A good idea at the time: Twin tyres

"The idea was picked up in the Eighties by Jerry Juhan, whose Lotus Esprit was outdragged in the wet by a Citroen Deux Chevaux [2CV], prompting him to speculate that two narrow tyres would give better adhesion in poor conditions than a single wide one."


The idea of twin tyres was originally dreamed up to supplement the load-carrying capabilities of the narrow-section tyres of Edwardian cars, which rarely lasted more than 10,000 miles.

In the Thirties, twin tyres were sometimes fitted to racing cars to give extra grip, especially in hillclimbs. This 1939 Alta has twin tyres for track racing. The idea was picked up in the Eighties by Jerry Juhan, whose Lotus Esprit was outdragged in the wet by a Citroen Deux Chevaux, prompting him to speculate that two narrow tyres would give better adhesion in poor conditions than a single wide one.

Late in the decade, he put his "multi-tyre" on the market, after patenting the idea in more than 40 countries, but the idea added unsprung weight and complications and failed to catch on.
http://www.the-car-addict.com/2011/10/rip-ja…

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<- the Facebook post that started my search

http://www.carbibles.com/ttyreopinion.html

AN OPINION ON TWINTYRE SYSTEMS

HERE'S SOME FIRST-HAND OPINIONS OF THE TWINTIRE SYSTEM FROM SOMEONE WHO HAS BEEN USING THEM SINCE THE YEAR DOT. TAKE IT AWAY MIKE FROM PERTH, AUSTRALIA:

I recall AVON started it off around 20 years ago but since they were the only manufacturer that it probably wasn't quite as widely accepted until Yokohama added theirs. The AVON does however still have a larger range of tyre sizes for twins - I think they go down to a 110 width for the 16" - but I'm not certain.

The Avon's are OK but a bit too hard compound for my preference. I like the Yokohama; they have a nice soft compound but wear very well indeed. Considering I have them on a Turbo 3Litre straight six they have lasted 65,000km with quite a bit of 'performance driving'. The only negative thing about the Yokohama is that odd 'memory' effect - where the rubber takes a bit longer to forget its standing-shape when you drive off after a long while standing still - especially if they were a bit deflated.

In respect of Wheels, there are about 3 styles I've seen in Perth:

  • The full dish which looks a lot like a normal flat wheel.
  • The mesh which is the cast equivalent that looks a bit like a wired rim.
  • The spoke which has 5 large spokes - a bit like ROH but better styling - that's the type I have.

On the outside of the wheel is raised alloy lettering which reads '

Crimson, Inc'.

Further around the side are three letters '

JIL

'. The centre hub has a removable black/yellow plastic motif with the lettering '

JJD WHEELS CONCEPT® PRESENTED BY CRIMSON'

. Mine have a 40mm offset.

When tyres are fully inflated, the gap between them is about 0.25" and the overall width is about 9.5". I used to run equal tyre pressures of 22PSI all round until I discovered you could tweak the performance by making the inside 4 tyres a little higher in pressure by about 5psi or a bit more until you notice the difference and can deal with it. So I used to have the front inside ones at 26psi, the front outside ones at around 20 to 22psi. The rear inside ones at 32psi and the rear outside ones at 26psi. This was my optimum setting for great breaking and plenty of warning when cornering really hard on stiff suspension. I varied the pressure just a bit if/when I noticed a change in wear pattern or if I had to compensate when swapping front to back to even out the wear overall. When I get my car back on the road I want to try 125/90 on the rear with 125/85 on the front.

I had to adjust the toe-in so it's not so severe (around 2mm) as the original 15" tyres had far too severe toe-in of around 6mm. The camber and castor should really be made more precise for twins since they track better. There was a little wandering at about 160 to 180km/h but I felt quite safe even up to 240km/h which was the cars limit, although I think I might select a slightly tighter toe-in for those long country trips. My car was one of those that had a bit of slop in the camber area and I think I could have had better tyre wear had this been set properly.

I suppose an automatic toe-in adjustment for speed might prove useful to further improve stability, save tyre wear and reduce fuel consumption - anyone care to comment on this? If so then feel free to email me.

The good thing was I never had a problem with a flat stopping me getting anywhere - the flat could usually be pumped up with that sealer stuff and it would be OK. The handling change is noticeable when one of them goes flat but you can keep going for ages - like 500km without any trouble and the flat one is not damaged and can still be used when the puncture is repaired. I wouldn't recommend travelling this sort of distance with a flat, even with twintyres, but it goes to show that they do the job they're supposed to.

By having the tyre pressures as I set them up meant I had lots of warning in terms of feel when I pushed it hard into a corner with a very predictable and surprisingly safe drift when they eventuallydid let go. I used to have Pirelli singles on an older car - they were great for road holding but gave virtually no warning when they'd let go - could be quite dangerous if you've never put the car to it's limits. I think it would be worthwhile trying Pirelli's with those tyre pressure settings (if they made the same sizes - that is).

It's like anything I suppose, there are lots of people that proclaim their particular selection over others but, I'd likely stick with the twins for the safety at least. Going through puddles at speed on ordinary singles was always a worry - with the twins it's so much safer and precise.

My recommendation if you wish to try twin tyres on your own car for any length of time is to have the camber and castor checked as precisely as possible, I'd even have it done when sitting in the drivers seat so the checks account for the included weight of the driver. Otherwise you might find the normal cars settings could be out quite a bit and this will give you premature wear and might even make the stability appear worse. If you can get those camber/castor correction units then thats the best thing as the twin tyres seem to tolerate less negative camber and less toe in as well but, naturally a bit of experimentation can give improved results.

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Sources:
http://www.boostedfalcon.net/viewtopic.php?…
http://forums.pelicanparts.com/off-topic-disc…
www.niche.iinet.net.au/Twin_advert.jpg
http://www.fordforums.com.au/showthread.php…
https://www.facebook.com/groups/1450854…