[Cloud9...68]

[quote name='flash' timestamp='1403316974' post='158803']

cloud - why not a 285/30? that's the same OD as the 17

[/quote]

Hmmm... Maybe an option worth considering. I've kind of had my heart set on a set of BF Goodrich G-Force Rivals because of the excellent reviews they've been getting, and they don't come in that size, and neither do the Hankook R-S3's that I currently have on my car, which I'm quite happy with. Most of the tires that come in 285/30-18 are quite expensive, and with the amount of track driving I do, which I plan to ratchet up in the second half of 2014, that would get pricey. Sumitomo HTRZIII's, however, do come in that size, and they're dirt cheap (only $149 apiece). I had those before, and actually like them a lot, even though they're not considered in quite the same league as some of the others I'd been considering. But since my main goal is getting lots of seat time, which is going to chew up tires fast, having the absolute ultimate tire probably isn't a primary consideration.



My other reason for considering a narrower tire is to reduce the sidewall roll, as a 285 section width is pretty wide for a 10" wheel, but I suppose a lower profile tire in the same width would accomplish much the same thing. Would you agree? Thanks for the recommendation - definitely an option I need to consider.



OP - sorry for the thread diversion. But when you bring up the topic of wheels, the discussion tends to wander a bit pretty fast.

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[flash]

p.s. - i run a 285-30 on the 10" on my car (yokohama advanAD-08)

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[Cloud9...68]

I wish I had paid attention to tire diameter when I picked my current tires. I knew what brand I wanted (Hankook R-S3's, which at the time were getting top reviews among track-able street tires), and I somehow got it into my head that a 285 width was correct for a 10" wide wheel. Unfortunately, R-S3's only come in a 35 aspect ratio in the 285/18, which puts the overall diameter at 25.9", vs. the 25" that is stock. So I've raised (numerically lowered) my final drive ratio by 3.6%, which is costing my some rpm's in key places on the track.



More research led me to conclude that a 285 mm tire is actually too wide for a 10" rim, and was planning on going with a 265/35-18 for my next tire purchase, which puts me at a still-slightly-too-tall 25.3 ". Flash's suggestion of a 285/30 tire (o.d. = 24.7") is interesting, so I took a close look at how my current tires are fitting on the rims, and found, for what it's worth, that they're actually pretty flush with the edge of the rim. These are the best pictures I could take to try to show this:



   



   



   



When I place a straight edge against the tire across the center of the wheel, and measure the gap between the edge of the rim and the straight edge (this can be seen in the top image), I measure only 2.6 mm. So, my feeling is that 1 285 tire isn't overly wide for a 10" rim, and with a lower profile, what sidewall roll might exist now should be diminished even more.



As far as the fronts, I have 8.5" wide wheels (so I have 1" wider than stock both front and back, which is the widest allowed by several of the racing sanctioning bodies), with 255/35-18 tires. These are exactly 25" o.d., but I was concerned that they really are too wide for the rims, but to my surprise, when I do the same straight edge-to-rim measurement described above, the gap is even smaller than for the rears - less than 1 mm.



So, my conclusion is that Flash's recommendation of a 285/30-18 for the back is a good one, and I think I will stay with the same 255/35-18 size I currently have on the front.



FYI, for the OP, my wheels are Enkei NT03's, with a front offset of 50, and a rear offset of 60. Both ends fit perfectly, with no hint of rubbing under any situations, and no need for spacers at either end.

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[parptarf]

I have bought the Alleggeritas so we'll see some time this week if everything fits.

8x18 ET50 with 225/40 and 10x18 ET65 with 295/30. I'm gonna use a 5mm spacer on the rear to get ET60. I might space out the fronts 5mm too but I'll test fit without first.



I also had a chat with the previous owner and he said there was quite a bit of room with 265 tires back and running a 10" wide rim at ET60. He thought the 295's will just fit without rubbing during cornering.

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[flash]

i'll take a pic of mine today. 285/30 fits GREAT on a 10" rim. if you go to the tirerack site, you will see that a 285 is right in there in the recommended rim widths (albeit at the bottom end). i was looking for a smoother ride though, so i wanted to have a little more flex (not there there is much with a 30 profile tire)



a 265 on a 60 will fit.

a 265 on a 65 will be close on the inside, in a corner, depending on camber angle, spring rates, yada yada.



ya know, we have a calculator here that answers all of this as well as any conversation. the bottom line is that you have to fit them on the car, drive the car to see if they clear with your setup. proof of this is a car i am dealing with right now. he is running a 285/35 and it rubs in the rear, up front on the clip. he does not have enough rear camber, and i think it will clear once he does. but it is an example of how the setup can affect things.

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[parptarf]

285/35? Isn't that too tall?



If all else fails a 265 tire will be my next go, I know that will fit But I'll see how the 295/30 goes first.

Luckily the Michelin Pilot Sport Cup tires are supposed to be in great condition and they were new last year. I could fetch a nice price for those and get a set of Pilot Sport 3.

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[flash]

yes - it is. but, he bought the wheels with those on them, and wants to run them until they wear out. i can't blame him, as they are michelin super sports.



regardless of tire, he needs more negative camber. he only has about 3/4 of a degree right now, and we want it at 1.5. that will make nearly 1/2" difference, which i think will make the tire clear, at his ride height, spring rates, bushing types, and loaded weight. if it doesn't we'll change out the tires to a 30 series.

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[Cloud9...68]

Flash,



So what's your thought of a 255/35-18 on an 8.5" wide wheel in the front? I think you're running the same size tire, but on a 9" wide rim. According the Tire Rack's guide, an 8.5" wide rim is the minimum for a 255/35 tire. But i was very pleasantly surprised that, for what it's worth, my current 255/35-18 tires are virtually flush with the edges of my 8.5" rims.

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[flash]

i have no problem with that combination. it sounds like your particular tires are small for their size. michelins are like that too. on the front, it's really all about how much the sidewall flexes, which is determined by the construction and pressure as much as the size, and whether that results in issues (like twitch or understeer).



in the rear, an overwide tire is a lot less of an issue than an narrow one, where you can suffer bump oversteer very easily.



of course, the weight of the tire is a huge factor. a pound on each of the wheels/tires is multiplied by a factor of at least 2. any traction you may gain can be quickly offset by a loss of acceleration, braking, and suspension stability, due entirely to the mass. this can be especially messy on short courses. for example, i would never run an 18 of any size in autocross, and would tend to run as small a diameter as possible.



it really depends on what the use is

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[parptarf]

Lots of people run 18" for autocross here. They all have lightweight racing wheels from BBS or OZ though.

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[flash]

yup - i see that a lot. still, that would be a mistake. the sheer weight alone would slow you down. they would be even faster with smaller diameter wheels.



but then, i see a lot of mistakes made by people at autocrosses. they set the car up like a track car, and are always slower than they could be. they just can't seem to get their head around the idea that an autocross car is not set up like a track car. we used to really piss off a bunch of guys with a bone stock car, by merely running smaller diameter wheels, and disconnecting the front sway bar. we would come in a full second faster than the fastest guy with the track type setup.

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[parptarf]

If a 18" racing wheel weighs less than say a 17" cup wheel, won't the 18" be faster?

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[flash]

not necessarily. the tires are usually heavier than the wheels by about 30%. depending on the size, a superlightweight 18" wheel with a tire can still mean more than the same width tire in a 17



but the big thing is that the same superlightweight wheel in a 17 will still be faster, because it's lighter.



i would run a 16 if i could, for autocross.

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[parptarf]

Hmm. you do have a point.

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[flash]

most people can't run 3 different sets of wheels, or spend time altering their setup for street/track/autocross. it's really hard to do, and the slightest geometrical change can mean the difference between 1st and 2nd. i see guys trying to use those dumb camber plates too, and go back and forth between street and autocross setups. in the end, they lose on both, because you can't get the alignment close enough, and when you are talking about hundredths of a second, it has to be right.



i love to see the guys that show up with stiff springs too. fun to watch them slide around. we always sprung soft for autocross. much better hook up.



anyway, back to the tire and wheel issue, i think you'll be ok, but remember that you need 1.5 times the diameter of the stud in thread engagement, in order to be safe (2x if using aluminum nuts). so, when you put your spacers on, measure the stud length to see if you need longer studs.

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[parptarf]

Wheels are now on the car and I found some twisties to test it out on and did some highway cruising. No rubbing, no vibrations and it looks perfect.

I ended up spacing out the front wheels too. So I'm sitting at ET60 at the rear and ET45 at the front.









So now I know, running my setup, a 10x18" rim at ET60 will work with a 295 tire.

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[Cloud9...68]

Those are beautiful wheels. It would be nice if they came in 17 x 9".

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[parptarf]

I would have preferred that myself. 8x17 and 9x17 at ET50 would be great.

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[flash]

glad it worked

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[Cloud9...68]

[quote name='parptarf' timestamp='1403787973' post='159054']

I would have preferred that myself. 8x17 and 9x17 at ET50 would be great.

[/quote]

Yeah, the few high-end (e.g. forged monoblock) wheels I've found that come in Porsche's 5 x 130 mm bolt pattern only come in 18" diameter and larger. Those wheels really look great on your car.

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