If that's your take, you're a member of the wrong forum. This is not a wild west show here. Go back to the New Members area and read / follow the posted rules, like the rest of us who value this place. Please conduct yourself accordingly.

I see that you went back and cleaned up, edited your recent posts (somewhat). That is a good start.

 

No Warp, that is completely wrong - but I could see how that might be interpreted without understanding the mathematics and physics behind it. true that wheel speed will be slower but you are forgetting about torque multiplication and rates of acceleration.

Your final drive ratio is the relationship between the revolution of the motor and the revolution of the driving wheel. For example, a final drive ratio of 2.07:1 means that for every rotation of the wheel, the motor rotates 2.07 times. A shorter final drive ratio of 2.09:1 means 2.09 rotations of the motor to 1 turn of wheel. It's not so much that your rear wheel is turning 10% slower at a given speed, your engine is also turning 10% faster per wheel revolution at a given speed and ratio torque force is being multiplied to a higher degree. That is the key difference on how you are incorrectly understanding it, and it is also the reason this works for both acceleration gain and power increase to the wheel. True that you can over shorten the gear ratio to a point where the rear wheel is barely turning at 4000rpm, but that is way on the extreme side and nowhere near what we are doing.

In short: Changing to a quicker (shorter) final drive ratio provides faster acceleration in all gears at all rpm's. Generally, taller ratios yield better fuel mileage and shorter ratios offer more acceleration and applied power at the wheel.

This is all factual, scientific and sound data based on mathematics and physics. And verified by performance enthusiasts in all arenas, no internet myths at all. The above is 100% correct in any technical discussion arena whether it is at the race track or MIT's Applied Physics department.

If you can provide any factual data to dismiss my above, and back up your claim that going to a shorter final drive ratio provides zero acceleration gain, results in excessive TQ dips, and is essentially a "wash" with no performance benefit, I again invite you to present that concrete information here. Just provide some independent source data we can all take a look at. If what you say is true there must be plenty of independent sources saying the same thing, since this is an extremely popular topic in all areas of performance motoring.

 

I'll refer you back to my post #34, where I explained using your own charts and data. I thought that your own data would be particularly acceptable to you.

Here's what I said in post 34, using the data and charts you furnished in post #33:

"Note that upon shifting, the overall gear ratio drops from 7.302 to 5.423, which is a 25.73% reduction in torque between the engine and the rear wheel. Also note that with the aftermarket gearing, this rear-wheel torque drop from shifting occurs at 56.2 mph, rather than carrying you through to 63.6 mph, when shifting at maximum power.

"While the aftermarket gearing will give a rear-wheel torque advantage in each gear, you also suffer the big torque drop (25.73% in my example) from shifting earlier , which comes from needing to shift to the next higher gear sooner, at an 11.6% lower speed in this case. So coincidentally , the gain in rear-wheel torque from the aftermarket gearing is almost perfectly offset by the reduction in the time you have to use it. There's no free lunch."

So you have mis-read or mis-understood my claim, or not processed it adequately. My claim is not that the torque dips upon shifting to the next higher gear are excessive, but that they occur earlier, with the lower final drive ratio. So while there is a rear-wheel torque advantage in each gear when going through the gears, you also lose that torque advantage sooner (at a lower rear-wheel speed or pavement speed) because of the requirement to shift to the next gear at a lower speed, at which point you more than lose the 11.6% percent torque gain you acquired by lowering the final drive ratio.

Since "horsepower" is a widely accepted unit of measure for power, or "work done", and you have requested an on-line reference or resource, here's a horsepower calculator:
http://www.metaris.com/hp-relations.php

You can plug in your rear-wheel torque, and your rear-wheel rpm, and get your rear-wheel horsepower.
Then you can plug in your 11.6% final drive reduction numbers, (which will increase the torque 11.6%, but also reduce the speed 11.6%), and notice that your rear-wheel horsepower is the same.

I realize that this can seem counter-intuitive, and it seems like lower gearing should give more power at the rear wheel, but that's the way it works.

 

I do understand what you are saying Warp, but you are not taking into account torque multiplication factors of ratio changes. I see how you could arrive at that conclusion not taking added factors into consideration, nor having done this upgrade yourself for an actual AB test, nor having read articles on this specfici topic such as the one I provided. Unless you think NHRs is wrong too? .

That calc you provided is not relevant and too simplistic to be applicable here. Horsepower and TQ at the engine are not relevant to this upgrade. I'll try and explain why.

Horsepower is the measure of how much work can be done in a specified time. One horsepower equals 33000 foot-pounds of work per minute. We don't use this at all for the type of change were doing here because engine HP is going to remain unchanged at the crank, and max HP engine RPM is also unchanged. Measured HP at the wheel would end up being same since that can only be calculated over time, whether that time is the distance of 1/4 mile or 3 miles. This is why a 400hp CAT tractor can pull multi-ton boulders and move slowly, but a 400hp drag car can do a quick 1/4 mile time. They both have 400hp but drive ratio gearing helps dictate the end result of that HP. Dynoing both of these vehicles would show they each still have 400hp.

TORQUE is defined as a FORCE around a given point, applied at a RADIUS from that point, it is a "right now" measurement. For this upgrade, we're not concerned with torque at the engine as that also remains unchanged at the crank and max TQ engine RPM remains unchanged.

What we are strictly doing is increasing the multiplied torque force at the wheel by shortening the final drive ratio by either 3%, 9.7% or 13%. And this produces the positive results in acceleration and applied torque to wheel for the same engine crank HP and TQ ratings. Please take the time to least least read the single NHRS reference for an unbiased set of data on how and why this does work in performance applications.

If you focus on strictly the engine side of things or start throwing horsepower into the mix then I again see how you can get thrown off. Think about it this way- If what you are claiming is true, that there is zero tangible benefit in shortening final drive ratio to achieve greater wheel torque and speed acceleration, then it would also be impossible for a longer handle wrench to make it easier to remove a stuck bolt.
Your "arm" is the engine with say 68hp and 80tq at max. The length of wrench is your "final drive ratio" pulleys. A longer handle wrench (shorter ratio) used by the same arm strength has greater multiplied torque at the bolt head and can pull it harder / faster, than the same arm using a short wrench (tall ratio). The longer the wrench, the greater the multiplied torque for the same exact arm strength. I know this is overly simplistic but it's the same physical principal.

Changing the gear ratio in the final drive pulley does two things. It changes engine speed relative to ground speed, and it changes the available max torque at the drive wheels in each trans gear relative to fixed engine torque. For achieving maximum acceleration you need the highest max torque a the drive wheels, to which end you would want to increase the final drive ratio. the small changes we are making here serve to remove the overly too tall factory gearing that was primarily designed for max economy and reduced wheel torque / acceleration. We're simply going to a slightly more optimal rear ratio that effectively increases wheel torque in each trans gear and provides faster acceleration. The only penalty is slightly reduced top end speed of each trans gear and some fuel economy. If you take the time to research this outside your own knowledge set I'm confident you'll arrive at the same conclusion.

 

Sorry, but those assumptions are all incorrect. Torque multiplication has been taken into account, and I've mentioned it in a number of my posts. A/B tests? Did lots of them, when I was spending a lot of time running motorcycles down the drag strip. Read tons of articles.

If you recall, I recommend using rear-wheel torque and rpm numbers to plug into the calculator to make things simpler. For example, plug in a 15% increase in rear wheel torque due a change in gearing (which carries with it a 15% reduction in rear-wheel rpm, so you need to plug that in too), and one can see that power at the wheel stays about the same, with the various gear ratio changes.

Not that these calculations can't be done starting at the engine, as long as you keep the crankshaft torque, rpm, or horsepower the same when comparing the different drivetrain ratios. And you don't even need to know the actual specs of the engine to figure out the percentage change. A given drivetrain ratio change will produce the same percentage of change in rear-wheel torque and speed, regardless of the power of the engine (excepting frictional losses in the drivetrain, which can vary a bit with different gearings).

As I mentioned earlier, some of these engineering concepts can seem to go contrary to intuition, such as rear-wheel horsepower remaining the same when the drive ratio is changed. I had difficulty getting a thorough grasp on some of them too, at first, when I first started working with them decades ago. Perhaps they are so familiar and "old hat" to me now, that I don't do the best job of explaining them.

Again, I apologize for the need to be brief, not having sufficient time to respond to everything you have said, point by point.

 

Sure Warp. I'll ask for a 3rd or 4th time, show us the "Articles" supporting your point of this all being a wash and non-beneficial. If what I posted is all wrong, there must be tons of articles and data to that affect. There must be tons of legitimate articles stating that shortening drive ratio does not benefit acceleration or wheel torque. I can't find those so please help us out.

Did you also discount the NHRS article, which echos my posted data here? Are you calling them incorrect as well?

I'm still going to ask, why are you posting here- I can't imagine hanging out in a DIY thread that I have no vested interest in doing, think is nonsense, and is completely ineffective. All you're doing is providing nonsense that will hinder those looking to get the right information.

 

LA Dog, you have made some good individual points in some of your posts, and the article you linked to is good. You just seem to have trouble putting it all together, or perhaps you're skipping over the parts which don't agree with your theories, or failing to read carefully enough.

A quote from the very article you linked to:

"So to everyone who thinks torque is a performance metric, well, put simply, torque is simply not a meaningful number for evaluating performance unless you also consider the rpm it's being made at. If the rpm didn't matter, we'd all just gear gear our bikes into the basement, and never take them out of first gear. We have FAR more torque at the rear wheel in first gear than any other gear. The torque and rpm being produced by our engine go through gear reduction in the primary, the transmission (except in 5th), and the final drive. The gear reduction through the transmission is deepest in first gear. You want torque? Just leave your bike in first gear all the time.

But nobody wants to ride around in first gear all the time. Sure, you've got lots of torque at the rear wheel in first, you can probably even pull a wheelie you've got so much torque. But you can't go very fast. Every time you upshift, you give up some rear wheel torque and trade it for some rear wheel rpm. By the time you get to 5th you may be able to go 100mph, but you don't have enough torque left at the rear wheel to pull a wheelie anymore.

Unfortunately, there's just no way to upshift and gain more rear wheel rpm without also losing rear wheel torque. So what we really want here, what really will help the performance of the bike, is to make more torque and more rpm at the same time."




No one here has disputed that you can produce a rear-wheel torque increase by lowering the gearing. That's not the issue. The issue is that torque alone is not a measurement of how much work can be done, the work of moving the bike. To convert torque (force) to actual work, you need to factor in the speed at which that that force is acting.

That's where the tradeoffs start to kick in. When you increase the rear-wheel torque by lowering the gearing, the inevitable consequence is speed is reduced. And then you need to shift sooner to the next higher transmission gear, which brings with it a large torque drop. Again, this is summarized in the article you linked to.


Repeating a pertinent section from the article again:


"Unfortunately, there's just no way to upshift and gain more rear wheel rpm without also losing rear wheel torque. So what we really want here, what really will help the performance of the bike, is to make more torque and more rpm at the same time.

Well, as it turns out, there's a term for that: it's called "horsepower"."

That's why I've tried to steer things in the direction of rear-wheel horsepower, because rear-wheel torque, alone, doesn't really tell you anything about real-world acceleration.

So now it's my turn to ask you:
Do you discount the NHRS article, which supports what I've been saying? Are you calling them incorrect as well?

 

And that is exactly what we are doing here and is expanded upon later in the article. Increasing torque to the wheel, and increasing engine rpm at the same time through gearing.

I didn't think it was possible to purposefully misinterpret that article through omission and cut/paste of certain sections. Horsepower is not the correct medium of measurement. If you read below that point where you cut it off, the clarification is presented and direction turns back to focusing on gear ratio:

...The term "horsepower" describes the total combination of torque and rpm, without specifying it's makeup. But for the purposes of evaluating performance, it's makeup doesn't matter. If it's not made of the combination of torque and rpm that we want (and it's not), we just run it through some gearing. That's what gearing is for.

But anyone reading the article is going to see that, as well as the following paragraphs below it providing good simple example / explanation of how running the shorter ratio provides the stated acceleration / performance benefits. Rear wheel torque and optimal drive gearing dictates everything about acceleration- not horsepower. You can have a same horsepower car and go really slow or really fast depending on your gearing ratios and rear wheel torque.

I'm still not seeing your case where there is zero performance and acceleration benefit from running a shorter ratio set of pulleys on our already too-tall geared bikes. Technical aspects aside, anyone who has done this upgrade to their bike will tell you your thoughts on it are mistaken.

 

LA Dog, here's a link to the article again, to make it easier for others to read the whole thing and decide for themselves what they think it says.
http://www.nrhsperformance.com/tech_power.shtml


Fat11LO, It's probably easiest and most convenient to use engine rpm as the constant. That will keep engine output (at full throttle) the same for all the gearing ratios you might want to plug in, making it easier to distinguish which changes in wheel rpm and torque are due solely to the gearing changes.

 

Thanks for re-posting that link Warp- Obviously you and I are not going to agree on these theories in general and I'm sure we could debate it till the cows come home- How about we agree to disagree and get the thread back on track? Those who decide to do the upgrade or review data can come to their own conclusions. Lord knows we have pages of detailed information here now.