Plus Sizing your wheels from OE sizes.
You need to know the make, model, year of your vehicle. That determines your wheel minimum and maximum size that it can be. It will also determine the bolt pattern, offset, and hub bore required for your vehicle. When plus sizing from the OE size of wheel it`s very important to retain the same diameter of tire. Otherwise your speedometer will read incorrectly. It can also cause longer stopping distances or overload the ABS braking system.
We decided to go with a set of the Ro-Ja /Motegi FF 5 wheels on a new 2003 Volkswagen Golf GTI. They come in an 18x7, but to run 225/40 tires which would be the proper plus size for the upgrade from 17`s we had to use either a 18x7.5 or 18x8. The next size up for the FF 5 is an 18x8, so that settled it for us. They are a tight fit on the front at the +37mm offset, but put the wheel lip at the edge of the fender. You could possibly go 18x9.5 on the rear with a different wheel and offset. The offset is +37 and weight 24 lbs each for the 18x8 FF5`s.
On the tires we wanted to try a set of the Kumho Ecsta Supra 712 with a 280/AA/A rating. We used the 225/40/18`s up front. With the 225/40`s up front we keep our speedometer the same. As to the rear tires we tried something different and used 245/40/18`s. The front tires weight 20.9 lbs each and the rear 22.0 lbs each. With the wheels added we had 44.9 lbs front and 46.0 rear lbs. The stock wheels were weighed at 45.2 lbs.
Well after a year we`ve ran through the front tires. Over 15,000 miles without rotating due to the staggered setup. If you keep the tires rotated then about 30,000 would be normal maybe even more. Of course we were not kind to the tires and took great pleasure in pushing them all the time. We were doing the dyno for the Supercharger upgrade when the car got squirmy on the dyno. It dropped off to the right and one of the tires took a good burn to the sidewall, but didn`t fail, but after that we had to get them replaced.
We decided to try a set of the new Nitto Neo Gen tires. 225/40/18`s all around. This isn`t a directional tire, but an asymmetrical tread pattern, somewhat like the Yokohama Parada`s. Lower noise level though than the Parada and less expensive. These are AA traction wet weather tires. They do not lose grip easily, even with the extra power from the supercharger we put on the car. Well, we are about 13K into the tires and are still loving them. The Nitto Neo Gen tires are quite impressive and we are satisfied with the performance we are getting from them.
Upgrading the wheel size is always a tricky thing. You don`t just slap on whatever looks good. If you do not keep the diameter of the tire the same then it can throw off the speedometer and can cause problems with the anti-lock braking control. If you have a OEM tire that is 26 inches in diameter and is a 17" wheel and you want to go to a 19" wheel, then you have to keep the diameter of the tire the same at 26" or as close as possible. Mercedes braking control system are an example of a system that doesn`t like the wrong size tires on the vehicle. It will make the ABS light come on. Always do your research and make sure you are getting the correct plus sized tire for your car. Also, if you own a truck and put 20" plus wheels on it there are programmers you can use to readjust the on board computer to the newer tire size. This puts less strain on the braking system. Upgrading the brake rotors is a good idea too.