Good choice: no way in HELL would I ever drive a car, at more than 10 mph, with tires 30+ years old.
How much is safety worth, of you/your occupants?
New tires, be they bias ply or radials, are cheap insurance.
Roger
Timothy is in Melbourne where the 10 year rule applies
In fact Antique Tyres won’t fit 10yr+ tyres if you bring them in claiming they are only to support a car being restored., as someone found out.
Recently someone had a part worn set of Olympics 550x18" for sale at, I am told, $ 300 each . Good luck with that as they were made in the 70s.
And certaainly MK Vs owner/ drivers entering in competition events { as they commonly do with their superior radial assisted cornering. won’t pass scrutineering with old tyres.
The scrutineers check dates on stack hats, extinguishers and tyres.
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Here is one from the Department of Commerce National Bureau of Standards of our federal government, dating from 1979, on police tires.
Pages 11-13 are relevant to this discussion.
Have I misread or does that show that the 2nd best braking was from Bias ply [ what I call cross ply] as opposed to radials.? { Set #2 out of 10, Dunlop Gold seal Bias ply]
I would think that the criteria for choice of tyre by a MK V owner would not necessarily be the same as for US police pursuit cars of the 70s.
A couple of factors worth additional consideration: wheels and spats.
Wheels for Mark V were C.3105 5Kx16 which are 5" rims. Early 120s and Mark VII cars had same wheels and then a 5.5" rim was introduced. Superficially the wheels look pretty similar, worth checking. Using 5.5" rims on the front will alter the steering geometry to about 0.5" wider track. Tread width and modern rubbers with different friction coefficients from the Dunlop super comfort 6.70 16 tires alter the steering ease and action.
Rear spat tire clearance can be problematic for people using a wheel not 5K16 and/or using too wide a tire sectional width. Tires can rub on spats in usage even when the static clearance is okay. Clearance from tire to spat typically is different for each side of car (spats and body parts are not so uniform as to give symmetric clearances).
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The DOC NBS study dates from the period when radials were beginning to take over the market from bias ply, thus the desire among police users for a comparison.
Driving traction and spinning traction in wet perhaps are not of really high concern to Mark V owners of today, cornering perhaps if we drive like Vard, but braking certainly.
Braking performance in wet conditions of 10 types tested came out in this order, with the middle runner being rated at 100%:
- Goodyear Flexten radial - 108.0%
- Dunlop Gold Seal bias - 103.5%
- Goodrich Pursuit radial - 103.4%
- Firestone Super 125 HR78 radial - 101.0%
- Armstrong bias - 100.5%
- Pirelli radial - 100.0%
- Dunlop Elite radial - 99.0%
- Firestone Super 125 HR70 radial - 98.2%
- Michelin radial - 95.7%
- Goodyear Police Special bias - 90.6%
Summary conclusions are given on pages 11 and 14.
In braking, the radial average was 2% better than the bias average.
In cornering, 8% better.
ASTM procedures are referenced, so we can assume that proper tire pressures, identical vehicles and uniform driving techniques applied in these tests. However, tread patterns are all different, and performance dry may be quite different than wet.
Spats clearance is of concern both to many XK120 owners and nearly all Mark V owners. Careful measurements seem to be a good idea.
There have been reports of lost spats on XK120 in spirited driving, though it should be noted that the method of attachment on XK120 is very inferior to that of Mark V.
Ah , averages. But if one takes the mean, Bias have 2 above and 1 below, where-as radials have 3 above and 4 below. : >)
For what it’s worth, in my experience there is an enormous difference in grip both wet and dry due to composition and tread pattern but radial construction gives better performance than crossply. Testing a number of different tyres with differences in composition and tread pattern will not necessarily indicate the relative merits of radial v. crossply.
Peter
Hello all. I would keep the bias ply tyres. I am about to replace the Firestones on my mk4 with the same tyre in WW form. I think they look better. I also have a 64 V8 Daimler to which I am going to fit original type tyres to. Not interested in how fast it corners… Cheers.
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The NBS test is of course not intended for classic car owners like us, really more for police users, and I could wish they had included more than just 10 selections, but I am impressed that the best radial was 5% better than the best bias ply in braking. And those are all tires of 40 years ago. Today’s choices ought to be even better. Although if you go for a radial with a “nostalgia bias look” tread and sidewall, some of the advantages may be reduced.
Peter
But you’re in Wet Grip Central, Perhaps grip in black ice would be more useful : >)
We never have ice here. (well not when the SS is on the road.) The problem is not ice but salt. On the first day of salt the SS hibernates until the spring rains wash it all away.
Peter
Hello All,
I have had a conversation with the owner of Antique Tyres here in Melbourne. He said straight away that he wouldn’t ever fit radial tyres to a MKV because it will affect the steering geometry, will place excessive pressure on the suspension and steering components causing increased wear and possible failure and finally will outlast a radial tyre fitted to MKV. He also said that if the tyre isn’t of the correct configuration it might rub against the rear spat or cause it to come off while cornering. This apparently happens to XK120’s spats when fitted with radials.
So there we go, I’m back to the cross (bias) ply’s and they are cheaper too!
Cheers,
Tim
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Well…I, for one, would REALLY like your tire dealer to esplain them ones to me, especially the first one.
Hi Paul,
I think he means that the car was designed and set up to run Bias Ply’s as that was all that was available.
I will fit them and drive at a gentlemanly pace (What else can one do in a MKV?
) and just enjoy the ‘period’ feel, as well as the $200.00 per tyre saving!
Cheers,
Tim
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Excellent! That way, if you drive leisurely, folks can get a good look at a classic beauty…plus, that $800 savings will buy LOTSA petrol!
He may be covering his own liability.
As I recall, when the XJ6 came out it was designed to only use radials, and there were warnings not to use bias plies.
The Mark V was never tested by the factory on radials at MIRA.
Affect steering geometry? - camber, caster and toe specs in the manual were worked out on bias plies; one would have to calculate and experiment to determine whether or not they should be changed when on radials. XK owners have not done this, they use factory specs.
Excessive pressure on suspension and steering? - radials allow increased maximum cornering speed, so there would be increased centripetal force acting on the ball joints, but the increase is only if you get above the bias maximum speed. At lower speeds they would be equal.
Increased wear and possible failure? - yes if you spend a lot of time in max cornering and your ball joints were already worn.
Outlast radials? - nope, the other way round if aligned correctly (but then we don’t know if the specs are good for radials).
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For what it is worth. Put Radials on my MK IX, 120.140, and 1940 Packard and now my MK IV. First four were definitively better in ride and roadability and handling. The new Stahl radials on the MK IV look as original. Can’t wait for restoration to be completed and check out the new feel. Has to be better than my 10 year old Dunlops which had turned to rock… Just my
Little nickels worth with absolutely seat of the pants engineering thrown in as to the radials advantage.
Thanks,
Gust Nelson
Rob, outlast? Is likely to be academic as unless one does more mileage that normal for an old car, their use by date will come around before they wear out. Personally whichever, I’d prefer a soft compound that would wear more quickly, but grip better.
Absolutely: Wear toughness, for non-race car toys, is utterly irrelevant.