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 characteristic is density and we all know that this works in titanium's favour but it's actually doubly in titaniums favour. Firstly, titanium is significantly lighter than steel. Secondly, you don't need to paint a titanium frame and this saves a small amount of additional weight.
So, how does this all add up in terms of ride quality? Well, as I mentioned at the start, they are very close. And if we were using strictly round titanium tubesets, there would be an argument to be made that they feel very, very close apart from the additional weight of the steel frame. But we don't use cylindrically round titanium tubes.
Our titanium tube sets are highly manipulated and in our view, this does add small but perceptible differences in how the frames ride. If you currently own a steel Cache, you're not going to be blown away by the difference in a titanium Cache. But like everything that falls under the law of diminishing returns, there absolutely are subtle differences.
In terms of weight, there is a 40%+ difference in weight between the two framesets. And if you were to go and shave that amount of weight off of a build kit, we all know that it would cost a lot of money to do so while keeping functionality the same. This is the same with the frame materials that we use in the Cache frames: one is expensive to work with and the other is REALLY expensive to work with. A titanium frame with a high end build kit can achieve a 15-20% reduction in total bike weight vs. a steel frame with a lower end or mid level build kit. But this increase in performance and reduction in weight comes with a higher price tag (US$4-6K premium) to the end user.
In relation to the "feel" of the bike, we are an engineering focused company and I just can't sign off on the "Titanium is magic" BS that is out there. For sure, it's an amazing material but it's also a mega-b*tch to work with, as are the ultra-high end stainless steels like Reynolds 900 series alloys and similar products from other manufacturers (this can't be overstated enough, especially in a production environment). Everything takes 3 - 5 times longer, it destroys cutting tools and the best vendors work with Wire EDM machining along with regular machine tools.
Welding technique needs to be spot on and if someone screws up late in the production process and a frame has to be scrapped, it's a significant cost to the vendor that goes straight into the recycling bin. There is no paint, so there is no way to hide anything: no Bondo under PU paint (carbon frames), no buffing out deep gouges (steel and aluminum) and covering them with thick power based paint. EVERYTHING is visible and this means that each and every titanium frame has to be perfect. All of this makes frames made with these materials very expensive (not to mention dumbass companies like us engraving the head tubes on our titanium frames adding even more cost to them. But at the end of the day, Titanium is still a metal that is in solid crystalline form at STP (Standard Temperature and Pressure) and its stiffness and flexural properties are governed by its moment area of inertial (cross sectional area) and elastic modulus. Its weight is governed by its tensile strength and density.
These are the properties that define the "ride feel" of a bike frame, along with tubing placement and geometry. So, if you've done your math right (which we think we have) in theory, you should be able to build a frame in titanium or steel that has the same geometry, the same tubing locations (i.e. dropped seat stays for increased bump compliance) and whose tubesets flex (bend) the same amount for a given load. That was always the plan with the Cache and both the steel and titanium frames were co-developed from the start to achieve this similar "feel".
In my mind the reason to buy a titanium Cache is not just "feel" but it's everything that titanium brings with it. It's feel, it's performance, it's an increased feature set (internal routing), it's the titanium "look", it's the corrosion resistance (and while we do ED coat our steel frames before painting to maximize rust protection, titanium is just - well titanium).
It's the skill of the fabricator which is by far, the most difficult frame material to build out of the four common frame materials. It's the knowledge that it's a frame for a long time and it's the most premium metal that you can build a bike out of. Perhaps that's a bit too holistic for some people and there are lots of other great options (we make one - Cache Steel!).
But for those that want the best, titanium is simply - the best.