Rub limits
 

Well, it's about that time... I'm going to stop putting tires on the stock wheels.

It's time to replace them.

There are all kinds of guides for fitment, dimensions, and a whole directory of wheels, but there's no definitive information on what's going to rub and where.

Does anybody know the offset limit where the a wheel/tire of stock size and width will rub at full compression, full lock, or both? Here's a little more information:

I hate the way the stock wheels are hiding way back there in the wheel wells. It looks like garbage. I'm staying with 17x7's, and the stock 215/45 size, but I'd like to pull them further out toward the fenders. Thinking of picking up Motegi Racing MR221 2-piece in a custom offset. I like the weight and the design.

I know this will initially alter the wheel rate for the same spring rate, and it will change the scrub radius. I will be replacing the entire suspension with an adjustable setup, but I want to be free to make adjustments based on performance and handling, not to tuck in wheels that don't fit properly.

I'm an engine guy, not a suspension guy. I'm new to most of this. If nobody knows the answer, I will do the only thing I know how to do: measure for myself. I will put the car on a lift, pull the stock suspension, find full travel for all 4 dampers. I will then crack them open, remove the springs, reinstall them, and bolt the wheels up. I will then use a floor jack to compress each corner of the suspension and do my own measuring.

I know it's not realistic to expect nothing to rub anywhere ever, and if you're worried about full lock and compression at the same time, you're probably a passenger at that point anyway. Some advice there from people who know about that would be helpful. Again, I do engines, not suspension. I can tell you all about valve springs, but nobody has ever suggested "lowering springs" for those.

Also, If I've overlooked something, tell me. If I'm going to DQ from most competitions by changing the offset, I'm going to be sad. If altering the offset can't be properly compensated by spring, damping, and alignment alterations, explain why.

You're way overthinking this.

AS far as having all bases covered, this would be very useful info for the community to have..

not really. It's quite hard to actually make stock wheel width and stock tire size rub anywhere. They're so narrow and there's just so much room to play with. Some people have 20mm spacers f/r on stock wheels and they don't even rub even when lowered. Once you get into track-set ups, alignment, corner balancing, specific class requirements, auto-x, big meaty set ups, etc then this becomes more in depth. If you're looking for that in depth of info, http://www.ft86club.com/forums/forumdisplay.php?f=39 would be better suited.

If you're just trying to bring out 17x7s with 215/45s out more, it's one of the most basic things you can do.

Just read the wheel directory. It is a collection of most wheel sizes/tire sizes that will fit. And some that don't! Anyway, by just reading what fits and what does not, I chose a setup that fits perfectly for me. I am sure you would be able to do the same, especially because you want a conservative setup.

Thanks. I agree.

I leave town for work on Thursday, so I won't be measuring this week. If nobody know the answer, I'll have to buy some adjustable spacers, probably from PBM, and maybe locate some donor shocks. That would save me the shop time associated with taking mine apart.


I understand that. Once you start moving them out, you're eating up that room though. It's like running a wider wheel. Yes, you have space on the inside, but you aren't using it. You're chewing up your outside clearance.

I searched every section of the forum for the information I'm looking for. Including google. I found nothing.

I appreciate the info about having lots of space to play with, even lowered, but I could measure static clearance in a driveway... I care if something rubs under compression. I would like to retain full suspension travel, because I use all of the suspension travel. Otherwise it's not worth doing the mods.

Also, If we determine you can space it out 20mm, that means you can run a 20mm wider wheel, and change the offset to compensate, because we know the inside edge is safe, due to the location of the stock wheel. Kill 2 measurement birds with one stone.

There is absolutely no cut and dry formula for rubbing. There are too many variables. You cannot just say lower X amount, have spring rate at X, dampers set at X, and you will not rub. Hell, a missing push/pop rivet on a fender liner with wind flapping around could make you "rub". I don't believe you're being realistic in that sense. It's trial and error on your car alone. Choose the suspension you want, then go tinker. There are a ton of fitment threads you can look at for how something looks/fits and most even post their alignment specs.

People run stock all the way to 10" wide on stock fenders on all 4 corners. Even the aggressive wheel set up guys run 10.5 or larger. There's no "flow chart" of sorts for you to follow when it comes to choosing a subjective wheel fitment.

I've read through, and there's lots of info on static clearance. But what happens when you take the suspension to full bump? Do those wheels still fit / clear? I know many of them do not, and many more have been
tucked in with camber adjustment, and rolling fenders.

Many of those variables can be eliminated completely though. I'm saying forget the suspension settings, and find the clearance at the limit of the suspension travel. Assuming the car is intact, and nothing is flopping around broken. Let me simplify the question with a dumb example... If you jump the stock car and bottom out the suspension completely, raised, lowered, who cares... The stock wheels will not rub anything on the car. The suspension will hit the bump limit first.. How far out can you push them while keeping that statement true? That's all I'm asking. No, I'm not building the car for jumping, it's just an example..

I was hoping the information already existed, because it will be the same for any wheel width at the stock tire diameter.

I would tinker, which I said I will do if the information doesn't exist, but I will tinker before I buy things, because custom offset 2-piece wheels are expensive.

What happens when you take suspension to full bump? It is as low as it can go.

If the wheels you have chosen fit, then yes! A proper setup, IMO, does not rub. My setup has NEVER rubbed. Be more specific, how wide do you want? how tall of a tire do you want? how low do you want your suspension?

Again you're way overthinking this. You're not going from some scene-kid "stance-bro" fitment (I hate that word, by the way). You're going EXTREMELY mild and conservative. It's subjective because you need to figure out HOW you want your wheels to fit before you go and order some spec and it comes out not what you were wanting. YOU need to determine your ride height, your alignment specs, not some obscure or arbitrary reasoning. YOU need to go outside to your car, measure things, find out what other 17x7 wheels and their fitments you like, find out what offset they are running then tweak to your own preference. It's really not that hard.

FWIW, stock wheels are what? 17x7 +45? (or something in the mid-high 40s). An extremely common set up is 18x9.5 +38 all around. That is 25mm less inner clearance, but the outside edge is 39mm further out. Look how much room you have...

The stocks are +48.

That is interesting. So, those are 63.5 mm wider than stock. At +38 offset, the outsides are 41.75 mm further out. The insides are 21.75mm further in.

So, That's the same as pushing 17x7's out to a +6.25mm offset. That's past flush...? There's no way that's not gonna hit the fender at full travel.

Either way, a 17x7 is no more conservative than any other wheel at the offset limit. If you push it out, eventually it will rub under compression. The unused space on the inside is irrelevant. This will probably happen before it gets to flush. Flush for a 17x7 is +25 F +18 R at stock height. If not, if it doesn't rub at perfectly flush at full bump, then my numbers are right there. I know the wheel pulls in under compression due to the suspension geometry. I know if I lower it, the wheel will pull in. The outside clearance limit at full bump is the same for everybody, regardless of wheel width, provided they keep the stock tire's outside diameter, and the stock geometry..

I will say again, If nobody knows, that's fine. I will measure it myself.

Full bump is the same for everyone, unless they've f*cked up their motion ratio or shock travel.

I'll probably buy the same offset all around and use hub centric spacers at the back. I hate spacers, but I want to retain the ability to swap front to rear as the tires wear, without re-mounting the tires.

And thats why theres too many variables. At a static 0 camber, 0 toe, suspension is non moving etc static environment, your statement could hold true.

Stop overthinking it. Go find something you like and go from there. Also please do not effectively "space out" a 7" wheel 40mm.

You cant omit these variables and get a "hard and fast" rule. Thats not going to happen.

Why not? The car handles great on N3000 215/45/17 tires. Why add a bunch more grip? I don't need it, and I don't want it. I'm not building the fastest car in the world, I'm building a car with great handling that handles really well at the limit. It drifts great, and the final power will be sub-300 at the wheels. I'm changing the turbo for a supercharger... Why get an 8.5 inch wheel and a 245 section tire if I can't spin the f*ck out of it, smoke the tire, and have a grand old time?

The only reason I'm not keeping the stock offset is I hate the way it looks. This is an aesthetics-only modification. All I'm doing is making sure I'm not sacrificing function for aesthetics. That means re-tuning the suspension to accept the altered offset, and making sure I don't hit anything. That's all.

You cannot omit all these crucial variables to find your "hard and fast" rule. Period. Go and tinker and look at other threads for fitment.

And aesthetics only for changing 7" wheel offset? Ever see chicken legs on a fat person? Thats not really achieving much aesthetic there.

Dont skip leg day, bro.

Funny. Every see the lotus Elise? With those skinny-ass wheels? Doesn't look all that bad.

Also, not strictly aestheics. I'm losing 7 lbs per wheel, 1.5 lb per tire over stocks, and 16 lbs per brake, as I'm doing those at the same time.

That's 98 pounds of unsprung weight off the car, and that's before the cast-iron uprights come off for aluminum ones.. That's another 6.5 lbs per corner, and then we address the control arms and coilovers. I'll have nearly 150 lbs out of the car on just the suspension.

I can spin my 245 MPSS on a 18x9. Stock engine auto trans.

How many other frs/brz have you driven? What tire wheel did they have?

imo extended studs, cheap spacers, lots of experimentation and patience. It is hard to get 17x7's to rub without doing something silly.

Personal anecdote: I put my 17x9 +45 RPF1's on with 245/40 tires, removed the springs and let the car sit on the bumpstops, no rubbing or clearance issues anywhere (front struts were changed to a 2.25" spring so that will be your first hurdle, although not the direction you are concerned with). As far as I'm concerned you have nearly +/-1" of clearance for offset tweaks if you stick with 17x7's. Those front wheels at full lock rub the inner fender liners but clear no problem with a 5mm spacer, the +35's are more common for that reason (among others).

For reference, the picture on the left side will show how much bigger and further outboard many have gone without issue, regardless of ride height. This might be your best tool to compare what 'fits' in the fitment thread, and what looks pretty in the pictures to what you want to do.

http://www.willtheyfit.com/index.php...t2=35#isPage=2

Since you mentioned it, SCCA Street class has rules about changing the OE offset, something small like +/-3 or 5mm is the maximum allowed. Since you mention aftermarket suspension though I don't think STX and above has any rules about changing offset.

Thanks. That's exactly what I was looking for.

Haven't driven many twins. Mostly other cars. Couple of turbo FRS's, 1 eforce car, nothing bigger than 18x8. No tire bigger than 245.

The bigger tire setup did the power-slide job alright, but the car felt bigger, heavier... It liked to push more during forward weight transfer in a corner, needed power to rotate. It just didn't handle as well. I'll give you that the entry speeds were marginally faster, but it just didn't feel as spritely. It felt like a Mustang. Stock suspension, btw.

Competitive STX autocross cars have no problem spinning the tires at launch or hanging the back end out on 17x9 245 sticky as fuck RE-71R's with just a header and tune. Hell I can do it on mine right now with a stock powertrain as I'm developing my setup and my car is just too loose.

Sticky 245's aren't a death sentence for fun. I totally understand not needing or wanting more tire though.

Well, that's interesting. I'm open-minded.

I'm nearly certain STX prohibits me from using forced induction, which would seriously suck, but I haven't read the appendix to find out if there are certain approved applications for the FRS.

That's correct, FI puts you into SM class, which is affectionately dubbed 'Spend Money' which you likely won't be competitive in. IMO just build what makes you happy and if you autocross/time trial go out there to have fun. If you want to win don't spend a cent until you know exactly what you want/need.

http://www.ft86club.com/forums/showthread.php?p=2192626

Some decent tire info for you in there as well.

But the point in the above post is that while you may not 'need' more tire, I'm willing to bet someone with experience could drive your car at 10/10ths, get out and the first words out of their mouth would be 'needs more grip' even at <250 whp levels with 215 street tires.

This is why I want to try RE-71R's in the stock 215 size. I want more grip, but not a ton, just enough to put the power down in corner exits without going all dorifto.



Okay maybe a little dorifto.. But less than it does now.
-Josh

That's awesome advice. I'm not out to win a whole bunch of races in this car...

I'm after a setup that I can push to 10/10ths everywhere... I have that right now, I'm just trying to make small improvements to address things I don't like, without ruining it. I'm good at that, but it involves lots of overthinking things.

For you motorcycle people, this is the SV650 of cars. I want to keep it that way.

You're also good at overthinking things, lol.

And I have a SV650 too.

lol :cheers: