E30 Strut Size Difference

If you’ve ever decided to replace the struts on your E30 3 Series, you’ll know that there’s a frustrating amount of conflicting information on strut sizes. The BMW E30 was designed with a strut housing that held shock absorber inserts, rather than the shock mounting directly to the chassis at the top and to the suspension arm at the bottom. These strut housings came in two sizes: 45mm and 51mm. Knowing which size your car came with is important when buying strut inserts. So how do you find out what your E30 has?

Depending on what you read, some parts of the internet will tell you that vehicles made before a certain date had the smaller struts, whereas others will tell you that smaller engines came with smaller struts and bigger engines with the bigger struts.

As bizarre as it sounds, the truth of the matter is there isn’t any rhyme or reason as to which E30 models came out with which strut size. With no strict rules, there’s understandably a lot of misinformation out there. It seems from the outside as if the BMW factory had two suppliers of each sized strut, and would simply fit whatever they had in stock to the vehicles that rolled past them on the production line.

The only way to be sure which one you have in your E30 is to get under your car and measure it (and because both were fitted, even RealOEM provides both sizes after entering an E30 VIN). To make things a little easier for our customers we visited E30 guru, Graeme Bell of Bell Motorsports in Hastings, to put together this simple guide. For our friends in the US, a dollar bill works just as well.

Once you’ve measured your strut size, you can choose from a number of Bilstein shocks that we stock in our Melbourne warehouse. If you want to go with standard replacement struts, then we recommend the Bilstein B4 that have been designed to OEM specifications. For those wanting more, the heavy-duty Bilstein B6 has been designed for performance driving scenarios, maintaining a predictable and precise connection with the road under trying conditions. The Bilstein B8 utilises the same mono-tube technology as the B6, but has been made for lowered suspension, suiting the needs of most E30 enthusiasts.

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