With the planned change in T-case this winter I have been playing with some numbers to see what my final low and high will look like. I was extremely happy with my low range when I had 4.70 R&P with ZF auto (2.48 1st) and BW T-case (H 1.206 and L 3.244) and 33" tires. What I wanted to figure out was how much lower I was effectively than stock with this set up and wanted to negate the tire effect. This would give me a goal to shoot for when number crunching. Since I want a low range that was a little lower than my previous set-up, I want to figure what I need to do to get the same with my 4:10 gears, LT230 T-case, and same ZF auto with 37" tires.

My goal is to have a high range that is as close to stock (effectively) as I can be, with a low range that is 15% lower than effective stock. Here are my numbers. I calculated the final ratio of many different set-ups and then subtracted the tire difference. Check over what I did and let me know what your thoughts are and if my math is correct.

TIRE:
From 29" tire to 33" tire: 13.8% change in bad direction
From 29" tire to 37" tire: 27.6% change in bad direction

DIFFERENTIAL:
From 3.54 to 4.10: 13.65% drop in good direction
From 3.54 to 4:70: 24.68% drop in good direction

FINAL ratio with stock items :
L 28.479
H 10.587

FINAL W4.70 and 33" tires:
4.70 x 2.48 x 3.244 = 37.81 LOW
4.70 x 2.48 x 1.206 = 14.05 HIGH
Take stock of 28.479/37.81 and you get .753. Take 1- .753 and you get a change of 24.68% lower than stock. Now negate 33" tire change of 13.8% and I get a low that is effectively 10.88% lower.

FINAL W4.10 and 37" tires:
4.10 x 2.48 x 3.32 = 33.75 LOW
4.10 x 2.48 x 1.22 = 12.40 HIGH
Take stock of 28.479/33.75 and you get .844. Take 1- .844 and you get a change of 15.63% lower than stock. Now negate 37" tire change of 27.6% and I get a low that is effectively 11.97% HIGHER. This would be horrible.

Since the tires effect the gear ratio a negative 27.68% to be 10%15% effectively lower, I would need a low that is 37.6% to 42.6%lower than stock. Right???

AVAILABLE OPTIONS THAT I SEE:
I can either change the gears in the T-case or change the diffs to 4:56s or both.


FINAL W4.10 and 37" tires With a 4.3RC set in the t-case:
4.10 x 2.48 x 4.3 = 43.72 LOW
4.10 x 2.48 x 1.22 = 12.40 HIGH
This makes the low 16% lower. Sounds like a good choice. The same thing with 4.56 gears (would obviously need to change the rear axle out to do this) would be 48.62L or (21%) lower.

Now for the high range to be about right I need the high to be lower by about 27.6% lower to off set the tire difference. Stock is 10.58, so I would need to multiply this figure by 1.276 to get what I should shoot for. This works out to be 13.50. So take out the constants of 4.10s and 2.48 first gear and get 1.32. It kind of splits the t-case available ratios of 1.22 and 1.4. I know that the tires will be slightly less than 37" tires and I want my speedo to be somewhat close, so maybe the 1.22 wouls be o.k. However for acceleration purposes, I am leaning towards 1.4s now as my vehicle doesn't ever need to go above 80MPH. Since I already have a 1.22 case in good shape, I am not to happy about this.

Soooo... I am thinking that it would be better to throw a Dana 60 in the rear of my vehicle with 4:56 gears. Put my 4:56 Dana 44 gears that the axle of mine originally came with back in. This would give me 13.50/ 2.48 = 5.44 and then take out the 4:56 gears and get 1.19. Then my 1.22 gears would be fine and I wouldn't need to worry about anything for the high range gears in my vehicle. This may kill two birds with one stone as my rear GBR equiped axle may not take the abuse of 37" tires anyways.........Thoughts, suggestions?????

Way

Go to 5:13's and never look back.

--D

Ratios available for the front are: 2.72, 2.87, 3.07, 3.23, 3.54, 3.73, 3.92, 4.09, 4.27, 4.56, 4.89, 5.38, and 5.89.

I think that 4.89s are about as low as one would want to go on a reverse cut Dana 44 front without making it too weak??? 4:56s are tempting as I already have the gears (big plus) and the carrier split on a Dana 60 is at 4:56.

Way

so go 4.56, why all the worrying?

Originally posted by 9V
so go 4.56, why all the worrying?

just guessing, but he probably only wants to do it once and be happy with the results.

j

IF your gonna' run with the 37" MTR (36.25" on a 10" rim) then your gonna' NEED to be below 4.56...I found that with a auto, 35" SSR's and 4.7's I would have liked to be about 10% lower...They were just a bit too tall for the stuff I like to do....Highway was 'alright', but a little low.

Honestly I think you should do some maxies and go to a 4.89's with a 37ish tire...If you can't/won't do the maxies then go to 5.38's.

Either way get a 60 with the split on the low side! Unless of course you spring for a crawler box...Then you can buy a 60 on the high side split for next to nothing.

--D

Almost definately planning on the 4.3 low gears. Definately want to do it only once. Not worrying, just doing some basic calculations to see where I was at and where I want to be with the planned mods. A few people have read through and not commented on any mathmatical errors so I to the best of my knowledge they are correct. I think that I would be very low with 4.88s and wouldn't be opposed to that gear ratio, but ultimately I was thinking of going with a crawler box if Timm Cooper releases his. I wish that there was a 1.5x or 2x vs. the 2.69x that Ashcroft has now. I think that the current one was designed for people to run stock diff gears and add this so that they could crawl better with there stock components. I do rock crawl 95% of the time I go wheeling, but now that I am in the front range area, other than penrose there isn't the luxury of driving 40 minutes and having Choke Cherry Canyon to play in, so I want my vehicle to be able to do other trails faster than 5MPH. I guess I could leave the gearing in the t-case alone and spring for a crawler box and maybe have the best of both worlds. However I question the ability of a crawler box to give an obstacle a good bump.

EDIT: Not to mention that I do not trailor my rig and want to be able to drive on the Interstate, and be able to push a 37" tire without too much difficulty.

Way

Originally posted by Way
However I question the ability of a crawler box to give an obstacle a good bump.

Way

Well here's what happens when you do try...WrrrrrrrrrRoarrrrrrrrrrr...bounce...bounce.. .CRUNNNNCH....Slap...Slap...Slap...

I've seen sooooooo many D44 guy's and gal's with supper low doublers simply DISTROY there font drive-trains trying. One pour gal on Dump Bump...Way too low. Got pissed and mashed the throttle...Probably thinking that the 4340 cromo shafts were gonna' hold up...Well she lost both inner and outers (both sides), the yoke at the pinion, and sheared her 1310 double cardon right in the middle! OUTCH! First day too.

--D

Way,
It was too damn late in my work day for me to bother with your math....

Anyway, for the front range (my playground for the last 13 years) I would agree that I can do most of the trails in 4h. However, I don't have sh!t for control if I do, ie to much throttle with no go. So I end up being in low a lot. I would not go above 4.8. You have to remember the torque and power curves, and our altitude. You're at close to 20% power loss at 10k feet, where most of the front range trails get interesting.

Having to drive awhile to the trail is my biggest reason for staying on the high side on gearing around here. By going around 4.56, you are going to retain your speed/comfort on the "highway". With 4.56 and 36.5 you should be able to stay in 4th for most of the climbs (road) or be in 3rd at about 3600 rpm, which is just below the shift point on most highway grades. 4.8 will give you the best engine brake with the stock gearing in the case, but you can live at 4.56 I would imagine with your skill level.

Remember also to figure in your "actual" diameter while aired down as well for the gearing computations off-road..

j

Thanks for the info. I think that I will put in the LT230 for now and save some money for maxi low gears. I will look at the local yards for a offset d70 and then go with 4:56 gears. At that point (most likely 1.5 to 2 years) from now I will have worn out the little 33" and will jump to 37" tires being confident that I won't break too many axles. Especially the rear. I feel that this may be the most cost effective way of doing it.

Thanks for the advice and Moab stories...LOL.

Bill R. if you read this keep us updated on your crawler box condition. Let us know if it gives you any trouble. If it can be broken, I am confident that you can get the job done. :)

Way

Originally posted by Way

Bill R. if you read this keep us updated on your crawler box condition. Let us know if it gives you any trouble. If it can be broken, I am confident that you can get the job done. :)

Way

Do you doubt my abilities? I feel so left out, you've hurt my feelings. :( :flipoff2:

I've seen Kyle break stuff on the trail, mmmmmm diesel torque:D :D

Johnathan

here's a handy little ratio comparison chart:


http://www.ashcroft-transmissions.co.uk/ratio.htm

Jamie

Originally posted by Jtisdale
I've seen Kyle break stuff on the trail, mmmmmm diesel torque:D :D

Johnathan

And don't forget the series type 4.7s, that was most of it. That's why I've tried to warn people on here against those gear sets.

FWIW, with my Goodyear MT/R 35's and 4.10's with an LT-230, my highway driving is right where I would want it. The only things that really slow me down are the Eisenhower (sp?) tunnel and Vail pass. I can live with that. Otherwise it drives great on somewhat level tarmac at altitudes of 9-10K feet. The low range was fine for Moab. For "Extreme" rock crawling I would want it a little lower. Eventually I will put the Maxi-Drive Low Range kit into my LT-230. I think that would be about perfect. Unlike Jeep guys, I don't really want a 1,000:1 crawl ratio. Talk about breaking stuff....

Just my .02

Do you doubt my abilities? I feel so left out, you've hurt my feelings.

Kyle, didn't remember that you had one.... I know what you mean on those 4.70 gears. I broke a ton of things, with the exception of the gears themselves. However, I think I would have broke almost the same amount of junk with 4:10s.

Thanks for the link to ashcrofts tech data. It is simple calculations to make, but his are correct, and definately save some time.

Way

Exactly...Mr. Way does do/want's to do extreme rock crawling...If he's gonna' be saving his pennies for maxi gears/underdrive then fine...but with a 37ish" tire he should be shooting for a minimum compound low of 55-60:1 (with an auto)...Especially with a tired 3.9L and a 5K+ pound rig!

Just a thought:

If your stuck on actually DRIVING your rig on highway for major trips, then you DO have to make compromises (and/or spend big bucks...I'm talking Rovers here). But please remember, when your on a run with the big dog's and you're lugging and then lurching over obstacles, then smashing bumpers into the next obstacle, DO NOT complain about your tall gears.

When you do go lower and you start grenading CV's, R&P's and rear axles on the REALLY tough stuff, please don't complain then either. Also please make sure you have spares! I HATE(ed) having to give out my last CV to someone who lost a CV on the first or second day...A good bro is another thing...Someone I just met entirely different. Heck, it's not like we can shoot over to NAPA and pick up a CV star and cage when we are 400 miles from the nearest part's source.

When the trail leader puts you in the end of the line, consider that a favor, not a slight...Been there, done that...Got pissed about being at the end of the line, then the Rovers started breaking...Myself, then Greg, then Rich...I wasn't there for the mass carnage in Curses this year, but it wasn't pretty.

I'm ALL FOR running tall gears to keep the daily driving happy. Just remember the limitations your set-up will have on SOME trials...Note I said SOME. There are only a handful of really-hard trails that demand a reasonable crawl ratio...In Moab for example: Lower Hell, Rim, Pritchet can all be done in ANY Rover with open diff's and 3.54s' if your good...Upper Hell, Prov.Grnds and Pickle ALL require very low range (that can handle the corresponding torque increase) if you want to actually ENJOY yourself on those runs.

I didn't chop a perfectly good (well that's a stretch...Sorta' good...) rover for jollies...I was simply sick and tired of gnashing my teeth every time I had to climb a 3' under-cut ledge...KNOWING I was going to hear the CRUNCH~! any second...Or backing on near flat ground while locked (in a comp.) only to hear CRUNCH!!!...Or climbing a sick line I knew I could do only to hear the POP POP POP of the teeth on my ring gear letting go (all in one week I might add.)

Besides...I love my 90...snif...snif...

-Rant off--

-D

Originally posted by RockRover


Lower Hell, Rim, Pritchet can all be done in ANY Rover with open diff's and 3.54s' if your good...Upper Hell, Prov.Grnds and Pickle ALL require very low range (that can handle the corresponding torque increase) if you want to actually ENJOY yourself on those runs.


-Rant off--

-D

Dude, I am so with you. I have done almost all but upper hell, proving grounds and pickle open, on ten splines and 32's with 3.54. (ok, so I do have a good left foot)

The ONLY time it gets dicey with that set up is when weight/gravity becomes a factor. I am just about done with the 3.54's and open diff's. (my new vanity plate - rovrtoy).

Life is so much easier when you have a trailer queen.

j

Originally posted by Way
Thanks for the info. I will look at the local yards for a offset d70 and then go with 4:56 gears. - snip -

Way


First off, Adam Way (and everyone else) please, feel free to discuss your ideas freely. It's nice to not be the only one who builds stuff by numbers and research, not the time tested "try it out and see" method. Your rig kicks. I appreciate intelligent design.

Here's my question. You said OFFSET D70. I fell out of my chair. Would you happen to know of a vehicle that has an offset D70? I'm planning on building a custom D70 (maybe a D60) rear end for my 109 soon enough, as the 10 spline ABS axles are just too weak. Sticking with 3.54 gears, I've got the reduction farther up the p-train.

Do you also know if you can safely open up the rover stub axles to fit the D70 axles through? I haven't got a spare to start mikeing. I believe the axleshaft dia is 1.615 if I remember correctly.


J-L

Originally posted by HandBuilt



Do you also know if you can safely open up the rover stub axles to fit the D70 axles through? I haven't got a spare to start mikeing. I believe the axleshaft dia is 1.615 if I remember correctly.


J-L

No friggin way are those axle going to fit in late model Rover stub axles. I had to bore my stub axles out about 25 thousanths to fit the 30 spline MaxiDrive rear axles (max diameter 1.305 inches) and there is only about another 25 thousanths of material left on the "notched" threaded portion of the stub axle (you know, where the washers line up). Any bigger holes and you will lose the integrity of the hub bolts holding the whole wheel assembly on.

Blister

Hey guys,

Here's a kind of stupid question being posed a little late in the game, but what the heck...

I had a set of 101FC axles I regretably sold. But, I am wondering why more people aren't getting sets shipped over and having the tubes narrowed, make custom inner shafts, run the massive CV's (which are cheap cheap cheap to replace BTW), and have SIII outer hubs with your Rover brakes/wheels???

Yeah, we're talking nearly as much custom stuff, but if you're looking for off-set D70's, then the 101 axles are basically that.

Sure, it's easy for me to question what everyone else is doing, I was just thinking that if I still had my 101 axles and was doing the craziness everyone else is that's what I'd probably be going for.

If not actually narrowing them, then just running them full width with some rims off-set inwards to not give such a wide stance (or whatever....).

Just thinking.

You guys can tell me to f-off now. :flipoff2:

I'll just go back to looking at my OX and CTM joints now...(patiently waiting for installation.....)

Originally posted by Blister


No friggin way are those axle going to fit in late model Rover stub axles. I had to bore my stub axles out about 25 thousanths to fit the 30 spline MaxiDrive rear axles (max diameter 1.305 inches) and there is only about another 25 thousanths of material left on the "notched" threaded portion of the stub axle (you know, where the washers line up). Any bigger holes and you will lose the integrity of the hub bolts holding the whole wheel assembly on.

Blister

Shit.

Soo, basically there is no way to get a D60 shaft through a late rover stub axle, without it knecking down? That's dissappointing. I would really like to run the same hubs, as it would simplify the whole process a great deal. I guess I'm looking at different bearings and I'll have to turn up some stub axles.

Any other ideas?

I'd really like to keep the rangie brakes, which are great, and I'd like to keep the same bolt pattern.

I'm thinking that a complete D110 salisbury from england is the way to go...

J-L

Originally posted by Serious One
Hey guys,

Here's a kind of stupid question being posed a little late in the game, but what the heck...

I had a set of 101FC axles I regretably sold. But, I am wondering why more people aren't getting sets shipped over and having the tubes narrowed, make custom inner shafts, run the massive CV's (which are cheap cheap cheap to replace BTW), and have SIII outer hubs with your Rover brakes/wheels???

Yeah, we're talking nearly as much custom stuff, but if you're looking for off-set D70's, then the 101 axles are basically that.

Sure, it's easy for me to question what everyone else is doing, I was just thinking that if I still had my 101 axles and was doing the craziness everyone else is that's what I'd probably be going for.

If not actually narrowing them, then just running them full width with some rims off-set inwards to not give such a wide stance (or whatever....).

Just thinking.


Well, I'd be interested to see what that would look like. The only down side is the drum brakes which are definitely not great.

I've been toying with mog axles, but they are pretty much completely wrong as the diff is on the wrong side and they are torque tube axles.

I think the volvo portal axles are the way to go. I've yet to see some in person, any good pictures of the axles themselves? Any idea how much they are worth, and info on gear ratios, rim sizes, etc?

J-L

Originally posted by Serious One
Hey guys,

Here's a kind of stupid question being posed a little late in the game, but what the heck...

I had a set of 101FC axles I regretably sold. But, I am wondering why more people aren't getting sets shipped over and having the tubes narrowed, make custom inner shafts, run the massive CV's (which are cheap cheap cheap to replace BTW), and have SIII outer hubs with your Rover brakes/wheels???


You are sooooo right my brotha'...I don't get it either. Maybe it's because of the bolt pattern and drum breaks that are truly putting people off. However when you look at it in a logical fashion you'll see it's NOT that difficult of a mod to bring it up to rover spec (bolt diameter etc). The FC101's are only 3" wider (1.5" on each side) than a stock rover housing...

Seems' most either don't want to partake in a major drivetrain swap (devaluing the vehicle), or are simply overwhelmed by the effort required to pull off a mod like that. It does take time and $, but in the end you have a product your not afraid to romp to your hearts content.

--D