low range gears

[davidvdm]

WOW SJC, I'm sorry I asked

I'll pick one or two Patrols tomorrow night, and bash some figures into the spreadsheet I designed to work out the Sani with dual TC's. It's fairly basic, but that's the way I roll

[Peter Connan]

Here is a very basic little calculator showing the effect of the Mark's 4x4 ratios on a 4.2 GQ (according to the manual, gear and final drive ratios are the same assuming a manual gearbox).

Gear ratios.xlsx

(11.03 KiB) Downloaded 278 times

Now in these cars, 2nd low is the only gear that works for sand. 1st high is too low, and 2nd high is too high.

Looking at that, the 2.48 and 2.65 ratios will probably leave you with a car that doesn't work well in soft sand, but with the 3.7, 3rd low should be just about spot on.

The lower the transfer ratios are, the closer the output ratios are together, thus the better chance there is of finding exactly the right ratio for any given obstacle.

[Mystical_Beast]

Hi Peter

I take it on your type of vehicle when referring to sand, are you referring to beach sand, perhaps towing a trailer?
What sort of gearing would your vehicle use in standard form to drive up a dune for example?

I looked at the table and understand the correlation you are making with the 85% reduction, my thinking however was the 43% reduction would have broader appeal.
Am I correct that with the 85% reduction you would not have enough momentum to drive up dunes etc>

On the highly reduced box wouldnt you effectively come to a dead stop trying to change gear, manual box deep sand, towing?
I have zero experience with the Patrol off-road.

However

A reduction ration of 3.535 to my mind looks like the perfect compromise?

Standard 3rd low is pretty close to reduction 5th low. I'm thinking standard 3rd low is what you would probably use in the dunes?
As said I have no experience in off-road environment with the Patrol.

But the 85% reduction is surely will have its limitations to technical trails and lose the ability to float on top of sand as not enough speed can be obtained?

What is your opinion on the 3.535 reduction ratio?

In your particular application with 3.535 reduction 3rd low is even better for you/closer to standard 2nd low with just slightly longer legs.

If there is a possibility to make these locally, a ratio would need to be decided on which would satisfy all the various Patrols.

[Mystical_Beast]

I have taken Peter's spreadsheet and worked it for all Patrol configurations.

The 3.535 ratio looks to work well across the entire Patrol Range.

2nd Low becomes 3rd Low pretty well matched across the range, giving the extra low first gear for those who really need to crawl.

Could anyone work out what Speed one could do in 5th gear low range for the various vehicles at peak Torque for the various engines?

To see whats available at the top end?

[Mystical_Beast]

I see I made a mistake with the 4.8 final drive ratio for Auto Trans, that one is for Manual 4.8

I will fix and post again, you can use the link below to calculate speed obtainable in each gear on different reduction ratios.



http://www.apexgarage.com/tech/gear_ratios.shtml

[Peter Connan]

Hi Peter

I take it on your type of vehicle when referring to sand, are you referring to beach sand, perhaps towing a trailer?
What sort of gearing would your vehicle use in standard form to drive up a dune for example?

Negative, I am talking about dune driving.

Never driven much on beaches, but I have done quite a lot of river-bed driving, where I have found ratios much less important (even when towing), as the sand is typically not as soft or deep.
I can't change gear quickly enough to maintain momentum, and haven't really seen anybody whoi can in a patrol. Our truck gearboxes are pretty slow to change.

The auto is of course a different story.

3.535 would be great. Not sure what how big a module you will be ablt to get, but it looks to me like 3.743 allows the largest module of all these ratios, which might be usefull when trying to optimise the design for strength, and I doubt that the difference between 3.535 and 3.743 is significant.

I am not sure for what type of usage the max torque speed in 5th low would be relevant to?

[Mystical_Beast]

I realise I made a hash not looking at the ratio table properly but am fixing that now.
I feel the speed at max torque is relevant surely?

I am putting a speed calculation together and will put it up shortly.

I hope my parameters are correct, but I have done some cross checking and it looks about right.

Getting back to relevance of low range speed at optimum torque, say you are towing in tough conditions, say deep sand but are able to keep a fair momentum, say 60 km/hr, I’d like to know that having a reduction box by whatever percentage, what speed I will do in each gear at optimum torque.

As a way of my checking that I haven’t reduced the transfer case to such an extent that I cannot do much more than technical trails.

[Mystical_Beast]

4.8 3600 RPM.xlsx

(20.32 KiB) Downloaded 285 times

[Mystical_Beast]

So using the Link I posted above

These are the speeds you would be doing in a 4.8 at 3600, maximum torque.

In my opinion the 3.743 reduction is too severe and looking at it on this particular vehicle I think the 2.86 ratio would be ideal.

Look, gear ratios and off road is not my field of expertise but in my opinion it would be pointless to reduce the ratio to such an extent that your only application would be a technical trail, but understand that one would really want to be able to idle over stuff.

I will put one up for the 4.2 petrol just for interest sake

[Mystical_Beast]

TB42 Man 2800 RPM.xlsx

(9.61 KiB) Downloaded 254 times

The calculation for the 4.8 was on standard 30 inch tyres

The one here below I worked on 33 inch tyres for the 4.2 Petrol which makes max torque at 2800 rpm according to what I could find.

Obviously tyre size makes a difference so I used the 33 inch as most seem to upgrade to that.