3. Tires and wheels: How much can I fit, what offset looks right?
Looks are very subjective when it comes to stance, but generally speaking wider is better, and the more meat the merrier. That means getting the wheels as close to the edge of the body with as much tire as practically possible. Historically, wheels were only available in limited sizes and offsets, so rodders were much more constrained on what they could package, but modern
multipiece wheels have made that obsolete. Now you can have wheels spec’d to what your individual car needs.
The basics to consider here are the intended ride height, suspension travel, inner fender shape, and turning radius. For example, a wide tire that clears at stock ride height may end up hitting the wheel lip or inner fender when the car is lowered. It may also run into the fender, control arm, or even subframe when turned to full lock. The first step is to establish what the car’s ride height will be since everything else will have to work around that. Now possible issues with upward suspension travel become more obvious.
For increasing wheel and tire width, a great cheap way to simulate the new package and dial-in what will and won’t work is with a wheel and tire fitment tool like the Wheel Rite from Percy’s High Performance. These tools are cheap through Summit Racing and can simulate wheel widths from 6 to 11 inches and diameters from 15 to 30 inches so you can see where issues will arise before you order wheels. That’s actually how we spec’d out the wheel clearance for Project EcoNova. (Look for the web exclusive on www.popularhotrodding.com.)
4. Tires: What do all those numbers on the sidewall mean?
There is a plethora of information on the side of tires, but we’ll just touch on the ones of top interest to hot rodders. Modern street car tire sizes are typically denoted by three numbers (example: 275/40R17); this is called P-metric sizing. The first number is the section width (measured at the overall widest point, not at the tread) of the tire measured in millimeters, 275 mm in the above example.
Followed by that is a number that denotes the tire’s aspect ratio, or sidewall height from bead to tread, given as a percentage of the width. For our 275/40 series tire; 275 × .40 = 110 mm. The last number indicates the diameter of the wheel the tire is intended to be mounted on in inches. If there is an “R” directly preceding the diameter that means the tire is a radial. If there is a “P,” for “passenger car,” preceding the section width, that means the tire uses the P-metric load and inflation tables. No “P”? That means it uses the Euro-Metric table.
Want to know how much speed your tire is capable of sustaining? The code directly following the size specs of the tire will tell exactly what speed the tire has been tested to withstand.
|Common Speed Rating
||168 (usually combined with a Z or ZR)
||168+ (usually combined with a Z or ZR)
||186 (usually combined with a Z or ZR)
||186+ (usually combined with a Z or ZR)
The treadwear number indicates the tire’s wear rate. The higher the number is, the longer it should take for the tread to wear down. For example, a tire graded 400 should last twice as long as a tire graded 200. This is also typically tied to the tire’s intended use, as higher performance and race tires will invariably have a lower treadwear because of their softer compounds.
This indicates a tire’s ability to stop on wet pavement and is graded highest to lowest as “AA”, “A”, “B”, and “C”. An “A” tire should stop in a shorter distance in wet weather than a “B” lower grade. These grades are usually tied to performance as well; ultra-high performance tires will almost always have a higher grade than all-season tires.
Graded "A", "B", or "C," this letter indicates a tire’s resistance to heat when properly inflated and not overloaded. High speed, under inflation, or overloading increases heat buildup and the chances of tire failure.
5. When are my tires too old to be safe?
Just because you only drive your rod on weekends and only rack up a couple thousand miles a year doesn’t necessarily mean those tires will last longer than the ones on your daily driver. That’s because tires can “age out” before they wear out.
General consensus in the tire industry is that about six years is the maximum safe range for most tires that are used/abused in less than ideal driving conditions, which is all of them. Sun exposure, dry or hot climate, rain, chemicals from road grime, and even extended parking all accelerate aging. Makes sense; no tire we know of is warranted beyond six years regardless of mileage. Actually, Ford once appealed to the Federal Government to impose a general six-year expiration date for most tires, and the British Rubber Manufacturers Association (BRMA) once recommended that “even unused tires should not be put into service if they are over six years old.”
If you work your tires hard, count on much less lifespan; heat cycling degrades rubber compounds and the more aggressive and softer the rubber compound, the faster the wear and aging process. Ultra-High Performance and competition tires age the quickest. If you like running your car in road race or track events, know that many events have an age rule; tires often must be under 2 years old, regardless of condition, or you don’t race.
So how do you know how old your tires are? Excluded obvious issues like cracks, dry rot, and bulges, visual inspection won’t usually tell what you need to know now, but the date coding on the sidewall will. Since 2000, the week and year the tire was produced can be found in the last four digits of the Tire Identification Number. The first two digits identify the week; the last two identify the year; i.e. 4205 would be the 42nd week of 2005. If your tires are pre-2000 the coding differs, the first two numbers signify the week of production, a single digit represents the year; i.e. 326 would be the 32nd week of 1996.