Adam's Brief
Fox Tuning Guide

My Fox on a dyno, Sept 2001.

Purpose

Engine Power Upgrades
[Adding more horsepower, torque, etc.]
Theory
An engine can be compared to an air pump.  To get more output from the pump, you have to be able to deliver more air to it, and also expel the larger volume of air that it'll pump.  Once this is done, other things can be done to the pump's internals to make it have a better output.

VW Fox

Suspension
[Improved Handling]
Theory
There are several reasons for lowering a car.  Most of them center around improving the handling characteristics and performance, but in addition to this, a lowered suspension alter the looks of the car.  When lowering a car, specifically one like our Foxes with a MacPherson strut suspension in front, it is important to remember that for the best handling, the control arms should be parallel to the ground.  If you lower the car beyond this, it will negatively affect handling.  When a car is lowered, its center of gravity gets lower, reducing the body roll during cornering and also weight transfer.  Lowering springs not only lower the car, but also stiffen up the suspension in order to compensate for less suspension travel, and also to help with cornering.  This is the reason why it is recommended to use actual lowering springs rather than cutting stock springs a coil or two.  Springs made for lowering are often made so they have a "progressive" spring rate, meaning that up to a point they are fairly 'loose', but beyond this point they are stiffer;  this really helps on a car that is still used as an every-day street car.  In the Fox case, however, since real lowering springs are scarce, one may have to resort to cutting a set of stock springs.  I do not know anything about cutting springs, so I cannot comment on the effectiveness of this solution.  In addition to stiffer/shorter springs one should also upgrade the shock absorbers.  A stock-spec shock will not last long with shorter springs, because it is not meant to operate in the range that a shorter spring needs shock absorbing.

VW Fox
Unfortunately all companies that ever made lowering springs for the Fox have discontinued them.  You might get lucky and find some old stock sitting around at a tuning shop somewhere, but chances are you won't.  Several Fox owners have done research regarding any possibly crossover of parts from other VAG products.  While almost none of this has been verified in practice, it works in theory:
Front:  Audi 4000 / VW Quantum non-Quattro/Syncro springs + Fox shock inserts.
Rear:  Corrado G60 springs + Fox shocks or A2 Golf springs & shocks. [I am still trying to verify this.]

If you are planning on getting custom springs wound, it is adviseable not to lower the car more than 1.25-1.50".  The Neuspeed springs drop the car approximately 1.0-1.25", and this brings the control arms paralell to the ground, the optimal position for handling.  Here's a picture of my car's control arms, with Neuspeed lowering springs.
Shock absorbers:  There aren't many options for Foxes.  If you have a big budget, go with Bilsteins.  For adjustability go with Tokico or Koni.  For the "best bang for the buck" go with Sachs Super Gas.  I'm using these with Neuspeed springs and am satisfied.  The rear end still sits down slightly under hard acceleration, but for price, I'm not complaining.

Wheels / Tires
[Improve handling & Looks]
Theory
The larger the rim size, and the smaller the sidewall size (prividing you keep the overall height the same), the less lean the car will have in turns.  This is because there is less sidewall to flex.  However, rims above 15" in diameter might not fit properly, and will also yield a harsher ride, due to less flex in the sidewall.

Tire sizes explained:  175/70-13.  175 = 175mm tire width.  70 = the sidewall height is 70% of the tire's width.  13 = rim diameter in inches.
Rim sizes explained:  5.5Jx13H2 ET45.  5.5 = rim width in inches.  The J refers to the design of the rim's lip (I have never seen anything other than a J).  13 = rim diameter in inches.  (I have not been able to determine what H2 means.)  ET45 = offset in mm.  [The offset is how far the mounting surface (the part that touches the brake when mounted) is from the centre of the rim - an ET0 would have the mounting surface in the exact middle, ET 45 means that the mounting surface is 45mm towards the outside of the rim moving the wheel closer to the inside of the car, and ET-45 would mean that the mounting surface was 45mm towards the inside of the rim moving the wheel farther from the inside of the car.]  Rims also have a hub size, which is specific to certain cars.  The hub size is the round hole in the middle of the rim, which centers the wheel once it's mounted on the car.  While it's possible to mount a rim with a bigger hub, it is quite dangerous, as the wheel may not be centered and will cause some serious steering/handling problems.  The bolt pattern, which isn't often stamped on the rim, is the number and spacing of bolts that hold the wheel to the car.  The Fox's bolt pattern is 4x100, meaning there are 4 bolts and they are 100mm apart.

Fox
The stock tire and rim size on Foxes is either:
5Jx13H2 ET45 with 155/80-13  or
5.5Jx13H2 ET45 with 175/70-13 or
5.5Jx13H2 ET38 with 175/50-13  [this was the factory-installed aluminum rims]
All rims have the 4x100mm bolt pattern shared by all 4-bolt Volkswagens and even some Audis.  Be careful with Audis, as some of them have a 4x108mm bolt pattern, and are therefore incompatible with the Fox.

In order to keep your speedometer showing the proper speed and your odometer the proper mileage, it is adviseable to stay with the same overall wheel diameter.  The following is a list of tires that have the same overall diameter:
155/80-13
175/70-13
185/60-14
205/50-15

When choosing rims to upgrade to, the following should be taken into consideration:

Any Volkswagen 4-bolt wheel will bolt up on a Fox, up to about 15" in diameter.  Above this, the rim might rub on suspension components, or on the body.  And even with 14"s, if the offset is wrong, the tire will rub on the body, even if the car is not lowered.  I have this problem with my rims - 6.5Jx14H2 ET33 with 185/60-14 designed for A3 Volkswagens.  While they bolt up without any problems, the tires rub on the inner fenders in the rear when the car goes over a bigger bump on the road.  Hondas share an identical bolt pattern and hub size, so they are another source for wheels.  BMWs, Nissans and other cars also have 4x100 bolt patterns, but their hub sizes might be different, making the wheels unsafe to use on a Fox.

One other option that is available which will make the car quicker (at the cost of a lower maximum top speed) is to run smaller-diameter tires.  The smallest-diameter tires available for 13" wheels are 175/50-13 and 195/45-13.  These will yield a much quicker acceleraion, but will lower your top speed, and also make your speedometer and odometer inaccurate.  Using this size tire will also help improve handling a bit, since they lower the car's center of gravity and reduce the sidewall height.

Brakes
[Improved Braking and Safety]
Theory
Brakes are among the most important upgrade you can do.  No matter how fast or slow your car is, if you can't stop it in time, you will be in big trouble.  For everyday driving, the stock brakes are adequate (otherwise, the factory would have used something better).  Here are various styles of front disc brakes explained:
Solid rotors:  This is exactly what it sounds like - a solid disc of metal.  Foxes come stock with these.
Vented rotors:  Many street cars come with these - essentially two solid rotors connected by fins to help with cooling.
Cross-drilled rotors:  These are usually aftermarket - the rotors have holes drilled right through the contact surface, again to help with cooling.
Slotted rotors:  These are also aftermarket - the rotors have grooves cut into them to help with cooling, and to get rid of the dust that is produced during braking.
And combination of the last 3 is possible, i.e. vented, cross-drilled and slotted rotors do exist.
Unless you do a lot of hard stopping withing a very short time (such that the brakes heat up so much that by the second or third hard stop they are too hot to work properly), you do not really need to upgrade to anything more than vented rotors and appropriate calipers.
For the rear brakes, again, unless your car sees track time, where the brakes would see many hard stops within a short period of time, you do not to upgrade beyond the stock drums.  The majority of braking is done by the front brakes, so you do not need to upgrade the rears on a street car.

Fox
We Volkswagen owners are very lucky because VW and Audi share brakes among many different models, and most brakes are interchangeable between various models, making brake upgrades a simple "out with the old, in with the new" job.
Front
Volkswagen brakes come in 3 sizes:  9.4", 10.1" and 11.0".  Only 9.4" and 10.1" are easily swappable onto our Foxes.  With 9.4" brakes you can use any rim size above and including 13", whereas with 10.1" brakes you have to use at least a 14" rim (and some 14" rims might not clear the brakes, so you'll have to test-fit them).

With all Fox brake upgrades, you have to switch the sides - whatever came on the left side on the donor car goes on the right side of the Fox and vice versa.  Good brake pad manufacturers include:  Ferodo, Mintex, Axxis Metal Master and others.

Rear
The stock drum brakes are good enough for even highly enthusiastic street driving.  If you still feel that an upgrade is necessary, Fox wagons came with larger drums in the rear (200mm vs. 180mm diameter), and many Volkswagens came with rear discs.  If upgrading to rear discs, it might be a good idea to also upgrade the master cylinder so that they get enough pressure, and while you're doing that, it would be worth your while to install brake proportioning valves so that you can adjust the brake bias (the balance between whether fronts or rears get more braking power).

Interior
Theory
Well, the theory behind modifying your interior is for it to be different.  This can be for looks, for functionality, for more information, or whatever else you want.  There are virtually no aftermarket parts specifically for the Fox, so doing anything is custom-fitting work.  Don't get discouraged, though, it's a lot of fun, and chances are you will end up with a completely unique setup if you work on it yourself

Fox
Here's a list of what can be transferred from other Foxes.  GL models, Wolfsburg models and even other Volkswagens can be a source for parts to make your Fox's interior different and/or better.

Exterior
Theory
Again, this is highly personal - modifying a car to suit one's tastes.  This can be for looks, for better lighting, etc..
PLEASE don't be discouraged by the lack of parts in this section - improvise, modify, adapt and even make your own parts!

Fox

Credits
The information found on this page is a collection of what I have learned from many people.
Big thanks go to Jonathan, Joshua, Karl, Heather, Kenny, Louis, VWoT, the two online VW Fox clubs, Dave @ Motronix, and anyone I may have forgotten!
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E-mail me with any and all comments, and especially if you can add to this page!
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