SPRINGS - LONG vs. SHORT
Many of our customers have questioned us on why our fork springs are so short, particularly on vintage applications. Here's the long (or short) answer.
In the past the material that manufacturers used to make springs was pretty poor. This meant springs would not only often sack-out but it also meant that fairly heavy gauge wire needed to be used. The heavier gauge the wire the less stressed it is at maximum travel. But this also means that the spring designs were pretty heavy (they weighed a lot) for a given rate.
Let me back up here for a moment. Springs can be made with a variety of wire gauges or diameters. The larger diameter the wire, the more number of coils are required for the desired rate. Thinner wire could also be used requiring less number of coils. I explain this in much greater detail in "Race Tech's Motorcycle Suspension Bible" if you're interested.
These two examples; thick wire, lots-o-coils vs. thin wire, fewer coils introduces us to the concept of a Hi-Performance Spring. The thinner the wire the lighter the spring for a particular rate. These are Hi-Performance. This also requires better materials that weren't available back-in-the-day. In fact it is very rare (and pricey) even today (note: there are only two wire manufacturers in the world that can produce the quality of material we require for most RT Hi-Performance Fork Springs).
It may have crossed your mind that a spring design using thinner wire with less coils would have more travel for a given length than a spring made with thick wire. This means we can design our springs shorter and still have the required travel. This also means we will need to use longer spring spacers but they are generally much lighter than spring.
Using a shorter spring has the added benefit that it will fit in more bikes if we employ different length spacers. If we tried to chase all the original spring lengths we could never make enough of any one particular design to be economical.
So there it is folks. You're gonna have to cut some spacers. But really that is the only down-side. The up-side is less weight, more applications and super-tough hi-performance springs.
Thanks for your interest,