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Steering box brace - any good?


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I drive my 710 and then my wife's Toyota iM. What a difference on the same corner in our neighborhood. It also has a small bump thrown in. The Toy is like riding on a large slab of steel a foot thick. All four corners are working on it.

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Well said Tom.

 

Universally I think we all agree that with the 510's sloppy steering, a box brace is a worthy investment. I don't think anyone would argue that a stiffer body isn't better for a high performance FINE tuned 510 suspension.

 

Let's be realistic though, the 510 was designed with semi trailing arm trail through rear suspension that literally steers the back end around corners with body roll. Great for spirited driving around town, but totally impractical for high performance handling. No amount of body stiffening will fix that. Ball park solution is to lower it, readjust toe and camber in the rear, correct steering geometry in the front, run stiffer springs, higher shock dampening, and stiffer sway bars. With sticky tires and double/triple the power that does put significant torsional stress on the unibody.

 

Here's the reality check, worn out shocks / tires, tire choice, and or low tire pressure have a far greater effect on handling, ride comfort, and damping frequencies than a strut brace, but once you modify the stock suspension there are infinite variables that influence handling differently for each particular modification and adjustment. I think it's fair to say a strut brace does not effect all suspension setups the same, so to say it makes a difference is purely anecdotal. Even if you did everything correctly in tuning all the suspension mods necessary to adversely flex the 510 body enough to effect tuning, at that point doesn't a body bonded roll cage become necessary? As Stoffregen points out, the tub falls apart under that kind of stress. Once you have a bonded roll cage though, a strut brace becomes totally superfluous. Is there a midpoint window where a strut brace makes a difference? If you can tell I'd say it's time for a roll cage.

 

If you are experimenting with some suspension parts in your garage, I would say your best investment for improving your handling from there would be a professional wheel alignment. Even then I defy anyone to tell the difference in handling between a strut brace and a 1/2" difference in rear ride hight. No one is saying it's bad for the car, or even that it doesn't look cool, just that it's unrealistic to say it improves performance in a street modified 510. 

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When I started road racing motorcycles we couldn't get the latest 125cc GP bikes so everyone was racing 8 year old 125s, what you could get was the latest sticky Michelin slicks. It was no surprise the frames would develop cracks. While our Datsuns are actually pretty good around the firewall/torque box area they're still 70s cars and they get run on modern tires that have way more grip then anything back in the day.

 

Now we could stitch weld the entire thing; that won't take more than 40-60hrs and 15lbs of wire so clearly quite practical

 

Despite being a good starting point the stock suspension is pretty much crap; my wife had a Geo Prizm (Corolla), we were following some friends around Lake Meads North Shore Road, they were driving Triumph Spitfires and MGBs, the Geo was glued to there bumpers. You just can't compete with newer.

 

I'd totally agree spend the money on suspension goodies like bars, springs and dampers first.

 

As for the braces; it may well be akin to replacing a worn motor mount on your modern car, after you fix the mount the car is suddenly much quieter inside. On a road car the contribution to the handling may be the difference between pulling .80Gs and .804Gs, so yeah probably not going to matter. If I've done everything else I would be tempted to try various braces.

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Just for the sake of argument, I'll point out that the 510 body shell is comprised of two basic sections, or boxes. The main body area is one huge six sided box. The front area, or engine bay is a box with only four sides. When a roll cage is installed, the already stiff main cabin becomes very rigid and it becomes even more necessary to use a strut tower brace because the stress points have been concentrated in two locations of the flexy four sided box at the front.

 

This is all perfect world scenario thinking. I'm not standing up and yelling that everyone needs to modify their chassis for strength or tuning.

 

It's also amazing how the technology has advanced the structural integrity of cars these days. A modern car (anything built after the mid 80's) is so much more capable than anything built before that. As a few have pointed out here, a stock modern sedan will outperform an old sports car. I remember a trip my brother and I took once in his MGB. It was a 2500 mile trip that ended on a rainy night through some back roads of northern Wisconsin. The road nearly killed us. The next day we took my grandmother's new 1997 Lexus GS300 for a spin. We were able to do nearly twice the speed in the same wet conditions on the same twisty road that we arrived in the night before. A modern sedan which weighed at least two times as much kicked the MGB's ass.

 

The old box of a 510 is no different. It has it's strong points, but they have to be taken in context of the era in which it was built. And with what we know now, we can definitely improve upon it.

 

BTW - regarding paradime's comment on the 510's IRS, we used to run 800 to 1000 lb springs in the rear just to keep roll steer to a minimum. With a lot of HP, that rear steer can be fun, but dangerous as hell.

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Very well said.

 

I've heard that door alignment get's warped when big HP/torque motors are stuffed into 510s, but never hood issues. Not to say it doesn't flex, but maybe the front is designed to flexes rather than bend like the passenger box?

 

I'm running 300lb. springs with 330hp, but I do have a stout 1.25" front, and 3/4" rear sway bars so body roll is held to a minimum. On hard acceleration though my car squats like a female dog pissing. Maybe I should man up and go with 800lb springs. I just don't know if my rumpled old ass can take that.  :lol: I've also been told that if you rase the pickup points and flatten the trailng arms out it doesn't bind and squat as bad. Waiting for Jeff's arms to come out before I try that. 

 

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A friend gifted us a set of Spec Miata suspension for my son's street car; the springs are something like 750-800 front and 450 rear. It doesn't ride nearly as bad as I thought it would.

 

Off on a bit of a tangent; modern cars are much wider track, which makes a huge difference. My 1200 is 3 inches wider than stock and it's still 3 inches narrower than our 91 Miata. New cars also tend to have longer control arms which also helps.

 

Naturally their is a price for the increase rigidity, new car are pig heavy. A V6 Camry is heavier than a 65 Ford Galaxy.

 

Tom

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Are you saying I have 1100lb. springs... Maybe my ass is tougher than I thought.

 

Fronts are 300 so I would expect the rears to be a close match. You mention the rear squatting excessively, so I assumed the springs were light. If you have coil overs then the rate at the rear is pretty much what the spring is rated at because the spring is basically over the axle. The stock spring location on the control arm acts like a cantilever. To feel like a 100 pound spring at the axle, a spring must be 3.8 times stiffer. So if your rear spring is in the stock location and has a 1,200 pounds per inch spring rate, out at the axle it will feel like 1,200 / 3.8 = 315

 

If you carefully measure the thickness of the wire, the width (diameter) of the coil from the outside over to the outside and can count how many coils between the top and bottom that are not touching the vehicle, I can work out the spring rate.

 

For example the stock 510 spring is 0.472 wire thickness, 5.12 diameter and 8 coils, although this might be total coils including the loops that sit against the body and control arm. It's likely less but anyway the rate is about 89 pounds per inch. 

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You guys make a lot of great points!  

 

I've driven over 50 510's from stock to very modified.  I personally think rack and pinion is required if you don't want your 510 steering to feel sloppy.  That's why over the years I have spent so much time on it.  Everything else just feels like a band aid.  

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Yes, the 510 can benefit hugely from rear geometry mods. Flatter control arm angles are one of those mods. And yes, a stiff rear bar too. But be careful that the rear bar isn't out of whack with the stiffness of the front bar. Too stiff a rear bar can bring the back end around in a second, especially under deceleration. Also, solid mounting the rear crossmember to the body (without those rubber bushings) makes for a more controlled setup. Less crossmember movement equals less toe change,.

 

There's been a lot of hypothesizing about front steer vs rear steer on the front end. Some say that the front steer is more conducive to high speed. I never had a problem with the stock steering box setup, but one way I controlled the sloppy steering (you're going to laugh), I ran a large diameter Momo steering wheel. With a Nascar style seating position (arms not so stretched out) and a large wheel, I could saw at the wheel like they do in Nascar and not wear out my arms. It worked for me!

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My current car "Hey" I pulled the rear bar, the front bar is 1 1/8th inch, 300lb springs all around custom rear coilovers and the rack and pinion Sam and I build.  I've been autoXing it since I started the suspension upgrades and I can honestly say that it's possible to get good lap times with the stock steering but I've found with rack and pinion it's way easier to "drift" my car when I loose control and it's much more repeatable.  Now sometimes I can get my fastest lap on the 5th out of the 12 laps we count for trophies.  Unlike before where it was one of the last laps I got my fastest lap.

 

 

To add just because a company sells something as a performance part doesn't mean it improves suspension.  I had T3 rear coilovers.  A friend told me about his secrete rear dampeners, so I build some coilovers using them.  Next autoX I got the fastest lap of the day in my 160hp powered dime.  The difference was amazing.  That's just one example I can give you.  In conclusion the steer box brace will make a difference, not sure if it will matter for what you do.   

 

 

Stoffregen I have a similar setup, moderate sized wheel and I sit very close.  So close it's not that easy to shift, so I'm working on a new shifter position.  I should probably add these pics that show the roll center.  Notice that "flat control arms" are helpful but the roll center is still to low.  

 

 

 

 

 

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You can't do much about roll centers in a strut suspension setup. You could raise it a hair by raising the inner control arm pivot, which would help.

 

 

Or a thicker "bump steer space" we made them super thick on Sam's car, they almost touch the brake rotors and his LCA's point slightly down now.  

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