Touring frame design and materials.

The frame and forks are the heart of your bike and the most important part of it. Bike frames are mostly designed for general uses. That does not include loaded, open-road touring. If you want to be set up for the open road, what specific things should be included in your frame and fork designs?

Apart from materials, there are design issues that do not cost any more (or less) to make. Why not include touring capability in your commuting bike?

A simple thing to check for on a bike is how long it is. If you want to fit mid-size tyres for rougher places, plus mudguards, and then you also want to have rear

panniers, you need some extra length in the bike. Heels should not clip the rear panniers. Toes should not hit the front mudguards. 

Here is a list of things that make a difference:

Frame design points for touring frames.

• Longer rear (chain stays) to allow heel clearance from panniers. At least 450mm on a 700C bike.

• Long enough front end for toe clearance from mudguards, with particular attention on smaller sizes.

• Enough of a gap between the tyres and the top of the fork and the rear bridges joining the stays, to accommodate mid-size (35C) tyres and mudguards together.

• In case you get into expedition touring or carry big loads, or use a trailer, front disc brake attachment points should be included and the fork blades should be strong enough for the use of disc brakes with a loaded bike.

• Attachment points for front and rear carriers, mudguards, three water bottles, spare spokes, light cables, front and rear cantilever/V-brake bosses and possible  gadgets. Quality screws and washers to match these should be supplied.

• Bottom bracket height may be a little low so as to keep the overall centre of gravity low. 270-280mm from the ground. The bike is slightly more controllable.

• A more laid back frame with slacker (less vertical) angles than on a racing frame. This makes the bike softer and easier to ride. But not so laid back that you are not over the pedals.

• Less sensitive steering from a lower head angle and a little more fork rake. On a medium size, 71 degrees and 52mm rake.

• An overall longer frame further contributing to ride softness. On a medium size, the wheelbase should be at least 1070mm to give you the clearances for rear panniers and front guards.

• Very slight increases in the wall thickness of the toptube and downtube. Very slight increases in wall thickness don’t add much to weight but do significantly increase stiffness. Normal bicycles were not expected to have front loads so this is a specific suggestion for fully loaded bikes. Many people enjoy touring without using front panniers. But this frame improvement makes you ready for the journey that develops. Rigidity reduces as frames get taller because they are less like triangles. On all large size frames we move the wall thicknesses of those two tubes up just another .1 of a millimetre.  

This subject is a bit to esoteric for most buyers (and sellers) to be discussing. Sometimes this is a pity and, Cyclocross bikes, are in our view, wrongly suggested for touring because people are not paying much attention to frame design generally.

Steel and Aluminium as frame materials.

If you read our history page you will see that there was a five year period when we used aluminium tubing. It was a bike industry fashion at that time. Most shops would not even stock steel bikes in that period. As a result we had frames in both steel and aluminium in exactly the same geometry and within 20gm of each other in weight.

Some people, including our most experienced testers, deliberately alternated between cr-mo steel and aluminium frames to assess what the difference was in feel. These were “apples and apples” tests. In the literature there are frequent references to steel being more “supple” or “resilient”. It is supposedly more comfortable to ride, especially over a long day. We would love to confirm this but the conclusion from our testing is that there is not much difference at all. If there was some kind of blind test where people did not know what they were riding, most could not tell from the ride feel alone.

We surmise there is some passion for steel. People say ‘steel is real’ suggesting other materials are unreal. There is also a big vested interest in the custom frame building fraternity. Some people might have just confirmed what they already thought.

In any case, World Randonneur designers downplay the issue of resilience in opting for steel. It is not a black and white issue. Bikes are great. Less “technical” bikes will still provide good service. You can walk up mountains if you don’t have the gears. You still get there. As designers we are just trying to perfect a machine that is already amazingly good.

Here are a few reasons why we think steel has an edge over aluminium in the frames ridden for general use plus touring:

• The area around attachment points on aluminium frames is a little more prone to failure (especially the upper rear carrier mounts) whereas on steel frames it is not. To avoid this, aluminium tubing needs to be thick (and heavy).

• Steel is the most repairable of all bike frame materials. It is weldable, formable, strong, ductile and tough.

• A dent, caused by a fall or in transportation, both possibilities, is less likely to morph into a break-point on a steel frame than on an aluminium one. And on an aluminium frame, failure may in cases be sudden.

• Double butted cr-mo steel tubes can be both lightweight and very strong.

• Steel is really stiff compared to aluminium (three times more).

• Whilst it is true that steel rusts this is not a problem due to the quality of the painting process, even if you get scratches. A quality steel frame might well be in use when 50 years old.

• Steel uses less energy to produce and the world will never run short of it.

• If you were to ever have a serious crash, the chance of no harm to your bike frame is a much greater if it is a steel cr-mo frame and fork than if it is aluminium or carbon fibre.

We use 4130 steel, an alloy steel commonly known in the bike industry as chrome-moly or cr-mo.  4130 is by far the most common of all the steels used to build high quality bicycle frames. The 4 in 4130 represents steel containing nickel, chromium and molybdenum, as distinct from plain carbon, nickel, nickel chromium and other steels. . The 1 in 4130 defines the percentage of chromium and molybdenum in the alloy. The last two numbers, 30, mean that the percentage of carbon, expressed as hundredths of a percent, is 0.30%. 

The Society of Automotive Engineers (SAE) specifies many grades of steel.  If it is 4130, as used in bike frames, regardless of who made it, the composition is fixed and controlled by SAE.

Alloy composition of 4130 grade steel (by weight)
SAE grade	% Cr	% Mo	% C	% Mn	%P max	% S max	% Si
4130	0.80-1.10	.015-0.25	0.28-0.33	0.40-0.60	0.035	0.04	0.15-0.35

 

In double butted tubes, the outside diamater remains the same but the wall thickness varies. This produces a lighter but strong tube. Stiffness, needed on bikes, is influenced by the diamater and wall thickness on the particular frame size.