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LC300 steering issues

Reader question:

Hi Robert – thought I’d as you a question please, as you seem to have broad coverage of lots of car topics.

I’ve got a 6 month old LC300 GXL, to which I have fitted a set of Cooper AT3 LTX tyres, and added a bullbar and a winch. The new tyres are 265/70R18 which is one size up from the OEM 265/65R18, so I don’t feel that’s outlandish.

But now it ‘bump steers’ if I hit any roughness in the road. On a smooth road it is just fine. But if there is some broken up bitumen on the roadside edge, as created by the wet weather on country roads, the whole steering wheel flys left and right quite quickly, as in a couple of time a second, and it shakes the whole car.

Have you come across this at all in your LC300 testing? Toyota are not particularly interested in getting to the bottom of things as I have deviated from OEM.

I am thinking of replacing the springs/shocks with TJM/Dobinsons/whatever heavier duty items, but I don’t think I’ve gone mad with the mods, and I really don’t need a lift, nor want to spend more on it.

Anyway, if you had heard of anything similar, I’d be interested to hear.

BTW – I was also wondering if I should get a wheel alignment due to the mods, but on a 6 month old car with highway only usage, I’d expect everything to still be in alignment. And:

  • That I swapped the front tyres to the rear (and vice versa!) just in case there was a defect of some kind in one of the tyres
  • And I have gone from factory pressures of 33PSI down to 29PSI on the front (but still 33PSI on the rear) to see if that made it softer, seeing that the Cooper sidewalls are about twice as thick as the OEM tyres.

When I tested the LC300 I found that the extra weight of the bar and winch warranted stiffer front springs, and therefore really a suspension redesign. Toyota disagreed, saying there was no need. I also felt the same way about the LC200. In my view, adding a bar and winch to any 4×4 requires a suspension change.

So if I were you I’d get a suspension kit suited for your new load on the car. The fact the bar and winch are ahead of the front axle exacerbates the problem.

Also, you’ve gone the wrong way with your tyre pressures. The more load on a tyre, the greater the pressure required, and offroad tyres need higher pressures as they don’t dissipate heat as well. Try 35psi on the front, and get the alignment checked too, it’s a cheap and easy check and the fact the car is only six months old doesn’t mean it doesn’t need it.

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1 Comment

  • by david deere
    Posted 12 January 2023 23:51 0Likes

    Thanks for answering my question. Seems like I had completely the wrong logic on the tyre pressures!
    I can see a suspension upgrade on the horizon…

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