4.388 Ring and Pinion

[AN7]

I was trying to explain you the difference between getting a shorter FGR and close gear ratios.


So if I never said that FGR gives a slower car, but it gives a quicker car under some circumstances why did you start with this??

Umm, this post you just made is totally useless without you trying to explain why you think that.

Like saying that "hot is not the same as cold..."


Tell us why you think that, and where you get your information from. (Hopefully not from Playstation)

 

[BRIAN_MP5T]

I was trying to explain you the difference between getting a shorter FGR and close gear ratios.


So if I never said that FGR gives a slower car, but it gives a quicker car under some circumstances??

The reason I instantly disregarded anything you said was that you simply told us that we were "Misled" but never explained why.

If someone told you that you were wrong and walked away, would you just say.. sure I must be wrong because this guy I have never met said so?


Quicker = Faster Acceleration
Faster = Better Top Speed

All I said was changing the Final to a lower ratio would make the car slower but quicker.

You said I was "Misled" LOL

All I want you to do is tell me how my statement is "Misled"

Nothing More.

 

[AN7]

Because you and DiegoRF was talking about GEAR RATIOS NOT FGR

because you are applying more power every time you change the gear, starting in more high rpms...

Shorter gears mean lower top speed better acceleration.

 

[BRIAN_MP5T]

Holy Eff, I feel like I am talking to a box of Corn Flakes.

I'm done and Unsubbed.

 

[zps2004]

OK so gearing isn't anything hard to understand or calculate. I have attached a simple spreadsheet which I made a while ago which takes information from a car like gearing, tire size, car weight, and dyno information, and it plots acceleration (in G) VS Speed. This has been used to show a number of different concepts for acceleration as well as been proven to be rather accurate for comparing different types of cars to each other.

On the sheet I uploaded I just used the dyno from corksport and it shows what the acceleration difference is for the two different gear ratios. I also interpolated the dyno to 6500RPM which I know we can not rev to, but it gets the point across. Stock final drive is in black and the shorter one is in red.

Now for some basics. Changing the final drive to a shorter one will make each gear accelerate with more forward force than before. Each gear will be shorter for speed as well. The amount the RPM's drop between each gear will be the same, so when you shift to 2nd the RPM's will drop just the same as they do with the stock final drive.

As far as acceleration goes it just depends on what you are doing. If you look at autocrossing where you are in 2nd gear all of the time there is a noticeable increase in acceleration all of the time as shown on the plot. So for autocrossing this would be great. Now if you are looking at some road racing stuff it might or might not help depending on the track. For example if you are going down a straight where you hit about 84mph you can see that with the shorter final drive you have to shift to 4th gear to get to 84, and that extra shift will cost you time and in 4th you aren't going to pull as strongly as the stock final drive in 3rd. This same thing happens for each shift, there is a point where you accelerate faster in a certain gear with the shorter final drive, but if you have to shift to the next gear as opposed to leaving it in the same gear with the stock final drive, it might not be the benefit you think at least for that straight away. If you are shifting the same on the track the shorter final drive would be faster, but if you have to make that extra shift with the final drive it might cost enough time that you might not be faster.

Now looking at this I might add a difference plot, where it plots over speed the difference between the 2 sets of data. so it would show how the acceleration advantage would switch from +to - depending on the speed.

 

[zps2004]

Also shorter final drive is just like having smaller OD tires. For autocrossing the Miatas which run the small 13" wheels and tires are great, but when you take the same car on a racetrack that advantage starts to go away due to extra shifting.

 

[AN7]

Holy Eff, I feel like I am talking to a box of Corn Flakes.

I'm done and Unsubbed.

Thank god.

For example if you are going down a straight where you hit about 84mph you can see that with the shorter final drive you have to shift to 4th gear to get to 84, and that extra shift will cost you time and in 4th you aren't going to pull as strongly as the stock final drive in 3rd. This same thing happens for each shift, there is a point where you accelerate faster in a certain gear with the shorter final drive, but if you have to shift to the next gear as opposed to leaving it in the same gear with the stock final drive, it might not be the benefit you think at least for that straight away. If you are shifting the same on the track the shorter final drive would be faster, but if you have to make that extra shift with the final drive it might cost enough time that you might not be faster.

That is absolutely correct.

 

[eyeballs]

Well that was mildly entertaining.

ZPS2004 - Without a doubt, that's the best explanation of gearing (FD) I've ever come across. Nice visual as well with the spreadsheet. Well done, sir.

 

[zps2004]

yea the spreadsheet is really handy to explain a bunch of things. One of the fun ones is to show how if you have a car with constant HP over a broad range if RPM, as long as you are within that max HP range the car will accelerate the same no matter what gear you are in.

So that is why with a CVT for max acceleration it just keeps the engine at Max HP. That is that will give you the best acceleration reguardless of basically anything else.