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Technical discussion / What is the difference for 3k, UD and 12k ?
« Last post by Andy on November 04, 2016, 04:38:19 AM »
The main type of carbon fiber used for the manufacture of bicycle parts are normal tow (under 12000 fibers) carbon fiber, like T700, or commonly known as 3k, 12k weave, and UD(uni-direction) carbon fiber.

Bicycle components, specifically carbon frames & rims are made using various grades of carbon fiber characterized mainly by their tensile strength and tensile modulus. Tensile strength is the amount of force needed to cause the fibers to break, while the tensile modulus is a measure of the carbon fiber's stiffness.

The cost of carbon fiber goes up with the increase in tensile strength, or increase in tensile modulus. And for carbon fiber weave also determines the cost of material with larger weave prepreg (eg.12k) costing less, due to the lower cost of manufacturing.

Carbon fiber layer(prepreg) has maximum strength only along the lengths of the fibers. That is why almost all the inside prepreg are using uni-directional carbon fiber while making carbon rims & frames. But the inside layup charts are still not identical. For example, the orientation are different( some are placed at 0 degree, some are 45 degree, 90 degree). This is very important to make carbon rims & frames with good strength & performance. That is also why using uni-directional fiber instead of woven carbon fiber (eg. 3k, 12k) creates stronger frames & rims.
Thus, the main use of woven carbon fiber is for appearance. But there is one mechanical benefit for 3k woven carbon fiber. Putting the 3k woven carbon fiber around hole area, it can prevent carbon fiber from laminating while machining holes.

For the weight difference, woven fiber has some area pass across each other. So, woven fiber is heavier than UD fiber. But, for rims, the size of carbon fiber is not large and only one layer different, the weight difference of woven fiber (3k &12k) and UD fiber is not big. Also, all rims have a weight range, for rims, it is +/-15g. So, sometimes, 3k rims & frames are lighter than UD.

For big size product (like frame), 3k frame will be heavier than UD. And for 12k, the weight different is not much difference.
Technical discussion / Road Bike Tire PSI Guide
« Last post by world bikes on November 04, 2016, 04:29:27 AM »
What is the correct road bike tire pressure to run?

As known to all that tires will mark recommended tire pressure, but according to the weight of each person is different, will also need to make adjustment on the tire pressure, this is a university asked, let's see how tire pressure to set.

Tire pressure, the higher the better?

Many cyclists are fond of playing the tire pressure to the top, because they feel that the grounding of the smallest of the tire, rolling resistance will be smaller, but in fact, the tire pressure too high, not only can't ride faster, instead it will consume their own strength faster.

ZIPP original said: "in general, for the average rider, we recommend tire pressure up to 140 psi ~ 120 psi minimum, this pressure values from the test, if more than 140 psi will increase the rolling resistance."

" exactly how to run tire pressure " has been a problem let everybody have a headache, but most of companies recommend not more than 140 psi, bellow is the suggestion scale:

It appears from the above chart that stubbornly making tire pressure high does not seem to be the most correct way, but must consider traffic, terrain and weather conditions. The following are several reasons for why the tire pressure is not suitable to hit the highest.
Technical discussion / Mountain Tire Pressure Table
« Last post by world bikes on October 27, 2016, 11:14:49 PM »

Tire resistance test results show that, in a very low tire pressure, the tire's resistance is high. With the increase of tire pressure, the tire rolling speed is faster, but the performance of the increase in certain tire pressure (Critical tire pressure) began to become flat. Later, higher tire pressure can only give a very slight increase in the performance of the bicycle. The reason is that with the increase of the tire pressure, the internal loss caused by the deformation of the tire is reduced, but the suspension system damage caused by the body vibration and rebound caused increased.
Under the critical tire pressure, it can optimize the comfort level, and also optimize the riding performance. At lower tire pressure, the tire rolls slowly. But higher tire pressure will not make you ride faster, but make your comfort level lower.
In addition: there are many factors on the influence of tire pressure, the table is for reference only.
1.   Tire quality: different tire quality use different pressure, the reason is very simple, just like the same ball basketball and football needs of the pressure is completely different, because the material is different to the hot melt, it has more than one kind of silicone material need a very hard of the tire to support, but if a class of rubber tires to beat 40 pounds that will be like a rubber ball bounce like everywhere.
2.   Road conditions: in theory, the soft tire pressure will help to increase the road holding, but the burden on the tire larger, wear is also larger, and the stability of the brake is poor. So if the car is used to riding Hill Road, if considering the road holding these drawbacks are acceptable; but if the downtown streets riding will consider to economic.
3.   Handling habits: the tame owners need comfortable tire pressure; the violent acceleration owners need hardcore tire pressure; the pressure Bay owners need the softer tire pressure.
4.   Climate: tire pressure of empty bike is different than when riding with half an hour later. Because the gas will change density as the temperature changed, so often occurs though the normal tire pressure is set, the road holding is getting worse as the high speed,, because the operation of the tire pressure rise caused by heat. Perhaps some people will think that tire pressure not too full, it will rise when riding, but if in the winter season, the asphalt road is icy, the tire how to get hot?
5.   There are many conflicts for the above four situations overlap,. For example, the tire pressure should not be fed in the hill's path, but if use hot melt tire need hard tire pressure. So the tire pressure is absolutely no formula, need all the external human factors combined to use tire pressure. Therefore, in general, it will be better to based on the requirements of factory to change tire pressure.
Site Feedback, Issues / Welcome to SMF!
« Last post by Simple Machines on October 23, 2016, 10:01:20 AM »
Welcome to Simple Machines Forum!

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