Optimum tyre width
One should look at rims and tyres as a system. The internal width of a rim determines the shape of the tyre. And to get the most ideal shape – and with it the function – of the tyre, one should adjust the width of the rim to the width of the tyre. Or the other way around of course. But because every tyre manufacturer has its own ideas about the perfect shape of the tyre, users having their own ideas, it is hard to say what the exact right combination is. There is a certain bandwidth that makes the most of a tyre-rim combination. Outside this bandwidth tyres will still fit the rim, only the function of the tyre is less than optimal because the tyre is out of its ideal shape or the air pressure is too high to avoid distortion when cornering. But it is not wrong per se. The optimum tyre width we state is also a guideline, based on our experiences and insights though. Feel free to experiment a little to find your optimum.
The maximum load – and thus the maximum weight put on the bicycle - for a rim is based on two factors: strength and stiffness. Let’s start with strength, in which case we can immediately state that there is no hard limit. If you are a ‘smooth’ rider traveling over even underground, the load on the rims will be much lower than if you are a rowdy biker, jumping everywhere and hitting every pothole. Luggage on a bike counts as dead weight, which has a much bigger impact on the load on a rim than a rider that will absorb a lot of the bumps by slightly hovering above the saddle and unweighting the bike that way. We set the maximum weight on the lower site, just to be clear. But we have built in a margin and you may decide for yourself if you want to take a risk. But have a closer look at the ‘intended use’ of a rim, that will give a good indication if a rim suits your use.
The maximum weight we state is the fully clothed rider and the eventual luggage. So we do not include the weight of the bike.
Apart from being less strong, a lighter (aluminium) rim will also be less stiff if you compare rims of equal width. Where as the strength of a light weight rim can be sufficient, the lower stiffness can have such an impact on the handling of the bike that the rim is not suited for the intended use. In that way, the relatively low maximum weight gives a good indexation if the stiffness is enough for your weight. On the other hand, smaller diameters automatically make for stiffer wheels. Please discuss with your wheelbuilder what is the best solution for you.
Maximum tyre pressure
|Bandenmaat mm||Ozone 24||Ozone 30|
|40||4 bar||4,2 bar|
|45||3,5 bar||3,6 bar|
|50||3 bar||3,1 bar|
|55||2,5 bar||2,8 bar|
|60||2 bar||2,5 bar|
Directional spoke holes
To avoid tension between the spoke nipple and the spoke, the nipple should be as aligned with the spoke as possible. And because the spoke is angled towards the rim – sideways and from front to rear – the hole in the rim for the nipple must be drilled under this same angle. The other advantage of these directional holes is that the hole can be marginally bigger than the spoke nipple and a smaller hole means a stronger rim. All RAD15 spoke holes are drilled under the correct angle for that rim.
The term ‘hookless’ is used for bicycle rims without the edge pointing inwards at the top of the side of the rim, the so called ‘hook’. The function of this hook is not to avoid the tyre jumping off the rim. Look at car or motorcycle rims, they do not have this hook and the tyres still stays on. It is the height of the combination of side wall and the rim bed (!) that prevents tyres jumping off. So this hook can be left away on a bicycle rim as well.
Hookless rims can be slightly lighter without the hook, think approximately 20 grams for a rim. But a bigger advantage is that the wall of the tyre is seated in a better way because it is not pressed inwards by the hook. And the same effect as with wider rims occurs here as well, although on a smaller scale: the tread is supported better by the side walls and unwanted movement is prevented further.
On the other hand, the wider edge on top of the rim wall with a hook protects the tyre against snake bites when a tyre is punched all the way against the rim by an obstacle. If you only leave away the edge, the top of the wall gets really narrow, almost sharp and will cut through a tyre in case of a good hit. By making the wall slightly thicker altogether or putting the hook on the outside solves this problem.
Rims are developed with a specific use in mind and are optimized for that goal. But still you will get an overlap for other uses. A very sturdy rim can be used for anything, but will be unnecessary heavy for some uses. The list below is as RAD15 sees the intended uses. Feel free to give it your own interpretation though.
Take in account that luggage put on a bicycle behaves differently than an anticipating rider. Do not under estimate the effect of ‘dead’ weight and play save when it comes to choosing a rim.
Beside the ‘intented use’, we have made a second grouping with light (L), medium (M) and heavy (H) use. This should clear up the overlap between different uses. It is also a guideline to educated guesses for what you actually need. If you are a heavy weight rider or destructive towards your material, you might consider stepping up a category. And the other way around, if you are light weight, clean rider or just love to take risks, you might try a category of rims lower.
XC- en marathon-racing, more focus on climbing, less challenging terrain, wheels on the ground
Up & down, rougher terrain with small obstacles, small jumps and drops
Strong focus on descending, rough terrain with bigger jumps and drops
Descending only, lots of obstacles, big jumps and drops
Smooth surface, possibly unpaved, no obstacles or jumps
Trekking Light (M)
Smooth surface, possibly unpaved, small obstacles, maximum 15 kg luggage
Smooth surface, possibly unpaved, small obstacles, maximum 40 kg luggage
The speciality of RAD15 is the possibility to offer every kind of spoke hole count or spoke patern in small series or even single rims. You need a 24” rim with 40 spoke holes? Or spokes placed by 4? Without a stiff upcharge, RAD15 will be able to offer most wishes within a reasonable timeframe. Send us a mail for an offer. Please note that this service is not yet fully available now, but will be later this year. Again: contact us for what is possible now.