Cotic Rocket… pricing
Here you go…
“One of the most notable features of the Rocket is it’s choice of material. Up to a point I’ve been expecting rolling of eyes and ‘what of have those silly steel sniffers at Cotic gone and done now?’ and ‘why on earth would you use steel on an FS bike? It’ll be flexy and heavy, surely?’ type questions. I’ll be honest with you, before I started this project I’d have been right there with you if someone else had built a steel FS bike. Although we love steel for our rigid frames, the Hemlock was aluminium because, well, that’s what you make full suspension frames out of, right? I’d not challenged assumptions at all with that bike, I’d just done what everyone else did. And that was the plan when the Rocket project kicked off. I was focusing on geometry and suspension feel and all the other improvements that I’ve talked about in the other essays I’ve written recently. But a couple of things made me challenge those assumptions.
Firstly, I’d come back from the trade shows in late 2009 quite disillusioned with the road bike market of all things. At Eurobike there was all the usual carbon loveliness and aluminium swoopiness, even a bit of ti, but anything steel and skinny tyred seemed to be trying incredibly hard to look like it’d been built in a shed in Italy in 1953. It made me sad, because I do love steel as a material for rigid frames. Despite the fact that any frame made from steel would be heavier than the above materials I felt that no one building something modern and forward looking in steel on the road was doing the material and it’s fans a disservice. You could build a road bike with lovely feel and durability at a great price and I thought there was a gap in the market, so I designed a road frame to fulfil this brief. Although we’ve not moved that project much further forward I’m really pleased to see that Condor have taken the batten and run with it with their Super Acciao. What this highlighted when we were talking about the road project was what we appreciated about steel; it’s durability, it’s strength, it’s feel and the look. I guess you could say there was an element of dogma involved, but it wasn’t that there were no advantages to using steel, it’s just that weight wasn’t one of them and we liked the other upsides.
Secondly, as i was kicking around the specification of the new bike with some of the guys I ride with and one of them asked why I didn’t just start with a BFe front end and graft the suspension onto that. His point being that with it’s 35mm seat tube and other large diameter tubes, it’s incredibly tough and strong and not exactly a shrinking violet when it comes to stiffness. With my firmly held assumptions I dismissed this out of hand, but when I mentioned it to Paul (Cotic’s organiser extraordinaire) he reminded me of our conversations about road bikes and asked why I hadn’t looked at it harder, so now my bluff had been called!
It was time to do some numbers and justify myself properly. Remember, one of the key things I wanted to improve on from the Hemlock was the stiffness of the connection between the front and rear ends, so I started with the seat tube as it’s where all the suspension pivots would be hanging from. This would be critical. I made a comparison between the 35mm aluminium seat tube we used on the Hemlock and the 35mm seat tube from the BFe. Let’s do a science bit now so you know where I’m coming from with this…..
Tubing stiffness comes from two elements; the material stiffness (the Young’s Modulus, or E) and the mechanical stiffness (Second moment of area, or I). Combine the two (EI) and you get compare the overall stiffness of the part you’re analysing when they aren’t in the same material. Usually rigid steel frames exhibit less stiffness than aluminium ones because steel is so strong that you can use it in small diameter, very thin wall tubes so despite steel being 3 times stiffer than aluminium as a material (E is around 77 for aluminium, around 210 for steel), the mechanical stiffness I is low because of the small diameter and thin wall. Because I is quartically related to diameter (d^4 is an element of the I calculation), increasing diameter from 35mm (usual steel down tube) to 50mm (usual aluminium down tube) makes the mechanical stiffness 4 times larger. And that’s before you consider that aluminium needs thicker walls than the steel tube. So the lack of material stiffness in aluminium is overcome by using mechanical stiffness. The reason you can’t build aluminium tubes as small and thin as steel ones is because aluminium is also very much weaker than steel (typically 300-400MPa Ultimate Tensile Stength vs 1300MPa for 853), so in simple terms the mechanical stiffness in aluminium tubes is a function of needing to use lots to stop is breaking.
So, that’s the simple version of the basis of my comparisons across different materials. The key difference in this case is that the mechanical stiffness is similar. The seat tubes being compared are the same outside diameter – although the steel is much thinner wall – and aluminium can’t play it’s ‘big’ hand here as you can’t go larger on the seat tube without running into all sorts of compatibility problems with front mechs, tyres, seatposts and seatclamps. So where the mechanical stiffness is similar, you mutliply it by the material stiffness (steel is 3 times stiffer than aluminium remember) and what do you know? The steel seat tube is massively stiffer than the aluminium one. Not a little bit, but massively stiffer. Sure it’s a little heavier too, but my main concern for this part of the frame is tying the suspension pivots to the seat tube as hard as possibly to give a solid ride feel. So, all of a sudden steel is in the game!
From here, the next stage is a full weight analysis of a steel version of the frame. The seat tube was a little heavier than the alumium one, so I needed to be sure that lot’s of ‘little bit’ heavier’s didn’t add to a whole lot heavier on the whole frame. The comparison was with the final 2011 spec Hemlock. Again, steel has the power to surprise. When you’re looking at making a hard riding bike that needs a lot of durability and strength steel comes into it’s own as it’s so strong and durable. Aluminium, conversely, needs to be used copiously in a frame of this type to make up for inherent low strength. That great big 50mm down tube on the Hemlock weighs about the same as the 38mm steel down tube on the Rocket, but the Rocket down tube is stronger. Same with the top tube. In fact the only place on the frame where it didn’t make sense to use steel was the swingarm, as the large machined pieces required for the bearing housings and dropout sections would not only have been unnessarily heavy, the machining of steel is very expensive compared to aluminium so it would have been much more to make. So the swingarm is aluminium in nice big sections to tie the pivots and axle together properly. Play to the strengths of the material in the location they need to be used.
What we ended up with is the Rocket frame, which is weight competitive with the similar aluminium bikes out there, but has a level of durability and stiffness which is really high. I also have to come clean at this point and also admit that I love how it looks too. There, I said it.
The key thing here is that steel was right for this application, right for the Rocket, where high loads are going into the frame from the long forks and the type of riding a 150mm travel trail bike encourages. This meant that the high strength of steel made the weight of the frame competitive with other materials with a level of strength and durabilty we were really happy with. In other applications – shorter travel frames for instance, say 100mm both ends – where loads are lower and the riding conditions aren’t expected to be as arduous, these don’t suit steel so well because you can’t go much lighter than the Rocket in steel whilst maintaining the durability. You end up with a short travel frame which would be very heavy for it’s class and massively over strength. So whilst the Rocket is a great use of the material, we won’t be dogmatically using steel for all the other suspension projects we’re working on. Just as with the Rocket, I’ll sit down and do the numbers and make an informed choice, only this time I won’t need pushing into it by other people 😉
I hope you’ve enjoyed these essays on the project. It’s been great to go into so much detail and really explain the processes and where all the ideas came from. We’ll have the first production frames shipped airfreight in mid-February for promotion purposes for a product launch, and at that point we’ll release photos because they will be the exact frames you’ll be able to buy in mid-March when the main bulk of the production arrives.
Cheers,Posted 6 years ago
but anything steel and skinny tyred seemed to be trying incredibly hard to look like it’d been built in a shed in Italy in 1953
didn’t look very hard then did you. ‘modern’ steel frames made with oversize tigged steel (spirit, deda, 853, true temper) are available if you look hard enough, some are made in a shed in italy but noodly stovepipe they are not.
38mm steel down tube on the Rocket, but the Rocket down tube is stronger.
38mm? pfft 1mm smaller than the columbus spirit down tube on a pegoretti.Posted 6 years ago
and that’s ‘only’ a road bike 🙄NorthwindSubscriber
OK, in case it wasn’t obvious enough that’s Cy’s message about the Rocket, no point replying on here to him unless he happens to be reading.
Your comparison with the Pegoretti strikes me as meaningless tbh, OD by itself tells you nowt without knowing thicknesses too, and road bikes have such different requirements for strength and impact resistance- you wouldn’t want to build a large, thin downtube on an mtb but you might do on a roadie since it’s less likely to get hit with a rock the size of a brick. The comparison with the old Hemlock downtube is sensible tbh.Posted 6 years agonicko74Member
MrSmith – Member
the doe-eyed market will love it.
the smart money is on a generic well proven taiwanese aluminium frame with a 5 year+ warranty and a proven history.
there are numerous options out there in the £899-£1100 price bracket.
I honestly can’t believe that this thread has gone on for 3 pages. “New Cotic FS costs money”. Whoop de frickin doo. The pricing of the Soul, Soda and Hemlock should have made it pretty clear that Cotic are more at the Orange end of the market than the On-0ne end; and given the price of the Hemlock, the Rocket was only going to be more expensive, as raw materials continue to increase in price.
If you like it and think it’s worth the money, you’ll buy it. If not, you won’t.
(I now think my £950 ’08 Soda is an absolute bargain!)Posted 6 years agowwaswasSubscriber
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