Handling
Safety Car
Joined: Feb 2007
Posts: 4,939
Likes: 448
From: CHOCOWINITY NC
I have talked to my Corvette alignment specialist and he was not aware of a rear caster specification for the C7. He also took a ride with me and described the sensation as bump steer which is what I have surmised it could possibly be. So where do I find the rear caster alignment specification and also how to set the rear caster. I have run out of ideas. The connections on the suspension have been checked and all seem to be in order. I would like to get him to set the rear caster and see if that solves the problem.
Are you lowered? That usually encourages exaggerated bump steer effect..
Melting Slicks
Joined: Nov 2004
Posts: 2,592
Likes: 393
St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
Pro
Joined: Jan 2010
Posts: 629
Likes: 65
From: Freedom PA
I'm not going to search all over for it, but believe me there was a list of tools required for dealers to purchase in order to qualify to sell C7s. On the list was a rear alignment caster tool, and the spec for rear caster was zero.
I think it may have been in one of the monthly GM TechLink issues.
ED
I think it may have been in one of the monthly GM TechLink issues.
ED
Drifting
Joined: Jun 2007
Posts: 1,425
Likes: 238
From: Macomb MI
Here's a link to the rear caster tool:
http://sandyblogs.com/techlink/?p=2328
Link to race alignment settings...shows rear caster at zero, but not the street spec.
http://www.corvetteblogger.com/docs/...ationGuide.pdf
http://sandyblogs.com/techlink/?p=2328
Link to race alignment settings...shows rear caster at zero, but not the street spec.
http://www.corvetteblogger.com/docs/...ationGuide.pdf
Last edited by xp800; May 27, 2014 at 11:43 PM.
Thread Starter
Racer
Joined: Mar 2002
Posts: 281
Likes: 0
From: Westerville OH
Yes, the C7 does have a rear Caster specification. Below is a link to the alignment specifications for street. It appears the caster is the same regardless of track or street.
https://i.imgur.com/1YDlc9O.jpg
https://i.imgur.com/1YDlc9O.jpg
Thread Starter
Racer
Joined: Mar 2002
Posts: 281
Likes: 0
From: Westerville OH
Yes, I am lowered. Curious why my other lowered Corvettes did not exhibit bump steer and why this Corvette only has a right rear bump steer. I am also curious why GM put the capability to set caster in the rear of the C7 and not other year Corvettes.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Safety Car
Joined: Feb 2007
Posts: 4,939
Likes: 448
From: CHOCOWINITY NC
Yes, the C7 does have a rear Caster specification. Below is a link to the alignment specifications for street. It appears the caster is the same regardless of track or street.
https://i.imgur.com/1YDlc9O.jpg
https://i.imgur.com/1YDlc9O.jpg
Really? Zero? In other words, NO caster...
Pro
Joined: Jan 2010
Posts: 629
Likes: 65
From: Freedom PA
Yes: really.
Why would that surprise you when there is no need for self centering on the rear wheels of a front steer vehicle. They just want to be sure that the pivot axis is vertical to minimize bump steer.
To the OP. Their is no reason to assume that your problem is caused by bump steer, whether by virtue of incorrect castor, or toe. A number of faults can cause side movement of the rear of your car other than alignment, but the cause can only be determined by a competent mechanic.
Why would that surprise you when there is no need for self centering on the rear wheels of a front steer vehicle. They just want to be sure that the pivot axis is vertical to minimize bump steer.
To the OP. Their is no reason to assume that your problem is caused by bump steer, whether by virtue of incorrect castor, or toe. A number of faults can cause side movement of the rear of your car other than alignment, but the cause can only be determined by a competent mechanic.
Thread Starter
Racer
Joined: Mar 2002
Posts: 281
Likes: 0
From: Westerville OH
Yes: really.
Why would that surprise you when there is no need for self centering on the rear wheels of a front steer vehicle. They just want to be sure that the pivot axis is vertical to minimize bump steer.
To the OP. Their is no reason to assume that your problem is caused by bump steer, whether by virtue of incorrect castor, or toe. A number of faults can cause side movement of the rear of your car other than alignment, but the cause can only be determined by a competent mechanic.
Why would that surprise you when there is no need for self centering on the rear wheels of a front steer vehicle. They just want to be sure that the pivot axis is vertical to minimize bump steer.
To the OP. Their is no reason to assume that your problem is caused by bump steer, whether by virtue of incorrect castor, or toe. A number of faults can cause side movement of the rear of your car other than alignment, but the cause can only be determined by a competent mechanic.
Pro
Joined: Jan 2010
Posts: 629
Likes: 65
From: Freedom PA
Ed
Thread Starter
Racer
Joined: Mar 2002
Posts: 281
Likes: 0
From: Westerville OH
Sorry for the misunderstanding. By all means all four wheels alignment should be checked, but don't make that your main point of reference. If you ask for alignment to be checked that's all they'll do. Give them all of your symptoms, and let them do the diagnosing.
Ed
Ed
Safety Car
Joined: Feb 2013
Posts: 4,875
Likes: 1,174
I have given my Corvette mechanic all the symptoms, he has driven the car and has ridden in the car with me. He has checked the alignment and all the suspension for anything loose. The alignment is spot on and the only thing he needs to do is obtain the necessary tool to perform the rear caster as another check. If you know of anything else that needs to be checked could you please advise because he is running out of things to check and the dealer has no clue as to the cause. This is not a little problem. If I were to take this car on a performance run through some twisties I would be a little hesitant. The car is not stable. Frustration is the word of the day.
No they are not. I suppose it is possible there is a problem with one of the tires that isn't visible to the naked eye... unlikely though.
I wonder if you could drive another C7 to see if it feels differently than your car. That might help you better describe the difference in handling characteristics which might give some additional clues.
Melting Slicks
Joined: Nov 2004
Posts: 2,592
Likes: 393
St. Jude Donor 05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17
Drifting
Joined: Jun 2007
Posts: 1,425
Likes: 238
From: Macomb MI
Since pretty much all the obvious has been checked, that's why I suggested trying a tire swap.
Another outside idea: eDiff problem? If it was not functioning properly and directing significantly more torque to one side, could this cause the rear end hops when going over bumps and the tires unload?
Could you have one bad rear shock, allowing uncontrolled wheel hop on one side?
Another outside idea: eDiff problem? If it was not functioning properly and directing significantly more torque to one side, could this cause the rear end hops when going over bumps and the tires unload?
Could you have one bad rear shock, allowing uncontrolled wheel hop on one side?
Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
The problem is the short sidewall tires and the heavy runflat tires. Basically, that setup is not going to work without magnetic shocks.
However, I recently watched a 458 accelerate over some city bumps and humps and it did not look good with the magnetic suspension going soft.
Anyway, the fix is wider tires and non-runflat tires:
265/35-18 tire on a 18 x 9.5 52mm wheel
305/30-19 tire on a 19 x 11 74mm wheel
or
265/35-19 tire on a 19 x 9.5 52mm wheel
305/30-20 tire on a 20 x 11 74mm wheel
And that first tire pair is about 1/2" less diameter than stock while the second tire pair is about 1/2" more diameter than stock. Both tire sets have the same sidewall heights at 3.65" front and 3.6" rear. There's a wider selection of tires in the 18/19 set.
Another setup is:
255/40-18 tire
295/35-19 tire
That's a front sidewall height of 4.0" and a rear sidewall height of 4.06".
And the BBS RS-GT wheels are spec widths for them at 18 x 9 and 19 x 10.5.
The Z51 tire sidewall heights are:
3.38" front and 3.37" rear
.
However, I recently watched a 458 accelerate over some city bumps and humps and it did not look good with the magnetic suspension going soft.
Anyway, the fix is wider tires and non-runflat tires:
265/35-18 tire on a 18 x 9.5 52mm wheel
305/30-19 tire on a 19 x 11 74mm wheel
or
265/35-19 tire on a 19 x 9.5 52mm wheel
305/30-20 tire on a 20 x 11 74mm wheel
And that first tire pair is about 1/2" less diameter than stock while the second tire pair is about 1/2" more diameter than stock. Both tire sets have the same sidewall heights at 3.65" front and 3.6" rear. There's a wider selection of tires in the 18/19 set.
Another setup is:
255/40-18 tire
295/35-19 tire
That's a front sidewall height of 4.0" and a rear sidewall height of 4.06".
And the BBS RS-GT wheels are spec widths for them at 18 x 9 and 19 x 10.5.
The Z51 tire sidewall heights are:
3.38" front and 3.37" rear
.
All those C6 ZR1's, Z06/Z07's and 427 Convertibles have 19/20 inch wheels with 3.37" sidewalls on the front and 3.30" sidewalls on the rear and they don't have the problem with a mishandling car from short sidewalls.
My C6 Z06 runs true, no tramlining or darting, and a bump in the road does not cause the car to become unsettled.
I can cruise at 80 MPH on longitudinally grooved concrete pavement with no side to side movement of my car.
I think you need to find something else to place the blame on as the items you listed are not the problem.
Last edited by JoesC5; May 29, 2014 at 02:57 PM.
Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
I have talked to my Corvette alignment specialist and he was not aware of a rear caster specification for the C7. He also took a ride with me and described the sensation as bump steer which is what I have surmised it could possibly be. So where do I find the rear caster alignment specification and also how to set the rear caster. I have run out of ideas. The connections on the suspension have been checked and all seem to be in order. I would like to get him to set the rear caster and see if that solves the problem.
If that doesn't correct the problem, then switch out the stock wheels/tires from a known good C7 Z51, to see if you have a bad tire. change one tire at a time, to isolate the bad tire(if you have a bad tire). Don't start changing tire sizes trying to correct your problem.
If that doesn't correct the problem, take it higher in GM and start reviewing the lemon laws in your state. Every time you take the car in for this problem, make sure the dealer makes out the paperwork showing you had the car in for service, and save your copy. most states have either 3 or 4 times for the dealer to correct a problem, or a total of 30 days out of service.
PS- It's not your job to run out of ideas. That's the dealer's/GM's job. Hold their feet to the fire, until you are happy with the car. See if you can get the alignment printout and post it for the forum to see. Maybe someone will spot something unusual.
Last edited by JoesC5; May 29, 2014 at 03:26 PM.