
Which end of the control arm would you change and how much?
My friend is a retired tool and die maker with 60 years experience. He has CNC lathe and mill in his home shop. He is recovering from knee surgery but maybe he would be interested in making some offset shafts. H may even have the material.
MCMLXIX
Glad to help where I can. Yes I think less than 5/8' would be a linear proportional response.
Doing this with some custom made a arm shafts is a terrific idea!. Then you could always go back if needed. As you may or may not like the "other" effects. That is what experimenting is all about right?
I took the Moog offset shafts and had the slots milled 1/4" forward to enable 5 degree caster. That worked well.
I saw someone here on C3 online who had some custom a arm mounting shafts machined from scratch. They were lowers.
But what he did was to put the two bushing mounting shafts offset on each end to fix a bent frame issue. It worked well. And his alignment was OK after that.
You could do the same thing for the upper shafts. And lower the two mounting bolts/studs on the main shaft. If you lowered them 5/8" it would have the same effect.
You could have two sets cut at two different heights and have some adjustability. At least with a bolt-on parts change.
I will look and see if I can find that thread.
I did look at my mounting tower and it does not stay flat for long, there is a taper almost immediately below the shaft. So your new plate/shaft thing would have to account for that.
Ok I updated my C3 front suspension chart. I added the extreme tall BJ and a arm mods, and made more careful note of the RCH etc.
As I noted before typical RCH for front run in the 2.5 to 5.0 " range. And you still need to ensure the front RCH is lower than the rear.
So I think that is 7 changes to the front suspension.
The last one is my paper attempt to see what it would take to reduce the front anti-dive. To make the car more compliant on the brakes in bumpy sections.
The stock front upper a arm stud is 2.75" higher in the front than the rear. I lowered that to 2.0" by lowering the front only.
That reduced the front anti-dive from 70% to 50%. That is a 28% reduction and should make a noticeable difference in case someone wants to try it. I picked that number since both the C5 Vette and a Winston Cup car use that amount.
11-15-2021, 12:32 PM
But hey you gotta experiment.
