To offset, or not?

[matchframe]

I am at the point of my restoration where I am concentrating on restoring my trailing arms (which are in good shape), or go with offset trailing arms. I do plan on buying larger wheels and tires, but not at first. So if I go with the OEM wheels and p255-60R15, with offset T-Arms, will it look strange?

And will standard T-Arms with oversize wheels and tires work?

Thanks!

Bill

 

[robert kirk]

Hi Bill, you might give mike "stingray6974" a try. He does these at home. He's in texas so freight would not be much. Mike does excellent work. Mike is a great guy, easy to get along with and his work is first class all the way. he is a mod on this forum so send him an im and let him know what your looking for. robert

 

[LIRacer]

Bill,

I went the offset route as I wanted to but 10 inch wheels on without doing surgery to the fenders. Looks awesome and handles like a c5 ...well maybe.

 

[matchframe]

Thanks, I really appreciate it.

 

[MaineShark]

Just how wide (tire size) can you go, with offset trailing arms, without modifying the rear quarters?

Joe

 

[LIRacer]

I have 15 x 10 inch wide wheel. THey stick outside of the fender only an inch.

 

[matchframe]

LIBoater,

If they stick out of the fender an inch, do you ever have a problem of the tires hitting the fenders?

Also, If get the offset trailing arms, but use factory rims and tires for a while, before I get the wider rims and tires, will it look odd?

Bill

 

[Stingray6974]

bill,
the offset trailing arms do not change the position of the wheel and tire. they just give more clearance between the tire and arm. depending on the offset of your wheels you may have a clearance problem with the spring and with the frame kick-up.

mike

 

[LIRacer]

The wheels neve hit the fender. I have composite springs and gas shocks.

 

[matchframe]

Thanks,

I think I now understand how the offset works!



Bill

 

[MaineShark]

Isn't changing the offset of the wheels a bad thing?

Joe

 

[matchframe]

Joe,

To my understanding, with offset trailing arms, you are not changing the offset of the wheels. The arms are made to keep the wheels in the same spot, but itself is offset out away from the wheels to allow more room for the tires. This more room allows wider wheels to have a more backspace to center the mass of the wheel and tire more centered over the bearings. Which is a good thing, in that it gives a more even and balanced wear for the bearings.

Thats the way I understand offset trailing arms work. I may be wrong, if so, I hope someone will correct me.

Bill

 

[Stingray6974]

bill, you have it correct. let me try to go into more detail.
stock wheels, 275-60 tires: the tires rub on the emergency brake cable bracket. this can be fixed by relocating the bracket to the top of arm or using offset arms.
10 inch wheels with 1-2" more backspacing: the tires will rub on the rear spring. requires changing the main leaf to a shorter one. any more backspacing will cause the tires to rub the frame rail kickup just above the trailing arm mount. to increase clearance to the frame reduce the backspacing of the wheel.

mike

 

[MaineShark]

Isn't offset measured from the wheel centerline?

If so, then installing a "deeper" wheel would change the offset.

I don't know that it's necessarily a bad thing (like Bill says, it would move the center more in-line with the bearings), but I do think it bears consideration.

Joe

 

[Stingray6974]

post deleted due do waking up way too early and explaining it wrong. see diaghrams in next post.

mike

 

[69autoXr]

You are confusing backspacing and offset. Backspacing is the distance from the rear lip to the mounting hub face, and offset is the distance from the centerline of the wheel to the hub mounting face. Positive offset is defined as a distance toward the outside of the wheel, where negative offset is toward the inside of the wheel. Therefore, an 8" wheel with 2" positive offset would have 6" backspacing, while an 8" wheel with 2" negative offset would have 2" backspacing. This is a good diagram showing wheel measurements:

http://www.rsracing.com/tech-wheel.html#wheeltrm

Chris

 

[Stingray6974]

thanks chris,
i had a feeling i was saying that wrong.

mike

 

[MaineShark]

So, using this system does change offset (by 1", in the case of switching from 8" to 10").

Is there any good way to know what effect that will have?

Joe

 

[LIRacer]

In order to make sure your back space is correct, I would suggest you measure before you put order your wheels.

 

[Stingray6974]

joe,
i just took some measurments. a stock vette wheel has 4" backspace. there is 1/2" clearance between the rim to the e brake cable bracket and from the rim to the spring. a 10" rim will work if it has the 4" backspace. to use a 10" rim with a 5" backspace will require the offset trailing arm and the shorter spring main leaf.

mike