Outer Limits 4x4 Board

Hi all,

Been advised against putting 33x12.5s on 8" rims, is this good advise or bogus.

youve been advised against putting that size tyre on that size rim? = Bogus.

Or you've been advised against putting that tyre & rim combo on a sierra? = has some merit.

Bit of both actually.

My main play is sand, and width is a biggy.

I have 31x10.5s at the mo, they are pretty hot, but if ya gunna play, play hard.

Im gathering bits for a major refit, and gunna go for 5.38 diff gears, suits 33s pretty nicely, so why not ?

i have got 33 on 15x8 rims. the only thing is you loose full lock in the steering as the tyres rub against the spring.

just for sand work , even with those gears , I,d still run the 31,s !!
Hi range is your friend !!

on mates rock crawler/winch challenge/dune buggy ..
we run 37,s for comps & 29's on the dunes !!!

wheelspin and speed is your friends on the sand.

moose wrote:just for sand work , even with those gears , I,d still run the 31,s !!
Hi range is your friend !!

on mates rock crawler/winch challenge/dune buggy ..
we run 37,s for comps & 29's on the dunes !!!

I have stock (3.9?) gears in her now, and 31" bajas, she does a ripper job, air down to 5psi and 2wd only. Only ever high.

Very occasionally I stuff up, usually when someone else is in the car an im a bit timid, and so, get out, free wheeling hubs in, low range, get out very easy, and free wheeling hubs back out an high an away.

I do notice the power difference loss with the hubs in, this is why they are never engaged, and partly why I want lower ratios.

She will go where no others go in 4wd, well, standfast other suzis of course.

She does work a bit but, so as I have been advised here many times, now that she is about to get a new everything, do the gears as well

nicbeer wrote:wheelspin and speed is your friends on the sand.

Absolutely and she does that well now, cant get to 3rd high very often but.

I recon as I will rise by 4-500 revs from stock, ie 29s and 3.9, by going 33s and 5.38, so, im higher up the torque curve.

torque curve in a suzuki? it is a flat line across zero

Zook_Fan wrote:torque curve in a suzuki? it is a flat line across zero

If its a shorty you can't get 15x8rims engineered in NSW but on a LWB its legal

It is, actually, not recommended to fit a 12.5" tyre to an 8" rim. Techncially, the minimum rim width for a 12.5" tyre is 8.5", but nobody pays any attention to that.

Ever wondered why all those paris/dakar cars run 7" wide tyres? and even 4 tonne, 800HP trophy trucks don't exceed 12.5"? if there was a ratio of effectiveness and 12.5" tyres were effective on a sierra, a trophy truck should have tyres about 5 metres wide to work.

It's because width is not your friend in sand. A wide radial tyre sets up a bow wave of sand in front of the tyre, so the effect is like your trying to drive up hill all the time- it saps power and hurts drivability.

33 12.5's also have pretty much the worst height/width ratio for drivability. You're looking for the tallest, narrowest tyre you can run - a long narrow footprint is better than a short wide one.


Steve.

Steve, I respect your knowledge greatly, but here you are only partly right.

Sand does set up a pressure wave, and yes its like trying to drive uphill, and it sux, is why you want as big a footprint as possible, or power.

With my lil toy, in 2wd only, on very soft sand, where you walk deeper than your ankles, (5-7psi) going slow, she will work real hard, an leave a bit of a track, but once I feed it to her, she gets up on top and floats, hence power is a ripper, and when I have always asked about more power on this site.

I get away with sand play simply because of the size of my footprint, and if bigger, there would be less that I could not conquer.

Diameter is the key to overcoming low power and the pressure wave, also a big footprint, actually, helps even with power.

The bigger the footprint, the less the square inch weight.

Air down a 6" wide tyre, and the same in a 12" wide, you have effectively doubled the size of your footprint, and so, halved the weight on the ground.

Sort of like snow shoes.

Question, why is a 33x12.5 the worst combo ?

mine are 12.5's........yet to take it on sand.......

I personally cannot see any significant gains in a sand oriented vehicle going from 31x10.5 to 33x12.5. I just personally think for the large effort required to go up to that size, you will find such small gains (if any). I'd stick with the 31's and have fun.

Also you say 5.38 diff gears are planned to go in there. They are not standard production, they are aftermarket only. personally I'd go the 5.12 Vitara C&P over the 5.38 as they are plentiful and cheaper if you should ever kill one. Also the 5.12 is probably going to be enough gearing for a 33 tyre for sand use (just lower than standard), and notably lower for 31s.

Highway-Star wrote:I personally cannot see any significant gains in a sand oriented vehicle going from 31x10.5 to 33x12.5. I just personally think for the large effort required to go up to that size, you will find such small gains (if any). I'd stick with the 31's and have fun.

Also you say 5.38 diff gears are planned to go in there. They are not standard production, they are aftermarket only. personally I'd go the 5.12 Vitara C&P over the 5.38 as they are plentiful and cheaper if you should ever kill one. Also the 5.12 is probably going to be enough gearing for a 33 tyre for sand use (just lower than standard), and notably lower for 31s.

I didn't think there would be a big difference, but in a non powered vehicle, anything helps hehe, tis why I have even gone with redline oils thru-out, a little here, a little there, and it all adds up.

Will the Vitara C&P fit, I didn't know. Do I look for a model, or are they all 5.12.

Thanks.

33x12.5 is the worst combo because you have effectively a square contact patch which has all the downfalls Steve mentioned. You want a long footprint to be effective in sand, snow, mud. Granted if you have high horsepower you can use a wide footprint to great effect but they are also usually in conjunction with a tyre like a bogger or paddle type tyre that gains most of its forward motion via the tyre throwing the debris backwarsd helping with forward motion.

Steve did say you need a larger footprint hence the tall skinny tyre which when aired down does give you a bigger footprint, just a usable one that wont sap any power the Sierra struggles to make

I think all 1.6 vitara manuals from '88 to '98 are 5.12 C&P. Only the front C&P fits though, rear is bigger. Someone will correct me if I am wrong, as some people really know there stuff about this.

I think you'll notice the difference with the gearing, because then you will be able to use 4wd high without as noticable powerloss which you mentioned above. I'd do this first, try it, then if you still want more think about tyres then.

Honestly my Sierra was terrific on the sand with standard tyres!

david123 wrote:Hi all,

Been advised against putting 33x12.5s on 8" rims, is this good advise or bogus.

I had 33x12.5" on 7" rims on my Sierra.

I now have 33x10.5" and personally feel its much better.

Mike

mike_nofx wrote:

david123 wrote:Hi all,

Been advised against putting 33x12.5s on 8" rims, is this good advise or bogus.

I had 33x12.5" on 7" rims on my Sierra.

I now have 33x10.5" and personally feel its much better.

Mike

Mike,

Why is this ??

I was recently reading about Kumho's development of tyres for the Paris-Dakar and similar events. Basically you are continually trying to climb out of a hole when driving on sand and wide doesn't help. Also keep in mind that the 12.5" wide tyre is going to have more rotational mass to overcome and windage which won't be helping either. Taller is great if you can gear it but too wide just may hurt you especially with a lack of power. Many years ago cars used to cross the desert in 2wd with only skinny BUT very tall tyres.....food for thought.