Custom forged wheels are usually ordered because a perfect fit is expected. Most fitment problems are caused by one thing: offset and backspacing were not defined clearly. This guide is written for B2B buyers, tuning shops, and wheel brands who need specs that can be quoted and produced without rework.
A simple checklist is included at the end. It can be copied into an RFQ and used for faster quoting.
What Wheel Offset Means (ET)
Wheel offset is the distance between the wheel’s centerline and the mounting pad.
- Positive offset (+ET): the mounting pad is closer to the outside face. The wheel is pulled inward.
- Negative offset (-ET): the mounting pad is closer to the inside barrel. The wheel is pushed outward.
- Zero offset (ET0): the mounting pad is exactly on the centerline.
Offset is commonly shown as ET in millimeters (example: ET35).
Why it matters: clearance to the suspension, fender, and brakes is controlled by offset more than most people expect.
What Backspacing Means (BS)
Backspacing is the distance from the wheel’s mounting pad to the inner edge of the wheel (inside lip). It is often shown in inches.
Backspacing is used a lot in North America, especially for trucks and off-road wheels.
Why it matters: inner clearance (to strut, upper control arm, inner liner, etc.) is predicted more directly with backspacing.
Offset vs Backspacing: How They Relate
Both values describe the same fitment, just from different angles.
To connect them, these items must be known:
- wheel width (and how it is measured)
- overall wheel lip shape
- whether width is measured as bead seat width (industry standard) or overall width
Important: wheel width is usually advertised by bead seat width (example: 20×10). The overall physical width is usually about 1 inch wider because lips are included.
Because lip shapes vary, small differences can appear even when numbers look “correct.” That is why a fitment checklist is recommended instead of relying on one number only.
Fitment Is Controlled by 4 Clearances
When custom forged wheels are ordered, these four clearances should be checked:
1) Inner clearance (suspension side)
This area is usually limited by:
- strut / coilover
- upper control arm
- tie rod end
- inner liner and wiring
If the wheel is pulled too far inward (too much +ET), rubbing can be created.
2) Outer clearance (fender side)
This area is usually limited by:
- fender lip
- bumper tab
- widebody edge
- mud flap area (trucks)
If the wheel is pushed too far outward (low +ET or negative ET), rubbing can be created during compression or steering.
3) Brake and caliper clearance
Brake clearance is controlled by:
- spoke profile (face design)
- caliper shape
- barrel ID
- offset (indirectly)
A wheel can “fit” the fender but still fail because the caliper hits the spokes. That is why a brake template is often requested for custom forged wheels.
4) Hub and center bore fit
Hub fit is controlled by:
- center bore (CB)
- hub-centric ring plan (if needed)
- bolt pattern (PCD)
A small CB mismatch can create vibration complaints, even when wheels look correct.
Common Mistakes Seen in Custom Wheel RFQs
These issues are often reported when orders are delayed or revised:
- Offset is given, but width is not confirmed
A small width change can change both inner and outer position. - Tire size is not included
A tire sidewall can rub even when the wheel clears. - Brake kit is not declared
Big brake kits change spoke clearance requirements. - Front and rear are not separated
Staggered setups require different offsets and sometimes different spoke profiles. - Suspension changes are not mentioned
Lowering springs, coilovers, and camber kits change the real clearance. - Units are mixed
Offset is in mm and backspacing is in inches. Confusion is created if units are not labeled.
Quick Fitment Planning (Simple, Practical)
A safe approach is usually built like this:
- Existing wheel specs are collected (size, ET, tire size).
- Target changes are defined (more concave, wider lip, flush fit, etc.).
- Inner and outer positions are compared before a new spec is locked.
- A brake template is used if caliper clearance is uncertain.
- A final spec sheet is approved before CNC is scheduled.
In B2B projects, this workflow is preferred because revisions are reduced and lead time is protected.
Fitment Checklist for Custom Forged Wheels (Copy Into Your RFQ)
The fastest quotes are produced when these details are provided:
A) Vehicle details
- Make / model / year / trim:
- Market region (North America / Europe / Australia / South Africa):
- VIN (optional, helpful for exact brake/suspension info):
B) Current setup (if installed)
- Current wheel size (Front / Rear):
- Current offset ET (Front / Rear):
- Current tire size (Front / Rear):
- Spacers used? (mm):
- Any rubbing now? Where?
C) Target setup (what you want)
- Target wheel size (Front / Rear):
- Target offset ET or backspacing BS (label units):
- Target tire size (Front / Rear):
- Target look: flush / tucked / aggressive:
- Concave goal: mild / medium / deep:
D) Clearance and constraints
- Brake kit brand/model (OEM or aftermarket):
- Brake template available? (yes/no):
- Suspension: stock / lowering springs / coilovers:
- Camber setting (if known):
- Fender: stock / rolled / widebody:
E) Wheel technical specs
- Bolt pattern (PCD):
- Center bore (CB):
- Lug type: cone / ball / shank:
- Load requirement (EV / truck / heavy use):
- TPMS requirement (yes/no):
F) Production and delivery
- Wheel type: monoblock / 2-piece / 3-piece:
- Finish: paint / polish / brush / chrome / anodize:
- Quantity:
- Target delivery country/city:
- Incoterms (EXW / FOB / CIF / DDP):
- Invoice details required (company name, address, invoice number format):
Suggested Spec Format (Clean and Hard to Misread)
This format is recommended in emails and purchase orders:
- Front: 20×9.5 ET35, PCD 5×112, CB 66.6, Tire 255/35R20
- Rear: 20×11 ET45, PCD 5×112, CB 66.6, Tire 295/30R20
Units are shown. Front/rear are separated. Tires are included. Errors are less likely.
FAQ: Offset, Backspacing, and Custom Forged Wheels
Does a “more aggressive” fit always mean lower offset?
Not always. Wider wheels can be kept inside by using higher +ET, but caliper and inner clearance can be affected. The full package must be checked.
Can the same offset be used when width is changed?
Usually not. When width is increased, the position changes on both sides. A new ET is often required to keep the same inner clearance.
Why is brake clearance not guaranteed by size alone?
Because calipers hit spokes, not only barrels. Spoke profile (face design) is often the deciding factor.
Is backspacing better than offset?
Neither is “better.” Offset is easier for most passenger cars (EU/Asia). Backspacing is commonly preferred for trucks (North America). Both can be used if units are labeled.
What is the fastest way to avoid revisions?
A brake template and a complete RFQ checklist are usually enough. Missing details are what slow projects down.
Get a Fitment Review and RFQ Quote
If a custom forged wheel project is being planned for North America, Europe, Australia, or South Africa, a fitment review can be supported.
Action:
- Follow our channel for weekly fitment guides.
- Send your RFQ using the checklist above.
- A spec sheet and a quote can be prepared faster when current setup photos and brake info are included.
Visit flexiforgewheel.com and submit your wheel specs to get a professional fitment check and wholesale quote.