You can have all the power in the world, but if you haven't got the right rubber on all four corners, then you and a tree are going to have a very intimate encounter.
Rubber, boots, ditchfinders; call them what you like, but those black circles around your Wheels are a lot more complex than you think.
While their most obvious purpose is to give your car grip, they're also an intrinsic part of the Suspension, with their flexible walls having a cushioning effect.
They may look simple to you, but tyre technology is a massive science, with thousands of hours and millions of dollars going into the compound, tread pattern and dimension of each tyre.
WARNING: Cheap tyres cost lives! Using old, worn or damaged tyres on your car puts your life at risk!
All modern tyres for road use follow a basic idea. Two hoops of steel, known as beads, are joined together with steel mesh with a U-shaped profile. This metal shape is covered in layers of rubber and material, with thicker layers on the outside. This outside layer is known as the tread, and side is the sidewall. The tread will have channels carved into it to drive water away from the centre towards the edge. This tread will have a minimum depth at which it's safe to use, and as you wear your tyre down you will you will approach that minimum depth. Once there, the tyre needs to be changed.
The chemical formula of the rubber is different for each tyre and each company. Softer rubbers offer better grip, but wear quicker. Harder tyres are long lasting, but will feel like plastic, especially when cornering. No matter what firm you choose, tyres do have a limited life; about six years. After this, the rubber will have dried out to a point where it's no longer safe to use, and the tyre ought to be changed.
You can check the age of any tyre by looking for the DOT code, printed on the sidewall. You should see "DOT XXYY", where XX is the week and YY is the year of manufacture.
Tyre sizes are a really weird one. They are probably the only time you'll see metric, imperial, and a percentage figure when describing one product. Each tyre will have a number stamped on it, like this:
185 is the tyre width, measured in millimetres.
65 is the sidewall, and is a percentage of the width. In this case, 65% of 185 is 120.25mm.
R is the type of tyre; a Radial.
14 is the inner diameter, meaning the size of wheel that it fits. This is measured in inches.
Once you add all these numbers up, then divide by 2, you get a number called the rolling radius. For the E30, you need a rolling radius of 298mm. If you change your rolling radius, you will affect not only the speedometer readout, but also the gearing of the car.
Lets take an example. You want to change from the balloon-like 185/65R14 tyre to something with a bit less profile and a bit more width, so you look at a 195/50 tyre. A reduction from 185/65 to 195/50 isn't a reduction of 15mm. The 65 and 50 represent a percentage of the width (195), not a millimeter value, therefore:
65% of 185 is 120mm
50% of 195 is 97mm
A change of 23mm in the sidewall is nearly an 8% difference, which will definitely be noticeable. So you need to match your profile and your width to your wheel size.
We've made the following table to give you the best combination of tyre width and height for your wheels.
This question is a big can of worms, since a lot of it is personal preference. Some are willing to sacrifice road noise for grip, others will trade off grip for wear. So here's our Hit and Miss list of tyres for the E30:
|Avon||ZV3||Tolerable in the dry, but useless in wet weather||NOT recommended|
|Continental||Premium Contact 2||As the name suggests, a premium tyre with very good braking characteristics||Recommended|
|Dunlop||Fast Response SP||Decent rated tyre from a premium brand manufacturer||Recommended|
|Falken||ZE914||The only Falken tyre worth buying, a good budget tyre and almost comparable to the Toyo Proxes.||Recommended|
|Goodyear||Efficient Grip||Exactly what it says on the tin||Recommended|
|Kumho||Ecsta Sport (KU31)||Favourable reviews. A capable mid-range tyre, but can be noisy as they wear||Recommended|
|Toyo||Proxes T1-R||Excellent grip and sexy tread pattern for a decent price, although not very long-lasting.||Highly Recommended|
|Uniroyal||Rainsport 3||Superior grip in both wet and dry, and very reasonably priced. Currently the best tyre for your E30||Highly recommended|
|Vredestein||Sportrac 5||A great tyre from a quality manufacturer, and still available in the elusive 205/55/15 tyre size||Recommended|