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I have recently started competing in autocross. Because of some after-market wheels/tires, which I bought before I started autocross, I can't compete in the Stock class. The class I'm in, Street Touring, mainly allows for suspension upgrades.

I'm not ready yet to put thousands of dollars in to my car, but I would like to make whatever cheap and effective upgrades I can that will be legal in my class, and leave my car suitable as a daily driver.

The logic behind starting with wheels/tires is clear to me: the benefits of other modifications won't make much difference if your tires can't transmit the force to the road. For example, an extra 100hp from a supercharger won't help much if you're trying to channel it through crumby stock tires and narrow wheels. A decent set of wheels and tires is relatively cheap and will have a big impact on handling.

When it comes to suspension however, I'm not sure how to decide what to upgrade first. One thing I'm considering is a strut tower brace, since they only cost on the order of $100 and is easy to install myself. There are also kits that just upgrade springs, or just upgrade sway bars, just suspension bushings, or full suspension upgrades.

My question is: Will there be a benefit to a STB when I still have stock struts/springs/alignment? If not, what suspension component should I upgrade first? If I think that I might, in a year or two, want to install a full suspension kit, does it make sense to spend money right now on a just-springs upgrade?

In case it makes a difference, I'm driving a 2008 Mazda 3s.

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4 Answers 4

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After adjusting the nut behind the wheel, I would suggest the following

  1. Swaybars - Keep the car from rolling as much in the corners.
  2. Alignment - Help keep the tires flat
  3. Springs & Shocks - help resist body roll and start to tune the transitional response of the car
  4. Alignment (again) - new ride height and roll will mean new alignment to get the best results
  5. Wheels & Tires - get better grip. I usually go for partly used road race tires with too little tread for racing but plenty of tread for a season or two of AutoX.
  6. Alignment (again) - make sure you are getting the best out of the new tires
  7. Strut Tower braces (ft & rear) - I put strut tower braces last because until you get better grip, you are probably not going to be getting enough traction to cause enough load to get the strut towers to deform.

Tuning a car for handling is part science and part black art. There are a lot of people who will tell you the setup that works the best for your car, but they often won't agree and won't be the best for how you drive your car.

Once you have settled down on driving style, start making small adjustments to the car and see what works best for you. Even after 20+ years of AutoX, I usually spend 1/2 each event getting to a consistent, fast as it will go time. Then I start dialing in tire pressures and such.

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Swaybars are the best bang for the buck. That's always where I tell people to start. Other than really flimsy cars (convertibles, original Neons, and anything similar) strut tower braces are only of a minimal help, and really only once you've got everything else done anyways.

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tl;dr: Tire pressures will give the best bang for your buck. Second best: stock wheels with good autocross tires.

These two sentences are critical:

I have recently started competing in autocross. ... In case it makes a difference, I'm driving a 2008 Mazda 3s.

If we're talking about truly novice (or early amateur) level competition, I would strongly advise that you leave your car alone. At this point, you are still working out kinks in the critical control system (i.e., the driver).

That said, here are some simple tips available on the MazdaSpeed forum for introductory autocrossing. You'll notice that they tend to focus on tips for the driver rather than changes to the car.

Why not change the car? Because, as a novice racer, you're going to have enough trouble just racing without forcing you to also be a test driver for experimental equipment setups.

When you're ready to change the car, adjust your tire pressures before you make any parts changes. One of the posters on that thread suggests:

I ran about 42 front and dropped my rear to 30, the car has very good rotation

You would be surprised how much difference you can make with a few psi. Experiment with different pressures, run laps, repeat until you have a setup that is optimal for your style.

Finally, I'd suggest you consider finding some stock wheels and putting some good autocross tires on them. That would drop you back to Stock class and eliminate most of this problem.

EDIT: following up on the comments:

Will there be a benefit to a STB when I still have stock struts/springs/alignment?

No.

If not, what suspension component should I upgrade first?

First, you need to start deciding on your priorities:

What are your goals? Are you trying to speed up the dynamic transitions in the suspension? Are you trying to increase the rotation of the car in turns? Increase oversteer? Decrease understeer? Where are you losing speed on the course? What are your tire temperatures? Are you hotter on the outer edges, inner, or middle of the tires?

Any of these questions could suggest a particular engineering plan. Until you decide on exactly what you want to do, it's nearly impossible to give you advice.

If I think that I might, in a year or two, want to install a full suspension kit, does it make sense to spend money right now on a just-springs upgrade?

No. You should only make upgrades based on measured performance data.

All that said, if you are really committed to making changes, I would recommend that you solicit the advice of winning competitors in your class. Who else is running the Mazda 3 at your events? What parts are they using? Why? What changes did they have to make to their driving style to optimize their setup?

And, absolutely most importantly, what did this all cost?

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I agree. The other advantage of having a second set of wheels is that you can switch back to your normal road tyres before leaving - very handy if you're at an abrasive venue and have trashed the rubber you were using! –  Nick C Apr 24 '12 at 12:28
    
This is all good advice, in general. However, as I tried to make clear in my question, it's nothing I didn't already know. Yes, tires are the first thing to upgrade. I said that myself. Yes, it's too soon for me to make a lot of changes, and I need more practice. I know that, but it wasn't what I asked. –  Colin K Apr 24 '12 at 13:03
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Also, I don't really have any desire to get back in to the stock class. Regardless of autocross, I prefer to have summer tires on my car, and if I spend ~$150 on tires, I'm not going to put them on the stock wheels which are only 6.5" wide. I put my winter tires on the stock wheels. I do autocross for fun, so I don't care if I'm not wining my class. As it is, right now I only compete against other novices, where I do very well. –  Colin K Apr 24 '12 at 13:06
    
@ColinK, fair enough: I responded to your comments in the answer. –  Bob Cross Apr 24 '12 at 18:14
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Strut tower braces made a world of difference in my 270hp FWD Ford Probe Turbo. This could be because of a weaker starting chassis strength perhaps, but I noticed the stiffness immediately and it gave me much more confidence in the corners.

After F&R strut braces, I did Eibach lowering springs and Tokiko HP Struts, and then rims with BFG KDW2 Summer Only tires, oversized.

While this may not be in the order of most effect first, it IS in the order of cheapest first

  • F&R Strut Tower Braces = $80 shipped
  • Eibach Lowering Springs = $220 shipped
  • Tokiko HP Struts = $250 shipped
  • Rims and Tires = $1200 shipped

Your stock swaybars are probably decent (unless you have a source for cheaper upgraded ones), just check your links to make sure they're in good shape (and attached).

After that, I'd start addressing any lightening you can do. Can you live without A/C, Power Steering, Rear Seats, trunk insulation, spare tire and jack, etc., or does that bump you into the next class?

After that, you could get an underdrive pulley for pretty cheap that will reduce the rotational rate of your alternator/whatever else you're driving with it, and be much lighter at the cost of some vibration on your accessories, should run you $80 or so. Replacing your stock seats for lightweight racing models can shave 50 lbs or so.

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