Wheels and Tires

[Mr Pickles]

Can someone explain wheels and tires to me like i'm an idiot please? I'm not sure what the numbers mean 275\15\8.5 or something? I don't know what any of that is. I'd like to get new wheels but I'm not sure about all this jargon talk.

 

[ZetaEpyon]

The three numbers you see for tires are tread width in millimeters, side profile height as a percentage of tread width, and wheel diameter in inches. Usually they're listed in that order, so your example (275/15-8.5) would be a 275mm wide tire, with a sidewall height of about 41mm (15% of 275), designed to fit an 8.5 inch diameter wheel.

Needless to say, an exceedingly odd size.

A lot of times you'll see the speed rating (letters) thrown in there too; my winter tires are 205/50VR17, for example.

Edit: TireRack has a good page that explains the stuff in detail.

 

[woodie1]

Originally posted by: MrLee
Can someone explain wheels and tires to me like i'm an idiot please? I'm not sure what the numbers mean 275\15\8.5 or something? I don't know what any of that is. I'd like to get new wheels but I'm not sure about all this jargon talk.

Are you sure there isn't a typo in your tire numbers?

 

[Demon-Xanth]

Metric:
width in mm/sidewall height divided by width-R for radial, sometimes LT for light truck-rim size in inches
ie:
245/40R18

American:
diameter in inches x width in inches-rim size in inches
ie:
33x12.5-16

 

[Demon-Xanth]

For wheels, there's other numbers to consider:
lug pattern: 6x4.5 is 6 lug with a 4.5" circle, 5x110 is 5 lug with a 110mm circle
diameter
width
backspacing/offset: the distance from the back of the rim or center of the rim to the face of where the wheel and hub meet.

 

[Billb2]

W@hat you're doing is real close to:
"i have a computer, I think it's a Dell, how do I overclock it?"

That being said, I'll just point out some of the issues you're going to hav to deal with:
Prices..like with anything else you buy, they will vary greatly and won't depend too much on service and quality. Shopping around is your friend.

If your car has a computer, the computer measures the cars speed (like for the speedometer) in some way related to wheel rotation. If you put tires with a different diameter on, the computer will be fooled and your speedometer will be off (high or low). That's not such a big problen. but a lot of computerized engine controls being baed on vehicle speed can cause big problems as can antilock brake systems. Some shops can "reprogram" your car's computer for the new size, some will only sell you wheel/tire combos that are the same, or nearly the same, diameter as your exisitng combination. If your new setup is way different that "stock" you may want to thing abour a new spare too for the times you may need one.

Figure out how you're going to deal with the computer issue first. It will save you alot of time and grief later.

Other stuff:
Whill the new setup fit into the fender wells? Without rubbing when you hit bumps, turn ,or do both?
Will the new wheels fit over the disk brake rotors, or drum brake drums?
Will the new wheels fit over the disk brake caliper?
Will the new wheel/tire combination affect the stopping ability of your braking system? Not likely, but a larger tire "footprint" (more rubber touching the road) many let you take advantage of increased stopping power by upgrading rotors and calipers to take advantage of the aggitional grip available. The additional grip will also affect cornering. And again, to take full advantage, aftermarket springs/shocks and/or swaybars may be something to think about.
Wider/taller/or offset wheels/tires will require a realignment, perhaps not to factory speifications. Perhaps even aftermarket suspension parts may be required. Not all shops are willing to do that, or have the knowledge/facilities to do it correctly. Make sure to find a shop that understands what you re doing and is willing and capable of doing what you need before you buy. Get their price upfront.

Now go read about all that jargon being forewarned about just what you're getting into......
Just like that guy with the Dell, without doing your homework, you can wate a lot of time and money and end up right where you started, and have some used parts to ebay.