Judder when steering on full lock

[jcassidy]

Hi All.

Had a quick search on this, but can't see anything in the archive on it.

When I have my 987's steering at full lock, there is a kind of "judder". It's not much, but it feels as though you are traversing cobblestones, or some series of small obstructions. Someone said that it could be due to the differing radiuses of the wheels at full lock, ie, the inner wheels are covering less distance than the outside ones, so they kind of judder.

Can anyone confirm if this is normal?

Cheers

[Westcoaster]

Hi All.

Had a quick search on this, but can't see anything in the archive on it.

When I have my 987's steering at full lock, there is a kind of "judder". It's not much, but it feels as though you are traversing cobblestones, or some series of small obstructions. Someone said that it could be due to the differing radiuses of the wheels at full lock, ie, the inner wheels are covering less distance than the outside ones, so they kind of judder.

Can anyone confirm if this is normal?

Cheers

I don't know if I would like to call this condition " normal" but mine does something similar, it was suggested by others that it was part of the way the steering on these cars work, or that the power steering fluid might be at fault. I forgot have the dealer specifically check the fluid at the last inspection.

Here is my post on the subject (can also be found by a search): http://www.renntech.org/forums/index.php?s...amp;hl=steering

[RFM]

As colder the tyres are, as much this phenomenon is present. Its called "Ackerman effect" and related to the front wheel geometry, nothing to worry about.

[jcassidy]

Ok, thanks for your help folks.

[stef]

Mine does this, too. I figured it was a normal side-effect of the stability module.

It only happens at very low speeds, although that's usually when I'm turning sharper anyway.

Here is a good description (or solution, in the case of go-carts) of the Ackerman Effect. Note the spindle angle, where the wheels connect to the tie rod.

[jcassidy]

Mine does this, too. I figured it was a normal side-effect of the stability module.

It only happens at very low speeds, although that's usually when I'm turning sharper anyway.

Here is a good description (or solution, in the case of go-carts) of the Ackerman Effect. Note the spindle angle, where the wheels connect to the tie rod.

Thanks Stef... very useful info.

[CJ_Boxster]

First... Try not to drive around town with the steering wheel in full lock... that puts strain on the power steering pump. Second... The wobble is due to alignment, Toe mostly, some porsches do it and some dont cause the toe from Pcar model to Pcar model is alittle different, I did my own alignment once and I think I made my toe slightly more straight than whats factory recommended and the wobble went away.

Edited November 27, 2008 by CJ_Boxster

[renzop]

Basically, at full steering lock one front tire is pointed in a different direction then the other. So when the car moves each tire is dragged sideways a little. That's the judder you feel and maybe hear. As pointed out this is kinda normal.

But the "problem" can be exagerated by the tires being not in the exact alignment that Porsche designed. And that can happen for several reasons:

1) Significant deviation from recommended toe setting.

2) Other alignment issues like large thrust angle cause by an incomplete accident repair or bent suspension parts

3) Wider than factory tires

4) Wheel offset and or large spacers - do you have aftermarket wheels?

5) Changes in ride height - a significantly lowered car will move the steering rack out of alignment with the hubs and can cause the ackerman to change leading to less than designed wheel deflection of the inside wheel at full lock.

Also the boxster has a pretty sharp turning radius - the wheels are angled further than a lot of other cars at full steering lock. This can make the judder more noticeable in the Box.

If you feel that the judder is significant or you are noticing uneven tire wear on the front tires, then you should go to an alignment shop and see what's going on.

[Richard Hamilton]

I think the 'juddering' effect occurs when a wide tyre is turning a tight radius - the outside edge is having to move a greater distance than the inside edge. I believe that it is the slippage that has to occur which causes the effect. On mine, it is only noticeable when reversing, and I have no idea why that is........