Tire/Rim purchasing - questions

[Dreadnaught]

Evening everyone. This is new territory for me as I know virtually nothing about rim/tire specifications or performance. The Mustang in question will be a stock 2007 (planned purchase spring 2007).

The rims in question are Foose Nitrous Chrome 18x8 offset RWD. The site I'm using since I don't know any other site (I goggled this) is Discounted Wheel Warehouse. The rims come with a tire pack, for $100 more I get 4 Nitto 404 255/55/18 wheels. Total price is right around $2,000. Here are the questions:

1.) The "8" in the rim dimension, is this a suitable size? I don't plan on taking it to the strip or racing, mostly highway driving.
2.) What does the offset RWD mean, and is that what I need for the Mustang since they are RWD?
3.) I'm totally inept when it comes to tires. I know what the dimensions pertain to, but I do not know if this is a good quality tire or a good size - opinions?
4.) Is the price right? If anyone has any credible sites to purchase these rims with a tire combo, could you please PM the address?
5.) Since i'm buying my rims and wheels seperate from the dealership, do I need to buy 18'' wheels from the dealership so future 18'' wheels will fit, or just go ahead with the standard 17'' wheels and have them just put the 18'' wheels on at the shop (was always unsure how this worked)?

Sorry for the barrage of questions, or if these questions were answered elsewhere in the forum - I always try and use the search feature but it was timing out for me tonight.

 

[anthony05gt]

1) the 8" rim is fine for that tire size
2) the term rwd or fwd that wheel producers use is general. The new stangs use more of a fwd offset. Be sure your new wheels have an offset of +45mm or at least +40mm if you want the stance to look right.
3) you don't want that tire size on a new stang. It's 29.04" tall and you should stay at 27" tall or 28" at the most. If you go with anything other than 27" tall you will have to recalibrate the speedometer with a hand tuner. You should go with a 255/45/18 to be at 27.03" tall. Both tires have the same width, but the aspect ratio is different. (which results in a taller sidewall on the 255/55/18)
4) price is not too bad , but you can do better with a wheel that doesn't require you to pay for the jackass foose name. Try tirerack.com and even see them on your car.
5) order the car with the standard wheels, just be sure to buy the proper offset on the replacements.
6) you'll love the car, don't forget to buy it.

 

[Dreadnaught]

Thanks for the info Anthony. I did checkout tirerack.com, alas they didn't have anything to my liking - I really like the Foose Nitrous rims .

That said, I may have to buy the rims and tires seperate if I'm unable to find a website that offers the tires I want on the rims I want. I've now decided to go with the 18x10 offset FWD 45mm, or is there a more popular number 18x_? So I'll be googling around today to find the website that offers them, just worried with the legitimacy of the website. On the one I mentioned in a previous post I can get the rims at 18x10 FWD offset, but the tire choices are Nito 555 225/40/18.

Do you think I could order the Foose rims on one site, and order a 255/40/18 tire on another, and the rims would match the tire? Sorry if the question seems juvenile.

Also, how do you get the 45mm offset - do you order it with your rim or tire, or does the offset come when the tire or rim is installed?

 

[LuS1fer]

Why risk the guesswork? Just ring them up and ask for rims suitable for the 2005 GT Mustang. I suspect that they have some specific rims for it because if they don't they're probably unique.

The stock wheels on the Mustang GT are 17 x 8. Most people usually take the opportunity to go wider when they replace the wheels. I've got Weld Evos on mine and they're 20 x 9.5 at the front and 20 x 10.5 at the back but the wider you go, the wider tire you need. So width itself is not an issue, just getting the right wheel.

If you go to a site like www.tyretraders.com and click on the tyre comparison calculator, you can see what effect different size tires have on the rolling radius. Basically, you want to keep it about the same.

Right, I've been on the 1010 Tire site and done a vehicle fitment check for the Foose Nitrous Chrome and this is the answer:

"The Foose Nitrous - Chrome wheels will fit a 2005 Ford Mustang GT

Foose Nitrous - Chrome 18" x 8.5" - 5/114.3 - 34mm $390.99"

And here:
http://www.dubspin.com/wheel.cfm?brand=4&cat=112

Love the look of the wheels but a few words of caution as I had a similar design on my Z28 (Boyd Coddington Smoothies). Firstly, you get brake dust caking round the points of the spokes so you have to keep them clean. Secondly, the indents in the rim design will be a pain to keep clean. thirdly, these wheels have a wide rim like my Welds. they look great but if you're ever going to upgrade your brakes, look elsewhere as they usually won't accommodate the big brake kits which require spokes pushed out nearer the rim. If you're bnever going to change the brakes, it's not an issue.

Finally, there is nothing to stop you buying the wheels and tires separately but most tire shops will charge you to fit and balance the tires whereas if you bought the tire there, that would be part of the price. So ring some shops before you buy separately to find out the overall cost.

On an 8.5" rim, you should be looking at a 245/255 tire. I've had 275s on a 9" rim and 245's on an 8" rim and as you know the Mustang has 235s on the stock 8" rim.

 

[Dreadnaught]

Good point LuS1fer with the cleaning issues, I was looking at the Nitrous rim and realized it would be a pain to keep those indents clean - but I'm sure I could do it.

The offsets of the Foose Nitrous wheel is 34mm? Do they come in 40mm or is there any way I can change the offset?

Also I'm worried about if I ever need to replace a tire, do I need to just replace one or the entire set - because I know that's happen to a few of my friends.

Ideally I want 255/45/18 tires with the 18x10'' foose nitrous - just having trouble tracking that down as a complete package. The best I could find is what I posted in my previous post.

If push comes to shove, I may just have ford upgrade my rims to their 18 inch chrome and call it a day and just be happy with basic chrome rims and a Mustang.

Tires...

 

[LuS1fer]

Personally I would never fit a wheel that wasn't recommended for the application. If they say it fits, it has to fit and if it causes any problems, you can send them back.

255/45's are perfect and are roughly the same rolling radius as the stock wheels.

There are similar designs to this wheel out there such as the Torque Thrusts. As a lessson learnt, I would avoid any with a hidden valve. the Boyds I had which I think they sell for the Mustang had a raised ridge on the inner rim to accommodate the hidden valve. All this did was create a dish that collected water when it rained. There were also quality issues on the inner rims where they welded the face to the rim. So where possible, try and inspect an actual wheel before you buy or at least study photos so you know where the problems will lie. You don't want to spend your life cleaning wheels.

There are worse options than to go with the Ford 18" upgrade. At least you're covered by warranty.

As for tire changing - you can replace tires one at a time if they get damaged. You will end up replacing them in pairs anyway through wear as the fronts and rear pairs should and will wear evenly at the same rate.

Just buy a quality set of wheels. You'll only ever buy one set.

 

[anthony05gt]

Whatever you do don't take some salesman's word that wheels will fit. Make him verify the offset and if he can't, don't buy.

 

[Infinity]

I'm eyeballing some 20x10 +45 fronts with 20x11.5 +60mm rears. It can most definitely be done.

 

[Dreadnaught]

I'm thinking of going with 275/40/18 in the back, and 275/45/18 in the front. From research, I know that the back tire will be wider than the front tire. I'm still a little hazy on what the middle number will do - it's almost as if the front wheel will be taller than the back wheel - is this correct? Wouldn't that look a little wierd, I don't intend to do any lowering. Also, I sometimes see like 18R or 18Z, what's the deal with that?

If I get different tire sizes, I'm assuming I'd need different rim sizes. 18x9.5 in the front and 18x10.5 in the back?

Someone give me a logic check . Tires/wheels are the last frontier to lineup before I know exactly what I want on my Mustang when I initally get her.

EDIT - LuS1fer I checked out those American Racing Torq thrust II - sick. They only come in 17'' but I've always wanted a lil more rubber and less wheel. Was planning on the 17x9.5. They are listed as polished (they aren't chrome) but how can they be as shiny as chrome?

 

[LuS1fer]

The 275 is the width of the tire in mm
The 40 is the height of the sidewall of the tire expressed as a percentage of the width so the 40 means 40% of 275 and a 45 is 45% of the width.
The letter is the maximum speed rating of the tire so for your Mustang you need a Z or W.

You can't really have a lower profile on the back than the front if you have the same width tire or the back will be lower than the front.

The things you need to know are these:
1. Bigger wheels add unsprung weight. In other words, your springs and dampers are designed to control the weight of your wheels, tires and brakes. Bigger wheels are often compensated for by less rubber on a lower profile but essentially the car will be working harder to control the weight when it hits ruts etc. This can lead to greater bump-steer ie the car deflects as the dampers and springs have more weight to control
2. Lower profile tires give better steering response because there's a lot less flex in the sidewalls so they'll sharpen the steering. They will also grip harder as they keep the tire tread flatter and more in contact with the road but ultimately they will not slide as progressively as a taller tire.
3. Lower profile tires are far less comfortable as they are effectively a cushion for the ride. There is less of a cushion so the ride will be harder.

Your speedo readings are based on the rolling radius of the stock tires which is why you have to keep the same rolling radius. That's why you need a tire comparison calculator like at www.tyretraders.com. You just put in the two tire sizes, press evaluate and it will tell you the rolling radius difference and the difference in your speedo reading.

I suggest you read this and it should become clear.
http://www.carbibles.com/tyre_bible.html

On the question of polished vs chrome, yes, the polished ones are very highly polished but need hard work to keep them that way. Chrome is easier to keep clean but will scratch more easily and if you hit the wheel is more prone to flaking plus in five years the chrome will peel on the inside rim and the wheels are useless. From that point of view, 20" rims may be better as you can get your hand in to clean the back rims.
As for polished, here are a set of the Boyd Coddington Smoothies on my old Z28 (these are 275/35 x 18's, I prefer the 35 aspect tires myself):

Boyds do the wheels for the Mustang in the sizes you want. Check out the Smoothie and also their new Junkyard Dog. They may be better these days but I had issues with that hidden valve raised section on the inner rim and weld spatter on the inside rims but you can get them reasonably cheap so you pay your money and take your choice.

 

[Dreadnaught]

Thanks LuS1fer. I will read the website you suggested, and hit you up with one or two setups for wheel/tire in a day or so - either mustangtuning wheels or steeda ultalight. I'd like to run with 275/40/18Z in the back and 255/45/18Z in the front now that I understand the middle number is a percentage of the first. I appreciate the detailed explanation and I am starting to get it .

 

[jsawyer]

I just put Foose Nitrous 20x8.5 with Pirelli 245 35 20's on my 06 GT that has Eibach Sportline srins on it. Stance is awsome fit perfect looks great. The rims are 5 Lbs heavier than stock (hurt performance slightly).

 

[jsawyer]

View attachment 46505
Here is the photo...my driveway is slanted, but it sets great!

 

[anthony05gt]

Here's instructions for tire math:
(275/40/R18 will be the size we use)

Take the first # and divide it by 25.4.....275 diivided by 25.4=10.826" wide

Take that answer(10.826) and multiply it by .40 (decimal point then middle tire #40) to come up with 4.330". That's the sidewall bead to tread height.

Multiply that # (4.330) x 2 to come up with 8.661". That is the height of both the top and bottom sidewalls.

Then add your last # in the tire size (18) which is the wheel height to get the overall tire height. 26.661"

 

[bigcat]

here is a very helpful source on tire comparison information......

http://www.dakota-truck.net/TIRECALC/tirecalc.html

 

[Dreadnaught]

Great info so far, and I'm now understanding how to use the calculators and actually understanding all the tire demensions.

Three big questions:

1.) How does one account for the speedometer error and any other errors. Going from base Mustang 17'' tires to 18'' 275/45/18 all around gives almost a -10 mph error at 60 mph.

2.) What is the purpose of going with two different wheels/tires in the front in back. Example: Front 255/45/18 Back 275/40/18. Why wouldn't you just go 275/45/18 all the way around?

3.) If you tire is wider in the back than the front, say 275 compared to 255, do your wheels need to be wider, say 18x8 up front and 18x10 in the back?

Thanks guys and girls.

Also jsawyer, those pics don't work .

 

[jsawyer]

Here it is...

 

[bigcat]

Here it is...

 

[LuS1fer]

1.) How does one account for the speedometer error and any other errors. Going from base Mustang 17'' tires to 18'' 275/45/18 all around gives almost a -10 mph error at 60 mph.

2.) What is the purpose of going with two different wheels/tires in the front in back. Example: Front 255/45/18 Back 275/40/18. Why wouldn't you just go 275/45/18 all the way around?

3.) If you tire is wider in the back than the front, say 275 compared to 255, do your wheels need to be wider, say 18x8 up front and 18x10 in the back?

1) Going from 235/55 x 17 mustang tires to 275/45 x 18 gives a maximum of 2mph error.
http://www.tyretraders.com/index2.html?lmd=38658.568646
2) The reason is simple - steering effort and steering deflection. The rear end only has to deal with outright grip so wide tires and wheels are the flavor of the day to keep the back end planted. The same tires on the front will be heavier and being wider make the steering effort greater and being a larger mass will bounce harder off bumps causing bump steer. To many, the additional grip offsets this disadvantage. More grip means less understeer. Howver, having a lighter, narrower wheel on the front improves the steering speed and control due to less weight and less friction from the narrower tire. A lot of cars have smaller front wheels than back - Lotus and of course Formula 1 cars. There's nothing wrong with mixing widths so long as you make the same rolling radius by adjusting the profile.
3) Yes. The width of the wheel needs to be the right width so the tyre sits square. Too narrow and the tyre will bulge in every direction and become more triangular with the sidewalls pointing inwards. Too wide and the tire will be stretched and the sidewalls won't be vertical but rather curving outwards. The sidewall does a lot of work controlling the tire and keeping it square to the rim so if it's stretched or pinched, it can't do it's job and can actually come off the rim.

 

[Dreadnaught]

Still wasn't able to get the tyretrader calculator to work, so I went with the one posted by Bigcat. Yes it's only 1-2 mph difference, I was using the wrong stock sidewall on the Mustang GT. So there is no way to correct that difference, or it meaningless?

Using the calculator a 275 is 10.83 inches wide, and a 255 is 10.04 inches wide. If I go with a 255/45 275/40 setup (which I intend to do, thanks for the reply LuS1fer), would the rims need to be 18x8 in the front and 18x10 in the back, or would all 18x10 work since the width of both tires is withint that 10 inch mark?