Cruiser Gearing @ RAD

[J Gallo]

I didn't realize there would be math this early......

Now back to my regularly scheduled Excel spreadsheet.

[bmx_tyler]

The 52.31 and the 54.92 is the distance that you travel per pedal. I don't ride a cruiser, YET. But on my 20'' inch bike, i run a 42*15 it is the around a 45*16. It will be easier to pedal the 42 because it is smaller then say the 45 gear, but it i get the same number on the PBP gear chart. I have to pedal more because it is a smaller gear in front. The Larger the gear the harder it is to get top speed but the easier it is to maintain that speed.

It depends all on you. That is where the spinners and the crankers come in. Some people like smaller gears, which is easier to get top speed, but they are pedaling there butts off. Others like the BIG gears so they don't have to pedal has often, but it takes them longer to get top speed, but watch out when they do.

I don't know if that helps a little better. It is something that you just have to put on and try to find the one that you like and feel comfortable.

[shifter]

The 52.31 and the 54.92 is the distance that you travel per pedal.

Not raging on you, just clarifying...

The distance you travel is the circumference and that equates, in this case, to 20" (inflated dia) x 3.14 = 62.8"

[bmx_tyler]

I couldn't ride the gear that is on my 20 inch on a crusier. That would be impossible. The only one that could ride that is maybe TODD PARRY. I was just trying to help you understand that the number you get with the gear ratio is the distance travled per pedal. The gearing on a 20 inch bike is total different from a crusier.

If I was to gear my two bikes the same. I would run a 42*17 with 20*1.50, on my class and around a 39*17 on a crusier with 24*1.50. i think the crusier has a smaller gear because of the bigger tires. I could be wrong.

I don't know what I am talking about. I don't even listen to myself

[Curtis Newkirk]

Shifter brings up one of those issues in BMX gear charts that has always bugged me. I have never seen a gear chart that uses actual distance traveled: (CR/RC) * (Dia. x 3.1416). Instead we use relative distance traveled: (CR/RC) * Dia and then we call it roll-out, but its not. Only by including Pi will we get the actual roll-out.

Newbies, I tell ya, bring up all of the questions and issues we forgot long ago

Anyway, that is just the techie perfectionist in me coming out. It is what it is and we use the relative number because that is what we do.

That being said, I think many top riders use a tooth or 1/2 tooth higher on the cruiser as opposed to class. I guess for Rad a "normal" relative roll-out would be between a 52.9 and a 55. Some run higher, few would run lower with the bulk probably around a 54.

[PAPAWHEELY]

Way to go Shifter. You've solved the mystery of the gear chart! I could never figure how you get a "ratio" of 52.31 out of 34divided by13. It turns out it's just a figure and not a ratio or roll out. Knowing that,now specific numbers can be figured by different brands or types of tires and not just sizes.
Matt

[hammerdown68]

To find a bikes gear ratio you divide the number of teeth in the front sprocket by the number of teeth in the rear sprocket. example: (40tooth front and 20 thooth rear) 40 didided by 20 = 2.00 (gear ratio). A gear ratio of 2.00 means that every time you pump the front sprocket around a full revolution, you rotate the rear sprocket (and rear wheel) two times. Basic standard gearing is 44 teeth in the frong and 16 teeth in the rear. (A relationship that is expressed as 44-16). This combination gives a gear ratio of 2.75 (44 divided by 16). Everytime you turn the front sprocket one full revolution you spin the rear wheel and sprocket 2 3/4 times. Hope this is helpful to anyone.. AWESOME day to all!!! H.

[PAPAWHEELY]

Knowing only the ratio doesn't help. An overall 44/16(2.75:1) combined with a 1.125 x20 tire is a lot different than a 1.75x24tire. That's why we use the gearing chart. It has the different tire sizes factored in.
Matt

[Curtis Newkirk]

Matt is right. Even the difference between, say, 1", 1-1/8", and 1/3/8" tires are significant.

The traditional way to do gearing in BMX is to measure the diameter of the rim and multiply this by the ratio (chain ring divided by cog). All of the gear charts measure roll-out this way.

I guess my point, and Shifters, is that this is not truly a roll out. To get roll out, what you want is the circumference which is the diameter times 3.1416. If you take the circumference and multiply this by the ratio you will get how far you travel in one full rotation of the crank.

The best part about doing it this was is that you can confuse all of your friends. Lets say you are running a 20 x 1-1/8 at a 40/15 ratio. By traditional measurements this would be 40/15=2.6667 times 20 (diameter) = 53.333 or a 53.3 "roll-out". If you did it the "right" way you would take the 2.6667 and multiply it by 20 X 3.1416 for a "true" roll-out of 167.58. This way when you are talking to competitors in staging and they say they are running a 53.3 you can say "Wow - I am pulling a 167.6!" and scare them before you get in the gate.

[shifter]

I guess my point, and Shifters, is that this is not truly a roll out. To get roll out, what you want is the circumference which is the diameter times 3.1416. If you take the circumference and multiply this by the ratio you will get how far you travel in one full rotation of the crank.

In theory, you have a given distance from the gate to the start - that's it; a finite distance. The objective is to find the means to maximize pedal/crank efficiency and cover that given distance fast and efficiently - faster and more efficiently that the next theoretical rider.

Now... even true roll out becomes nearly void when you consider the race line. That'll add just as much to the mix in terms of distance traveled.

Confusing???

Anywho... we know where the 53.2 type figures come from now - at least the newbie's in on the secret!

[greg]

boy, you guys really need to figure out how crank length comes into play with all of your math. It can be quite a bit difernt going from 175s to 180s.

Personally, I like to stick with the 180 crank length on the cruiser, and 175s on the 20". I've found that given the same ratio-rollout-synth number thingy----on both bikes, they seem to "feel" the same using the different length cranks. When I go with the 175s on the cruiser, it "feels" hander to push it out of the gate. I atribute this to the larger wheels having more rotational weight to get moving, thus the longer cranks give me more leverage to help overcome this.

I dont think this has anything to do with what you guys are talking about, but I just wanted to be part of the conversation with all the smart dudes.

[awsm4]

And to think there was a time when Spence had the nerver to call me something to the effect of a ultra-techi nerd Dad. Gear charts are only good for a baseline and for comparing different gear ratios to one another. Funny thing is - my son likes riding the same ratio with smaller gears...some like running the larger gears - I guess that is where all the fine tuning us Dad pit crews do comes into play. 2 rounds of wedge and 1/2 pound of air out of the front tire and the bike will corner like its on rails...

[JasonStout]

Hey guys- I'm back- It's been a while and it looks like you've been busy crankin' out gear ratios!

I was kidding about not knowing what those numbers meant...I'm a violin teacher and I can't stand not knowing.... I also have a large amount of the gear ratio chart memorized and I don't know my extended family's birthdates....go figure!

I knew a flood of math equations and story problems and numbers would fly around- but not from me...

also- another correction- I mis-counted....I was running a 36-16 on a 1.5 tire- now on a 1.75 tire thanks to this forum! Funny- I didn't even know what gear was on my back wheel!

I run a 38-17 one another cruiser and a 41-18 on my race cruiser, and a 36-16 on my other other cruiser!

Now it's time for the indoor gears!

I'm not scared!.....I run the bike with the 38-17 or I gear down to a 40-18.

What about you guys- do you change for the indoor or just crank the high gears with the Holiday legs?

JS

[JAlvey]

I think I ran a 36-16 on my cruiser last indoor season (with 1.75tire/175mm cranks). I might try slightly lower this year.

[shifter]

Last week I was just getting the feel for riding BMX. Last night I was still getting the feel, but there's no question that I'm spinning WAY to much. I'm going to/have to adjust (for RAD) from 39-17 to something taller. I'm spending tons of energy pedaling me heart out! Yharrr!