29" and Acceleration...- Mtbr.com

1. ## 29" and Acceleration...

Hey I was wondering if the difference between 29" and 26" wheels affects the acceleration of a bike... (without changing gear ratio)

(this may sound crazy, but I'm doing something for a science experiment with wheels, acceleration, and all that- - any feedback would help a lot..)

thanks

2. ## Inertia

Naturally, a wheel which has more mass will have a greater inertia, so yes, it will accelerate more slowly. But, that inertia will also help you when rolling over roots and rocks you encounter on the trail.

Check the FAQ section for more answers.

3. Those big wheels do look really heavy don't they? Well, they're less than 10% heavier. All rotation parts, are roughtly 300g heavier in total.
Some think that rotational weigth is the most important, and it is, but there's so little of it, that in the end it makes very little difference. Very roughly 2kg rotational on a bike, 10kg static. 80kg average rider. Rotational is peanuts.
To picture this, that a strong wheel truing stand, wheel mounted with tires, ready-to-roll. With one quick arm movement, you can wind the wheel up to some 20mph. Compare that to the force you need to deliever with all of your body to get the whole bike there, and you'll know that the 10% increase in the rotational factor, is really peanut. It will be FELT much more clearly than the maybe 1% it's representing, as a bike is not completely still underneith us while acceleration out of the saddle.
Some feel MTB is all about accelerating, and are even convince climbing is an acceleration (it's not). In reality, I'm sure most riders spend most of their total power output to conquering rolling resistance and airdrag, not acceleration, let alone the 2 wheel weight factor. And yes, for that slight increase in weight, and immesurable slower accelration, 29" offers a theoretical 10% lower rolling resistance (working on some 50% of your total, so 5% power savings).

Grin factor has been tested to increase a whopping 70% (seventy) over any previously ridden 26" bike.

4. Originally Posted by Cloxxki
Some feel MTB is all about accelerating, and are even convince climbing is an acceleration (it's not).
If you are looking at acceleration as a change in speed, then if you maintain a steady speed up the hill, one might think that you are not accelerating. However, in order to balance out the force of gravity, one must accelerate in order to go up a hill at a steady velocity. Force = mass*acceleration. If you are to balance out gravity and travel at a steady velocity up a hill, you must be applying a force, which is the your total mass*your acceleration. This is a very trivial look at things, since we are neglecting rolling resistance and wind resistance.

So, while you may not be moving faster, you are indeed accelerating.

If you took physics at some point, you may recall the problem involving an object traveling in a circle at a steady velocity. It is not changing speed, but it is accelerating. Same difference.

5. Originally Posted by Cloxxki
Grin factor has been tested to increase a whopping 70% (seventy) over any previously ridden 26" bike.
These are the only numbers you need to worry about when compaing 26" to 29er. They have been proven true by boffins in labs around the world.

6. Scientific research to the most preferred treadmill size amongst various rodents, has proved that as little an increase in size as 10%, convinced the 99% smartest animals to convert right away. Increased gyro was experienced, but dismissed as to little to be irrelevant. The 1% of the rodents with the lowest IQ, that had previously been confronted with a smaller treadmill, just kept coming to the same mill, as that's was what they knew to work for a fact.
In a double blind test, animals with similar IQ that first were confronted with the larger treadmill, just stuck to that.

Not part of the experiment, but researchers reported a very significant Grin Factor increase amongst the 99% smartest rodents. They came to the large treadmill more often than they ever did with the smaller one in the past. Also, they seemed to be more popular with the opposite sex, and produce more beautiful offspring.

The professor in charge of the research expects that over the course of time, the rodents that prefer the smaller treadmill will just stop to exist, as since the introduction of the larger treadmill, only the smarter onces are reproducing anymore. The last surviving, and stubbornly out-holding small treadmill enthousiast rat still has a life expectancy of about 6 months left. Unfortunately, the poor thing has gone into isolation, and only seems to use the treadmill when he's tired of smalling his head against the walls of his terrarium. The larger treadmill he was offered has yet to turn a full rotation, and is used only for scratching nails.
After hearing out this research, treadmill manufacturers around the world have responded with common sense, and are only selling the smaller varaty from previously built old stock, as production lines have totally been converted, as were the rodents themselves. One manufacturer was quoted "If such a significant majority of our customers prefer the larger sized mill, why would we keep forcing them onto the older small ones? This is a tough business, and we have to stay close to our customer's demands. We run our business based on common sense, not prejudices. We're not in the bike bizz, for crying out loud!".

This is how I remember the facts, it may need some shaving.

Now go ride,

J

7. Originally Posted by Cloxxki
Scientific research to the most preferred treadmill size amongst various rodents, has proved that as little an increase in size as 10%, convinced the 99% smartest animals to convert right away. Increased gyro was experienced, but dismissed as to little to be irrelevant. The 1% of the rodents with the lowest IQ, that had previously been confronted with a smaller treadmill, just kept coming to the same mill, as that's was what they knew to work for a fact.
In a double blind test, animals with similar IQ that first were confronted with the larger treadmill, just stuck to that.

Not part of the experiment, but researchers reported a very significant Grin Factor increase amongst the 99% smartest rodents. They came to the large treadmill more often than they ever did with the smaller one in the past. Also, they seemed to be more popular with the opposite sex, and produce more beautiful offspring.

The professor in charge of the research expects that over the course of time, the rodents that prefer the smaller treadmill will just stop to exist, as since the introduction of the larger treadmill, only the smarter onces are reproducing anymore. The last surviving, and stubbornly out-holding small treadmill enthousiast rat still has a life expectancy of about 6 months left. Unfortunately, the poor thing has gone into isolation, and only seems to use the treadmill when he's tired of smalling his head against the walls of his terrarium. The larger treadmill he was offered has yet to turn a full rotation, and is used only for scratching nails.
After hearing out this research, treadmill manufacturers around the world have responded with common sense, and are only selling the smaller varaty from previously built old stock, as production lines have totally been converted, as were the rodents themselves. One manufacturer was quoted "If such a significant majority of our customers prefer the larger sized mill, why would we keep forcing them onto the older small ones? This is a tough business, and we have to stay close to our customer's demands. We run our business based on common sense, not prejudices. We're not in the bike bizz, for crying out loud!".

This is how I remember the facts, it may need some shaving.

Now go ride,

J

Excellent!

8. Originally Posted by Cloxxki
Scientific research to the most preferred treadmill size amongst various rodents, has proved that as little an increase in size as 10%, convinced the 99% smartest animals to convert right away. Increased gyro was experienced, but dismissed as to little to be irrelevant. The 1% of the rodents with the lowest IQ, that had previously been confronted with a smaller treadmill, just kept coming to the same mill, as that's was what they knew to work for a fact.
In a double blind test, animals with similar IQ that first were confronted with the larger treadmill, just stuck to that.

Not part of the experiment, but researchers reported a very significant Grin Factor increase amongst the 99% smartest rodents. They came to the large treadmill more often than they ever did with the smaller one in the past. Also, they seemed to be more popular with the opposite sex, and produce more beautiful offspring.

The professor in charge of the research expects that over the course of time, the rodents that prefer the smaller treadmill will just stop to exist, as since the introduction of the larger treadmill, only the smarter onces are reproducing anymore. The last surviving, and stubbornly out-holding small treadmill enthousiast rat still has a life expectancy of about 6 months left. Unfortunately, the poor thing has gone into isolation, and only seems to use the treadmill when he's tired of smalling his head against the walls of his terrarium. The larger treadmill he was offered has yet to turn a full rotation, and is used only for scratching nails.
After hearing out this research, treadmill manufacturers around the world have responded with common sense, and are only selling the smaller varaty from previously built old stock, as production lines have totally been converted, as were the rodents themselves. One manufacturer was quoted "If such a significant majority of our customers prefer the larger sized mill, why would we keep forcing them onto the older small ones? This is a tough business, and we have to stay close to our customer's demands. We run our business based on common sense, not prejudices. We're not in the bike bizz, for crying out loud!".

This is how I remember the facts, it may need some shaving.

Now go ride,

J

Thanks! The grin factor of this post is +110%

9. ## It's really about work

There's hundreds of factors that are involved concerning the force required to accelerate a body at rest. Some of these are distance of mass from the axel, friction between your tire of choice and and the surface (velociraptor vs. nano, concrete vs. sand), torque supplied by a lever which is your crank (165, 170, 180, ?),..... There are some very long formulas reqired to find force when dealing with accelerating rotational masses and the kinetic energy stored in that rotational mass. You also have to consider the difference of energy losses due to the different angle of attack on any given obstacle found between the 29er and the 26. You can see that the forces required and acting upon each of us, depending on setup, changes dramatically and can affect your performance dramatically.

My 29er with nano raptors requires no lmore force than a 26 with velociraptors over the same distance traved. But there's the rub. You cannot leave gearing out of the 29er equation because it effects the distance traveled per revolution of crank and it effects the amount of work required. Work = force x distance. The key is, since we are the engines supplying the work how do we bring the amount of work required between 26 and 29er's closer together so that they are negligable. 29er will always have an issue with force but that is somewhat negated by energy loss due to angles of attack and stored kinetic energy. But you will never bring the work required issue closer together if you don't do something about gearing.

10. Originally Posted by nzumbi
If you are looking at acceleration as a change in speed, then if you maintain a steady speed up the hill, one might think that you are not accelerating. However, in order to balance out the force of gravity, one must accelerate in order to go up a hill at a steady velocity. Force = mass*acceleration. If you are to balance out gravity and travel at a steady velocity up a hill, you must be applying a force, which is the your total mass*your acceleration. This is a very trivial look at things, since we are neglecting rolling resistance and wind resistance.
You are mixing up force and work.

Originally Posted by nzumbi
If you took physics at some point, you may recall the problem involving an object traveling in a circle at a steady velocity. It is not changing speed, but it is accelerating. Same difference.
Same thing, even if it accelerates, work done is 0, as force is perpendicular to the path. You do not have to perform any work to maintain rotation of the wheel - you perform work to overcome rolling and air resistance and to lift your overall center of gravity up the hill.

With 29r wheels, with a steady pace, you have to lift about 1kg more mass (~1% increase) while battling 10% less rolling resistance.

11. Originally Posted by Axe
as force is perpendicular to the path.

I had no intention of discussing work done. separate issue. I was clarifying the acceleration bit.

Oh, and if you are on a hill, the force of gravity is not perpindicular to the path. Ever done an inclined plane problem?

I admit that I haven't done any newtonian physics in a long time. Quantum Mechanics was a pain in the ass on my way to getting my bachelors in physics though. But I left all that stuff behind long ago.

12. The only true test of whether a 29 climbs better than 26 incher is to have two very similar bikes set up with similar tires and to supply an equal weight rider and something like an electric motor to drive the cranks. You would then run them at equal wattages and then time the results. I would think if you would want to test at between 200 and 300 watts for around 30 minutes on a dirt uphill.

I think dragging a human being into the equation opens up way too many variables.

One factor to consider is that an electric motor would probably need to accelerate less because the bike would not slow down and speed up so much due to the less steady output of a riders pedal stroke vs. an electric motors more steady output.

This could also be done with full suspension bikes vs. hard tails as well.

It seems to me that 29 inch advocates are sure willing to throw the 10% advantage gain around very loosely but get real scientific when it comes disputing perceived disadvantages of the 29 inch wheel.

Grin factors can be also alleged to Single Speeders, full suspension bikes, different brands of bikes, shocks, forks bars, pedals, shifters, tires and on and on.

13. Originally Posted by nzumbi
I had no intention of discussing work done. separate issue. I was clarifying the acceleration bit.

Oh, and if you are on a hill, the force of gravity is not perpindicular to the path. Ever done an inclined plane problem?

I admit that I haven't done any newtonian physics in a long time. Quantum Mechanics was a pain in the ass on my way to getting my bachelors in physics though. But I left all that stuff behind long ago.
Yes, on incline force of gravity is not perpendicular to the path of your G.C. That's why you perform work to get up the hill, as I said in my reply. But you do not perform any work to maintain angular acceleration of the wheels. So at a steady pace wheels mass and radius does not matter.

You said: "However, in order to balance out the force of gravity, one must accelerate in order to go up a hill at a steady velocity. "

That is incorrect. You do not accelerate to go up the hill at a steady velocity. Definition of acceleration. Since we are bragging, if I was grading you physics classes (got to do that on the way to my Physics Ph.D., though after that I left for greener pastures) that post would have been 0/10.

14. Originally Posted by Axe

You said: "However, in order to balance out the force of gravity, one must accelerate in order to go up a hill at a steady velocity. "
Got me there. That was a dumb statement. I should never try and be rational before 7AM.

In fact, in my case, I mostly always suffer from decceleration on hills.

Hopefully 29's will help with that.

15. Originally Posted by Axe
...if I was grading you physics classes (got to do that on the way to my Physics Ph.D., though after that I left for greener pastures) that post would have been 0/10.

...LOL...

16. I have video footage of the Open Dutch SS Championships, last June. 2 29" riders rocket off the starting line, leaving all others on 26" bikes in the dust.
It's like 1.5Mb, so who'll host it? I never found my confirmation mail from fooriders.com

Thanks!

17. ## Science...

...schmience. Math is Satan's work.

All we need to know is that Jeebus rolled a Dos Niner.

Boyokasha,

Sean

18. Originally Posted by richwolf
The only true test of whether a 29 climbs better than 26 incher is to have two very similar bikes set up with similar tires and to supply an equal weight rider and something like an electric motor to drive the cranks. You would then run them at equal wattages and then time the results. I would think if you would want to test at between 200 and 300 watts for around 30 minutes on a dirt uphill.

I think dragging a human being into the equation opens up way too many variables.

One factor to consider is that an electric motor would probably need to accelerate less because the bike would not slow down and speed up so much due to the less steady output of a riders pedal stroke vs. an electric motors more steady output.

This could also be done with full suspension bikes vs. hard tails as well.

It seems to me that 29 inch advocates are sure willing to throw the 10% advantage gain around very loosely but get real scientific when it comes disputing perceived disadvantages of the 29 inch wheel.

Grin factors can be also alleged to Single Speeders, full suspension bikes, different brands of bikes, shocks, forks bars, pedals, shifters, tires and on and on.
The bottom line is that there is really only one true test. You need to try one on the trails you ride the most. Maybe you get more grins with a big hit bike, who knows? A 29er is the only bike for me, but that doesn't mean it's great for you. You can debate what's best using physics and formulas all day long, but it's kind of like arguing about whether chocolate ice cream tastes better than strawberry. Viva choices...

19. Originally Posted by RobW
The bottom line is that there is really only one true test. You need to try one on the trails you ride the most. Maybe you get more grins with a big hit bike, who knows? A 29er is the only bike for me, but that doesn't mean it's great for you. You can debate what's best using physics and formulas all day long, but it's kind of like arguing about whether chocolate ice cream tastes better than strawberry. Viva choices...
Actually you need to mix vanilla in with chocolate along with some candy chunks to get a great tasting ice cream. For strawberry you need to mix in cheesecake to make it work.

Actually this discussion was not so much about grin factor as efficiency and acceleration. It is too bad that there is no real good testing out there. The 29 inch crowd will throw around their statistics but when it come to proof they bring out the grin card. It is not so easy for me to just jump on a 29 incher and make an assessment. Who is going to loan me a bike in my size, set up properly for me to evaluate???
Now if you are short, ride in Julian CA occasionally, then perhaps we could get together and swap bikes for a while.

20. Does anyone else here get the feeling that mice are smarter than us? Not discounting physics and engineering, but do all the calculations mean anything if the opposite is felt when riding a 29er? I decided to buy a 29er after my first test ride convinced me that it felt better than any other bike (all 26") I had ridden. I felt like Superman on a 29er and a slug on my 26" bikes. Since then I have not looked back. I do get on a 26" every now and then just to be sure.

21. Originally Posted by Cloxxki
I have video footage of the Open Dutch SS Championships, last June. 2 29" riders rocket off the starting line, leaving all others on 26" bikes in the dust.
It's like 1.5Mb, so who'll host it
I will host it due to the fact there is one really handsome 29er rider in the video.

Mail it to me

P::..

22. Here is the proof!

This, as Cloxxki said was the Dutch Singlespeed Championships. So this acceleration is not down to fast gear changing, we all start on a level playing field.

P::..

23. Originally Posted by nightfire
Here is the proof!

This, as Cloxxki said was the Dutch Singlespeed Championships. So this acceleration is not down to fast gear changing, we all start on a level playing field.

P::..
Looks massive compared to the other bikes. I love it!!!!!!!!

24. That's because they are massive. Cloxxki is on a 22" and I am on a 23".

P::..

25. Ya that video proved it. I ordered my 29er today!

26. Originally Posted by nightfire
That's because they are massive. Cloxxki is on a 22" and I am on a 23".

P::..
Just my size. It looks like it fits him perfect

27. Originally Posted by richwolf
Ya that video proved it. I ordered my 29er today!
I can't make up my mind on what frame. What are you getting?

28. Originally Posted by richwolf
Actually you need to mix vanilla in with chocolate along with some candy chunks to get a great tasting ice cream. For strawberry you need to mix in cheesecake to make it work.

Actually this discussion was not so much about grin factor as efficiency and acceleration. It is too bad that there is no real good testing out there. The 29 inch crowd will throw around their statistics but when it come to proof they bring out the grin card. It is not so easy for me to just jump on a 29 incher and make an assessment. Who is going to loan me a bike in my size, set up properly for me to evaluate???
Now if you are short, ride in Julian CA occasionally, then perhaps we could get together and swap bikes for a while.
You are correct, the grin factor is off topic in this post. I have a problem with all the arguments over efficiency. In my mind, the change from 26 to 29, while very tangible when on the bike, is an incremental change. For every gain going to big wheels, there will be a legitimate claim of a loss. More stable? Slower to accelerate. Smoother ride? Weaker wheel build. Tastes great? Less filling. Seriously, it could go on all day long. My assesment of 29ers has prompted me to sell my 26" bikes, and I'm having another 29er built right now to add to the stable. 29 inch wheels are an advantage to me, where I ride, how I ride, and help me have more fun, but then, I like my strawberry ice cream unadulterated... You do have the right idea though. You really need to ride one on your home trails for a day.

29. ## Nothing but 29ers

Everybody's got an opinion, and well, the start of this thread was about the difference in accelaration between a 29er and a 26. There is a mechanical difference between the two. But that's true in almost evey bike setup. No one sets up thier bike the same and everone is looking for that small mechanical advantage to be bigger, faster, better. It just depends on how you want to deal with those differences. Myself, as soon as I got my butt kicked at the Waco Nationals (Sport 50+) by someone on a 29er, 10 years my senior, who out climbed and decended better than any bike around - I knew there something to the 29er. After my first ride, I sold my K2 Razorback SL and my Airborne Lucky Strike race bikes and now have my bike nirvana with a heavly modified 293 (I think the only thing left off the original bike is the rear triangle) and a custom Ti 29er.

You'll never see me on a 26 again. But I also only ride and race xc, which is where the 29er seems to excell. Having said that, I early on found I personally had a problem with the bikes feeling slugish and feeling that I was exerting too much effort during the races with heavy climbing involved. Once I modified my gearing, those were problems of the past. Not only did I feel I had the acceleration that I had on my 26 but accelarated faster. I've said it before I don't think any 26 can out sprint a 29er. And not only did I reagained my endurance but enhanced it due to the mechanical advantage provided by the 29er with the same effort I applied to the 26.

I am all about 29ers, but I also believe you have to be smart with them to make them as efficient as possible. Everthing depends on how you personally want to ride.

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