Abour tyres & Diff Rates

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P

pablosubo

10 Year
Joined
Jan 15, 2011
Threads
12
Messages
38
Hello! Once again here, and once again needing help!!!!:crybaby:


The thing goes like this.

In some month time, I will be changing my tyres since my 31" Kuhmo have serve me for more than 2 years...

The thing that I would like to increase the diameter in order to gain height.

My rig is a BJ-70, which means that i´ve got under the hood a 3B diessel engine with out turbo, which means 90 hp. Futher more, since it´s the miliar version, it has a 4th gearbox.
With the 31 tyres i find it to be a perfect combination in order to have enough power on off road, and enough velocity on road. Right now I´me with the original diff relationship of 4.11

The thing is like this. I´ve been serching which diff relations are aviable, finding bot 4.56 and 4.88

I believe than using 4.56 relationship, wich woild increase the relationship by 11%, will do OK with 34" tyres, which represents an 10% of diameter increase.

The overall perfomrance will be affected ony by a 1% in power increase (+11-10 = 1%) which means that my TLC will have 1% more power an 1% less speed. This 1% in power increase will help to move a thiker tyre.

I think that the 4.88 diff relation is too much (19% shorter!).
If I put a 35" tyre, the overall difference would be of 6% (+19 - 13= 6%). And going for 36" i think is too much (not mentioning the prices and how i would get thoes tyres on its place!).


What do you thing about this? I would really appreciate your feedbak.

BTW: I´m still haven´t uploades fotos of my bb. I´ve been doing some pretty nice mods building a bumper and mooving the p.t.o winch in order to increase my entrance angle. Right now i´m waiting for the OME suspension kit which will give me some +50 mm of heigh increase to use the 34" tyres....

REgards!!!

Pablo
 
turbo it, 33's and 4.11's - all around great setup.
 
Thanks Glenn for the answer, algouth i´m sill a little mess up.

The turbo gives power at high RPM.
When rockcrawling RPM are low and if I mantain my 4.11 diff with 33" i´m worried no having enoug torque....
Still with the idea of 4.56 and 34" (or may be 33" if 34 is too much).

Another thing is that my 3b has already 300.000 km, and althoug it looks pretty in shape, i´m not sure hoy it would tolerate the tubo.

I would reallyt appreciate other oppinions.
Regards!
Pablo
 
Hey Pablo,

i've driven my BJ70 on 255/85R16's = 33's, stock 4.11 diff ratio and stock suspension.
The engine is the updated, "more powerful" 95hp 3B with the rotary injection pump.
It's pretty much okay for daily use and a little weekend fun in the mud, but the overall ratio is too long for some serious action.

With your setup and thinking about rock crawling i would go for the 35's and the 4.88 ratio.
If the 35's don't fit that nice you can still lift the body about 1" or 2".
On the other hand you gained more height, there is a huge range of 35's out there and your rig is ready for even larger tires.

Additionally you can find massive information about any modification you have to do on your BJ70 to fit 35's on IH8MUD (suspension setup - SOA vs. SUA, gear ratios, bodylifts).

good luck
 
If you want lower crawling gears consider the Marks's 3.05 and you can preserve your highway economy. I have Marks gears and 35's and it rock crawls pretty good at Moab. Lower transfer gears are available 4:1 (Toybox, Advance Adapters) but costs escalate.

In any event do the upgrades incrementally so you know the impact of each upgrade. With improved skill and experience on the terrain you wheel on you will be a better judge of what you need.
 
Thanks a lot for all the advices. One thing I did not mention is that I cannot lose too much speed in highways. Where I live, I mut do at least 700 km in order to go either to the sand, mud or mountan... that´s why i must make a good overall desition...
4.88 will kill me in the highway....


Yesterday I sarted to evaluate Tcase mods.
The cost are almost the same if you consider that diff cost must be multiplied by 2, while tcase not.

I will try to get a 33" tyre to test it how the 3B with 4.11 dif relations takes it on highways (acording to Tonito, its experience was good... but I must test it in my rig with 5 hp less...).

If this looks OK, I might modify the Tcase to 3.05 and get a good overall result: 4.11 dif + 33" + Marks Tcase gears (choice 1).

If the 3b cannot´ move the 33" in highway, then there are 2 options.

Choice 2: 4.11 diff + 33" + Mark´s 3.05 + Turbo

Choice 3: Swap to 4.56, go for the 34 and after thar evaluare either Turbo or Tcase mod.

As you can see, options are listed in $$$ order. The most attractive optoin tecnically speaking is Case 3: I get the big tyres (34"), I will mantain my speed in higways (since i´m leaving almost the same relationship as the original) and I got the extra HP I need either from the turbo or the Tcase, depending the test...
But case 3 is also the mostg expensive options of all... I then is when I need to really evaluate how much I love my rig....:flipoff2:
It´s a Lot of maney (consider I have 50% more in order to bring all this from usa to Argentina!!!). But also is my passion.

Ok, I´ll take a time to reevaluate all this. Meanwhile, if any other idea comes in, I will really appreciate all the oppinions you have.

Thanks a lot for helping me out! An :beer: for a great 2013!!!!
Pablo
 
I had the 3B/H55 combo on my BJ70, running 33s and I could cruise on the highway at 60 MPH no problems unless you hit the hills, then you'd bump back to 50MPH on moderate hills and a bit slower on the really steep stuff. Wasn't hardcore for wheeling, but the first gear on the H55 is pretty low. It's a 3B, doesn't leave you much to work with:grinpimp:

As far as the Mark's transfer case gears, I am in the process of installing the overdrive set on my Troopie, 8% overdrive in Hi and 44% reduction in Lo. Pretty nice mod for somebody looking for speed on the highway and low end on the trail without having to re-gear the diffs:meh: And being in Argentina, Advance Adapters is a USA distributor of Mark's $WD stuff, so that may save a bit of coin on the shipping.
 
phrogg4evr said:
I had the 3B/H55 combo on my BJ70, running 33s and I could cruise on the highway at 60 MPH no problems unless you hit the hills, then you'd bump back to 50MPH on moderate hills and a bit slower on the really steep stuff. Wasn't hardcore for wheeling, but the first gear on the H55 is pretty low. It's a 3B, doesn't leave you much to work with:grinpimp:

As far as the Mark's transfer case gears, I am in the process of installing the overdrive set on my Troopie, 8% overdrive in Hi and 44% reduction in Lo. Pretty nice mod for somebody looking for speed on the highway and low end on the trail without having to re-gear the diffs:meh: And being in Argentina, Advance Adapters is a USA distributor of Mark's $WD stuff, so that may save a bit of coin on the shipping.
Click to expand...

Thanks for the feedback. Do you remember which diff realtionship did you have?
I´m with H41, so it would be as if I wold be in 4th all the time.
Supponsing you had 4.11, if you coud cruise at 60 mph with the 3b and in 4th gear (5th = 0.845) this means that I will be ok mantaing relationship with the 33".

Thanks a lot for the imput!
REgards.
Pablo
 
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