Sidewall/Width Ratio

[champagneG35]

Ok I know there's another tire thread in here but I didn't want to hijack it, I have a question to the tire gurus out there. I know the stock size on my car is 225/45/18 in the front and 245/45/18 in the rear. If you go larger in the front or rear, say up to 255 or 265 would you have to then get a shorter sidewall to compensate for the larger overall tire ? If I remember correctly the 2 sizes are tied together somehow like the width affects the height or something so a 225/45/18 would be shorter on the sidewall than a 245/45/18 but I can't remember at what point it affects it like would I have to get a 40 sidewall on a 255 or 265 to remain at the same height ? I know it's more of a worry with the front as to not throw off the speedo. Anyone know the answer to to the mystery

TIA~~~Mike

[Rex]

Look for the overall diameter of the stock tire, it's probably something close to 26", that should help you decide which lower profile wider tire you'll need.

Keep in mind you can/should only go "so" much wider ont he same wheel width.

[rg_g35x]

I'm not a tire guru, but the profile (sidewall part) (the 45 in 225/45/18) means that the sidewall height is 45% of the width. So a 225/45/18 is 225mm wide, so it's 90mm sidewall height (225 X 45% = 90). So, on a 265, you'd need a 35 (265 X 35% = 92.75 - not exact but close) to maintain roughly the same overall size. It becomes more complicated if were you were to upsize the wheel (to a 19, for instance.)

I think Rex has some very good advice - to check the overall diameter - much larger and it might rub the fenders. Also, watch that going too wide might rub, and the stock wheels will only take a tire so wide, or it won't fit properly on the wheel.

Just my .02

[champagneG35]

Thanks guys, both good ideas and the percentage thing was the part I couldn't remember

I was looking on tirerack.com and a few other sites that have reviews and specs and so forth, according to them provided it doesn't rub in the rear I should be able to go to a 265 with it still fitting on the 9" width rim, it's on the low end of the recommended range of 9-10.5 but it's still makes the cut.

I don't really have a reason to want a wider tire I think it handles awesome with what it has, however certain tires I was thinking about instead of the Pilot Sports like the Bridgestone Potenza RE-01R, Yokohama Advan Neovas, and the Advan A-048s aren't available in the stock rear size but were with a slightly narrower and slightly wider tire size with different sidewall heights. If I were to choose one I'd want to go wider instead of narrower but stay close to that range of height

[Hookm36]

rg_g35x......you said it would be more dufficult if you went with 19's ? I am looking at putting 19X8.5 in front, and 19X10 in rear.....What tire size do you reccommend to use ? Also, how wide are the stock 18' rims ?

Thanks

[joe603]

Check out this website for comparing different tire sizes:

http://www.bigcustomwheels.com/info_specs.jsp

[rg_g35x]

Joe603 - that's a great link.

hookm36 - Unfortunately I'm not knowledgeable enough with the tires to be able to give a solid recommendation on the tires going to a 19", but the site the joe603 posted a link to seems to be very useful.

I think the two most important things to keep in mind is the overall diameter and the offset. Bigger (or smaller) diameter will throw things off like your speedo reading, but I think that there may be a domino effect of the speedo being off - possibly things like ABS, TPMS, VDC etc may be affected by the speedo being off... The offset is important since you don't want the tires to stick out past the fenders, or stick too far in and rub on the inside fender, or suspension components.

[champagneG35]

rg_g35x......you said it would be more dufficult if you went with 19's ? I am looking at putting 19X8.5 in front, and 19X10 in rear.....What tire size do you reccommend to use ? Also, how wide are the stock 18' rims ?

Thanks

I'm not sure about the front wheels yet but I read somewhere (can't remember where) that the rears were 9" wide for the 18" wheels. Also according to tirerack.com a 265 is the widest that will fit on a 9" wide rim within their recommended wheel size/tire fitment FWIW.

[joe603]

I'm installing on my stock 19's the following sizes.

245/35-19 front 275/35-19 rear

Some will say that 275's won't fit on the rear rims at a width of 8.5", but I've seen the size on other G's. The front/rear size ratio will also work with the VDC. It's all about the size difference between stock and aftermarket...you have to stay close to the stock size ratio.

I'll post pics when I get my car back today.

[Hookm36]

I really appreciate all of your help from all of you. I am not sure what the offset is, or how it works. I definately dont want it rubbing anything, but want it as close to the outside fender as possible without rubbing. I am going to order the tires through Discount Tire.....will they be able to help me set it up ?

[C-Kwik]

I'm installing on my stock 19's the following sizes.

245/35-19 front 275/35-19 rear

Some will say that 275's won't fit on the rear rims at a width of 8.5", but I've seen the size on other G's. The front/rear size ratio will also work with the VDC. It's all about the size difference between stock and aftermarket...you have to stay close to the stock size ratio.

I'll post pics when I get my car back today.

Be weary that squeezing a wide tire into the slimmest recommended wheel width may cause a slight bulge in the center of the tread, which can accelerate the wear in that area. I suspect this already occurs with the 245's mounted on OE 18's which have only an 8" wheel width as mine had higher than normal center tread wear and many other owners have reported the same issue. I have not seen the same complaints from owners with the 19's which has a half an inch greater wheel width. I've noticed the same trend with Z owners that have the non-Rays 18's.

[champagneG35]

I really appreciate all of your help from all of you. I am not sure what the offset is, or how it works. I definately dont want it rubbing anything, but want it as close to the outside fender as possible without rubbing. I am going to order the tires through Discount Tire.....will they be able to help me set it up ?

I really have no clue but have my doubts about an online tire company being that helpful with wheel offset. If you're changing wheel size and going to be dealing with spacers and or adapters depending you really need to know what the stock offset is or find someone that does.

I have adapter spacers on my '72 240Z cause it has front wheel drive wheels on it and the offset would have been way off without the adapter on there, there's a site I got them from I believe in Canada that specifically made them for my car doing exactly what I needed to do which was get the Honda lug pattern and front wheel style rim to work with my Z this was a very common swap do to the specific lug pattern the Z has and shares with no other vehicle..lol. There probably is a place and maybe even the same place that could do it for the G.

I'll see if I can pull some links real quick. Though you might not even need it if the offset does not change with you new wheels which is why you need to know what the offset is on it's current wheels which would be the difference in distance between the center of the wheel and it's mounting point. It is shown more clearly in a diagram here: http://www.1010tires.com/WheelOffsetCalculator.asp

[champagneG35]

Be weary that squeezing a wide tire into the slimmest recommended wheel width may cause a slight bulge in the center of the tread, which can accelerate the wear in that area. [highlight]I suspect this already occurs with the 245's mounted on OE 18's which have only an 8" wheel width[/highlight] as mine had higher than normal center tread wear and many other owners have reported the same issue. I have not seen the same complaints from owners with the 19's which has a half an inch greater wheel width. I've noticed the same trend with Z owners that have the non-Rays 18's.

Seriously the rears are 8" I thought I read somewhere that they were 9" wide ?

Edit: nevermind you're right. I did look up though the recommended width for the 245/45/18 Pilots is between 7.5-9"
Modified by champagneG35 at 11:05 AM 4/24/2007

[joe603]

Camera Phone pics of my new tires!!

[Hookm36]

so your saying i need to find out what the offset is on my factory 18' rims, and try to use the same offset w/ the wheels I will be getting ? Discounttire is located near me, the actual store, not just on-line is what I was referring to...

[champagneG35]

Yes that's what I'm saying. In other words if the stock wheel has an offset of 0" meaning it's set dead center, and you purchase a wheel with 2.25" offset, then you would need an adapter or spacer to bring the new wheel back to a 0" offset. hope that makes sense, it's kinda late and I'm tired.

Oh hmm never been to the store not sure how much they know about that stuff but you could ask I guess, If they sell actual wheels too and not just tires I'd say you have a better shot. If not I would check out the performance shops or wheel shops for more help with it.

[Hookm36]

Yeah they specialize in rims/tires of all sizes......They seem pretty knowledgable, Ill see what they say or recommend. I just noticed the inner side of the front tire is wearing a lot more than the outside of the tire...........this sis something I need to get fixed before getting the new wheels/tires. Have any idea what the problem could be ?

[champagneG35]

It's your camber and you should get it aligned or at least have it checked when you replace your tires not before. Reason is because your current tires have gotten used to wearing a certain way and if you change it now after they've worn you wont have even contact with the road surface and will notice a a handling decrease, you'll also risk the chance of chewing up the remaining tread even faster. My tires are the same way it's just something our cars seem to do after a while especially considering I believe the factory sets in a little camber on purpose to give better handling in corners. Downside is more inner wear over time.

[Hookm36]

appreciate the advice.....I bought new wheel/tires, will get on thursday, and prob get allignment on saturday............ill post pics