Tech Talk: Wheel & Tire Tech

Regardless of your car or truck type and the amount of safety and performance build in, tires are the last piece of the puzzle making it all translate into the final driving experience (and where the phrase "when the rubber meets the road" came from probably)



Some Terminology: 

• Tire Pressure Monitoring System (TPMS): sensors mounted inside your wheel that send wireless info to a computer that tracks your tire pressure and displays details or just a warning when below spec levels 
• Tread Pattern: there are 4 main pattern categories (section dedicated below)
• Symmetric, Asymmetric, Directional/Unidirectional, Combination of Directional and Symmetric
• Tire Sizing Format: Width, Aspect Ratio, Wheel Diameter (in order) 
• EX: 245/40R17 
• Where: 245 is the Width, 40 is Aspect Ratio, and R17 refers to Wheels Diameter
• Filling Gas type: Air vs. Nitrogen 
• Offset and Back Spacing: Indicated in (+) or (-) numbers in mm

Did you know: 

• Harder rubber compounds are better for MPG 
• Harder rubber compounds also tend to last much longer (50,000+ miles per rating) 
• There are also "Low Resistance" hard compounds used specifically for better MPG 
• This is what most Hybrids or Fuel Efficient special models use 
• However, with harder rubber compound you give up some traction in hard cornering 
• AND in maximum grip off the line if you PUNCH it (Prius cars are horrible on factory tires in this case and almost always break traction and abruptly engage the traction control robbing you of critical power you may need to get out of the way on a left turn in a busy intersection for example) 
• Nitrogen also can aid with MPG (more stable pressures maintained constantly in tire) 
• For max MPG you would want to run the MAX allowed PSi for the tire 
• Overall diameter is what your speedo is mapped to 
• If you change factory wheel size or tire size refer to this calculator site and check
• Larger overall diameter and weight will effect your actual speedo and MPG 

Details - Offset and Back Spacing: 

• The offset of a vehicle's wheel is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. 
• It can thus be either positive or negative, and is typically measured in millimeters. 
• Offset has a significant effect on many elements of a vehicle's suspension, including suspension geometry, clearance between the tire and suspension elements, the scrub radius of the steering system, and visually, the width of the wheel faces relative to the car's bodywork.
• Zero Offset - The plane of the hub mounting surface is even with the centerline of the wheel.
• Positive Offset - The plane of the hub mounting surface is shifted from the centerline toward the front or outside of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
• Negative Offset - The plane of the hub mounting surface is toward the back or brake side of the wheel's centerline.

Details - Treat Patterns & Types:

Also called tire tread designs, tire tread patterns are the arrangement of continuous ribs, independent tread blocks, circumferential and lateral grooves, as well as the thin sipes molded into the tread to fine-tune noise, handling, traction and wear. Tire treads patterns feature different basic designs to help them meet anticipated driving conditions.

• Symmetric Tread Patterns:
• A symmetric tread pattern is the most common and features continuous ribs or independent tread blocks across the entire tread face where both inboard and outboard halves feature the same pattern. 
• Tires featuring symmetric tread patterns allow using multiple tire rotation patterns.
• Asymmetric Tread Patterns:
• An asymmetric pattern is designed to blend the requirements of dry grip and water dispersal/snow traction where the tread pattern changes across the face of the tire. 
• An asymmetric tread pattern usually incorporates larger tread ribs/blocks on the outboard side to increase cornering stability on dry roads by offering greater contact area. 
• This also helps to reduce tread squirm and heat buildup on the outside shoulder. 
• The inboard side usually features smaller independent tread blocks to aid wet and/or winter traction when driving straight ahead. 
• Tires featuring asymmetric tread patterns allow using multiple tire rotation patterns.
• Directional (Unidirectional) Tread Patterns:
• A directional (also called a unidirectional) tread pattern is designed to roll in only one direction.
• It incorporates lateral grooves on both sides of the tire’s centerline that point in the same direction and result in v-shaped tread blocks. 
• These grooves enhance hydroplaning resistance at high speeds by pumping water more efficiently through the tread pattern. 
• Unless they are dismounted and remounted on their wheels to accommodate use on the other side of the vehicle, directional tires are to be used on one side of the vehicle and are intended to be rotated from the front axle to the rear axle. If different tire sizes are used on the front vs. 
• rear axle, the tires become location-specific and prohibit tire rotation unless remounted.
• Asymmetric and Directional Tread Patterns
• Asymmetric and directional tread patterns have v-shaped tread grooves that are offset compared to the centerline of the tire. 
• Tires featuring asymmetric and directional tread patterns must be treated as directional tires for tire rotation.
•  However, if different tire sizes are used on the front vs. rear axle, they become location-specific and prohibit any tire rotation possibilities.

Details - Tire Compounds and Rating: 

• This is the letter you see at the end of the numeric sequence on the tire sidewall 
• Currently shipping rating are as follows: L/M/N/P/Q/R/S/T/U/H/V/W/Y
• These determine everything from vehicle weight to operational temps (region / season) and max vehicle speeds ratings
• An Excellent short detailed article here 

Air vs. Nitrogen: 

• How can you tell: A Green valve stem cap means Nitrogen 
• Why Nitrogen: 
• Nitrogen has larger molecules than air 
• What this means ultimately is less sensitivity to temps 
• Which is KEY in varying temp regions and also for higher performance cars with softer compounds which means running higher tire temps and experiencing a much smaller delta with Nitrogen 
• The other big driver is Nitrogen absorbs less moisture (shifting temps is one common cause) and less moisture inside the tire is ideal for preserving the life span of the TPMS sensors (which can corode over time and fail)
• And less of a need to top off (larger molecules escape and defuse less) 

Some really good tools available to you: 

• TireRack has been my go to source for well over a decade now 
• They have excellent info readily available on line 
• And offer a live chat call center feature you could ask any in depth questions you have 
• For just about any important tire related topic (well beyond the basics here) go to: 
• TireTech link on TireRack

Need new tires? Want to upgrade wheels or tires, read below: 

• Tires and wheels can be very pricey 
• And often factory wheels leave a lot to be desired (or you may live in a region that would truly require seasonal tire changes) 
• And some of us car geeks have many sets for normal vs. track day uses 
• Whichever the case you have some options
• Here is what I do: 
• ALWAYS ALWAYS support your local loyal vendors (I DO) 
• That said
• I start with my research on tires on TireRack (no better all in one source) 
• Another good one is DiscountTire
• There you can see ratings and user feedback 
• Look for the best deals and rebates 
• Once I have it from there I usually can check with my local DiscountTire outlet 
• Again I'd rather buy local and they usual meet or beat the on line price 
• But, if I ask TireRack to do research and answer bunch of question out of respect I purchase from them (specially if I'm buying wheels and tires together as a package) 
• Tip/Trick: 
• If you're a car geek like me and own some economy sporty car well suited for the weekend canyon run or the occasional track day 
• You'd really want a second set of wheels / tires 
• I usually get more performance oriented wheels/tires as one package from TireRack 
• Even with TMPS mounted, balanced shipped it's cheaper than the alternatives 
• And if you don't want the original OEM wheels, sell them (you get a good portion back)