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.

Gresp15C

My suggestion is to look up how gear ratios are calculated for bikes... there are a few different terms, but a common one is "gear inches," which is the number of inches that you move for one complete revolution of the pedals. Also think about "cadence" which is revolutions per minute of your pedals. There are online calculators that will work these things out for you, along with things like the speed that you can ride for a particular gear combination at a particular cadence.

This is practically pure math, which scares some people, but is not really all that difficult. There's no absolute answer because each rider has their own preferred cadence and top speed. For instance for myself, 30+ mph is unattainable due to wind resistance and my own strength, so I have no use for gearing that can reach that speed.

delbiker1 

If you can hit 30+mph on a flat stretch of road on your bicycle, you should think about racing. I would be willing to wager that you have not personally seen anybody hit 40 mph unless they were going downhill on a fairly long hill with a steep enough grade.

JohnDThompson 

Apart from downhill and tailwinds, reaching and maintaining 40mph speed is more about the rider than the gearing. True, you'll need a gear high enough that you won't spin out when you reach that speed, but first you need to be fit enough to reach it and maintain it.

indyfabz

Guess it's still winter in many places.

Steve B.

dedhed

It's all about position.

shelbyfv

Isn't there a trend toward 70-11?

Bandera

Found that other missing Sock.

TimothyH

What is a "gear stepping system?"

I don't understand what that means.


-Tim-

fietsbob

Denise went 184 MPH on a bike with a very big gear , she had to be towed* to 110 MPH
before the cadence was reasonable ..

*(By a Dragster with a wind break, on the back, used by the previous record holder, a guy named Fred ..

Leebo

It's 4/1.

Ferrouscious 

No, it's 4/2.

livedarklions

Eleventy seven to umpteen.

livedarklions

Any second now. That guy is waiting for a replacement lid for his water bottle before he can give us a progress report.

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.

livedarklions

I could actually follow that, thanks!

Do you adjust the formula if you're using a wheel with other than a 27" diameter or is that just a convention?

Litespud

AFAIK it's a convention - the actual rollout would depend on many factors - tire width, pressure rider weight etc. I guess that at some point, people glommed onto 27" as being the nominal diameter of a standard wheel and went from there. GI remains a wide-accepted frame of reference for gearing rather than anything else. I imagine if a "standard bike" rider was chatting with a Moulton rider, they would both understand the significance of a "108" gear", even if that number didn't reflect anything actually happening on either of their bikes

burnthesheep

Dang it! Beat me to it. 5 internet points awarded to you.

Phil_gretz

In 1972, Eddy Merckx set the one-hour world record turning (according to Wiki) 104 gear inches. So my answer to the original question is that 52T in front and 13T in the rear should be plenty fast for you. Actual mileage may vary.

livedarklions

Given that the OP mentioned wanting to do speeds in the 40 mph range, it might be worth noting that Merckx's record was just a fraction over 30 mph.

Phil_gretz

So instead of turning 100 rpms, as Merckx did, the OP can turn 130.

LesterOfPuppets

STEPS is for ebikes. I think they only assist up to 20 mph though.

livedarklions

Yeah, no big deal. If a hummingbird can.....

LesterOfPuppets

I like tight rear clusters. 12-26 is pretty good. If I need to climb hills I like a triple on front.

52x12 is big enough for me to pedal up to 40 mph. I don't really bother pedalling over 40. I have pedalled up to 42-ish but over 40 seems like a waste of energy.

I find the fastest way to get to top speed is to start in a high gear. Start in 52x17, then click towards the 12 as needed.