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What Back and Front Tooth Ratio is Fastest???

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What Back and Front Tooth Ratio is Fastest???

Old 04-03-19, 09:25 AM
  #51  
rutan74
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Originally Posted by allout1
What's a good back:front tooth ratio and gear stepping system from standstill to top speed on road bikes?

I have seen that some riders are taking road bikes up to 40+ mph. I'm just looking for the 30+ mph range on the road, and I'm not looking for expensive produce or parts. I don't care how old or what it looks like to be honest as long as it stays together, handles, and gets to top speed rapidly.

Some back:front gear ratios are better than others, right? I'm messing with two bikes right now which are just older road bikes that have mountain and cruiser features. They're just fun and project bikes. I noted on the second one I bought yesterday that it was going much faster with very minimal effort compared to what the first one could do without much more effort. The first one is 21spd and the second, faster one is 18spd, however I don't believe the number of sprocks but the number of teeth matters.
Don't know if anyone posted this but this is a cool website that allows you to actually play with gearing both front and rear. It is really a neat little toy to play around with if you are wondering about gears and gear ratios and it even gives you top speeds in those gear choices.

I just checked the link and it still works. Check it out and have fun playing around. If the link is blocked here for some reason, it is "gear-calculator" dot com/# with of course the www's.

Bicycle Gear Calculator

john
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Old 04-03-19, 10:50 AM
  #52  
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Whats "fastest?" & whats "quickest?" are 2 very different questions.

Low gearing will help you get moving in less time.
High gearing will help your top speed after you've got yourself moving.
How much force you can drive into the pedals, the speed & timing of your shift will determine your actual rate of acelleration to speed.

When I lived in Hawaii in the late '90's I had a Trek 6500ZX with rigid forks and 1.75inch road slicks. (That bike has Rockshox Recon & 1.95inch knobbes, and 2x11 XTR now)...Anyway, In Hawaii, it was a standard 3x7 system with a 12-28 freewheel hub. I would draft city busses, delivery trucks all day long on my adventures. I got tired of spinning out so I "upgraded" to a double road crankset & everything went to h-e-double-hockey-sticks. My raw acelleration power was gone & I never managed to keep a good strong cadence with my established/practiced shifting habit.

My point is there is more to it than just top gear.

All my bikes range from about 28.5 gear inches to about 110 Except the Trek mountain bike. It about 15 gear inches to about 89, now & useless for anything over 22-25 mph even when I'm motivated. If you are going to hang with traffic on a 700c road bike...I suppose nowadays, a 52-36 or a 53-39 crankset and an 11 or 12 to 25 or 28 cassette would be smart places to look. Combine that with good high strength/high torque starting technique to overcome that 35-38 inch low gear & be able to push the 125-130 inch top gear.

175mm crank arms would help in the torque department.
Cadence is about how coordinated & practiced you are, but "spinning" 165-170mm cranks is generally regarded as easier...I ran 170mm for a while & felt "bound up." I have a 33 inch inseam, FWIW. I now run 172.5 to 175's where my torque is higher, my power is higher, my cadence is negligably lower. 87 vs 89 rpm. So I suppose it depends a lot on you, your physical dimensions, your abilities (strength profile, masher/spinner) & how the traffic environment behaves.

Practice your shifting & understand how your gears relate to eachother.

Gears being equal, Much the same applies to 26 inch wheeled mountain bikes too, but you'd be a touch slower in the top end but a touch quicker on the take-off due to wheel circumference.

The trick to riding in traffic at the speeds and methods you are intimating is to stay in the draft. That gets hard & it gets dangerous.

Good luck.

Look at his cadence at speed & how long it took him to get there. Tall gears.

Last edited by base2; 04-03-19 at 11:11 AM.
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Old 04-03-19, 11:32 AM
  #53  
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Not to be ignored, the ratio of speed to air resistance.. resistance Much greater
with a little bit of speed increase..

So, your computer on a trainer inside can thus register a higher speed ..
than you, doing the work, outside on the road..
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Old 04-03-19, 11:00 PM
  #54  
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Okay, thanks, all.

How about bigger rings than 53? Is it realistic? I think I can customize what I want on my crank such as a big, circus ring on the top and two regular road rings below, eh. Maybe something semi compactish below the big, circus one. Hmmmm It's all flat streets around me anyway.
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Old 04-03-19, 11:45 PM
  #55  
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It is possible though difficult to find larger than a 53 tooth front chainring. And it is possible to find cassettes with 10 or 9 teeth, though I believe that may necessitate a different axle than is typical.

Take a look at this gear calculator page:
https://www.bikecalc.com/speed_at_cadence

At 53/11 you could already pedal yourself to 42mph at just over 110 RPM cadence. You could hit almost 46mph with 53/10 if you can fit the cassette. But I use the term "you" loosely.

This graph is useful in determining how many watts of power you would need to apply to hit and maintain a speed:
https://www.gribble.org/cycling/power_v_speed.html

The chart tops out at 35mph, presumably because people don't tend to pedal their way much beyond that. Already at 35mph you'd have to be powering up to about 800 watts if you weigh 165 and ride a 17 pound bike with whatever frontal area they've plugged into that calculator. Already at 35mph the aerodynamic drag is robbing you of 719 watts.

Bigger gearing is certainly possible; we recently had a thread where someone was showing off a 70 tooth chainring. I have no idea where one would find a derailleur that would work with that, but hey, the chainring exists. And I've seen pictures of larger ones that barely clear the ground. But to drive one with a rear cog of 11t at a typical 80-110 cadence would mean being in some of the best shape a blessed human is capable of, or would mean affixing a motor, electric or otherwise. Also at 800 watts (or more for faster speeds) you'll go through bike chains, chainrings, and rear cogs in pretty short order, I imagine.
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Old 04-04-19, 09:21 AM
  #56  
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Originally Posted by Litespud
"Gear Inches" is a useful and widely-accepted measure of mechanical advantage when cycling, but it is not the number of inches travelled during one crank revolution. GI is usually calculated as (crank teeth#/sprocket teeth#)*27", 27" being the nominal diameter of a standard bicycle wheel, so, for example, a 52-13 gear would develop a "108" gear". However, wheel circumference, rather than diameter, determines the wheel rollout, or the distance travelled by one wheel revolution, and circumference is 3.14x greater than diameter. The actual distance travelled (in inches) is 3.14-fold greater than the calculated gear inches. Therefore, in the 108 gear inches example above, the bicycle would travel ~339" (108" x 3.14) with one crank revolution.

Gear inches is the diameter that the wheel would be if it were direct drive.

Think of a penny farthing- to go faster, make the wheel bigger- to the limit of what you can reach your legs around so 48- 60 diameter wheel = 48-60 gear inches.

A low gear on a modern bike of 34/34 is 1:1 = ~27" the diameter of the wheel. A high gear of 120" is the equivalent of having a 10' diameter wheel.
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Old 04-04-19, 09:50 AM
  #57  
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Originally Posted by daoswald
It is possible though difficult to find larger than a 53 tooth front chainring. And it is possible to find cassettes with 10 or 9 teeth, though I believe that may necessitate a different axle than is typical.
<snip>
Also at 800 watts (or more for faster speeds) you'll go through bike chains, chainrings, and rear cogs in pretty short order, I imagine.
As far as 800 watts goes: A class 3 e-bike is limited to 750 watts, 28 miles per hour & is required to have a working speedometer. At least in the State of Washington. Your local laws may vary. Assuming you are a human person...well, you know how hard that would be. But I just wanted to throw the e-bike thing out there, "just in case."

Second, finding a derailleur that would have the kind of capacity needed could be a challenge. That's the magic behind 3x systems. More gear inches, less capacity.

Capacity is the most chain uptake a derailleur is rated to handle & operate properly. Just adding gear teeth in one place with out subtracting them from another is a recipe for disaster. Shimano XTR handle up to 47 teeth (or some such number) capacity now.

There is more to it than just smacking a bigger ring on the bike & calling it good. The whole system must be analyzed to achieve the desired objective.

Last edited by base2; 04-04-19 at 10:01 AM.
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