Motorcycle Chassis and Suspension Specialists
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    Triumph   Thunderbird    
           
       < Application: Sports / Touring 110kg
Problem:     Excessive brake dive
Comments / observations:
>       
         
    "Interested in fitting Progressive Springs. What is the cost to supply?"    
   
We don't usually fit progressive springs, but can supply if you wish. Our preferred mods (check our website for "Hold That Road" Triumph Magazine Test) are to fit a straight rate spring, our Provalve and modify rebound damping to suit spring. We also fit modified Ikon Shocks that are longer than standard to take advantage of the much improved ride and traction.

The front forks also have problems with too fast a dive rate, spring too soft, rebound too soft and again, a harsh feel. If you want to fix the front end problems, we would strongly recommend a new spring and our Provalve kit. This will give you a plush ride, very controlled dive and we match rebound settings to the new spring.


FRONT:
  • Provalve Service Set-up and spring

REAR:
  • Ikon shocks including spring and damping mods
 
   
   
"Thanks. I'm looking for progressive fork springs - I think your reply is referring to Shocks, am I right?"
   
   
The mods we were talking about regarding springs were for the front forks in preference to using progressive springs. The other parts would further improve fork action and control the motorbike significantly better than not using them.

Fork springs will support the weight of the bike and rider, this is approximately 1/3rd of the equation for your front forks.  To get the best out of your forks you must consider upgrading compression damping (gets you to 2/3rds of the equation) and rebound damping (to get to 3/3rds - everything working properly).  That's why we recommended the other parts.

When you fit a bigger spring, whatever damping there is will be overworked.  The Thunderbird is already too soft damping with a too soft spring.  So when you fit a bigger spring it will not solve all the problems with the Triumph's front end.

Progressive springs have two spring rates combined into one spring, however, there is a crossover point when the soft and hard rate combine, so your already soft standard damping has to not only contend with the normal compression rate from the spring but a heavier rate too, it doesn't create the most stable conditions for your bike. Hope this clears it up for you.