Spreader Bar - Does the frame flex
Thread Starter
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
Spreader Bar - Does the frame flex
So I pulled the bolt out of one side of the spreader bar (and put in a couple of zip-ties) and went for a short drive around the block.
Road is pretty normal, a few cracks etc nothing major
Car has what I like to think of as a decent frame
Just drove around, didn't throw it into any corners or anything weird, watch the control arm and listen to how little the engine is working...
Here's a couple of sections of the video, You can see the spreader moving in-out around easily around 1/16"+
Now imaging what must be happening when a corner is made with some speed or aggression
I know this isn't a good demonstration or anything but it does show how the top of the frame where the control arms mount can move around even under old-man driving
M
Road is pretty normal, a few cracks etc nothing major
Car has what I like to think of as a decent frame
Just drove around, didn't throw it into any corners or anything weird, watch the control arm and listen to how little the engine is working...
Here's a couple of sections of the video, You can see the spreader moving in-out around easily around 1/16"+
Now imaging what must be happening when a corner is made with some speed or aggression
I know this isn't a good demonstration or anything but it does show how the top of the frame where the control arms mount can move around even under old-man driving
M
Last edited by Mooser; Aug 30, 2016 at 03:42 PM.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Doesn't surprise me in the least how much the frame flexes, you can feel it when travelling on our poorly surfaced roads here. I often thought that the original C1 frame with its X member was probably more resistant to flex. If you look at the lengths they went to strengthening the frame for road racing it highlights the issues of the standard item.
Safety Car
Joined: Feb 2012
Posts: 4,705
Likes: 983
From: Orlando FL
2026 Loser of the Year
Joined: Sep 2013
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From: New Or-leens Loo-z-anna
I accidentally "corrected" the frame sag on my project.....I used a floor jack under the main crossmember to lift the front end.
Now the measurement from rail to rail is within 1/16 inch....I'd better stick a spreader bar in there before it "closes" again.
I did...however....put a nasty concave dent in the bottom of the crossmember.........
(rookies......
)
Now the measurement from rail to rail is within 1/16 inch....I'd better stick a spreader bar in there before it "closes" again.
I did...however....put a nasty concave dent in the bottom of the crossmember.........
(rookies......
)
Safety Car
Joined: May 2004
Posts: 4,345
Likes: 1,574
From: los altos hills california
Great video, thanks Mooser. One of the forces that acts on the frame is camber thrust. You can see a correlation between control arm movement and the spreader bar, where I would presume camber thrust to be the major factor here. Any idea how much camber you have?
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Thread Starter
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
The car is a big block so there's a lot of weight sitting between those arms but still, flex happens. I'm guessing there would be an easy 1/8"+ movement taking a normal on-ramp.
Hard to believe but when I bolt the bar back in the difference even pulling into the driveway is noticeable somehow.
Everyone says the bars make a difference, I wanted to SEE the difference.
M
The ORIGINAL and bestest
Joined: Oct 2000
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From: Toronto Ontario
Toronto Events Coordinator
Cool vids Mooser. 
I am a firm believer in the positive benefits that a spreader bar offers these cars. I drive my car quite aggressively on a regular basis; several years ago I removed the spreader bar to do some other work, and the lack of it was immediately noticeable!!
One of the best "bang for your bucks" mods there is.
I am a firm believer in the positive benefits that a spreader bar offers these cars. I drive my car quite aggressively on a regular basis; several years ago I removed the spreader bar to do some other work, and the lack of it was immediately noticeable!!
One of the best "bang for your bucks" mods there is.
Le Mans Master
Joined: Apr 2001
Posts: 9,556
Likes: 288
From: Granbury Texas
Most street drivers will never notice it. However, when you put sticky RACE tires (slicks) on a C2 or C3, you will find significant frame deformation and suspension point degradation from spec. This will give you NO confidence in your car placement on the track, and therefoire slower lap times. It "may" also lead to premature (ya know, after 50 or 60 years) frame cracking. Flexing a frame hudreds of times per lap at 1.2 to almost 2 Gee will certainly wear that frame out quicker than on a street driven car. The Owens Corning race team treated frames as "consumables" and replaced them regularly.
Race Director
Joined: Jul 2004
Posts: 12,680
Likes: 329
From: Scottsdale Arizona
Doesn't surprise me in the least how much the frame flexes, you can feel it when travelling on our poorly surfaced roads here. I often thought that the original C1 frame with its X member was probably more resistant to flex. If you look at the lengths they went to strengthening the frame for road racing it highlights the issues of the standard item.
Great video Mooser. I'm almost surprised that there wasn't more flex. I was shocked at how much my handling and general stability improved when I added the spreader bar. This mod started me down the path of working on my suspension. I love the end result but no I ndividual change was as significant as the spreader.
Melting Slicks
Joined: Jun 2011
Posts: 3,114
Likes: 597
Great video Mooser. I'm almost surprised that there wasn't more flex. I was shocked at how much my handling and general stability improved when I added the spreader bar. This mod started me down the path of working on my suspension. I love the end result but no I ndividual change was as significant as the spreader.
I think the only real way is to have real time suspension measurements with and without the bar to see the change in the contact patch of the tire while cornering.
As for preserving the structure of the frame is were I put my, " I agree worth doing".
It may also help reduce body rattle noises, and rattle noises in the interior, again worth doing.
But for improving street driving handling I think this is a "placebo effect" were the driver pushes the car harder and this feeling is the wow factor.
After driving your corvette on the track with street WOW factor is hard to get.
My 2 cents.
Safety Car
Joined: Feb 2012
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From: Orlando FL
Safety Car
Joined: May 2004
Posts: 4,345
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From: los altos hills california
I suppose it is too late to ask, but when and how did these start to show up? It is indeed a great improvement.
Le Mans Master
Joined: Apr 2001
Posts: 9,556
Likes: 288
From: Granbury Texas
I would have to agree with cagotzmann on this. The lower control arm is pretty solidly mounted at a place that I wouldn't think flexes all that much. The upper is a different story. If you consider the camber change for 1/16" over the height difference between those two points, say 12", that is less than a third of a degree. Can't imagine that is enough to notice.
I suppose it is too late to ask, but when and how did these start to show up? It is indeed a great improvement.
I suppose it is too late to ask, but when and how did these start to show up? It is indeed a great improvement.
Race Director
Joined: Jul 2004
Posts: 12,680
Likes: 329
From: Scottsdale Arizona
Over the years there has been two camps in the spreader bar debate: makes a big difference and makes a small difference but is worth doing. I've also seen pics of broken shock towers due to metal fatigue. I tend to think that there is a pretty wide range to the degree of flex present at the time of the mod which probably accounts for the variation. Anecdotally, it also seems to make a bigger difference in convertibles though I'm not sure why that would be the case since the fame differences are in the birdcage area, not the front end.