Who follows the 1" per rev. gearing rule (rollout ratio)?

[simplechamp]

I've read a lot about gearing lately, and didn't quite understand the term "rollout ratio" so I decided to research a bit. A pretty common standard for gearing is 1 revolution of the motor to rotate the tire 1". So if your tire had a circumference (2*pi*radius) of 20" you would setup your gearing so that the final ratio was right around 20:1. This gives a rollout ratio of 1:1, or simply 1.

Supposedly this is a good, safe setup to start with when gearing a vehicle, and will allow your electronics to run effectively and efficiently, and avoid thermaling, etc. That isn't to say you shouldn't gear higher, but the farther you go past 1 will start heating things up more and drawing much more current.

I calculated my gearing to get a 1:1 rollout for the E-revo and supposedly it will put me right at 30mph which is exactly what I want. Also, that tells me I could go a bit faster without worries of overgearing.

Just wanted to see what others think of this method and if they follow it. If you are having thermal issues/puffing packs/smoking ESCs go to the speed calc and see how close you are to a rollout of 1. You might be surprised. And if you are under 1 and still having issues that's a sign there are probably other issues at play that need to be remedied.

Again, please remember this isn't a hard and fast rule, your mileage may vary, there are many other factors at play in such a complex system.

[_paralyzed_]

most of us use a much simpler rule and leave the math alone. we use BrianG's speed calc and for monster trucks never gear for much more than 40mph. Temperature will tell the tale from there whether or not you can gear up or have to gear down.

everything you state is correct and if you are a stickler for details go ahead and use it, but you're thinking too deeply into it IMO, it's not rocket surgery!

[simplechamp]

You still can use the gearing calc to do the math, I used it also. At the end once it spits out all the numbers you just divide tire circumference by total reduction ratio. That's all it is, one division after using the speed calc, doesn't get much simpler than that. I think the way I discussed it makes it seem overly complex. Give it a try, like I said the result might surprise you. I mainly want to see what others have their rollout at, so would a few of you mind humoring me and posting your rollout?

Everything I said above can be summed up as: tire circumference/total reduction ratio = rollout, try to get it close to 1

[SpEEdyBL]

For me, as long as temperatures are within an acceptable range, the gearing is fine. The best thing to do is just experiment. Start with the smallest pinion gear that you can and go up from there, checking temperatures every few minutes. Also Speed = Motor RPM*(tire circumfrence)/(88*Final Drive ratio). So at least get a pinion gear that is large enough for reasonable speeds.

[BrianG]

This is interesting. I have heard this 1:1 rollout rule too, but never thought much of it.

For instance, say I have truggy tires that are 5.65". That's 17.75" circumference. That would mean I would need a total diff and spur/pinion ratio totaling 17.75:1 in order to follow this rule? Following that logic, most truggies have a 4.3:1 diff ratio. That would mean the spur/pinion ratio would have to be 4.13:1. And if I'm using a 48T spur, that would mean I need a 11.6T pinion (ok, round down to 11). Which would put the top speed of a 2000kv motor on 5s at 33mph. Sounds pretty good to me.

If everyone agrees this is a good rule of thumb, I can add this feature to the calc page.

[simplechamp]

Speedy: I think experimenting is good. But for me (and many others) it's not feasible to go out and buy every pinion and every spur for a vehicle just to experiment. Calculating a rollout of 1 will give you an appropriate starting point, and from there you can buy just a couple pinions and spurs to fine tune the rollout/gearing to where you want it.

BrianG: Yes, you want your tire circumference and final drive ratio to be equal (at least to start). I was going to suggest you may want to add it to the calc. All it requires is one more division as I previously mentioned, and I think it's helpful to find a good, reasonable starting point to fine tune your gearing. You need more torque? maybe try it at .8 or .9 Feeling the need for speed? go up to 1.3, (just examples, not exactly sure what are reasonable min and max points yet)

[BrianG]

It should be easy enough to do. I was thinking of adding it in one of two ways:

1: Create a new page. Enter the pertinent info and it will spit out the right pinion to use.

2: In the top speed estimator page. This page is more for calculating top speed for a specific gearing, but there is a little pinion table (by clicking the gears icon) where I could indicate the 1:1 rollout pinion somehow.

[simplechamp]

I hadn't thought of it that way, where it would assume 1:1 and give you gearing as an output. That's a really good idea.

I was thinking of it basically just spitting out your rollout on the speed calc page along with the other calculated values (which you could do too, but I like the ideas you have as they take away the task of plugging in a bunch of combos trying to get to 1:1). It would still be nice to have the rollout shown on the speed calc page in the results, because you might not always want it to be exactly 1:1. Or for people who are having problems they could input all their info in the speed calc (or a simplified rollout calc) and see if their rollout is too high or too low.

It would really be optimal if you could input any combination of the variables to solve for one that was left out (be it pinion, spur, rollout, tire circumference, etc.), but you are the programmer, not sure if that would be too difficult to do. There is a simple calc on another site that is like this, but only solves for rollout, I can send you the link if you'd like.

[_paralyzed_]

eh. I don't care for it......

[zeropointbug]

I think it would be silly, so silly in fact, I don't even know why I'm typing this?

[simplechamp]

I don't see why there's such an issue with it. It would be one number added on to the speed calculator results. Rollout is an important number when gearing, and even if you don't agree with the 1:1 ratio it still is good to know the rollout on your vehicle. If people think it's just some useless number they can ignore it, but others may be able to benefit quite a bit and save themselves a puffed lipo or fried ESC.

BrianG: You seemed a little interested at least, so I'm not sure what others will say, but I still think it would be a nice calculation to add on. I think my first post maybe went overboard and people are thinking this is some big complicated thing.

[JThiessen]

My .02 - for a lot us we can digest that info and make decisions on gearing with some amount of informed intelligence. For quite a few users, its best to just give them one number, and let them run with it. Too many choices will end up with a hundred posts of "what gear ratio do I pick for my XXXXX". I dont htink anyone is saying the 1:1 thing is bad in any way, just that the results of the speed calculator have been good so far, so why change what isnt broken....standard human psychology.

[BrianG]

I think the point is that most people simply say "gear for 30-35mph" and that's it, and then the user has to go find the right combination that will achieve that end. The 1:1 rollout would be just a decent starting point in place of (or to complement) the 30-35mph rule. Really, both rules produce very similar results; one is based on experience, the other on an actual calculation.

[_paralyzed_]

yep, nothing against it, we are just use to a different way.

[simplechamp]

Originally Posted by JThiessen

just that the results of the speed calculator have been good so far, so why change what isnt broken....standard human psychology.

It wouldn't be changing anything about the way the calculator works. The calculator already outputs tire circumference and final gear ratio. All I'm asking for it to do is take two numbers from the speed calc and divide them, nothing more. People who don't want to use it can pay it no attention, but it will be helpful to some people.

It's one extra number, based on numbers that are already being given in the speed calc. That's all I think it should be, not a whole re-tooling of the speed calc. It would just show you what your rollout ratio is along with all the other values the speed calc gives. How is that complicating things?