Unsprung weight/rotating mass

[daveco]

I have read a few website that mention that for every kg saved of unsprung mass, it equates to 10 times (some say 20 times) that of car weight.

I was looking to clarify this, as I can reduce the weight of my alloy wheels by 2.5kg on each corner by going for an alternative size/design.

[Mignon]

For wheels the effect is about an extra quarter of the actual mass saved so not worth bothering about. For engine internals it's a different equation.

[designforlife]

I went from OEM wheels to lighter aftermarket on my old Mitsubishi... wheels were about 2kg lighter a corner.

The difference was night and day, and swapping the OEM wheels back on felt like driving with an anchor dragging the car at first.

This was on a lightweight 1.6l with 175bhp...i daresay on more powerful cars the difference may not be as noticeable.

[daveco]

Thanks for the input folks. Conflicting information!

I've been told by several mechanics that reducing unsprung mass is the way to go for improved handling yet engineers, engineering websites etc say there shouldn't be much difference at all.

Working purely on the basis of reducing weight = better handling, surely reducing this weight will mean the car can respond quicker to steering inputs?

Also, by reducing the wheel size from 18 inch to 17 inch means overall tyre diameter is changed, so there should be an improvement in acceleration?

[designforlife]

i noticed better pick up acceleration wise, and turn in felt a little more precise.

It's going to vary depending on the car in question.. less unsprung weight is never a bad thing, but unless it's a track car these are marginal gains, and forged lightweight wheels aren't usually cheap...although if you are on a budget, rota slipstreams are excellent for cost vs weight.

going from a 18" to 17" wheel would also reduce weight...depends how you want to balance looks and performance.

[daveco]

designforlife said:

i noticed better pick up acceleration wise, and turn in felt a little more precise.

It's going to vary depending on the car in question.. less unsprung weight is never a bad thing, but unless it's a track car these are marginal gains, and forged lightweight wheels aren't usually cheap...although if you are on a budget, rota slipstreams are excellent for cost vs weight.

going from a 18" to 17" wheel would also reduce weight...depends how you want to balance looks and performance.

Those Rota slipstreams seem remarkably light, about 7kg for 17 inch wheels? That would mean 5kg per wheel saving in weight over the MV2s.

[designforlife]

yeah i was going to run them on my mitsu but got a really good price on a set of Ultralite D1 (buddyclub p1/kosei K1 reps), and they were about the same weight.

My dream lightweight wheel is the desmond regamaster, but the 15" are around £1k for a set...used!

Edited by designforlife on Thursday 29th November 13:04