BBMGT3

Am looking at carrying a dedicated set of wheels to wrap Cups or Trofeos around as I drive my gt3 on the road a lot and don't want to waste this scarce rubber!

There is a myriad of wheels available at various prices, weights and fabrication process. So, off I went to try and understand the benefits of lower wheel weight.

No one seems to argue that reducing unsprung mass has benefits all around. But the "ratio" of sprung to unsprung weight varies from 1.14 / 1 all the way to 10:1. More commonly accepted is between 4-8:1. But very little consensus.

I'd be very interested in hearing from anyone who has had experience going from OEM wheels to various different ones, as well as anyone who can shed some light from an engineering standpoint as to what is a good rule of thumb when equating sprung mass vs. unsprung mass.

Thanks

TRAKCAR

Sorry; I don't know tha ratio, but the real question is how much does it help and how much do you feel it?

I know light weight helps and I do feel it, but IMHO at our level I look for the strongest wheel at the lowest price.

aj986s

I don't know that there's necessarily an "optimum" ratio of unsprung weight versus sprung. I've always used 6:1 as the rule of thumb (IIRC was from Fred Puhn's "How to Make Your Car Handle"). What the ratio says is that for every pound you can remove from unsprung weight (like wheels, brakes, etc), the handling and acceleration improvement would generally be equal to 6 pounds of weight removed from the sprung weight (almost anywhere on the chassis).

But light isn't always better. Strong/quality is important, especially if a tracked car. Find a couple of good quality wheels that are in your quality, price & appearance range, then consider the weight amongst those.

avader906

cheap / durable / light - chose 2

BBMGT3

Thanks for that, and its interesting to know that 6:1 ratio. As Avader said, cheap/durable/light, choose 2. Depending on how beneficial lightness is, I will be more inclined to invest $$ in it. So, as an example, the OEM wheels are 24lbs front and 30 lbs rear (on a 997.1 gt3). Superforgiatas are 16lbs front and 20 lbs rear, total of 8x2 + 10x2 = 36lbs savings. Applying 6:1, its like stripping 200+ lbs from the car; which is huge. On the other hand, if that "multiplier" is lower, say 1.5-2, then its not worth spending the extra THOUSANDS of dollars...

aj986s

I just discovered that Puhn's book is actually available online here. The book is a bit dated, but a lot of the theory still applies. What I'd forgotten is that the ratio is dependent upon the type of vehicle and its suspesion design. If you peruse some of the book, you'll find a chart that shows how different designs compare in their sprung weight versus unsprung. Solid axle cars, for example, have more unsprung weight, and consequently the ratio is lower. It looks like an independent suspension sports car is going to be somewhere around the 5-6:1 range.

kyrocks

Anyone have issues with the OZ ultraleggera HLT centerlock for $2600 at TireRack??

Glock Guru

That almost sounds like the mato of some Porsche Tunner Shops....


Price, Service, Selection, ........Pick one.

-Troy

nash

Those are good wheels, though they are not forged and therefore not as light as other choices. In the RS fitment they are just about the same weight as stock, which certainly isn't bad. I think they are a good choice for a reasonable price.

On Pole

Strength
Fitment
Weight
Serviceability
Styling

savyboy

OZ Superforgiata's are the way to go if you are going to bother with new wheels. I have a new unmounted set (2010+ GT3RS fitment 19" w/OE offsets)) with TPMS and new Trofeos mounted and aired up. Don't need them afterall and if somone is local (N.Cal/Reno) I will work a cool (but not crazy) deal. Get it while the getting is good. Not real keen on shipping prefer local delivery/pickup

Serge944

It's the distance from the axis of rotation that matters - the energy of the rotating mass is proportional to the SQUARE of the distance from the axis. The energy is also proportional to the square of the angular momentum...so the faster you go, the bigger the difference unsprung weight makes.

Tire weight/width makes the biggest difference as its the furthest from the axis of rotation.

Trying to have some kind of magic ratio of sprung vs unsprung weight is silly when the tire diameter/width alone has such a huge impact.

Nordschleife

The reality is - the less unsprung weight the better. All this talk about 'optimum unsprung ratios' is BS, or more politely post hoc justification.

If you are serious about saving unsprung weight, you are going to spend a lot of money. Not the least of the benefits is a major increase in driver/passenger comfort.

However, Ti behaves differently than FE, so the switch to Ti sptings requires a lot of work, and this is just for starters.

R+C

NelsonF

You have a pm.

NJ-GT

I got a 2007 GT3 RS back in 2008. With Magnesium wheels (BBS) and PCCB from a 996, I removed 92 lbs of unsprung weight. This car weighs 3,140 lbs with no fuel (U.S. version).

So, using the 4:1 factor, I saved 368 lbs, the equivalent to 2,770 lbs. Well, I drove a 996 with 2770 lbs and less power (380Hp) and that car was a rocket. My RS with 415Hp and the equivalent to 2,770 lbs was slow. I think the ratio is closer to 1:1.

I personally use a 1:1 ratio for unsprung weight reduction, and I want unsprung weight as close to 0 as possible.