RE: Bicycle tech for Caterham
Discussion
Given that a carbon tub / parts can't be repaired after a crash it's difficult to justify the cost on the Caterham.
For cosmetic parts, this works fine, but for the main structure, for a carbon tub style chassis, the tooling alone for this is in the region of £10-25k for a mould.
Added to this the cost of the materials and lead time to construct at between 4-6 weeks initial build, then a further week for each chassis. Even with multiple moulds, factor in the skilled labour and prices would rise astronomically. For example, look at the price of a BAC Mono.
A steel chassis is more economically viable, and easier to manufacture, and a line could yield a chassis every few hours for far lower costs and infrastructure, I know having worked for Caterham for a year on their SP300R, the difference in production speed between something of a moulded chassis or bonded in the case of the SP300R to a Caterham 7 chassis was a lot, plus the much more skilled labour required to do so.
Agreed this isn't cutting edge technology, however saving weight without drastic cost increases is always a good way to go. Caterham would have to massively increase their list prices going to full carbon tub, which would reduce their market share significantly which isn't in their interests to do so. If and when I'm in a position this could be an option I'd tick for my own one.
There's also the performance, a well designed steel space frame chassis will have comparable stiffness to weight ratios to a carbon tub, the main bonus is what has been mentioned in that a steel chassis is repairable, compared to a carbon which has to be written off in a shunt, instead of being able to remove the damaged section and replace it.
For cosmetic parts, this works fine, but for the main structure, for a carbon tub style chassis, the tooling alone for this is in the region of £10-25k for a mould.
Added to this the cost of the materials and lead time to construct at between 4-6 weeks initial build, then a further week for each chassis. Even with multiple moulds, factor in the skilled labour and prices would rise astronomically. For example, look at the price of a BAC Mono.
A steel chassis is more economically viable, and easier to manufacture, and a line could yield a chassis every few hours for far lower costs and infrastructure, I know having worked for Caterham for a year on their SP300R, the difference in production speed between something of a moulded chassis or bonded in the case of the SP300R to a Caterham 7 chassis was a lot, plus the much more skilled labour required to do so.
Agreed this isn't cutting edge technology, however saving weight without drastic cost increases is always a good way to go. Caterham would have to massively increase their list prices going to full carbon tub, which would reduce their market share significantly which isn't in their interests to do so. If and when I'm in a position this could be an option I'd tick for my own one.
There's also the performance, a well designed steel space frame chassis will have comparable stiffness to weight ratios to a carbon tub, the main bonus is what has been mentioned in that a steel chassis is repairable, compared to a carbon which has to be written off in a shunt, instead of being able to remove the damaged section and replace it.
Sf_Manta said:
There's also the performance, a well designed steel space frame chassis will have comparable stiffness to weight ratios to a carbon tub, the main bonus is what has been mentioned in that a steel chassis is repairable, compared to a carbon which has to be written off in a shunt, instead of being able to remove the damaged section and replace it.
These are exactly the reasons why steel endures in bicycle frames despite CFRP frames technically outperforming them for at least 20 years. It has little to do with perceptions of "ride quality", etc. Steel frames (especially lugged and brazed) can easily be repaired, following dinks from lampposts and so on; moreover, they may have been designed and constructed by a skilled individual framebuilder in a shed (etc..) nearby, rather than a giant factory in a far-off land. A steel bike might be a personal thing that you were involved with the design of. Functionally, it's barely different from the mass produced CFRP bike from China which maybe weighs a sandwich or two less.Equus said:
wemorgan said:
I gather that crash simulations have been performed. I don't know the results, but imagine comparable performance to the regular steel was a target.
The problem with simulations is that they're not able to simulate the often complex circumstances of real-world accidents. You can run a 'simulated' chassis head-on into a 'simulated' concrete block, for sure (and even simulate diagonal front impacts), but the sort of racing accident that sees a car bounced end-over-end, or ricocheting between the armco and other traffic?
Let's be clear, the butted steel tubes that Caterham are using are regular steel (not any of Reynolds fancy alloys), just much thinner, except at the node points.
Sf_Manta said:
... For example, look at the price of a BAC Mono.
You're aware, I assume, that the BAC Mono has a steel spaceframe, not a carbon monocoque?Sf_Manta said:
... a well designed steel space frame chassis will have comparable stiffness to weight ratios to a carbon tub
That's simply not true. Not even close.Yes, but the high-energy, high acceleration crashes are a fairly manageable subset. The crash scenarios you described earlier are slow and generally use more the of energy absorption capability of the car - i.e. all four corners, so despite the infinite possibilities, they'd most likely be a somewhat lesser energy set of cases than direct impacts.
wemorgan said:
That's not an issue of materials, but design.
Agreed, but the two are difficult to separate.... if the Ariel had used much heavier gauge material, for instance, then the design flaw wouldn't have had quite such a dramatic effect.With the Atom, the problem was that you've got a curved tube (effectively 'pre-buckled') sitting across a very rigid, triangulated node point. It's pretty much like folding a cardboard tube over your knee.
The potential problem with the Caterham butted tube (and note that I said 'potential', before AER gets his panties in too much of a tangle; I'm merely speculating on the possible risks in the absence of any established track record of crashworthyness on butted-tube automotive spaceframes) is that once the chassis has distorted enough in an impact for there to be significant bending or buckling loads in the middle of a tube, instead of the pure tension/compression they're designed for, the very thin walls of the non-butted sections will have absolutely negligible strength and will just fold up with minimal resistance.
Edited by Equus on Monday 4th April 13:29
Jodyone said:
These are exactly the reasons why steel endures in bicycle frames despite CFRP frames technically outperforming them for at least 20 years. It has little to do with perceptions of "ride quality", etc. Steel frames (especially lugged and brazed) can easily be repaired, following dinks from lampposts and so on; moreover, they may have been designed and constructed by a skilled individual framebuilder in a shed (etc..) nearby, rather than a giant factory in a far-off land. A steel bike might be a personal thing that you were involved with the design of. Functionally, it's barely different from the mass produced CFRP bike from China which maybe weighs a sandwich or two less.
Subjectively, a steel frame is miles more comfortable than any carbon frame though. Quote - Subjectively, a steel frame is miles more comfortable than any carbon frame though.
The above is a wild generalisation.
A good designer can produce a layup which combines stiffness and comfort.
The reason most don't do it is because of the complexity of layup required, which translates into increased person hours to build the frame and ultimately its cost/sale price - the latter increasing exponentially the further back up the value chain the cost is incurred.
Any bike designer has to balance stiffness, ride quality, weight and durability.
Like everything in engineering, there are tradeoffs to be made. However, in all the stakes except durability, carbon fibre has more potential than any other current material used in frame building.
The above is a wild generalisation.
A good designer can produce a layup which combines stiffness and comfort.
The reason most don't do it is because of the complexity of layup required, which translates into increased person hours to build the frame and ultimately its cost/sale price - the latter increasing exponentially the further back up the value chain the cost is incurred.
Any bike designer has to balance stiffness, ride quality, weight and durability.
Like everything in engineering, there are tradeoffs to be made. However, in all the stakes except durability, carbon fibre has more potential than any other current material used in frame building.
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