low range gears

Transmissions, Transfer Boxes, Axles, Drive Shafts
Mystical_Beast
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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 19:43

Just for interest sake as I believe it might be relevant

On the 4.2 Petrol at 4200 RPM, Max Power, Your speed in 5th LR would be as low as 51 KM/HR, Basically flat out.

Is that not too low?

so lets make this easy to read

4200 RPM IN 5th Gear Low Range (Flat out)

2.02 - 95 km/hr
2.484 - 77 km/hr
2.86 - 67 km/hr
3.743 - 51 km/hr

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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 20:10

4.2 Diesel Man 2000 RPM.xlsx
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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 20:11

Not sure what the 4.2 Diesel gear ratios are, so I left them as for the Petrol 4.2 if I had that right.

But keeping the 33 Inch tyres and working on 2000 RPM, where would you be in Low Range across the various Reduction Ratios.

My opinion is that 3.743 Reduction has its application but is way too severe.

Open to correction.

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Re: low range gears

Post by davidvdm » 21 Sep 2017 21:01

Looks like Beast and Peter have everything covered, but I'm gonna post my calculator anyways for interest sake. It reveals some other information that may be of interest to some. Allows you to input tyre size as well as torque figure to see how it translates through the drive train up to your side shafts.
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Gear ratio calcs Rev2.xlsx
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1997 Nissan Sani MK3 2.7TD - Hillbilly (SAFANI)
MQ C200 SFA
MQ H260 LSD Rear
MQ Transfer as second low range
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33"x12.5x15" tires on 8.5J rims - Want 35's
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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 21:54

That looks like a great spreadsheet David.

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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 22:03

David

In trying to understand your calculations with respect to TC1 & TC2 I don’t understand why the RPM outputs are the same?

Would you mind explaining/elaborate if you will?

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Re: low range gears

Post by Mystical_Beast » 21 Sep 2017 23:01

i FOUND THIS

http://rber.net/gearing.php

So if you use total ratios as provided by Peter, you can set your red line, gear change point etc and determine your speed

Quite cool actually

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davidvdm
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Re: low range gears

Post by davidvdm » 21 Sep 2017 23:07

My setup will have two TC's and not relevant to your calcs. Thus by leaving the second TC at 1:1 and thus a straight through, it is not part of the equation and will not affect your calcs. I try and keep things "flowing", so the RPM left of TC1 is the input RPM. RPM on the right is after the reduction of the TC and the input RPM to TC2. As TC2 ratio is 1, the output RPM will be the same now.

Hope that makes sense.

I also went about a round about way to get wheel size into the calcs. It's just how I built the calcs to prove them for myself, and they just got left as is and never cleaned up, but now become handy if you change wheel size as it shows distance and speed results, which may help the guys when they want to "imagine" crawling those big rocks :wink: .
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MQ H260 LSD Rear
MQ Transfer as second low range
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DIY rock sliders
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Madman EMS

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Peter Connan
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Re: low range gears

Post by Peter Connan » 22 Sep 2017 05:37

Julian, remember that you still have your high range gear ratios in tact.

To my mind, if you are expecting to be able to reach 60km/h, you would probably be better off in high range.

Even with 3.735:1, you still have a lot of overlap between high and low.

Speaking for myself only, I would not be interested in a ratio higher than 3.5:1. Any less than that, and I would not be gaining enough to make the expense worth while.
Actually, at half the value of my car (the R25k you estimate), I just can't justify a set of lower ratios.

I honestly doubt such lower ratios would appreciably increase the number of places you can theoretically reach. The object is to significantly reduce the speed at which things happen, and thus increase the control you can exercise over the situation, and the ampount of speed you need to reach that torque, thus improving the wheel's ability to stay on the ground, which in turn means that traction is more constant. And therefore, it reduces the possibility of vehicle damage.

Most of the standard combinations of engine and tire (up to 33", not talking about wildly over-sized tires here) have enough torque to break traction on almost any surface I have ever driven on in 1st low at the torque peak. I don't think we actually need more torque at the wheels than that, just more control.
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Peter Connan
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Re: low range gears

Post by Peter Connan » 22 Sep 2017 05:53

In fact, i would be inclined to say that the ideal transfer case ratio would be one where 5th low sits between 1st and 2nd high.

But then the transfer case should ideally also have synchromesh, at least on high range.

And of course, should you ever find enough traction, you would be able to destroy virtually any axle or propshaft...
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