Hello folks! Looking for some advice

C

Cassi

I'm a big dude, looking to get a recumbent trike to ride to and from work; try and get into better shape. (I specifically am looking for a recumbent trike because I'm heavy enough that I find regular upright bikes very uncomfortable to try and ride, but I've been using a recumbent exercise bike for over a year. I'm looking at a trike because it's been long enough since I last rode regularly that I don't trust my ballance anymore) I'm looking to DIY because boy howdy are recumbent trikes pricy, and I can't find any second-hand within even unreasonable driving distance. So, hoping I'll be able to build one.

Once the plans are back up for sale, what would folks suggest as the best plans to pick up for a trike for a really heavy rider, and what tips or tricks would folks suggest for construction.
 
The plans are already specified on the "safe" side in terms of Steel gauge etc. so at worst you might (in really extreme cases) go up one gauge.
The penalty is (of course extra weight of the frame). For example 3 metres (10ft) of 38.1mm square box tube with a 1.6mm wall thickness will weigh 5.5Kg (just over 12Lb). Step up to a 2mm tube wall thickness and the same length of steel will weigh 6.8Kg (15 Lbs).
If you look at many commercial tadpole trikes you will find they are very light Aluminium and that lightness comes with a weight limit. For many of the commercial trikes that is in the 300# or thereabouts range.
My advice is to get a length of the standard steel sections of about 10 foot and support each end and try standing in the middle, if it doesn't bend with your weight as a point load, then your distributed weight should be fine.

For 3-wheeled trikes people get a bit "nervous" about side-loading of the wheels, but you won't find too many (any) commercial trikes with a single-sided axle much bigger than 12mm and most have a spoke count of 36. It isn't necessary to go to 40 spokes.
Disc-braked front wheels are the norm, but Sturmey Archer drum brakes are easier to deploy and less "fussy" (IMHO).

By making your own frame and building your own wheels from component parts you can get a really nice recumbent for a good price.

Good Luck!
 
It's better to go up in size than gauge if strength/weight is the concern.
If ease of weld is a concern, then going up gauge is your option.

On wheels. Both our HP and Azub use 15mm shafts, and 36 spokes. Never had a wheel fail in itself.

On the other hand, I have a set of custom wheels now. Front, 20" RYD Andra 40 with Novatech hubs and 36 13 gauge spokes. Rear is 26" Andra 40 and -dare I mention it, a Rolhoff- with 36 spokes.
 
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I agree with Maddox. Going up in gauge is a better option for a heavier rider. Stresses are spread over a larger area.
 
Square 1" 16swg with 200lbs force at one end of a 24" beam gives 0.8" deflection. Double the gauge and that deflection drops to 0.54" but double the size to 2"square and it drops to 0.10". Both options double the weight so add the same amount of extra steel.

If you go past the point of elasticity to permanently deform the beam such as in an accident then I suspect the heavier gauge will handle deformation better
 
Popshot said:
Square 1" 16swg with 200lbs force at one end of a 24" beam gives 0.8" deflection. Double the gauge and that deflection drops to 0.54" but double the size to 2"square and it drops to 0.10". Both options double the weight so add the same amount of extra steel.

If you go past the point of elasticity to permanently deform the beam such as in an accident then I suspect the heavier gauge will handle deformation better
Click to expand...
How does aluminium compare like for like ?

Does this flexing add to the ride quality ?

Paul
 
2" square 16swg 24" long steel beam with a 200lb force at one end deflects 0.10" Aluminium in the same sizes deflects 0.29". It's not a good idea to have much flex in an aluminium frame because it will fatigue and as such an ally frame tends to use more metal than a steel one would to reduce the flex to a minimum. This is why ally frames are often no lighter than steel.

A very good point about ride quality Paul. Any road bike rider will quote you "only steel is real". This refers to a quality steel frame such as high end Reynolds tubing. These steel frames are very flexible and zero suspension plus skinny tyres means a massive difference in ride quality dependant on frame material. A lot of committed road bike riders will not use an aluminium frame because of zero give in it and is like riding a jackhammer. By comparrison a high end Reynolds floats over bad road surfaces. I'vevowned two Reynolds tubed bikes, one state of the art 40 years ago and one still state of the art. They were brilliant. Steel copes with flexing well and if you can calculate the loads each piece of frame will be subject to and not exceed elasticity limits you can select just enough steel to provide a better ride. Top end Reynolds tubes are 0.5mm thick in the middle and are thicker at the ends where they are brazed or welded. A traditional diamond frame is a perfect shape from an engineering point with tubes in tension or compression. Our frames are awful in utilising beams so 0.5mm thick steel is not an option here.
 
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