SleepR1

Dudes, you go with 18s cuz they look COOOL

nocab72

DiscountTire sells a Nitto 555R in 305/45R-18 hahah!

$240/each!!! Plus I don't think it will fit in my wheelwell (no specs)...hahaha

K

SleepR1

29 inches overall diameter? That's SUV sized!

nocab72

Maybe I'll get four and put them on my X5...

k

jimlab

Here's what a P315 Hoosier looks like on a 17 x 11" wheel (Kevin Wyum's car). Notice the modification to the trailing arm mounting point in order to clear this combination, and his tires stuck out substantially from the side of the car...



In comparison, here's a P275/40-17 on a 17 x 9" (+40mm) wheel on my car. Even with the fender lip on the outside, and ample clearance on the inside with a stock trailing arm.



I don't think that a 9.5" wheel in the rear is an issue at all, and I know that people put 10s on the back of the car regularly, but an 18 x 10.5" seems to be pushing it substantially. With backspacing that will keep the wheel in the fender well, I foresee fender lip or trailing arm clearance problems or both.

Since we're talking about fitment and traction, is it really worth going to such extremes when a few extra mm of tread width aren't going to make much difference at all in traction? I'm starting to think that far too much emphasis is being placed on maintaining stock or near stock tire diameters, even at the expense of using widths that are questionable on our cars.

At this point, I'm not sold on using a 9.5" rim in the front and 10.5" in the back because of potential (actually, looks like almost unavoidable) clearance problems. I believe that a 9"wheel in the front, with up to a P275 width will clear with coil-overs. I believe that a 10" wheel with up to a P285 width will clear in the back, again with coil-overs and M2-style trailing arms. I don't think that a 9.5" and 10.5" fitment is nearly as "safe" as even the 9" and 10" combination, and until I've seen that someone else is running 18 x 9.5s and 18 x 10.5s, I'm not stepping up to order my wheels.

Brad

Which is probably the case with your car, and nocab72.

To throw something else in the mix, what about unsprung weight? I know increasing unsprung weight is bad for optimal handling characteristics. I understand increasing wheel/tire weight will increase traction, increasing tire diameter will increase traction, and increasing wheel circumference will increase traction. But how much will this affect your handling?

For example, let's compare a 17x10 wheel with a 275/40-17 tire and a 18x10 with a 295/30-18 tire. The 295 has more contact area than the 275...but as stated before this may only increase traction by a few percent. Also, the 18" setup has a shorter sidewall than the 17" setup, so the 17" has a little advantage there. Clearly the 18" will get more traction due to it's weight and larger wheel circumference (rock on the end of the string example).

But at what point does increasing the tire/wheel size/weight give only a small increase in traction, but adversely affect handling?

Please tell me if I am wrong, but my assumption is a 17x10 wheel with a 275/40-17 tire will give almost as much traction as a 18x10 wheel with a 295/30-18 tire, but have more optimal handling characteristics.

fdracer

the short answer is you can't put all that power to the ground on the street no matter what you do. on the track, however, you'll be able to w/ slicks. but when you do hook up w/ that much power get ready to start breaking driveline parts. i'd say ari has spare driveline parts that equate to about 5 fd's worth of parts. the best thing you can do for traction on the street is tune your boost vs. gear and rpm so you don't overpower your tires. it's pretty much the only way.

jimlab

You're probably right there, but the appearance will certainly be different.

I didn't think to weigh the wheels/tires on my Z06 when I had the chance, but even the 18 x 10.5s in the back with P295/35-18s were pretty light. The Z06 wheels are reportedly 19.2 lbs. for the 17 x 9.5" fronts, and 22 lbs. for the 18 x 10.5" rears, so I think that's a fair indication of what's acceptable for an 18" wheel. I was shooting for 20-23 lbs.

According to another post I found on Z06vette.com, the front 17 x 9.5s with Goodyear F1 Supercar P265/40-17s were 42 lbs. total. The rear 18 x 10.5s with P295/35-18s were 46.5 lbs. That is pretty light for a combination that big.

I'm starting to rethink my Boyds wheels, but mostly because they're telling me a I can't have a 10" or 10.5" wheel with the "soft" lip. In order to get that wide, I'd have to use the "stepped" lip (which I think is ugly) and have the rim stretched... at $250 a piece.

I may end up just finding someone's combination that I like the looks of and buying the same thing. I really didn't want to spend this much time and effort pondering what to do for wheels and tires.

Brad

Yeah, no doubt 18" looks better than 17". But I thought you preferred function over form

Wow, that is pretty impressive. I figured just wheel weights between a 17x10 and 18x10 would be fairly close...but once you add those big tires the difference would be greater.

When it's all said and done, we are probably over analyzing the situation and nothing you can do will really solve traction problems. Get a combo that looks good and offers the most traction possible and doesn't affect handling too much (I know you really want the 20" Davin's).

SleepR1

Jim,

Well, I'll be ordering a set of 9.5 wide fr and 10.5 wide rr for my new track setup next spring/summer. I'll be running Hoosier R3S03, 245/40-17 front and 285/30-18 rear, http://www.hoosiertire.com/rrtire.htm

The staggered widths and diamaters are for both clearance and handling.

The larger diameter wheel in back will clear the rear trailing arms. Assuming 11.5 inches overall wheel width (nominal is 10.5), the back space works out to 7.52 inches with a 45-mm offset (1.77 inches). Front space will be 3.98 inches, which is just under the max front space for the rear wheel positions.

The 285/30-18 tire size will be short enough to help with clearing the rear fender lips. They are 0.3 inches shorter than stock (24.9)

The fronts will be a non-issue with 9.5 x 17 and 245/40-17. Assuming 10.5 overall wheel width, back space works out to 7.1 inches, which is just under 7.25 inches of max clearance (with stock OD springs front). Front space is 3.4 inches which is also just under the max clearance of 3.5 inches for the front wheel positions.

FWIW, Hoosier R3S03 is a rather wide 245/40-17. It's more on par with a 255/40-17, and comparable to Michelin's Pilot Sport Cup Comps in 255/40-17 (10.9 wide by 25 OD mounted on 9.5 wide wheel).

Hoosier Racing Tire dimensions are listed below, as mounted on 9.5 and 10.5 wide. Note--you must add 0.2 inch of tire section width for each extra 0.5 inch of rim width, to the specifications in a tire dimension table. The dimensions below have already accounted for the wider rim widths I'll be using:

Fronts: 245/40-17, 10.9 wide, 24.5 OD, 17 wheel diameter
Rears: 285/30-18, 11.6 wide, 24.6 OD, 18 wheel diameter

Wheels will be Volk CE28N purchased from Rishie (Automotive R&D)

Fronts: 9.5 x 17, 47-mm offset
Rears: 10.5 x 18, 45-mm offset

My suspension uses the stock outer diameter springs (H&R Sports), stock R1 Showa shocks, Eibach swaybars fr/rr. I run 1.5 degrees of negative camber fr/rr.

Last season I ran 8.5 fr/9.5 rr x 17 SSR Comps, 42-mm offset fr/rr. Tires were Hoosier R3S03 in 245/45-17 fr and 275/40-17 rr. Tire ODs were 25.3. Tire widths were 10 and 11, respectively.

In looking at my clearance from last year, 11.6 on 10.5 wide will definitely be pushing the envelope for the rears, no doubt. The key will be the short overall tire diameter of a 285/30-18. Not only will the shorter tires lower the car's ride by 0.75 inches (last year car rode higher than I liked), but the shorter tire profiles fr/rr will keep the tire shoulders away from the body work too.

Handling will a bit of adjustment. The 285/30-18 sidewall will be 3.3 inches, while the 245/40-17 will be 3.75 inches. Last year the tire sidewalls were 4.15 inches. Lower sidewalls are effectively stiffer springs. Noting that the rear spring rate will increase relative to the fronts (comparing sidewall tire heights), oversteer will be dialed in somewhat. However, note the rear tires are wider by 0.7 inches. Wider rear tires dial in understeer.

What's the net effect on handling? Nearly zero--THEORETICALLY.

My setup is aiming to put wider rubber for better cornering grip, while maintaining the handling balance of same-size wheel/tires all around

Why the Volks? The CE28Ns are the lightest racing wheels available. For comparison, here are some weights:

10.0 x 18 CCW P4 Mesh, 22 lbs
9.0 x 17 SSR Integral A2, 19 lbs
9.5 x 17 SSR Comp, 16 lbs
9.5 x 17 Volk CE28N, 14.5 lbs (as I recall)

Hoosier Racing Radials are the lightest in the industry:
245/40-17, 18.5 lbs
285/30-18, 21 lbs
245/45-17, 20.5 lbs
275/40-17, 21 lbs

Compare those weights with Kumho V700 or BFG R1A in similar tire sizes. Those weights will range between 25 and 30 lbs!

Anyhow, Jim--I guess I'll be the first to try my own setup. I'll call it the SleepR1 Extreme Fitment

jimlab

In our conversations, though, you were recommending an 18 x 10.5" wheel with 50.4 mm (~2.0") offset, which would equal 7.75" backspacing and 3.75" of front space. From what you're saying about maximum front space being (I assume) about 4.0", that means the front should "tuck" without any problems, but the rear is what worries me. With an M2-style trailing arm, you're right about the larger wheel being farther away from the trailing arm, and with coilovers, I don't suppose that the springs are an issue either, but I haven't heard of anyone running 10.5" wheels yet, and why push it if there's no reason to?

I also happen to like having a little more tire than wheel, within reason. If the wheel/tire falls over and I hear the rim hit the floor, there's not enough tire on the wheel in my opinion. The tire should protect the lip of the rim in my opinion, and I think it looks better as well. I'd be more comfortable with 18 x 9s and 18 x 10s with the same tire sizes, to be perfectly honest.

Stock fitment on the Supra was a P255 on the 17 x 9.5" rear wheels. It looked like hell. A P285 fills out the wheel perfectly, and so did the P275 drag radials. My P265s on 17 x 9s looked great, but 275s on the same wheel width also looks good. I think that dropping a half inch of wheel will not only widen my selection, but have even better clearance and less chance of rubbing or hitting anything. It's also half a pound or so per corner that I don't need.

jimlab

No, that's Wyum. I have to have both.

The 3.27:1 rear gear will go a lot farther towards solving the problem than anything I could do with a street tire, so I'm not really trying to solve my traction problems with the tires. Besides, there's always RaceLogic traction control.

As I said before, there's not much benefit of using a P285 or P295 over a P275, unless the P275 is so tall that it creates fitment problems. I also refuse to run an overly sticky "track" tire on the street. I won't run the risk of sandblasting my new paint or needing new tires in 3,500-4,000 miles. Been there, done that. Any extra grip isn't worth it on a street car.

That's the general idea.

Brad

Geez Jim, you sure are a smiley guy.

Does the face behind the computer smile as much as you indicate in your posts?

jimlab

I only throw them in to let people know that I'm not snarling at them.

No. Life is rarely as funny as the people on this forum are.

Brad

I know...it's great. I get to laugh at the people who are too stupid to know their head from their ***, laugh at the people who think they know the difference, and then I get a laugh from people who do know the difference and try to explain it to those who don't. And THEN, I get to laugh at them again for trying to tell the people who do know the difference that they don't know their head from their ***.

Did that make sense?

Hmmmm, I just made myself think (uh-oh). Maybe I'm one of those guys who thinks he knows the difference, but really doesn't, and get's laughed at even by the people who really don't know the difference! Yikes...no more thinking for me.

SleepR1

Ahh, Jim we have different applications. Mine is for "road racing" (within quotes since I'm not racing anyone in particular, nor am I racing for a trophy or prize money )

Generally, the wider the rim, the better for more contact patch. For maximum cornering potential from the tires, nominal rim width should be at least as wide as the UNMOUNTED tire bead width.

Real life example is with a Hoosier 245/45-16 Motorola Cup tire. A loose, unmounted Hoosier in 245/45-16 measures ~9-1/8 inches from bead-to-bead. Minimally you'll want a 9-inch wide wheel to maximize the Hoosier 245/45-16's cornering performance. What's funny is that EVERYONE puts a 245/45-16 Hoosier on an 8 or 8.5-inch wide rim. With the narrower size rim, the Hoosier gets squashed more than it should, and the contact from the 245 is NOT maximized.

This rule is EVEN more important as you decrease the tire's sidewall profile. You get little to no tire sidewall "bulge". Notice that rimwidth ranges for 30 and 35-series tires vary only about an inch. 40 to 45-series tires allow more flexibility (literally) for narrower rims, and that is reflected in 1 to 1.5 inch rimwidth ranges. Move up to 50 and 55 series, and you can have much as 2 inches in variance between the widest and narrowest rim you can fit; 225/50-16 tire size rimwidth range is between 6.5 and 8.5 inches!

In your case, Jim, you're looking for the fat-tire-bulge "look", and that's ok. You're not concerned with cornering potential, so it makes sense for you to mount a narrower rim on a wide tire. I wondered you used 9s on 275s!

If you don't know what a loose tire's bead width measurement is, then another good "thumb rule" is to pick a tire size that's only 110% wider than your wheel width--or conversely--pick a wheel width that's 90% of the tire's section width.

For a 275/40-17, I'd pick a 9.5 as a mimimum width, but 10s are ideal IMO. For a 285/30-18, I'd pick a 10 wide, and for 295/30-18, 10.5 wide.

The easiest one to do is a 255/40-17, 9-inch wide wheel Although most tire manufacturers state 10s are usable for 255, I'd stay with 9.5 as a max width for this tire, otherwise you will hear the rimlip hit the ground if your 255/40-17 mounted on a 10 x 17, falls over

Chronos

haha, it looks like a case of happyface virus infested this thread!

Btw GotBoosted7: Jimlab isn't the only one eyeing those Davins!!! I'm thinking about possibly trying them out for road racing? what do you think?

AHH IT'S INFECTED MY POST AS I TYPE! RUN!! SPARE YOURSELF!!!

SleepR1

chronos, how about staying on topic, if you want to take the time to post a comment eh?

jimlab

Here's a perfect example of what I'm talking about... P345s on 14" wheels in the back...



It looks stupid, it exposes the wheel to damage, and... it looks STUPID.

The front wheels are better, damn near perfect. However, you'd probably still hear the clunk of a $700 rim hitting the floor if they fell over, and that's my simple "test" for proper fitment. Tire tread nearly vertical with the section width extending just slightly past the edge of the wheel. Not something that looks roughly spherical, like those rear wheels and tires above. Too much wheel, not enough tire. I don't believe for a second that doing something like that makes the car corner any better.

Don't get me wrong, I'm not advocating shoving tires on too small of wheels. In fact, I would probably not have run P275s on 9" wheels and only swapped the 275s onto the 9s to hold the car up. They are worn out Nitto drag radials from my Supra (17 x 9.5" rear) and I simply needed four wheels and tires to transport my RX-7 to get painted. I had P265s on them previously, and that is a better match for a 9" wheel, in my opinion. You'd probably say it was still too narrow, and I'd say it was just about right. The Supra came stock with P255s on the rear 9.5s, and it looked like the Corvette above... like ****, in other words.

Every time I see a wheel/tire combination like that, I have to wonder if they just went cheap on the tires and bought the narrowest tire they could. It reminds me of the idiots with the 10" deep-dish wheels with negative offsets sticking out the sides of their Mustangs and Civics (with chrome S-10 mud flaps sticking out at an angle) with P235s or P245s mounted on them because they were cheaper. We call it the "bulldog" look, because the car looks like one of the bulldogs in the Foghorn/Bugs Bunny cartoons with its front legs turned in. I ain't tryin' to go out like that, homey.

spunup

here is that thread if you are still looking- https://www.rx7club.com/forum/showth...hreadid=123741

SleepR1

The rear wheel of the Corvette is a little more wheel than I'd do as well. Probably 12.5 or 13 would have been about right? I agree wholeheartedly about the sidewall being pretty much straight up and down when mounted on the right rim width. I think the front wheels could go about 0.5 inch to an inch wider

I've come to realize this is about 110% of the rim width; thus a 255 tire width is about what you'd want on a 9-inch wide rim; and yes I'd use a 9.5-inch wide rim for a 265 rather than a 9-wide

I'm coming from the perspective of maximizing the tire's contact patch. You do that by fitting the widest rim the tire spec will allow, within your aesthetic reasoning. Personally I go for midway, or slightly wider than midway of the tire spec, to acheive aesthetic appeal

I saw a 993 Porsche Twin Turbo last Friday. It had 11 x 18 BBS LMs with 285/30-18 Pirelli P-Zero Asymmetricos in back. IMO, I thought the 11-wide rim was too wide for the 285/30-18, as it look "almost" like the Corvette's rear wheels you posted above.

If you do the 90% or 110% rule, you'd get the look and performance you want. In this case the 90% rule applies, for the 285/30-18; thus 90% of 285 is 256.5 mm. Convert to inches, and that works out to 10.09 inches. So there you have it--a 10-inch wide will look and work perfectly with a 285/30-18

IMO, 295s would look fabulous in the back of an FD Rx7, so using the 90% rule, I'd choose 10.5-wide rims for the 295s to achieve the aesthetic appeal and performance from the 295-mm wide Pirelli P-Zeros.

You'll have to wait until this summer for a pic of that size on my car...that's how long it will be before I have the money saved up

Originally posted by jimlab
Here's a perfect example of what I'm talking about... P345s on 14" wheels in the back... It looks stupid, it exposes the wheel to damage, and... it looks STUPID.

jimlab

Well, I'm not in a hurry to run out and buy tires and wheels just yet, because it'll be a little while before I need them, but...

I'm leaning towards the Bridgeston S03s or Michelin Pilot Sports in P265/35 and P285/30 on 18" wheels. 9.0" in the front (I know, I know) and 10" in the back.

The Sports are closer in size, according to Michelin (25.3" and 25.0") than the Bridgestones (25.4" and 24.8") but I doubt it's noticeable. The Pilots are also about $190 more for the set of 4, not that that's an issue either.

The Bridgestone seems to be an excellent street tire, and has higher ratings in most categories than the Pilot, which may be the deciding factor. I've also had good luck with Bridgestone tires in the past.

It's unfortunate that the selection of P295/30-18s is so limited. I will not run the Asimmetrico because it sucks as far as hydroplaning resistance (and I may get caught in the rain in this state, even in July) and it has horrible tread wear and noise ratings, and I have to live with both.

The Continental, on the other hand, is a little too hard (tread wear 280) for my tastes, although it doesn't do too badly in the ratings. Dry and wet traction aren't in the same league with the Pilot and S03, according to Tire Rack surveys, but they are supposed to be quiet, and long-lasting. With a tread wear rating of 280, they ought to be.

The Yoko AVS Sports don't score as well in almost all categories as the Michelins or Bridgestone tires. Still, some people seem to like them well enough, and they're a little softer (but still reasonable) with a 180 tread wear rating. P295s would be impressive. But i doubt you'd miss the ~10mm and 1/2" of rim, and the difference in sidewall height is only ~3 mm... not enough difference to make a difference.

SleepR1

I dunno Jim...you'll wish you had 295s on 10.5s, once I get my pics up! I'll probably have to roll the rear fender lips as a safety measure. They will be W-I-D-E.

BTW the S-03s are also 280 UTQG, same as the Continentals.

FWIW, if you get the Porsche OE N2 Sport Contact 2s, I'm sure they will perform better than the normal Sport Contact 2s. Porsche has stringent standards for rubber tire manufacturers to meet in order to become the original equipment tire for a Porsche....

jimlab

Not according to Bridgestone's web site... 220 AA A down the line.
http://www.bridgestonetire.com/dpp/s...sproductid=227

I'm not going to put a tire and wheel combination on the car that even remotely might require rolling fender lips after just painting the car. Besides, exactly how much wider does a P295 look next to a P285?

SleepR1

Ahh, yes you're right 220 UTQG...my mistake You know comparing UTQGs between different tire makers is a worthless exercise, don't you ?

The 295 is definitely noticeably larger than 285/30-18.

Go look at a new Porsche 996 C4S. It comes with 295/30-18s in back, versus a 993 C2S/C4S/Twin Turbo, which came with 285/30-18 stock. Noticeably larger especially with those big Continental Sport Contact 2s.

Check out this website. It'll show a 295/30-18 right on the website--ummmmm---MEATY

http://www.conti-online.com/generato...master_en.html

BTW, the BBS RK needs to be wider, perhaps 10.5 instead of 10

In summary, Jim, I'd say stick with 10 wide in back and 9 wide up front. You'll be fine

For those considering 295/30-18 with 10.5 in back, I'd have the rear fender lips rolled just for safety's sake. The wheel/tire face will be flush with the outer most part of the rear fender lip, but shouldn't stick out. The concern comes when the car squats under acceleration. The lip might rub ever so slightly...