racerdude5
Well-Known Member
I posted on another thread asking about Torque Thrusts on a Duster
"I've ran Torque Thrust IIs on the back of my duster with an 8.25 for over a year now. The wheel is 17x8 with about 4 or 3 inches of backspacing. The tires are Pirelli P6 Four Seasons P245/45R17 and I've had no problems at all. They work perfect. If I could I would go with a little less backspacing for the rear wheels even if that means rolling the lip of the fender, so I think at around 3 inches give and take a half inch and you might have to roll the lip. I didn't have to and I have about an inch of clearance between the inner side of the quarter panel and the side wall of the tire. I would do this to bring the rear track width nearer to that of the front track width since the front is about 4 inches wider than the rear. For up front I just ordered a pair of 17x8 Torque Thrust IIs to match the back. They have a backspacing of 5.5 inches. To maintain a decent scrub radius of around 3 inches I would go with at least 1 to 1.5 inches of positive offset. The tires I bought at $63 a piece (new!) Are Kumho Ecsta AST's with a size of 215/45R17. I made a tool out of PVC piping that I bought at Lowes for about $7 and cut and drilled it to the specs of the wheels I'm looking at with the tires section width and max diameter and slid them on to the wheel studs after putting a floor jack under the LCA to maintain ride height with the wheel and tire off and spun the hub and turn the steering wheel to check all the clearances."
Offset is important, it effects scrub radius and track width as well as clearances in the fender to the fender, subframe, and other suspension components.
**For the front:
Unless you're gonna do some major modifications, 8 inch wheels are probably your max without rubbing the frame rails or the fender. (Results May Vary). I would stick around 1-1.5 inches of positive offset (moving the barrel inwards forwards the frame). For 7 inch wheels that means a backspacing of 4.5-5 inches and for 8 inch wheels a backspacing of 5-5.5 inches. I would stick with a tire that has a max diameter of 24.5 inches and a section width of about 9 inches so you will have a little protection from curbs shall you accidentally bump into one when parking. Note that these are the measurements approximately that fit my car and although they should only be used as general guidelines if looking at wheels and tires. I recommend getting a tire that has a "rim protector" which can be identified by the sidewall having a thick rubber flange when mounted on the wheel that pertrudes about half an inch past the lip of the wheel.
The reason I recommend those offsets are because they are probably the best compromise between clearance in the fender and scrub radius.
Based on measurements on my car I worked out the following:
.5 inch positive offset wheels give about 3 5/8 inches of positive scrub radius.
1 inch positive offset wheels give about 3 1/8 inches of positive scrub radius.
1.25 inch positive offset wheels give about 2 7/8 inches of positive scrub radius.
1.5 inch positive offset wheels give about 2 5/8 inches of positive scrub radius.
I made these calculations using the distance from the center of the lower ball joint to the flange on which the wheel mounts (the mounting surface of the hub) which is about 5 3/8 inches on my car. The height from the ground to the center of the lower ball joint to the ground on my car (with wheels and tires that have a maximum diameter of 24.8 inches) was about 8.5 inches. Based on the info I found on The Hamtramck Registry's AMA Specifications document of the 1974 Plymouth Valiant, the steering axis has an inclination of 7.5* (degrees) from vertical. Using that angle as the vertex (at the center of the lower ball joint) of an imaginary triangle and the height of 8.5 inches as the length of the adjacent side to that angle, I found that the base length of that triangle was about 1.25 inches. Subtracting this length from the distance of the mounting flange on the hub/rotor we get 4 1/8 inches as the distance from the center of the lower ball joint that the steering axis intersects the ground as an imaginary line when the the center of the ball joint is approximately 8.5 inches from the ground. To find your scrub radius subtract your offset from 4 1/8 inches. So if your offset is positive 1 inch for example (it moves the centerline of the tread pattern in one inch) and your scrub radius will be equal to approximately 4 1/8 inches less 1 inch which equals 3 1/8 inches. If your offset is negative 1 inch your scrub radius will increase an inch from 4 1/8 inches to equal 5 1/8 inches because 4 1/8 - (-1) = 4 1/8 + 1.
Based on the average offset/backspacing I noted offered in factory Mopar "police", " rallye", and "steel" wheel reproductions of widths of 4 inches to 8 inches and diameters of 14 inches to 15 inches that the offset of mopar wheels equipped from the factory had positive offsets ranging from .5 inches to 1 inch. I made this calculation by looking at the specs of repro wheels listed on the Coker Tire Website. With this said the factory scrub radius would be approximately 3 3/8 inches positive.
I hope this info will help you guys choose your wheels and tires. I spent about 3 weeks and a few hours a day doing research and calculations.
"I've ran Torque Thrust IIs on the back of my duster with an 8.25 for over a year now. The wheel is 17x8 with about 4 or 3 inches of backspacing. The tires are Pirelli P6 Four Seasons P245/45R17 and I've had no problems at all. They work perfect. If I could I would go with a little less backspacing for the rear wheels even if that means rolling the lip of the fender, so I think at around 3 inches give and take a half inch and you might have to roll the lip. I didn't have to and I have about an inch of clearance between the inner side of the quarter panel and the side wall of the tire. I would do this to bring the rear track width nearer to that of the front track width since the front is about 4 inches wider than the rear. For up front I just ordered a pair of 17x8 Torque Thrust IIs to match the back. They have a backspacing of 5.5 inches. To maintain a decent scrub radius of around 3 inches I would go with at least 1 to 1.5 inches of positive offset. The tires I bought at $63 a piece (new!) Are Kumho Ecsta AST's with a size of 215/45R17. I made a tool out of PVC piping that I bought at Lowes for about $7 and cut and drilled it to the specs of the wheels I'm looking at with the tires section width and max diameter and slid them on to the wheel studs after putting a floor jack under the LCA to maintain ride height with the wheel and tire off and spun the hub and turn the steering wheel to check all the clearances."
Offset is important, it effects scrub radius and track width as well as clearances in the fender to the fender, subframe, and other suspension components.
**For the front:
Unless you're gonna do some major modifications, 8 inch wheels are probably your max without rubbing the frame rails or the fender. (Results May Vary). I would stick around 1-1.5 inches of positive offset (moving the barrel inwards forwards the frame). For 7 inch wheels that means a backspacing of 4.5-5 inches and for 8 inch wheels a backspacing of 5-5.5 inches. I would stick with a tire that has a max diameter of 24.5 inches and a section width of about 9 inches so you will have a little protection from curbs shall you accidentally bump into one when parking. Note that these are the measurements approximately that fit my car and although they should only be used as general guidelines if looking at wheels and tires. I recommend getting a tire that has a "rim protector" which can be identified by the sidewall having a thick rubber flange when mounted on the wheel that pertrudes about half an inch past the lip of the wheel.
The reason I recommend those offsets are because they are probably the best compromise between clearance in the fender and scrub radius.
Based on measurements on my car I worked out the following:
.5 inch positive offset wheels give about 3 5/8 inches of positive scrub radius.
1 inch positive offset wheels give about 3 1/8 inches of positive scrub radius.
1.25 inch positive offset wheels give about 2 7/8 inches of positive scrub radius.
1.5 inch positive offset wheels give about 2 5/8 inches of positive scrub radius.
I made these calculations using the distance from the center of the lower ball joint to the flange on which the wheel mounts (the mounting surface of the hub) which is about 5 3/8 inches on my car. The height from the ground to the center of the lower ball joint to the ground on my car (with wheels and tires that have a maximum diameter of 24.8 inches) was about 8.5 inches. Based on the info I found on The Hamtramck Registry's AMA Specifications document of the 1974 Plymouth Valiant, the steering axis has an inclination of 7.5* (degrees) from vertical. Using that angle as the vertex (at the center of the lower ball joint) of an imaginary triangle and the height of 8.5 inches as the length of the adjacent side to that angle, I found that the base length of that triangle was about 1.25 inches. Subtracting this length from the distance of the mounting flange on the hub/rotor we get 4 1/8 inches as the distance from the center of the lower ball joint that the steering axis intersects the ground as an imaginary line when the the center of the ball joint is approximately 8.5 inches from the ground. To find your scrub radius subtract your offset from 4 1/8 inches. So if your offset is positive 1 inch for example (it moves the centerline of the tread pattern in one inch) and your scrub radius will be equal to approximately 4 1/8 inches less 1 inch which equals 3 1/8 inches. If your offset is negative 1 inch your scrub radius will increase an inch from 4 1/8 inches to equal 5 1/8 inches because 4 1/8 - (-1) = 4 1/8 + 1.
Based on the average offset/backspacing I noted offered in factory Mopar "police", " rallye", and "steel" wheel reproductions of widths of 4 inches to 8 inches and diameters of 14 inches to 15 inches that the offset of mopar wheels equipped from the factory had positive offsets ranging from .5 inches to 1 inch. I made this calculation by looking at the specs of repro wheels listed on the Coker Tire Website. With this said the factory scrub radius would be approximately 3 3/8 inches positive.
I hope this info will help you guys choose your wheels and tires. I spent about 3 weeks and a few hours a day doing research and calculations.
