speed factor
 

Heelo, i would like to know how if the crankset size is the main factor for spped in a bike. Of course besides frame and componentes weigt. I mean , for example, two diffrent bicycles with the same weight , one with a crank 48 ad the other with a 52. Is the 52 going to be faster, or there are other factors? like I imagine frame design or the rear wheel number of speeds. How they interact with the crank?

best regards

I suspect the rider will be the biggest difference on any bike. Roger

Chainrings, cassette, and wheel size impact the the final drive ratio. For every rider, there is a comfortable cadence range (most fall into the 70-100 rpm range on flat ground). For different gearing combinations, that rpm range will produce a speed range. The strength of the rider determines how fast he or she goes. Certainly the chainring can be a limter on a steep climb or a long descent if it's too big or too small.

Sheldon Brown has a great tutorial on his web site that explains the inter-relationships among crank (chainring) size, rear cog size, wheel size and rider characteristics. Here is the link: http://www.sheldonbrown.com/gear-theory.html

I would argue that gradient is #1 with the rider being second. Example: I can get over 50 mph down the right hill while a pro can only reach 40 on the flats. :D

Aerodynamics is a key factor in speed, for both bike and rider. As for gearing, you need a gear that will allow you to put out a maximum effort in a cadence range of about 90 to 105 for the length of the test. And, of course, lowest possible friction in all moving parts.

I find that how long I can hold onto the window of the car determines my speed.

Gearing should fit the riders ability in order to maximize the power the rider is capable of producing. In other words, if I attempted a century on a bike with a 39/52 chained to a 11-21 cassette, I would have few gear choices in the flats without seriously crossing my chain or mashing and seriously lack a gear small enough to get me through the hills. Both of these things would affect efficiency, which in turn affects speed.

However, by using a 48/36/26 crankset and a 12-26 cassette, I have many more gear choices in the 17-19 mph range I generally ride when it's flat and calm, and some very easy gears for going up hills. Sure, there's no 53-11 combo to have me screaming down hills at 60mph, but I'm probably not capable of doing that anyway even if I had the gearing.

So for me, the touring setup is "faster" than the racer setup.

The number of speeds of the rear wheel and the size of the chain wheels have nothing to do with how fast a person can ride. It is the rider that decides. It has to do with mechanical advantage. Sure, a 52/11 is faster than a 48/13 in theory, but if I can't spin the cranks at the same cadence, then I won't be going faster. I will go about the same speed in reality.

I am only so strong and can't get any stronger because of mechanical advantage. I can only turn the rear wheel at x amount of revolutions. Whether this is done with a 52/11 or a 48/11. But, as mentioned above, if I try to use too high or too low of a gear ratio, I will tire more quickly and not go as fast over a longer distance. Sure, I can use the 52/11 to pedal and only have a small cadence, but I will tire my legs quickly and not be able to keep the speed up. But if I find a gear ratio where I can get the proper cadence for me, I can pedal at the speed for hours. The same is true for a gear ratio that is small.

If you are trying to get more speed, don't change the crankset or the cassette, change the rider. You need to train harder and properly. Unless you are constantly using the big/small already, then you do need a better gear ratio.

Thanks for your answers, I am sort of new and I don´t know yet the differents sets of speeds and its capabilities. I am using a trek 7.3 for communting, this bike has a 48/38/28 and cassete 11-30 , 8 speed. I use the 38 with 1 0r 2 when I go for medium speed due to busy streets, traffic lights etc. But when I get an open long avenue or similar, I use the 48 with 1 or 2. Then feel like I could get more speed and stronger pedaling and the bike does not let me. So I guess I may need a bigger crank and a different cassete, waht would be a step further of what I have now?

best regards

It all boils down to how much power you can put out with your legs for how long, and how to match that output to the basic physics requirements of road speed, load, wind, and grade. A bigger chainwheel results in more rear wheel speed and more roadspeed for a given crank speed (or cadence), but tht road speed requires more power from your legs. If you can provide it, you can go faster. If not, well, you might go slower!

It's elementary, but not simple!

Road Fan

So you are spinning out on the 48/11? First of all, you are a monster, that is a hard gear! If you are not spinning it out (i.e cadence around say 100 rpm in that gear), then you need more strength.

If your derailleurs have the capacity, you should be able to replace the big chainwheel with a 52, or replace the whole crank with maybe a 52/42/30.

How fast do you want to go? A combination of your 48 chainring and 11 cassette cog and a cadence of 100 rpm will result in a speed of 35 mph. That's faster than the pros ride. I don't think you need a change in gearing.
What do you mean by 1 or 2? If those are the two larger cogs then try 3, 4, 5, etc for higher gearing.

I have tried the sheldom brown gear calculatir and is pretty amazing , the only thing I don´t know how to calculate is the crank lenghts , from 150 mm to 190mm, I can seize mine, I will approximate the others

When you talk about the cassette , what does it means the different numbers? for example 11-30 8 speed

The cassette has 8 cogs, with the smallest cog having 11 teeth and the largest cog having 30 teeth. The cranks usually have the size stamped on the back side of the cranks.

I have to agree with the above statement. I doubt you are pedaling fast enough, your cadence isn't high enough. Though it is not impossible for someone new to be going 35 mph, it is unlikely unless you are going down a steep hill. What is your cadence? Cadence is the rpm's of the cranks. People are different, but the most efficient is usually around 90-100. I actually like to spin a little faster, around 110-120.

Do you have a computer on your bike? How fast does it say you are going?

You must clairfy what 1 or 2 means as the other replies have stated. I'd bet money you don't need different gearing. Yours seems perfect for commuting.

I don´t have a computer in the bike, that can be a good improvement. I meant I use the 38 in the smallest and the second smallest position in the cassete and the same with the 48, then I fell I would like to have something a little faster

This sounds as if you need to learn to turn the cranks faster (higher cadence). Suggest you get a good computer with cadence, like the Cateye Astrale 8. It's cheap and you'll get your money's worht many times over. Learn to ride in the 85 - 105 rpm range, selecting gears to keep you in that range (I like to ride in the 90 - 100 range, others will vary some).

Al

Computers are nice, but not necessary. I use one that doesn't have cadence capabilities. I just count the revolutions for 30 seconds, then double. Now I don't do that, since I know the feel of my cadence if I am pedaling too fast or slow. You can have a friend drive next to you and see how fast you are going. Remember this and what gear you are in, check Sheldon Brown's Gear Calculator and determine your cadence. More work, but can be done.

If you really want to do the math, you could use gear inches and speed to determine your cadence.

Speed is determined by gear inches and cadence. To go faster, increase your cadence, unless you are already have a high cadence, then a bigger chain wheel is needed. Unless your cadence is higher than 100, you don't need to change your gear inches.

I find a cadence meter to be especially helpful when I'm tired on a long ride or when fighting a head wind and my body doesn't feel quite right. Using a cadence meter I can find a gear that will put me back into that higher efficiency range and pretty soon I'm feeling better and my speed may increase even though I've selected a lower gear.
I'm sure that if I tried to calculate my cadence by counting rotations for 30 seconds by the time I've made the calculations my cadence will have changed up or down 5 to 10 rpm, maybe more.
Computers with cadence are very inexpensive, less than the cost of a new tire.

I'm sure a computer would be more accurate and could be helpful. If I was a racer, I would get one. With me, 110-115 is a natural cadence, one that I am happy with. I only started timing my cadence to see what I was doing. It's pretty flat here in Cleveland and every time I counted my cadence I was always within the 110-120 range.

But I could see a cadence computer being very helpful, especially for newer riders trying to find their sweet spot. All I was saying is that if the OP didn't have one there are other ways to get a rough idea of the cadence.

Thanks for the help, I did not know about the cadence factor and I will start measuring this.



[QUOTE=SweetLou;5947160]The cassette has 8 cogs, with the smallest cog having 11 teeth and the largest cog having 30 teeth.


So what is the difference with for example a 12-25, 10 speed in terms of performance? what´s the meaning of the cogs having more or less teeth and the cassete more or less speeds.


Best regards

It has nothing to do with performance. Well, I guess it does in a way. It all has to do with gear inches. A 12-25 10 speed will have a much lower range of gear inches. Also, the difference between each cog will be less. What this means you can get a better choice of gear for your cadence. When in the 16 tooth cog, it might be too hard to keep up your cadence and when in the 18 tooth cog pedaling at your cadence is too easy. So, if you had a 17 tooth cog, it would be perfect.

So, you might think having a cassette with each cog one tooth more than the next is ideal. Not necessarily, if you live in a hilly area, you will need a larger range of gear inches. Maybe a 30 tooth cog to get up the hill and an 11 tooth cog so you can fly down the hill.

If you are a professional racer, you don't need such a range, because you have very powerful legs and can easily ride up a mountain in a smaller cog. So a shorter range of gear inches is preferred.

The speeds of the cassette or freewheel really don't matter that much. It is the overall range that matters. If you have a 6 speed freewheel and a 10 speed cassette, with each being a 12-27, then your range is the same. What will change is having more cogs so you can get a closer match for your abilities. With the 6 speed, you might have a gear that is a little too hard and the next size is a little too easy. But it isn't that big of a deal. I have a few bikes, with a freewheel with 6 speeds, cassettes of 7,8 and 9 speeds. The gear inch range is about the same on each bike and I can ride any just as well. No real difference in performance because of the drivetrain.