# Smaller Wheels = Better Acceleration?

Show 30 post(s) from this thread on one page
Page 1 of 2 12 Last
• 07-29-14, 10:32 AM
Kevin Backalive
Smaller Wheels = Better Acceleration?
Is it true that smaller wheels, let's say 20" offers better acceleration whereas Bigger Wheels offers higher Top Speed?
And does Smaller Wheels climb road better? :)
• 07-29-14, 11:09 AM
tdong
Everything is still depend on the engine which is you. different bike use for different purpose.
• 07-29-14, 11:13 AM
bikemig
• 07-29-14, 11:54 AM
tds101
All depends on the sprockets/cogs & the engine powering the wheels. I can get pretty much the same speed on all my bikes.
• 07-29-14, 12:28 PM
fietsbob
Kevin , climbing a hill is working against Gravity , are you wanting to go faster as you climb the hill you shift to a harder gear..

to go fast the air had to be pushed out of the way..

Mass at rest takes energy to accelerate it. weigh everything.. its math .. go for it. calculate .. Newton is a start.

'gear' is a ratio x wheel diameter , same gear F:R in a smaller wheel is a lower one..

Heavy duty tube + puncture resistant tire of small diameter , Vs the super light rims and tires on a pro racing bike though larger

too many variables for a Blanket Generalization ..
• 07-29-14, 02:23 PM
jur
Acceleration is better on small wheels. Simple physics.
• 07-29-14, 02:40 PM
fietsbob
Physics is Math, the heavy small vs light and larger . got the calculations on that?
• 07-29-14, 02:59 PM
smallwheeler
Quote:

Originally Posted by jur
Acceleration is better on small wheels. Simple physics.

Quote:

Originally Posted by fietsbob
Physics is Math, the heavy small vs light and larger . got the calculations on that?

http://s2.quickmeme.com/img/7f/7f0ce...01b13f2676.jpg
• 07-29-14, 04:07 PM
dynaryder
Srsly. :rolleyes:

Hay FeetsBob,ever see these?
Attachment 396202
• 07-29-14, 05:12 PM
fietsbob
Meh, who cares.. :roflmao2: wheres the frickin spokes ? .. 406-47 on 32 hole .. CR 18are bomb-proof

the lower mass + short trail have some complaining about 'twitchyness' .. cant please everyone..

set them all side by side, stand back and see which one moves first
• 07-29-14, 05:39 PM
cplager
Quote:

Originally Posted by jur
Acceleration is better on small wheels. Simple physics.

If it were the wheels by themselves, it would depend on the weight, not size (light 700 c wheels would accelerate faster than heavy 20" wheels).

All that being said, the weight of the wheels is almost irrelevant compared to the total weight of the system (rider + bike + wheels).

Or, as correctly posted above, it's the engine.
• 07-29-14, 05:45 PM
tds101
Choo-Choo!
• 07-29-14, 06:41 PM
jur
Not just the weight of the wheels but more importantly the moment of inertia. For two wheels of identical weight, one 700c and the other 20", most of the mass is concentrated at the rim. Therefore the 20" wheel has a much smaller moment of inertia, which is a function of radius squared. Hence faster acceleration. Simple physics.
• 07-29-14, 07:01 PM
smallwheeler
from an ancient, dust-covered thread entombed in the sands of time (but, readily available because: the internet- where nothing ever truly dies). suitable entertainment whilst devouring the best nasi goreng you've never tasted:

https://i.imgur.com/KfbyDFS.png

Quote:

Originally Posted by makeinu
Many of us around the folding bike forum are engineers and, as engineers, we cringe at the seemingly endless supply of fallacies perpetuated about small wheels (by both proponents and opponents alike).

Below is a short summary of what I've found to be the most common myths and the facts which dispell them. Theoretical and experimental proofs of the facts have been posted over the years in this forum and elsewhere and are left as an exercise to the reader.

Myth: Small wheels are slower because you have to pedal more.
Fact: No. The invention of the mechanical geartrain eliminated wheel size from the consideration of how fast one needs to pedal at a given speed. If this were not the case then even 700c or 26" wheels would not be able to go faster than a walking pace.

Myth: Since small wheels have less inertia they accelerate faster.
Fact: No. Since a properly designed geartrain will make small wheels spin faster (so you don't have to pedal more) they will not have less inertia and they will not accelerate any faster unless they are lighter. Physically speaking this is really the same myth as the "pedal more" myth, but, paradoxically, proponents of small wheels usually cite the former while opponents usually cite the latter.

Myth: Since bigger wheels have more inertia they are faster.
Fact: As above, bigger wheels do not have more inertia unless they are heavier. Anyone that's ever ridden a bicycle knows that a heavier bike is not faster. Although some "flying start" world speed record bikes have purposely added weight to their (small) wheels, "flying starts" are an exception because the extra weight allows one to essentially cheat by generating and storing energy before the clock starts ticking.

Myth: Small wheels are slower because they generate more friction by spinning faster.
Fact: While this may be true in theory, the effect is likely far too small to make any measureable difference. Most world speed records are set on small wheels and to the best of my knowledge the aforementioned friction is not even a consideration for these bikes which are literally designed to be the fastest bikes on earth.

Myth: Small wheels are generally slower because they are more difficult to manufacture and/or profit from the manufacture of quality wheels.
Fact: This may actually be true.

Myth: Small wheels are weaker/underbuilt.
Fact: No. Just as stretching pizza dough into a bigger pie makes it thinner and more likely to tear, so also bigger wheels are weaker. Most small wheels are seriously overbuilt to the same specifications as their larger weaker counterparts.

Myth: Small wheels are unstable and/or have poor handling at high speeds.
Fact: No. At high speeds the most important parameter influencing handling/stability is trail which can be arbitrarily set with a properly designed frame for every wheel size. The source of this myth probably stems from the fact that a small wheel fit to a frame designed for a large wheel will result in less trail and, thus, less stability just as we might expect any number of strange problems to occur from using incompatible parts. Small wheels are also clearly more nimble at low speeds; So small wheels can have the best of both worlds.

Myth: Small diameter wheels have difficulty on rough surfaces and bumps.
Fact: While this may be true if tire width is not increased to compensate, since the tires used by smaller wheels require less material to go around the circumference of the wheel, the weight penalty for increasing tire width is much much lower. One could argue that larger diameter wheels actually have more difficulty on rough surfaces and bumps because they can't accommodate wide tires without a significant weight penalty.

Myth: But wide tires are slow.
Fact: No. Wide tires are actually faster because they have lower rolling resistance and, once again, small wheels are superior in this regard because they can accommodate the wider faster tires without a significant weight penalty. While increasing wheel diameter can also lower rolling resistance for skinny tires, comfort is inherently compromised unlike with wide tires on small wheels which can regain comfort by simply having their pressure lowered.

Myth: Small diameter wheels are less comfortable.
Fact: Not if wider, lower pressure tires are used, at which point they are more comfortable than large diameter wheels with skinny tires without incurring a significant weight penalty.

Myth: But low pressure tires are slow.
Fact: Yes, low pressure tires have greater rolling resistance on smooth roads, but lower pressure tires may actually be faster on rough roads. However comfort is not as much of an issue on smooth roads anyway. So small wheels again offer the best of both worlds with the least weight penalty: wide high pressure tires with low rolling resistance on smooth roads and wide low pressure tires for comfort and low rolling resistance on rough roads.

Myth: Small wheels are less able to climb curbs, logs, offroad obstacles, etc.
Fact: True.

Myth: Small wheels are dangerous because they are more likely to fall into potholes and stop short, sending the rider flying.
Fact: No. Wheels do not fall into potholes at speed, they mostly sail over them (falling mere centimeters for every meter traveled forward at even moderate cycling speeds). Moreover, naturally occurring potholes do not have tall steep edges like curbs, so there is no reason to expect a wheel that has fallen in to stop as opposed to roll out as if going over a miniature ramp. The actual danger of a pothole is that the impact may cause one to lose control of the bike as the sideways forces on the wheel surprise or overpower the rider who may then be unable to correct the steering before crashing. If this were not the case it would be near impossible for a pothole to cause a crash with a 26" wheel (or even a 20" wheel) and, yet, we know that hitting a pothole is not an uncommon crash cause. So small wheels are actually safer because they give the rider more leverage to hold the handlebars steady and allow the rider to correct the steering more quickly. Wheel trail can not help in these situations because the self correcting property of trail depends on the interaction between the rolling wheel and an even road, which is literally undermined in the case of a pothole.

Feel free to post more myths and facts if you have found a convincing scientific proof.

• 07-29-14, 07:26 PM
keyven
Quote:

Originally Posted by jur
Acceleration is better on small wheels. Simple physics.

Pretty much this.

Someone asks a simple question and ends up with a dozen complicated answers.

It's like they suddenly turn to one another and start discussing astrophysics - at least to noobs like me. Sometimes generalization is good.
• 07-30-14, 04:55 AM
cplager
Quote:

Originally Posted by jur
Not just the weight of the wheels but more importantly the moment of inertia. For two wheels of identical weight, one 700c and the other 20", most of the mass is concentrated at the rim. Therefore the 20" wheel has a much smaller moment of inertia, which is a function of radius squared. Hence faster acceleration. Simple physics.

tl;dr: You're wrong. And you're wrong.

Do the math. If the weight distribution of the wheels is the same (e.g., the mass is all at the edge of the wheels - not a bad approximation if you drop the mass of the hubs), the radius drops out of the energy equation. So, it's the weight of the wheel, not the size that matters. (Hint -bigger wheel spins more slowly for the same linear speed)

And again (and most importantly), you're not just accelerating a wheel, your accelerating wheels, a bike frame, and a rider with her stuff. So, even if the wheels were lighter, it would hardly matter.

Saying "simple physics" over and over doesn't do anything useful (except possibly convince us about you except how little attention you paid in your high school physics class).
• 07-30-14, 04:58 AM
cplager
Quote:

Originally Posted by keyven
Pretty much this.

Someone asks a simple question and ends up with a dozen complicated answers.

It's like they suddenly turn to one another and start discussing astrophysics - at least to noobs like me. Sometimes generalization is good.

That's great and all. But it's wrong.

I like the KISS principle, but keeping it so simple that it is wrong isn't helpful.

If you don't want to do the math yourself, at least listen to somebody who did.
• 07-30-14, 05:39 AM
chagzuki
This is a laugh.
I have to say, what seemed simple when unformulated in my head seems more complex as I try to picture all the factors.

And I can't be bothered.

But yes, small wheels accellerate faster, and that's what provides the fun factor.
At traffic lights on the brompton I shoot off in front of all the regular sized bikes and then shortly after the roadies overtake me and I watch them slowly recede into the distance.
• 07-30-14, 08:09 AM
keyven
Quote:

Originally Posted by cplager
That's great and all. But it's wrong.

I like the KISS principle, but keeping it so simple that it is wrong isn't helpful.

If you don't want to do the math yourself, at least listen to somebody who did.

Ok fair enough. I like simple too, but I guess I was looking at it the wrong way.
• 07-30-14, 08:24 AM
prathmann
Quote:

Originally Posted by cplager
tl;dr: You're wrong. And you're wrong.

Do the math. If the weight distribution of the wheels is the same (e.g., the mass is all at the edge of the wheels - not a bad approximation if you drop the mass of the hubs), the mass drops out of the energy equation.

I think you meant to write that it's the radius of the wheel that drops out of the energy equation - the mass definitely stays in. And tends to be smaller if the wheels are smaller with the same type of construction. While I agree that the wheel mass is such a small part of the total that it doesn't affect the overall speed or acceleration much, it's a part that is felt quite easily by the rider when starting up and the bike is being tilted from side-to-side and also steered back and forth a bit. So there's a different feel to a bike with light wheels.
• 07-30-14, 05:10 PM
cplager
Quote:

Originally Posted by prathmann
I think you meant to write that it's the radius of the wheel that drops out of the energy equation - the mass definitely stays in. And tends to be smaller if the wheels are smaller with the same type of construction. While I agree that the wheel mass is such a small part of the total that it doesn't affect the overall speed or acceleration much, it's a part that is felt quite easily by the rider when starting up and the bike is being tilted from side-to-side and also steered back and forth a bit. So there's a different feel to a bike with light wheels.

Um whoops. Yes, the radius drops out leaving only mass.

Whether or not you can feel the difference between light wheels and heavy wheels is another question entirely...
• 07-30-14, 09:39 PM
iFold
There are many factors concerning acceleration. My skateboard doesn't accelerate faster than my 20"er, on a rough road. :p

But all else equal except wheel diameter, then the smaller wheels has better acceleration than bigger wheels due of course to wheel diameter. You can complete a pedal stroke (single revolution) easier on small wheels.
• 07-31-14, 04:54 AM
cplager
Quote:

Originally Posted by iFold

But all else equal except wheel diameter, then the smaller wheels has better acceleration than bigger wheels due of course to wheel diameter. You can complete a pedal stroke (single revolution) easier on small wheels.

You're talking about hearing differences, not things inherent smaller wheels. (My 26" wheeled bike is geared (very slightly) lower my 20".
• 07-31-14, 12:02 PM
fietsbob
Quote:

does Smaller Wheels climb road better?
the work is getting You , and the bike, up the Hill . the smaller wheel really wont help or harm .. the gravity pull remains the same.

tell us about the hills on your island. Kevin .. (you still there?)

a sprint from a stop sign on the flats is another situation entirely , though not really its the Mass of You and the bike
you have to accelerate .

that is the same Newtonian situation. taking a Body at rest into a body in motion..

start in a Low gear and upshift as you over run the gear, and either will move you ahead fast enough.
• 07-31-14, 12:18 PM
mconlonx
It depends.

In a perfect world, because math and physics, the same person applying the same amount of force after overdrinking the same amount the night before should theoretically be able accelerate small wheels faster.

However, we don't live in a perfect world and we really don't care about wheel acceleration, do we? No, we don't: we care about how fast we can accelerate ourselves. Assuming we did not overdrink the night before, in which case we don't really care about the acceleration characteristics of different diameter wheels, and only vaguely about how fast we can accelerate ourselves, usually maxing out somewhere south of the PukeLevel of exertion.

Try this test: go to the the beach with a high-performance 20" (451) wheel running 23mm wide tires pumped to 120psi. Also bring along a fatbike with 26 x 4.8" tires set at 8psi (note, actual diameter on these can be larger than most 29" wheel/tire setups). In deep, loose sand, you will probably accelerate the wheels of the 20" bike faster; you will accelerate yourself faster on the bike with much, much bigger wheels/tires.

In any case, bring along a pitcher of bloody mary you mixed up before you left for the beach test -- because of the overdrinking the night before, you will need it, and because you did this physics test on the beach after a night of overdrinking, gosh-darnit, you deserve it.
Show 30 post(s) from this thread on one page
Page 1 of 2 12 Last