Racing Arms – Part Four


Over the past several issues, we’ve taken the time to carefully examine front suspension control arms (a-arms) in drag race applications.  To recap, factory setups regularly lack sufficient adjustment to provide enough caster for racing.  They also lack the right bushings for race applications and they typically don’t have built in provisions for travel limiters.  A good drag race a-arm (such as the pieces manufactured by TRZ Motorsports shown in the accompanying photos) will be built from high strength, lightweight 4130 chrome moly steel, and they’ll be TIG-welded.

Fair enough, but there are a couple of other things you should consider when contemplating aftermarket a-arms.  One is the cross shaft found on the upper a-arm.  Here, the folks from TRZ a-arm doesn’t rely upon the stock (heavy) steel shaft.  Instead, the cross shaft is milled form billet aluminum.  We asked a mechanical engineering friend about the use of aluminum here, and he assured us the loads in drag racing wouldn’t be sufficient to compromise the structure, even when you take regular wheel stands (and particularly, landings) into consideration.

Another thing you should think about when buying aftermarket a-arms (drag race or otherwise), and that’s respective ball joints.  While there are extended ball joints available today for stock a-arms (the rationale is to improve the front suspension geometry – it changes the arc of the a-arm travel, and helps to maintain camber in a wheel stand situation), they aren’t necessary with purpose-built a-arms.  The reason is, the geometry has already been “fixed” when the a-arm was built.  What about the old ball joint spacers of old?  Those pieces (which were quickly outlawed by race sanctioning bodies) allowed the car to have more suspension travel.  Trouble was, they were poorly built and broke with regularity.  That’s why they were outlawed.  With a good race arm, you should be able to service it easily (without going out of your way to find replacement parts).  That’s why TRZ simply uses replacement ball joints for the given car (1970 Nova a-arms use replacement ball joints for a 1970 Nova).  Service parts are available just about anywhere.  Here, the top ball joint bolts in and the bottom one presses in, just like stock.

What about spring types?  TRZ offers a-arms in two different configurations – one with a stock lower spring pocket and another for coil over-shock applications.  For cars like the first generation Camaro or 1968-74 Novas, you’ll need to make a modification to the shock mount on the upper frame.  TRZ offers a kit just for that application.  If you’re using a stock style spring, then the a-arms are simple bolt-in.  What’s best, a stock spring or a coil over?  You’ll get a lot of answers to that question, but for the average (heavy) car, a conventional spring will actually work better.  A conventional spring (or a specialized drag race conventional style spring) will store a good amount of energy.

TRZ’s Todd Braasch offers his (considerable) insight: “One question I get asked a lot is, what’s best; a coil-over or standard spring for racing?”  Lots of variables there.  But we tend to narrow it down to the power of the car, the tire they’re running, and they type of shock they’re going to use.  I always tell people under 900-1000 HP that a standard style coil spring (like Moog, Moroso, or the Landrum Santhuff springs) combined with a decent shock will be best to make sure they have a lot of stored energy and travel.  And they can control it with the shock.  If they’re making over 1000 HP, then I do offer up a coil-over as an option with the plus’s being easy spring swaps and spring “tuneability” (350 lb. springs, 375 lb. springs, 400 lb. springs, etc.) and it helps when scaling and setting ride heights to get the cars nice and level.  The downsides being coil-overs don’t have a lot of stored energy or useable travel.  But if they’re making over 1000 HP then you don’t usually need 5″ of travel and can get by with limiting it to 3″ or so.  Which is just fine with a coil-over setup.  We do have some customers that like the standard spring, but their car weighs very little, and they make over 1000 HP.  Ron Rhodes uses our arms, Santhuff springs, and very tight Santhuff shocks.  (The car weighs under 2600 lbs. and makes probably 1500 HP.)  In a setup like that, you can do it but you NEED a high dollar shock like a Santhuff or a Menscer or something like that to really be able to almost lock down the travel using the shock regardless of the amount of stored energy in the spring.  That kind of power, combined with a spring with a lot of stored energy, needs a great shock.  You won’t get by with a QA1 for bolt-in out of the box Strange or a similar shock.

As you can see, you have a wide range of options (springs, shocks, format), but Todd’s advice (above) pretty much gives you the straight scoop.

Before we leave, the final thing you should think about when it comes to aftermarket a-arms is the actual lower shock absorber mount.  The problem here is the size of some aftermarket shock absorber bodies, and in particular, the adjusters.  Plenty of these drag race shocks have big adjusters on either side of the shock.  And guess what?  They don’t fit inside stock a-arms.  And many aftermarket a-arms have a shock opening in the lower a-arm that needs to be ground away so that you can actually fit the shock body.  That’s not the end of it either: In many cases, once you get the shock in, you can access the adjuster (which, to me at least, is a wee big counter-productive).  TRZ provides you with the largest possible opening for the adjusters to pass through, and the inner pocket that surrounds the shock has been relieved so that there is actually room for the adjuster knobs.  Finally, the shock mounts are designed with built-in weld-nuts.  You don’t need to stick a wrench inside the control arm to fasten the shock.

In the end, it’s pretty clear that the TRZ a-arm package has been designed and built by racers for racers.  No matter what package you choose (application or shock/spring type), the pieces are extremely crafty.  Welds are fabulous; the weight is low (as much as 15 pounds less than stock per side) and, of course, the geometry is spot-on for drag racing.  We’re big fans of the product.  For more, check out the accompanying photos:

Upper a-arm cross shaft.
The upper a-arm cross shaft on the TRZ piece is manufactured from billet aluminum.
As you can see here, the upper incorporates a pair of ½ X ½-inch high strength rod ends. The strength here well surpasses the loads you’ll encounter on a drag strip.
Cross bracing of the a-arm.
Speaking of strength, note the well-thought out cross bracing. Like the rest of the a-arm, the brace is chrome moly.

Adjustable travel limiter.

Adjustable travel limiter.
TRZ Motorsports configures their upper bars with an adjustable travel limiter. Review the series for a recap.

"Stack of dimes" welding.

"Stack of dimes" welding.
Here’s a look at the “stack of dimes” welding on the TRZ a-arms. They’re (obviously) nicely TIG welded. Many aftermarket a-arms are production line welded using a wire feed system. You get what you pay for.
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