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Crazy Canuck
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Discussion Starter #1 (Edited)
I've noticed a lot of people asking questions on here about tire sizing who obviously don't understand what they mean. So, I thought I'd be a good forum denizen and put my knowledge and writing skills to work.

Tire Sizing Decoded

For this example I'm going to use a tire sized as follows: P245/45ZR18

P = Passenger Car tire (whereas LT is for light trucks like pickups and SUVs)

245 - tread width in millimetres. In other words, the width of the tire where it contacts the road.

45 = aspect ratio of tire's sidewall to width (as a percentage). So, in this example, the sidewall would be 245mm x .45 = 110.25mm.

Z - speed rating (i.e. how fast the tire is rated to go). A 'Z' rating happens to be the highest for passenger cars, able to travel at 186mps (300 km/h). However, most passenger cars make due with far less capable tires (what normal car can go that fast anyway?)

R - radial. This harkens from before radials were the norm, back in the days of the infamous bias-ply tires (before my time though).

18 - wheel/rim size in inches. Enough said.

Calculating Tire Diameter

This following may seem a bit complex to some, which is why I've also included a link to a javascript calculator made for this purpose.

Tire Diameter (mm) = (((tread width x aspect ratio) x 2) + (wheel size x 25))

Note: The above formula assumes all values are in their original formats (i.e. mm or inches). To convert millimetres back into inches just divide by 25.

Links:
Miata.net

Why Does Diameter Matter?

Since the circumference of a tire is directly proportionate to its diameter (you do remember grade 5 math don't you?), the one will change with the other.

The speedometer (and odometer/trip-meter) in a car are calibrated based on the size of tire the car came with. If you put on a tire that is bigger or smaller than the original, your speedometer will no longer be accurate (although most aren't too accurate anyway - Car & Driver did a test on that a few years back - if I recall correctly, japs were most accurate, euros were least accurate, and domestics were somewhere in the middle).

If you put a larger tire on your car, it will take less revolutions of that tire (versus the orginal smaller tire) to move a given distance. Thus, your speedometer will tell you you're going slower than you really are, making it likely you'll encounter the local constabulary sooner or later.. not a good thing. Putting on a smaller tire will have the opposite effect, making your speedometer show you're travelling faster than you really are... at least you can't get a ticket for that.

As well, the ECUs in some newer cars don't like it when the tire size is changed, and will throw a big hairy fit as a result. So, in short, it's best to keep the diameter of your tires the same as orginal equipment.


What is a Plus-1?

This is basically used to describe the act of increasing the size car's wheels/rims by one-inch while keeping the overall diameter of the tires fairly constant. As a rule of thumb, this is done by increasing the tread width by 10mm (i.e. 255 instead of 245) and decreasing the aspect ratio by 10% (i.e. 35 instead of 45), and increasing the wheel/rim size by one inch. It's quite difficult to get the diameters to match exactly, so generally you just have to make due with the closest match.

Hopefully this information has been useful to you. I'm sure other forum members will insert their valuable information after, so go read that too...
 

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^^That was some excellent information about tires...

But I think what most people want to know is what are the best sizes for the 3rd Gen Altima specifically. It starts with the rim that you have our going to be getting.

If your upgrading to a bigger rim like an 18" or 19" or even a 20"....
an 8.5" wide rim seems to be the widest with a +50mm offset at least.
8" wide rim is really the best width with a +45mm offset, you can get away with +40mm with a 8" wide rim. Anything between +40 to +45mm offset is what you want. Anything smaller then +40mm you need a 7 to 7.5" rim or you will have rubbing issues. You have a 8" wide rim with a +35mm offset you might get away with a 225, but thats a narrow tire for the rim size. A 235 may even still have a rub issue.

Tire size, 245 are about the widest for best fit on a 8" or 8.5" wide rim. Some have tried 255, but not without rubbing issues.

The idea is to keep your new wheels & tire selection close to stock diameter..
use the tire calculator blitzboi gave is really helps, I use this one:

http://www.powerdog.com/tiresize.cgi

Note: are lug pattern is 5X114.3 or 5X4.5" the lugnuts are M12X1.25 RH
 

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Crazy Canuck
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Discussion Starter #3
altimateone said:
But I think what most people want to know is what are the best sizes for the 3rd Gen Altima specifically.
Probably, except I have no knowledge yet of L31 Altimas. My '05 3.5 SE 5sp won't be ready for pick-up until Tuesday this week (I ordered it on March 24th). It's supposed to have the new 5-spoke 17" rims on it, so I hope I like those better than the old 6-spokers (for some reason I don't like most rims with an even number of spokes)...

Thanks for adding your specific knowledge of what tires/rims fit on these cars without rubbing...
 

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Crazy Canuck
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Discussion Starter #4
altimateone said:
If your upgrading to a bigger rim like an 18" or 19" or even a 20"....
an 8.5" wide rim seems to be the widest with a +50mm offset at least.
8" wide rim is really the best width with a +45mm offset, you can get away with +40mm with a 8" wide rim. Anything between +40 to +45mm offset is what you want. Anything smaller then +40mm you need a 7 to 7.5" rim or you will have rubbing issues. You have a 8" wide rim with a +35mm offset you might get away with a 225, but thats a narrow tire for the rim size. A 235 may even still have a rub issue.
In some cars I've modified in the past, changing the wheel offset too much made them really twitchy. Is this an issue on altimas when you go to a +40 offset for example?
 

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+40mm offset is what I have on 19X8 rims, +40mm is about = to 1 9/16". Thats off from center, so you got 5 9/16" on the inside and 2 7/16" on the outside of rim. If you want to go with a 8" wide rim I recomend +40mm at minimum. Any less with this size rim on the 3rd gen Altima will kick the rim out to much and rub. I think the handling is excellent and tire wear is perfect providing your camber is adjusted right. I lowered my front 1.8", my rears sit stock.

I dont think its twitchy at all...not like the Mazda6 I test drove. That car will react to the slightest steering movement.

The stock 17" alloys are 7" wide the 16" steels are 6.5" wide. If you kept a stock size rim, you could find a offset that is more centered. But even the stock 17" rim has an offset of +35mm off center, so the factory doesn't put there wheels on center.
 

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blitzboi said:
Probably, except I have no knowledge yet of L31 Altimas. My '05 3.5 SE 5sp won't be ready for pick-up until Tuesday this week (I ordered it on March 24th). It's supposed to have the new 5-spoke 17" rims on it, so I hope I like those better than the old 6-spokers (for some reason I don't like most rims with an even number of spokes)...

Thanks for adding your specific knowledge of what tires/rims fit on these cars without rubbing...

Congrats on your new car when you get it...

I'm beginning to like the new front end of the 05...it had to grow on me as I see more and more on the road. Yeah the old 6spoke 17" which I had are pretty plain, I went to 19X8 with a 6 spoke except they split at the ends like 12 little spokes...alot like the new rims on the SE-R. When the SE-R first debut thats the first thing everyone noticed that the rims looked alot like mine :thumbup: copy cats! :mad: :p I've had my rims for over a year..
 

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Crazy Canuck
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Discussion Starter #7
altimateone said:
I dont think its twitchy at all...not like the Mazda6 I test drove. That car will react to the slightest steering movement.
Sounds like my Protege5 (company car). It's got great handling, like it's on rails even with the stock 16" alloys and tires. But it gets annoying on the highway because it changes lanes too easily.. doesn't like to stay going straight. I haven't driven a Mazda3 yet to know if they've dulled down the handling any or tightened it up even more.
 

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Thats funny I was looking at the Protege5 first, then decided I needed more room so I almost bought the Mazda6, but the sales manager wouldn't budge off sticker cause it was there new model year. I ougt to thank him for steering me towards the Altima instead... :)
 

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Crazy Canuck
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Discussion Starter #9
altimateone said:
Thats funny I was looking at the Protege5 first, then decided I needed more room so I almost bought the Mazda6, but the sales manager wouldn't budge off sticker cause it was there new model year. I ougt to thank him for steering me towards the Altima instead... :)
The P5 is okay for work stuff... its trunk is big enough to hold all my tools and parts (corporate computer support). However, it's a bit small to be used as a family vehicle. I'm single and all, but I'm a six-footer, and some of my close relatives are as tall or taller, so a bigger car just makes sense for me when I have to transport people. The height thing is also why I'm a wierdo and didn't get the sunroof on my car.. it cuts into my headroom!
 

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blitzboi said:
The P5 is okay for work stuff... its trunk is big enough to hold all my tools and parts (corporate computer support). However, it's a bit small to be used as a family vehicle. I'm single and all, but I'm a six-footer, and some of my close relatives are as tall or taller, so a bigger car just makes sense for me when I have to transport people. The height thing is also why I'm a wierdo and didn't get the sunroof on my car.. it cuts into my headroom!
thanks for the info...i ended up ordering the 245/40/18 in toyo proxies...
chrome....$1445.00
 

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altima04 said:
altima25s said:
thanks for the info...i ended up ordering the 245/40/18 in toyo proxies...
chrome....$1445.00[\
ooo nice u got pics or a website so i could see them?

no but i will try to get one...I dont even have the rims yet becuz they are a custom order so im still waiting...but soon as i get em(within 7-10 buiz dayz) im gonna take a pic and post it.....you can see the rims @ www.streetdreams.org

Go to the drop down box for name of brand and chose kaizer...its the spade II
 

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blitzboi said:
The P5 is okay for work stuff... its trunk is big enough to hold all my tools and parts (corporate computer support). However, it's a bit small to be used as a family vehicle. I'm single and all, but I'm a six-footer, and some of my close relatives are as tall or taller, so a bigger car just makes sense for me when I have to transport people. The height thing is also why I'm a wierdo and didn't get the sunroof on my car.. it cuts into my headroom!

Hey does anyone know a good website(other then tire rack---terrible rims) that you can see the rims on your car?? A good website though...that carries such brands as kaizer and niche and gianelles ect...
 

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altima25s said:
Hey does anyone know a good website(other then tire rack---terrible rims) that you can see the rims on your car?? A good website though...that carries such brands as kaizer and niche and gianelles ect...
www.rimstop.com this is a good website to view wheels on your car.
 

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Crazy Canuck
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Discussion Starter #15
Tire Pressure...

Okay, so this has nothing to do with the original purpose of this thread, but I didn't want to start a new one...

I cannot seem to find the recommended tire pressure for my '05 Altima 3.5 SE. I looked in the manual and it tells you to find the sticker on the driver's-side centre (B) pillar. No dice... the sticker there tells me all sorts of things (VIN, mfg. date, colour code, engine type, etc.) but not tire pressure. And yeah, I have checked all the other door jams to no avail...

The car is wearing Bridgestone Turanza P225/55R17 rubbers and they're all currently around 30psi, but I don't know if this is right or not... can anyone tell me where Nissan conveniently hides this information? I don't want to call the dealer if I don't have to.
 

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Best tires for my Altima

The OEM Contintial 205/65/16's that came on my Altima have a couple of thousand miles left on them. They haven't rode that good after 15,000 to 20,000 miles and they only have less than 30,000 on them. I want to so with 205 to 225 60 or 65's. What brand and size has anyone used that they like. Has anyone put Yokohama's on a Altima yet.?
 

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blitzboi said:
I cannot seem to find the recommended tire pressure for my '05 Altima 3.5 SE. I looked in the manual and it tells you to find the sticker on the driver's-side centre (B) pillar. No dice... the sticker there tells me all sorts of things (VIN, mfg. date, colour code, engine type, etc.) but not tire pressure. And yeah, I have checked all the other door jams to no avail...
In my '02, it's on the underside of the center console lid.
 

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Crazy Canuck
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Discussion Starter #18
Afty said:
In my '02, it's on the underside of the center console lid.
I looked a few weeks ago and you're right, it's under the lid of the main armrest storage bin (not the shallow top one) on my 2005 Altima. I think perhaps Nissan should update its owner's manual to tell people where it actually is.. still says it's on the driver's-side "B" pilllar in mine.
 

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Tire Pressure

The car is wearing Bridgestone Turanza P225/55R17 rubbers and they're all currently around 30psi, but I don't know if this is right or not...


I had encountered the same problem several months ago, but I was able to locate the information over a website that shows recommended pressure for different tires for specific car makes and models. If I remember correctly , the recommended pressure was 30/32 psi for rear/front tires. The recommended pressure vary from summer to winter by 2 psi. I was driving around with 36 psi, considering that a safe tire pressure Vs maximum pressure of 40 or 44 psi that the tire was rated for. But the ride felt wobbly and I realized that the dealer was right when he warned me that I have set the pressure too high.
 

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blitzboi said:
I've noticed a lot of people asking questions on here about tire sizing who obviously don't understand what they mean. So, I thought I'd be a good forum denizen and put my knowledge and writing skills to work.

Tire Sizing Decoded

For this example I'm going to use a tire sized as follows: P245/45ZR18

P = Passenger Car tire (whereas LT is for light trucks like pickups and SUVs)

245 - tread width in millimetres. In other words, the width of the tire where it contacts the road.

45 = aspect ratio of tire's sidewall to width (as a percentage). So, in this example, the sidewall would be 245mm x .45 = 110.25mm.

Z - speed rating (i.e. how fast the tire is rated to go). A 'Z' rating happens to be the highest for passenger cars, able to travel at 186mps (300 km/h). However, most passenger cars make due with far less capable tires (what normal car can go that fast anyway?)

R - radial. This harkens from before radials were the norm, back in the days of the infamous bias-ply tires (before my time though).

18 - wheel/rim size in inches. Enough said.

Calculating Tire Diameter

This following may seem a bit complex to some, which is why I've also included a link to a javascript calculator made for this purpose.

Tire Diameter (mm) = (((tread width x aspect ratio) x 2) + (wheel size x 25))

Note: The above formula assumes all values are in their original formats (i.e. mm or inches). To convert millimetres back into inches just divide by 25.

Links:
Miata.net

Why Does Diameter Matter?

Since the circumference of a tire is directly proportionate to its diameter (you do remember grade 5 math don't you?), the one will change with the other.

The speedometer (and odometer/trip-meter) in a car are calibrated based on the size of tire the car came with. If you put on a tire that is bigger or smaller than the original, your speedometer will no longer be accurate (although most aren't too accurate anyway - Car & Driver did a test on that a few years back - if I recall correctly, japs were most accurate, euros were least accurate, and domestics were somewhere in the middle).

If you put a larger tire on your car, it will take less revolutions of that tire (versus the orginal smaller tire) to move a given distance. Thus, your speedometer will tell you you're going slower than you really are, making it likely you'll encounter the local constabulary sooner or later.. not a good thing. Putting on a smaller tire will have the opposite effect, making your speedometer show you're travelling faster than you really are... at least you can't get a ticket for that.

As well, the ECUs in some newer cars don't like it when the tire size is changed, and will throw a big hairy fit as a result. So, in short, it's best to keep the diameter of your tires the same as orginal equipment.


What is a Plus-1?

This is basically used to describe the act of increasing the size car's wheels/rims by one-inch while keeping the overall diameter of the tires fairly constant. As a rule of thumb, this is done by increasing the tread width by 10mm (i.e. 255 instead of 245) and decreasing the aspect ratio by 10% (i.e. 35 instead of 45), and increasing the wheel/rim size by one inch. It's quite difficult to get the diameters to match exactly, so generally you just have to make due with the closest match.

Hopefully this information has been useful to you. I'm sure other forum members will insert their valuable information after, so go read that too...
Blitz, I have a 2003 Altima, and I had put 19's on it, but the rain in San Francisco put a million pot holes out there and as a result my rims got tore up, I went back to the originals until I get some new ones. My question is how much meat can I put on my tires if I get 19's again, and how much meat for 18's..... this is where I am thinking that this might be a better bet to help me deal with the pot holes that will pop up from time to time.....and when say meat I mean the width from the tire to the rim as I drive down the road. Thanks for the Advice.
=M=
 
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