The Triumph TR-4, the best of the Sport Triumphs.
I had two and a half complete sets of steel wheels for this car, but out of the ten wheels only two were not bent in some way. I found out this is a very common malady. I put between 300 and 400 miles (480 and 640 kilometers) a week on this car and the vibration was sending me around the bend, sorta'. You would think that after a couple of years of this I would have been used to it by now, but not so. I endeavored to find NEW wheels.
It turns out it is impossible to buy the original steel wheels these days, but several different places can provide wire wheels or reproduction period mags. Unfortunately both of these options can be rather pricey, so I investigated other avenues (my wife says I'm just squeaky, whatever that means).
Some Wheel basics.
The original wheels were 4 1/2 inch wide, 15 inch diameter rims with a "4 on 4 1/2" bolt pattern and "+ 1 1/2" offset, or a backspacing of 3 1/4 inches.
The "4 on 4 1/2" bolt pattern indicates that the wheel is mounted to the vehicle with four lugnuts, and if you measure from the center of any mounting hole to the center of the mounting hole FURTHEST away that distance will be 4.5 inches.
The other dimensions can be determined with the help of the diagram below. This is a cross-section view off a Triumph wheel. To the left is "outside" or away from the vehicle, to the right is "inside" or towards the center of the vehicle.
Dimension "A" is the rim width. In this case 4 1/2 inches. Note that this is not the total width of the wheel, which would be dimension "C" plus "D".
Dimension "E" is the rim diameter, and again this is not the overall diameter, but just the diameter that the tire would use.
The Offset of a rim (wheel) is determined by subtracting dimension "D" from "C" in the diagram below, and heed the sign! "D" is measured from the mounting plain of the wheel to the inner edge, and "C" is measured from the mounting plain to the outer edge. In the case of my stock TR-4 wheels "C" is 3 1/4 inch and "D" is 1 3/4 inch, for an offset of "+ 1 1/2".
The Backspacing is simply dimension "C".
The Triumph bolt pattern is very common. Ford has used it on many vehicles for the past 40 years or so, and many Japanese imports use it. Unfortunately many of these uses are 14 inch rims and most of the Japanese vehicles are front wheel drive, which can use an extreme offset.
Also, on the early TR-4 (early style upper ball joint) a big limitting factor is possible interference with the ball joint. Because of this a maximum backspace of 4 1/2 inches is possible (on a 15 inch wheel). I am unsure if this would be the same for all TR-4s.
So the upshot is, I needed a 15 inch rim with a 4 on 4 1/2 bolt pattern, and not more than 4 1/2 inches of backspacing.
And this is the look I ended up with after much debate and soul-searching. OK, so these were the first cheap wheels I found.
And the nice thing is I got all four wheels for literally only about $10 more than a single reproduction mag and less than a single wire wheel.
What I ended up with was a 7 inch wide, 15 inch wheel with 4 inches of backspacing, which gives an offset of + 1/2.
A 7 inch wide wheel is wider than I wanted, but 6 inch wide wheels are very hard to find on a 15 inch rim. A 7 x 15 size is pretty standard, that leaves only the bolt pattern and backspacing as "odd" things to match. And good news, the backspacing is common.
As you can see, the tires extend beyound the fenders slightly, and can make contact with the fenders under compression in dips. To prevent this I installed new suspension bumper stops and put a 1/4 inch spacer behind each. Since then I have not made tire to fender contact.
The tires I mounted are 205/60/15s. The contact patch for these are much greater than the 165/86/15s that fit on the stock rim. Correspondingly the traction is much greater. This is a good thing and a bad thing. The car sticks in the corners much better know, but you don't get much warning before traction goes away.
Because the lower profile tires are wider the total difference in diameter is not that great. Because of this the speedometer error is only about 1 MPH at 55 MPH and the engine only turns about 50 RPM higher at 60 MPH (97 Km/Hr).
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E-mail me at: Triumph_TR4@hotmail.com