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Bug-Eye Wheels and Tyres

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twas_brillig

Jedi Knight
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I've been going through posts regards wheels and tires in order to come up with what I want to put on our Bug-Eye project car (using 13 x 5 rims) and have come up with the following summary:

Rick Horler in <span style="font-weight: bold">"Original Sprite & Midget - The Restorer's Guide"</span> states:

"Made by Rubery Owen, the road wheels, of 13in diameter and 3.5in rim width, were formed with a 'D' rim pattern". He identifies the OEM tyres as "Dunlop Gold Seal 5.20-13 tyres were standard, these being a tubelss crossply of four-ply construciton. Heavier duty Dunoop Fort six-pl.y tyres could be ordered for an additional 7.2.6"

The <span style="font-weight: bold">Austin-Healey Sprite Mark I Workshop Manual</span>, Issue 6, from The British Motor Corporation (no date)advises:

"The Austin-Healey Sprite is fitted with 5.20-13 tubeless tyres upon 15x4J ventialted steel disc wheels, each wheel being secured by four nuts"

"Tighten the road wheel nuts to a torque wrench reading of 37 to 39 lb. ft. (5.02 to 5.4 kg.m.). Do not overtighten."

From 'General Data' in the same workshop manual:

Pressures:
Front 18 lb./sq.in. (1.27 kg.cm2)
Rear 20 lb./sq.in. (1.41 kg.cm2)
For sustained speeds in excess of 80 to 85 m.p.h. (129 to 137 k.p.h.) increase pressures to:
Front 24 lb./sq.in. (1.69 kg.cm2)
Rear 26 lb./sq.in. (1.83 kg.cm2)


Web sites that have been referenced in this forum:

Everything to do with tires:
https://www.carbibles.com/tyre_bible.html

Tire comparison/calculator sites:
https://www.mintylamb.co.uk/?page=tyre.htm
https://www.1010tires.com/TireSizeCalculator.asp
https://www.miata.net/garage/tirecalc.html

Determining modern vs original tire sizes:
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=45
https://www.tirerack.com/tires/tiretech/45_conversionchart.html
https://www.carbibles.com/vintagetyresizes.html

Wheels:
https://www.tirerack.com/wheels/tech/techpage.jsp?techid=101

Wheel width vs. tyre size:
https://www.carbibles.com/tyre_bible_pg2.html
(about a third of the way down)

Application:
The original Bug-Eye tire size of 5.20/13 doesn't apear in the Tire Rack chart (the smallest 13 inch tyre shown is 5.60 x 13); members on the Forum have advised that the modern equivalent of the original 5.20 is 145/13.

Carbibles provides these equivalents in their vintage tyre table: 135/80-13; 145/70-13; 165/60/13, and 130/100-13 in their script calculation on page one.

We have one running BE with 155/80-13 tires on it. Comparing rolling radii:

145/80-13 has a rolling radius of 281.1 mm
155/80-13 RR is 289.6

175/65-13 278.85 mm
175/70-13 287.6
185/70-13 294.6

The 175/70-13 appears to the optimum tire size for the new rims for our second Bug-Eye - I'll be checking for availability tomorrow..

Additional wisdom/thoughts sure are welcome.

Doug
 
Miss Agatha is running 155/80-13. Seem fine and look right.
 
Jack - agree on the 155s: they look good on our yellow Sprite, and I tried targetting their overall diameter/radius for the new fat rim/tyres on the project.

Doug
 
I had 165/70R13 on the bugeye at one time. It looked right to me, but this is a difficult size to find.
 
165/65-13 BRIDGESTONE POTENZA RE92 is another choice. :thumbsup:

Steve
:cooler:
 
The size tire is going to be controlled to some extent by the wheels you actually use. Wheel offsets will bring the tire into an interference with either the leaf springs on the inside rear or the fender lip on the outside rear/front. With "stock" Sprite/Midget wheels, I was never able to get away with anyting bigger than 155s before I had some rubbing problems. That was probably for the good, because the wheels are pretty narrow for 165s. With 13x5 wheels, I'd think you could get away with the 165s. I'd start with one tire mounted on a rear wheel and check for interference with the body work and leaf springs.
 
I recently purchased a set of Toyo Extensa A/S 155/80-13 tires. Will be using these on stock rims. This is a new design from Toyo with many different sizes. Will have the Frog up and running in a month or so and will let you know how they handle. Purchased from performanceplustire.com.
Scott in CA
 
Tire pressure info:

*************************************************************

From the Haynes manual "MG Midget Austin-Healey Sprite, 1958 thru 1980"

Crossply tyres:
Normal car load: Front 18 psi; rear 20 psi
Maximum car load: Front 18 psi; rear 24 psi
Sustained high speed driving: Front 22 psi; rear 28 psi

Radial tyres:
Normal: Front 22 psi; Rear 24 psi
Maximum: Front 122 psi; Rear 26 psi
Sustained: Front 28 psi; Rear 30 psi

************************************************************

From 'General Data' in The Austin-Healey Sprite Mark I Workshop Manual, Issue 6, from The British Motor Corporation (no date)advises:

Pressures:
Front 18 lb./sq.in. (1.27 kg.cm2)
Rear 20 lb./sq.in. (1.41 kg.cm2)
For sustained speeds in excess of 80 to 85 m.p.h. (129 to 137 k.p.h.) increase pressures to:
Front 24 lb./sq.in. (1.69 kg.cm2)
Rear 26 lb./sq.in. (1.83 kg.cm2)

************************************************************

The Haynes manual identifies wheels as
Pressed spoked: 4 1/2 JSL x 13
Pressed disc: 3.5D x 13
Wire: 4J x 13

They also show Tyres
Type: 5.20 x 13X Crossply or 145SR x 13 Radial
 
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