Jarring when hard turning

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greg4907
Posts: 3
Joined: Mon Dec 11, 2017 8:42 pm

Jarring when hard turning

Postby greg4907 » Sat Dec 29, 2018 9:56 pm

I have a 17 plate f-pace r sport and have had some issues with jarring when turning on full lock. Obviously this is only at low speed. We have taken the car back t the dealer who advised all f-pace vehicles do this. After some debate he confessed it is a design fault which can be largely fixed by changing the wheel spec on the vehicle. He demonstrated on other vehicles that the problem was common and I also spoke to a mate with a similar vehicle and discovered he has also been having problems.

Does anyone have more detail on this issue and suggestions as to what we should do? We are concerned about the long term impact and if the problem goes away with a different wheel spec then we figure Jaguar should change the wheels as the ones it was sold with are clearly not correct for the vehicle.

Thanks

mike020150
Posts: 2216
Joined: Wed Feb 08, 2006 6:26 pm

Re: Jarring when hard turning

Postby mike020150 » Thu Jan 03, 2019 6:10 pm

I suspect the effect you have experienced hasn't been well explained to you. Coincidentally, I have mentioned what I believe you are experiencing in next month's Jaguar Enthusiast magazine. It's not a fault and isn't essentially a wheel/tyre problem. However, it is more noticeable as tyre profiles get smaller.
At the heart of this effect is the front suspension geometry. You may recall hearing about Ackermann angles for steering geometry where the inner wheel turns further than the outer for a given movement of the steering wheel. No car has ideal Ackermann steering geometry because the size of the space under wings would have to be enormous to cope and/or front wheel tracks would have to be narrower. Similarly, the angles adopted influence how the steering feels at higher speeds.
Consequently, real life engineering is a compromise and manufacturers use lower Ackermann angles for better high speed cornering knowing that tyres have to absorb the forces of conflicting arcs in low speed, large lock movements. Especially when it's damp, very low profile tyres are known to cry, 'enough' and skip sideways releasing rather than absorbing the energy built up in the manoeuvre.

The choice is between a fine handling Jaguar with good high speed feel and grip and a less capable machine but one which doesn't 'skip' during car park manoeuvres. I know which I'd rather drive. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S

greg4907
Posts: 3
Joined: Mon Dec 11, 2017 8:42 pm

Re: Jarring when hard turning

Postby greg4907 » Fri Feb 01, 2019 12:52 pm

Many thanks for the response. My concern was that I have not had this issue with Disco 3, S-type, Audi A6 which I would have considered (at least the last two) as more performance vehicles than the 2.0D F Pace. Quite significant skipping particularly in wet weather as you note.
Keep up the good work.


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