why my old bike( with thinner wheels) is faster than a mountain bike?

Question

maybe because the force of friction with the ground is smaller

barreign??

Answer 1

1. Skinny tires have less friction because of smaller area of contact with road...as mentioned by yourself.
2. Skinny tires require higher tire pressure --over 100psi, so there is a LOT LOT less rolling resistance. Those tires feel like a rock when pumped up. MTB tires are fat and squishy in comparison capable of only 40 to 60 psi. The knobbier the tire, the less efficient it is for street use.
3. Skinny wheels are larger around than 26" mtb tires
4. Gearing on a road bike are designed for acceleration and carrying speed, while a mountain bike is geared for hills.
5. Road bikes are generally lighter than comparable mtb bikes.

Answer 2

The biggest factors that affect speed on a bicycle are, the wheel size and the gear ratio. Check your old bike wheel, it is most likely 27" and your mountian bike is 26" wheels, a larger wheel goes that much farther with each pedal revolution. Look at the sprockets and count the teeth, your old bike probably has bigger front sprockets for a higher gear ratio, mountain bikes usually have smaller front sprockets for hill climbing. A modern road bike has 700c (approx. 28") wheels and large front sprockets (48-58 teeth)

Answer 3

Touring bikes are designed to be faster, and to go long distances. They are lighter, their tires have less roll resistance, and they are geared differently from mountain bikes. Mountain bikes are designed for climbing and riding on rough terrain. Mountain bike tires also have a greater roll resistance because of the knobby tread.

Answer 4

You answered your own question thinner wheels less friction on the ground and less weight on the bike.

Answer 5

The friction with the road is the primary factor. However, the gearing, weight of the bike, and rider position has an effect also.

Answer 6

what does "faster" mean to you?
- it accelerates faster from a stop? because the wheels and overall bike are lighter
- it cruises faster on the straight and flat? because your position on the bike is more aerodynamic, more powerful, and your tire pressure is higer
- it has a faster top speed? again because of position and aerodynamics, maybe a bit because you have higher gearing available (but I suspect not)

Also a possible factor - overall running condition / maintenance of either bike

Answer 7

In this case it is most likely that your bike with the "thinner wheels" is pumped up to a higher pressure, has less tread, weighs less and is more aerodynamic (rider position) than a mountain bike. On the road it will be quicker. I would hazard a guess that if you took it on the terrain that mountain bikes are designed for it would be slower.

OK I'll try and dispel a myth or two here

The size of you area in contact with the road (on any bike) will be a factor of your total weight x gravity / pressure in you tyres.

I.e. contact area for a bike total combined weight 200lb and 100 psi (more correctly referred as pounds per square inch gravity. psig) in the tyres, will have a contact area of about 2sqr inches.(ignoring the effect of tread). The shape of the contact area has the greatest effect on rolling resistance.

For metric people a bike/rider combination of 100 kg will exhibit a force of 981 newtons (kg/m/sxs) If you put 700 kpa (thousand newtons per square metre) in the tyres. Gives about 14 Square centimetres

To try to explain what makes a low rolling resistance tyre. Let start, by looking at train wheels. Train wheels have the lowest rolling resistance of any vehicle in common use. One really hard surface rolling on another really hard surface.

What makes it low rolling resistance is that the difference in contact area unloaded and full laden is very small. Therefore the energy required to maintain the contact patch is very small.

It is probably worth noting at this stage that larger wheels spin slower at a given speed and therefore use less power in the bearings.(There is a complex series of low rolling resistance metal on lubricated metal contact patches in the bearings.)

When we start looking at pneumatic tyres things change significantly. Firstly many tyres have tread every time the tread flexes it consumes energy, increasing rolling resistance. On hard surfaces such as asphalt slick tyres have lower rolling resistance.

Asphalt also has irregularities in it so to smooth this effect, usually a thin layer of a relatively soft compound makes an improvement.

The larger irregularities (stones) Bring into play an other factor commonly known as roll over resistance. To minimise this tyres designed to give in the sidewalls will have the advantage. Things like carbon forks help also.

To summarise a low rolling resistance tyre (for the road) will be high pressure, soft compound, treadless, with sidewalls designed to give.

Rolling resistance makes about 20% of output power @ 20mph (32 km/h). So in this case it is more likely that the riding position has more to do with the speed difference than the rolling resistance of the tyres

Since you like maths

power for rolling resistance = weight (kg) x gravity(m/ss) x coefficient of rolling resistance (typically .005 for a road bike only a little higher for a Mtn bike) x speed (m/s)

Power for wind resistance =.5 x coeficient of wind resistance(typically .9) x frontal area ( 0.4 m2) x density of air (1.22 kg/m3)x speed (m/s)cubed

Typically around 200 watts at 32km/h (20m/h)

Answer 8

thinner wheels means less contact with the road so you get less friction, and less rolling resistance. road bikes are lighter than mtbs, so naturally, they roll faster.

Answer 9

that is easy its because ur barrings are broke in more than ur mont. bike
ps. barrings are in the hub of ur bike the little round metal balls