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I've grown bored of the stock steel rims my car came with and now I've got a good opportunity to buy some new ones. I've taken mesuraments just to make sure but I'm not exactly confident that these the new ones will fit my current Citroen BX. I took the mesuraments from my spare tire. Width is in inches.Wheel mesuraments As you can tell my tool wasn't capable of measuring the width but I deduce the width of the new rim is larger than mine, judging by the measurements on the image.

Since they're one inch bigger in diameter but I'll buy +1 tires. Am I measuring strud diameter correctly?

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First of all, don't use the spare for your measurements. The problem with using the spare is, while it obviously fits your car, it usually won't be made to the same spec as what is on your vehicle for normal use. This is due to several considerations, mainly getting it to fit into the hole where it's stored.

Your best bet is to go to a website which will tell you exactly the fitment of the wheels which will go on your car. For instance this website shows all of the dimensions for the different years of BX's (I used 1990 because it was middle of the road and had to go with something). This website shows the BX has several different engine sizes (1.1, 1.4, 1.5, etc.). Along with it, there are several different wheel/tire combinations which are available.

There are three measurements which are the same:

 Bolt Pattern (PCD)      4x108
 Thread Size (THD)       M12x1.25
 Center Bore (CB)        65.1

Each of these measurements are metric, so in MM. (The code in parenthesis is what is on the website I gave you, to help you be able to understand their charts.)

The rim diameter, width, and offset are a little bit more tricky. There are several different ones listed on here. The easiest way to figure out which one you have is to look at the markings on the tires which are on the car. However, you could use any one of the following, as the BX was equipped with each:

 Tire          Wheel
 185/60R14     5.5jx14 ET18
 185/60R14     6jx14 ET15
 185/55R15     6jx15 ET15
 195/50R15     6jx15 ET15
 205/50R15     6.5jx15 ET15
 195/45R16     6.5jx16 ET15
 205/45R16     7jx16 ET15

As you can see, there are seven different rim sizes which you could use (assuming your car is a 1990, but I'll also venture to assume the sizes didn't change much between the years the BX was available). You need to remember with this, though, the tire width dictates the size of the rim. Wider tire; wider rim. As for the measurements which are given, you can find the tire size explanation pretty much anywhere and see what they mean (tread width in mm; aspect ratio; rim size in inches).

The wheel sizes need a little bit more explanation, though, due to the fact measurements given for European sale is different than what's given here in the States. The sizes given are thus (using the first wheel size listed as the example):

 5.5     Wheel width in inches
 14      Wheel diameter in inches
 ET18    Offset in MM

In your case, the offset listed is a positive offset. There can also be a negative offset for some wheels. Measuring the offset can be quite tricky and is the hardest thing to get right. Using a website which has all of the figures available for you in the first place is a much easier way to get any of these measurements, because they will for the most part be accurate.

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    This was exactly what I was looking for and you even got my model right! Thanks! – EChan42 Sep 11 '16 at 12:07

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