Hi-Speed Handling Question !
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
Likes: 0
From: Ogden, Utah
Hi-Speed Handling Question !
Drove our 93 Corvette to work yesterday so I could leave early. On the way home it was the perfect time to get the baby up to 3 digits. Got her up to 125 mph, then a farmers combine pulled onto the road , had to slow down. Car ran great was still pulling strong when I had to back off. My question is; over 110 mph the front of the car feels like it is lifting up and it tends to wonder a little, nothing that couldn't be controled. Does anyone know if this is normal, or if I need a stronger front spring, shocks etc. Does this happen to any others out there?? Anything information will be appreciated.
Thanks in advance. :seeya
Thanks in advance. :seeya
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: Hi-Speed Handling Question ! (Bob Lapine)
At 140 I felt like I was bolted down. Cornering at 120 was like on rails. Something on your cars is not right.
Start cheap -
Air pressure in tires (low air can make front end seem to float).
Alignment (will make front twitchy).
Tires (worn or out of balance).
Worn bushings (who knows where you are going).
Shocks (at speed you could start undulating).
There's certainly more, but it's a start.
Start cheap -
Air pressure in tires (low air can make front end seem to float).
Alignment (will make front twitchy).
Tires (worn or out of balance).
Worn bushings (who knows where you are going).
Shocks (at speed you could start undulating).
There's certainly more, but it's a start.
Racer
Joined: Apr 2002
Posts: 389
Likes: 0
From: Micco FL
Re: Hi-Speed Handling Question ! (Bob Lapine)
162 MPH and it felt a little light, but I think I just confused that with how little effort it took to change lanes. At 135-140 it felt like a slot car. All this is to say don't confuse how easy or quick you can move around at high speeds...this is the nature of the beast (speed). However if you accurately detected a lightness in the front end I firmly agree with those above...there is something amiss.
Cruising
Joined: Mar 2002
Posts: 13
Likes: 0
From: Saint Paul MN
Re: Hi-Speed Handling Question ! (Bob Lapine)
Have you or a previous owner made any suspension mods? A lowering kit on the rear spring would affect the front if nothing was done up front. If you have a rear lowering kit it would use nylock nuts instead of castle nuts with a cotter key.you could also measure your wheel well height to make sure you are running flat or slightly nose down. My car started riding nose high after I switched to the 84 z51 spring set.
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
Likes: 0
From: Ogden, Utah
Re: Hi-Speed Handling Question ! (John Row)
Thanks John
I got new tires, and had the front end aligned late last year, the car has over 81,000 miles. It might be the shocks, I am thinking of getting some new front ones at least and then will check the bushings out. Thanks for taking the time for your advice
Bob :D
I got new tires, and had the front end aligned late last year, the car has over 81,000 miles. It might be the shocks, I am thinking of getting some new front ones at least and then will check the bushings out. Thanks for taking the time for your advice
Bob :D
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
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From: Ogden, Utah
Re: Hi-Speed Handling Question ! (vvv90)
Thanks V V V 90 for the advice, I will have it checked out pronto, its got new tires, and I had the entire car aligned late last year.
Bob :D
Bob :D
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
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From: Ogden, Utah
Re: Hi-Speed Handling Question ! (PTz-92-LT1)
Thanks PTZ-92-LT1
I appreciate your advice, I will have things checked out, I got new tires all around, had a 4 wheel alignment done late last year, I am thinking bushings or shocks. I am thinking it might be shocks, the car has 81,000 miles on her, might be time.
Thanks
Bob :D
I appreciate your advice, I will have things checked out, I got new tires all around, had a 4 wheel alignment done late last year, I am thinking bushings or shocks. I am thinking it might be shocks, the car has 81,000 miles on her, might be time.
Thanks
Bob :D
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Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
Likes: 0
From: Ogden, Utah
Re: Hi-Speed Handling Question ! (jrbooth)
Thanks JRBooth
No as far as I know the suspension is stock, I haven't lowered or did anything like that to the car ! I will have to have it checked out soon. thanks for your help...
Bob :D
No as far as I know the suspension is stock, I haven't lowered or did anything like that to the car ! I will have to have it checked out soon. thanks for your help...
Bob :D
Racer
Joined: May 2001
Posts: 320
Likes: 0
From: TX
Re: Hi-Speed Handling Question ! (Bob Lapine)
Make sure you check the rake angle. This is the angle of the car front to back. If the rear is level or lower, you need to raise it up. Vette's like the rear about 0.5 in higher in the rear than on the front.
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
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From: Ogden, Utah
Re: Hi-Speed Handling Question ! (kkonen)
kkonen;
What is the best way to check my 93's rake?? Do I have to go to an alignment shop and have them do it ? If I can do it myself how do I go about measureing it.
Should I check the front end for bushings, bad shocks first then check the rake so I would eliminate one area first then check the second etc.
Apprecidate your advice
Bob
What is the best way to check my 93's rake?? Do I have to go to an alignment shop and have them do it ? If I can do it myself how do I go about measureing it.
Should I check the front end for bushings, bad shocks first then check the rake so I would eliminate one area first then check the second etc.
Apprecidate your advice
Bob
Racer
Joined: May 2001
Posts: 320
Likes: 0
From: TX
Re: Hi-Speed Handling Question ! (Bob Lapine)
Put your car on level ground. Measure just behind the front wheel to the body. Do not use the top of the wheel well. Do the same just in front of the rear wheel. Pick a point that should be straight on the car. This will give you a good idea of the rake of the car. To set it perfectly, you need a perfectly level surface, I use an alignment rack. This ensures proper weight distribution.
I hope this makes sense.
I hope this makes sense.
Racer
Joined: Feb 2002
Posts: 390
Likes: 0
From: St. Louis MO
Re: Hi-Speed Handling Question ! (Bob Lapine)
Can't really offer any insight - wanted to add that my '94 exhibited exactly the same symptoms. Was driving home from a family gathering late one evening and had some ricer playing games with me. Kept nosing into the rear bumper and then passing on the right, only to get in front of me and hit his brakes! Got my attention. I decided to run around him and give him a quick look a my tail lights. Had the car up to 135 when I noticed the front end was starting to bounce. As I continued on the throttle the car started an up and down motion, like it was trying to go airborne. I stuck with it for a moment trying to decide what was up and it kept getting worse. I let off the throttle and gingerly applied the brakes until it got back to normal handling (around 90 mph). As far as I know the car is stock, no suspension or height mods. I've check the rake and it's exactly .5 inches front to rear. It's got 60K miles and still has the original shocks - I'm thinking the shocks are the culprit, but not sure. Any further suggestions on this topic???
TIA
:confused:
TIA
:confused:
Thread Starter
Instructor
Joined: Jan 2000
Posts: 132
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From: Ogden, Utah
Re: Hi-Speed Handling Question ! (Topload)
Topload :
Thanks for the info, my 93 has 81,000 miles on her. I had new Bridgestone Protenza Tires put on last year, also had a 4 wheel alignment . When they aligned her the mechanic asked if I raced or just cruised, I told him that I just did alot of high speed crusing, trips etc. He set the alignment to factory specs, and also said that the front end was tight. Like you I am thinking "shocks" I have Bilsteins all around and plan on replacing the fronts for now ASAP, will see if that helps.
Thanks
Bob Lapine :cheers:
Thanks for the info, my 93 has 81,000 miles on her. I had new Bridgestone Protenza Tires put on last year, also had a 4 wheel alignment . When they aligned her the mechanic asked if I raced or just cruised, I told him that I just did alot of high speed crusing, trips etc. He set the alignment to factory specs, and also said that the front end was tight. Like you I am thinking "shocks" I have Bilsteins all around and plan on replacing the fronts for now ASAP, will see if that helps.
Thanks
Bob Lapine :cheers:
Pro
Joined: Jan 2001
Posts: 681
Likes: 2
From: Newton (Wichita Area) Kansas
Re: Hi-Speed Handling Question ! (Bob Lapine)
This is a interesting problem. I'm trying to think things thru here. Sounds like there's definitely an aerodynamics issue. My question is how will changing shocks fix this?
Ideally shocks (dampers) are designed to damp the oscillations of a spring and don't to the spring rate. If we assume the car is travelling at 125 mph for a minute or two the front leaf spring has plenty of time to come to equilibrium given the loads on it stay the same (car's not turning, windspeed is constant, etc). Given enough time and constant conditions the effects of the damper fade away since the spring is not being compressed or relaxed anymore. If the car's frontal area is shaped in a such a way that it's going to achieve some degree of lift at 125 mph then it's going to do that eventually regardless of he dampers.
Another thing to consider is headwind. If the vehicle is going 125 mph into a headwind of 25 mph then the actual airspeed is 150 mph. This makes it hard to compare experiences.
Anyway, just some thoughts. Any aero engineers or experienced road racers out there? If the new shocks do help, let us know. Never hurts to replace old ones anyway!
Ideally shocks (dampers) are designed to damp the oscillations of a spring and don't to the spring rate. If we assume the car is travelling at 125 mph for a minute or two the front leaf spring has plenty of time to come to equilibrium given the loads on it stay the same (car's not turning, windspeed is constant, etc). Given enough time and constant conditions the effects of the damper fade away since the spring is not being compressed or relaxed anymore. If the car's frontal area is shaped in a such a way that it's going to achieve some degree of lift at 125 mph then it's going to do that eventually regardless of he dampers.
Another thing to consider is headwind. If the vehicle is going 125 mph into a headwind of 25 mph then the actual airspeed is 150 mph. This makes it hard to compare experiences.
Anyway, just some thoughts. Any aero engineers or experienced road racers out there? If the new shocks do help, let us know. Never hurts to replace old ones anyway!
Racer
Joined: May 2001
Posts: 320
Likes: 0
From: TX
Re: Hi-Speed Handling Question ! (jmr302)
You are correct if you are on a smooth surface. However, we tend to drive on bumpy roads. The small bumps have a greater effect as the speed increases. This can set up oscillations in the spring resulting in varying aerodynamics. Therefore, shocks are very important for high speed driving.
Would new shocks help you? Assuming they have the correct dampening rate, they will. I think stiffer is better (to a point) but more experienced racers would know.
Would new shocks help you? Assuming they have the correct dampening rate, they will. I think stiffer is better (to a point) but more experienced racers would know.
Pro
Joined: Jan 2001
Posts: 681
Likes: 2
From: Newton (Wichita Area) Kansas
Re: Hi-Speed Handling Question ! (kkonen)
That's a good point, kkonen!
If the front end is underdamped it's going to bounce around and the rake of the car won't stay anywhere near constant.
If the front end is underdamped it's going to bounce around and the rake of the car won't stay anywhere near constant.
Melting Slicks
Joined: May 2000
Posts: 2,029
Likes: 63
Re: Hi-Speed Handling Question ! (jmr302)
Mine did that too, especially after I installed new shocks (Bilsteins). I was really disapointed with it, i felt my car was undriveable at high speeds. It felt like rebound dampening in my shocks was too weak.
While I was wondering which shocks to replace them with I installed front A-arm poly bushings and a new front sway bar with poly bushings too. Wham! the problem was gone. Now I feel the shocks are working perfectly. I've driven 10K miles since and I am very happy with my suspension (after that i have installed some more bushings and rear bar too, see my sig). I drive mostly on street and very rarely on road courses.
BTW, my car had about 70-75K miles when I renewed the shocks, the previous set was totally dead and they were NOT the originals but cheap Gabriel replacements. So, IMO you can only benefit from changing new shocks to your car.
ToniH
While I was wondering which shocks to replace them with I installed front A-arm poly bushings and a new front sway bar with poly bushings too. Wham! the problem was gone. Now I feel the shocks are working perfectly. I've driven 10K miles since and I am very happy with my suspension (after that i have installed some more bushings and rear bar too, see my sig). I drive mostly on street and very rarely on road courses.
BTW, my car had about 70-75K miles when I renewed the shocks, the previous set was totally dead and they were NOT the originals but cheap Gabriel replacements. So, IMO you can only benefit from changing new shocks to your car.
ToniH