Discussion
On full lock (both ways)in my car it sounds like the tyres
are dragging across the road rather than steering?
I only notice it doing low speed manoeuvres, the car also
wants to follow every rut on the road and it looks like the
tyres are wearing on the outside edges.
Any ideas folks?
BTW it's a TVR chimaera without PAS
are dragging across the road rather than steering?
I only notice it doing low speed manoeuvres, the car also
wants to follow every rut on the road and it looks like the
tyres are wearing on the outside edges.
Any ideas folks?
BTW it's a TVR chimaera without PAS
jr6yam said:
On full lock (both ways)in my car it sounds like the tyres
are dragging across the road rather than steering?I only notice it doing low speed manoeuvres
It's down to the Ackerman geometry.are dragging across the road rather than steering?I only notice it doing low speed manoeuvres
The full explanation is a bit long winded; I'll happily go into the details, pros and cons it if you wish, but it's anorak stuff. Basically, if you don't have full Ackerman you get quite a bit of tyre scrub at walking pace, but as cornering speeds increase the different loads on the inner and outer tyres mean that this doesn't matter and, indeed, it might arguably be more efficient... different designers have different opinions on the optimum amount of Ackerman geometry.
jr6yam said:
...the car also wants to follow every rut on the road...Any ideas folks?
Yes. It's a TVR. 
They all do that to some greater or lesser extent, though the uneven tyre wear indicates that you have a geometry problem.
Getting a full 4-wheel geometry set-up by someone who knows what they're doing (eg. someone like Steve Guglielmi) will doubtless make a huge improvement, but don't expect it to ever handle and steer like a Lotus.
Sam_68 said:
but don't expect it to ever handle and steer like a Lotus.
Interesting that you would say that.I have no opinion on the matter, but recently I was chatting with a "car guy" whose name is well known here.
His view is that Lotus go to great lengths to work with a tyremaker to develop a tyre for a given new model. The tyre design, he said, typically has a very sharp corner at the hinge, and it is this distinct edge that gives certain Lotuses their steering feel and precision.
flemke said:
The tyre design, he said, typically has a very sharp corner at the hinge, and it is this distinct edge
that gives certain Lotuses their steering feel and precision.
I'm sure that when Lotus work with a tyre manufacturer to develop a model-specific tyre, they do take such considerations into account, yes.that gives certain Lotuses their steering feel and precision.
It doesn't explain the steering feel on all the Lotus' that didn't have tyres sepcifically developed to suit their geometry (to some extent Lotus can select the best available off-the-shelf tyre, but then so can everyone else...), or the steering feel when non-OE spec. tyres are fitted, though.
For example, the original S1 Elise was a revelation in terms of steering feel, despite being fitted as standard with non-model specific Dunlops, and my Elan retains the very distinctive 'Lotus' steering feel despite being fitted with budget CEAT tyres at the moment.
My personal opinion is that upright geomentry and careful attention to balancing the roll axis inclination against spring rates (hence dynamic weight transfer; hence the way the steering loads up in corners) plays the major part, but whenever I've attempted to discuss the matter with anyone who would really know, they tend to become a little bit vague and evasive.
Sam_68 said:
flemke said:
The tyre design, he said, typically has a very sharp corner at the hinge, and it is this distinct edge
that gives certain Lotuses their steering feel and precision.
I'm sure that when Lotus work with a tyre manufacturer to develop a model-specific tyre, they do take such considerations into account, yes.that gives certain Lotuses their steering feel and precision.
It doesn't explain the steering feel on all the Lotus' that didn't have tyres sepcifically developed to suit their geometry (to some extent Lotus can select the best available off-the-shelf tyre, but then so can everyone else...), or the steering feel when non-OE spec. tyres are fitted, though.
For example, the original S1 Elise was a revelation in terms of steering feel, despite being fitted as standard with non-model specific Dunlops, and my Elan retains the very distinctive 'Lotus' steering feel despite being fitted with budget CEAT tyres at the moment.
My personal opinion is that upright geomentry and careful attention to balancing the roll axis inclination against spring rates (hence dynamic weight transfer; hence the way the steering loads up in corners) plays the major part, but whenever I've attempted to discuss the matter with anyone who would really know, they tend to become a little bit vague and evasive.
flemke said:
Any idea how much mechanical trail they tend to run?
As you'd expect, they vary - indeed the caster sometimes changes from one series to another (for example, IIRC, both the Elan and the Esprit used different caster figures from one series to another within their overall production runs).The caster and mechanical trail figures are nothing unusual, though - they are well within the range that would be considered 'normal' for any car. I don't think you will ever pin it down to just one element of the geometry or set-up; it's always going to be a combination of several factors arranged to work with each other
Sam_68 said:
flemke said:
Any idea how much mechanical trail they tend to run?
As you'd expect, they vary - indeed the caster sometimes changes from one series to another (for example, IIRC, both the Elan and the Esprit used different caster figures from one series to another within their overall production runs).The caster and mechanical trail figures are nothing unusual, though - they are well within the range that would be considered 'normal' for any car. I don't think you will ever pin it down to just one element of the geometry or set-up; it's always going to be a combination of several factors arranged to work with each other
It seems that the suspension guys wanted a certain size front tyre, whilst the marketing guys wanted a wider one, because it "looked better". As often is the case, the marketing guys won.
After a few months of production, and some very disagreeable real-world experiences with a car that was too tail-happy to be available to one and all, the spec was changed back to the narrower front tyre.
This was told to me by someone directly involved in the process.
Check the spacers on the top BJ's are at the front, if you put them back the wrong way you screw the KPI. Folks have also been known to fit the wrong TRE's (and even invert them) which will screw the tracking at any deflections, just as completely inappropriate ride heights can.
Nothing wrong with TVR handling when set up correctly and suitable tyres selected, which is harder than it sounds
as there are few tyres in the sizes used that were designed for such a lightweight..
Try asking Chimjunkie for his opinion - he's tracked with lots of Lotii as well as owning one, so could give you a fair assessment of the relative capabilities. You can make a TVR into a track car, but try as you might it will be harder to make the Lotus into an intercontinental tourer
Nothing wrong with TVR handling when set up correctly and suitable tyres selected, which is harder than it sounds
as there are few tyres in the sizes used that were designed for such a lightweight..Try asking Chimjunkie for his opinion - he's tracked with lots of Lotii as well as owning one, so could give you a fair assessment of the relative capabilities. You can make a TVR into a track car, but try as you might it will be harder to make the Lotus into an intercontinental tourer
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