Hilux suspension

even stock standard they are one stiff spring. My exes would almost throw itself off the road on minor corragations and they will lift rear wheels quicker than quicker than than the front due to the springs not having any give

You must have a different model than mine. They only work on three leaves until heavy loads bring them down onto the two shorter and heavier flat ones. If you try bouncing them unloaded with the shocks disconnected, those three are as soft as can be. Even if you put one upside on the ground and jump on it, it will bend it easily.

I don't know where your located but where I am (in Qld) those 31 inch tyres are illegal.

When I got my Hilux, the previous owner had bigger tyres and heavy duty shocks and the ride was horrible. The missus refused to ride in it.

Put original 205/16 tyres back on and standard shocks, ran the tyres at close to recommended pressure as Splits said above and the ride is fine. Has a steel bull bar so I run a few pounds more than recommended in the front. I change the rear pressure depending on the load as per the recommendations and it's all good.

Reducing the pressure will soften the ride but you may create other problems. Too little pressure will wear the outside edges while too much wears the centre. You may find to get the ride acceptable, you have to go so low the edges wear first and the walls become so flexible that on road handling is compromised.

Those tyres are not only illegal in Qld as Lex said but NSW as well. I am not sure about other states. They are two inches (50 mm) in diameter over standard size and about 12 mm wider. The width is not a problem legally but the maximum permissible increase in diameter is only 15 mm. That much oversize will make your overall gearing higher and that is the last thing you need when towing. It will also change the brake ratio resulting in an increase in stopping distance.

Right now your car has oversize tyres, vastly stiffer springs, non genuine shocks and pressures way above factory specifications. You are now way off into the unknown and only a suspension engineer could tell you exactly what that combination is doing to the car and if the front sway bar is handling weight transfer properly on corners.

The only thing to do is as I said before, return it to standard and go from there. Unless you are going to use this car as a play thing in extreme conditions, it should meet your needs in stock form. It has a towing capacity of 1800 kg and Toyota recommend in the owner's handbook a tow ball weight of 5 to 10 percent of trailer weight. Unless you have one of the heaviest campers on the road, you should have no problems with a standard car.

Mario Play around with tyre pressures first, 40 gives best economy and wear but their is no way I will round 40 in my Jack. Try 35 , then 30. The bigger tyres have got nothering to do with the stiff ride, it is the pressure you are running and the extra leaves. For the record two of my mates have this model sr5 and both ride very well and they both run the 255 , which incidently ride better then the 205.
HD shocks improve handling not ride generally.
Cheers Pete

"they both run the 255 , which incidently ride better then the 205"

Interesting. I think the 205/16 ride much better than the 255/15 on the SR5.

Work better in sand too.

Lex that is a matter of opinion and tyre pressures, but the wider tyres sure as hell handle better. The standard HT tyres on the d4d are pathetic, and reach their handing limit at very low speeds. We run about a Doz at work, some we have fitted with a wider lower profile geolander which is much improved
My old Runner had 205s by the way
Cheers Pete