Lab or street? Both! How TOUR tests
Ride tests are essential, but laboratory tests are also important - an overview of the TOUR test philosophy.
What makes a good road bike? And how do you determine and quantify the more or less successful riding impression? Ride, ride and ride again? In any case, riding is a good idea, because after all, that's what bikes are made for. And of course there are some experienced testers working in the editorial team who have already tested many bikes and can make well-founded comparisons. But in addition to these subjective factors, objective facts traditionally play a major role at TOUR.
Our aim is to quantify driving impressions, put them into figures and make them objectively comparable. Where this is easy to do, measuring is common, for example with weight; after all, everyone has a set of scales standing around. But our ambition goes further. We want a reliable overall picture of a bike, regardless of the daily form of the test riders. That's why we also use laboratory technology to scrutinise the bikes. In the TOUR laboratory, we record stiffness values in several set-ups to determine comfort, riding stability and the reaction of the bike to hard pedalling.
As a performance criterion, we measure the aerodynamics of competition bikes in the wind tunnel. Together with the weight, this provides a good indication of how fast a bike rolls under which conditions - assuming the rider has the same performance. Based on the collected data and experience, we can make well-founded purchase recommendations and make things comparable that cannot be compared on the basis of manufacturer specifications, as there are too many different test and measurement methods in circulation.
Higher stiffness is very noticeable downhill. - Jens Klötzer, Test Manager
How TOUR tests: Downhill course
The truth is on the road. We set off with current and historic bikes to compare our test system and adjust the grading scales.
Somehow, all bikes move when there is air in the tyres. A Vitus Carbone 9, built in 1988, is no exception, but in principle a few hundred metres on the road is enough to understand how much development has progressed. In direct comparison to modern bikes, the butter-soft design of the Vitus is blatant. In hindsight, it's hard to understand why the Tour de France heroes once raced down the valley on it. With every manoeuvre, the frame's own life must be taken into account; the more the rider weighs, the wilder it becomes.
Our lightweight testers, who weigh around 70 kilograms, therefore carry up to 20 kilograms of well-belted additional ballast on the test rides. Keeping up with the best race all-rounder of 2023, the Specialized Tarmac SL8, proves to be impossible with the Vitus, even without ballast. In comparison, the Tarmac rides like it's on rails and can't be rattled at all. This shifts the comfort zone towards significantly higher speeds. More confidence means braking later and carrying more speed through the bends.
Old versus new
We ride the Vitus the full 520 metres down the winding side road on Monte Baldo near Lake Garda. It works, but it's not much fun, no matter how much the bike glistens and evokes nostalgic memories. Sorry, but this is inadequate by today's standards. Canyon's Endurace comes close to the SL8, but doesn't achieve the same level of fearlessness. Accordingly, we rank it slightly behind the Specialized in terms of riding stability. We cap the values at the top. More stiffness does not lead to an even better rating. The same applies to all other stiffness values that are capped (bottom bracket stiffness) or capped (front/rear comfort).
How TOUR tests: System stiffness
Which part of the road bike is particularly important when we plunge into fast descents? What is decisive for riding stability? The new TOUR test on riding stability has the answers.
Road cycling is a game with the forces of physics. The forces flow from the ground via the tyres, wheels, fork and frame, handlebars and seat post or saddle to the rider. What we feel is influenced by the entire chain of these components. Vertically, the frame, forks, wheels and tyres are quite torsionally stiff and together form our "chassis"; transversely to the direction of travel, the composite offers significantly less resistance. At high speeds, when turning into corners, over bumps or other influences, such as crosswinds, the laterally compliant road bike develops a life of its own, which is at the expense of riding precision.
The frame is the weakest link in the chain of tyre, wheel, fork and frame, through which the events are transmitted from the ground to the rider, and is therefore usually the dominant link in the riding experience. From a physical point of view, we are dealing with a series connection of springs; in this arrangement, the weakest link in the chain dominates the overall impression. This is easy to understand: If the tyre is slack, all control goes out the window, no matter how stiff the frame and fork are. We always measure the frame and fork together in our new set-up - just as they do on the road.
Stiffness values
This means that every road bike can be measured without exception, regardless of how the fork and frame are integrated. The combined stiffness of frame and fork is 9 Newtons per millimetre (N/mm) and more for very stiff systems (which we give a grade of 1.0), very weak frame-fork systems reach 5 N/mm or less and are given a "poor" rating. Such bikes are rideable, but are far beyond the current technical possibilities.
According to TOUR measurements, the lateral stiffness of the tyres is many times higher than that of the fork and frame at 40-50 N/mm. Wheels tend to be a tad stiffer; typical values are 45-50 N/mm for front wheels, extreme constructions reach 60-75 N/mm. The overall stiffness including tyre and front wheel is just under 7 N/mm for a very stiff bike. The overall stiffness is always lower than the smallest individual stiffness in the stiffness chain.
New test bench for driving stability
New clamping, new values: Very good frame sets achieve values of 9 N/mm and more.
With the new test stand for riding stability, we test the fork and frame together; we can include wheels and tyres in the calculations - so we have a complete overview of which component has which effect. The value range for frame plus fork is 5 to 11 N/mm. We consider values above 9 N/mm to be very good. The range of grades corresponds approximately to the previous assessment of separately measured frame and fork stiffness. However, a direct conversion of the previous unit (Newton metres per degree, Nm/°) into the new unit (Newtons per millimetre, N/mm) is not possible.
Interplay of forces
When leaning, changing direction quickly or travelling over bumps at an angle, forces are exerted at right angles to the direction of travel, which act on all components between the ground and the rider. More lateral stiffness increases downhill control of the bike.
Tyres, frame, wheels - how the influences shape the overall impression
- Frame and fork: They are the most compliant components in the chain of forces and therefore characterise the riding impression. Forks are generally stiffer than frames. We test the fork and frame together - as the bike is ridden in the test - and determine a stiffness value for the front part of the frame. Typical values for frame and fork are 6.5-10 N/mm. We test the rear end separately in the setup for bottom bracket stiffness.
- Impeller: The lateral stiffness of the wheels is relatively high. Flange width, rim type, type and number of spokes can double the stiffness of a wheel. Road bike wheels are between 35 and 75 N/mm; the most common values are 45 N/mm
- Tyres: On modern rims, wide tyres are relatively strong even at low pressure: the lateral tyre stiffness of 40-50 N/mm is roughly at the level of the wheels. The stiffness of the tyres naturally depends on the air pressure. There is a limit pressure for each tyre type. If the pressure falls below this limit, the tyre becomes laterally unstable and the handling becomes unpredictable.
How TOUR tests: Comfort on the handlebars
What do you really feel when riding over bumpy roads? With a new measuring method, TOUR makes comfort measurable on the handlebars for the first time.
Vertical forces also influence our riding impression on the road bike. On a smooth road, the differences are barely noticeable, but this riding condition is rare. In most cases, bumps in the road shake the system and are transmitted to the body in the form of shocks and vibrations; these are not only unpleasant, but also cause fatigue in the long term and reduce performance.
How much of this reaches the rider depends on the tyres and the air pressure used. On a road bike, however, the frameset makes a significant contribution to the impression of comfort. Good, i.e. comfortable framesets overlay the tyres, become the "weakest" link in the suspension chain and determine the impression of comfort, which in this case is a positive factor. High riding stability and comfort are not contradictory - a well-built road bike is laterally stiff, but flexible in the vertical direction.
The system concept takes effect
This is why TOUR introduced comfort measurements on road bikes back in 2006. At the rear, the frame and seatpost were always analysed together, as integrated seatposts were already an issue back then. At the front, comfort was previously measured in isolation via the removed fork. Today, however, it is almost impossible to replace the stem and handlebars with other brands; in addition, manufacturers advertise that they improve comfort with specially developed, compliant handlebar units. With our newly introduced comfort measurement at the front, we are continuing the system concept.
The frame, fork, stem and handlebars are regarded as a single unit, and power is transmitted via the brake levers, which is also where your hands are in most riding situations. Comparatively comfortable road bikes are more compliant on the handlebars than the best seat posts. Because the handlebars carry much less weight, significantly lower stiffness values make sense for a comparable impression of comfort. We rate values of 50 Newtons per millimetre and less with a 1.0. Suspension systems such as the Specialized Roubaix can achieve up to 20 Newtons per millimetre. Bikes with 150 Newtons per millimetre and above are rated as Poor.
How TOUR tests: Seating position
How do you sit on a road bike? Traditional frame measurements only provide limited information. New measuring points help with realistic categorisation.
The fit of a road bike determines how comfortable we feel on it. However, it is not easy to deduce how you sit on a road bike from geometry tables, as a number of individual dimensions determine the overall picture. The stack-to-reach (STR) quotient introduced by TOUR was the first to express whether a frame should provide a sporty, stretched or comfortably upright riding position. However, the increasing integration of handlebars and stem makes things more complicated. On the one hand, the stem and handlebars can often only be replaced with great effort in order to customise the riding position.
With one-piece carbon handlebar/stem combos, the choice of different handlebars is limited to the usually narrow range offered by the bike manufacturer, and changing them is extremely expensive. In some designs, such as the Cervélo S5, the handlebars are far removed from the typical standard dimensions. Established frame dimensions are therefore only of limited help, in some cases they are even misleading. In order to better characterise the seating position, we are introducing a new measuring point in our geometry measurement that includes the handlebars and stem.
The Stack+ and Reach+ coordinates describe the position of the hands on the brake levers in relation to the bottom bracket in the standard set-up in a comparable and relatively exact way (see below for details on the measuring point). The quotient of the two values Stack+ and Reach+ (STR+) is a realistic indication of whether you are sitting on the road bike in a sporty, stretched position with a lot of elevation or rather upright with relatively high handlebars. The spectrum lies roughly between 1.0 (very sporty) and 1.25 (very upright). In future, we will also indicate the values in the test reports; the graphical categorisation will also make it clear where the bike is positioned.
Measuring points
In future, our classification of the seating position on a road bike will include the stems and handlebars or handlebar units. As before, the basis is the measurement of stack and reach, i.e. the height and length of a frame measured from the bottom bracket to the mounting position of the stem. Instead of up to the end of the head tube, the measurement for Stack+ and Reach+ is "extended" up to an imaginary position of the hands in the brake lever position.
The measuring points directly on the handlebars are clearly traceable and exclude the influence of brake levers mounted at different heights, which can have a significant impact on the riding position. The values given apply to the lowest possible handlebar position, i.e. without spacers under the stem, but including the necessary covers.
How TOUR tests: New rating
The changes to the test procedure have an impact on the grading and presentation in our road bike tests. Here we explain what has changed.
Due to the readjustment of the test, old and new tests are no longer comparable on a one-to-one basis. This is regrettable, but unfortunately unavoidable. The scores will shift slightly, even if the grades are, as before, based on what makes sense for users and what is technically possible. New criteria and different weightings will make it more difficult to achieve the previous top marks. As we have contradictory requirements that get in each other's way - such as minimum weight and best aerodynamics or high rigidity and low weight - an overall score of 1.0 is, as before, not achievable.
New weighting of the partial grades
The best competition bike according to the TOUR classification, the Specialised Tarmac SL8The new weighting gives it a score of 1.5, which is mainly due to the fact that we have weighted the performance criteria of weight and aerodynamics slightly higher and the combined stiffness of the frame and fork slightly lower than before. The poor comfort at the front also pulls the score down slightly - comfort was previously completely disregarded for competition bikes, but is now included in the final score with five per cent.
Marathon racers and gravel bikes are slightly less affected by the changes. Important changes here are also the greater importance of comfort on the handlebars; we also give more weight to the ease of maintenance of these bikes. Here, too, there may be shifts in the grades, but these are in the range of a tenth at most in the final grade. At the end of the 2024 vintage, we will be able to take stock of how the bikes position themselves after the new evaluation.
In the long term, we expect manufacturers to continue to work their way forward with new tricks. Our benchmark in the respective categories remains achievable values. For example, we set values for the best aero grade that have already been achieved by test bikes. Stiffness values will continue to be capped where it seems appropriate. In this way, we try to set a reasonable framework for sensible further developments.
The most important changes in the TOUR test
- Weight: Weighed complete bike weight, without pedals and accessories, measured in the TOUR laboratory. Includes 25 per cent in the final score across all bike categories (previously: 20 per cent).
- Aerodynamics: Measurement in the GST wind tunnel. This is only recorded and graded for competition bikes and is included in the final grade with 25 per cent (previously: 20 per cent).
- Driving stability: Measurement of the system stiffness of the frameset in the TOUR laboratory. The proportion of the overall score is a uniform ten per cent across all bike categories (previously: frame 15 per cent, fork five per cent).
- Comfort: Comfort stiffness measurement on the test bench in the TOUR laboratory. Handlebar comfort has been introduced as a new criterion, accounting for five per cent of the final score for competition bikes and ten per cent for endurance road bikes and gravel bikes. The comfort measurement on the saddle remains unchanged, accounting for ten per cent of the overall score for competition bikes and 20 per cent for endurance road bikes and gravel bikes.
- Start: Bottom bracket stiffness measurement in the TOUR laboratory. The percentage is reduced from ten to five per cent for endurance racing bikes and gravel bikes. For competition road bikes, it remains at ten per cent.
- Equipment: The function of the gears, brakes and tyres are each given five percent of the grade for all categories (previously: ten percent each). The grading is based on component tests and impressions during test rides, but not on the price or weight of the parts.
- Maintenance and adjustment: Is only graded for endurance road bikes and gravel bikes and contributes ten per cent to the final grade (previously: five per cent)
Criteria and weightings in the new TOUR test procedure
Overview of the weighting of the test criteria in the various categories in per cent. The biggest difference is aerodynamics, which only plays a role in competition bikes - but an important one. On the other hand, the comfort of the bike is weighted lower, and is more important for endurance and gravel bikes.
The most important terms relating to the TOUR rating
- TOUR grade: Overall grade, formed from the partial grades and weightings according to the bike category.
- Info section: Manufacturer's website and available frame sizes of the test bike. The tested size is bolded in each case.
- Geometry: Comparable data on frame geometry and seating position measured in the laboratory.
- Equipment and partial scores: The most important equipment details as well as information on the mounted gear ratio, the effective (measured) tyre width and weights of the wheels, which are weighed including tyres, cassette and brake discs.
- Strengths and weaknesses: The spider diagram visualises the performance in the most important test criteria in the TOUR lab. This makes it possible to recognise at a glance where the bike has its strengths. The larger the blue area, the better the bike in question.
- Field of application: Depending on the gear ratio, seating position and additional features such as storage compartments or mudguard eyelets, this expresses the optimum area of use for a bike: A touring bike is orientated to the left, an aero racer to the right. The ranges can vary in width.
- Underground: Depending on the tyre width, tread and comfort impression, we assign the optimum terrain for the test bike. This area can also be narrower or wider.
- Seating position: Expresses whether you are sitting comfortably upright on the bike or stretched out like a racer.
Simulation calculations for professional races
Based on our own wind tunnel tests we carry out simulation calculations for professional races and publish them as part of the Tour de France Tech Briefings, for example. We analyse the question of which bikes can offer a technical advantage in which situation.
To do this, we set realistic power and weights for the drivers, combine them with our wind tunnel data and let the drivers race virtually over modelled sections of the track. Varying power and acceleration after corners make the simulation as realistic as possible. This is how we arrive at driving times for the sections of the track that are decisive for the race, which make the influence of the wheels visible - assuming that the drivers always behave the same way in a scenario.
