I've done a bunch of weighing and measuring over the last couple of days, and here's the summary: read through to the end if you're having trouble sleeping.
Doug
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We own two Bugeyes: a yellow one running on 155/80R13 tires, and a silver painted project BE that will have 175/70R13 tires on 5J 13 rims that have a 5 inch offset (ie the distance from the inside face of the mounting flange to the inside edge of the rim is 5 inches). The wheels are generic alloy; I bought them out of the UK but have no idea who made them..
I tried the wide rims and 175 tires on the yellow BE, and ran into interference problems at the front on the passenger side with the tire hitting the body frame on hard right turns. I did not have the nose piece on for any of this checking. On the drivers side, a hard left turn left approximately 3/8 inch of clearance to the body frame; with 5/16 inch spacers on the passenger side, there was no longer rubbing but there was still zero clearance. I’ll want to get the frame/alignment checked out in the spring (the snow is a wee bit deep right now), and have my fingers crossed that the silver BE (it will be getting front discs and rear brake upgrade) won’t have that problem
I would suggest that if you’re considering a wider tire and/or rim than the above 5 inch/175/70 combination, you should try to borrow the exact combination and check for clearance.
I took a bunch of measurements; hopefully the listing below will make sense. I’ve identified which car I was installing and measuring with by their colour (yellow; silver).
Bottomline: this combination (the 175/70R13 tires) gives nearly 2 inches wider contact area than the original 1960 era tyres, just tucks nicely inside the body work at the rear, and appears to have adequate lateral clearance at the rear. The weight of the original tyres and steel rims matches the weight of the wide alloy and modern radial tire.
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Tread widths: the ancient Dunlop has a surface contact width of about 3 ¼ to 3 ½ inches
The Kumho has a surface contact width of about 5 inches (4 ½ to 5 inches)
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Ancient wheels/tires (Silver) BE (we bought this car in 1971 and it’s been stored ever since, so I’m assuming the tires are from the 1960s. If anyone is really worried about concours: the Dunlop Gold Seal doesn’t appear to have any cracks in the sidewalls or tread (cursory glance) and still has a bit of the original casting nubs showing. The Michelin makes a billiard ball look like it’s suitable for driving in the wet).
Tire Size and Brand: Driver’s Side rear: Michelin 5.20 13 X radial; bald
Passenger side rear: Dunlop Gold Seal 5.20-13 Bias Ply; excellent tread
Stock Rim: (nothing stamped; I’ll take an empty rim into a shop and ask them to measure at some point)
Overall width (outside of steel to outside of steel): 4 15/32 inches
Backspace (measured from edge of rim to mounting face of centre section): 3 5/16 inches
Weight: 5 ½ pounds (all weights are approximate, using a basic bathroom scale)
Rim and Tire (Michelin):
Maximum overall width (rubber to rubber) 5 ¼ inches
Backspace (rubber to mounting face of centre section) 3 27/32 inches
Measured circumference of tire: 71 ½ inches
Weight: 10 ½ pounds
Rim and Tire (Dunlop):
Maximum overall width (rubber to rubber) 5 1/2 inches
Backspace (rubber to mounting face of centre section) 3 7/8 inches
Measured circumference of tire: 72 ¼ inches
Weight: 11 pounds
Track (rear):
Outside width, sidewall rubber to sidewall rubber, of rear wheels: 50 5/8 inches
Clearance (from outside of rubber to outside of bodywork): Left: 1 17/32 inch Michelin
(this shows how much the tire is inset under the body) Right: 1 21/32 inch Dunlop
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Existing wheels/tires (Yellow ) BE:
Tire Size: 155/80R13
Brand: Kumho 795 Touring A/S
Age: need to check to see if they’re safe
Wheels: stock BE rims; see above for dimensions
Rim and Tire:
Maximum overall width (outside of rubber to outside of rubber): 5 27/32”
Backspace (rubber to mounting face of centre section): 4”
Measured circumference of tire: 71 ¼ inches
Weight: 11 ½ pounds
Track (rear):
Clearance (from outside of rubber to outside of bodywork): Left: 1 7/16 inches
Right: 1 1/16 inches
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New wheels/tires (Yellow) BE:
Tire size: 175/70R13
Brand: Kumho 795 Touring A/S
Toyo Eclipse (I bought two Kumho and 1 Toyo, to check best fit and appearance; will probably take the Toyo back and save a few bucks)
Age: 2009 (?)
Wide Rim: 5Jx13
Overall width (outside of alloy to outside of allowy): 6”
Backspace (measured from edge of rim on inside to mounting face of centre section): 3 ¾”
Rim and Tire: Kumho 795 Touring A/S
Maximum overall width (rubber to rubber): 6 31/32”
Backspace (rubber to mounting face of centre section) 4 7/32”
Measured circumference of tire: 72 inches
Weight: 11 ¾ pounds (approx – bathroom scale)
Rim and Tire: Toyo Eclipse
Maximum overall width (rubber to rubber): 6 31/32 inches
Backspace (rubber to mounting face of centre section) _4 ¼ inches
Measured circumference of tire: 71 3/4 inches
Weight: 12 pounds (approx – bathroom scale)
Track (rear): Kumho
Outside width, rubber to rubber, of rear wheels: 51 1/8”
Inside width, rubber to rubber, of rear wheels: 38 ½ (approx)
Clearance (approximate) to body tub on inside, drivers side: approx 1inch
passenger side: approx 1 ¼ inch
Clearance (from outside of rubber to outside of bodywork): left: ½ inch
Right: 3/32 inch
(Note that the above figures don’t add up: 38 ½” +6 31/32 + 6 31/32 should equal 51 1/8” not 52 3/8”)
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Front Clearance (yellow BE; drum brakes):
With the Toyo Eclipse on the driver’s side, there’s approximately 3/16 inch clearance to the body on a hard left turn; with 5/16 inches of spacers on the passenger side lug nuts, there is zero clearance to the body on a hard right turn. No idea why.
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Published Data:
1 – Stapleton (The MG Midget A-H Sprite High-Performance Manual) advises “With the Sprite/Midget, the realistic limit on backspace is 3.70in (94 mm)”