Ok i ve order this week a set of black zr1 style wheels.They are all 18x9.5.

Im looking for the good tire size,is it 275/35zr18 or 285/35zr18 or 275/40zr18

Also what could be a fair tire i was looking at the dunlop Direzza DZ101 at 170.00$ or the Falken GR Beta FK-451 for 181.00$ each and free shipping on discount tire.What do you think of these tire or what would you have to suggest me,and yeah im on a tight budget.

Thank you

 

You want to find a tire that is close to the diameter of your stock tires. The V8 4th Gens (excluding the WS6/SS coupes) came with two tire sizes:

235/55-16 (26.18" diameter)
245/50-16 (25.65" diameter)

Of the sizes you listed:

275/35-18 (25.58")
275/40-18 (26.66")
285/35-18 (25.85")

.. the 275/40-18 is a bit too large. Nothing you couldn't correct for in the PCM, to keep your speedo and odometer accurate. Will fill up the wheel wells a bit. The sidewall will be a little taller. But if your car is lowered, it might cause some rubbing.

The 285/35-18 is probably the best choice, but the 275/35 would be OK too.

Go to Tire Rack. Click on "tires by size". Put in the size you want.... "search". You will get a long list of available tires. Click on "survey results" for a tire you are interested in, and it will give you a numerical rating from 1 - 10 for things like dry and wet traction, tread wear, noise, ride comfort, etc. At the bottom of the survey screen, there's another button that allows you to pull up a list of all the comparable tires, and rates them against each other.

 

I would agree with Injuneer - I just did the 275/40'/18's beacsue I wante dto fill up the well - I put in 1" Hotchkis springs and that is the most I would want to go - It all clears just fine - the Eibach Sportlines and Prolines would lower it too much.

But all three would fit that you have listed - Just consider where you drive (the road quality) and the comfort level you want (bigger sidewall with the 40 series will give a more plush ride than the 35 series).

Pics are on page 3 in sig - I love the 18 Zr1-s! Good luck with yours.

 

Ok my car is not lower and will never be because here in Quebec the road are awfull.I run a set of adjustable koni shock on stock spring.I dont know what was the stock size on my formula because the last owner install some ****ty 235/60r16(not even a good size).

You say that the 275/40-18 is a bit too large and that the 285/35-18 is probably my best choice.

But maybe i dont understand something.285 is larger than 275 right?So how come that the 275 is too large and the 285 would be the best

I already know that with 275/35-18 the clearance/rubbing will be perfect.

But is there gonna be a clearance/rubbing issue with the 285/35-18?

Wow i never thought that i will be a little lost when trying too find the good tire size

 

285 is the "section width" in millimeters.... the width of the tire at its widest point. So, yes, a 285 (11.22") tire is wider than a 275 (10.83") tire.

But I was talking about the outside diameter of the tire, or tire "height". To get the outside diameter from the tire specs, you convert the section width to inches, add a decimal to the "aspect ratio" (the 35 in the tire size means the sidewall height is 35% of, or 0.35 X the section width), multiply the aspect ratio times the section width - that gives you the sidewall height. Then add 2X the sidewall height to the wheel diameter.

285/35-18:

285/25.4 = 11.22"

0.35 X 11.22 = 3.93"

2 x 3.93 = 7.86"

18" + 7.86" = 25.86" = the outside diameter of the tire

275/40-18:

275/25.4 = 10.83"

0.40 x 10.83 = 4.33" (the sidewall is taller)

2 x 4.33 = 8.66"

18" + 8.66" = 26.66" = the outside diameter of the tire

So..... the 275/40 is "larger" than the 285/35 when you are talking about the diameter.

Why do you want the diameter to be close to stock?

-it affects the speedometer. If you put an oversize diameter on the car, and don't program the correct diameter into the PCM, yoiur speedometer will read lower than actual speed. If your car originally had the 245/50-16 tires, and you put the 275/40-18 on it, the speedometer will read 57.7mph when you are actually going 60mph, or 96.2mph when you are actually going 100mph. Not a lot of error.

-it affects the torqu multiplication at the rear wheels, just like changing to a lower numerical rear axle ratio. It you have 3.73 gears, the larger diameter tires will make it feel like you have 3.59 gears (if there was such a ratio).

-it raises your car 1/2"

-the tires will stick up 1/2" farther into the wheel wells. This generally isn;'t a problem, but there was a post here recently where a guy with a GFX setup had the oversize tires ripping off the rivets that hold the ground effects on the car.

The 275/40-18 is no big crisis... and its the tire that was used on the Corvettes, so a lot of places will sell the 18x9.5 wheels with the 275/40's as a package.

None of the tires will cause you a problem.... you just need to be aware of the impacts of using a larger than stock tire diameter.

 

Ok now i understand better,thank you.

So if
245/50-16 (25.65" diameter)
the closest one would be
275/35-18: (25.58")

And if i want a little smoother ride that will not really affect the performance of the car with a little taller side wall, because of the bad road that we got here, i can go with the 275/40-18(26.66") .And since my car is not lower i will not experience any clearance problem(this is the most important think to me CLEARANCE).

And i just change the pcm tire size(height) with my hpp3.But the hhp3 graduate by 0.25inch so i ll put 26.75". I know its not a super tuner but i got it dirt cheap to change my gear ratio since i got a 3.73 and now i will be able to change the tire size.

Am i right?

I may sound like a jerk with all my question and im kind of sorry for that but since im a quebec(canada)customer that buy all is stuff in the us i must be sure to order the good part/size/model etc.

Just for an example if i order from the US:

Falken fk-451 275/40zr18:
147.00$us each so that give 169.00$ each in canadien fund

A set would cost me 676.00$ can and discount tire offer free shipping in the US.I ship everything at a us warehouse at 2 min from the lines and at 45 min of my home.
I go pick them up and pass the lines and pay 15% of taxes:102.00$can
TOTAL:778.00$CAN

If i take my tire here in canada:

Falken fk-451 275/40zr18:
Canadien price:around 270.00$can that give 236.00$us each

A set would cost me 1080.00$can + 15% of taxes :about 1250.00$ can that give 1090.00$us
-------------------------------------------------------------------------------------------

So if i order from the us it would cost me:778.00$can or 676.00 us

And if im ordering from here in canada it would cost me:1250.00$can or 1090.00$in us fund

For a big difference of 600.00$can or more of saving.

Another quick one without calculating the taxes:

BF Goodrich g-Force T/A KDW in 275/40zr18 in the US: 219.00us or 250.00$can
BF Goodrich g-Force T/A KDW in 275/40zr18 in Can:400.00$can or 350.00$us

 

So anyone

I just need to know if the clearance would be ok with 275/40-18

and

If i put 26.75" for the pcm tire height size since the hpp3 its graduate by 0.25" and i cannot put 26.66"

With these two question answer i will be able to order my tire as soon as possible.

Thank you

 

I'll make your life more difficult.... what is the offset on your 18x9.5" wheels? If it is in the range of 45-56mm, you are probably not going to have a problem with clearance. The guy who had the problem had some sort of GFX package, and the tires were ripping the mounting rivets off... at least that's the way he explained it.

As far as the diameter, when you select a specific brand of tire, find out exacctly what diameter they are. The dimension I gave you is the theoretical dimension. When you look at the dimensional tables for a specific tire, it may vary from that dimension by +/- 0.10" or even a little more. I would even go so far as to actually measure the rolling diameter after you got the tires mounted and on the car. Mark the tire and the asphalt with a piece of chalk. Roll the car forward until the mark on the tire is again on the ground, and mark the asphalt again. Measure the distance between the two chalk marks on the asphalt. Divide that number by "pi" (3.1416) and you will have the rolling diameter of the tire. That is what you put into the PCM, or to the nearest .25" with the HPP. The maximum possible error in the speedo would be less than 0.3 mph at a true 60-mph. You will get more variation than that due to tread wear or inflation differences.

 

Your not making my life difficult , right now you made it easier,my wheels are 18x9.5 with 56mm offset,koni adjsutable shock and stock spring(stock height) so with all your info i assume there will be no porblem for the clearance.

And thank you for the info on finding my personnel wheel/tire combo height with the chalk marks,it will be pretty easy.

I ll be ordering this monday And i ve change idea im going to take your advice and order the 285/35zr18.

Thank you