RapidC84B

D K

Rear caster???

RapidC84B

Yes... C7 has eccentrics at front and rear of the LCA so you have the set caster. C5 the front was fixed and the UCA had no adjustment. C6 UCA had adjustment on the aluminum cars, but the front of the LCA was fixed. I have no idea why they designed it this way, but it 100% has a caster setting.

mfain

Caster has some affect on bump steer on independent suspensions that use a toe link. Increasing or decreasing caster raises or lowers the outboard end of the toe link with respect to the inner end, which will affect the bump steer. Perhaps DSC has done some analysis. I would throw a bump steer gage on it and see what the two different settings yield. Remember that the caster angle will change (from that set at static height) with travel since the control arms' pivot axes are not parallel. Auto manufacturers often add a little dynamic rear toe-in bump/roll steer to slightly tighten the car under hard cornering - keeps the car from swapping ends on a off-ramp. LOL Maybe DSC "optimized" the bump steer by changing the caster angle for track performance, vice street manners.

Pappy

Dane@LGmotorsports

0.0

1/8 Total Toe Out Front

3/16 Total Toe In Rear

truth.b

OP,

There's a pretty lengthy wirte-up somewhere on the forum on why they decided to go with + rear caster. Later on today I'll look through my saved pages and try to post a link. The short version is because of the toe change under suspension compression. I can only suspect GM goes with a 0.0 caster setting because in theory that might be easier to set during assembly.

davidfarmer

I'm with Dane until I see proof otherwise. All of my C7 clients are too cheap to actually do any track-side setup/analysis, so I'll probably never know.

RapidC84B

GM's acceptable range for general street use is +/- 0.8. For their track specs it says 0.0.

NTMD8R

You might want to read through this thread......

https://www.corvetteforum.com/forums...ar-caster.html

Lot's of info and experience there

I have set my C7 Z06 with -0.8 to -1.0 degrees positive caster (laid back),
and 0.5 mm toe OUT each side.

sstrano

Rear caster isn't exactly an easy thing to test, let alone quickly since changing it also means chasing toe and camber around too. I just stuck with zero because I think that it will minimize bumpsteer/toe change back there with both balljoints in line and I have no bitch about it, and looking at photo's in roll, the car definitely seems to toe out less in the rear, in roll, than my C6's did.

Then there is the big question about which way is which on rear caster. Is positive on the rear mean upper ball joint forward, or backward? I don't know there is a consensus, at least that I've seen. I mean DSC says +.7. ok, well in front positive is the upper ball joint laid back. But in the post above NTMD8R seems to think that negative is the upper joint laid back. I don't really know because when I do this by angle finder tool doesn't indicate positive vs. negative if uses arrows to indicate which way it's leaning. I know if it's forward or back, but not sure all are on the same page as to which way is Positive, and which is Negative. Which will be a source of great debate, and a damn good reason to use zero, aside from the fact that's the spec the people who likely know what's what best give. And in lieu of evidence otherwise, I am with the others who think it's nuts to try and stray given the limited and possibly misunderstood information.

Toe. I personally run zero front toe. I run 1/8" in per side in the rear.

Sam

X25

My current targets (Camber/Caster/Toe; in degrees):
Front: -3 / 7.5-8 / 0
Rear: -2 / 0.8 / 0.05

My 2 cents:

• As was also mentioned, GM spec for rear caster is actually 0.0 +-0.8, so even DSC spec is 'within spec'.
• DSC asks for 0.8 rear caster, but also asks for TOE OUT at the rear, which sounds insane, since apparently toe curve is changed with that caster. Many who do that positive caster still do not make it negative toe at rear.
• On the top of all this, DSC's Mike stated the adjustable toe links popular with our crowd do change the toe curve drastically, and that we probably don't need toe out at the rear with them.
• And finally, these suggestions are based on stock height. I'm not sure about the impact if your car is lowered.

This time (with my new '19 Z07), I ended up reaching my desired rear camber by removing all UCA washers, not an adjustable toe link. That said, since I'll leave the rear at slight toe in (not toe out as suggested by DSC), perhaps I should switch back to zero rear toe, too. Thoughts?

Long story short, I'm not sure I have a grip on the whole story of how these different parameters work together (do you have adjustable toe link or not, are you lowered, do you have zero or 0.7 rear caster, etc.). Based on all this discussion, perhaps my safer bet would be zero rear caster.

RapidC84B

SouthernSon

Turn loose of some of that money David and buy a ZR1 so you can figure it out for us! You can't hide that money forever.

RapidC84B

He has to maintain his stay-at-home-dad status... a life I honestly aspire to

fmcokc

Actually, it's really easy to test on the C7. 2 -1/4" pins and a digital angle finder are all it takes. If you use a camber kit like the one from AMT, the caster stays static while you adjust the camber and toe.

Dialing in the caster in the rear really does seem to help with putting the power down on corner exit.

Here is a post from 2016 explaining that positive caster in this case means upper ball joint toward the rear. When I first read about this that was also my first question. This is post #4 from the above referenced thread.



Mike Levitas is a Daytona 24 hour winner and owns TPC Racing. Mike/TPC also preps the Porsche 997.2 911T I race.

Mike is also a big time Corvette guy and owns a C7 Z06. Mike has mad skills on setting up the suspension on a car. He has an amazing God given talent on suspension setup.

He has done EXTENSIVE suspension testing with his C7Z. Mike, his friend Randy Pobst and I agree the setup from the factory is TERRIBLE, DANGEROUS and SCARY when driven 10/10s. Mike's been close friends with Randy for decades. The car exhibits snap oversteer without any warning. Happened to me resulting in a bad situation and to Mike as well. Mike is a better driver than I and was able to catch his but told me is scared the hell out of him. The car is so bad even with the GM suggested track alignment WHEN DRIVEN HARD he was going to sell his after only 300 miles.

Instead, he invested many hours working on the suspension setup. Just last week he informed me he got it to where it's his favorite car to drive of the may cars he owns. He shared his setup with me and it is remarkable. I was scared to drive the car at 10/10 prior to using his setup. What he provided TOTALLY transformed my car. I can't believe it's the same vehicle. So easy to drive with the setup he told me to go with it's unreal. It's really hard for me to put into words the transformation. It truly is game changing.

The biggest problem he found was in the rear caster. Other changes were also warranted but the rear caster is the biggest factor in making the car dangerous/undriveable at speed.

Here's the hot setup which Mike informed me gave him and 7 others with C7Zs 1-2 seconds per lap WITHOUT the car wanting to snap oversteer:

1. Pull 1 washer from behind the attachment point of both upper control arms, front and rear. Total of 16 washers as there are 16 bolts.

2. FRONT: -2.0 camber and -0.5mm toe each side for total toe out of -1.0mm. Most alignment racks measure in degrees. The -0.5mm equals right at -0.03 to -0.04 degrees depending on tire diameter. Mine is set at -0.03 degrees each corner.

3. REAR: -1.7 camber and -0.5mm toe each side for total toe out of -1.0mm.

4. The rear uprights MUST be laid back 0.8 - 1.0 degree of positive caster. The 0.8 works best on just about every car they tested. DO NOT go less than 0.8. Laid back/positive caster means the top of the shock is laid back closer towards the rear of the car relative to the bottom of the shock.

Hope this helps.

Rick

RapidC84B

davidfarmer

the LAST thing I would buy is a C7 anything....worst Corvettes in 3 decades. I have real estate and airplanes to spend money on, I'm happy to help "tool hoarder" sort his problems out at the track however.

AND0

Why would this be I wonder?
The stock link has an eccentric, is there a very soft bushing at this point that deflects greatly where the aftermarket will not? So it's more of better dynamic toe control rather than changing the toe curve?
The adjustable toe link mounts in the stock location, does centering the mounting significantly alter suspension geometry?
Doing some crude math assuming a 15" long tie rod, assuming the difference from the eccentric rotated from it's lowest position to it's highest position is 1". If you raising the inner tie rod mounting point by 1" you will get ~0.060" toe in bump steer for an inch of suspension compression. The tire also moves laterally in compression, so this number does not translate directly to an alignment change. Does anybody know what the scrub radius of the C7 rear suspension is? It looks like you could really tune your rear bumpsteer curve with an eccentric and an adjustable rear toe link.
It seems like anyone who uses a C7 at 10/10th would do well to measure and plot a rear bumpsteer curve to KNOW what is going on at the rear.

Absent suspension geometry effects, the rear wheel should toe in under acceleration. The line between the two ball joints, what would be the steering axis up front, is inboard of the centerline of the tire, so the force the tire exerts against the ground will tend to turn the front of the tire inwards to toe in. Additionally that same force is out at the end of a lever, the control arms, and when exerted against the cars center of mass, the control arms will twist forward and deflect the bushings towards toe in. Imagine pushing the tire forward with your hands for a good visual representation.

davidfarmer

static toe in has nothing to do with deflection

RapidC84B