Category Archives: Project GTI

OEM Spindle Options for GTI: Steering Ratio Comparison

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The stock GTI spindles are cast iron which means heavy, rusty, and even prone to cracking under heavy track use. Fortunately, there are a couple of OEM forged aluminum options that remedy all of the above. The Audi S3/VW Passat spindle is geometrically identical to the GTI spindle except for having a slightly shorter steering arm. The Audi TT spindle offers a lower lower ball joint mounting point to improve roll center which is great, but it it also has a much longer steering arm. The length of the steering arm directly effects how far the wheel is angled per amount of tie rod travel. The longer the arm, the less wheel angle you get for a given amount of tie rod travel.

The stock VW GTI arm has a 10cm steering arm. The forged aluminum Audi S3/VW Passat spindle has a shorter 9.6cm steering arm. Finally, the Audi TT has a much longer arm at 13.3cm. The plot below compares the resulting ratios.

SteeringAngle

As you can see, the GTI and S3/Passat spindles are similar with the S3/Passat being a bit quicker. It also shows how much slower the TT spindle makes the steering ratio. The TT suspension was designed as a total system. This shows mismatching components in a system can have cons you need to be aware of.

Project GTI: Background

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GTIsmf21

So like I said in the intro, I bought a new Volkswagen GTI in 2010. It’s the perfect car for my needs.  First of all, its a nice, comfortable car. I’m 6’4 and the GTI is the ONLY car (on my interest radar) with factory seats that I’ve sat in that i can clear a helmet in. I can drive it on long road trips without feeling cramped. It has a solid on-center feel that makes long drives on the highway effortless. It has a solid stereo with good features, good utility and cargo space, and good gas mileage. So it fits the daily driver bill.

And most importantly, its fun to drive. Stock, it has decent power and a solid suspension. I did two autoxes on bone stock suspension and was surprised with the results. The car rotated very well and body roll was reasonably controlled. It was fun to drive. So it fits the ‘fun to drive’ bill as well.

Since this is the background post of a project that’s now three years old, I’ll go ahead and get to the good stuff. Here are the mods to date:

Power:

  • APR Stage II flash. More boost, more power! I’m making around 275hp and 310ftlbs at the crank.
  • Ultimate Racing 3″ downpipewith ceramic cat and no resonator. Quicker spool, more top end power.
  • Audi S3 Intercooler. Cooler and more consistent intake air temps.
  • Carbonio Intake. Some noise and who knows what else. 
  • VW Tiguan pipe. Deletes the factory noise pipe which funnels sound into the cockpit. Quicker spool.
  • Neuspeed Turbo-Outlet-Pipe. Replaces the restrictive factory pipe and provies a more secure clamp interface.

Suspension:

  • Bilstein B8 Sport shocks/struts. (MK6 model #s)
  • VW Drivers Gear springs. Linear rate, a little stiffer than stock.
  • Hotchkis 27mm hollow sway bars front and rear. 
  • 034 Motorsport strut mounts. Much stiffer rubber keeps the strut planted.
  • Audi S3 spindles. Forged aluminum, stronger, lighter, and shorter steering arms quicken steering.
  • Whiteline Anti-Lift Kit. Adds castor, reduces front end lift, and stiffens the rear LCA mount.
  • Autotech transmission mount insert

Brakes/Wheels/Tires:

  • Stoptech 328mm ST40 brake kit
  • Stoptech Street Performance pads for daily and autox
  • Hawk DTC-60 pads for track
  • VW Goal wheels (17×7.5″) with Dunlop D1 Star Specs for summer, autox, and track
  • Stock Detroit wheels (18×7.5″) with stock all seasons for winter/off season

Other:

  • Audi S3 smooth underbody tray
  • Audi S3 rear trailing arm underbody covers

Wow, that list really got long after a few years. The boring part is that I think the car is just about done. The springs, shocks, mounts, and spindles is my most recent mod and they really completed the package. The car rides great in daily use and really feels good on track.

Here’s a few of my track and autox videos.