Fitting Bigger Wheels

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Would you like bigger wheels on your board?

Now, why would you? Suppose you are aiming for the off-road experience, the small, stiff regular wheels won’t help you in the forest or on serious gravel.

Also, using 5-6″ pneumatic wheels means more versatile commuting and smoother ride in general.

Why won’t we just put bigger wheels on existing trucks?

Most standard trucks don’t have the clearance needed without getting into serious rubbing between the wheels and the deck. You can always cutout the deck to provide clearance or lift the deck on pads to avoid wheel byte.

There are also other solutions like specialized trucks or specifically designed wheel hubs.

All of these solutions work good. But what about regular trucks with bigger wheels? When you don’t necessary want to rise your board up? Or modify it extensively? Is there a solution?

Standard trucks with bigger wheels

The usual approach is to fit some kind of offset extenders on the trucks and mount the wheels on them. The problem here is that the trucks will see increased loading due to larger moment arm. And they are not designed for this.

Let’s explore different approach

I want to suggest a different approach to this problem. My aim is to find a unified solution that will fit all of the trucks (maybe with slight adjustments), will allow any extension and will be structurally sound. In addition, it is very simple and straightforward.

This was my “exploratory” finite element model:

My simplistic model, it’s nowhere near the final product, but allows me to run different parameters with ease

Now, let’s see what happens here. I want to fit a newly manufactured bracket on the existing trucks, right at the axle where you normally mount the wheels. The new axle will shift upwards, in doing so, it effectively lowers the deck and thus making it more stable. A standard alloy M8 bolt will fit there, they are dirt cheap and available in different lengths.

This will increase the bending loads on the truck. In order to alleviate this, we will connect the two brackets together (there is another one on the left) thus creating a counter balance. The lower bolt works in tension, and the trucks are actually loaded less.

Not sold yet? Let’s explore this further

There is nothing like a comparative analysis :). Suppose we have a 120 kg person on the board, centered. Then each wheel will see 30 kg of vertical load. Here is how it looks like with standard trucks:

Vertical deflection of the truck, the numbers are mm, fairly stiff. This is expected

These are the resultant stresses in the loaded truck. The numbers are kg/mm^2. But let’s ignore the numbers for now

For a moment we will ignore the numbers and just relate to them as a given situation – this is the way the standard trucks were meant to be used.

Now, we will fit the new bracket:

The structure became stiffer.

Note the deflection which becomes smaller, but we actually INCREASED the moment, because the wheel is now at offset.

Stresses in the structure

You can also see the stresses, which are in the 6-7 area, vs. 9 with the standard truck. For now, please ignore the hot spot on the very right, it is not real.

What happened to the new bracket?

Not very much, the stresses are fairly low:

These are very good news. Now that we feel comfortable with the concept, I wanted to see the fit of a new structure.

The intention is to make the bracket from Aluminum. This is the design:

Kind of “Artist Impression”

For the fit check we can also print it:

I used the only trucks that I have with the only M8 bolt that I have 🙂 In this particular design the tying between two brackets is realized with 2 M6 bolts, which are more than enough.

It is a preliminary design and should be validated with final stress analysis. It can be further simplified and made very cheap to manufacture.

I think it has potential and can open a more flexible hardware fitting niche.

I would love to hear from you, what do you think about this approach?

Enjoy,
Dani

P. S.

There are still some unsolved topics here. The main one, in my opinion, is the rotation around the original axle, it has to be retained somehow.

I’m still working on this and it will be solved. Please feel free to suggest solutions for this. Also if you would like to maybe try it out, then let me know.