Suspension Travel

[Brammofan]

According to the Brammo Enertia Specs, the front forks have 5" of travel.
Recently, when I was showing my bike to the Heart of America Motorcycle Enthusiasts club, one member asked to "swing a leg" over it. 
This guy's about 6' 5", 240 lbs., and supposedly a "seasoned veteran racer."  He liked the bike, generally, but he said, "What's the deal with the suspension?  Are your forks frozen?"  He put his weight on them and the travel seemed to be around 3".  He suggested that I measure the travel by putting a nylon cable tie around the fork, putting my weight on it, and measuring the distance.  He said that being able to use the full 5" of travel would make the bike's ride smoother, but more important than that, it would be safer.

Although I've noticed that the ride is rather firm, I've never thought to measure the travel of the front forks.

I would like some input from the forum, especially any of you who have owned multiple bikes.  Is this something I should be concerned about?

[Richard230]

I don't think I have ever seen suspension travel that meets the travel specifications of the manufacturer when you just sit on the bike and compress the suspension. Perhaps this is due to spring binding, anti-bottoming devices and/or air compression resistance.

However, if you take the springs out of the fork tubes and move the forks through their full travel with the caps off of the tubes, you will usually get the full specified range of travel.

The same is true for many rear suspensions, to a lesser extent. Perhaps this is due to the rubber bumpers that are usually installed on shock absorbers. They can eat up as much as in inch of travel on the shock, which could amount to even more travel with a single-shock system that uses a system that multiplies the travel of the suspension compared with the travel of the shock, due to its geometry.

[webman]

Brammofan:

What happens when you get on your bike and the suspension compresses is called 'static sag.'  It's normal for a bike's suspension to compress about 2-3" in this situation, depending on the type of bike, loading, etc.  You absolutely would NOT want the suspension to compress the full 5" in this situation, because if it did, there wouldn't be any compression room left for it to absorb bumps.  Most bikes' forks are very difficult to compress fully from a stationary position, precisely because the force of the bike hitting road undulations, potholes, etc. is much greater than you can exert by sitting on the bike.  Your friend is likely used to riding machines with softer springs, which is why he felt like the bike was 'frozen.'  The suggestion about using a zip tie on the fork leg is a common trick roadracers use to check how much travel they're actually using on the track, and is used to help them fine-tune their preload and compression damping adjustments, neither of which is easy to do with the nonadjustable fork on the enertia.  Looking at the photos of the empulse prototype, you can clearly see the compression and preload adjusters atop the fork caps.  It also appears that there's a rebound adjuster at the bottom of the fork, between the two 'radial brackets' that support the brake calipers.  WHOO HOO!  Fully adjustable forks are a given for bikes in this price range, so good for Brammo.

I hope this long-winded response helps to clarify things.

eric aka webman

[Brammofan]

Thanks, gentlemen!

[mykb13]

Don't forget that some of the suspension is used up under the bike's own weight so that when you accelerate or go over a speed bump and the front end gets light, the forks have room to extend and reach back down for the road.  The 5 in of suspension travel would have to be measured from full extension (no weight on front wheel) to full compression (heavy braking).

I use the zip tie test on the track and street.  If you're using all of the suspension then it's set to soft because you never want to completely bottom out and then hit another bump with no room for more shock absorption.  If you did, you'd lose contact with the road surface like when we were kids and would jump curbs on our non-suspension bicycles.  Likewise, if you're not getting even close to using all of the suspension, then it's probably set too hard and the bumps are unnecessarily beating you up!  Might as well use most of the suspension since that's what it's there for.