Tire Advice

[IBCoupe]

So I bought wheels a few days ago. Mailed in the check, and the guy's going to keep them at his shop 'til it warms up enough for me to fetch them or have them mounted/balanced/installed there.

But I need to buy tires, and I'm starting to have fitment concerns. I think I should be okay, but I'm not sure what to do about tires. I'm starting to think that a stretched tire would be the best route, but I don't have a clue, so I'm opening it up to anybody else to chime in.



Front:
19x8.5 +25

Rear:
19x9.5 +30

My current plan is to put 245/45/19's on the front and 275/40/19's on the back. However, this calculator seems to suggest that I might run into trouble in the back's. I think a 255/45/19 in the rear would be better, but am I going to have to roll my fenders? 245/45 in the front and 255/45 in the back each give me an extra 10mm protrusion.

The problem with that is that 255/45's are a pain in the butt to find. I think a 245/45 will fit on the 9.5's, but I don't know if that's going to be a lot of extra work.

[downedzephyr]

i would roll if i were you, it's better to have it done and not have to worry about it later

[AlexM.]

Roll rear fenders and then also check out this tire site if you haven't already.

http://www.tyrestretch.com/index.php

Stretching your tires also reduces chances of rubbing.

[IBCoupe]

Sweet. I think I can get away with buying four of the same tires and not stretching them. I think a 245 is the narrowest tire that'll go on a 9.5" wheel without stretching. I'll definitely roll my rear fenders. Might need to do the fronts, too.

[downedzephyr]

i don't think you need to roll the fronts, they're practically rolled stock.

[IBCoupe]

Okay, thanks! I assume that's because the front ones move?

[AZhitman]

Ugh. <rolls up sleeves>

First off, use a real tire size calculator. Miata.net has the industry standard. Also, use TireRack.com to find actual specs on tires you're considering. This will eliminate a lot of guessing.

Second, I see no discussion of maintaining original OD. You kinda need that, or you're gonna run into issues with speedometer, ABS and VSC (if your AC's have it).

Third, I know you've already addressed the staggered-tires-on-a-fwd-car issue (which I'll still clown you about), but I hope you've considered the weight of this wheel / tire upgrade... 19's are hefty.

Fourth, "stretch" is a continuum, not a definitive line. Having less tire than wheel exposes your pretty investment to curb-checks, which I anticipate you'll collect in short order. If you don't, there's a strong statistical (and stereotypical) probability that *someone* in your house WILL.

Last, do NOT buy tires unless you mount the wheels (naked) and set the car on them (you can use wood blocks to cradle the bare wheel in the center, not on the lip). This will allow you to measure available space with the suspension loaded and compressed (and front wheels turned).

The ONLY way this is gonna be not applicable is if you copy a known functional (and identical) setup. Check brand as well - tehey can vary in size significantly.

[IBCoupe]

First off, use a real tire size calculator. Miata.net has the industry standard. Also, use TireRack.com to find actual specs on tires you're considering. This will eliminate a lot of guessing.

I like Miata, but it doesn't examine lateral growth. It gives you a nice picture, but it doesn't tell you anything: Miata doesn't ask about wheel width or offset. That's why I used the one I link to - it illustrates all the dimensions involved, and even gives you an analysis at the bottom. I think I prefer it to Miata, even though it's the industry standard. I get the same percentages in OD as Miata, but I get a whole lot more, too.

Here's that link again: http://rimsntires.com/specs.jsp

Second, I see no discussion of maintaining original OD. You kinda need that, or you're gonna run into issues with speedometer, ABS and VSC (if your AC's have it).

Because I've already taken that into consideration. That's why I didn't ask about it.

Third, I know you've already addressed the staggered-tires-on-a-fwd-car issue (which I'll still clown you about), but I hope you've considered the weight of this wheel / tire upgrade... 19's are hefty.

I bought Rays LM GT4's. Because they're forged, they're going to be lighter than the stock 17's - our stock wheels weigh in at about 24 lbs. without a tire; according to the Nissan NISMO website, these weigh 20.5 lbs in the front, 20.9 in the rear. The lower-profile tires should be about 4 lbs. lighter, too. I'm switching from hiking boots to cleats.

My hope right now is that I can get the same tires on the back as the front - 245/45/19 looks like it will fit on both the 8.5" wide wheels and the 9.5" wheels, but there isn't a lot of outward bulge on the 9.5" (245mm is 9.6"). Don't know if that's significantly bad, or if it's perfectly fine.

Fourth, "stretch" is a continuum, not a definitive line. Having less tire than wheel exposes your pretty investment to curb-checks, which I anticipate you'll collect in short order. If you don't, there's a strong statistical (and stereotypical) probability that *someone* in your house WILL.

Heh. She won't drive my car; belt-line's too high.

Last, do NOT buy tires unless you mount the wheels (naked) and set the car on them (you can use wood blocks to cradle the bare wheel in the center, not on the lip). This will allow you to measure available space with the suspension loaded and compressed (and front wheels turned).

Hadn't thought of that; thanks for the heads-up.

The ONLY way this is gonna be not applicable is if you copy a known functional (and identical) setup. Check brand as well - tehey can vary in size significantly.

Okay. My only problem is that the wheels are on the other side of the State, waiting for warm weather to arrive.

[IBCoupe]

So, here's what I'm faced with:
4 x Hankook Ventus V12 (245/45-19)
Lateral clearance front: 10mm less than stock
Lateral clearance rear: 5mm less than stock
OD: -9mm (59.2mph @ "60.0")
Price: $668.00

4 x Pirelli PZero (255/45-19)
Lateral Clearance Front: 15mm less than stock
Lateral Clearance Rear: 10mm less than stock
OD: +1mm (60.1mph @ "60.0")
Price: $1068.00

Cheapest summer rubbers in either size.

[AZhitman]

I have the V12's. They're insanely great tires for the money.

Actually, they're insanely good PERIOD. I bought them over more expensive options, and they get a REAL workout on the C5.

Same tires F & R will look silly (they'll LOOK wider in front due to the bulge).

BTW, the 19" tires are 2 lbs heavier than your OEM tires. Looks like weight will roughly be a wash. Interesting.

[IBCoupe]

Good to know! I'll stick with the Hankooks, then, and I'll get some fatter tires in the back.

Unfortunately, if I'm going to go with staggered tires and want to stay +/- 3.0% in the rear, that means I've got to switch to 275/40's.

Means this is what I end up with:
2 x Hankook Ventus V12 (245/45-19)
2 x Hankook Ventus V12 (275/40-19)
Lateral Clearance Front: 10mm (0.4") less than stock
Lateral Clearance Rear: 20mm (0.8") less than stock
OD Front: -9mm (59.2 @ "60.0")
OD Rear: -9mm (59.2 @ "60.0")
Price: $704.00

Looking like it'll be necessary to roll the rear fenders. The guy I bought them from has a Nissan-focused performance shop, and he said he's got the fender roller there. That's probably what I'll do.