Whilst browsing a few tyre sites for a friend, it is suprising (to me) just how many of them still carry this warning in the Tyre Legality section.
· A two-axle vehicle with single rear wheels must not have radial ply tyres on the front axle if cross ply tyres are fitted to the rear axle.
I assume that this statement is a legacy from the 70?s when Cross-ply tyres were common place, and Radials were just becoming popular, also at the time that this rule would have applied most cars would be rear-wheel drive. Supposing cross-plies were still available to fit, and considering most cars are now front wheel drive, is it still sensible to ?publicise? this statement.
I only ever had one car that had cross-ply tyres fitted, and at the time they seemed o.k, was it simply the superiority of the Radial that brought about their demise or were they really carp?
Billy
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Radials give hugely superior grip but the ride quality on crossplies was very good. They do tend to tramline though. I still have a car with them fitted.
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I only ever had one car that had cross-ply tyres fitted and at the time they seemed o.k was it simply the superiority of the Radial that brought about their demise or were they really carp?
When I first started driving (1960) cross-plies were standard fitting on UK cars. Some keen drivers fitted radials for better roadholding and fuel economy. (I think the only types commonly available were Michelin X and Pirelli Cinturatos)
Radials gave higher grip but many people felt that when their limit was exceeded they lost grip more suddenly than cross-plies (or you were going faster on a given corner) so the effects were more expensive and often more painful.
I'm sure graphs of slip angle/cornering force bore out the different characteristics of the two types.
Modern radials (and suspensions designed for radials) seem more forgiving.
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>>Supposing cross-plies were still available to fit, and considering most cars are now front wheel drive, is it still sensible to ?publicise? this statement.
Yes!! What wheels are driven doesn't have much to do with it. Crossplies have lower cornering stiffness - i.e. give more slip angle per unit lateral load. This lower cornering stiffness means that if fitted to the rear (with radials at the front) any car will be closer to oversteering. i.e. fitting cross plies at the back only is still as dangerous now as it was then.
Virtualy all cars, whether front, rear or all wheel drive are, fundamentally, understeering **. Yes, rear wheel drive cars can be encouraged to break traction by injudicious use of the throttle - just as some front wheel drive cars can be made to oversteer by lifting off mid-corner.
** I know this contradicts the usual bar-room "wisdom", but I'm on about how the car behaves under neutral conditions, not what happens when you provoke bad behaviour via the throttle.
Number_Cruncher
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It's exactly the same logic of "fit best tyres on rear, regardless of front, rear or all wheel drive"
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im sure ive put before that i used to adore crossplies
reason?
you could push them over the limit but still control the sideways slide as the slip angle was so gentle and if you knew what you were doing bring the vehicle back into line,not like a radial thats like an advert for a well known supermarket in the way of when its gone its gone ie once you lose the slip on a radial its very very hard to get back on line again as you have outrun the tyres grip totally
the vehicle i used to have most fun in?
a bedford cf pickup with that gorgeous 2.3 slant (the victor thread reminded me of burning xr3"s off from traffic lights in the 80"s in it,(it was a p/x from a mate)
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I used to have great fun with a Morris Minor 1000 with Michelin cross ply tyres - they also proved good for up to 40k.
- - - - - - - - - - - - - - - - - - - - -
What\'s for you won\'t pass you by
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forgot to add like riding on air on crossplies,wonder if these are the answer to speed humps?
not like this modern rubbish profile stuff
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Ah Morris 1000s on cross ply tyres - good training for later life for me....especially as 1980s BMW engines started to write cheques that their rear ends couldn't cash !
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I remember reading an article in Road and Track in the late 60s where it was mentioned that bias ply tires (cross ply tyres) generated maximum lateral force at about 25 degrees slip angle, where radial ply did the same at 12 degrees, give or take.
I wonder if the key factor is the belt, not the ply configuration, since most bias ply tires were not belted and most radial ply tires were.
I shudder to think of what the contact patch actually looks like on a cross ply at 25 degrees slip angle!
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>>I wonder if the key factor is the belt...
I'm not sure - I think it's a good question.
One of the differences between the two types of tyre that isn't obvious is the longitudinal stiffness. Radials are much stiffer. This meant that the longitudinal stiffness of suspensions for cross-ply tyres could be made quite stiff - as the tyre would deform.
For example, the longitudinal tie bar on the front suspension of a Morris Minor is quite stiff - there's a thin rubber at the front end, and a solid connection near the lower trunnion. On a Marina, the tie rod is much more compliant. This suspension member transmits the braking force to the body, a small proportion of any side force and also the sudden longitudinal load applied as the wheel encounters a bump - it is this load which the two tyre types deal with differently.
Number_Cruncher
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3 litre capris with cross plys on the back. Now that is a fabulous training aide!
------
< Ulla>
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i ran capris in the 70/80"s and i can assure anybody crossplies were not needed on any axle to have lets say moments if you got carried away ;-)
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I used to have great fun with a Morris Minor 1000 with Michelin cross ply tyres - they also proved good for up to 40k.
I didn't realise that Michelin EVER made cross-plies - for many years Michelin X seemed the only choice to cross-plies (I'm sure there were other radials, I was only a boy).
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Is it not the case that motorcycle tyres were predominantly of cross ply construction until quite recently?
I recall old Bridgestone tyres having a reputation for being carp back in the 70's (?) and yet now they can do no wrong.
When did that change?
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according to this site, cross-plies re still very much alive for bikes.
tinyurl.com/2q5bnm
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Hmm so from reading some answers here, it seems to be the case that car manufacturers have designed car suspension around the tyre, rather than the tyre manufacturer conforming to the standards of the car manufacturers, are there any other component bits of cars that have radically set a manufacturing precedence?
Billy
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........... car manufacturers have designed car suspension around the tyre rather than the tyre manufacturer conforming to the standards of the car manufacturers
The improvements in tyre performance have been enormous. Changing the factory-fit crossplies in favour of radials transformed the road-holding of my 1967 Hillman Hunter.
--
L\'escargot.
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the road holding on hilman hunters was often improved by reattaching the front struts to something on the innerwing (metal i think it was called)
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