Tyres, again

[APersoons]

I know that the subject of tyres has been discussed many many times before, but I don't think this option hasn't been discussed before.


I've always had the standard size fitted to my car (XVS then Cinturato's, loved both), but I like the idea of a little fatter tyre in the rear and keeping the light steering, after all didn't the lightweights have different sizes front to rear?
What do you think about this combo:

Front:
5.5" Wheels, 185VR15 aquajets
Diameter: 674 mm
Section Width: 188 mm

Rear:

6" Wheels, 205/70VR15 aquajets
Diameter: 669 mm
Section Width: 202 mm

I contacted Dougal a few months ago and suggested fitting wider tyres at the rear and keeping the 185VR15's at the front.
He didn't like the idea but forgot to ask him why.

Diameter doesn't seem to be the biggest issue since there'll only be a 2.5mm difference in ride height.

What are your expert opinions and thoughts with regard to the consequences/problems with this approach?


Axel

[Heuer]

Bad idea. If Dougal says don't I would tend to follow his advice. You are likely to upset the cars handling because it will no longer be neutral through corners. It will understeer which is not typical of an E-Type. What exactly are you trying to achieve by doing this change other than creating what the Americans call a "no go showboat"?

Best plan would to be to put the 185's on 5.5 or 6" rims. It will make them look a lot wider but you won't affect the handling although you will get a harsher ride.

[GSR 54D]

185's on 6 inch rims, less railway carriage look without the bulk!



John H

[APersoons]

Good point about the understeer, certainly wouldn't want more of that, to the contrary.

What I wanted to achieve with this is to reduce the "railway carriage look" and retaining the steering feel and travel.

I once drove a fast road '62 with 205 Cinturato's (they fitted!) but the front tyres would rub on the bonnet quite rapidly when cornering in tight bends.

Has anyone experimented with fitting a little harder springs or anti-roll bar in the back to increase the oversteer just that little more?

[Heuer]

We call this the 'Game of Consequences' - change something and then have to change something else to compensate. Norman Dewis did all that testing with different combinations on your behalf over thousands of miles and ended up with the E-Type that was delivered to customers. I very much doubt anything you do will improve things beyond that. You can change it but in my experience it will certainly not be for the better. e.g:

"I once drove a fast road '62 with 205 Cinturato's (they fitted!) but the front tyres would rub on the bonnet quite rapidly when cornering in tight bends."

So if you want to "reduce the railway carriage look" buy a hot hatch or a 911. If you want to own an E-Type, as designed, stop worrying about what bystanders think and drive the thing. The best view of an E-Type is over the bonnet from the drivers seat. Who cares what it looks like from some angles standing still? Actually most people just think (and say) GORGEOUS!

[Mark Gordon]

Amen, David, Amen!

[APersoons]

Wise words indeed David.

The 'Game of Consequences' as you mention is the reason I had my other car completely stock when I restored it, even back when everyone was shouting I was mad to do so (back in the days when the Pirelli P4000 was said to be THE tyre of choice, and some fitted volvo calipers with a larger brake pad area, which under heavy use could make the brakes very hot very quickly ).
On one occasion a well known E-type specialist and race engine rebuilder told me I was waisting my money to rebuild the original brake system, even in a road car.

As I said here before, I've since driven that completely stock car (metalastik bushings even) for over 20,000 miles, and I'm also very convinced that Jaguar, especially when it comes to the actual driving, got it almost all of it very right indeed.

The reason I'd like a little more oversteer than standard is purely personal.
I've always found it a car that likes to be driven into a corner a little slower, point it where you want to go and then use the right pedal to lighten the front and drive out accelerating with adequate, yet controllable oversteer.
I'd just like a little more of that...

Nothing wrong with that I hope?

[Heuer]

Ah - you should have said! It is quite easy to alter the balance of an E-Type providing you have 185 tyres and have not done anything to the shock absorbers. All you need to do is alter the tyre pressure ratio front to rear. The standard Jaguar pressures give you a very neutral balance so the car will neither oversteer nor understeer unless it is severely provoked. Change the rear pressures to 35psi and the front to 30psi and you will get more oversteer. This is the combination I arrived at after a lot of experimenting but your preferences may be different. Don't go too wild though - I found anything above 35psi made the car a bit bouncy on long straight runs. Going below 30psi at the front reduced steering feel and it weighted up too much in corners. Still a game of consequences I am afraid as I now only get about 8,000 miles out of my Michelin XVS rears! Go out and play and see how you get on letting us know your findings. If nothing else it is a good excuse to be out driving, preferably on a favourite route to compare and contrast.

Interestingly I was reading a Denis Jenkinson book and these are the pressures he used during his travels through Europe.