Hilux 4x4 Forum

Hi guys
what's the biggest size tyre that can be fitted on a standard 15" hilux steel rim without having to do diff. modifications?

Depends on how strong your engine is.

I have seen some Hiluxes running 33" without suffering.

I'm running 33's on the one Hilux with V6 conversion and 31's on the other with standard 22R motor. Both with standard diffs and no problems. Speedo is spot on against GPS with 31's but the 33's give a significant under-reading.

I don't think the diffs are a problem with motors that don't deliver a lot of power / torque like a V8, but I think you're going to find the 2.5 to be sluggish and underpowered with 33's.

The engine is the 2kd 2.5 ...quiet sluggish. ... with 225/75R15 tyres at the moment !!!
Got stuck 2 times in deep sand with 1.8 bar pressure tyres? think maybe tyres too thin !!!
First time in Kaudum then in Mudum n.p

For thick sand try 0.8 bar

Your tyres are not the best for sand driving. The bigger the footprint in sand, the better. The footprint of a tyre is affected by the diameter but more so by the width, and then a bigger profile allows you more deflation which increases the footprint.

Yours are just over 28" in diameter, 225mm tread width and a profile height of just under 169mm.

By comparison a 31" tyre (31x10.5-R15 which your vehicle should still be able to handle), has a diameter of 31", tread width of 267mm and a profile height of just under 203mm. It may not seem much by direct comparison, but it's behaviour in sand is very significant, especially when deflated.

That's what I would fit taking into account your sluggish motor and fitment without any major modifications.

Otherwise you could look at 235/75-R15 tyres which have a diameter of just under 29", a tread width of 235mm (only 10mm more than yours) and a profile height of 176¼mm (just 7½mm more than yours). Not a huge difference and you probably won't notice too much difference in the "slugishness" of the motor in handling that size, but it will give you a little more deflation ability. It will make a difference in the behaviour of the tyre in sand, but will it be enough to keep you from getting stuck? Maybe, but I would still prefer the 31x10.5-R15.

33" would be even better but then your motor is really going to battle and you will need to do some more serious mods to get then to fit without fouling.

Then deflation ... as Pieter suggests, try going lower tyre pressures. 0.8bar as he suggests is ok, but I wouldn't like to run long distances with such a low pressure, especially in hot conditions. The continual tyre sidewall flexing creates heat of it's own and if it gets too hot it will fail .... then you're left with a shredded tyre. Run at 0.8 bar where you really need to but re-inflate to 1.2 bar for general sand driving.

Thanks Pieter-Andy for your comments (31"×10.5-R15) it will be. Maybe next thing to do is to look at fitting a 3.l engine with autobox.... would that be possible? ?

When Driving 50 km from home, the bigger tyres with the bigger footprint would be fine.
The only problem, when you are over landing, you are driving long distances to use the longer profile, once in a blue moon.
The bigger tyres will slightly increase your consumption over the whole trip - as they will slightly drain power from your vehicle.
I drive the D-4D 3.0, on which I went slightly smaller than spek - to 245 X 15 X 75 - to get better over-all fuel consumption.
You should not have got stuck in Kaudum or Mudumu (Mudumu only has thick sane in the eastern part of the Park) on the pressures you were using,
unless you were towing, or did not maintain momentum, but, if you get stuck, all you need to do is lower tyre pressure.
I realize that with a heavily laden over landing vehicle, you may not be able to lower your tyres to o.8 bar, but first dropping to 1.5 or then 1.2,
should be more than enough to get you out most over landing situations, with a heavily loaded vehicle.
Should you be driving dunes, you would be advised to travel much lighter, so that your tyres can be let down lower.
I travel with a heavily laden camper so seldom deflate to less than 1.8 or 1.5 in extreme cases.
Driving the sandy/dune sections in the early mornings is more advise-able, when the sand is more compacted.
The sand becomes more aerated, as the sand is warmed by the sun later in the day, then becomes more difficult to drive.
I would stick with the tyres you have or go to 245 X 15 X 75, but even this small amount will increase your fuel consumption.
Safe Travels...

Hi Edge
I also drive with a camper on the back, like your one (just seen the photo ) the extended version, and yes was loaded in 3rd gear low (diff lock Not engaged) engine lost power, changed into 2nd ...too late. These tyres only done 13.000 km so i will just wear then down and change to slightly bigger tyres also for better clearence. Thank you for your reply
(By the way what modifications have you done to your hilux?)

mingos wrote: ↑Tue Dec 10, 2019 6:15 pm Hi guys
what's the biggest size tyre that can be fitted on a standard 15" hilux steel rim without having to do diff. modifications?

I fitted BFG 245/75 right form the start. Was not bad, but eventually chipped the 2.5 to be able to overtake trucks easier.

But looked a bit too wide for the rim.

The standard 16" 2.5 steel rim is a 6J. Assume 15" might be similar. A narrow rim. Fitting wider (or to wide) tires will cause it to bulge.

The biggest problem with the 2.5 engine (even more so if you have the lower spec version of the 2.5) is that it has not power/torque at very low revs.
And if heavely loaded even more so. Especially under 2000 rpm.
I have fitted a Dastek UniChip to mine to eliminate that issue . Made a major change to how it drives.
Mine has similar outputs to the higher spec 2.5 that were fitted to the DC Hilux and Fortunner.

Hi Edge
I also drive with a camper on the back, like your one (just seen the photo ) the extended version, and yes was loaded in 3rd gear low (diff lock Not engaged) engine lost power, changed into 2nd ...too late. These tyres only done 13.000 km so i will just wear then down and change to slightly bigger tyres also for better clearence. Thank you for your reply
(By the way what modifications have you done to your hilux?)

Everything that is needed.
Send me an email to edgew60 at gmail dot com & I will send you everything that I have done.
You will have less power with bigger wheels...
Safe Travels

For a start just deflate more. Easiest and cheapest to experiment with.

And 225/75/15 is already bigger than the standard size, which was decent in offroad situations.