How Wheel Size Affects Cart Fit (and How to Choose the Right One)

How Wheel Size Affects Cart Fit (and How to Choose the Right One)

TL;DR — Just tell me what to order

Wheel size affects shaft height, balance, and how level your cart sits on the dog — but how much it matters depends on the cart model.

For the Training Cart (wheel choice is the primary fit decision):

Start by measuring from the ground to the breastbone (point of sternum). That measurement is your best proxy for ideal shaft height.
Training Cart wheel guidelines:
  • 20” tires → breastbone ~15” or greater
  • 16” tires → breastbone ~13”–17”
  • 14” tires → breastbone ~12”–16”
  • 11” tires → breastbone ~10”–14”
If your dog falls outside these ranges, contact us — custom guidance is expected here.

For Heritage Carts (wheel size is more standardized):

  • Medium & Large Heritage Carts
    → come standard with 20” wheels
    → include axle height adjustment to fine-tune fit
  • Small Heritage Cart
    → comes standard with 16” wheels
    → 20” wheels optional
    → also includes axle height adjustment
Wheel size matters, but axle height adjustment also helps on the Heritage Carts.
If this TL;DR answered your question, you’re done.
If you want to understand why, read on.

Why wheel size matters more than people think

A cart isn’t just “bigger” or “smaller.” It’s a balance system.
Changing wheel diameter changes:
  • Axle height
  • Shaft height
  • Center of gravity
  • How forces load onto the dog’s body
That’s why wheel choice is a bigger deal on non-adjustable carts (like the Trainer) and a more moderated decision on adjustable carts (like the Heritage line).

Shaft height, balance, and the breastbone measurement

The most reliable single measurement we’ve found is: Ground to breastbone (point of sternum).
Why this works:
  • It closely matches where shafts naturally want to sit
  • It correlates well across different builds
  • It aligns with real-world setups
In a well-fit cart:
  • Shafts are level or very slightly uphill
  • Weight feels neutral
  • Braking and turning feel controlled, not awkward

Adjustable vs. non-adjustable carts

Training Cart

  • No axle height adjustment
  • Wheel size directly determines shaft height
  • Fit range is narrower
  • Wheel choice does the heavy lifting
  • If used primarily for training, the wheel height is more forgiving

Heritage Carts (Small, Medium, Large)

  • Axle height adjustment is built in
  • Wheel size sets the baseline
  • Adjustment allows fine-tuning for individual dogs
  • Fit is more forgiving within the intended size range
This is why you’ll see fewer wheel options on Heritage carts — the adjustability is doing that work also.

What happens when a cart is too tall

Across all carts, being too tall is the bigger issue.
A cart that’s too tall:
  • Raises shafts above the natural line of pull
  • Shifts the load in the cart forward
  • Puts more pressure on the top of the withers/back of the dog
  • Reduces stability when braking or turning
  • Raises the center of gravity of the cart
This is why we’re cautious about oversized wheels on smaller dogs — adjustment helps, but physics still applies.

What about a cart that’s a little low?

Within reason, a slightly low cart is often:
  • Easier for dogs to tolerate
  • More stable
  • Less disruptive to braking mechanics
This doesn’t mean “low is good” — it means too tall is worse.

Why ranges overlap (and that’s intentional)

Dogs vary in:
  • Chest depth
  • Harness configuration
  • Working posture
  • Personal comfort
Ranges overlap because real dogs overlap. These are guidelines informed by testing, not rigid rules.

The bottom line

  • Measure breastbone height first.
  • On Training Carts, wheel size is the primary fit decision.
  • On Heritage Carts, wheel size + axle adjustment work together.
  • Avoid carts that are clearly too tall.
  • When in doubt, ask — precision is the point.
Carting rewards careful setup. We build our carts to support that — not fight it.