Strange bumping noise on full lock!

[MRx450h]

Hi all.

This problem just started out of the blue.... full service history well maintained lexus rx450h.

On full steering lock, either direction, a very lumpy bumping coming from the passenger side front wheel. Felt like I was going over a pothole.

Its one big bump per revolution. 

I tested it driving around, and I was absolutely certain I had a flat tire if I had never felt one before. Got out, tire is fine. 

Cant see anything wrong from the outside. I did clump a kerb with that wheel not to long ago, not at high speed. But its been fine since then.

The steering is otherwise responsive and fine. 

Anybody help?

Thanks!

 

[NemesisUK]

"Scrubbing" is very common come the colder months. It's just the tyre skipping on full lock, the sidewalls aren't flexible enough to accommodate the tighter steering angle and the tyre deforms and looses contact with the road, then snaps back.

It's far more associated with extreme low profile, say, 40, 30 etc.. summer tyres. What tyres do you have? I had it on my RC, first time it happened I thought I'd driven over a brick! 

Have a read of this previous thread on the subject

 

[MRx450h]

thanks for replying.... its not a jerk or a scrape though. its a definitive bump, exactly like going over a pot hole or driving over a small brick. only on absolute full lock....  I dont hear anything that sounds like a scraping..... the steering doesnt jerk either. Its so strange!

[NemesisUK]

Yup, that's exactly how it feels

[Spiderrog]

If you Google Ackerman effect you will find an explanation about how tyres will cause this effect especially when cold, it does not seem to happen during the summer warmer months. There are some tyres which overcome this problem. I have just come over to a RX450h from a Jaguar F Pace and the problem was a well known issue on the Jaguar and I imagine it will be similar on other 4 x 4's as well. I now also get this clump when reversing out of my drive and the steering is in full lock. I hop this helps . It's all to do with the geometry of the wheels turning arch and the loads on the individual wheels