Evora suspension geometry question.

[Spinney]

Can anybody please enlighten me as to why the front wheels seem to 'hop', for want of a better description, when manouevering on full lock at parking speeds? I'm told this is a peculiarity of the Evora suspension setup and although I've owned many performance cars with wide rubber, over the years, none of those have ever behaved similarly so I'm just curious to understand why the Lotus does.

Any ideas please fellas?

[tim_marra]

https://en.wikipedia.org/wiki/Ackermann_steering_geometry

Lotus doesn't use it.

[KennyN]

I've had a few Mercedes that do exactly the same, it's quite disconcerting at first!  Mercedes put it down to the tyres and cold temperatures, which does seem to make it more repeatable.  It doesn't disappear completely when the temperature is higher, but it does seem to happen less.

On the Mercs, the wheels do sit at a weird angle when on full lock, which I'm told is normal, but I'm not sure whether this is the same on the Evora?

[tim_marra]

The weird angle is the Ackermann geometry doing its thing.

[KennyN]

3 minutes ago, tim_marra said:

The weird angle is the Ackermann geometry doing its thing.

Agreed, it does seem to be visibly more noticeable on some Mercedes models compared to other brands.

Mercedes issued a statement putting the tyre skip down to the cold temperature highlighting the effect as the rubber was less compliant when cold, which makes sense, although it could be an attempt to sell more winter tyres 😆

Mercedes-Benz UK statement issued 24/1/17 and reproduced verbatim:
We're sorry to hear that a small number of customers have experienced an issue with certain models, generally at cold ambient temperatures while manoeuvring at low speed with steering lock applied. The experience is of the front tyres apparently 'skipping'. This is a comfort issue, and does not affect the safety or performance of the vehicle.

This characteristic comes from flexibility within the tyre sidewall, the grip between the front tyres and the type of road surface being driven over. It is something which can be felt only at very low speeds, and when a certain percentage of wheel lock is engaged for turning. This is demonstratively more evident in colder temperatures due to the changes in the tyre rubber elasticity.

Winter tyres and all-season tyres on 18- or 19-inch wheels improve this characteristic and we would always recommend their use in temperatures which fall below approximately +7 degrees Celsius. The use of 18-inch wheels with summer tyres also improves the issue.

We do, however, appreciate that is not always possible or practical for customers to fit alternative tyres or wheels, and our technical experts in the UK are investigating alternative ways to help minimise this characteristic.

[mik]

59 minutes ago, tim_marra said:

The weird angle is the Ackermann geometry doing its thing.

Anti-Ackerman on the Evora.

which is why this happens.

[Spinney]

Interesting. I've had quite a few Mercedes but have never experienced this issue with any of them. Maybe I just haven't owned the particular models which are susceptible. 

I did find it slightly disconcerting the first time I felt it happening in the Evora but Jamie at Bell & Colvill has assured me TADTS. I wasn't particularly concerned by it, but just curious as to the reason so thanks for the replies. 

[KennyN]

It was particularly noticeable on C class and S class models, probably not helped by speccing the biggest wheels with rubber band tyres available from the list of options.  I also had an A45 AMG, it was fine from a tyre skipping point of view, it just clunked loudly when selecting drive or reverse...quality German engineering!

[Spinney]

That may well explain why I haven't noticed it in any of my Mercedes Kenny. I tend to go more for the comfort option on my daily cars with higher profile tyres and smaller wheels. Interesting that I haven't noticed it in any of my toys before though.

I do recall some folk complaining about the tyre skipping on the Mercedes forums I frequent, now I think about it, but I think that tended to be more associated with the performance A Class cars. 

Talking about quality German engineering, I've owned Mercedes cars for many years and it definitely seems they aren't as solidly built as they used to be. At one time a description that was often applied was they felt 'hewn from solid' and that really was how they felt. That has certainly declined over the years, probably not helped by that unfortunate period from the late 90's to early noughties when they rusted out so very quickly. I bought an E Class in '98 that started to rust around the wheel arches within 2 years. It was sorted under warranty but reappeared again soon after so I got rid a bit sharpish!

Trouble is, I just can't bring myself to change from them for my daily cars now. I've tried BMW and the 5 series I had was possibly the most unreliable car I've ever owned - and that includes comparisons against Lotus! 😄 Also owned an Audi A6 and whilst that was reliable, it was just so very dull. Maybe I need to change completely - but what to????

[Techyd]

43 minutes ago, Spinney said:

That may well explain why I haven't noticed it in any of my Mercedes Kenny. I tend to go more for the comfort option on my daily cars with higher profile tyres and smaller wheels. Interesting that I haven't noticed it in any of my toys before though.

I do recall some folk complaining about the tyre skipping on the Mercedes forums I frequent, now I think about it, but I think that tended to be more associated with the performance A Class cars. 

Talking about quality German engineering, I've owned Mercedes cars for many years and it definitely seems they aren't as solidly built as they used to be. At one time a description that was often applied was they felt 'hewn from solid' and that really was how they felt. That has certainly declined over the years, probably not helped by that unfortunate period from the late 90's to early noughties when they rusted out so very quickly. I bought an E Class in '98 that started to rust around the wheel arches within 2 years. It was sorted under warranty but reappeared again soon after so I got rid a bit sharpish!

Trouble is, I just can't bring myself to change from them for my daily cars now. I've tried BMW and the 5 series I had was possibly the most unreliable car I've ever owned - and that includes comparisons against Lotus! 😄 Also owned an Audi A6 and whilst that was reliable, it was just so very dull. Maybe I need to change completely - but what to????

I would highly recommend a Lexus for daily work - aside from the full steering lock 'hopping' as well, its been trouble free and enjoyable motoring for me.  I have an IS300h - rear wheel drive and the chassis is well balanced and there is plenty of grip.

[KennyN]

I can relate to what you've said Brent, it is difficult to overlook Mercedes as a daily driver having tried the majority of the competition.  Thankfully, they have moved on from the unfortunate period that you refer to and now seem to be back on form.  In particular, the more recent interior updates have set them apart from BMW, in my opinion, they are now much closer to Audi in this respect.

I just need to remember not to get carried away when I look at the wheel options 😄

@Techyd The Lexus is an interesting option that I did consider a few years back, there was certainly no need to go crazy on the options, they came pretty well loaded from what I can remember.  It was only the lack of a local dealer that put me off at the time.

[Techyd]

I had a tax ride in a new E-Class just the other week, its very bling inside, too much for me personally - but mostly because the interior lighting which the driver may have had set to max (and the colour was set to lilac) - I did get a little queasy in the back which surprised me.

[KennyN]

There is no accounting for taste when it comes to some of the options and the settings, it can get a bit 70's disco with some of the lighting options!  Thankfully, it can be toned down, or switched off, which is usually required once my son has been fiddling with the settings...I'm sure he does it just to wind me up 😆

[Spinney]

I remember considering the Lexus LS400 back in the early 90's but eventually went with an E Class, mainly because I needed the practicality of an estate. The Lexus was certainly well equipped though, a la traditional Japanese - v - European. Back in 2007, I did own a Mercedes CL for a couple of years  and absolutely loved that but missed the practicality of an estate, so as an off the wall choice, bought a Subaru Outback 3.0Rn to run alongside it, figuring I could use that for runs to the tip and, being 4 wheel drive, useful in the snow. Now that was one well built car but bloody hell, it drank petrol even more quickly than my big engined CL!

As things stand, I was thinking maybe to try Volvo next time, but I'm not enamoured with the idea of a smallish 4 pot engine, even if it is turbocharged, (I don't really know why except I've always liked a biggish displacement multi cylinder engine in the daily hack) so will probably end up in an E Class estate again. 

I'm nothing if not consistent/boring. 

[MattyB]

It always sounds painful to me - surely some components must be under some severe pressure to bounce the wheel back into alignment. I mean, isn't some part of the suspension under strain from the lateral friction of the tyre, before tyre tyre gives way and 'skips' back?

 

[tim_marra]

It only occurs in extreme circumstances i.e. full lock, low speed, and most noticeable when reversing. It is actually a better set up for performance driving as it maximises the tyre contact patch during cornering.

[Bibs]

It's only the tread blocks realigning. They're much softer than the suspension components.

[paranoidandroid]

Was going to ask about this as it’s really noticeable, as others have said particularly when reversing on full lock. Was a bit disconcerting at first. My previous Mercedes Cls did it slightly but nothing like as bad as the Evora!

[Spinney]

I’ve just been reading a test drive of the Alfa Romeo Stelvio Quadrifoglio and the tester comments about the car doing the same thing while manoeuvring on full lock. Clearly much more commonplace than I’d realised.