Skip to content
CampingCalc

Bike Rack Load Calculator: rack load and rear axle load

Two e-bikes at 110 lb plus a 33 lb rack weigh 143 lb at the rear – but because of the lever the rear axle carries about 200 lb more, while the front axle is unloaded by 55 lb. This calculator checks the rack load and shows what the rear load does to the axle loads.

Units

Per the rack manufacturer (rear racks 110–165 lb / 50–75 kg, hitch racks 100–200 lb). For wall-mounted racks the vehicle manufacturer's approval also applies.

Rear racks 22–44 lb (10–20 kg), hitch racks 33–66 lb (15–30 kg).

Bikes

Leverage on the axles

Distance front to rear axle (data sheet); camper vans 11–13 ft (3.45–4.04 m), Class C 12–15 ft (3.8–4.5 m).

Rear rack on a motorhome with a long overhang: 5–8 ft (1.5–2.5 m); hitch rack on a camper van: 4–5 ft (1.2–1.6 m).

Axle loads (optional, from weighing and label)

Result

Reserve on the rack

22 lb

110 lb of 132 lb used

Rack load110 / 132 lb
Extra load on the rear axle
197 lb
lever factor 1.38
Unloading of the front axle
54 lb
  • The lever calculation is a static approximation. For wall-mounted racks the vehicle manufacturer's approvals (rear wall load) apply in addition; axle loads can only be determined reliably by weighing.
Show calculation
  1. 1Bikes in total: 55 lb + 55 lb = 110 lb
  2. 2Rack reserve: 132 lb − 110 lb = 22 lb
  3. 3Mass at the rear: 33 lb rack + 110 lb = 143 lb
  4. 4Lever factor: (13.12 + 4.92) ÷ 13.12 = 1.38
  5. 5Extra load rear axle: 143 lb × 1.38 = 197 lb; unloading front axle: 54 lb

 

How it's calculated

The rack load is simple: the sum of the bikes against the rack manufacturer's rating. More interesting is the leverage: everything hanging behind the rear axle loads it more than its own weight and at the same time unloads the front axle.

Extra load rear axle = m × (L + d) ÷ L Unloading front axle = m × d ÷ L
m = rack + bikes (143 lb / 65 kg), L = wheelbase (13.1 ft / 4.0 m), d = distance rear axle → load center (4.9 ft / 1.5 m): +196 lb (89 kg) rear, −53 lb (24 kg) front

This is the moment balance of a two-axle vehicle (statics). The longer the overhang and the shorter the wheelbase, the stronger the effect – on motorhomes with a long rear overhang the lever factor is often 1.5 to 1.7.

For wall-mounted racks the approval of the vehicle or coach manufacturer (maximum rear wall load) applies in addition; for hitch racks the receiver's tongue weight rating. Axle loads can only be checked reliably by weighing (front and rear axle separately). This calculator does not replace weighing.

Worked example

Class C motorhome (wheelbase 13.3 ft / 4.04 m, load center 6.2 ft / 1.9 m behind the rear axle), rear rack rated at 132 lb (60 kg) weighing 37 lb (17 kg), two e-bikes at 53 lb (24 kg) each. Weighed: rear axle 4,079 lb (1,850 kg) (GAWR 4,409 lb / 2,000 kg), front axle 3,307 lb (1,500 kg).

Inputs

  • Maximum load of the rack: 132 lb
  • Weight of the rack itself: 37.5 lb
  • Bikes:
  • E-Bike 1: 52.9 lb
  • E-Bike 2: 52.9 lb
  • Wheelbase: 13.3 ft
  • Distance rear axle → load center: 6.23 ft
  • Current rear axle load (weighed, without rack): 4,079 lb
  • Rear gross axle weight rating (GAWR): 4,409 lb
  • Current front axle load (weighed): 3,307 lb

Result

26 lb

Reserve on the rack

Extra load on the rear axle
211 lb
Unloading of the front axle
67 lb
Rear axle load with rack
4,289 lb
Front axle load with rack
3,240 lb

Calculation

  1. Bikes in total: 53 lb + 53 lb = 106 lb
  2. Rack reserve: 132 lb − 106 lb = 26 lb
  3. Mass at the rear: 37 lb rack + 106 lb = 143 lb
  4. Lever factor: (13.25 + 6.23) ÷ 13.25 = 1.47
  5. Extra load rear axle: 143 lb × 1.47 = 211 lb; unloading front axle: 67 lb
  6. Rear axle new: 4,079 lb + 211 lb = 4,289 lb (reserve 120 lb)

The variables explained

Maximum load of the rack
Rack manufacturer's rating; for hitch racks additionally the tongue weight rating of the receiver.
Wheelbase
Distance between the axles, from the data sheet.
Distance rear axle → load center
Where the bikes hang: the vehicle's overhang plus half the rack depth.
Axle loads
Weighed values without rack (CAT scale) and the gross axle weight ratings (GAWR) from the certification label.

Common mistakes

  • Checking only the gross weight: with a rear garage plus rack the rear axle is often overloaded even though the GVWR is met.
  • Underestimating e-bike weight: with battery and lock many weigh 57–66 lb (26–30 kg).
  • Not securing rack and bikes or not removing batteries – batteries weigh 7–9 lb (3–4 kg) and belong inside the vehicle.
  • Ignoring handling: an unloaded front axle means less steering force and traction, especially with front-wheel drive.

Assumptions and limits

  • Static consideration without dynamic surcharges; road shocks briefly increase the load considerably.
  • Vehicle as a rigid two-axle vehicle; tandem axles simplified as one axle.
  • No legal assessment – the certification label, manufacturer approvals and state regulations are authoritative.