I’m wanting to replace the wheels on my Eunos but am confused as to what aftermarket (or secondhand) wheels will fit. There is a great thread here (http://www.mx5oc.co.uk/forum/yaf_postst249_Wheel-fitment–what-other-vehicle-wheels-will-fit-my-car.aspx) but I’m confused by offsets, PCDs, etc. Would anyone car to explain please ?!
It would appear I may need spacers; is that the case ?
Thanks
PCD stands for pitch circle diameter and is an engineering term meaning a number of equally spaced events around a diameter. In the case of NA / NB cars the 4 x 100 means that there are 4 equally spaced events, in this case holes, on a 100mm diameter. MK3 cars are 5 x 114. Different cars do have different set-ups, Ford 4 stud wheels are typically 4 x 108, Alfa’s can be 4 x 98 and so on.
Offset refers to the mounting face of the wheel, where it would bolt onto the hub and the distance that is off set from the centreline of the wheel. An offset of zero means that the hub face is on the centreline of the wheel / tyre and can most easily be pictured as bike wheel, where everything is central. As the mounting face moves off the centreline, the reasons being dictated by the suspension geometry design, then positive offset so + 20, + 35 etc. mean that the mounting face of the wheel moves towards the inside edge of the wheel, pushing the wheel outwards for a given mounting position. Negative offset does the opposite, bringing the wheel more inboard for a given mounting position.
The centre bore or spigot ring diameter is the diameter the protrudes from out of the hub and the wheel can sit on. There are varied opinions on the need, but the spigot is very important of steel (or aluminium wheels ) that mount using flat face washer nuts, typically commercial vehicles. However the correct spigot bore would be 54.1 for NA / NB models and 67.1 for MK3 cars
So the “standard” for NA / NB cars is 4 x 100 ET (offset) 38 (it can vary between 35 to 45) 54.1 bore.
MK3 cars are 5 x 114 ET55 67.1 bore.
There are many permutations of width and offset that can fit and can be made to fit.
Also, do not get hung up on centre bore as long as the hole is the size required of bigger, you will be fine.
That’s a great reply, thank you for taking the time. eBay here I come !
I forgot to say that the offset on MX-5’s is negative.
Is it? I would have said that the MX-5 has a positive offset, in that the centreline of the wheel is inboard of the mounting surface of the wheel. Mazda express the offset as a positive number.
Maybe lost in translation. I belive positive pushes the wheels outward
The How to Build a High-performance Mazda Miata MX-5 book, (and a quick Google search) implies that a positive offset brings the centreline of the wheel closer to the centre of the car.
Every day’s a school day.