1/2/2014 IDeA Center

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Date: 3/20/2013

From: Clive D’Souza and Edward Steinfeld, IDeA Center, University at Buffalo

To: Marsha Mazz, U.S. Access Board 

RE: Summary analysis of wheelbase measurements on wheeled mobility devices

Introduction

The following memo is a brief analysis of the wheelbase dimension for wheeled mobility devices in the 

anthropometry of wheeled mobility database.

Wheelbase Definition

For the purpose of this analysis, wheelbase is defined as the distance from the center of the primary 

drive wheel to the center of the caster measured parallel to the floor. The larger of the dimensions 

measured on the right and left side of the mobility device were considered for the analysis.

The sample considered is the analysis of wheelbase is a sub-set comprising 242 the overall sample of 

500 wheeled mobility users. Only one set of casters on mid-wheel drive wheelchairs were measured and 

so these devices are not excluded in the current analysis.

Table 1 shows the minimum, maximum and percentile values of the wheelbase dimension for manual 

wheelchairs, front- and rear-wheel drive power chairs, 3- and 4-wheel electric scooters. 

Table 1: Range and percentile values for wheelbase (inches) by mobility device type

Mobility Device Type

Sample 

Size

(N=242)

Min

Value

Percentile Max

Value 5 10 25 50 75 90 95

Manual Wheelchair 158 11.9 14.7 15.1 15.7 16.5 18.3 20.2 20.9 23.9

Power chair - Front 

wheel drive 40 13.2 13.6 16.4 18.8 20.2 25 27.2 27.9 29.1

Power chair - Rear 

wheel drive 30 12.2 14.1 15.8 16.6 17.9 19.4 20.7 21.3 21.6

Scooter - 3 wheel 11 28.2 28.2 28.3 30.3 32.4 34.4 36.4 . 36.8

Scooter - 4 wheel 3 33.8 33.8 33.8 33.8 34 . . . 34.5

Observations:
1/2/2014 IDeA Center

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1. Wheelbase dimensions for manual wheelchairs and rear-wheel drive power chairs were similar 

to each other but slightly less than the wheelbase for front wheel drive power chairs

2. Both 3- and 4- wheeled electric scooters had a larger wheelbase dimensions compared to 

manual and power wheelchairs. This sample had just three 4-wheeled scooters which limits

detailed comparisons with 3-wheeled scooters

For platforms designed to accommodate wheeled mobility devices, additional space beyond the 

wheelbase should be provided. It would be very difficult for the occupant to have the powered device 

come to rest on a platform that is the exact length as its wheelbase or even a few inches more. Fine 

control (for example less than 1 in. increments) is difficult when operating powered wheelchair and 

scooter devices. 

The wheelchair scale we used had a leveled surface of length 30 in. long with a bevel of 5 in. each at 

both ends (i.e., total length of 40 in.). Power wheelchair and scooter users often had trouble getting 

positioned exactly on the leveled portion of the platform requiring additional time and verbal assistance 

from an assistant/aide to get properly situated. Larger devices including power wheelchairs would often 

get positioned with two wheels on the bevel edge. We have observed that this causes an uneven weight 

distribution on the scale and could cause power wheelchairs to tip over when making short quick 

forward-reverse maneuvers in trying to get positioned on the platform. Including some aids to facilitate 

positioning would be a good idea also, for example, lines on either end with contrasting color and raised 

ridges at the ends of the level part of the platform.

Recommendations

Based on the data in Table 1 and the observations above, we recommend: 

- a minimum flat surface of 40 in. length for platforms accommodating wheeled mobility devices 

including scooters

- a minimum flat surface of 33 in. length for platforms accommodating wheeled mobility devices 

excluding scooters

- aids that can help wheelchair users mount the platform and position their chairs fully on the 

level surface.