Resources / Tire Fitment Guide
Tire Fitment Guide: Rim Width, Tire Size and Overall Diameter
Your existing tires fit new wheels when two things match: the tire's rim diameter equals the wheel diameter, and the wheel width sits inside the tire's approved rim-width range. For new tires, also keep the overall diameter within about 3% of stock and match or exceed the load index and speed rating on your door placard.
- MOQ 4 pcs
- Drawing approved before cutting
- Front & rear sizes, no surcharge
- Wheel load ratings 690–1,200 kg
- 1. Same diameterAn R18 tire mounts only on an 18" wheel. No exceptions.
- 2. Width in rangeWheel width must sit inside the tire maker's approved range.
- 3. Diameter within ~3%Overall diameter close to stock keeps speedometer, ABS and gearing right.
- 4. Load & speedLoad index and speed rating equal to or higher than the placard.
Tire and wheel fitment calculator
Enter sizes the way they appear on the sidewall, e.g. 245/40R18, LT285/70R17 or 35x12.50R20.
Rim-width ranges are estimates based on the typical ETRTO / TRA pattern for each width and aspect ratio. The tire manufacturer's data sheet for your exact tire is the final word.
Will my current tires fit my new wheels?
Yes, if the diameter matches and the new wheel width falls inside the tire's approved rim-width range. Every tire size has a measuring rim width (the width it is designed and tested on) and an approved range around it, typically from about half an inch narrower to an inch wider.
Check the diameter first
The last number in the tire size is the rim diameter: 245/40R18 fits an 18" wheel only. Moving to a 19" or 20" wheel always means new tires.
Then check the width
| Wheel width vs. tire's approved range | What happens | Our view |
|---|---|---|
| Inside the range | Correct sidewall shape, full bead retention, handling as the tire maker intended. | Recommended |
| Narrower than the range (tire "bulged") | Sidewall rolls more in corners, steering feels vague, the tire sits proud of the rim flange. | Avoid |
| Wider than the range (tire "stretched") | Bead tension rises, the rim flange is exposed to curbs, and the bead can unseat at low pressure. | At owner's risk |
Example: a 245/40R18 tire has a measuring rim of 8.5" and a typical approved range of 8.0"–9.5". It fits an 18x8.5 or 18x9 wheel well, but on an 18x10.5 it would be stretched.
Wheel width is measured at the bead seat, not across the outer lip. See the Wheel Fitment Guide for how width, offset and bolt pattern work together.
Is the tire itself still worth keeping?
Remounting makes sense when the tires have good tread, even wear and no sidewall damage. Tires older than about six years (check the 4-digit DOT date code, e.g. 2321 = week 23 of 2021) are usually better replaced at the same time.
How do I choose tires for new wheels?
Keep the overall diameter within about 3% of the stock tire, ideally within 2%. Going up one inch in wheel diameter normally means a wider tire with a lower profile, so the rolling diameter barely changes. This is called plus-sizing.
Plus-sizing from a stock 225/45R17 (overall diameter 634 mm / 25.0"):
| Wheel | Tire | Overall diameter | Change vs. stock | Verdict |
|---|---|---|---|---|
| 17" | 225/45R17 (stock) | 634 mm / 25.0" | 0.0% | Reference |
| 18" | 235/40R18 | 645 mm / 25.4" | +1.7% | Good |
| 19" | 235/35R19 | 647 mm / 25.5" | +2.0% | Good |
| 19" | 245/35R19 | 654 mm / 25.8" | +3.1% | Borderline |
| 20" | 235/30R20 | 649 mm / 25.6" | +2.3% | Good, but very low sidewall |
A larger overall diameter makes the speedometer read low: at +3%, an indicated 100 km/h is really about 103 km/h. Also check that the bigger, wider package clears the fenders, suspension and brake calipers at full lock and full compression.
Planning larger all-terrain or mud tires on a truck or SUV? See forged off-road and beadlock wheels.
Load index and speed rating
Every new tire must carry a load index and speed rating equal to or higher than the values on your vehicle's door placard. In 245/40R18 97Y, 97 is the load index (730 kg per tire) and Y is the speed rating (300 km/h).
- Lower profile, less air volume. A plus-sized tire often needs an XL (Extra Load) or Reinforced version to reach the same load index as stock.
- Heavy vehicles. EVs, large SUVs and pickups need the higher load index. Check the placard rather than the tire you are replacing.
- Wheel load rating is separate. Each FLEXIFORGED wheel design has its own load rating, between 690 and 1,200 kg per wheel. We confirm it against your vehicle's axle loads before cutting.
Staggered setups and AWD
A staggered setup runs wider wheels and tires on the rear axle. It is common on rear-drive performance cars, and front and rear sizes in one FLEXIFORGED order carry no surcharge.
- Rear-wheel drive: keep front and rear overall diameters close; small differences are normal on factory staggered cars.
- All-wheel drive: front and rear rolling diameters must stay within the vehicle maker's limit, or the center differential and transfer case work constantly. Use the factory staggered sizes as your guide, or run a square setup.
- Rotation: a staggered set cannot rotate front to rear, so tires wear out faster as a set.
TPMS, valves and run-flats
TPMS sensors
Most direct TPMS sensors can be moved to new wheels. Tell us the sensor type in your request: clamp-in (metal stem, nut on the outside) or snap-in (rubber stem). It affects the valve hole and the space inside the barrel.
Fit new valve seals or cores when sensors are moved. Some vehicles need a relearn after the change.
Run-flat tires
Run-flat tires have stiff sidewalls and need a matching bead seat profile on the wheel. If you plan to run them, say so before the drawing stage.
Many owners switch to conventional tires plus a repair kit when moving to forged wheels. That choice is yours.
Mounting and balancing forged wheels
- Use a shop that handles premium wheels. Ask for a leverless or touchless tire machine, or plastic-protected mounting heads, to protect the finish.
- Lubricate the bead with proper mounting paste and seat it at the tire maker's maximum seating pressure, never more.
- Balance with adhesive weights placed inside the barrel. Clip-on weights scratch the rim flange.
- Torque the lug nuts or bolts to the vehicle maker's specification with a torque wrench, in a star pattern.
- Re-check the torque after the first 50–100 km.
What to send us with your request
FLEXIFORGED makes custom forged wheels. We don't sell or mount tires. Tires are bought and fitted locally, and we size the wheel so your chosen tire sits inside its approved range. Send these with your quote request:
| Item | Example |
|---|---|
| Vehicle, year, model, drivetrain | 2022 BMW M4 Competition, xDrive |
| Current tire sizes (front / rear) | 275/35R19 / 285/30R20 |
| Planned tire sizes, or "keep current tires" | 275/35R19 / 285/35R19 |
| Target wheel diameter and width | 19x9.5 / 19x10.5 |
| Brakes and suspension changes | OEM carbon-ceramic, lowered 25 mm |
| TPMS sensor type, run-flat or not | Clamp-in sensors, no run-flats |
PCD, offset and center bore come from the Wheel Fitment Guide. Not sure about sizes yet? Browse finished projects by vehicle on Shop by Vehicle, or see how a custom forged wheel project runs from drawing to delivery.
Tire Fitment Guide FAQ
Can I use my old tires on new forged wheels?
Yes, if the new wheel has the same diameter as the tire and its width sits inside the tire's approved rim-width range. The tires should also have good tread and be less than about six years old.
What rim width is best for a 245/40R18 tire?
The measuring rim width for 245/40R18 is 8.5 inches, and the typical approved range is 8.0 to 9.5 inches. Confirm the range on the data sheet for your exact tire model.
How much can the overall tire diameter change?
Keep it within about 3% of the stock tire, ideally within 2%. Larger changes affect the speedometer, ABS and traction control, and on AWD vehicles front and rear diameters must stay within the vehicle maker's limit.
Do bigger wheels need XL tires?
Often, yes. A lower-profile tire holds less air, so the XL or Reinforced version is frequently needed to match the load index on your door placard.
Can I stretch tires on wide forged wheels?
We recommend staying inside the tire maker's approved rim-width range. Stretching beyond it raises the risk of the bead unseating and exposes the rim flange, and it is done at the owner's risk.
Do you sell or mount tires?
No. FLEXIFORGED supplies custom forged wheels only. Tires are bought and mounted locally. Send us your planned tire sizes and we size each wheel so the tire sits inside its approved range.
Will my TPMS sensors fit the new wheels?
Most direct TPMS sensors can be moved to new wheels. Tell us whether yours are clamp-in or snap-in so the valve hole and inner clearance suit them.
Send your tire sizes. We'll size the wheel to them.
Share your vehicle, current and planned tire sizes, and target wheel size. We return a drawing for approval before anything is cut. MOQ is 4 pcs.
Figures on this page and in the calculator are estimates for planning. Final tire choice, mounting, clearance checks and road approval in your country are the responsibility of the vehicle owner and installer.