Convert between ET (offset) and backspacing — instantly. If you’re running JDM or European wheels on an American car, or shopping US brands for an import, this is the converter you need. Enter your wheel width and either value to get the other, plus outer lip depth and sidewall angle — everything you need to spec fitment before you buy.
ET / Offset ↔ Backspacing Converter
JDM and Euro specs use ET (offset). American wheel brands use backspacing. Convert between the two instantly — enter your wheel width and either value to get the other, plus lip depth and hub centreline.
Positive ET = wheel face outward
Negative ET = wheel face inward
Higher ET = more tucked
Lower ET = more poke / flush
Euro cars: ET+35 to ET+50
US trucks: ET+12 to ET+25
Stance: ET+0 to ET-25
Track: ET+35 to ET+55
Measurements are mathematical conversions — actual fitment depends on tyre width, suspension geometry, camber, and vehicle-specific clearances. Always verify fitment on your car before purchase.
WHAT IS ET OFFSET?
ET stands for Einpresstiefe — German for “insertion depth.” It’s the distance in millimetres between the wheel’s mounting face and its centreline. A positive ET means the mounting face is pushed toward the outside of the wheel (tucked look). A negative ET means it’s pushed toward the inside (poke/lip look).
Most OEM wheels run ET+30 to ET+55. Fitment and stance builds typically target ET+0 to ET+20 for flush, or negative ET for aggressive poke.
WHAT IS BACKSPACING?
Backspacing is the distance in inches from the wheel’s inner lip to the mounting face. It’s how American wheel manufacturers (Weld, American Racing, Pro Comp, etc.) specify their wheels. The formula: Backspacing (mm) = (Wheel Width mm ÷ 2) + ET.
FAQ
Does ET change if I run a spacer?
Yes. A 10mm spacer effectively reduces your ET by 10mm. ET+35 with a 10mm spacer behaves like ET+25. Hub-centric spacers are preferred over lug-centric for safety and vibration reduction.
What ET should I target for flush fitment?
This varies by car and suspension geometry. As a starting point, lower ET = more poke. For flush fitment on most lowered cars, target an ET that places the outer lip of the wheel within 5–10mm of the fender lip at static ride height. Use a wheel offset simulator or measure your current setup and work backward.
Can I run negative ET on a car designed for positive ET?
Yes, but you need to check inner clearance carefully. Lower ET pushes the wheel outward, which can cause the inner barrel to contact struts, control arms, or callipers. Always measure clearances before purchasing, and consider running adjustable coilovers to dial in exactly where the wheel sits at ride height.
Does changing ET affect speedometer or odometer?
ET alone doesn’t. ET only changes where the wheel sits laterally on the hub — it doesn’t change the rolling diameter, so speedometer accuracy isn’t affected. If you’re also changing wheel size or tyre profile, that’s a separate calculation. Use our Tyre Size Comparison Tool for that.