29 Inch MTBs
These bikes are quite the fad these days. They are a fine choice for a rider, providing they are around 6 feet tall or taller. Here's why.
Tall riders over 6 feet can give can free up a lot of geometric space to make these wheels work for them. Notice when a tall person is on a 29" wheel bike, it 'looks' right. When a short person is on one, it look god awful.
Actual Wheel Diameter Differences
- 29x2.2 Kenda Nevegal - 29.375" (approximate, uncompressed)
- 26x2.1 Kenda Nevegal - 26.500" (approximate, uncompressed)
Essentially, the axles are raised, the toe clearance is reduced, and the fork clearance is reduced all by 1.4375". Then their are the geometrical considerations.
On the image below; note that to maintain the same 'real' wheelbase and 'real' trail (not ground wheelbase or trail) on an average 23" top tube MTB, the top tube must grow over 1.14 inches, pedal clearance drops about 1.4 inches, steering quickens by over 2 degrees, suspension travel is reduced considerably, and fork and tire selection are reduced to only a handful of options.
Most people are not in a position to give any of these features up for the supposed (and probable) gain of having a larger wheel to roll over the surface easier. By giving up suspension travel, though, this gain is reduced still.
Comparison of two actual frames
Here is a comparison of two frames, one a 26" and one a 29" wheel frame. The represent standard issue type product rather than extreme niche product.
- The 29" bike attempts to offset the increased top tube length by steepening the seat tube angle.
- To keep the head angle in line with accepted norms, the 'real trail' has increased by 0.37", a drastic increase. 13% more leverage on the system.
- Toe clip overlap is comprimised by 0.81" on the 29" frame, leading to problems for riders with larger feet.
- The chainstay length (unshown) had to be increase to 17.5 (fron 16.7")to fit the larger wheel, combined with the large trail, the thing will ride like a truck.
- The wheelbase is increased about an inch. A 2.2% increase
- The overall length of the bike is up 3.17", total garbage for riding tight singletrack or rocks.
- the rider is shifted more forward on the rear wheel making it worse for decending amd steering.
note that the 29" frame will handle like a truck compared to the 26" version. Also, the manufacturer of the 29" bike recomends this size for a much smaller rider than I have given it credit. I went by comparable top tube sizes (approx 23") that most average sized men will end up using.
Here you can see the shift of the rider forward on the bike.
The Case for Large Niners
Here is where I can finally be positive, the large bikes.
When frames become larger, the drawbacks to 29" wheels diminsh while the advantages get more pronounced.
- With pedaling clearance well over 12", TCO is no longer an issue
- The top tubes and wheel bases of either wheel choice become similar.
- The 'real' trail is extremely close to comparable with only a 1 degree shift in head angle.
In addition to that:
- The increased wheel diameter helps to support the larger heavier rider on softer terrain
- The wheels roll better over rough surfaces
- The scale of the bike is more suited to the larger rider.
The only real drawback to either bike at this point is that the 29" wheel bike's OAL is almost 3" longer. A point that may not matter given all the other considerations.