One of the most common questions we get is:
“I have a 7K axle with an 80” spring center—can I just upgrade it to a 10K or 12K axle?”
It sounds simple, but in reality, upgrading from a 6K, 7K, or 8K single wheel axle to a 10K or 12K axle is almost impossible in most cases. Here’s why.
1. Hub Face to Spring Center Spacing
Every axle has two key measurements:
- Hub Face (HF): The distance from hub to hub where your wheels mount.
- Spring Center (SC): The distance between the spring hangers on your trailer frame.
For single wheel axles like 6K, 7K, and 8K, the hub face to spring center spacing is much tighter than it is on 10K or 12K axles.
Example:
- 7K Axle: 95” hub face / 80” spring center → 15” difference total (7.5” per side).
- 10K Axle: 74” hub face / 47” spring center → 27” difference total (13.5” per side).
That’s a huge change.
2. Why the Spacing is Different
10K and 12K axles have much larger hubs, drums, and brakes than single wheel axles. That extra size takes up more room, so the spring centers have to be moved inward to make space.
This is why you can’t just swap a 7K axle with 80” spring centers for a 10K axle. The geometry doesn’t line up.
3. The Road-Legal Problem
Let’s say you tried anyway:
If you mounted a 10K axle under a trailer frame built for an 80” spring center, the hub face would have to push all the way out to 107”.
That’s:
- Wider than the legal road limit in most states.
- Wider than the actual lane of the road itself.
- Completely unsafe and impractical.
4. What’s the Realistic Upgrade Path?
For most trailers with an 80” spring center, the maximum axle capacity you can upgrade to is an 8K axle.
At Trailer Parts Unlimited, we stock an 8K axle with a 97” hub face and 80” spring center. That means:
- You can keep the same trailer frame width.
- You don’t run into clearance or legal issues.
- You get a stronger axle without redesigning your whole trailer.
Final Takeaway
If you’re running a 6K or 7K axle and want more capacity, the jump to a 10K or 12K axle isn’t realistic because the hub face and spring center geometry just doesn’t work.
But the good news is—you can step up to an 8K axle with the same 80” spring center and still gain strength and reliability.