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Spitfire/Hurricane wheel sizes?


Test Graham

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Mason quotes Hurricane wheels at 800x10in. Spitfire the History quotes Spitfire wheels at 7-50-10. These descriptions don't seem compatible, unless the 7-50 is meant to be 750, implying a smaller wheel size on the Spitfire than the Hurricane. I understand the 10in to be the tyre width (and height), and the first measurement to be the wheel diameter - but 800?

Can anyone provide an explanation of these numbers, and explain (if further explanation necessary) the difference between the wheels on these two aircraft? I'm thinking Mk.I in both cases, if that helps.

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800 x 10 would be 8 inch wide[cross section] by 10 inch hub diameter.

7-50 would be 7 inch wide x 10 inch hub diameter, with the wall of the tyre being 50% of the width. So overall diameter of this wheel would be 50% of 7 x2 +10 = 3.5 x2 +10 = 17 inches.

Without a third number on the 800 x10 tyre it is assumed the wall is 100% of the width therefore 8 inches so overall diameter is 8x2 +10 = 26 inches.

I'm using the info we use on tyre sizes on our vintage cars, of the same period.

hth a bit

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OK, I accept that I've reversed the hub and tyre sizes. However, thanks to comment by Ross McNeill on the Flypast site, there's a Hurricane wheel shown as 7.5 X 10 1/4 (moulded on the tyre), and a Hawker drawing reference of 8.00 x 10 1/4, which also gives the other as an alternative.

I don't think either of these aircraft types had the tyre half-hidden by the hub, so I think that 7-50-10 is more likely to be an error for 7.5 -10. Interesting information, though.

Now for the Spitfire?

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The 7-50 could be a misprint for 750. The hub does not 'hide' any part of the tyre. The % is just a standard way of giving the wall height measurement., from the steel wheel hub edge [or tyre beading] to the tread.

On my vintage racing car one type of wheel takes 400- 425 x 17, that is 4 to 4 1/4 inches across by 17 inch wire wheel. With the wall also 4 or 4 1/4 inches. The modern equivalent I can get is written 100/90/17 : 100mm [almost 4 inches], 90 is the % so the wall height so it is 90mm, by 17 inches wheel.

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I don't know about deciphering the "formulae," but, according to a July, 1940 Dunlop chart, 7.50 x 10 = a nominal diameter of 24.25" x 7.55" width, with maximum dimensions being 24.85" & 7.85", and 8.00 x 10 = 25.4" x 7.9" width, with maximum dimensions of 26.05" & 8.2". The Spitfire wheel well drawing quotes a maximum permissible diameter (to allow for the permitted clearance of .025" throughout the whole travel) of the inflated (to 47psi) tyre to be 24.51".

Edgar

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Black Knight. So the percentage is referring to the tyre cross-section. OK Edgar's post says that the 7.5 x 10, if somewhat over-inflated, would not fit into the Spitfire. Perhaps it should be 7x10? Does your chart quote that, Edgar? Or does it quote designations such as IVV17 (Hurricane) or JV17 (Spitfire)? The Spitfire Mk.V manual doesn't quote dimensions, though the Hurricane MK. II manual does say 8 x 10 1/4.

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I don't know about deciphering the "formulae," but, according to a July, 1940 Dunlop chart, 7.50 x 10 = a nominal diameter of 24.25" x 7.55" width, with maximum dimensions being 24.85" & 7.85", and 8.00 x 10 = 25.4" x 7.9" width, with maximum dimensions of 26.05" & 8.2". The Spitfire wheel well drawing quotes a maximum permissible diameter (to allow for the permitted clearance of .025" throughout the whole travel) of the inflated (to 47psi) tyre to be 24.51".

Edgar

If you look at my previous post, regarding my car tyre, there was a lot of leeway on the actual measurement of a tyre, there still is, the numbers are 'nominal'

Taking your reference.

1) 10 being the wheel hub diameter. 7.5 being across the tread, but also the wall height. Gives us 10 plus 2 times 7.5 inches = 10 + (2 x 7.5) = 10 +15 = 25 inches diameter nominal, The difference being taken away by the amount the tyre, [the beading edge] sits into the steel wheel. The beading edge is the inner diameter of the rubber tyre, which has a wire beaded edge for it to sit tight into a groove in the metal wheel.

2) similar sums for the 8.00 x 10, 8 inch wide, 8 inch wall 10 inch metal wheel. Gives us the sum of 10 + (2 x 8) = 10 + 16 = 26 inches diameter

Tyres then as now are not 100% accurate in measurement. When I want new racing tyres I have to go through maybe 100-150 to get 5 with exactly, or very nearly, the same measurements.

_________ __________

I_________[ ]__________I } = tread width [ eg 8.00, or 7.50 ]

wall + wheel + wall = total diameter [ eg 8 + 10 + 8 = 26 ]

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For wheels the dimensions that matter are:-

1) The diameter of the wheel casting at the point on which the tyre sits. For Spitfires this progressed from 10", 10.25" with split rim, 12" with split rim and finally 13" with split rim on some Seafires.

2) The width of the wheel inside the rim at the point where the tyre sits.

3) The centre line of the above width and its relationship to the centre line of the bearing set up...the offset, which varies from aircraft to aircraft.

The overall diameter of the tyre is an issue and the aspect ratio on Spitfire tyres, the hight to width dimensions of the tyre cross section must be contained within the wheel well. This aspect ratio of the tyres reduced as Spitfire development progressed.

Wheels only got bigger on Spitfires to incorporate bigger and more powerful brakes...until finally they tipped up on their nose and the wheels/tyres reverted to earlier sizes. This why you see the four aperture 10.25" wheel on some Seafire 47's.

PeterA

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