Carbon fibre front stay and subframe

[cal44walker]

http://www.carbonmods.co.uk/Products/Ca ... MK750.aspx

I was looking into the possibilities of making a few carbon fibre front stays and rear subframe. Anyone had a go at a project like that before?

Matt

[theoutsider]

There is a reason why the subframes on bikes are all steel or ali,because it needs a lot of strenght.If you do your in carbon it may hold your weight without actually riding the bike,but in the first bend it will snap like them cheap pack of crisps.About the front stay I`m not sure if it needs strenght but there is no point in making one,it won`t make the bike go any quicker,and the standard one is not that heavy.Good luck anyway but I hope I won`t buy your bike on ebay because you died or something

[ozracer]

The reason they are made from steel or ali is because it is cheap. The Ducati MotoGP bikes frame and swingarm is made from carbon and it doesn't snap. It's actually too stiff. The carbon would have to be fairly solid for the subframe though.

[Cammo]

A South African member on the old forum (about 5 years ago) had made a 1 piece carbon fibre subframe/seat unit for his race nc30. You don't need a subframe if the seat unit is strong enough to hold you.

It was proper vacuum formed stuff and would have been plenty strong enough. Also looked wicked.

[Spike16]

if ur on about making a rear subframe ul need it pre-preged and really strong in the right places, not an easy task hence even 125gp bikes have a small ally tube subframe to support them. front subframes are alot easier but it will be quicker and easier to make a tube one from ally

fair shout if u wana make one tho its possible and would be good and light if its successful

[vfrman]

I have a carbon front stay on my NC30. Michael Austermann made it for me along with a custom carbon dash and carbon infill panels.

[g-force performance]

There is a reason why the subframes on bikes are all steel or ali,because it needs a lot of strenght.If you do your in carbon it may hold your weight without actually riding the bike,but in the first bend it will snap like them cheap pack of crisps.About the front stay I`m not sure if it needs strenght but there is no point in making one,it won`t make the bike go any quicker,and the standard one is not that heavy.Good luck anyway but I hope I won`t buy your bike on ebay because you died or something

I beg your pardon Outsider, but that was a really off-base post. If you pick up any magazine regarding Formula-1 cars, you will see that the majority of the chassis parts, including the steering arms can be made from CF. Looking at the MotoGP bikes, many of the rear tail sections are one-piece (monocoque) designs that are all CF seat/tail section combos. The old Aprillia 250GP racer very successfully used this design for many years. Now let's go to aircraft. That's where CF was pioneered. Many aircraft are made from over 70% CF including main airframe components and severe structural components.

The reason that CF is not found in production bikes is because it is EXTREMELY EXPENSIVE and requires very expensive machines (vacuum furnaces and autoclaves). It would be cost prohibitive to make parts for a production bike and be able to sell it to the average customer. Bikes like the $250,000 Brittan have mostl CF parts because that's what the bike is about. CF is actually stronger than Steel, which is stronger than Aluminum, which is stronger than Magnesium (which some subframes are made from). It's also the lightest of the bunch. But....you do have to know what you are doing. THAT'S the tricky part of working with CF. You really have to understand mechanical engineering and the properties of CF to know how to best make the parts.

That said, we are looking to work with a "proper" CF shop to make a tank, seat section, airbox, front fairing stay, and any other parts that we can to lighten the bike. (to add to my rebuttle to your post, the upper fairing bracket can benefit the bike's turn-to-turn transition because the weight is removed from up high and forward of the bikes CG). If anyone is interested in teaming with us to get these parts developed, please let us know. I have a few CF experts in mind here, one being a former aerospace CF expert.

Cheers,

Mike Norman
G-Force Engine Development
http://www.mngforce.com

[RonniB]

Hi Matt,

front fairing/clock stay I made last year (and Lange made one before that), I used industrial prepeg plate that were cut to size and I bonded it with epoxy and rivets. weight is 230g compared to the two stock units which is 800g and tyga alloy version which is 450g. Easy to make and very strong (can rock the bike from side to side holding the tip of the stay).

Durbahn has made carbonfibre subframes with success in the past, look at www.durbahn.de (pay attention to the RC30 and 51 projects), this without autoclave or vacuum, just oven and good moulds.

You can make effective, but ugly, carbon structures by using the foam method, basicly you make a slightly undersize styrofoam part, cover it with carbon (thickness is vital) and let it cure under pressure.

But for price/efficency I think a alloy subframe (very small 600g) is a better choice, that what you see on 90% of the moto2 bikes aswell. Durbahns lightest subframe was just over 500g, with years of development. You can make a alloy subframe (using 20x20mm square tube and a few alloy rivnuts) in a couple of hours (if you can weld)

Ronni

[tygapaul]

Leaving aside the idea of a carbon subframe, there is another issue with regard to a carbon self supporting seat unit and that is the practical one. For most of the riders of 400s there are still a lot of electrical components (battery, coil, regulator, CDI) that need to be housed under the seat cowling and the easiest way to access them is to remove the seat cowling to reveal all the components so they can be worked on. GP bikes are designed not to have any components under the seat cowling (traditionally the home of the exhaust) and all the electrical parts are located near the frame or up front.

On an NC30 or NC35, you could do the same as on a GP bike but there is precious little room within the confines of the engine/frame area. The other way would be to have the components held within the seat cowling and then simply unplug the harness by putting a big plug inline. Undoing each component just to get the seat cowling removed would be somewhat counterproductive to making things simplified by doing away with the subframe though the weight saving benefits would still apply.

A separate carbon subframe is relatively simple to make but quite expensive depending on the target weight and complexity of parts expected to be attached to it.

There is another reason GP bikes use more carbon than your average race bike and that is that in the event of an accident, the repair of components is of minor concern. However for most riders in most circumstances, in club race for example, it would be preferable to sustain a bent alloy meter stay in morning warmup (that can be bent back in shape) rather than to have a super stiff carbon one which transfers all the energy to the components around it resulting in possibly more damage to say a fairing. This argument has been used regarding step hangers where it can be considered beneficial for the hanger to bend a little in a crash rather than risk snapping of frame lugs etc. because the hanger is too stiff though. How much is here say and how much is fact I am not sure.

[RonniB]

Paul got some valid reasons and good logic.
But it's very easy to move components away from the underseat area on a race bike, it helps weight distribution aswell, parts/steps needed is:

- Stick coils or new rear coil bracket (can be mounted on front sprocket cover upper edge)
- Lipo or small Lead/acid battery (max 4ah) positioned on the side of engine, under engine (Lead/acid) or on top of airbox or in the front fairing (Lipo)
- HRC or integral rear brake resovoir
- CDI moved to front fairing, airbox top or side of engine
- Reg/rec removed (total loss) or repositioned to side of engine or frame spars (genny retained)
- New wireloom to accomodate the above

Then only thing to consider before making the selfsupporting seat, is where to fasten the rear of the fueltank and the exhaust, both could be integrated in the seat design.

Personally I would go for a Speedfiber RSW seat unit in carbon (800g) and a bespoke alloy subframe (approx 600g, Rick O is 800g and it's quite bigger than needed to accomodate OEM cdi, reg/rec and other mountings). Then you got a seat unit/subeframe weight of 1400g, which is 100g heavier than durbahns lightest selfsupporting setups.

But if you go with the carbon subframe I would love to watch from the sideline, sounds wicked

Ronni