Carry a passenger on my bike

[cwah]

Hello all,

I very often miss the ability to carry passenger when I go out... not fun when other are taking the tube while I cycle out....

I thought about this:

Weld another tube to the seat tube and add a motorbike seat to the bike.

What do you think?

 

[flecc]

I think with the weight of two people the seat tube could snap in two at the entry point to the frame.

They sometimes do that even with one person, but of course much depends on the weights of the people concerned.

 

[los monty]

I think with the weight of two people the seat tube could snap in two at the entry point to the frame.

They sometimes do that even with one person, but of course much depends on the weights of the people concerned.

Love the picture feel slim again

 

[billadie]

I think with the weight of two people the seat tube could snap in two at the entry point to the frame.

They sometimes do that even with one person, but of course much depends on the weights of the people concerned.

Damn! That wasn't meant to be published. I usually wear a helmet, honest.

 

[cwah]

It would be quite lightweight. About 130kg for 2 people I think.

So it shouldn't break?

 

[flecc]

I think that could well snap it, especially as the bike hits a bump in the road. Even with rear springing a jolt from the road surface is still transmitted as an additional force. It's the passenger's weight that's the main problem, applied so far back it's a severe bending force at the point where the seat tube meets the frame.

A Bowden cable connected from the top of the seat tube to the head stock and under tension would offset that tube breaking force.

 

[Gringo]

I think its a flawed concept, it's not just the seat tube but the whole frame was not designed for those type of stresses.
And then there's the law.

CARRYING PEOPLE & THINGS
According to the Road Traffic Act, two people are not allowed to ride a single bike (a ‘backie’ for instance, or carrying a standing passenger on a BMX bike with ‘stunt pegs’) unless the cycle is “constructed or adapted for the carriage of more than one person”, such as a tandem. If you carry a passenger on a bicycle which isn’t so constructed or adapted, you are breaking s.24(1) of the Road Traffic Act. Ditto for your passenger, unless the passenger is under the age of ten and therefore below the age of criminal responsibility. The maximum penalty for this offence is a fine of £200.

Unhelpfully, there’s no explicit guidance on what constitutes a bicycle “constructed or adapted for the carriage of more than one person.”

Highway Code, rule 68, simply states that the cycle must be “built or adapted” to carry “a passenger.”

While there is no case law to guide us, it seems expedient to mention that commercially-available child-carrying products, such as child-seats, would comply with this particular Road Traffic Act rule. That is so long as the passenger weighed the same or less than the maximum weight prescribed by the product and was fitted to the cycle according to the manufacturer’s instructions. A child seat which complies with the relevant European Standard would probably meet the requirement for proper adaption for carrying a passenger.

Carrying a passenger or passengers on a rear rack, not designed for the purpose (an Xtracycle rear rack with padded seat and footrests is an example of a designed for the purpose add-on), is also forbidden. Many people in the Netherlands carry passengers on their bikes but Dutch roadsters have beefy racks, usually much stronger than the sort of tubular aluminium racks common in the UK. However, it’s not the weight that’s at issue (many racks are rated to carry up to 25kg) but the practicality: dangling legs over a rear rack is dangerous and section one of the Road Traffic Act is concerned with safety.

 

[Clockwise]

I'm not sure a folder is the best choice of bike for carrying more people. When you are on a bike a large amount of your weight is on the pedals, adding the full weight of a person onto the seatpost/seat isn't good. If the bike wasn't folding and was a hardtail you could have it supported like a pannier and use a banana seat like on a chopper.

I wouldn't tho as it just creates lots of problems. To give you an idea a 10 stone person(63kg) is like lugging 63l of water, enough to fill a small shopping trolly with bottles?

 

[flecc]

A number of Brompton owners use add-on cycles, the rear end of a Brompton pivot attached to the seat post of the front bike, making it an articulated tandem. The Henshaw family of A to B magazine do this.

 

[MikeyBikey]

Brompton trailer tandem seemed only for children though, maybe too much flex for leverage applied by weight of an adult? Steve Parrys tandem brompton had a LOT of extra bracing for two! I bought one of those 'alligator' tow bars to try, way too floppy. Never managed to get anyone to try being passenger!
"Looked too dangerous" :-( . How about a sidecar!

 

[Geebee]

Theres even an instrutable Build a Bicycle Sidecar

 

[cwah]

I think that could well snap it, especially as the bike hits a bump in the road. Even with rear springing a jolt from the road surface is still transmitted as an additional force. It's the passenger's weight that's the main problem, applied so far back it's a severe bending force at the point where the seat tube meets the frame.

A Bowden cable connected from the top of the seat tube to the head stock and under tension would offset that tube breaking force.

I'm not sure how that would work. Do you have a picture or something to help a bit?

 

[cwah]

Theres even an instrutable Build a Bicycle Sidecar

that would completely kill the benefit of having a brompton lol

Or even a bike as it would become so massive.


My goal is to keep it small, otherwise I'd just buy a yunda mundo or equivalent

 

[cwah]

Something like this would be good:

Maybe not possible on a brompton

 

[jerrysimon]

Something like this would be good:
Maybe not possible on a brompton

Yes she does look nice. Alas I am married. I think that is what you need though

cwah your posts always make me smile and brighten up my day

As a kid I can see you with one of these always giving lifts to your mates.

Jerry

 

[Hugh]

cwah your posts always make me smile and brighten up my day


Jerry

I wish I could get some of whatever he's on

 

[flecc]

I'm not sure how that would work. Do you have a picture or something to help a bit?

Like this below, strong rigid clamps at headstock and top of seat tube with a Bowden cable inner pre-tensioned between them. Still not very satisfactory since you'd need to ensure the seat tube couldn't slide down in the frame under the load, slackening the Bowden cable:

 

[MikeyBikey]

that would completely kill the benefit of having a brompton lol
Or even a bike as it would become so massive.
My goal is to keep it small, otherwise I'd just buy a yunda mundo or equivalent

A cargo bike is the best solution, a Brompton is already operating at the top end of it's design strength with 1 on board, the rider. My 1992 Brompton developed the classic, fatal, main frame and triangle cracks. Brompton said it was "end of life metal fatigue" and tho they claim to have cured this with the new joints and stronger triangle, my 2009 Brompton does not look any stronger! So don't break your ride overloading it watch the "Team Clonc" vid on YouTube, they asked Brompton for extra bikes coz they broke ridden like the Berroca ad on tv.

 

[peerjay56]

I think its a flawed concept, it's not just the seat tube but the whole frame was not designed for those type of stresses.
And then there's the law.

CARRYING PEOPLE & THINGS
According to the Road Traffic Act, two people are not allowed to ride a single bike (a ‘backie’ for instance, or carrying a standing passenger on a BMX bike with ‘stunt pegs’) unless the cycle is “constructed or adapted for the carriage of more than one person”, such as a tandem. If you carry a passenger on a bicycle which isn’t so constructed or adapted, you are breaking s.24(1) of the Road Traffic Act. Ditto for your passenger, unless the passenger is under the age of ten and therefore below the age of criminal responsibility. The maximum penalty for this offence is a fine of £200.

Unhelpfully, there’s no explicit guidance on what constitutes a bicycle “constructed or adapted for the carriage of more than one person.”

Highway Code, rule 68, simply states that the cycle must be “built or adapted” to carry “a passenger.”

While there is no case law to guide us, it seems expedient to mention that commercially-available child-carrying products, such as child-seats, would comply with this particular Road Traffic Act rule. That is so long as the passenger weighed the same or less than the maximum weight prescribed by the product and was fitted to the cycle according to the manufacturer’s instructions. A child seat which complies with the relevant European Standard would probably meet the requirement for proper adaption for carrying a passenger.

Carrying a passenger or passengers on a rear rack, not designed for the purpose (an Xtracycle rear rack with padded seat and footrests is an example of a designed for the purpose add-on), is also forbidden. Many people in the Netherlands carry passengers on their bikes but Dutch roadsters have beefy racks, usually much stronger than the sort of tubular aluminium racks common in the UK. However, it’s not the weight that’s at issue (many racks are rated to carry up to 25kg) but the practicality: dangling legs over a rear rack is dangerous and section one of the Road Traffic Act is concerned with safety.

I'm fairly sure that Cwah is cycling in Paris, at the moment at least. But the general points you make are still valid.
I think Flecc's idea of a tension cable, combined with the additional supporting post going down to the rear suspension pivot point (assuming the diagram is accurate) rather than into the existing seat post, would be stronger. However, as someone has already said, a brompton is probably already at or near it's design limits.
Nice idea though Cwah

 

[GaRRy]

Been a long time since we have had a crazy idea from cwah.

Must admit this one is nowhere near the madest.

Now all we need now is Eddieo back and all will be back to normal.