Q 1: What is the Renthal TwinWall?

A: The TwinWall is a handlebar designed, developed and manufactured by Renthal to achieve the best combination of strength and safety. The handlebar consists of two aluminium alloy tubes, one within the other.

The external tube is manufactured from an alloy which has particularly good resistance to mechanical damage and is anodised to prevent corrosion. The interior tube is manufactured from an ultra-high strength alloy and is hard anodised to give it increased wear resistance from twist-grip and control movements. Rubber seals are used to cover the ends of the outer tube to keep out water and cleaning fluids, etc. The handlebar is laser marked in the middle for accurate handlebar positioning.

Q 2: Why a large diameter handlebar from Renthal?

A: There is demand from off-road riders for a handlebar of larger diameter. The most commonly used triple top clamp fixing diameter for larger handlebars is 1 1/8 inch (28.60mm). The Renthal TwinWall handlebar is of this diameter.

Q 3: Why is the TwinWall handlebar so strong?

A: Within the confines of having a centre diameter of 1 1/8 inch (28.60mm) and the standard diameter at the control ends of the handlebar of 7/8 inch (22.22mm) we have used a wall profile which gives the best combination of lightness and resistance to bending. This, combined with the use of ultra-high strength aluminium alloys with good elongation and impact strength, results in a handlebar which will not bend except as a consequence of a severe crash.

Q 4: If the handlebar is so strong why does it need a cross brace?

A: It does not actually need the cross brace! The handlebar will run quite successfully without one. However, the addition of a cross-brace turns a very strong handlebar into an immensely strong handlebar.

Q 5: Why two tubes?

A: To eliminate the possibility of the handlebar breaking due to fatigue failure. This is virtually impossible because any crack which develops in the exterior tube will not propagate to the interior tube.

Q 6: Any other advantages in using two tubes?

A: Yes, there are further advantages. The outside of a handlebar can be damaged due to the over-tightening of the clamps or crashing. This damage, under very unfortunate circumstances can become the starting point for the propagation of a crack and eventually cause a fatigue failure.

A single wall bar must be made forgiving enough to be damage-tolerant while at the same time providing sufficient strength. The design of a single tube handlebar is therefore always a compromise between the two factors.

The Twin tube construction enables the use of two different types of material. The mechanical properties of the interior tube are different from those of the exterior tube. The exterior material of the TwinWall handlebar is chosen to be highly resistant to mechanical damage. The material of the interior tube is therefore protected from mechanical damage and can be selected to achieve maximum strength. With the TwinWall handlebar we can manufacture a bar that is incredibly strong and safe because we produce the combination that delivers the best of all possible worlds, without the compromise.

A: The Twin tube construction does not work for a 7/8 inch (22.22mm) diameter handlebar. This is because the interior tube does not have enough strength as it cannot be made large enough to withstand the stress, should the exterior tube fail. A failure in the outer wall would cause so much load to be transferred to the inner wall, which because of its small diameter would also fail due to lack of strength based purely on its small diameter. With the new larger diameter 1 1/8 OD bar the interior tube is of 7/8 OD inch diameter, the diameter of a standard handlebar and is therefore strong enough to ‘stand alone’ in the event of outer-wall failure. It is the same principle as used in aircraft structures. The principle of one part of a construction being able to fail without the whole structure suffering catastrophic failure.

Q 8: Does this mean that the new larger diameter Renthal handlebar is a better product than the standard size Renthal handlebar?

A: Both Renthal handlebars are excellent products. The vast majority of off-road motorcycles come with standard 7/8 inch Triple Top Clamps for which there is huge range of 7/8 inch handlebars available.

The Renthal 7/8 inch bar is the strongest, safest handlebar manufactured in this size. It withstands, without bending, the majority of crashes which a rider could have during a race. In a hard crash the bar will bend, saving possible damage to more expensive items on the bike. The Renthal TwinWall is much stronger than a standard 7/8 inch bar. It could almost be said to be too strong – almost to the point of being over-engineered. True, it will not bend except in severe crashes. However, the bar is so strong that it can transfer the loads generated in a crash to much more expensive and difficult to replace items such as a triple top clamps and the frame.

Q 9: Which Renthal handlebar should you choose for your bike: the Renthal larger diameter TwinWall or Renthal 7/8 inch bars?

A: You must consider the advantages and disadvantages that are important to yourself:

For the Renthal TwinWall: Immense strength and a virtual guarantee of elimination of a fatigue failure. Unlikely to bend except in severe crashes.

For the Renthal 7/8 inch diameter bar: Less costly and slightly lighter than the TwinWall, the 7/8 inch bar bends before other very expensive parts of the motorcycle in the event of a crash. Also, the 7/8 inch diameter bar does not require an expensive Triple Top Clamp with a 1 1/8 inch diameter handlebar fixing point.

A: Yes, it is slightly less flexible than a standard Renthal 7/8 inch bar. All large diameter handlebars will be less flexible than 7/8 inch bars made from the same material. This is purely a result of the increased diameter; the larger the diameter of the tube, the less flexible the handlebar. As basis for comparison, Renthal TwinWall is 14% less flexible than a Renthal 7/8 inch bar, a difference not really noticeable when riding. A handlebar of exactly the same dimensions made of steel would be 300% less flexible. This is because aluminium and its alloys are three times more flexible than steel. There is one exception to this: aluminium metal matrix alloys are considerably stiffer than other aluminium alloys.

A: We hard anodise the handlebar to reduce wear because the expected life span of a TwinWall handlebar is so long there might be problems with the twist-grip and other controls wearing the handlebar.

Q 12: Are the rubber seals really necessary at the joint between the inner and outer tubes?

A: Yes they are necessary, because even though there is an anti corrosion compound between the two tubes the seals physically prevent water, power washer fluid, petrol and other chemicals from entering. Some power washer fluids are quite corrosive and if they were to enter between the two tubes they could cause long term corrosion which is highly undesirable. Such corrosion could, eventually, lead to failure of the handlebar.

Q 13: Why do you not knurl the centre of the handlebar?

A: Knurling in the centre of a handlebar at the point of maximum stress, outboard of the triple top clamp handlebar fixing points is a serious stress raiser and is a starting point for fatigue failure.

Q 14: Which teams have helped with the testing of the Renthal TwinWall?

A: Kawasaki USA, Kawasaki Europe and Suzuki Europe helped with preliminary track testing and development prior to January 1998. Pro-Circuit Kawasaki, Chaparral Yamaha, Suzuki Europe and Kawasaki USA helped with final testing by using the handlebars in all races since January 1998.

Q 15: Why do you need all this endless rider testing: surely with modern technology you can simulate and calculate almost everything beforehand?

A: It is true that you can simulate and calculate most things at the design stage. Early prototypes were therefore sufficiently safe to be tested by top riders. However, there are many unexpected incidents which happen in racing which are very difficult to predict or simulate. For a critical safety product, such as a handlebar, we see exhaustive rider testing as an important safety measure, which cannot be compromised. With this new handlebar we can confidently say that it is one of the most exhaustively tested products to come to the market in the history of off-road riding.

TwinWall Handlebar Fitting Instructions