Wheels & Tyres
From the Jensen FF Mk1 sales literature: “ Spare Wheel: In special carrier underneath luggage compartment. Disc wheels with tubeless Dunlop R.S. 6.70 X 15 tyres which are suitable for sustained speeds of upto 110 m.p.h. without increased pressure”
Photos of old crossply tyres and wheels.
I asked the Jensen list about tyres:
The advise of the tyre specialist I have always used is that 185’s are the tyre for the 5″ wheels with an aspect ratio is 80. He also tells me that for road use the, 205 x70 x15’s would be better but they will bulge. From a cost point of view and to get the car on the road, I had decided to put 185s on the 5″ wheels I have (Bridgestone at £38 each from the tyre specialist). I am tempted to fit 205s on the 5″ wheels as 195s don’t seem to be readily available. It would appear that if you are happy to give up the fully chromed mark 1, 5 inch wheels the best solution is the later half chromed 6″ or even later alloy 6.5 inch wheels with Pirelli 4000, 205 x70x15 . Is the above correct?
I also asked a follow up question:
1) What are the widest radials (which retain or approximate to the correct rolling radius) that will go on the stock 5 inch fully chromed steel Rostyle wheels which I have.2) For reasons associated with classic rallying wheels can only upgraded by a max of 1″ from “original equipment” i.e. to 6″ wheels. That is unless Jensen did 5 1/2″ wheels as standard? (as some people seem to suggest?) Did Jensen do 6″ wheels? and if so, what are the widest radials that can be used on 6″ wheels that retain the correct rolling radius.
The responses were:
1. The FF concept was so far ahead of its time that the practicalities were limited by the then available technology, electromechanical ABS rather than electronic and cross ply instead of radial tyres. The limiting factor in road holding and braking then and now with the FF, and with current ABS systems, is ultimately the skill of the driver and the quality and size of the “footprint” on the road. Push it too far and you WILL lose it. Hence the need to have the biggest sensible “footprint”, i.e. 6 inch + wheels with quality 205/70 tyres – anything wider and lower ruins the aspect ratio, looks daft on the car, will wreck the suspension and steering and of course requires a speedo recalibration. Michelin/Pirelli/Yokos are definitely the best. For pure road holding the latter two are better as they have softer tread compounds – and wear quicker! But then they are cheaper than Michelins. Also beware American “tires” as they have low speed ratings – go for VR or HR. When I got the FF it was on American Firestone “tires” 205/70 with no speed rating whatsoever (remember the USA had severe speed restrictions then) on 5-inch wheels – and for that matter the Mk 1 was shod with similar tyres. They were obviously beloved of rebuilders as they were cheap – also they were black and round. When you have the money get the proper kit
2. There is no such animal as a 5.5 inch Rostyle on a Jensen On my Mk 1 which is correctly fitted with fully chromed 5 inch rostyles I have 205/70 Dunlop SP Sport Radials and these have been running successfully for 5 years or so. Actually they are just too big for the wheels and bulge out a bit at the bottom, which I don’t like – but I can’t afford to replace them. The ideal tyre size is 195/70 but 185/70 is the direct conversion of the old cross-ply. The Mk 2 FF is sized with 6 inch wheels which were correctly part chromed I have since run the car on 6.5 alloys shod with Yokohama 205/17 and this has proved to be the perfect combination. It does require spacers to clear the front suspension, and I have them on the back as well. I have 5 x 205/70 Pirelli 4000s for the 6-inch wheels and indeed one is already fitted and it looks superb. As someone who has driven on all combinations I would never recommend anyone putting any FF on 5-inch wheels – whether you opt for 6 inch or 6.5 inch is a matter of personal preference. When it is time to renew the Yokos I will go to 215/70 if they are still available. I know people who have gone up as far as 235 and down as far as 50, mostly because they are cheaper, but I think they look odd and God only knows what they are doing to the front end.
3. My Healey has 5″ rims and i was advised that 185/70×15 was the biggest tyre for that rim. my Jensen has 5″ rostyles and we aim to put on 185×15 m&s to increase ride height and grip on snow! Otherwise I’d like a bit more rubber for standard road use
4. I have 205 x 70 x 15 V rated Michelins on 7″ Cheviot mags on the CV-8, and 235 x 60 x 15 Pirellis on the stock 6.5″ alloys on the Interceptor.
5. I’m right in the middle with 215 x 70 x 15 Z rated Pirellis on 7″ Campagnolos on the Islero.
6. Hi, I would suggest 195/70 would be the proper dimension for You, then the car will be soft and nice to drive. Good Luck!
7. I would go no wider than a 185 – which isn’t all that wide! Check the spec width for various tires on the many tire sites on the net.
8. 205 is right, more than that will be tolerated but will crown a bit more. I’d talk to the racing guys about what works on a given rim width in available tires. Let us know what you end up with.
9. The 5,5″ wheels I had were so bad I scrapped them. Not only rusty cosmetically but one of them showing some cracking at the stud holes as well. So I may dig out a set of 5,0″ wheels I have in storage. These carried some aged and cracking ER70VR15 when I put them away. To save space the tyres went at that time. They did look too wide for those rims. I don’t think I’ll go for anything wider than 195 so to get a reasonable ground clearance 80-section is the lowest profile I’ll use. The problem up that road (sorry, couldn’t resist 🙂 is to get the speed rating for an Int. Alternatively I may refurbish period 6,5″ Wolfrace wheels, even if that will load the old kingpin suspension a lot more than the original equipment.
10. Monte regs (classic rally assoc) state max 1″ wheel increase up to max 5.5″ and max tyre size 205(min aspect 70) so we figure not worth changing 5″ rostyles and 185 is about the biggest for those rims and widely available. Not concerned with speed rating as will be m+s.
Photos of new tyres.
Having considered all this I bought 5 Pirelli P4000 205 x 15 x 70 which I put on the existing fully chromed 5″ wheels. Firstly, I liked the look of the original wheels and didn’t particularly want any aftermaket 6″ ones such as the period Wolfrace. Secondly, for any of the “historic/post historic road rallies there is a restriction on wheel and tyre sizes. You can not use wheels or Tyres any wider than 1″ more than original. So max. would have been 6” and 205 tyres. Hence I settled for my original wheels and the 205 tyres and finally the P4000 should be easy to get anywhere ( as I understand it with the FF in particular, you must have exactly the same tyres on all wheels because manufacturers detailed specifications differ with the same size tyre). The only problem I’ve had was that the Knock on balance weights pop off because the tyres bulge a little and when driving the weights are eased off. The tyre place has said they will put stick on ones on free of charge.
A comparison (there’s a tire-size calculator at www.miata.net/garage/tirecalc.html). of the old radial tyre and the new one is:
The stock radial tires on Interceptor Mk1 would have been 185 80 15s. The diameter of that size is 26.7 inches, the circumference 83.7 inches, and their number of
revolutions per mile is 757.0.
The new Pirelli P4000 205x70x15s have a diameter of 26.3 inches, circumference of 82.6 inches, and make 767.0 revolutions per mile. Thus, speedometer reading with the 205’s is 1.3% to fast. When speedometer reads 60 mph I will actually be travelling at 59.2 mph
Spare Wheel Carrier
I had to lower the carrier brackets to take the larger tyres
I managed to pick up a set of stainless steel wheelnuts.
The knock on lead weights were being pushed off by the 205 tyres which bulge a little and eventually force the weights off. This happened twice on the front tyres, but not the back ones. Southam Tyres ballanced them again for free using stick on weights. They checked for clearance between the weights on the inner side of the wheel and calipers. Some four weeks on and they are still in place. I have now tapped them down with duct tape to ensure they remain in place.
I asked the List about pressures for the new radials. The replies were:
1.28 front/32 rear for normal use. Up 4 for sustained motorway use.I’ve used these for years with no problems on the FF on both 6 and 6.5 inch wheels and I follow the same pattern on the Mk 1 with 5 inch wheels.
2. Pirelli 4000 is just right with the GKN Alloys, but here in Norway, I don`t find 4000 Pirellis. Luckily for me the car has 4 brand new ones. I drive with 30 Psi all round, no crooked wear or roar.
WHEEL ALIGNEMENT AND GEOMETRY:- see section on Steering.