1967 Suspension Improvements

[Kenny H.]

I'll be starting the process of doing a frame-off restoration on my 67 small block coupe in the coming weeks, and I'm looking for input on possible suspension improvements / suggestions I can do to make the car handle better. The car won't be raced, but I'd like to make the car handle as good as possible for some spirited driving. Other than making permanent changes to an otherwise stock vehicle, what can be done to make the C2 suspension perform better? Opinions on stock rubber versus polyurethane bushings on the a-arms? Aftermarket a-arms to improve suspension geometry? When I bought the car 15+ years ago it had a sway bar on the rear, which I removed since it's a small block car. Any thoughts on adding a rear sway bar for street driving?

Comments on offset trailing arms? Any expereinces, good or bad, on using these? Thanks for any help or suggestions you can give me.

[Keith B.]

Re: 1967 Suspension Improvements

Using radial tires will be your best bet. Unless you are going to track the car rebuilding with OEM parts is the way to go.

[Patrick H.]

Re: 1967 Suspension Improvements

I have found that the only useful places for polyurethane bushings are the rear strut rods and the rear spring ends, as these two locations seem to degrade quickly. In addition, adding them doesn't result in any extra squeaks or harshness.

Otherwise I would recommend nothing but original style rubber bushings.

Making sure that suspension components are all blueprinted and like new will give you the most benefit.

[Timothy B.]

Re: 1967 Suspension Improvements

Using radial tires will be your best bet. Unless you are going to track the car rebuilding with OEM parts is the way to go.

I agree, use the OEM parts, assemble it correctly install radial tires and enjoy your car.

If you want to go real fast and handle buy a newer Corvette.

[Duke W.]

Re: 1967 Suspension Improvements

The best way to improve "handling" is to have sticky tires, but most 15" replacement sizes today are "van tires" that don't provide much grip, so the first thing to do is find some decent tires. The Avon CR6ZZ DOT legal racing tire is about the only game in town, and it's available in V-rated 205/70, and 215/70R-15 sizes. The foundation of any "suspension" is tires, and installing a "performance suspension" on van tires is akin to building a house on dirt without a solid footing, but the vendors don't care - they just want your money.

The OE high roll center suspension geometry provides lots of roll stiffness from the springs (which is why C2s don't need big anti-roll bars) and and works well with the widest tires you can fit in the wheelwells. (Remember that the purpose of the suspension is to optimize the characterisitics of the tires.) Wider tires prefer lower roll centers, which yield less camber and toe change, which is why modern Corvettes have roll centers close to the ground, but that means bigger anti-roll bars are required for good roll control.

The next thing is to install rebound adjustable shocks like Spax or QA-1 so you can dial in the damping to your driving environment and preferences. Bob Riley had stated that 90 percent of setting up a suspension is shock tuning.

Now you need to set the alignment at "sport" settings- minus 1/2 degree front camber and maximum caster you can get within the adjustment range up to 2 degrees. Rear camber should be at least minus 1/2 and up to minus one degree. These negative camber settings will also help provide tire clearance to the fender lips. Toe-in should be 1/32" at each corner.

The base springs and front anti-roll bar provide road-friendly ride rates and good roll control, but can be a bit twitchy at the limit and suddenly transition to oversteer at the limit, especially with low grip tires. This can be mitigated by installing hard bushings in the front anti-roll bar to control arm links. Start with the OE 3/4" bar and if it's still twitchy at the limit with the hard link bushings, find a 13/16" front bar that was OE on base suspensions beginning sometime at the seventies. Don't use a rear bar with either of these front bars. This set up should yield about 3-4 degrees of roll per g, which is okay. If you want less roll, install the '75-up FE7 1 1/8" front and 7/16" rear bars. Keep in mind that anti-roll bar contribution to roll stiffness is a function of bar diameter to the fourth power, so a small change - as little at 1/16" will make a noticeable difference in roll, but more importanty, it will effect understeer/oversteer balance. Anti-roll bars not only control roll, but they are the key element in achieving proper understeer/oversteer balance.

So most of the money will go into tires and shocks. The rest is just alignment and bar tuning. Don't spend money on "suspension kits" that include poly bushings, stiffer springs, and big bars. For the most part they are a waste of money unless you have racing tires and plan to do some serious competition or unless you want to turn your Corvette into a buckboard on van tires.

Duke

[Kenny H.]

Re: 1967 Suspension Improvements

Thanks everyone, your responses is what I was looking for. I'm not planning on racing the vehicle, I just like C2's (I've owned several) and want the best handling 48 yr old car I can have, within reason. At the risk of opening up a can of worms, what are opinions on how the C2 suspension rated in 1967 in comparision to the competetion then?

[Steven B.]

Re: 1967 Suspension Improvements

Kenny, back in the day, and recently, have built a few B/Prod and A/Prod suspensions. Since you are not racing the car, including auto-X'ng, go with the above---tires, adjustable shocks, front bar, bushings, and tuning. Check clearances in the steering box. You may need to rebuild. The old Greenwood specs. work well. If you have any money left some lighter wheels for unsprung weight but be careful of the offset. As far as comparing '67 suspensions to the comp (sports cars) most others had less power and needed a suspension to compensate. The Corvette suspension was good by '67 standards and the car had power to assist in getting around corners. Similar to straight axles you could help the steering with the right foot. Have fun. Steve

[Duke W.]

Re: 1967 Suspension Improvements

The term suspension covers a lot of ground beginning with basic architecture such as independent (of various types) and rigid axle. Beyond that you get into high level technical specs such as ride rates/frequencies, roll centers, roll stiffness, anti-dive, anti-squat, and lower level details such as camber, toe, and caster curves. Unfortunately, few enthusiasts understand these terms. You have to have at least a high level engineering understanding of suspension design. The aftermarket capitalizes on consumer ignorance by never going beyond stiff springs, big bars, and solid bushings. They want your money, and don't ask any tough questions. I once asked an aftermarket suspension rep at a trade show what the ride frequencies were with their springs versus the OE springs, and I got the "deer in the headlights" look as he likely had no clue what "ride frequency" means.

Consider the following. When the 1963 Corvette was introduced, few cars had independent rear suspensions even though the three-linnk design was a compromise compared to modern five-link designs (upper/lower control arms with a toe link or five independent links). Ferraris had solid axles through 1964. The new Porsche 911 had semi-trailing arms, which is not as good an architecture as the C2/3 three-link, but a vast improvement over the previous 356 swing axles, and Mercedes was still using the low pivot swing axle. Perhaps the best contemporary IRS design was Jaguar, which is somewhat similar to the Corvette three-link design.

If you follow my basic recommendations, you can have a C2 Corvette that handles as well with similar limits (like about 1g on a skidpad) as many contemporary sports cars/sedans, without a bone-jarring ride, and, again, the key issue is tire grip. The rest is just tuning.

Anyone who is seriously interested in suspension tuning should get Fred Puhn's "How to Make Your Car Handle". It's probably out of print as it was initially published in the seventies, but used copies are probably out there. Also, the Chevrolet Power Manuals from the seventies have a good section on vehicle dynamics and suspension design.

The best available book is Bill Milliken's "Race Car Vehicle Dynamics". It's used in both undergraduate and graduate level university courses and is considered "The Bible" among suspension engineers.

Duke

[Kenny H.]

Re: 1967 Suspension Improvements

Thanks Duke, I intend to follow your recommendations, including getting those reference books. My degree is in mechanical engineering, like you I believe, so gaining a full understanding of the suspension system will be my first order of business. Just so I understand your tire recommendation above, it says the Avon is a DOT legal racing tire; any recommendations for a street tire since I don't intend to race the car or is this a street recommendation as well? Thanks for the input.

[Gene M.]

Re: 1967 Suspension Improvements

Kenny,
I like the Goodrich Radial TA. As you know the midyear does not have much extra room for wider rubber. I also run gas charged shocks which seems to complement the radials too. A 6" wide rim is about all that safely fits without tire rub and tire bulge when going with wider 70 series tires. I run 205 front and 215 rears.

[Duke W.]

Re: 1967 Suspension Improvements

Just so I understand your tire recommendation above, it says the Avon is a DOT legal racing tire; any recommendations for a street tire since I don't intend to race the car or is this a street recommendation as well? Thanks for the input.

"DOT legal racing tire" means it's a road legal tire, but they have stiffer sidewall construction and soft compounds and are intended for competition or those looking for maximum grip in a road legal tire. Unfortunately, there is nothing currently available in Corvette sizes for OE wheels between DOT legal racing tires and van tires such as high speed rated summer high performance tires with wear ratings of 300 or less.

Any tire that has a speed rating less than H and a wear rating of 400 or more is a van tire. Maximum grip is about 0.75g and nothing you can do to the suspension will improve this in a meaningful way.

I run DOT legal racing tires on my Cosworth Vega (Toyo Proxes RA-1) and '91 MR2 (Yokohama A008R). I don't race them anymore and only drive them a few hundred miles per year. Given that both model tires will yield about 10K miles of normal road driving, wear is not an issue, and I still occasionally enjoy letting the 1g cornering and braking capability of these tires pull my socks down on a twisty road.

Duke