Control Arms & Avons (again)

It’s been a long break, but after getting absolutely every possible run out a set of Hoosiers, I wanted to try another readily available set of tires. Around the same time, Paco Motorsports’ trick adjustable Rear Upper control arms went on sale with some factory seconds (ie: cosmetic blemishes).

I’ve coveted them for a while because the stock rear adjusters tie toe to camber, and these allow you to do 2 really interesting things:

  1. Adjust toe and camber individually.
  2. Play with suspension geometry a little bit. Because the upper rear arm is nearly infinitely adjustable, you can use the stock alignment cams to set toe, but also set track width, and then compensate by making the upper arm longer or shorter to maintain your alignment.
  3. Easy, consistent adjustments. Each 180° turn on the control arm translates to a 1/4° change in camber.

It’s one of those things that gives you plenty of rope to hang yourself with, but if you take your time and plan out what you’re doing (and take lots of measurements), you can do a lot of good as well. Which means I’m probably going to end up metaphorically hanging from the end of that rope…

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There were some concerns about the strength of the threaded components, so I took a few measurements. The gist of it is: the shaft is 3/4″ diameter, and it is a fully threaded sleeve on the control arm portion so there’s thread engagement far beyond the front and rear “nuts” it looks like it has. Barring some weird metallurgy issue, these should be plenty strong.

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Finally installed with the car. Between the adjustable upper arm, the adjustable offset upper-outer bushing (in the knuckle) and the stock cam adjusters, there’s a lot of adjustment now built into the suspension to make (or break) the setup.

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On to the tires: There is a readily available Formula Atlantic (I think?) Avon A11 compound Radial Slick in a 240/600R15 size. It’s about 1/2″ taller and wider than the Hoosiers I’ve been running. I’m not thrilled about the taller bit, as it may end up with some interference with the chassis, but the wider should be nice. And they allegedly last longer than the Hoosiers, while being as easy to get.

Ideally, I’d be on a 275/35/15 Hoosier A7 or a 21.5 x 10.7 x 15 Avon, but those are friggin expensive, and unobtanium on the used market, so I’m going to see how these do, then end up settling on either these, or the 23 x 9.5 x 15 Hoosiers after this set.

And finally, last night I had a buddy come by to help drink my beer and measure while I adjusted from under the car. While the last set of tires wore fairly evenly, it was apparent that the rears needed a little bit more camber, and the fronts needed to be adjusted. I think they got knocked out of alignment over a couple big bump at an event, because we found about -1.5° degrees camber on the left side and -3.5° on the right. Definitely not ideal.

After roughing in the rears to be even, I threw the “Me Simulator” 210 lbs of steel plates into the driver’s seat and we got to work. The alignment numbers I ended up on are:

Front Camber: -2.75°
Front Toe: 5mm out
Front Caster: as much as I can get away with and hit my camber number…

Rear camber: -1.75°
Rear toe: 0″

We’ve got an event this weekend so we’ll see how she runs, and go from there.

 

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Fun in the Workshop day

Today I:

Made a bracket / hook to keep the coolant re-route on the race car from chafing on the intake manifold support bolt heads and bracket.

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Cleaned up the diff mount brackets to install the Delrin lowers to compliment the Delrin uppers.

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Modded the old Horrible Freight press. Made the release operable w/o the handle, tacked the handle’s 2 parts together, and added a ring to hook a bungee to so the handle reciprocates. More of a fun ‘playing with the welder’ project, came out alright though.

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