I have followed the many many conversations on tire choice over the years that has to have covered every topic one can possibly think of as to what tire is best suited for our E’s.
I finally came across the most succinctly presented reasoning for which tire to choose that will best compliment the characteristics and aesthetics Jaguar designed into the E Type. That came from Harry Metcalfe in his You Tube blog Harry’s Garage. His latest video is covering his recently completed XJ Coupe V12 and although a bit off subject on tires, listen to what he has to say around the 3 minute mark. He presents strong evidence of what size tire to choose and why. The sound of that roaring V12 aint’t so bad either.
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I saw that and can respect the choice to enjoy a car in its period configuration.
That said, my only complaint is sometimes people assert that cars on older spec tires ‘perform’ better than cars with newer compound tires. That all depends on one’s definition of “perform.”
Feeling and performance are two separate things.
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His comments were interesting, and general enough that we could all use them to reinforce our views. His point about the effect of big wheels and tyres on the none-too-stiff structure and curious rear suspension of his XJ Coupe are equally valid for the E-type but I wouldn’t take it as outright prohibition on any size larger than the original.
The structure concern would come from a wheel and tyre that are significantly heavier and / or stiffer than the original - would one step larger in diameter or lower in profile take you significantly beyond the range of original sizes in those areas?
I think his point on the rear suspension was that increased cornering power could reveal undesirable behaviour. That’s a fair comment to the extent you exploit that increased cornering power, but should be balanced against the improved performance you could expect from the modern tyre in other areas more frequently encountered - precision, response, directional stability etc.
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Harry Metcalf is a farmer. He may also have started Evo magazine and be a car nut, but he is still a farmer. I check out his videos, and find some of the things he says in Harry’s Garage to be …er…… interesting. Equally on Harry’s Farm, but for different reasons. (My first paid employment as a ten year old was as a milk hand on a small farm.).
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If In recall correctly the tires on his XJC 12 are 205/70-15"s which are also on Ser III E Types, with a lot of folk using them on their 6 cyl E Types as well. They work well to very well depending upon whether the tire is a performance tire or all season. He seems surprised by the layout of the rear suspension, which really says everything you need to know about his car knowledge.
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I was also surprised by the layout of the rear suspension, when I eventually understood how it worked. Maybe that also says everything you need to know about my car knowledge!
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Well Clive you are not on your YouTube channel casting aspersions on it. Corvette used the same set up for years as well. Seems to work, is compact, but way overbuilt and heavy for an e type.
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That is true: I always wondered if Jaguar overbuilt it, in anticipation of it being used in the bigger sedans.
I’ve always assumed the system was set up for the higher volume cars, to be as common as possible for the sports car. Any compromise to be on the low volume E-type, although probably not too severe as it needed to support the luxury image. The low profile enabled by the driveshaft-as-upper-link matched the packaging and styling so everyone was happy.
My (theoretical) reservations centre on the way the rear system is nominally independent in vertical wheel motion while lateral and fore-aft loads make it more like a de Dion system, with the wheels connected and transferring loads from side to side through the drive unit. I understand that principle has done decades of service for Jaguar and Corvette, but it still bothers me.
Bothers me enough to cut out chunks of structure in order to fit a full upper A-arm and a lot of related stuff. Will it be worth it? Well the data says it will - in physical terms, we’ll see where opinions fall when the car finally runs. Good enough reason to be in Utah in December?
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As I am quite sure you are aware, in all street suspensions, there are compromises. There has to be, because what works perfectly well on a racecar does not work all that well in a street car.
In that regard, I think Jaguar got it pretty well close to as perfect as one can get, with the balance between street and high-performance. My 2 liter Rover has a de Dion rear suspension, and in many ways, I think it is better system than the Jaguar system.
Again, as I’m sure you know, the compromise in the de Dion system is the room that it takes for the cross tube, which would not work well in a small sports car, but works quite well in a large sedan.
It was also introduced on the Mk 10 at about the same time. That car weighed 4200 pounds, svelte by today’s standards, so it was definitely built with use in the sedans Lyons so loved.
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Thanks Paul,
Your points are well taken. Clearly the vast majority of owners, over the decades, have been very satisfied with the performance. Peter and I are belong to the small group who think it could be improved. Then we’re in the smaller subset who think we can do that.
I say that with all due respect to the original engineers - I knew some of them, I had lunch and gossiped with them at the MIRA test facility. I played football with them and drank in the pubs around Coventry, as we did with engineers from Triumph, Chrysler and the supplier network. Of course they knew what they were doing. We’re changing it today because we don’t have the constraints of the time:
- we have sixty years of progress and experience to draw on. There’s a lot of knowledge out there.
- we have design and analysis capability that didn’t exist then. We know the suspension behaviour to a degree that simply wasn’t possible with a drawing board. Nor - critical point - by physical driving evaluation. That may be a controversial statement in some quarters but I make it firmly, from direct experience.
- we only need our system to fit one variant of a single model, not a range of saloon and sports cars. With our car we can swing the compromises wherever we choose
- we have no constraints on budget or piece cost. We can use exotic materials or processes for the fun of it. (We’re doing this for fun, we cannot allow it to feel like a matter of grave consequence).
- perhaps most important - we only need to please one customer. If we can’t achieve the ideal performance balance, we own the failure, we’ll go back and do it again.
I hope this will explain our thinking. I appreciate any and all responses, I’ve learnt a lot from this forum.
I share your liking for the de Dion system, Paul. I enjoyed working on one many years ago, on a car where the additional cost and complexity of IRS wasn’t justified in pure performance. I’m not sure the Rover 2000 is the best example to draw on though, isn’t it complex beyond mortal understanding?