Condensed Answer: In most cases, a frame that can handle 150mm of travel can operate with 160mm. That said, the difference in travel is too small for the switch to have a large impact on the bike’s performance.
More Travel = More Head Tube Stress
The longer the fork is, the higher its leverage against the head tube becomes. During regular cycling, this isn’t a major issue, but if there’s impact (e.g., overcoming a road irregularity or landing a jump), the stress exerted by the fork against the head tube is magnified immensely.
For that reason, the head tubes of frames designed for forks with lots of travel are over-built. Otherwise, the head tube might crack or completely “rupture”. When that happens an accident is guaranteed because the rider loses complete control over the bike.
To avoid similar scenarios make sure that the head tube is certified to withstand the travel of the new fork. In most cases, frames that can safely operate with 150mm of travel can do so with 160mm too.
But to be on the safe side and preserve the warranty of the frame, consult the specifications and conditions presented by the frame’s manufacturer.
Slacker Head Tube Angle = More Head Tube Stress
The longer fork elevates the front end and thus slackens the head tube angle (the angle between the head tube and the ground). The slacker head tube angle amplifies the force that the fork can exert against the head tube even more.
The stress points are the welds connecting the head tube to the top and down tube.
Changes To The Geometry Of The Bicycle
The longer fork will influence the bike’s geometry as follows:
- Slacker Head Tube Angle
The longer fork will elevate the front end and thus slacken the head tube angle. Normally, 20mm of extra travel slackens the angle by approximately 1 degree. In this case, the change will amount to about 0.5 degrees and can therefore be seen as minor.
The advantages of a slacker head tube angle are:
- The front wheel is pushed away from the rider and makes it easier and safer to overcome irregularities when descending on off-road terrain.
- The chances of going over the handlebars are smaller.
- It becomes easier to lift the front wheel when you have to overcome an obstacle.
The disadvantages of a slacker head tube angle are:
- More weight on the rear wheel makes climbing more difficult.
- Less aerodynamic position (the back is more vertical)
- Reduced front wheel traction
- Poor steering responsiveness at slow speeds.
- Slacker Seat Tube Angle
The elevated front end will slacken not only the head but the seat angle too. (The angle between the seat tube and a horizontal line passing through the bottom bracket.)
The slacker seat tube angle positions the rider closer to the rear wheel and makes the back position more vertical. The front-wheel traction is reduced too. Consequently, climbing gets harder.
- Taller Bottom Bracket
The elevated front end will raise the bottom bracket too. In general, 1 degree of slackening achieved via a longer fork lifts the bottom bracket about 7mm. Thus, in this case, the elevation is only 3.5mm.
A taller bottom bracket provides frame clearance but makes the bike less stable because the center of gravity is higher. The cornering capabilities of the bike are also hurt.
In this case, however, the elevation isn’t massive and the negative effects won’t be as noticeable.
- Longer WheelBase
The wheelbase is the distance between the front and rear axle. And since the slack head tube angle positions the front wheel further away, the wheelbase gets longer.
A longer wheelbase makes the bike more stable at the expense of cornering.
Is The Switch From 150mm To 160mm Of Travel Worth It?
In most cases, the answer is no simply because 10mm of travel will not make a massive difference. That being said, if you have the option to do the switch safely and you plan on covering hard downhill, the change could be seen as acceptable.
However, it’s worth noting that the climbing capabilities of the bike (which are already hurt at 150mm) will get worse.
Summary: What You Need To Know
- Longer forks exert more force against the head tube.
- If the frame can support only forks with 150mm of travel, then going even to 160mm will void the warranty and create an opportunity for frame failure. In other words, the switch makes sense only when the frame is strong enough to endure the additional stress.
- The longer travel will slacken the head and seat angle and thus hurt the climbing capabilities of the bike. If you want a technical climber, it’s better to stick with forks that have 120mm of travel.
- The changes to the geometry include a taller bottom bracket and a longer wheelbase.
- The switch from 150mm to 160mm of travel is of questionable value and in most cases makes little sense.