BONNIE MOD #23
TEC Progressive Fork Springs

Back in January, I installed some pretty awesome TEC rear shocks. My intention was to replace the fork springs at the same time. Unfortunately, TEC was back ordered until April. Well, guess what? It was a wait but I finally received the fork springs, as promised, end of April.

Before we begin the install, exactly what is a progressive spring, why do I need it, and why is it better than the stock Triumph fork spring? Well, first off, we don’t neeeeed it, we WANT it! Ha, ha, but seriously…

(let me preface this by saying that my glory days of Physics are behind me, so if I’m speaking out of turn, please correct me.)

The stock OEM fork springs of a Triumph Bonneville are linear – they have a constant compression rate, meaning that they exhibit the same compression during the entire length of travel.

Progressive springs, on the other hand, have a variable rate. They are purposely designed to have a softer compression at the beginning of the load and gradually become stiffer as the load increases. In other words, they provide a refined cushioning while traveling over small bumps. Harder bumps, however, will probably feel the same regardless of either spring.

If you look at the above two photos, you see that the first one, the stock OEM spring, has the exact same coiling along the entire length. There is no variation in compression. The second photo, the TEC, has the spring beginning with a tighter coil that gradually progresses to a looser coil. The beginning of the compression travel is more subtle. [update/2015.05.15: note that the TEC spring is approx 5-10mm longer.]

The bottom line is that you’re going to have a better riding experience with a progressive spring during normal travel.

So I ordered a pair of TEC Bonneville T100 progressive springs – only $79. A seriously good deal!

They arrived promptly, well packed. Always a trademark of TEC.

To install these, it will be necessary to remove your handlebar assembly in order to gain proper access to the fork caps. However, if you have clip ons, this may not be necessary. For my situation, I have a drop handlebar that drapes across the fork caps, so the following steps apply.

Before starting, make sure to cover the tank with a heavy towel. You’ll be sorry if you don’t.

Onward… remove the handlebar assembly from the top yoke. Start by removing the clamps holding down the bar. Note: I have extenders, hence the extra pieces.

Place the handlebar assembly out of the way. No need to undo the brake and throttle controls. Leave them on the bar.

Now we move to the fork caps. Note: the yoke/triple clamp remains in place. It doesn’t get touched in this mod. The fork caps require a 22mm socket.

Unscrew the fork cap. Be very careful as you get near the end of the thread. There is a lot of stored energy built up. Hold the fork cap as you unscrew it so that it doesn’t suddenly pop off. Trust me, it will pop!

Once the cap is removed, the fork spacer will pop up for sunlight. As you can see, there is quick a bit of travel that has been suppressed.

Pull out the spacer.

Now we get to the final player, the spring. The ideal tool to pull it out is a bent coat hanger. I prepared one and then stupidly forgot to bring it with me to the garage. Luckily, I had a telescoping rod that I had as part of a flashlight. Regardless, you’ll need something a minimum of 12″ long. A coat hanger is the easiest and cheapest solution.

Clip onto the side of the spring and slowly pull it out. There is a washer on top, so don’t lose it.

Here it comes… don’t lose the top washer.

Pull the spring out VERY SLOWLY. Otherwise, oil will drip all over your bike. Pull it out slowly and allow the fork oil to drip back into the fork.

Feed in the TEC progressive spring. Make ABSOLUTELY sure that the tighter wound portion of the spring is at the top. (Hmmm… what would happen if placed in upside down? Might be a good experiment…) Place the washer back on top.

Okay. Here goes a bit non-best practice. Best practice would be to measure your fork oil level. Hell, it would probably be super best to replace your fork oil. However, I’m only at 4500 miles. Plus, as you can see in the photo below, there was no difference in the oil level when switching between the two springs. I decided to go this “lazy” route.

And now we go in reverse. Put the spacer back in.

There always has to be a bitch part of every mod, right? Well, here it is. The TEC springs appear to be about 5mm longer. Not much at all but enough so that screwing the fork cap back on is a BITCH. It takes a lot of force. You need to push the spring down enough so that you can thread the cap onto the fork tube. I had to put some serious weight into the effort. A simple socket wrench wouldn’t work. It wouldn’t allow me the leverage to apply enough force. I have a long T-Bar for my sockets that saved the day. It allowed me to apply my body as a downward force onto the cap. I’m serious, this was not easy but it got done. Make sure to torque down appropriately, but quite honestly… there is so much upward force applied to them, not sure how much torque is really necessary.

[update/2015.05.15: Joey in the comments made me go back and look and realize that the TEC spring is approx 5-10mm longer. This accounts for the difficulty in screwing down the fork cap. I plan on getting a pipe cutter and trimming the spacers. I might go the route of PVC thus keeping the OEM spacers intact. Not sure yet.]]

We just finished the right side of the fork. Rinse and repeat for the left side. No surprises, trust me.

Once all set, place the handlebar assembly back in place and torque down the clamps. I highly recommend placing a Sharpie mark at the 6 o’clock position of each bolt. During future travels, if you see any of the marks shifting, you know that the bolt is loosening.

My final thoughts? Along fairly smooth roads, the TEC springs make the road even smoother. Along smooth corners, the bike definitely feels a bit tighter. Along bumpy roads, meh, not so much. And by bumpy roads, I mean the horrible pothole ridden roads we have here in New York City. I’m not sure what springs will polish those. At the super low cost of $79 though, definitely worth it. Not the huge improvement as felt from the TEC rear shocks but definitely an improvement.

Tools Required:
5mm Allen Wrench
22mm Socket
Coat Hanger

Company URL:
TEC Bike Parts, USA

Price:
$79 + Shipping