I've been getting a lot of wheel fitment questions recently and thought that creating this thread might be helpful given my experience. Like the lighting thread, I will try to put as much info here in the first post and if you have more that you would like me to add to it then send me a pm and I will go edit it in for easier information retrieval. Also, this is not a thread for arguing. If you don't want to space your wheels then don't; this thread is for people who want to and are looking for information.
My car came OEM with the Handling Package 18's with OEM PS3 tires. These are 18x8" ET55, 235/40 R18. All of the numbers I've calculated for spacer and wheel fitment have used this as the starting platform because I know what does and does not work on it without throwing in camber arms or (when available) camber plates. The fitment calculator that I use is located here. The wheel diagram itself is relatively useless, but the numbers listed on the bottom will tell you everything you need to know before making a decision.
First off, the maximum offset that I have achieved before wheel rub is ET35 by using 20mm adapters. The only way I was able to articulate my suspension to get the rub was by doing gradually increased speeds at full lock into my driveway, which has a relatively steep incline. This is with the OEM struts and Eibach Pro-Kit springs (.75" drop). Even though I firmly believe that I could safely run that offset without putting myself in the situation to cause rub, I want to make sure people are aware because you never know when you could be turning a corner quickly and not see a pothole. Know where your limitation is and then determine your work-around.
So that means that anything up to and including a 15mm spacer is safe and will work without rub, right? Well, not really. The front hub would need to be pulled off in order to remove the studs and replace them in order to have enough length for any spacer over 8mm in thickness. Removing the hub will also require new bearings to be pressed in. For my car and schedule it wasn't remotely feasible, but maybe for you and yours it is. The largest wheel spacer that you can safely fit on OEM studs that is currently readily available is 5mm. I can say that I have run larger on the OEM studs, but I have my own torque wrenches and made sure that I set up a good safety net of torque checks and re-torques. I'm not advising that you go larger than 5mm for safety sake without properly investing your time and money.
Should you be so inclined, the front fenders have room to be rolled. With rolled fenders you *should* be able to safely adapt 20mm up front. I currently have a 15mm set of adapters up front that are sourced from a C30, but I do not recommend going this route. Another member gave me the information and I double-checked the part specifications and went for it, but I was not able to mount my wheels without doing some 'modifications'. Even if his wheels mounted up fine, I can not openly recommend purchasing them. What it boils down to is that my OEM studs were too long, and the recesses in my wheels were not large enough to accommodate the nuts that mounted the adapters to the hub. There is a reason they are not listed for our Focus.
So that means that anything up to and including a 15mm spacer is safe and will work in the rear, right? Yep. If you go anything larger than a 15mm in the rear, you will need the more expensive hub adapters instead of regular spacers because you won't be able to get the longer stud into the hub without pulling the hub. I actually have 20mm DRM adapters in the rear right now and they work great. The only possible issue you might have regarding 20mm in the rear is that you may not be able to fully dial out the negative camber induced by lowering your car as there isn't a lot of room for the top of the tire to swing out.
It also needs to be mentioned that not all tires are alike-even if they are listed as the same size. The first number in a tires size is it's width, but that can come from any area when measured from sidewall-to-sidewall. The PS3's are very wide at the rim protector but actually taper back in to meet a narrower tread. If you went to replace them with different tires that had a 235mm tread width with no rim protector, it would greatly affect what spacers you could run. If your spacers were already installed could lead to having a very long, slow drive home... just food for thought.
Stupid knowledge for those that may be curious- ET comes from the German word Einpresstiefe (insertion depth). It is synonymous with the word offset. This number dictates the mounting surface of the wheel to its center line. A positive offset has the mounting surface closer to the outer edge, zero offset would be direct center line of the wheel, and negative offset would have the mounting surface closer to the brakes (i.e.-deep dish wheels). ET55 on a 8" wheel is NOT the same as ET55 on a 8.5" wheel. Tire Rack for more info.
My car came OEM with the Handling Package 18's with OEM PS3 tires. These are 18x8" ET55, 235/40 R18. All of the numbers I've calculated for spacer and wheel fitment have used this as the starting platform because I know what does and does not work on it without throwing in camber arms or (when available) camber plates. The fitment calculator that I use is located here. The wheel diagram itself is relatively useless, but the numbers listed on the bottom will tell you everything you need to know before making a decision.
First off, the maximum offset that I have achieved before wheel rub is ET35 by using 20mm adapters. The only way I was able to articulate my suspension to get the rub was by doing gradually increased speeds at full lock into my driveway, which has a relatively steep incline. This is with the OEM struts and Eibach Pro-Kit springs (.75" drop). Even though I firmly believe that I could safely run that offset without putting myself in the situation to cause rub, I want to make sure people are aware because you never know when you could be turning a corner quickly and not see a pothole. Know where your limitation is and then determine your work-around.
So that means that anything up to and including a 15mm spacer is safe and will work without rub, right? Well, not really. The front hub would need to be pulled off in order to remove the studs and replace them in order to have enough length for any spacer over 8mm in thickness. Removing the hub will also require new bearings to be pressed in. For my car and schedule it wasn't remotely feasible, but maybe for you and yours it is. The largest wheel spacer that you can safely fit on OEM studs that is currently readily available is 5mm. I can say that I have run larger on the OEM studs, but I have my own torque wrenches and made sure that I set up a good safety net of torque checks and re-torques. I'm not advising that you go larger than 5mm for safety sake without properly investing your time and money.
Should you be so inclined, the front fenders have room to be rolled. With rolled fenders you *should* be able to safely adapt 20mm up front. I currently have a 15mm set of adapters up front that are sourced from a C30, but I do not recommend going this route. Another member gave me the information and I double-checked the part specifications and went for it, but I was not able to mount my wheels without doing some 'modifications'. Even if his wheels mounted up fine, I can not openly recommend purchasing them. What it boils down to is that my OEM studs were too long, and the recesses in my wheels were not large enough to accommodate the nuts that mounted the adapters to the hub. There is a reason they are not listed for our Focus.
So that means that anything up to and including a 15mm spacer is safe and will work in the rear, right? Yep. If you go anything larger than a 15mm in the rear, you will need the more expensive hub adapters instead of regular spacers because you won't be able to get the longer stud into the hub without pulling the hub. I actually have 20mm DRM adapters in the rear right now and they work great. The only possible issue you might have regarding 20mm in the rear is that you may not be able to fully dial out the negative camber induced by lowering your car as there isn't a lot of room for the top of the tire to swing out.
It also needs to be mentioned that not all tires are alike-even if they are listed as the same size. The first number in a tires size is it's width, but that can come from any area when measured from sidewall-to-sidewall. The PS3's are very wide at the rim protector but actually taper back in to meet a narrower tread. If you went to replace them with different tires that had a 235mm tread width with no rim protector, it would greatly affect what spacers you could run. If your spacers were already installed could lead to having a very long, slow drive home... just food for thought.
Stupid knowledge for those that may be curious- ET comes from the German word Einpresstiefe (insertion depth). It is synonymous with the word offset. This number dictates the mounting surface of the wheel to its center line. A positive offset has the mounting surface closer to the outer edge, zero offset would be direct center line of the wheel, and negative offset would have the mounting surface closer to the brakes (i.e.-deep dish wheels). ET55 on a 8" wheel is NOT the same as ET55 on a 8.5" wheel. Tire Rack for more info.
