[alloz]

Gday guys, I'm still new to lil zooks & the aussie terrain is VERY different to my present sticky muddy STEEP virgin jungle trails of Java (Indonesia). My aussie jeep wrangler goes fine, my aussie sierra goes fine BUT my sierra here (SJ410 'jimny) runs out of steam going up impossibly steep muddy volcanic climbs The other zooks scream their heads off & go & go until they make it & I must & I do (i've aussie pride to defend) but wheres my endless horsepower like my indo brothers?
auszookers-----> what does your collective genius have to tell me ?

[bumstein]

Hi Alloz!!

Righto.. This is off the top of my head so not such a comprehensive account but here's a few things to check.

What size tyres are you running and have you adjusted your gearing to suit? If you are running large tyres without changing the gearing the wee motor doesn't have the oomph to rev freely.

If this is not the issue, then it's either fuel, spark or respiration.

Fuel-

is the carby working well? Does it rev freely in lower gears on the road?

Check the jets for blockage.

Is the fuel fresh?

Change fuel filters.

Make sure he fuel pump is working well and keeping up.

Spark-

Are the spark plugs in good condition and are they the right plugs?

Is the spark reaching the plug? Are all leads in good condition?

Is the timing set properly?

Respiration-

Is the air filter in good order?

Are there any restrictions in the intake system?

Is your catalytic converter in good condition? This one can be a silent cause of restriction and power loss.

Is there good compression in all cylinders?

My money is on running large tyres with stock gearing.. Failing this its a systematic approach to exclude possible causes and narrow down the search

Good luck! I'm sure you'll find it

[Reubs]

Got transfer case crawler gears?

[vet 180]

Bumstien is on the money.

TBH I think its nothing more than driving style or gearing. Having driven similar terrain to what you are describing and making steep muddy hills that hilux's and cruisers couldn't my guess is it's simply a case of gaining momentum at the right time and revving the living piss out the car and never letting the revs drop once you have it. It's how suzuki's are made to be driven.

[Santos]

Even if you DO have gearing for bigger tyres do you actually NEED bigger tyres?


205/70/15 = 26 inches

225/75/15 = 28 inches only gains you 1" upwards (not 2!)

Wider tyres filled at the same PSi do not give you more rubber on ground, it just changes the shape from long skinny to short wide.

195/70/15 will take you places for a quarter of an inch height penalty. Some will strongly argue that with gearing the difference of having oversised tyres to stock set up is negligible. My blind faith in physics believes it has to.


Also to add to bumstein list

Spark
-is the dizzy points? condition? are they set correctly (or swap for newer hall effect one)

-Is the vacuum advance working? you test it with a little hand operated vacuum pump, i have ocasionnally found these faulty on sierras and swifts which means the dizzy is only operating on mechanical advance

[fordem]

Santos wrote:

-Is the vacuum advance working? you test it with a little hand operated vacuum pump, i have ocasionnally found these faulty on sierras and swifts which means the dizzy is only operating on mechanical advance

A failed vacuum advance should not cause an "lack of steam" problem - the vacuum advance advances the ignition timing when the vacuum in the intake manifold is high, ie. under part throttle conditions such as highway cruise, it is primarily a fuel efficiency thing so when it fails the consumption increases - I've been running my Swift with no vacuum advance for longer than I can remember, and believe me, that thing has all the steam it needs.

[Santos]

Look at it another way. A connected faulty vacuum advance is a potential vacuum leak.

[fordem]

Still unlikely to cause a "lack of steam" problem - vacuum leaks on carbed engines cause a weak mixture at idle and if it's a large enough leak (which this won't be) the engine won't idle, but once the throttle is open (which it has to be if you're looking for "steam") the vacuum is minimal, further reducing the air flow through the port.

[alloz]

THANKS GUYS.....its times like this I wish I was back downunder. Your suggestions have me thinking it IS my Suzuki driving style (not aggressive enough) & tyre size. (currently 255x80xR15)
I'm going to firstly swap wheels with a buddy for smaller & wring the little zooks neck, next adventure (like the rest of the club do!). Special thanks to bumstein for 1st reply.
Feel free to give your 2bobs worth on what tyres I should run....to mesh correctly with original gearing !! Cheers...Alloz (the all ozzie guy)

[bumstein]

Ah thanks very much mate!! Very nice of you to acknowledge

Tyre size to match original 1.3 gearing is 205 70R15.

Your tyres are waaaaaaaaaaaayyyy to big. They are 18.11% larger than standard.

Here's a comparison on size of standard vs yours



My suggestion is decide on the tyre size you want to run then select gearing to suit.

Standard gearing - standard tyres
225 75R15 - either 1ltr transfer case or 4.16 reduction gears.
Run 31's - 4.9 gears

Visit LROR's site and all the hearings are there with a guide on what tyres they suit.

[Gwagensteve]

D'oh- beaten! Anyways- here was my response. Change the gearing. Your tyres spec out to over 31", if that's accurate, your gearing is something like 20% out. 1.0's have a tall first gear and a tiny clutch- it's going to be hating the gearing being that far out.

You need 4.88 diff gears from an lj50. Even 4.56 from an lj80 would be a big improvement and shouldn't be too hard to find where you are.

[Gwagensteve]

My 2c- do diffs before transfer in a 1.0 litre for your use because the risk is you'll have inadequate wheelspeed in mud and high range won't be lowered enough for road use. (1.0 sierras already have 1.58 high range, not 1.409 like a 1.3 which is what LROR's tables are based on)

[bumstein]

Oh right you are Steve! I was thinking his was 1.3, my oversight

[alloz]

Many thanks oh great ones...............and YUP I just replaced the clutch & the new one feels same same--->shithouse. I'm going to buy tyres today. Unfortunately Java does not have "shops" or "wreckers" to whip into & fetch what I really need. Changing gearing 'over here' means finding someone with a clapped out set & finding someone else with a dirt floor shelter to fit them & despite being a 4Wdriver, I'm not going down that track <--pun intended

[bumstein]

Haha!! Nice pun

If you budget allows, order some from LROR

[Gwagensteve]

Whole third members swap over in the case of lj80. No need to do any complicated/difficult work. I think the whole job could be done with a 10 and two 12mm spanners. I bet there's some junk lj80's sitting around somewhere considering how many of them I've seen in Bali. It's nowhere near as difficult as changing a clutch.

In fact, I bet you could swap diffs with someone with an 80 who wanted more road speed/lower revs.

Swapping to stock sized tyres will erode off road performance which is what your complaining about now.

[Santos]

Alloz gives us feedback on how the smaller tyres go if you do try it out. Personally i am going against the grain and recommending a 195r15 (195/80/15 , 27") or 205/70/15 (26.3) LT tyre with good offroad tyre tread to get maximum steam from the 970cc of fury & your new aggressive foot. Done a bit of tropical jungle mud in 2wd beaters in brazil i imagine indonesian conditions are pretty similar. Humid, slick and slidey rather than deep and boggy?

Smaller tyres is the cheapest direction you can take. I find quality stock second hand wheels are crazy cheap here in australia as everyone is 'going bigger', probably the same in Indo. You don't need to sell you 31's. You can even start upgrading your diffs/gearing later down the track using the smaller tyres as it will always put more steam on the ground.

I find the whole science of it best explained in these 3 articles
Wheel Tech 1: Wheel Weight slows you down
Wheel Tech 2:Width Matters
Wheel Tech 3: Wheel Diameter effect on Performance

Granted these are 'Ricer' articles rather than offroad but the Physics of it does not change, these things WILL happen when you deviate tyre size irrespective of how much gearing you have to compensate.

PracticalMotoring.com.au #26 Offroad Myths# wrote:

3.Wide tyres have a greater contact patch – nope, same as narrow, just a different shape. Narrow tyres have a long and thin patch, whereas a wide tyre has a short but wide patch. Narrow tyres have lower rolling resistance than wide so are generally better for offroad and fuel economy. Wide tyres have better cornering grip, in general, but that’s not because of a greater contact patch area. .

Full article here

If after that all that, you are running 16-20psi , had a few testbed trips and you are finding ground clearance a problem with no amount of driver ability can compensate for shitty small tyres put does 31 back on, burn them clutches, fry the engine and tell me i am nuts

fordem wrote:

Still unlikely to cause a "lack of steam" problem - vacuum leaks on carbed engines cause a weak mixture at idle and if it's a large enough leak (which this won't be) the engine won't idle, but once the throttle is open (which it has to be if you're looking for "steam") the vacuum is minimal, further reducing the air flow through the port.

The vacuum is not 'minimal' the actuator on the sierra dizzy is the only vacuum i can't hold close seal with fingertip and to remain place (how i test all other vacuum actuators on car) If the seal is broken that force is going to suck in a lot of air and mess up the 'how much fuel signal' for the main jet. The port sits before the throttle but AFTER the venturi. You open the throttle it will suck air in .
It's a single barrel carburetor, you want a 100% of the airflow passing through the venturi to make sure the main fuel is picking up as much fuel as it possibly can.

I also checked the Sj410 factory manual and the carburetor does use an extra enrichment circuit activated by manifold vacuum. I don't mean to sound like a zealot but if enough of these little things are out of alignment it does affect 'steam', taking a few extra minutes here and there is worth it

[Gwagensteve]

I'm really puzzled as to why you'd go to smaller tyres rather than fix the gearing. I could understand going to a narrower tyre to increase ground pressure in slick mud, but with smaller diameter tyres you're shortening the footprint, reducing ground clearance and increasing how hard the car as to work (you've just made every obstacle a bit bigger to deal with) Sure, you'll get some revs back, but overall you won't have made the car more capable. It's not just ground clearance too - the smaller tyres have a shallower sidewall which means you can't air down as far without risking rim damage (and the tyres are more susceptible to coming off the rim at low pressure)

I ran my LWB SJ410 on 34" tyres with a standard motor and it never lacked off road performance in steep terrain, because it was properly geared. (in that case 6.4 transfer gears, standard diff ratios) I subsequently went to a 660cc turbo triple and lowered the gearing even further by adding 5.12 diffs and again, it was absolutely fine off road in all conditions.

Yes, when I ran that motor with my 35" tyre combination, the car felt like it lacked the torque to generate wheel speed, but my 35" wheel/tyre combination weighs nearly 50kg per corner. That's a long way from a 31" tyre

As we're in Victoria we certainly do have our fare share of steep muddy hills. wheel speed and drivability on slick muddy climbs are very important areas for our cars performance.

[Santos]

No puzzle

Reducing ground clearance? Never banked my car between ruts. in fact i usually find one wheel stays in rut and wheels, i have 40mm lift dakkars springs, i liked to keep my centre of gravity as low as possible. Stable.

Working the car harder? How? It might sound like i'm working it harder but it isn't getting the same strain. I always note that the people breaking diffs and gearboxes are people with big tyres. 31's are pretty heavy compared to stock tyres.
It effects acceleration, fuel consumption and other things. Read through the 3 links on wheeltech. Smaller diameter tyres will always improve acceleration. Power(Kw) is (torque NM x rpm)/9549 from there you underdive it for mechanical advantage.
Or another way to look at it.
If your tyres are smaller you effective crawl ratio is always higher.
Eg 27 with 4.11 diff is the same as 31 with 4.68 diff, but if you had that 4.68 diff with 27"tyres you got an equivalent 5.3 diff on 31. Tyre diameter is'always the 'final gear in power to ground

Shortening the footprint? Lost here. 900kg vehicle running the same air pressure has close to the same surface are of contact patch on the ground

one looks like this

IIII
IIII
IIII

The other like this

III
III
III
III

I have considered doing a science experiment of painting the tread of tyre , lifting up the car and dropping it down to stamp a piece of paper, then lifting up swapping out 4 much larger tyres with identical tyre pressure, paint repeat drop. I think for it to truly work i would need same brand/model tyre in both sizes to eliminate variances in construction, tread shape, material composition blah blah Needless to say unlikely i will ever get round to it



I can respect that we all have our own experiences and we all tackle things differently. Its why i started out with saying i am going against the grain. Generally my suggestions are cheap simple alternatives. I always in awe of how well a stock suzuki performs.

[Gwagensteve]

You're overthinking it.

A shorter tyre has a correspondingly shorter footprint. Don't think this is true? Exaggerate the example. Make the tyre 2m diameter- does that make a footprint longer? Of course it does. A longer footprint works better than a shorter footprint. Evidence? Have a look at a bulldozer- long footprint=capability.

Yes, a bigger tyre is heavier. Yes is takes more power to push it, but the advantages outweigh the disadvantages, and when a car is so easy to gear it's a no brainer. I've owned and or driven sierras running everything from stock tyres to 36" tyres. Bigger tyres get the car further, which it sounds like what the OP needs- lack of steam or not- he needs to be making it easier for his car to climb, not harder. That's a gearing issue.

[Santos]

sorry can't see this footprint thing, your downward force is at the same point over the axles, a tyre is a round circle, the downward pressure flattens contact patch, a bull dozer has a nice flat long track

that with fact for a tyre to be bigger is for all intensive purposes needs to be wider. What you gained in width you lost in length. The only way you can regain that length is by running a lower pressure. The lowest i've run is 12 on sand and 16 elsewhere on some very exceptional occasions 20 gets me through a lot of stuff . I haven't had it come off a bead

What it comes down to is i am saying 'mechanical advantage' outweighs tyre size in my experience. The car is lighter more responsive and steers. I have had the same car with pretty much the stock set up for 12 years. I am almost certain you have been offroading more in the last 6 month than i have in the previous 6 years. It doesn't actually negate anything i've said or experienced.

[Santos]

Gwagensteve wrote:

he needs to be making it easier for his car to climb, not harder. That's a gearing issue.

Like of said in previous post, smaller tyres give more gearing. Whack in the LJ diffs and he will have more gearing with 27 than 31's, more mechanical advantage and therefore steam

[vet 180]

Gwagensteve wrote:

My 2c- do diffs before transfer in a 1.0 litre for your use because the risk is you'll have inadequate wheelspeed in mud and high range won't be lowered enough for road use. (1.0 sierras already have 1.58 high range, not 1.409 like a 1.3 which is what LROR's tables are based on)

This x100

If it where me I would consider slapping on some stock tires for now and building up widetrack diff's on narrow track spacing with vitara 5.12 centers and lockers. Or just build up the diff's and leave you car as is as it's reasonable simple to do. Then put you 255/80's back on which is a pretty cool size for a sierra.

One thing that Gwagonsteve has alluded to is that a bigger tyre will have a better foot print, deflate better and generally drive steep muddy hills better when gearing is equal. So I would try and gear it is possible.

Any pics of your beast?

[Gwagensteve]

Santos, you need to do your paint contact patch experiment. It will prove I'm correct. Tyres deform at the contact patch, it's the air that determines this. Put 10 psi on a large tyre and more rubber touches the road than 10psi on a stock tyre. If this wasn't true larger tyres wouldn't offer increased traction. If you can't visualise this you'll absolutely have to do the experiment yourself, although the experiment you describe has been done and you'd be able to find it with some searching. It proves my point. It's why, on slick mud, 9/34 swampers and equivalent sized centipedes outperform almost any tyre on a Sierra- it's all about ground pressure and footprint shape.

Vet- the op can't work out how to find lj80 diffs which are common where he lives. He's going to have no chance of finding and fabricating all the things you've suggested, and it might not make the car better anyway- increased track width is of almost no concequence in mud. My own car lost capability in mud when I swapped to 5.12 geared WT diffs from 4.1 geared 1.0 litre diffs, even the I added a front locker when I went WT.

[MrRocky]

I wouldnt even have 12psi as a start pressure for offroad in a zook.
Im normally 6psi on a 235/85r16 (32) and have never lost a bead driving very enthusiastic. Tyre brand/size and rim brand/size are overlooked by many but can be the difference between going to 10psi as a minimum and getting away with 4psi sensibly driving.
Small tyres are great until theres a rut or a cutout and your diffs get hung up or smash the side if your car.
A zook motor should be on 4k at least @ 110 high range gearing and as low as you can get it in lowrange

[alien]

re: pressures - with 31" KM2's i opened a bead twice running 8psi. Only tyre that's ever done that for me. Kumho KL71, Grabber SRL, Cooper STT and Simex ET all ran 6-8psi no worries. The KM2 needed 10psi to stay on the rims.

So far as the OP... I agree with Steve. I would question tyre choice though. Something SUPER aggressive in a 31"+ tyre is no where near as meaty when scaled down to a 215/75 or similar. If gearing is not an option, a far more aggressive tyre might see you holding your gears a bit longer at lower RPM with more grip.

Now, something different - given you're in a lot of mud, have you checked your flywheel/clutch isn't covered in crap and slipping?

[drakan69]

Santos wrote:

Shortening the footprint? Lost here. 900kg vehicle running the same air pressure has close to the same surface are of contact patch on the ground

I'm guessing you arrived at this given p=m/a?
Deflating any tire does increase it's contact patch but all tires are constrained to the tire geometry as a whole. A larger tire has larger constraints, and therefore a larger area at the same pressure as a smaller tire. Your assuming the air pressure inside the tire is equal to the ground pressure of the tire, which would be true for a certain pressure and a certain load, however ground pressure isn't linearly proportional to tire pressure.

Santos wrote:

sorry can't see this footprint thing, your downward force is at the same point over the axles, a tyre is a round circle, the downward pressure flattens contact patch, a bull dozer has a nice flat long track

As you deflate a larger tire your contact patch becomes a longer flater shape, much like the track of a bulldozer. The longest flattest shape and therefore the biggest tire at the lowest pressure will have the least ground pressure and therefore wins the contact area competition.

[Santos]

Thanks drakan that actually helps

[drakan69]

My pleasure, it was merely a little more explaining of what Steve said above.

Given that Alloz already has the 255/80r15 in my eyes his next step should be to regain some of the lost torque, diff gears provide the cheapest and easiest way of doing this while still keeping the advantages his vehicle already has.

[vet 180]

Some visual assistance:

http://expeditionportal.com/mscott/User ... down/5.png

and here in reference to tyre size:

http://static.evo.com/content/kbis/bike ... _final.png