What size spacers?

[technoticmedia]

So I just got my Rota SVN 17x7.5+45 wheels for track days. I have some 225/45R17 Nitto NT01's to go on there. I test fit a wheel without a tire on the car to make sure they cleared the DT BBK and that was fine. However, it looks as though I only have ~1/2 inch of space between the wheel and my coilovers. I'm thinking with the big tire it is going to rub on the coilover.

Currently the alignment specs are -2.0F, -1.0R and I want to bump it to -2.5F -1.5R.

I am thinking that I'll need some 15mm spacers to properly fit them in there. Although, then I might need to modify the fender a little if it rubs.

Any ideas would be greatly apprecaited!! I need to figure this out in the next couple of days because I'm going to calabogie next weekend for a track day. Thanks!

[meb]

I don't know if the tires will contact the fenders...you have to try this...you may get away by trimming a little of the inside of the rear plastic fenders as these usually present a probelm first.

Spacers...a wider track is always a good thing and 15mm spacers on 45mm offset wheels will yield a net 30mm offset - I had 23mm offset at one point.

If you using 15mm spacers front and rear the handling balance will not change but grip will increase.

If you install 15mm spacers up front only, front grip will increase and understeer will increase.

If you install 15mm spacer in back only, rear grip will increase and oversteer will increase.

Increasing track width increases roll resistance. If you increase roll resistance up front you get more understeer for example. You can actually tune the handling by altering track width.

Personally, if I were doing this over I would retain the stock front to rear track width relationship - the Mini's front track is slightly narrower than the rear and this helps turn-in and balance. So if you install 15mm spacers front and rear you will preserve this balance while potentially increasing grip/cornering power.

There is a hypothetical point where too much width will hurt transient repsonse...I don't know where that is but I suspect my 23mm offset was perhaps a bit too much for tight transient corners.

As well, scrub radius changes and this can be a good thing but you should at least diagram the changes. As the tire is pushed farther out, SAI or King Pin will fall to the inside of the tire's center line placing the pivot closer to the tire's centriod contact patch. With most front drivers, this pivot point falls outside the tire's centerline while the meat of the contact patch is on the inside of the tire's centerline. In theory, and in practice, if the two are relatively close steering feel will increase...you may also notice some kick-back into the steering as well...it's a compromise.

Increasing track width will also place more strain on some suspension components - tie rods and bearings for example.

Doc, Greg, if you're reading in, keep me honest...I'm old and forgetful!

[Mike87]

I ran 225's at the track on stock s-lite 17's. They rub in the rear on the outside edge under hard cornering. Expect to trim the outer plastic. If you run 15mm spacers, you will rub even more.

Good Luck,
Mike

[technoticmedia]

meb, thanks for some great information. I definitely need a few minutes to dissect all of that. I'm going to get the tires mounted today and see how they fit without spacers before I order anything.

Chad from DT suggested I alter my alignment settings to -2.25F, -1.8R

[meb]

Not sure I would do that if you are planning to increase track width.

Since roll moments change - for the better - you can using lighter spring/damping and swaybar settings, but also, less agressive camber settings. If camber compensation is too much in roll you may find the tire cornering on its inside edge. Though not as bad as cornering on the outside edge for different reasons the meat of the tire is lifting off the ground when its needed most.

I don't know a lot about your car so take this as theory...meaning be careful and be open to experiment. I would keep the alignment where it is if you plan to install 15mm spacers. run the car, observe what it does, then make a change...I wouldn't be surprised if you actuall backed off front camber a hair...swaybar balance also plays into this equation but should be used to fine tune understeer/oversteer. Springs, dampers and track width should establish fundamental balance and grip.

Remember that a wider ttrack allow the tires to perform more work...you may not need more than 2 deg neg camber...and my personal feeling is that once past 2 deg neg with this car, tire wear will increase (if your set up is fairly stiff and track is wider), and you may notice some braking instability from high speeds as well as shorter braking distances...

[technoticmedia]

Ok so got the tires mounted today, and just test fit them on the car... With the current alignment settings, it rubs ever so slightly on the inside, on the coilover adjuster. I'm thinking 5mm spacers are all I will need. I grabbed an extra hubcentric ring I had and put it on the hub backwards, and then held the wheel on. There was plenty of room once I did that and the rings are 3/8" thick (~9.6mm).

Therefore, I think 5mm should do just fine! I'm definitely going to be careful and experiment with some different alignment settings. I want to get rid of the toe out I have in back, and increase some camber in the rear for sure though.

Thanks again!

[meb]

tow out in the rear is not a good idea for street or road course driven cars...very unstable. For an autoX course, sure.

Stock tow and camber settings in the rear make for a stable ride.

[onasled]

How are the rears? Just make sure you are clearing the trailing arm as that can be the issue there with wider tires.