carbon fibre frame

[coln72]

G'day all,
I manage a team that races human powered in 24 hour events. As you can understand that weight saving becomes a significant issue for us.

In the past we have made the chassis of our vehicle from 2" CrMo tube with 1.5" CrMo (both 1.1mm wall thickness) for outriggers for the front wheels (the chassis is basicaly a big cross shape).

We are in a position to start building a new chassis and I am floating the idea of using carbon fibre tubing but I am unsure of the sizing I should go.

Do I stick with the current tube sizes (2" & 1.5") or do I need to go bigger or smaller diameter tubing?


Are there any issues that people have come up against using carbon tubing?

etc, etc..........
I know this sounds a bit of a dumb series of questions, but I need to start somewhere as the team has no experience with carbon.

Sorry, I dont have a picture of the bare frame at the moment, but here is a link to the finished vehicle from last year.

http://picasaweb.google.com/RacvEB/R...23997350496898

[Notso Swift]

Against Cr-Mo with CF you should go bigger and thinner

Now that I have said that I do not think you should do it
I presume you will not be making your own tubes with a custom layup, do you have access to the facilities to do it right, like an autoclave. Also Carbon has a tendency to fail in a spectacular way, where steel is more likely tp bend.

CF has strength in one direction only, unless you are sure of the exact stresses in each area you need to over-engineer for every area. As a consequence you find it is not lighter, and often les rigid.
Early bikes made in Carbon had this exact problems, remember the first carbon bikes appeared in the late-80's, yet it took until last year for the last of the pro peloton for the final manufactures to universially addopt CF. Those bikes that are finally light and stiff enough are usually monocorque, where they load up stress areas, or carbon lugged, since I assume (which I shouldn't do) you will not be in a position to use this sort of tech you will be using Aluminium (which services the majority of mid-range bikes). so now you need a secure way to bond the Aluminium to the carbon, then, after that you need to do an overlay. By the time you do this you are very close to the weight of a premium steel, but without the durability. I had one of these old style carbon bikes from about 1994 when it was high end tech (still own actually, just do not use it) and I can tell you that the thing is loose as all hell, very comfortable, but not exactly effecient.
Lastly good quality high modulas carbon is bloody expensive since the aerospace guys have spec'd in in the latest designs (esp the Boeing Dreamliner) the demand is outstripping supply for at least the next 10 years for the 4 big producers
Other options.
Oversize Alu. in a suitable grade, 7001. welded correctly it is very light, can be quite rigid, to its detriment as there is a high transfer of shock which can cause fatigue
Titanuim (usually alloy with Mg and Alu), unbeatable, the same weight as Carbon, the dynamic priciples of steel... a little dear which has killed it in the market: people want nice new carbon bikes that only last a few years, not a Titanium that costs 20% more but last 10 years! (me included with my nice shiny black Look)
Both cases (and with steel as well) double or tripple butted is the way to go.
Usinf the simplest tube on a bike as another example: seat posts, Alu is often ligher than cheaper CF and Ti is generally superiour again. The top CF that matches Ti cost the same, funny about that!

Check out the Columbus or Dedacciai websites, they make various tubing for custom frambuilders and they will have specs available (you may need to send an email, it may not be published)
Deda do Ti, but there are more manufactures with different alloys, google will be your friend.

[bludvl_x19]

G'day Colin.

As a fellow HPV Racer (this is one of our bikes from a few years back http://www.wonthaggisc.vic.edu.au/hpv/03-n15.jpg) I would suggest staying away from Carbon Fibre for mainly safety reasons. I have wittnessed a CF bike hit a pole at ~60km/h, and it just exploded, with fragments going everywhere. Once CF fibres go into your skin, they cannot be removed, which is one reason that I will never get into a CF-framed or -skinned bike. Also, CF has no real performance gain over Aluminium or Cro-Moly in this application, and believe me, the team I used to/still race for have investigated this avenue thouroghly (sp) over a number of years.

May I ask your reasons for going for CF? What weight is your bike (sans rider) currently?

My suggestion, if you haven't already, would be to look at your frame and see if there are any bars that can be removed without damaging the structural integrity of your bike.

If you still want to go down this route, I could suggest talking discreetly to some of the teams that already use CF, I would say talk to BYR, but good luck getting anything out of them.

Cheers,

Mick

[AU N EGL]

I am not sure of the HPV rules, but as an ex bicycle racer, 1970 - 1990 (sans 1977 when I race cars for a year) why dont you just use a normal racing bicycle? or a semi time trail with disk wheels.

Have all your riders the same size, so minimal seat hight changes are needed with rider changes.

Good Luck with your project.

[bludvl_x19]

The basics of the HPV rules state 3-4 wheels, all braked, and must have headlights.

TT bikes are actually inferior to the recumbent design, as the low frontal area of the recumbent overcomes any losses due to not being able to use your weight to turn the pedals, an once you have a cadence, it is remarkably easy to hold.

Just for people's info, thse races are held over 24hrs, with eight riders pedalling the bikes. Very rarey does the winner fail to cover 800kms in the 24hrs, and top speeds during the races are ~65/70km/h depending on the rider and the bike (although Trisled managed to take a bike to over 100kmh in the Burnley Tunnel, unfortunatly they have removed their link)

Mick

[AU N EGL]

Originally Posted by bludvl_x19

The basics of the HPV rules state 3-4 wheels, all braked, and must have headlights.

TT bikes are actually inferior to the recumbent design, as the low frontal area of the recumbent overcomes any losses due to not being able to use your weight to turn the pedals, an once you have a cadence, it is remarkably easy to hold.

Just for people's info, thse races are held over 24hrs, with eight riders pedalling the bikes. Very rarey does the winner fail to cover 800kms in the 24hrs, and top speeds during the races are ~65/70km/h depending on the rider and the bike (although Trisled managed to take a bike to over 100kmh in the Burnley Tunnel, unfortunatly they have removed their link)

Mick

Ok Mick

Thanks. I know recumbent have their advatange in many places. Old mt climber here so when ever some one mented that recumbent were better, I would take them for a ride into the big hills or mountains.

Good Luck with your project and race.

[bludvl_x19]

Originally Posted by AU N EGL

Ok Mick

Thanks. I know recumbent have their advatange in many places. Old mt climber here so when ever some one mented that recumbent were better, I would take them for a ride into the big hills or mountains.

Where they promptly got off and wlked their 'bent up the hill.

Nah, plans are for not racing anymore, I've left school for uni, and I have no plans to ride again. But plans change.

Mick

[bludvl_x19]

I would recomond talking to Ben at Trisled www.trisled.com.au as they have experience with composite bikes, and as a commercial operation, would be more than willing to help you out.

Mick

[coln72]

Thanks for your input guys.

An ex rider has some contacts in a team that uses CF on the production side but not on the exact tubing size yet which is why I am picking your brains.

Ready to race in last years event we were sitting on 27kg when it was weighed during scruitineering. The lighter bikes in our class were about 22 to 24kg. Unfortunately, I dont think we can remove any bars as over the years I have found that we need them. If fact it has been made stronger over the years that I have been involved (strong enough to survive an impact into the barriers at 50km/h).

Another reason is that we need something else to talk about during the presentations.

If you are interested here is the link to the event
http://www.racvenergybreakthrough.net/Default.asp

[bludvl_x19]

In my experience, around the high 20kgs mark is about bang on the money, you aren't going to be able to go much lighter without jepordising the integrity of your bike. We had bikes that weighed 18kg each, and we found that they were just too light, they need to have a bit of weight in them to survive the Berwick Bump (an overtaking manouvre that I have been on the wrong end of many a time.) I think that the design that you have is suitable for the purpose, are you just going to CF to say that you have a CF bike? I'm not being critical, I'm just seeing if you have thought about the reasons for going to the composite.

Another thing that I am interested in is, having competed in 5 RACV Energybreakthroughs, and numerous others, how are the students going to be able to build this bike (or at least bluff that they did)? As I understand it, this is a major component of the Design and Construction award.

I'm intending on going to this years race, I'll look out for you. I'll be with Notre Dame, probably pit crewing.

Cheers,

Mick

[coln72]

purchase CF tubing and the students cut to size and hot glue together into its final form. This is when myself and and ex team member reinforce and tape the joints (I'm not going to be more specific than that ).

The main reason for trying cf is that I am sick of the kids sooking about we would be 5 sec a lap quicker if we had a cf trike........ Hopefully it will shut them up if we are not and if we are that would be great

Yes the Berwick Bump, I am familiar with that one. Fire Truck is damn hard to roll

[bludvl_x19]

Originally Posted by coln72

purchase CF tubing and the students cut to size and hot glue together into its final form. This is when myself and and ex team member reinforce and tape the joints (I'm not going to be more specific than that ).

The main reason for trying cf is that I am sick of the kids sooking about we would be 5 sec a lap quicker if we had a cf trike........ Hopefully it will shut them up if we are not and if we are that would be great

Yes the Berwick Bump, I am familiar with that one. Fire Truck is damn hard to roll

wink wink. Can't say that sort of thing doesn't go on. And thats where I stop talking

How about this, in motorsport, and sport in general, it's about finding time any way you can. Training is a great way of finding time, and cheaper too. Get them out on their bikes!!

Mick

p.s. Fire Truck can be rolled, ya just gotta know where, and when to hit it.

[coln72]

thats the plan too

"p.s. Fire Truck can be rolled, ya just gotta know where, and when to hit it. "

please do tell

[Notso Swift]

Looking at what you guys who know what you are talking about have said I can only come back with one thing

Titanium!

If you really want to blow every one else away then maybe Magnesium, but that is just getting silly

[bludvl_x19]

Originally Posted by coln72

thats the plan too

"p.s. Fire Truck can be rolled, ya just gotta know where, and when to hit it. "

please do tell

It's a bit easier to explain person to person, but I'll give it a go.

Approaching the corner, let FT go outside you, when it turns in, turn across it's tail at about the back of the rear wheel. Keep turning through it, and over she goes. It works really well because the marshals are looking at the bikes coming towards the corner, once you start exiting the corner, they have already forgotten you. Just be prepared for the entire Berwick squad to come after you if they find out who did it.

Actually, this works for every 3 wheeler, you just have to adjust the point of impact depending on the bike.

Mick

[coln72]

if other teams start playing dodgems with us I'll think about what you said Mick.

Notso Swift - give me some and a welder to stick it together and we'll use it

[bludvl_x19]

Originally Posted by coln72

if other teams start playing dodgems with us I'll think about what you said Mick.

Notso Swift - give me some and a welder to stick it together and we'll use it

How do you think they start?

Back to the topic, Al is the best material to use because it is relativly cheap, easy to work with, doesn't shatter the same way that CF or fibreglass, and it's light to boot. Just stick with what you have and focus on improving the riders, the training process, and the strategy that you use for the race. Just my opinion though.

Mick

[coln72]

I have an issue with Al, as another one of our schools bikes was Al and it had all sorts of issues with cracking and bending the main frame.

For us it would be the same learning curve as CF. Guess I will have to check out our budget and see if I can make a CrMo frame (with an Al roll cage as we usually do) and experiment with CF.

[bludvl_x19]

[quote=coln72]I have an issue with Al, as another one of our schools bikes was Al and it had all sorts of issues with cracking and bending the main frame.[quote]

Im gonna go out on a limb and say that you broke the back ie the main part of the cross going towards the back wheel? If that's what it was, then I know a fix for it, to stop that happening, give me a PM if you want more info.

Mick

[coln72]

It broke everywhere from memory, but it wasn't my trike