Steel vs Titanium
By: Noel Buckley
Recently a customer asked us what the difference in ride quality is between our Cache Steel and Cache Titanium. This is a common question that we get and one that makes a lot of sense to answer given the roughly three times price increase of the Cache Titanium over the Cache Steel. So, to jump straight to the point, the short answer is that it’s "not that different" (and frankly I think it's very misleading to claim anything else if a bike is well engineered).
However... as the saying goes: The devil is in the details.
Anyone who knows steel bikes knows that the Cache Steel is not a "cheap steel bike" (and this applies also to our soon to be launched MTB hardtail). It is priced above the standard Hi-ten and 4130 steel bikes but it’s not as high as a western made craftsman's product because we make them in batch production, not as custom geometry one offs (even if the quality is similar). The quality of the materials in Knolly's steel bikes are second to none and while we don't use Reynolds tubing in our product (I'll explain why in a minute), our steel frames use a steel with similar properties to Reynolds 853, their highest offering in non-stainless materials.
We custom form ALL of the tubes in our frames, hence we need to have access to the steel in its annealed state. This state makes it impossible to use a high end off the shelf tubeset, as the tubes are already hard. For both the titanium and steel frames, we have opened a significant amount of custom tooling for these bikes, something that is almost unheard of in this world. 99% of the hardtails on the market make use of stock tube-sets that are mitered and perhaps bent and then welded into a final configuration. We're different because every tube in our steel or titanium Cache has touched a tool that is proprietary to Knolly.
Some tubes are relatively simple and some are incredibly complex. The Cache Titanium seat tube is the most complicated with four main operations which require about a dozen steps to complete, including multiple annealing stages to avoid the tube cracking or splitting during formation. This particular tube took us 16 months to develop with our vendor and they are probably the only bike frame production facility in the world that could pull this off.
In terms of material properties, ultimately you can distill properties for most metals down to a few important characteristics:
Modulus of elasticity (elastic modulus)
And despite all of the hype about titanium being "unique", offering a certain type of flex, "feeling springy", being more supple, etc... both titanium and steel can ultimately be defined by these 3 properties.
For example, if you have a cylinder of titanium and a cylinder of steel, you can - in theory - make them have virtually identical bending (i.e. flex) properties by controlling the tube's diameter and the material's Elastic Modulus. Because high end steel's elastic modulus is significantly higher than titanium's, a smaller diameter steel tube will have the same stiffness as a larger diameter titanium tube. Hence, you'll see that on the Cache frames, the steel down tube is 42mm in diameter and the titanium down tube is 47mm in diameter (for - example - a size 60cm frame). Despite one tube being made in titanium and one in steel, they are designed to have similar bending characteristics (flex) under the same load.
Wall thickness is generally determined by the material's tensile strength: a combination of the tube being strong enough to not fail, but also ensuring that the wall thickness is sufficient to avoid easily denting the tube and / or the tube failing due to a buckling load.
Now, we get into the smaller details. We do some things on the titanium frames that are not done on the steel frames, particularly in the front triangle and these tweaks affect another characteristic called the "moment area of inertia". What this is referring to is the cross sectional area and we manipulate this a lot more in our titanium frames that we do in our steel frames. For example:
The top tubes on our steel frames are double butted, but externally cylindrical. The top tubes on our titanium frames are not only double butted, but they are also tapered, being larger diameter at the head tube and slightly smaller diameter at the seat tube.
The down tubes on the steel frames are bent. Whereas the down tubes on the titanium frames are not only bent, but aggressively ovalized and slightly tapered.
The seat tubes on the steel frames are butted and bent. And on the titanium frames, they are butted, bent, tapered and squish formed.
All of these details cost a lot more money to do on the titanium frames because the tooling is a lot more complex and is amortized over a vastly smaller number of frames. Additionally, titanium is notoriously difficult to work with and its propensity to work harden is high. That means that even simple operations may need to be repeated multiple times, further increasing costs.
The final characterist