E type Roll Centre and Handling

[Tom W]

Are you intending to increase the stiffness of the body shell as part of the suspension modifications?

[nichmoss]

I think that Clive has decided not to post anymore so it's unlikely that he will explain any body stiffness modifications. It may be he has been called away and can't contribute but it appears to be that he doesn't want to show anything else.

It's a shame really as this could have been an interesting discussion but, he obviously made a mistake in his analysis of the rear wheel camber change and may not be inclined to discuss further. He clearly had a lot of experience but when he calculated the rear camber change and got it wrong, instead of going back and re-checking his work, he assumed that the Jaguar suspension department had done a poor job. I realize that he thought he had better tools to work with than Jaguar did in the early sixties but this is a bit of an insult to the Jaguar engineers. He has now convinced himself that there are major issues in the suspension design that really don't exist so, his modifications are not likely to be of much interest anyway.

Cheers, Chris

[Tom W]

Yes, a shame. I thought it was an interesting topic, even though it’s not something I’m about to substantially change on my own car.

[CliveR]

Chris, thanks for your constructive thoughts, and apologies for taking so long to respond. I didn’t have access to my original data as I was away from home for the past four months. You’re correct, my camber curve for the original car was seriously wrong. After getting home I had time to look at the history, it actually took two mistakes to be so wrong. First I took a shortcut to make a rough rear model by loading rear coordinates into my existing front file - in doing that I omitted a minus sign on one coordinate then compounded that by being careless with the output, using the SAE (US) convention by habit. That defines a camber curve which goes negative with upward wheel movement as negative in the front suspension but the same curve becomes positive at the rear (I know what you’re thinking, I didn’t write the rule!). Our RACE software doesn’t do that so I accidentally switched the direction of the curve in moving the front suspension to the rear. Result of all that – a curve that clearly made no sense, apologies for the confusion. I’ll also admit I didn’t question the result as closely as I should because (as you astutely note) I had ingrained reservations about the original system and in any case we were already committed to changing to a full double wishbone system, so estimating the original curve was background interest rather than direct input. I think you overstate my position in saying there are “major issues” in the original system – clearly it hit a wide range of targets at the time but I do feel there are opportunities to improve its performance when we narrow the sights to one variant of one model, for one particular owner. More important though, we need more adjustability in some critical parameters at the rear, such as camber curve and roll centre height, to match the changes we plan at the front. I can elaborate on that separately. The modifications will be quite extensive, I’ll describe and debate them to whatever level of interest exists, from zero to bone-crushing detail.

I have no intent to denigrate or insult the original engineers, I really don’t think they would take my comments in such a way. They would outline the background and inevitably bounce the question back to the dubious things I’ve done over the years. I’m open to any comments on my past efforts and disasters (do you know anyone else who admits to being associated with the TR7 project?). To name just one who played a leading role in Jaguar programmes of that era, I worked for Mike Kimberley when he was MD of Lotus. He’s an excellent engineer and leader. I’ve taken part in frank engineering discussions with him, he usually won but there would be no hard feelings either way. This project is not inherently critical of the original – its context is different as we don’t have its constraints. We’re doing a focussed high-performance car which only has to please one person in a limited set of conditions; the parts are not required to fit any other body style or range of cars; we don't have cost targets and we have tools, techniques and materials not available sixty years ago. This gives us freedom to change areas where we see benefits, basically getting more separation of the suspension functions (drive, cornering, ride control, braking) to individual parts. It’s not as clever as the original but it gives us more scope to optimise each function without the conflicts inherent in (for example) one pair of mounts dealing with drive, braking and cornering loads. Specifically:

- a separate wishbone above wheel centre makes it more powerful in tuning. With no drive responsibility its position can be adjusted to get the performance we need to match the front
- we can arrange a small amount of controlled steer through suspension travel, for better cornering power and stability.
- the differential unit now only needs to drive, its mounts can be optimised for that purpose without compromising suspension behaviour.
- as you note, the original upper structure doesn’t allow space for an upper wishbone so we’ve moved the structure up - a light, hollow section is now integrated in the wheel arches, above the rear floor. This not only allows us to fit a wishbone, it also gives a stiffer structure as the beam extends forward to meet the rear of the sill, which now contains a thin wall beam through its entire length. The diff mounts are integrated in the rear structure. Carrying this through to the front, the overall structure will be significantly stiffer than the original.

Going back to the rear camber curve, when I correct my errors the result matches your curve well, considering you measured physical parts on a car and I scaled off a drawing with a 6-inch Mickey Mouse ruler. These are the two blue lines in the attached chart, which uses yours as a basis for ease of comparison. (Curves are separated vertically for ease of comparison, no implication on static camber settings). Using the metric of degrees camber change per metre suspension travel (curious, but it’s the industry standard) you have -32.5, I have 35 – pretty good agreement considering we have different data sources and mine will include some bush compliance. The red line is the figure of 1.25 degrees per inch you quoted for the Phil Porter book, converted to 49 degrees / metre and extrapolated as a straight line as in your chart. I’m not convinced that number is realistic - even if it’s mechanically feasible I think so much camber change would have drawn complaints for reacting to white lines or feeling restless on road grooves, especially if carried over to the luxury saloon cars. It’s a lot higher than anything in my database - closest is an M3 at 31 deg/m; a 911 Turbo is 22.3. I think it’s open to question, without further verification I prefer to believe the range that you and I estimated. The upper three curves in the chart (green, black & pink) are variations of a double wishbone system. It shows we can cover the range from 35 to 45 deg/m by changing the upper wishbone length and inboard pivot position. It might even be feasible to make an attachment bracket which could be flipped from a “road” to ”track” setting, if we were looking for more complication. We’re aiming around 40 deg/m, willing to accept the above-mentioned disturbances in exchange for the increased cornering power that comes with the greater camber change. More important, it makes the rear parameters more adjustable so we can keep it balanced to the front changes. That’s a subject for another day.

I understand some feel this project has moved too far from the original to hold much interest. I have gone back a couple of times to see what simple reversible changes we might extract for more general use, but really haven’t found anything significant. There’s a well-known mod to lower the front upper wishbone pickups for a steeper camber curve, which in itself would tend to reduce understeer - but my analysis says that also adds a lot of roll understeer, which will tend to make the car feel dull or cumbersome and reduce the effect of the camber change. At the same time the front roll centre will rise significantly (more understeer tendency) so I question if there's an overall gain. To correct the roll steer you could lower the steering rack but you still have the roll centre height problem, fixing that will not be simple as camber and roll centre height tend to be linked. That’s what brought us to extensive changes to balance the parameters. (A history question for the experts here – is the steering gear and its mount derived from or related to the XK?)

This might be a good time to address a question raised a few times, why I’m changing the original car without driving it first? Simply because that’s what a vehicle development engineer tries to do – first understand the system, then improve it. I don’t need to drive it at this stage to understand it. If you have a new steering rack fitted to your car and the initial alignment printout says the toe is out of spec, I don’t think you’ll take it away to see if it really needs to be adjusted – more likely you’ll get it fixed first. I won’t play my bass if the tuner tells me it’s playing the wrong notes. I fix it, then play it. In the same way, the software tells me the status of around forty suspension parameters – there is not much to gain from evaluating those aspects of the car if they don’t meet requirements. Whose requirements? Mine and the people, mostly smarter and more talented than me, that I’ve been privileged to work with over the years. I know how a sub-optimal roll steer or castor curve feels, I don’t need to drive it. First fix it, then drive it. Driving too early can actually be counter-productive – if you don’t like something, which of those forty overlapping and interacting things do you want to change? (Ref. the camber change in the previous paragraph – you might mistakenly decide the camber change was a bad move if you didn’t know the roll steer and roll centre had also changed). Yes, I know that’s the way Norman had to do it, and he has my total respect. The man was clearly a giant of his craft. However…many of those forty-ish variables I mentioned weren’t on his list of things to be checked or adjusted because they couldn’t be drawn, measured or simulated at that time – essentially they didn’t exist so the engineers of the day got on with it and fixed what was available to them. Obviously they did a good job, you love the way your car drives. My belief is that they would have gone even further if they could – the technical answers are not difficult if you can measure and implement them. My confidence is that the step will be worthwhile. I was fortunate to be learning the craft at Lotus twenty years later as new means of measurement and simulation became available. The giant figures of that era - Roger Becker, John Miles, Alistair McQueen among many - had breath-taking skill in subjective evaluation but they embraced and developed the new tools with enthusiasm because they recognised the amount of drudgery and errors they could save, reserving their skills and time for the critical parts that people still do best. So, I’m very comfortable looking at data, picking up likely areas of improvement, adjusting it in software until I like what I see then ordering parts to match. We’ll build this car with good kinematics, we’ll evaluate a few different bushes on the car, then we’ll get on with the fascinating and enjoyable craft of tyre testing and damper tuning with confidence in the platform beneath.

To get back to the point, my summary of the rear end status is – it will be lighter, stiffer and give more adjustable handling behaviour than the original. I know some consider the lack of originality offensive, personally I think this is the kind of car the Jaguar engineers would have enjoyed building, perhaps as an update, if freed from their constraints. I think they’d delight in the result we’re going to achieve and hope some members of this forum might even have the chance to form their own judgments one day.
I’ll post an update on the front suspension in the near future, since that’s where this all started.

To briefly answer Tom W’s question, yes we’re doing pretty extensive structure modifications to ensure we get the benefit of the suspension changes. The rear was pretty straightforward as the components and existing steel defined what could be done. The front was more complex, we used some FEA guidance on the detail. The structure is actually being made now while we’re waiting for suspension stress work to be completed and the car owner to emerge from a business trip in the Indonesian jungle. I’m having a break!
If you read this far, thank you for your patience. Comments and corrections appreciated. If you’re interested in detail of the suspension parameters I mentioned above, RACE (our suspension software supplier) has a very good library describing and defining them. https://race.software/education/suspens ... r-library/
Cheers, Clive

[nichmoss]

Hello Clive

Pleased to hear you are back to the forum. Your curves now look more like I'd expect and well done for finding the issues in your original data. Perhaps "major issues" with the original design was a bit harsh but I take your point that this set up was used for many cars and models so will be a best effort to suit different situations. Your modifications are a radical change but if that's what you need to suit the major mods to the front suspension then I suppose it makes some sense and, as you say, you don't need such a clever design that can be dropped in to any model as required.

Interestingly, you can't see any simple mods that would significantly improve things and that is a justification of the original design, in my eyes.

It sounds like you are adding reinforcements to the shell as needed for the new rear wishbone. I've said before that the structure is not that strong in this area due to the way the cage is mounted - it concentrates the load in the few location points and that's the only place where the structure is strong. A couple of interesting points would be how you are reinforcing for the new wishbone rear pick up and how you now will allow the drive shafts to not constrain the suspension and also how you mount the diff for NVH requirements. Many ways to do such things so, if you can share, I'd be interested.

As for the front, again, it will be interesting to see what you do, especially as the frames are not too stiff or strong. I am sure reinforcements will be required. You can analyse these frames simply without FEA but it's what you feel comfortable with.

In both cases, you are moving sufficiently far from the original that the car won't really be an E-Type but more like a Modsports racer (for me) and so, not everyone will be interested. If you're unable to share images and analysis, fair enough as the person paying for this can restrict what you can say.

Good luck, Chris

[Gfhug]

My two penny worth. An E Type is a pleasure to drive just like a Tiger Moth is a pleasure to fly. Both are of their respective eras and changing suspension or wing shape might modernise them but detracts from the reason for enjoying them. If someone needs power steering on their E or changed suspension why not just buy an F Type? It is also a pleasure to drive and is of its era.

Some of the upgrades we as owners have incorporated, such as relays for the ignition or headlamps, a brake light switch on the pedal, etc. change no aspects of the dynamics of the car yet can be seen as properly beneficial.

Was it James Hunt who was reported as saying some of the most fun he ever had in a car was in an Austin A30/A35? I’m sure one of those could be modernised but it would no longer be the fun car Hunt knew and enjoyed.

Geoff

[christopher storey]

This might be a good time to address a question raised a few times, why I’m changing the original car without driving it first? Simply because that’s what a vehicle development engineer tries to do – first understand the system, then improve it. I don’t need to drive it at this stage to understand it. If you have a new steering rack fitted to your car and the initial alignment printout says the toe is out of spec, I don’t think you’ll take it away to see if it really needs to be adjusted – more likely you’ll get it fixed first. I won’t play my bass if the tuner tells me it’s playing the wrong notes. I fix it, then play it. In the same way, the software tells me the status of around forty suspension parameters – there is not much to gain from evaluating those aspects of the car if they don’t meet requirements. Whose requirements? Mine and the people, mostly smarter and more talented than me, that I’ve been privileged to work with over the years. I know how a sub-optimal roll steer or castor curve feels, I don’t need to drive it. First fix it, then drive it.

I am going to speak my mind. I have rarely heard such nonsense as "I don't need to drive it at this stage to understand it ...I know how a sub-optimal roll steer or castor curve feels, I don't need to drive it....First fix it, then drive it", and this from a man who has never answered , as far as I can trace, the question about whether he has actually driven any E type, and if so in what conditions and circumstances . Quite apart from anything else, if you do not know how a car behaves before you modify it, how do you later assess the results of the modifications you make in practical , rather than merely theoretical terms. Or is this to be akin to an aeroplane which is put into service without any test pilot input?? Recent events show where that leads

[TGN]

Was it James Hunt who was reported as saying some of the most fun he ever had in a car was in an Austin A30/A35? I’m sure one of those could be modernised but it would no longer be the fun car Hunt knew and enjoyed.

Geoff

I’ll let you know next year, when we get his van back on the road.

[ysmalkie]

Maybe I am an odd ball, but (while restoring my car to an original as close as possible) I actually really enjoy posts from someone who has gone out on a fairly difficult mission.
Clive, I would encourage you to post, as I am really interested what you come up with. Thumbs up if you succeed. If you fail, I am sorry for the poor bloke down under ;-).

I for one am reading the posts with interest would really like to see the result. Not that I would ever consider to convert my car to such an extent (NEVER!).
Similarly, I would gladly see how you can convert an e-type to a electric, for pure reading pleasure, NOT for undertaking it. For that I can convert a Polski Fiat! ;-).

Maybe some of you more doubtful could let the man speak?... I do prefer than reading the posts here than going over to the e-type section on the other forum where there is a lot of 'noisy' posts... ;-)

Tadek

[Gfhug]

I’ll let you know next year, when we get his van back on the road.

Trevor, welcome to the forum and for an intriguing first post. Do tell us more when you are able to. And tell us about your E Type, too.

Geoff

[mgcjag]

Clive has posted a lot of info on this topic on Jag Lovers

[ysmalkie]

I know - I have read it.

and I am still very much curious what comes out of it.
Tadek

[chrisfell]

“ Was it James Hunt who was reported as saying some of the most fun he ever had in a car was in an Austin A30/A35?”

IIRC Hunt’s A35 was a van / countryman version. I think the fun he referred to was while the vehicle was stationary.

[Rich70]

Hi Clive, I’ll be keen to see what you come up with. I found this interesting video of Evolution Etypes IRS, it shows some extensive modification work that you might find helpful:

[PeterCrespin]

IIRC Hunt’s A35 was a van / countryman version. I think the fun he referred to was while the vehicle was stationary.

I doubt it. Gently rocking on its springs, more likely...

[chrisfell]

“ Gently rocking on its springs, more likely...”

Perxactly.

[CliveR]

Hi Chris, thanks for your comments. My thoughts below.

Interestingly, you can't see any simple mods that would significantly improve things and that is a justification of the original design, in my eyes.

It sounds like you are adding reinforcements to the shell as needed for the new rear wishbone. (clip). A couple of interesting points would be how you are reinforcing for the new wishbone rear pick up and how you now will allow the drive shafts to not constrain the suspension and also how you mount the diff for NVH requirements. Many ways to do such things so, if you can share, I'd be interested.

As for the front, again, it will be interesting to see what you do, especially as the frames are not too stiff or strong. I am sure reinforcements will be required. You can analyse these frames simply without FEA but it's what you feel comfortable with.

In both cases, you are moving sufficiently far from the original that the car won't really be an E-Type but more like a Modsports racer (for me) and so, not everyone will be interested. If you're unable to share images and analysis, fair enough as the person paying for this can restrict what you can say.

Clearly the original design did a fine job of meeting its targets. I view our project as respectful updating, and it’s not simple. The rear suspension and drive system are highly integrated and the key parts that define the wheel geometry very specialised, so it’s difficult to make a subtle change – it quickly tends towards “all or nothing”. Considered in isolation the rear gives a pretty good camber curve - the problem comes if you’re going to adjust the front and then want to balance the respective ends. We are and we do, so we’ve ended up doing completely new rear suspension to get adjustability of the dynamic items the standard system won’t allow. The new system allows us to adjust not only camber curve but also steer, roll centre height and other parameters in line with current thinking. The front is equally hard to make meaningful changes. I mentioned the roll steer vs. roll centre height question before, my study says it would require both upper and lower wishbone pivots to be moved to get the curves I'm looking for. At that point I start to question other areas such as what the torsion bar gives me that a coil spring wouldn’t, why don’t we support the damper on both sides at the wishbone attachment, why not lower the steering rack to reduce the roll steer, how about a little more castor… as at the rear, this quickly leads to new suspension. That in turn, leads to some pretty significant front structure changes, which is another discussion in itself.

We’re happy to share information as we progress, comments welcome. The attached pictures show the diff mounting underway, wishbone mounts will attach to brackets on the new structure. The ZF diff has three isolated mounts so NVH should be good with a suitably stiff structure. The other pictures show the rear structure rails relocated above the floor to give space for the upper wishbones. Peter, the car owner, decided to extend the rails rearward to protect the fuel tank. The driveshafts will have sliding CV joints to separate them from suspension motion. The whole assembly, including new structure, will be lighter than the original as we’re replacing the diff and lower links with lighter equivalents.

The front - another subject, drawing breath for that one!

The car will be finished to a high standard so should be a better aesthetic proposition than the Modsports cars I recall from the 1970s, but I take your general point. I’m very happy to get feedback from anyone, positive or negative, that has some bearing on the functional or subjective aspects of what we’re doing. My years working in China, though, have accustomed me to being paid to have my intellect and capability challenged, so I won’t respond to insults without a completed bank transfer.

[CliveR]

I am going to speak my mind. I have rarely heard such nonsense as "I don't need to drive it at this stage to understand it ...I know how a sub-optimal roll steer or castor curve feels, I don't need to drive it....First fix it, then drive it", and this from a man who has never answered , as far as I can trace, the question about whether he has actually driven any E type, and if so in what conditions and circumstances . Quite apart from anything else, if you do not know how a car behaves before you modify it, how do you later assess the results of the modifications you make in practical , rather than merely theoretical terms. Or is this to be akin to an aeroplane which is put into service without any test pilot input?? Recent events show where that leads

I recognise your scepticism, can we hold that as a polite failure to agree until the car is finished? I'd be happy to arrange for you to drive the car, we could then have a meaningful discussion on its merits and deficiencies. Meanwhile, I think I've answered your questions in my various posts, including the one about my E-type driving experience. Regarding your penultimate sentence, I have not suggested we dispense with the "test pilot" - on the contrary, I have clearly stated we use that indispensable skill sparingly and wisely, for select areas where a computer cannot adequately substitute for a person. That was a central tenet of my forty six years in vehicle development, and remains my aim in this project.
Regards

[christopher storey]

Clive : I have recently seen all your pictures on Jaglovers, and your project is undeniably an interesting one. I hope you will get a lot of pleasure from bringing it to fruition

[CliveR]

My two penny worth. An E Type is a pleasure to drive just like a Tiger Moth is a pleasure to fly. Both are of their respective eras and changing suspension or wing shape might modernise them but detracts from the reason for enjoying them. If someone needs power steering on their E or changed suspension why not just buy an F Type? It is also a pleasure to drive and is of its era.
------
Geoff

Good points Geoff, the Tiger Moth comparison is apt. If I owned one and found I could use the decades of research into wing profiles to fit new wings which were visually close to the original but gave better stall behaviour, manoeuvrability or handling I'd be very tempted to do that. I recognise many would consider the elemental man-machine struggle to be part of the original charm, but I'd have few qualms about upgrading critical parts to current levels of corrosion protection, for example. Ultimately each of us will decide where the balance point lies.
I'm not so convinced about the F-type comparison. To me the badge is incidental, it's a different car from a different era. Coincidentally one of the lead suspension designers of the F-type, Raoul Popescu-Ghimis, is now the CEO of RACE Technologies, whose suspension analysis software we've been using. Raoul has been extremely supportive of our efforts as we've both drawn on our databases of high performance cars to ensure we're setting the performance in the right direction. I try to imagine what the Jaguar engineers might have created a decade or two later if the original constraints were relaxed. Actually I think handling performance is the relatively easy part as much of it can be simulated and expressed in charts. Harder is to keep the balance of qualities that made the original car special - ride suppleness, road and engine noise, plus the intangibles that make the difference between an ordinary car and a special one. Perhaps this is what Christopher Storey had in mind when he expressed doubt that we could do the work virtually. I that respect I agree, it's very subjective and emotive. These days it's called Vehicle Integration and has entire departments measuring and plotting. I think in olden times it was simply "Norman says..."
Clive