Question: Why don’t they make the hubs for 29″er wheels with bigger diameter hub flanges so the wheels can be stronger?

Answer: The matter of wheel strength for 29″ers has been a concern ever since the modern 29″er hit the scene almost ten years ago now. Longer spokes are often times pointed at for being the culprit here. However; is that really the case? Let’s take a look at somethings that may clear up this matter for us.

Wheels have several things that can affect their strength. The way the materials are used, the way they are assembled, and how these two work together are the basics of wheel strength. Particular things such as the spokes, their shape, number and length can affect wheel strength to a degree. Rim diameter, profile, and design are other critical factors. Hub flange strength is important to anchor those spokes well. Let’s assume we are using high quality, well made parts in our wheel assembly and we have the best wheel smith putting it all together.

So, in this scenario, why would a 26″er wheel be stronger than a 29″er wheel? Lots of you are going to say it’s the long spokes. In reality, it’s the geometry of the wheel that is the issue. Let’s take a rear wheel as an example.

Back in the 80’s, when wheels had but 6 speeds, wheels were pretty much symmetrical in nature. That is to say, the angles at which the drive and non-drive side spokes left the hub flange were identical, or nearly so. Now with the addition of each speed up to the 9 we have today in a mountain bike cassette, compromises in wheel geometry had to be made to accomodate the space taken up by the cassettes. Take a look at any rear wheel with a multiple speed cassette. You will notice the drive side spokes leave the hub at a much shallower angle than the non-drive side spokes do. Front wheels are not exempt either. Disc brake rotors cause the same compromises in spoke angles. This is called “dish and causes wheels to be weaker than they would be if they had symmetry of spoke angles from drive side to non-drive side.

This is the biggest influence on wheel strength beyond materials design. In fact, hub flange diameter, and thus spoke length, are much less of a factor. Increasing flange diameter has not been proven to show much, if any, increase in wheel strength.

So, in terms of our original question, the hub flanges have a nominal effect on wheel strength. Increasing the distance between the hub flanges and having a dishless wheel has a much more dramatic effect on wheel strength.

What can be done then? Wheel overlock dimensions have been set since the onset of the 90’s for mountain bikes at 135mm for a rear wheel and 100mm for a front. Is this as good as it gets? Well, some things are pointing to changes in this area.

Niner’s W.F.O 9, an all mountain 29″er that is currently in developement, has a 150mm OD rear hub, a width commonly used for tandem bicycles and some down hill specific machines. (Guess why!) Lenz Sport’s Lunchbox full suspension 29″er also already is using this rear over lock dimension to get a dishless, thus stronger, rear wheel. But what about the front?

Well, that is being looked at by Paul Components who showed a 120mm OD front disc hub aimed at 29″ers at the recently held NAHBS in Portland, Oregon. Word is a suspension fork manufacturer is also looking at this standard as well.

For now it’s best to use a rim, spoke count, spoke guage, and hub design best suited to you and your riding style and to have a competent wheel smith put it all together.