Suspension lowering question
Thread Starter
Instructor
Joined: Mar 2014
Posts: 110
Likes: 1
From: SoCal CA
Suspension lowering question
I just put new suspension under my 77 and would like it lower. I bought a set of 8" bolts for the back, but the front is showing 27 5/8" to the wheel well. I have 255/60/15 on 8" wheels. My question is how low can I go and still be streetable?
Thread Starter
Instructor
Joined: Mar 2014
Posts: 110
Likes: 1
From: SoCal CA
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Measuring the fender is an imperfect way to determine ride height. Section 3 of the Chevrolet Chassis Service Manual shows the correct way to determine ride height. In a nutshell, you measure the height of the inner pivot of the lower control arm to the ground. Then measure from the ground to the lower surface of the ball joint. You subtract the smaller value (ball joint) from the larger (control arm pivot). The spec is 2.5" plus or minus 0.5" for 1969 Corvettes. Your year may be different. This method eliminates any variation due to different tire sizes.
In my case, with aluminum heads, intake, water pump, and headers, the car was too high in front with 460# springs. Cutting ~half a coil from the springs brought my car in spec. Cutting coils stiffens the springs. Mine are about 550# with the shortened springs. Not noticeably stiffer to me.
Pete
Last edited by PeteZO6; May 15, 2014 at 12:06 AM.
Thread Starter
Instructor
Joined: Mar 2014
Posts: 110
Likes: 1
From: SoCal CA
OK, I'll jump in here. Same tire and wheel size, I measure 27 1/4" ground to the front fender lip. Go here:http://www.californiastingrays.us/Ve...Ruff_1969.html and scroll,down about half way, you'll see a side shot of my car for an idea of how it looks. Just about where it should be.
Measuring the fender is an imperfect way to determine ride height. Section 3 of the Chevrolet Chassis Service Manual shows the correct way to determine ride height. In a nutshell, you measure the height of the inner pivot of the lower control arm to the ground. Then measure from the ground to the lower surface of the ball joint. You subtract the smaller value (ball joint) from the larger (control arm pivot). The spec is 2.5" plus or minus 0.5" for 1969 Corvettes. Your year may be different. This method eliminates any variation due to different tire sizes.
In my case, with aluminum heads, intake, water pump, and headers, the car was too high in front with 460# springs. Cutting ~half a coil from the springs brought my car in spec. Cutting coils stiffens the springs. Mine are about 550# with the shortened springs. Not noticeably stiffer to me.
Pete
Measuring the fender is an imperfect way to determine ride height. Section 3 of the Chevrolet Chassis Service Manual shows the correct way to determine ride height. In a nutshell, you measure the height of the inner pivot of the lower control arm to the ground. Then measure from the ground to the lower surface of the ball joint. You subtract the smaller value (ball joint) from the larger (control arm pivot). The spec is 2.5" plus or minus 0.5" for 1969 Corvettes. Your year may be different. This method eliminates any variation due to different tire sizes.
In my case, with aluminum heads, intake, water pump, and headers, the car was too high in front with 460# springs. Cutting ~half a coil from the springs brought my car in spec. Cutting coils stiffens the springs. Mine are about 550# with the shortened springs. Not noticeably stiffer to me.
Pete
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
As already mentioned, other than possibly for cosmetics, static ride height really should not be left to the question of fenderwell heights; rather suspension geometry and ground clearnance.
Geometry wise, you would be better off if you don't go lower than ~1" Z height up front, and no lower than to where the inner U-joints are ~1/2" above the outers out back (both measured with 1/2 tank fuel and approx. driver's weight aboard). To get the body closer to the ground plane than that you should consider drop spindles and/or raising the diff in the chassis.
As for ground clearance, I can't speak to the roads on which you drive, but bear in mind that the lower you go the more spring you'll need to keep from bottoming. That said, IMOE 1" Z on the street with F41 coils and an all iron BB is a good recipe for dinging up a perfectly good bellhousing.
Of course, if you don't care how your car actually drives or how often your frame bangs the road, then slam away...
TSW
Geometry wise, you would be better off if you don't go lower than ~1" Z height up front, and no lower than to where the inner U-joints are ~1/2" above the outers out back (both measured with 1/2 tank fuel and approx. driver's weight aboard). To get the body closer to the ground plane than that you should consider drop spindles and/or raising the diff in the chassis.
As for ground clearance, I can't speak to the roads on which you drive, but bear in mind that the lower you go the more spring you'll need to keep from bottoming. That said, IMOE 1" Z on the street with F41 coils and an all iron BB is a good recipe for dinging up a perfectly good bellhousing.
Of course, if you don't care how your car actually drives or how often your frame bangs the road, then slam away...
TSW
Last edited by TheSkunkWorks; May 15, 2014 at 03:36 PM.
Thread Starter
Instructor
Joined: Mar 2014
Posts: 110
Likes: 1
From: SoCal CA
Thanks for the info. I think the front is a done deal @ +/- 27 1/2" front (seems the half coil is the answer, which was done before the install). Now for the rear I just want it to look even. I will definitely pay attention to the inner and outer u-joints
Racer
Joined: Jul 2013
Posts: 294
Likes: 10
From: Palmer Alaska
As already mentioned, other than possibly for cosmetics, static ride height really should not be left to the question of fenderwell heights; rather suspension geometry and ground clearnance.
Geometry wise, you would be better off if you don't go lower than ~1" Z height up front, and no lower than to where the inner U-joints are ~1/2" above the outers out back (both measured with 1/2 tank fuel and approx. driver's weight aboard). To get the body closer to the ground plane than that you should consider drop spindles and/or raising the diff in the chassis.
As for ground clearance, I can't speak to the roads on which you drive, but bear in mind that the lower you go the more spring you'll need to keep from bottoming. That said, IMOE 1" Z on the street with F41 coils and an all iron BB is a good recipe for dinging up a perfectly good bellhousing.
Of course, if you don't care how your car actually drives or how often your frame bangs the road, then slam away...
TSW
Geometry wise, you would be better off if you don't go lower than ~1" Z height up front, and no lower than to where the inner U-joints are ~1/2" above the outers out back (both measured with 1/2 tank fuel and approx. driver's weight aboard). To get the body closer to the ground plane than that you should consider drop spindles and/or raising the diff in the chassis.
As for ground clearance, I can't speak to the roads on which you drive, but bear in mind that the lower you go the more spring you'll need to keep from bottoming. That said, IMOE 1" Z on the street with F41 coils and an all iron BB is a good recipe for dinging up a perfectly good bellhousing.
Of course, if you don't care how your car actually drives or how often your frame bangs the road, then slam away...
TSW
My car was lowered purely for looks by the 2nd owner and to do that the springs were heated. Yep old school trick, not a good way at all. So I put new 460# springs in and it brought the height back but I have a real suspension again. I would consider cutting 1/2 coil but no more since any good bump or frost heave at speed will likely turn my car into a road scraper.
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