The secret code of wheel fitment….

Once again there has been a common thread on the various club pages recently, that of wheel fitment on the various cubes. So in this article we will take a look at how to break down the code on the side of the wheel and the way this can be used to get a good fit for your new different diameter wheels.

So lets step into the shoes of Robert Langdon and crack the code….

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So the stock wheel size of the Gen 3 is 16″ in the UK (there are some markets where a 15″ is available) and the gen 2 runs 14 and 15″ when they leave the factory. This only tells part of the story though as a Mitsubushi Shogun that is the same age as a cube also runs a 15″ wheel and you’d never get the wheel and tyre from one of those in a cube wheel arch!

We’ll start this whole journey with wheels which have 5 key numbers –

  1. Diameter
  2. width
  3. offset
  4. hub size
  5. bolt spacing

Diameter is pretty easy that’s how big the wheel is and is measured in inches. As above the stock sizes of the cube are 15″ and 16″ but these can be enlarged or reduced depending on the look you want.

dia

Width again is measured in inches and the cube wheels are 6″ wide on the gen 3 and 5″(14″) and 5.5″(15″) for the gen 2. The width is normally followed by a J and this stands for the rim profile. This is what the tyre bead fixes to and there are loads of them for different purposes but cars are usually J.

width

Width is intrinsically tied to offset, this is probably the most difficult of the numbers to get your head around and bizarrely is measured in mm! Offset is the dimension from the centre line of the wheel to the mating face of the wheel to the hub. A zero offset would have the wheel meet the hub directly in the middle of the wheel, there is then a positive and negative offset that can shift the wheel in or out from the hub. The gen 3 cubes stock offset is ET42 and this needs to be factored in the most when looking at new wheels to ensure the wheels will fit your car. Often when going up a wheel size the width of the wheel will increase as well and because of this you’ll need to keep an eye on what the offset is so that the wheel doesn’t start colliding with suspension parts or the wheel arch.

For the super nerds among you and for anyone who hates it when things aren’t fully explained ET comes from Einpresstiefe which is the German for insertion depth.

offset

Hub bore size is something that a lot of people are unaware of and is rarely listed on wheel sale posts but is an incredibly important thing. If you’ve ever taken a wheel off you’ll know that on the centre of the wheel you’ll have a slight lip. This helpfully allows you to get the wheel centred so it’s easier to get the lug nuts on. That’s not its only job though as it also takes a fair amount of the load of the car, or rather reduces the load on the lug nuts by not letting the wheel move off centre when the car is sat on the floor. Aftermarket wheels use what is called spigot rings to change the oversized hub core to that of the car you are fitting them to. when buying wheels remember you’ll probably need to factor these into the cost as you are probably going to need some. This is also the reason that you’ll see people talking about having Mini wheels machined to fit the Gen 2 cube as whilst the wheel is a near perfect fit diameter, width and offset the hub bore is not and so needs enlarging to get them onto the car. Gen 3 centre bore is 66.1 gen 2 is 60.1

centre

The last thing to factor in is the bolt pattern. Get this wrong and the wheels will never fit the car as you just can’t fix them on! Gen 2 cubes are 4×100 and Gen 3 are 4×114.3, this number on a 4 stud hub is the dimension in mm between the centre lines of the bolts opposite each other. On a 5 stud hub the number is the diameter of a circle that falls through the centre lines of the bolts. This means that measuring the pacing of a 4 bolt hub is not to tough but doing it on a 5 stud can be a bit more difficult!

pcd

So from the above when looking at wheel adverts the size will likely be listed as 17×7.5j ET35 4×114(most folks seem to ignore the bit of a mm!). Aftermarket wheels can have multiple bolt fittings as well making the centres look a little like swiss cheese so you may find 2 lots of pcd listed! you will probably have to contact the seller to find out what bore the wheel has though or if they are from another car find out what that car is and then google to get the centre bore size and compare. We can use this as an example to compare the wheel against that of a stock Gen 3 who’s wheel is 16x6j ET42

For starters the wheel is obviously an inch bigger in diameter, if buying wheels without tyres it’s kind of obvious but means you can’t use your existing tyres! Again it’s sucking eggs but as it’s an inch in diameter it’s 1/2″ radius so doesn’t always look like that bigger change. The difference in diameter matters very little to how they fit the car though as when we cover tyres in a later article you’ll see how this is dealt with. Just note that there is an upper limit to wheel diameter (you have to be able to get a tyre of appropriate size onto them) and the bigger you go the less tyre side wall you will have and the harsher the ride will become.

The bit that is the key to fitment is the width and offset or more specifically the relationship between them. If the wheel width gets an inch and a half wider 6-7.5 you’ll have in effect 3/4 inch more wheel into and out of the arch. This is where you get the rubbing and clashes as if you don’t have 3/4 of an inch between the wheel face and the suspension strut it’s not going to work! As such you have to alter the offset to counter act some or all of the increase. The joy of odd units means you have to remember that to have the same inner face line for the wheel you need to change the offset by 19.05mm (the equivalent of 3/4″) you do this by taking it away from the 42 so you get ET23 (ignore the .05 as you’ll never get that in an offset!) Be aware however this will put all of the additional wheel width onto the outside of the wheel and could again cause issues with the arches.

Looking at the above example we swap from a 42 to a 35 offset this means the mating faces are 7mm closer to the centre of the wheel. We know the wheel moved 19mm further into the arch (and out of the arch) with the change in width and so we take this 7mm away from the 19mm and the wheel back rim is 12mm closer to the suspension and other parts in the wheel arch. Be aware that 7mm has to go somewhere and it goes onto the outside so the wheel’s external face is now 26mm proud of where the original wheel sat.

DSC_4943_zps3df9f717

See why it gets tricky and people almost always answer the will these wheels go on my car with a non committal they should/could unless it’s a wheel they have specific experience of!

The more extreme the change between the wheels the more important this becomes however as from the factory cars generally have loads of tolerance on the inside and outside and so can be fairly forgiving when changing wheels. Trying to get really wide wheels onto the car or trying to get that perfect cigarette paper to arch fitment starts you having to look really hard at these numbers and there relationship as well as taking some careful measurements on the car itself.

Hopefully the description and pictures have helped make this a little easier to understand and allow you to get the wheels you want without the pain of them not fitting when they arrive!

In the next article we’ll look at how to order the shoes to go on your cars new feet and try to keep you from getting speeding tickets you just can’t understand!

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