Check the alignment settings. Rear toe out can easily induce wild oversteer. Ask me how I know.

 

i was thinking the same thing. i haven't wanted to splash the cash for a hunter balance untill i replaced the suspension rubber, but who knows when that will be.

i did a rear to front alignment check with some string, and it was way out.


thanks again for all the responses--that is almost all.

 

A tire produces grip by means of tractive slip (acceleration) or side-slip angle (cornering). Both at the same time reduces the available grip for both which leads to further instability.

The front axle will be in pure side slip so there is plenty of lateral grip available. The rear axle, due to the addition of tractive slip will exhibit reduced lateral grip.

Side slip angle rate rear > side slip angle rate front = oversteer, if uncorrected = spin.

The grip is reasonably modelled by the friction circle or friction ellipse.

 

I had the same Kuhmo's you've got. They are terrible for breaking loose and when they do, you have a hard time getting traction back. I had no traction at all in 1st and could mat it in 2nd at 35-40 mph and spin 'em hard. My advice...be careful on those tires.

 

I had the same tires on my LT1, and never had those problems, unless there was something on the road.

Also I had the same KYB shocks, and didn't have these problems...

However, the 1992 has softer springs than earlier models...

 

hope you're feeling better!!!!!!!

 

Ive never had many issues with my 93 at insane highway speeds even at wot. i routinely used to do highway sweepers at 275 km/hr and accelerating out (god i love the 403 ) at wot and even through bumps it was steady. My best guess? Alignment. I would never ever do fast curves without having the alignment done first, and i used to do it every other week. I remember the one time i had all the poly bushings done on the car and i took it out for a spin. we tired to get the settings near where they were before removing everything and even though it looked pretty good.. the car was a disaster to drive. any throttle at making left turns at 15 mph and the back was sliding. I couldnt believe it. It had bump steer on highway on-ramps just like my brothers solid axle 97 camaro did, it skipped over bumps like the back wheels were turned the wrong way (which theey probably were).

In all after the poly job the 40 km i drove to the alignment shope were incredibly scary. After it was done it was like driving a whole different car. thats why im suggesting get ur alignment done. Only reason your car will be swapping ends that fast is if your wheels are trying to go in a different direction you want them to.

 

good concise, scientific analysis. clarifies and condenses something that seems obvious after reading it. but the best explanations usually do.

so when you combine enough drive acceleration, lateral forces and speed, your butt will spin. the greater the proportional torsional acceleration and speed, the lesser g force is needed to overcome the dwindling available traction: even to a point of unnoticable side loading. i can definitely testify that it took little to no g force to break me loose. the evidence being that after enough spins to bleed off 70mph, i was still on the road--in the same lane i started in. any kind of curve with inertia would have put me in the ditch. this lack of g loading prior to the spin is what prompted me to post. if i had done this on any kind of a corner, i wouldn't be surprised. i mean, that's why i floored it--i was on the straight-away.

and yes, the rubber on my kumho's seems way too hard for my set-up. these tires were highly recommended by vette owners on tirerack's site. but i think most of these guys liked them because they were inexpensive, had good street manners, a cool tread and moderate resistance to being quickly smoked off the rear. that's why i bought them. but when it comes to pushing moderately to hard on a two-lane rural road, they just don't cut it. when i buy again, it will be something with a treadwear of 140. i believe the forum member who suggested this number posted that after two years, tire rubber becomes hard and loses performance--so you should buy a tire that will wear out in two years. a two year performance life cycle on tires is not what weekend drivers want to hear, i know.

this brings up the question, how old were the tires when i bought them? they were on sale, and that may have been because they had been sitting around the warehouse too long. for performance purposes, forget that, for any purposes--you need good braking in a minivan full of kids--tires should have a born on date. i don't know if they do, but if they don't, it is probably to mask this very problem. unless mandated, manufacturers will usually only provide information that is flattering or increases the sales of their product. depending on the demand and the size of inventory, some tires may hang around for some time in retail stores and even longer in distributor's warehouses. i will definitely inquire into tire age before i purchase another set. maybe i'll get an answer. buying a popular, well known brand may help to offset this problem.

this brings me back to needing a rear wing. 70 mph seems to be the break point--literally. the kind of driving that prompted this post definitely calls for a rear wing to create the downforce needed to help offset the lack of lateral grip encountered during speed and hard torsional acceleration; especially, when you have stiff suspension components and worn out suspension rubber. if the rear end is going to skip, for whatever reason, i want somebody pushing it back down onto the road. the great thing about a wing is that the faster you go, the better it works.

also, it looks like a good four wheel alignment is needed under the above conditions. if your rear wheels are pushing out of the curve--increasing g. loading--when you have the above induced minimal traction, you're gonna spin. it's one thing on an autocross track, but another on a rural road with a ditch on both sides. i don't mind busting me up: i've had concussions, a broke neck, broke back, dislocations and too many fractures. i just don't want to wreck the car unexpectedly. when i do wreck, i want it to be because i was doing something reckless, not seemingly average.

and thanks bogus, i'm feeling better today--i took an extra pain pill, and i'm gonna go look at the car.


thanks to every one for helping me understand what happened. i know that i should have rolled into the throttle, but under those road conditions with a moderately powered stock 85, i shouldn't have to worry about rolling into the throttle. that should be saved for a stronger motor, but probably practiced with this one. i guess i've moved into a bigger league, and need to apply some big league solutions.


thanks again, frog.

 

thanks, i put something like that in my last post. it took me a while to write it, so i didn't see yours.

you know after reading your post, the alignment seems like it is probably the single biggest factor in my spin. as i posted before, after a string test, the front and rear alignments were definitely in oppositon. the spin was so fast and so far out of the car's character, i couldn't believe it. i haven't driven the vette much since buying it, and it was poorly maintained prior, so i wouldn't be surprised if it hadn't been aligned for many years. i've been spending my money on fixing peripheral problems, new tires and shocks, a planned exhaust upgrade, matching steering wheel and seat covers, and rear wheel bearings--most of which are sitting in the corner of my bedroom waiting for install. evidently, the last thing i wanted to spend my cash on was an intangiable and unglamorous high quality wheel alignment. but i now have a new perspective.

this is probably the principal solution for those who have experienced the same symptoms but at higher speeds. the lower the speed the problem manifests--the greater the combat between the front and rear wheels, and the greater the need for the alignment. the hunter alignment machine has been highly recommended by members in the past. i did a search on their website, and was pointed to the one location in tucson that has one. as i said before, i've put off getting one because of the perceived cost (i haven't actually called yet), and the need for new suspension rubber. i've been waiting untill i replaced one to perform the other. but i can now see that if i don't get a good four wheel alignment, i may not have anything to put the rubber on.

i'll get one done

i've spent a lot of time on this: analyzing and trying to find the reasons for and solution to my spins. one reason is that they scared the crap out of me, another is that they scared the crap out of me, but mainly it's because when you mix a corvette and a curvy road together with speed, testosterone and after shave, and then throw in a bad wheel alignment--you could get whacked. my alignment must be so waaay off--so way off that speed and wot allowed the rear wheels to pursue their own line (talk about independent suspension). it seems to me that a good alignment is critical on a vehicle that gives, at best, minimal feedback before breaking loose.



guinea-pig frog.