Handling issues on uneven roads
Burning Brakes
Joined: Sep 2006
Posts: 1,071
Likes: 86
From: Rotonda FL
Hello All
I have been experiencing some handling issues on some of the local roads that are less than smooth. The roads in question are tar and chip and i find my 79 darts and bolts let or right depending on the road. The car handles fine on regular highways. It has the 25560R15 tires and I wondered if the wide tire tends to follow imperfections in the road surface.I'm thinking, and hoping, that a wheel alignment will correct the problem. Is the anything special about aligning the corvette or is it something any decent alignment shop can handle. Any advantage in have a GM dealer do the alignment.
Thanks in advance
Jim
I have been experiencing some handling issues on some of the local roads that are less than smooth. The roads in question are tar and chip and i find my 79 darts and bolts let or right depending on the road. The car handles fine on regular highways. It has the 25560R15 tires and I wondered if the wide tire tends to follow imperfections in the road surface.I'm thinking, and hoping, that a wheel alignment will correct the problem. Is the anything special about aligning the corvette or is it something any decent alignment shop can handle. Any advantage in have a GM dealer do the alignment.
Thanks in advance
Jim
Adding to this are modern wide low profile radial tires, which the C3 chassis was not designed for. Modern vehicles were designed to include more caster to take advantage of power steering and modern tires and track better. You should have a minimum of 3 1/2 to 4 degrees positive caster, with 5+ being better to improve your tracking. I added tubular upper A arms that add caster (currently about 5 degrees) and a spreader bar (to reduce flexing of the A arm attachment points under load) and my 77 tracks very well with 255/50R17 tires.
Thread Starter
Heel & Toe
Joined: May 2018
Posts: 24
Likes: 1
From: Wiarton Ontario
Hunting and darting are somewhat common on C3's for a number of reasons. It is usually attributable to a lack of positive caster. Positive caster makes a car harder to steer, and older chassis (before power steering became almost universal) were designed with less caster. This is exacerbated by the fact that the front of C3 chassis "settles" as it ages, losing additional caster.
Adding to this are modern wide low profile radial tires, which the C3 chassis was not designed for. Modern vehicles were designed to include more caster to take advantage of power steering and modern tires and track better. You should have a minimum of 3 1/2 to 4 degrees positive caster, with 5+ being better to improve your tracking. I added tubular upper A arms that add caster (currently about 5 degrees) and a spreader bar (to reduce flexing of the A arm attachment points under load) and my 77 tracks very well with 255/50R17 tires.
Adding to this are modern wide low profile radial tires, which the C3 chassis was not designed for. Modern vehicles were designed to include more caster to take advantage of power steering and modern tires and track better. You should have a minimum of 3 1/2 to 4 degrees positive caster, with 5+ being better to improve your tracking. I added tubular upper A arms that add caster (currently about 5 degrees) and a spreader bar (to reduce flexing of the A arm attachment points under load) and my 77 tracks very well with 255/50R17 tires.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Go to the alignment shop FIRST. Tell them your problem, then ask them to do an inspection and assessment of the front end suspension and steering; also have them check the stability of the trailing arms. Let them know that you expect to pay them for that service and, depending on what needs repair, you might choose to do your own work. That way, they are not getting 'stiffed' for doing a FREE inspection.
If stuff needs to be repaired, either DIY or have them do the work. Then you can get the alignment work done.
BTW, it is common to have 'darting' problems with a small car and wide tires. And the most important factor to eliminate that issue is to have about 1/8" (or slightly less) toe-IN set on the front tires. This will allow the car to track straight and not 'hunt' over bumps in the road.
If stuff needs to be repaired, either DIY or have them do the work. Then you can get the alignment work done.
BTW, it is common to have 'darting' problems with a small car and wide tires. And the most important factor to eliminate that issue is to have about 1/8" (or slightly less) toe-IN set on the front tires. This will allow the car to track straight and not 'hunt' over bumps in the road.
Team Owner
Joined: Sep 2002
Posts: 38,356
Likes: 2,079
From: California
I hear a lot Corvette guys say that our cars weren't designed for wider tires! Dumb comment!
The chassis was designed to align so the tire tread could be flat on the ground. That doesn't matter whether it is skinny or wide! What is happening, is that on a rough or uneven road, those can be upsetting a wide tires foot print more than that of a skinny tire and thus exacerbates good tracking.
There is an argument for limiting the suspension travel, so the suspension doesn't put that wide tire up on edge or completely off of its footprint as it travels to the ends of its arc!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Whether the car was "designed" for wide tires...or not...is not the issue. What matters is the resulting "load per square inch" on whatever tires are on the car. The lighter the loading, the more likely the tires will wander with the pavement, rather than staying directly aligned with steering intent--if the front wheels have neutral toe adjustment.
But, a little bit of toe-in will all but eliminate that wandering.
But, a little bit of toe-in will all but eliminate that wandering.
Burning Brakes
Joined: Dec 2005
Posts: 1,164
Likes: 224
From: Pawleys Island, SC
Team Owner
Joined: Sep 2002
Posts: 38,356
Likes: 2,079
From: California
Toe in is also beneficial as you do get deflection and that could cause the tires to point outward heading you toward the side of the road at $hit, instead of it trying to search for straight.
I run heavy rods, arm bushings and everything to minimize any deflection, therefore I run mostly zero toe! The more radical the toe, the less ease of accurate aim that you will get from your car going into a turn. The design takes care of Ackerman effect pretty decently, so no redesign of the spindle on our cars is needed. Is it perfect, no, but the toe in actually helps that, as that was designed around toe-in.
I am not even going to try to explain Ackerman as you go wider on your tires. People with stock or street modified Corvettes don't need to worry about that!
I run heavy rods, arm bushings and everything to minimize any deflection, therefore I run mostly zero toe! The more radical the toe, the less ease of accurate aim that you will get from your car going into a turn. The design takes care of Ackerman effect pretty decently, so no redesign of the spindle on our cars is needed. Is it perfect, no, but the toe in actually helps that, as that was designed around toe-in.
I am not even going to try to explain Ackerman as you go wider on your tires. People with stock or street modified Corvettes don't need to worry about that!
Last edited by TCracingCA; Jun 1, 2018 at 08:19 PM.
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Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
Team Owner
Joined: Sep 2002
Posts: 38,356
Likes: 2,079
From: California
The stock guys probably won't run one, and the big block guys that need it the most have a hard time fitting them! Some chassis are assembled better than others, if the frame is flexing that much (and they do), then your alignments are moving all over the place enough to worry, if you want true handling.
And just because I got an email asking to explain Ackerman, I will spend the time to explain things to the most simplistic and least time consuming explanation! I used to sit with Dick Guldstrand and talk cars, as I think we had the best handling C3 in his GRA club of all time and it wasn't his shop that set it up (335 rear tires in the 1990s helped that greatly too
), but couldn't get in depth explanations on all of this, so I bought every Smith book, Herb Adams book, and all of the others and all of them stop far short on the answers and engineering. Ackerman in my option is designed fixed, but it is a side to side thing! So if the inside tire is steering thru the arc tighter than the outside tire, with toe in factory settings, more turning has to occur to get that inside tire straight than the outside tire that is already in the Turn arc being toed in. So straighten the toe like me, thus any turn of the wheel in either direction is already starting the turn on both wheels simultaneously ,so unlike Smith, Adams, Guldstrand minds stuck on design Ackerman doesn't change, changing those tie Rods changes Ackerman! It just isn't a slip angle or scrub only effect!
So again, if your inside tire is toed in, then the starting point is earlier lengthening essentially the arc to get the steering to the max limit! The outside tire start of arc is already pointed inward to the direction of your turn.
Ok taking that to the discussion here, going wider on tires results in naturally more scrub. So changing toe can have an affect on a lessor scrub benefit, but on our cars without reengineering components, you will never make that go away totally.
And just because I got an email asking to explain Ackerman, I will spend the time to explain things to the most simplistic and least time consuming explanation! I used to sit with Dick Guldstrand and talk cars, as I think we had the best handling C3 in his GRA club of all time and it wasn't his shop that set it up (335 rear tires in the 1990s helped that greatly too
), but couldn't get in depth explanations on all of this, so I bought every Smith book, Herb Adams book, and all of the others and all of them stop far short on the answers and engineering. Ackerman in my option is designed fixed, but it is a side to side thing! So if the inside tire is steering thru the arc tighter than the outside tire, with toe in factory settings, more turning has to occur to get that inside tire straight than the outside tire that is already in the Turn arc being toed in. So straighten the toe like me, thus any turn of the wheel in either direction is already starting the turn on both wheels simultaneously ,so unlike Smith, Adams, Guldstrand minds stuck on design Ackerman doesn't change, changing those tie Rods changes Ackerman! It just isn't a slip angle or scrub only effect!So again, if your inside tire is toed in, then the starting point is earlier lengthening essentially the arc to get the steering to the max limit! The outside tire start of arc is already pointed inward to the direction of your turn.
Ok taking that to the discussion here, going wider on tires results in naturally more scrub. So changing toe can have an affect on a lessor scrub benefit, but on our cars without reengineering components, you will never make that go away totally.
Last edited by TCracingCA; Jun 1, 2018 at 10:06 PM.
Thread Starter
Heel & Toe
Joined: May 2018
Posts: 24
Likes: 1
From: Wiarton Ontario
I am pretty sure that I read an article detailing how to do your own front and rear toe measurements and adjustments, but i can't find it now hat I need it. Seems to me ha it suggested setting the rear tracking first, then the toe - rear then front. It was also done with strings and wooden blocks. I'll keep looking and hopefully find it.
Le Mans Master
Joined: Nov 2016
Posts: 9,256
Likes: 949
From: Lake Tahoe, CA
Hello All
I have been experiencing some handling issues on some of the local roads that are less than smooth. The roads in question are tar and chip and i find my 79 darts and bolts let or right depending on the road. The car handles fine on regular highways. It has the 25560R15 tires and I wondered if the wide tire tends to follow imperfections in the road surface.I'm thinking, and hoping, that a wheel alignment will correct the problem. Is the anything special about aligning the corvette or is it something any decent alignment shop can handle. Any advantage in have a GM dealer do the alignment.
Thanks in advance
Jim
I have been experiencing some handling issues on some of the local roads that are less than smooth. The roads in question are tar and chip and i find my 79 darts and bolts let or right depending on the road. The car handles fine on regular highways. It has the 25560R15 tires and I wondered if the wide tire tends to follow imperfections in the road surface.I'm thinking, and hoping, that a wheel alignment will correct the problem. Is the anything special about aligning the corvette or is it something any decent alignment shop can handle. Any advantage in have a GM dealer do the alignment.
Thanks in advance
Jim
https://www.corvetteforum.com/forums...alignment.htmlhttps://www.corvetteforum.com/forums...at-home-2.html
Last edited by caskiguy; Jun 2, 2018 at 09:42 AM. Reason: add more content
Racer
Joined: Apr 2009
Posts: 331
Likes: 44
From: Cincinnati Ohio
Agree on alignment, but check the obvious things first. How much play is in steering wheel when parked? I had one that 'chased rabbits' on bumpy roads and it turned out to be a loose rag joint. The steering box also has an adjustment to take up play in it. These are simple to check and will cause the problem you are having. If these are OK, then jack up front wheels and see if top to bottom play, this is sign of ball joint issue.
Thread Starter
Heel & Toe
Joined: May 2018
Posts: 24
Likes: 1
From: Wiarton Ontario
Thanks for the links....a lot of good info there....very similar to the info that i had read elsewhere. Thanks again.
Drifting
Joined: Aug 2015
Posts: 1,939
Likes: 477
From: NSW, Australia
C3 of Year Finalist (track prepared) 2019
At stock height maybe (though I'd still recommend a little toe in), but if you're lowered then 0 toe on the rear will be twitchy as hell! If the halfshafts are level or close to it then the rear suspension will toe out on bump and rebound - toe out on bump in the rear of a car is nasty when cornering at any speed, you definitely want static toe in to counter the rear toeing out in bump!