1.1.4 Adjustability and Range of Size

The Design Challenge of Human Diversity

We come in all shapes and sizes. As designers, we face a fundamental challenge:

To address this challenge, designers employ two primary strategies: adjustability and range of sizes.

Strategy 1: Adjustability

Adjustability refers to the ability of a product to be changed in size or configuration, allowing a single product to accommodate multiple users of different dimensions.

How Adjustability Works:

Products with adjustability features typically include:

• Moving parts

• Telescoping components

• Folding elements

• Expandable sections

• Height/width/angle adjustments
  

Real-World Examples:

• Office chairs: Adjustable seat height, armrests, and backrest tilt

• Bicycle seats: Height adjustments to fit different leg lengths

• Car seats: Forward/backward positioning, height changes, and backrest angle

• Crutches: Telescoping legs to match user height

• Smartphone stands: Adjustable viewing angles
  

Benefits of Adjustability:

• One product can serve multiple users

• Adapts to changing user needs (like growth or changing activities)

• Can accommodate a wider percentile range

• Often more economical than purchasing multiple products
  

Limitations of Adjustability:

• Can add complexity to the design

• May increase manufacturing costs

• Could introduce potential failure points

• Might compromise aesthetics or structural integrity

• Users must understand how to make proper adjustments
  

Strategy 2: Range of Sizes

Range of sizes involves producing the same basic product in multiple different dimensions to fit various user groups.

How Range of Sizes Works:

Instead of making one adjustable product, manufacturers create:

• The same design

• In multiple fixed sizes

• Each targeting different percentile ranges
  

Real-World Examples:

• Clothing: XS, S, M, L, XL sizes

• Shoes: Numerical size ranges

• Bicycles: Different frame sizes (S, M, L)

• Kitchen utensils: Children's and adult versions

• Sports equipment: Youth and adult dimensions
  

Benefits of Range of Sizes:

• Each size can be optimized for its target users

• Often simpler construction without adjustment mechanisms

• May provide better ergonomics for specific user groups

• Can target specific demographics precisely
  

Limitations of Range of Sizes:

• Increased manufacturing complexity

• Higher inventory requirements

• Environmental impact of producing multiple versions

• Users must select the correct size for themselves
  

Choosing the Right Strategy

Designers must make informed decisions about which strategy (or combination of both) to use based on:

1. User diversity: How wide is the range of users who will use the product?

2. Frequency of use: Will multiple users share the product, or is it for individual use?

3. Cost considerations: What manufacturing approach is most economical?

4. Usage context: In what environment will the product be used?

5. User capabilities: Can users understand and make proper adjustments?
   

Combined Approaches

Many successful products combine both strategies to optimize usability:

• Bicycles: Come in different frame sizes (range) AND have adjustable seats and handlebars

• Backpacks: Available in S/M/L (range) WITH adjustable shoulder straps and waist belts

• Eyeglasses: Multiple frame sizes (range) WITH adjustable temple arms
  

Connection to Percentiles and Ergonomics

The choice between adjustability and range of sizes directly relates to the percentile data we discussed earlier:

• Adjustability: Allows a single product to span a wider percentile range (e.g., 5th-95th)

• Range of sizes: Targets specific percentile ranges more precisely (e.g., small = 5th-30th, medium = 30th-70th, large = 70th-95th)
  

These strategies help ensure products address the importance of workspace envelopes, reach, clearance, and other ergonomic considerations we've discussed.

Design Thinking Application

When applying these concepts in your design projects, you should:

1. Identify target users: Determine the range of users your product must accommodate

2. Analyze critical dimensions: Which body measurements most affect usability?

3. Evaluate strategy options: Would adjustability, range of sizes, or a combination work best?

4. Test with users: Verify your approach works with real people across your target percentile range
   

By understanding when and how to apply adjustability and range of sizes, you'll develop the ability to create products that comfortably fit diverse human users, enhancing both usability and user satisfaction.