Perhaps one of the most discussed topics on any kit car forum is “which set of wheels and tyres to invest in?”. Everyone has an opinion and, as there is no ‘right answer’ the topic continues to attract attention. So here’s our tuppence worth.
Classic cars deserve classic wheels. Wire wheels are popular and so are ‘racing’ wheels, by which we mean wheels that were fitted to race cars of the era. Cross spoke alloys also feature strongly because of their classic leanings. Your wheels will have to fit into a defined space which is constrained by the donor vehicle on one hand and the kit on the other. There may be different constraints for the front wheels than there are for the rear wheels and there are tweaks that can be made to fine tune your selection.
The standard wheel tyre combination on the popular Z3 is 16″ x 7″ rims that have a 40mm offset with 225/50/R16 tyres. In 2018 Pirelli launched a range of modern vintage-style tyres including a set for the Ferrari GTO 250. The front tyre being 215/70/R15 with the rear tyres just 10mm wider. At 696mm diameter this makes their rear tyre 10% greater than the standard BMW tyre which is 632mm. This just provides some context.
When going for the classic look we consider knock-off wheels to be a very strong contender , almost a must-have. These wheels require the use of hub adaptors. Having said that, our Dunlop racing style wheels are bolt-ons but come with spinner style hub caps. Bolt on wheels like the Dunlop style and the cross spoke alloys require a lot less faffing than do the wire wheels but it’s up to you where to draw the line.
The wheel offset is another much discussed component of wheel choice. Not only will this impact the overall look of your project but it has serious implications concerning the fit of the wheel. Fit, form and function all need to be right. The point at which the wheel fits to the hub (or hub adaptor) along with the wheel offset, wheel width and the position of your wheel arches all come in to play here. Standard BMW 7″ rims have an overall width of about 205mm. The inner width, where the tyre bead lies, is about 178mm the rest being made up of the thickness of the wheel rim itself. The centre line of the wheel is therefore about 102.5mm.
The backspace (the distance from the point at which the hub meets the wheel rim) is around 142.5mm and the front space is around 62.5mm. These two numbers are significant because they define the point beyond which it becomes unsafe to extend the wheel and tyre into the body of the car (back space) and the point beyond which the wheel will start to protrude beyond the line of the wheel arch (front space). There’s a bit more allowance in the front space because defining exactly where the wheel arch ends is open to some interpretation.
If you choose a wire wheel with a front space which is greater than that of the original wheel and then add a spinner onto that wheel then you might find that your dream machine begins to take on chariot-like overtones. If you find yourself at this point then you might consider tweaking the hubs to bring them inboard a tad. If you really want to go to town, like we do, then you might choose a centre laced wire wheel whose spokes are recessed from the front of the rim by just about enough so that the spinners do not extend beyond the rims. You can see what the implications of this are by checking out some images and by taking a look at our “thinking about wheels” document which gives you some numbers to work with and some ideas to consider.