Weight of 2015 IRS vs Solid 8.8

[Jimtmich]

I haven't seen any data. Is there a significant weight difference between the 2015 IRS and a solid 8.8? We have 2 options on the 2015 IRS to add to the discussion as well.

[CraigS]

Over all, all the IRS parts vs a solid axle, I am not sure there is a significant difference. However the difference in unsprung weight is significant. IE; going over a bump w/ solid axle the entire axle has to move to absorb the bump. But w/ IRS, the hub and brakes, 1/2 of the axle, 1/2 of the control arms is all that needs to move. (my 1/2 may be off a little but you get the idea that only part of a control arm moves because one end is fixed to the frame).

[Mark Reynolds]

Is your question about overall weight, un-sprung weight or both? Overall I would guess the weight is more since it is designed to handle about twice the horsepower.
If un-sprung remember the brake, wheel and tire selection can make a huge difference.
You would really need to make a spreadsheet and fill in all the individual part weights to make sense of it.

[Jimtmich]

I’ve been driving mustangs as dd most of my life so I’m used to the unsprung weight. I am planning on 2015 irs but wanted to know if it was a significant weight penalty that I should plan on a few extra hp to get the power to weigh ratio where I want it. The other nagging problem is I really like the fia wheels and there is no pin drive width option for the 2015 irs. I’m leaning towards the fia car that really begs for those wheels.

[CraigS]

... The other nagging problem is I really like the fia wheels and there is no pin drive width option for the 2015 irs. I’m leaning towards the fia car that really begs for those wheels.
Maybe I can make you feel a little better about a MkIV vs FIA. The FIA wheels are 15 inch and maximum rear width is 9.5 which means you have very limited tire choices because of the diameter and they aren't wide enough either. I do see the allure of the wheels as they really have captured the look from the 60s especially in the center section. But the Halibrand replica 17 rears are 10.5 width and the 18 rears are 11 width. Much better for traction.

[Avalanche325]

If you are that worried about weight, I will assume that you are concerned about handling. The shorter A-arms for pin drives are not good for handling. Shorter arms generally have a smaller sweet spot geometry-wise. That is one reason that deep dish wheels are a thing of the past.
can't imagine that it would make any difference on the street. Maybe not even on the track. But on paper, yes.

I watched an interesting engineering video that showed un-sprung weigh is not as big a deal as it is made out to be. There are a whole lot of "it depends" in the equations.