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From: Huntley Perry
Remote Name: 192.168.1.1
Date: 27 Nov 2001
In response to your request for comments on appropriate tyres for your Jupiter E2SAL813, I went through a similar search during restoration of my Jupiter E1SA100R, and offer the following for what it's worth.
Examination of new or nearly new Jupiters indicate that most, but not all, were shod with the Goodyear "Diamond Treads". I have factory photos of E0SA1 and the chassis at the 1950 New York Show. Both are equipped with diamond treads. Referring to Ed Nankivell's book "The Jowett Jupiter, The Car That Leaped to Fame", photo 4 on p.11 shows the ERA chassis at the 1949 London Motor Show equipped with Avon tyres; see also The Autocar, Oct 7, 1949, p.1105.
Again to Ed's book, the front Jupiter on the production line in photo 24, p.26 wears diamond treads, whilst the second car is fitted with a different brand, Dunlop perhaps? Also, the front Jupiter in photo 25 wears the alternate brand. I cannot make out the tread on the 2nd Jup, nor can I positively determine whether any of the cars are RHD or LHD.
Curiously, the 1/5 scale Jupiter (Ed's book again, photo 15, p.18) wears 3 diamond treads plus one undetermined on the LF! I wouldn't recommend this in full scale as the handling might be a bit unpredictable.
Turning to factory sales literature, the original big blue folder shows the diamond treads in at least 2 views. The 1952 "green" folder also shows diamond treads in two views. The 1953 "red" folder shows diamond treads in 3 views. None of the blue, green or red folders specify a brand of tyre; only the 5.50x16 size.
As an aside, my only Jowett Javelin folder (probably 1945 or 1947) also shows diamond treads, but in a 5.25x16 size, whilst the factory Provisional Technical Data for the R.4 Jupiter calls out 4" wide rims (more later) and 5.90x15 Super Cushion tyres.
The Motor of Nov 22, 1950 calls out and shows Goodyear 5.5x16. Incidently there is also a good view of the tool box and its soft lid behind the seat, together with the tyre pump bag.
The Jupiter featured in the September 1951 issue of Mechanix Illustrated clearly wears the diamond treads. However, this is not true of the Jupiter reviewed in the February 1953 issue of Auto Age. I cannot make out the brand of tyres here, but suspect Dunlop.
I suspect E1SA100R originally came with the 5.50x16 diamond treads as this was on the spare, althought the road wheels were fitted with later 6.00x16s, the make of which I neglected to record.
Incidently, the official name of the "diamond treads" is GOODYEAR DELUXE ALL-WEATHER as marked on the sidewall of my sole survivor. No doubt the appellation "diamond tread" comes from the distinctive tread pattern.
In sum then, it would seem that the preponderance of Jupiters were orginally fitted with diamond treads, but other makes were used as well. I think it unlikely that a small company like Jowett had exclusive contracts with a major tyre manufacturer, but rather bought in small batches for the best price at the time. Perhaps Ed Nankivell can shed some light in this respect. Also, I found no evidence that there were any tyres selected especially for export only. More likely what ever was in the JCL supply at the moment.
Having said all of the above, I searched for appropriate tyres for E1SA100R, with diamond treads as first choice. These are readily available from Lucas Automotive (no relation to the Prince of Darkness), 2141 West Main, Springfield, OH 45504, 1-800-735-0166. UNFORTUNATELY, not in 5.50x16, the closest size being 6.00x16.
A word here about tyre sizes. In the "old" days tyres had a "square" cross section. That is, tyre width was the same as tyre height. Thus, a 6.00x16 is 1/2" wider than 5.50x16, and is (approximately) 1" larger in unladen diameter (5.50 + 16 + 5.50 = 27"; 6.00 + 16 + 6.00 = 28").
I would not recommend fitting 6.00x16 tyres to Jupiter wheels which have 3" wide rims as there is more likelyhood of the tyre unseating during hard cornering. In addition, there are some serious clearance considerations. On E1SA100R, the Dunlop Gold Seals (my final choice) are quite close to the lower front edge of the front wings. It is even worse at the lower front edge of the rear wings. Here, the wheels move down and FORWARD during rebound, and when unloaded the tyres actually contact the wings. This makes changing a wheel difficult unless the car is jacked up by the axle. Correction was supplied by a suitably padded crowbar and careful nudging. It should be further noted that the 6.00x16 in lieu of the 5.50x16 will slightly decrease acceleration.
I have not been able to find a supplier of 5.50x16 diamond treads. As you probably know, Coker Tire, 1317 Chesnut Street, Chattanooga, TN 37402, 1-800-251-6336, provide a variety of tyres in 5.50x16 size. These include Firestone, B.F. Goodrich Silvertowns, and Michelin in 500/550x16 and 550/600x16.
Likewise, Universal Vintage Tire, 2994 Elizabethtown Road, Hershey, PA 17033, 1-800-233-3827, carries the Firestone and Dunlop in 5.50x16 sizes. You might also want to contact Vintage Tyre Supplies at: www.ftech.net/~vintage or email@example.com. Be sure to request their Illustrated Guide, as well as the Coker catalog. Both have much useful info and many tyre related goodies, and illustrate various tyre treads.
As I mentioned above, I selected the Dunlop Gold Seal in 5.50x16 as being the most period authentic available for E1SA100R. The ones I received are marked "tubeless", but I installed tubes anyway as I was unsure if the rim beadseat area would work with tubeless tyres, and also if tubeless valves would work in the holes for tube valves.
One last note: my Dunlop Gold Seals were manufactured in Zimbabwe. One of these days I will buff that off the sidewalls.
I intend to contact Goodyear Great Britain (Stafford Road, Wolverhampton, WV10 6DH) and inquire if they make the diamond tread in 5.50x16, or know of a source for the vintage/antique car market.
Hope the above is of some help.
P.S. In going through old correspondence recently, I came across your e-mail of 21 Oct 99 seeking a source for battery covers for the Jupiter. If you've not found any yet let me know; I can help.