Spare wheels and LSD

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MarkHawkins
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Spare wheels and LSD

Post by MarkHawkins » Sun Dec 17, 2017 8:48 pm

While getting a leaking rim fixed this weekend on OPJ, the thought struck me - could I use the 14" 60 profile spare I carry on the rear of the car and drive on it when it has larger 15" wheels at the rear and LSD? So far I've only used the smaller spare to hold the car up or move it just a few feet.


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Spare wheels and LSD

Post by DARK STAR » Sun Dec 17, 2017 10:52 pm

I wouldn't risk it, the diff will think you're going round in circles.


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Spare wheels and LSD

Post by MarkHawkins » Sun Dec 17, 2017 11:10 pm

That's what I thought - at least a smaller spare can be used on the front, or hold up the back when parked.


Custodian of :

1968 '4b Coupe HBL 725G
1972 '5a M/overdrive ALJ 513K - ALJ 513K
1977 '6a M/overdrive - OPJ 62R

ex 1974 '5a auto - VLN 826M
ex 1985 GTC M/overdrive B205 AMT - number 413
ex 1984/85 SS1 number 0007 (1300)

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Spare wheels and LSD

Post by halfpenny » Sun Dec 17, 2017 11:12 pm

A diff isn't designed to work continuously - and you may find the car will handle rather oddly. Probably ok at up to 30mph. I wouldn't risk it on the front even considering no diff present



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Spare wheels and LSD

Post by Roger Pennington » Sun Dec 17, 2017 11:16 pm

You don't say what size & profile the existing 15" wheels are, which is surely significant?


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Spare wheels and LSD

Post by MarkHawkins » Sun Dec 17, 2017 11:36 pm

Something like 205 / 60 15 - there is quite a lean on the car when I put the spare on!
Spare wheels (or lack of them) have come to my attention recently after experiences of modern cars that carry no spares at all, just a can of gunk.


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1968 '4b Coupe HBL 725G
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1977 '6a M/overdrive - OPJ 62R

ex 1974 '5a auto - VLN 826M
ex 1985 GTC M/overdrive B205 AMT - number 413
ex 1984/85 SS1 number 0007 (1300)

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Spare wheels and LSD

Post by Roger Pennington » Mon Dec 18, 2017 12:24 am

Ok, in that case I'd tend to agree with the others.


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Spare wheels and LSD

Post by reliant-reviver » Mon Dec 18, 2017 9:29 am

Put spare wheel on front, move correct profile wheel and tyre onto back axle.


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Spare wheels and LSD

Post by MarkHawkins » Mon Dec 18, 2017 10:55 am

The car has larger wheels at the back that than the front - I believe this was a deliberate decision by the P.O. to make steering lighter and reduce the height at the front while maintaining rolling diameter on the driven wheels.
With the promise of relatively good weather, I've driven it to the office today to give it a run prior to Vintage Stony on Jan 1st and Bicester Heritage on the 7th.


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1968 '4b Coupe HBL 725G
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ex 1985 GTC M/overdrive B205 AMT - number 413
ex 1984/85 SS1 number 0007 (1300)

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Spare wheels and LSD

Post by DARK STAR » Mon Dec 18, 2017 1:31 pm

The previous owner obviously had a strange concept of chassis dynamics.
An LSD will tend to induce understeer (corrected by stamping on the accelerator in corners :lol: )
Ride height higher at rear will tend to induce oversteer - so 'balancing' the induced understeer.
When you get round to it, put the same diameter wheels all round, you can then adjust the handling from a sensible base!


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Spare wheels and LSD

Post by halfpenny » Mon Dec 18, 2017 4:52 pm

Continual working of the lsd will also likely wear out the clutches quite quickly



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Spare wheels and LSD

Post by scimjim » Mon Dec 18, 2017 8:35 pm

That depends what type of LSD it is - and I think Dave Phirrips knew how to pedal a race car :D


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