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....I hadn't noticed it pulling while driving it... What are the adverse affects ?
Like Tadge said in that "Ask Tadge" thread that Boiler_81 posted up:
Rear caster accuracy and symmetry is important because it affects ride steer. Students of suspension geometry will understand that even small changes in rear steer angle can have big effects on vehicle handling.
He mentions "ride steer" - commonly called bump steer, and analyzed by reviewing the toe-curve (change in toe with suspension compression/rebound).
The toe is set in a static situation - on an alignment rack. 0° toe means the tire is set to roll perfectly straight. Toe-in means that the front of the wheel/tire points in slightly toward the center of the car - like a person who's pigeon toed. Toe-out is just the opposite.
Ride steer that Tadge refers to is the change in toe when the suspension bounces up and down. If you're cornering very aggressively, say in a hard right turn on a track, the left lateral G-force compresses the left side of the suspension, and the right side lightens up.
Some analysis of the C7 toe-curve has been done by some performance shops that do race car alignments, and IIRC the rear toe tends toward more toe-in during suspension compression - which will result in steering the rear end to some extent.
The analysis suggests that the toe-curve is best with the rear caster adjusted to a slightly positive setting.
When the ball joint axis is perfectly vertical, the rear caster is 0°. When the top ball joint is forward of the bottom (i.e., the ball joint axis is leaning forward) the caster is negative.
So....what appears to be best, at least for tracking the car, is for that axis to be leaning back slightly - positive caster.
Some of the track hounds have gone to +2.0° or more of rear caster with good results, but apparently +0.8° to +1.0° is good for a track car.
The Chevy spec is 0.0° +/-0.8°, so a street car set to +0.8° is within Chevy specs (at the limit, but within!).
Many forum posters feel that a negative rear caster setting can result in a tendency for "snap oversteer", so recommend at least 0.0° or maybe a little positive even for street driving.
And if the rear caster isn't the same for both sides (Tadge mentions "symmetry" in his discussion), there can be a difference in handling depending on which way you are turning.
Bottom line - if the static alignment when set on a stationary rack adjusts the camber and toe to within spec, but disregards the rear caster, the rear end may not be as stable when cornering as it should be with properly adjusted rear caster.
BTW - the alignments from the factory are....shall we say....challenged!! There are some cross-camber and total-toe specs on that spec sheet I posted up in a previous post, and cross-caster for the front. However, there's no cross-caster spec for the rear, so one side could be -0.8° and the other +0.8°, and handling might be very different when cornering in different directions. A few forum members have had their factory alignments checked with fairly widely different settings - so rear caster does not seem to be carefully set when the car comes off the assembly line.
Ok, here's a question. I'm not too familiar with alignments and etc. but are adjustable casters common on other high performance cars (euro/Japanese)? Is this something most alignment specialty shops would know about (as opposed to gm dealerships)?
Not common at all - no adjustable rear caster on most production cars. I believe I've read that a model or two of Mercedes may have it, and F1 race cars are able to adjust it.
There are certainly some, but not enough so that alignment shops know about it.
To my knowledge there are no commercial alignment racks/machines that can check rear caster. It has to be checked manually by attaching some sort of straight-edge to some part of the rear suspension, then using an angle gauge to measure the caster. It won't be automatically printed out on sheet that shows all the other alignment specs that the machine measured.
There will be very few shops that will know how to set up the rear caster on the C7, even those that do race-prep alignments on high end race cars. You'll probably need to educate them on the importance, and maybe how to do it.
Unfortunately this is correct. I had my 2016 at Les Stanford this summer and asked if they could do the rear caster. The service writer checked with the service tech who indicated he did not have the tools. Les Stanford is the third highest volume Corvette dealer in the country. If they don't have the tools, I'm thinking the odds of a smaller dealer having them is rather small.
Originally Posted by Bill Dearborn
Because he doesn't count. He isn't their interface into GM or who provides the training. The dealership I take my car to has an excellent Corvette Tech and when I asked him about rear caster he had to look it up. When he got the info he found out the dealership didn't have the tools and the person who manages the tools (has a desk right next to the mechanic's work station) told me he wasn't going to order a thousand dollars worth of tools for one car. I said they all require it and his answer was you are the only one who has asked. If the vast majority of Corvette owners don't ask it won't get done and you know exactly how many will ask 0.01%.
This thread is a very sad commentary on the capability of GM to support the cars they sell. I'm not surprised that most Chevy dealers don't have the capability to align the C7 as many don't even know what oil they are supposed to take. As I said, it is very sad indeed.
This thread is a very sad commentary on the capability of GM to support the cars they sell. I'm not surprised that most Chevy dealers don't have the capability to align the C7 as many don't even know what oil they are supposed to take. As I said, it is very sad indeed.
What's cheaper. Hire a pro mechanic to change oil and look stupid. Or hire stupid oil changers that look smart.
The reason dealerships make so much money is because the owner rob's people like you and me by employing CHEAP misfits.
That's from sales to yard boy.
Because he doesn't count. He isn't their interface into GM or who provides the training. The dealership I take my car to has an excellent Corvette Tech and when I asked him about rear caster he had to look it up. When he got the info he found out the dealership didn't have the tools and the person who manages the tools (has a desk right next to the mechanic's work station) told me he wasn't going to order a thousand dollars worth of tools for one car. I said they all require it and his answer was you are the only one who has asked. If the vast majority of Corvette owners don't ask it won't get done and you know exactly how many will ask 0.01%.
Bill
This is where the frustration sets in. Something is clearly wrong when the driver's side rear tire is set back .5 inches further than the other side, and it could be the alignment... a rear caster issue that 1) no Chevy dealer knows about, 2) no Chevy dealer has the tools to fix if they did know about it, or 3) no Chevy dealer wants to buy the tools to fix it if they did know about it). I'm no rocket scientist and I'm not familiar with GM's org structure or what have you, but if the car has their name on it and there's a problem, they better be able to fix it. Buy my own tools to fix an issue with their car is
Last edited by scottkwilson; 01-06-2017 at 04:45 PM.
Unfortunately this is correct. I had my 2016 at Les Stanford this summer and asked if they could do the rear caster. The service writer checked with the service tech who indicated he did not have the tools. Les Stanford is the third highest volume Corvette dealer in the country. If they don't have the tools, I'm thinking the odds of a smaller dealer having them is rather small.
Hello Boiler,
Sorry to have to inform you of this, but we do have the equipment to do the alignment to the GM revised specs. If you wish to have that work performed, please contact me.
Sorry to have to inform you of this, but we do have the equipment to do the alignment to the GM revised specs. If you wish to have that work performed, please contact me.
That is good news, I was in late last Spring or early Summer and they told me they didn't have the tools. I went so far as to email the GM information on the correct P/Ns for the tools to the service person. They were going to look into it and get back with me. I never heard back.
When I do track days next Summer, I will come in and have my car set up with the track specifications.
Thanks
Originally Posted by LES STANFORD CHEVY
Hello Boiler,
Sorry to have to inform you of this, but we do have the equipment to do the alignment to the GM revised specs. If you wish to have that work performed, please contact me.
Alright folks, here's an update. As predicated, the dealer (Rick Hendrick Chevrolet, north of Atlanta) was clueless about the C7 rear caster adjustment. They knew nothing about it, said it can't be adjusted, and chalked up my rear driver's side tire being set back .5 inches further than the other side due to me lowering the car on factory bolts. In their opinion, everything was "normal"... and if there was an issue, it was my fault because I lowered the car - so typical. Do anything to your car and that gives them an excuse to wipe their hands clean. I gave them every shred of evidence- I sent them links to this thread and the great feedback I've received from the community. I told them what tools to use, how to get them (borrow from GM if they don't want to purchase), and I even gave them specs for what I wanted the rear caster to be set to (+0.8° - thank you BEZ06!). I even sent them the post from Tadge that explains in great detail about C7 rear caster and how it's adjustable... and important!!!!! Sweet mother!! There's nothing else I could have done to correct their ignorance. Anyway, I immediately called BS!, then got on the horn with Butler tire in Buckhead to see what they had to say about it. Immediately they knew what I was talking about. Straight up, the guy on the phone told me caster can move the tire forward and back, and that he was aware that the C7's is adjustable... and that they could do it. Thank the Lord! I wasn't going to be totally F'ed after all with this C7 rear caster issue and chevy dealer incompetence. Butler tire's alignment is $175... $75 more than the dealer, but at least it seems they are knowledgable and competent. Wish me luck! Anyone with half a brain can see there's something wrong with that rear tire of mine. Too bad Rick Hendrick didn't care. What these dealers don't know is that we vette guys have a one strike and you're out rule!!!
Lastly, thanks everyone for the great feedback. I'll let you know if the wheel centering improves after getting the car back from Butler.
Last edited by scottkwilson; 01-06-2017 at 04:50 PM.
It would be interesting to learn how they set the caster on the rear suspension. When setting it on the front suspension, you used to measure the caster by turning the wheel left or right quite a bit with a gauge attached to the spindle. I don't know what the procedure is with the new computerized alignment equipment. Anyone??
It would be interesting to learn how they set the caster on the rear suspension. When setting it on the front suspension, you used to measure the caster by turning the wheel left or right quite a bit with a gauge attached to the spindle. I don't know what the procedure is with the new computerized alignment equipment. Anyone??
Well.....here's a repost of the picture I put up in post# 7 of this thread:
You can see there's an adapter that goes into two holes on the rear suspension knuckle, and then you can also see the digital angle gauge that is the official GM tool for measuring the angle (caster) of the inclination of the axis between the upper and lower ball joints. That angle gauge has studs that mount on the back of it and are inserted into the holes in the adapter.
Many owners are using a much less expensive digital gauge that they just hold up against the adapter in order to read caster.
Bottom line - no alignment machine that I know of can measure rear caster. The rear caster measurement is an entirely manual procedure that requires the alignment technician to get under the car, install the adapter to the knuckle, place the gauge on their rack and zero it out, install it on the adapter, and read the angle of caster.
There won't be any digital readout/printout like there is for all the other alignment specs - it must be written on the alignment sheet for you to see what they set it at.
Any luck getting the work done at the wheel alignment place ? I'm working on my dealer at the moment looking for answers...
Did you notice any difference?
Dan
Alright folks, here's an update. As predicated, the dealer (Rick Hendrick Chevrolet, north of Atlanta) was clueless about the C7 rear caster adjustment. They knew nothing about it, said it can't be adjusted, and chalked up my rear driver's side tire being set back .5 inches further than the other side due to me lowering the car on factory bolts. In their opinion, everything was "normal"... and if there was an issue, it was my fault because I lowered the car - so typical. Do anything to your car and that gives them an excuse to wipe their hands clean. I gave them every shred of evidence- I sent them links to this thread and the great feedback I've received from the community. I told them what tools to use, how to get them (borrow from GM if they don't want to purchase), and I even gave them specs for what I wanted the rear caster to be set to (+0.8° - thank you BEZ06!). I even sent them the post from Tadge that explains in great detail about C7 rear caster and how it's adjustable... and important!!!!! Sweet mother!! There's nothing else I could have done to correct their ignorance. Anyway, I immediately called BS!, then got on the horn with Butler tire in Buckhead to see what they had to say about it. Immediately they knew what I was talking about. Straight up, the guy on the phone told me caster can move the tire forward and back, and that he was aware that the C7's is adjustable... and that they could do it. Thank the Lord! I wasn't going to be totally F'ed after all with this C7 rear caster issue and chevy dealer incompetence. Butler tire's alignment is $175... $75 more than the dealer, but at least it seems they are knowledgable and competent. Wish me luck! Anyone with half a brain can see there's something wrong with that rear tire of mine. Too bad Rick Hendrick didn't care. What these dealers don't know is that we vette guys have a one strike and you're out rule!!!
Lastly, thanks everyone for the great feedback. I'll let you know if the wheel centering improves after getting the car back from Butler.
My experience with the largest Hendrick Corvette dealer in the Charlotte area was a train wreck as well. Hendrick will never get a single penny of my money ever again.
Hey all, just following up on this post to share some good news. Butler Tire fixed the rear caster... now my tire is beautifully centered in the wheel well, just as it should be. For anyone else having this issue, don't waste your time at the dealer. My advice is to call around to some speciality shops... you'll pay a little more, but it's worth it. When you start talking to the tech about rear caster on the c7, if they don't know what you're talking about right away... don't waste your time and move on.
Good luck everyone! And don't take no for an answer!
01-01-2017, 03:01 PM
