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What can you tell me about gear ratios?


Lewis
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I know that having the right ratios is important, and that lower is better up to a point, but how low do I want?

What should my crawl ratio be in an ideal world?

I've worked out my low 1st to be 45.7:1 - is this good bad or what? I know its not as low as a 90 on Simex with 4.1 R&P's

3000rpm in low 1st will give me 662ft/min whilst idle will give me 165ft/min

Can anyone help me to understand what I want?

Regards, Lewis :)

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I seem to remember White90 saying that low 1st with an Ashcroft underdrive engaged (so low-low-1st) is about right for winching with an 8274. I think the underdrive drops it by about 3x? can't remember. So a lot lower than you have is what you want :)

Ashcrofts site has the ratios but it seems to be down at the moment... but I did find this

Stock LT230 Low Range 3.321:1

Low Range with Underdrive 8.933:1

which means that your crawl ratio with an underdrive will be about 122:1

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Hi Lewis,

how about reverse calculating it ?

you know the m/min you will get with the winch and can assume an engine speed say 2500rpm

you know the tyre dia you will use 40" go well with portals ;)

the missing figure is the overall gear ratio

then from there its breaking down the various ratios g/box-T/box- diff- portal box

this should show if you need an under drive too

HTH

Steveb

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I think you are on the right track Lewis. The distance in feet or metres per minute is more meaningful than ratio counts. A 45 :1 gear ratio is quite useful on 29 inch diametre tyres but not too clever on 40 inchers.

Having super low gears can be useful, and very destructive if the driver doesn't have mechanical sympathy and a deft feel for what is happening to his vehicle in certain terrain conditions because the engine won't necessarily let you know by laboring, that there is an enormous amount of torque being developed. If I am not careful, if for example I get a front wheel bound up in a rock undercut, I can let the clutch at idle ( 278 :1 ) with the puny 2 1/4 litre petrol and grenade everything from the transfercase down to the portal gears and the engine would have barely dropped 100 rpm.

Bill.

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I'm geared about the 65:1 on 37" tyres and i'd say it's about perfect, but i would like another gear below it say 120:1

A problem i have encountered is that it can be very hard to develop momentum when you need it, i have once had to use high box to charge at something before.

I think at 45:1 on 37's you are going to be struggling a bit, and might find low speed control a thing of the past.

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Sorry I should have included more information

The gear ratio was calculated using this website

I used the values for the R380 and Defender LT230 ( in fact I have an LT77 but this is not listed), along with 3.73:1 ratio diffs which is closest listed to my actual 3.7: diffs, and listed my tyre size as 38.5"

I'm not particularly interested in matching my crawl speed to a winch, as the car is for fun in the most part and competition is far behind that in my prioritories. Plus with an electric winch the line speed can hardly be called a constant. If the crawl speed ended up anywhere near the winch line speed then that would be an added bonus

The reason for my enquiry is that having driven a few vehicles with lower gears than my own I am left wanting somewhat, especially with my planned increase in tyre size.

What I really want is a low 1st much like dirtydiesel's 65:1 for playing on the rocks and those times when you absolutely positively got to bulldoze that tree. But I dont want to suffer from a narrow band of low gears with the inabilty to gain speed for long hill climbs. I recently drove a 4 wheeled dump truck that had and almost perfect range of gears

According my my calculations I need something like 5.4:1 R&P to acheive a 65:1 low 1st

Bill do you know what is available for Toyota 60 series cruiser axles?

Steve, the mogs are for a future project ;)

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Im slightly lower than Dan for whats its worth (low first is 72:1 on 39.5') - no hassles with slow speed control and hill descents give you enough time to read a newspaper and have a ciggy if you want :), another suggestion (if you want more options than than you can shake a stick at) would be an Atlas 4 speed transfer case ATLAS Linky then you can have your cake and eat it, ultra low low low and plenty of top if ya wanna cruise with the neons on :)

for wierd Toy stuff try Inchworm Link

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According my my calculations I need something like 5.4:1 R&P to acheive a 65:1 low 1st

Bill do you know what is available for Toyota 60 series cruiser axles?

I don't know ifyou got the same range of toyota trucks in the UK as we did Lewis, but in the 1970's and 80's we had Toyota Stout 1 1/2 ton pickup trucks and Dyna forward control vehicles. both the Stout and the 1.5 ton single rear wheel Dynas had 6.1:1 ring and pinion diffs that fitted into LandCruiser housings. Even at that ratio they were still a very strong diff.

Bill.

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I'm geared about the 65:1 on 37" tyres and i'd say it's about perfect, but i would like another gear below it say 120:1

A problem i have encountered is that it can be very hard to develop momentum when you need it, i have once had to use high box to charge at something before.

I think at 45:1 on 37's you are going to be struggling a bit, and might find low speed control a thing of the past.

What T-box and R&P are you running to achieve that, i've got 37's on mine and need to get this right so might as well do it now whilst she is still unfinished!

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another suggestion (if you want more options than than you can shake a stick at) would be an Atlas 4 speed transfer case ATLAS Linky

for wierd Toy stuff try Inchworm Link

Cheers for the links dude, but I cannot justify an Atlas without a complete drivetrain upgrade. An Atlas 4speed behind an LT77 and 200TDi would be the very definition of a gold tooth on a rat

I don't know ifyou got the same range of toyota trucks in the UK as we did Lewis, but in the 1970's and 80's we had Toyota Stout 1 1/2 ton pickup trucks and Dyna forward control vehicles. both the Stout and the 1.5 ton single rear wheel Dynas had 6.1:1 ring and pinion diffs that fitted into LandCruiser housings. Even at that ratio they were still a very strong diff.

Bill.

Thanks Bill,

What T-box and R&P are you running to achieve that, i've got 37's on mine and need to get this right so might as well do it now whilst she is still unfinished!

I dont want to sound like an uber-geek who spends all day waiting to quote someone elses vehicle specs, but I'm going to risk it:

Rwd LT77, G wagon T/case, and Mog 404's

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LT77 (3.59:1) x LT230 (3.32) x R&P (4.75:1) gets me 56:1 in low first. Not quite 65:1 but fine for my little 35"s and a significant improvement of most 90's low first of 42:1

And by using a RR LT230 (1.192:1 hi range) I find the spread great.

gearing.jpg

Downside is the need for (expensive) aftermarket R&Ps as the stock rover 4.7s don't last long (but are cheap). Toy centres or axles might be a better option.

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Sorry I should have included more information

The gear ratio was calculated using this website

I used the values for the R380 and Defender LT230 ( in fact I have an LT77 but this is not listed), along with 3.73:1 ratio diffs which is closest listed to my actual 3.7: diffs, and listed my tyre size as 38.5"

What I really want is a low 1st much like dirtydiesel's 65:1 for playing on the rocks and those times when you absolutely positively got to bulldoze that tree. But I dont want to suffer from a narrow band of low gears with the inabilty to gain speed for long hill climbs. I recently drove a 4 wheeled dump truck that had and almost perfect range of gears

According my my calculations I need something like 5.4:1 R&P to acheive a 65:1 low 1st

Strictly speaking your tyres only measure 37" though.

I too thought 65:1 was good enough untill i tried 117:1,

It's so much easier to finess something with low gearing, the down side is that low first ends up too low for hill decents, i have to use 2nd or 3rd to stop it endo'ing down hills.

Toyota dyna diffs should be easy to come across, what do the 80series rears have in them and will the 60 series shafts fit the 80 series diff.

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Toyota dyna diffs should be easy to come across, what do the 80series rears have in them and will the 60 series shafts fit the 80 series diff.

80's have a mixture - depending on all sorts (what colour cloth on the trim etc)

Most UK spec with lockers are 3.727:1, the diffs fit into 60 series housings too

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