Plus Sizing Wheels: How to Pick the Right Tire Size
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Short answer: when you go to a bigger wheel, use a lower-profile tire so the overall tire diameter stays within about 3% of stock. That keeps your speedometer, ABS, stability control and gearing working the way the factory intended. Also match or beat the original tire's load rating, and pick a tire width that suits your new wheel width.
What "plus sizing" means
Plus sizing means increasing wheel diameter while shrinking the tire's sidewall, so the overall height of the tire stays about the same. "Plus one" is one inch bigger, "plus two" is two inches, and so on.
The tire size on the sidewall tells you everything you need. Take 255/40R19:
- 255: tire width in millimeters.
- 40: aspect ratio, so the sidewall height is 40% of the width (about 102 mm).
- R19: fits a 19-inch wheel.
Overall diameter (in) = wheel diameter + 2 × (width × aspect ratio ÷ 2540)
Plus-size examples
| Vehicle type | Stock size | Overall diameter | Plus-size option | Overall diameter | Difference |
|---|---|---|---|---|---|
| Sports sedan | 255/40R19 | 27.0 in | 255/35R20 | 27.0 in | 0% |
| Sports sedan | 245/45R18 | 26.7 in | 245/40R19 | 26.7 in | +0.1% |
| Midsize truck | 265/70R17 | 31.6 in | 275/65R18 | 32.1 in | +1.5% |
| Midsize truck | 265/70R17 | 31.6 in | 305/50R20 | 32.0 in | +1.3% |
Lifted trucks often go well beyond 3% on purpose to fit bigger tires. That's fine with the right lift and clearance, but plan to recalibrate the speedometer and check gearing.
The four rules of plus sizing
- Keep overall diameter close to stock. Within about 3% is the common guideline for street cars. Bigger changes throw off the speedometer and can confuse ABS and stability systems.
- Match or exceed the load index. Lower-profile tires can carry less weight. Check the load index and speed rating on your original tires, and choose a tire that meets or beats both. "XL" (extra load) versions help on heavier cars.
- Match tire width to wheel width. Every tire has an approved rim-width range. A tire too narrow for the wheel is "stretched"; one too wide bulges and feels vague.
- Check clearance. A wider tire on a wider wheel needs room at the fender, strut and brakes. That's where offset comes in: see Wheel Offset and Backspacing Explained.
What changes when you go bigger
- Sharper steering from the stiffer, shorter sidewall.
- Firmer ride, because there's less sidewall to soak up bumps.
- More wheel exposure to potholes and curbs.
- More weight, unless the wheel is forged. Read Why Wheel Weight Matters.
- Higher tire costs in larger, lower-profile sizes.
How we size a custom set
When you order Koncept Forged wheels, we look at the wheel and tire together. Tell us the diameter and look you want, plus any lift, lowering or big brake kit, and we'll spec the width and offset to suit the tire size you plan to run. If you're unsure on tires, ask us and we'll suggest sizes that fit.
FAQ
Will bigger wheels mess up my speedometer?
Not if the overall tire diameter stays close to stock. Go much larger, as on a lifted truck, and you'll want to recalibrate it.
How big can I go?
It depends on your brakes, suspension and fenders. Most cars can go up one or two inches comfortably. Trucks with lifts can go much larger.
Can I keep my old tires?
Only if you're keeping the same wheel diameter and the width suits the new wheel.
Planning a bigger setup? Send us your vehicle and target size, and we'll spec the wheel and tire together.