I need a little better understanding of the wheel/tire issue. For a given outside diameter, is there a weight-saving in having more wheel and less tire, or vice versa?

For example, for the same model wheel and same model tire, which will weigh more:

17X7.5 wheel and 215/50-17 tire

18X7.5 wheel and 235/40-18 tire

19X7.5 wheel and 235/35-19 tire

 

Assuming the wheels are made by the same manufacturer and the same model, weight saving is when you have less wheel. Bigger wheels push the weight further out thereby increasing inertia (or the ability to change direction/turn). Autox'ers typically use the smallest diameter wheels with the widest rubber.

 

Thanks for the info.

 

I remember seeing on tirerack, the some same tire size weight can differ as much as 7 pounds.
If i remmber right, it was michelin sport ps2 and yokohama advan neova ad07, and it was 225/40/18

 

Same size tires from different manufacturers do have differerent weights. Bridgestone's S03 is one of the heavier tires but they have phenominal w/d grip. Toyo's T1S is one of the lighter tires but their sidewall is a bit thin given a better street ride but more sidewall flex during transitions. Everything is a compromise.

 

Also hurts braking by giving the wheels more mechanical advantage/momentum for the brakes to overcome.

 

So the rim is the heaviest component of the wheel system, and moving it away from the axle increases wheel inertia/momentum, increasing the load on the engine, and on the brakes, and probably on the steering as well -- increased wheel momentum will mean increased gyroscopic effect.

But I'm still wondering whether an inch of wheel spokes weighs more or less than an inch of sidewall height, and which combo would have the lower unsprung weght.

 

Taken from https://acurazine.com/forums/showthread.php?t=20434 :

235/45-17 .....4.2in .......12.7in ....25.3in ......79.6in ..............796 ..........-0.5%
235/40-18 .....3.7in .......12.7in ....25.4in ......79.8in ..............794 ..........-0.2%

Wheels: OZ Superleggera (One of cheapest lightweight, name-brand rims)
Tires: Toyo T1-S, Bridgestone S-03, Yokohama AVS ES100

Toyo T1-S 235/45ZR17 97W 241880 7.5-8.0-9.0 23.8
OZ Superleggera - Race Silver 17" x 8" 5/120* 40 17.1
23.8+17.1 = 40.9 lbs

Toyo T1-S 235/40ZR18 95WRD 241770 8.0-8.5-9.5 22.9
OZ Superleggera - Race Silver 18" x 8" 5/120* 40 17.4
22.9+17.4 = 40.3
Tacking on 0.3% of difference (I think?!?) = 41.509 lbs

*I know 5/120 isn't the TSX's bolt pattern, but this was the only size with the same offset for comparison.

In summary, Toyo/OZ 18inch setup is 0.609 lbs heavier than the comparable 17inch setup.

Similar comparison with Bridgestone S-03's with the same OZ's

S-03 235/45R17 25.3 lbs
OZ 17x8 5/120 17.1
25.3+17.1 = 42.4

S-03 235/40R18 26.0 lbs
OZ 18x8 5/120 17.4
26.0+17.4 = 43.4
Tacking on 0.3% of difference (I think?!?) = 44.702

In summary, S-03/OZ 18inch setup is 2.302 lbs heavier than the comparable 17inch setup.

Yokohama AVS ES100 235/45 WR17 26.34 lbs
OZ 17x8 5/120 17.1
26.34+17.1 = 43.44

Yokohama AVS ES100 235/40 WR18 24.94 lbs
OZ 18x8 5/120 17.4
24.94+17.4 = 42.34
Tacking on 0.3% of difference (I think?!?) = 43.6102

In summary, AVS/OZ 18inch setup is 0.1702 lbs heavier than the comparable 17inch setup.

For the most part (aside from the heavy S-03's), it appears that staying at 17 will be a lighter setup.

P.S. Did this in like 10mins while at work, so if there's mistakes, oh well. Otherwise, it should be relatively accurate, though not too sure on that 0.3% difference thingy.

 

Thanks for all that data, HoRRo! I guess I started this thread in the wrong section.

Reviewing what you posted, I don't think the 0.3% and 0.5% difference in OD (compared to OEM) is relevant to the calculation: to make the 17" and 18" setups comparable, you would multiply the 18" total weight by the difference in OD between the two --796/794 -- which is pretty close to 1.0, and can therefore drop out of the calculation.



So for each tire except the Bridgestone, the 18" setup is lighter. The Bridgestone figures differ from the other two in that the 18" tire is actually heavier than the 17" -- sidewall reinforcement? If the Bridgestone weights were transposed, each 18" setup would be 0.5 - 1.0 lb lighter.

I post this knowing my ventures into math are usally

 

So using this hypothetical, which wheel/tire combination would "perform" better in terms of acceleration? in terms of handling?

Setup #1:
17x7" wheel = 24 lbs.
215-50-17 tire = 23 lbs.
Total = 47 lbs.

Setup #2:
19x8.5" wheel = 23 lbs.
235-35-19 tire = 22 lbs.
Total = 45 lbs.

For all intents and purposes also, note that the overall diameter in both setups is the same. Setup #2 weighs less, but would it actually "out-accelerate" setup #1? Of course, using a wider tire will yield more road holding, but still... I remember reading several articles outlining the drop off in performance gains after plus sizing past an 18" wheel...

 

I don't know anything about an 18" ceiling -- but it make sense that there are limits to what can be gained from increased tire patch size and sidewall stiffness. At a certain point, the car will just get over-tired.

I plussed my RSX from 16" to 17", going from the stock 205 tire to a 225. On paper, the new combo weighed marginally less than the old, but the old Michelins had a lot of KMs and probably weighed less than a Kleenex tissue.

My initial seat of the pants feeling was that the wheels were slightly slower to spin up. The gains in cornering, in balance, and in point and shoot, however, were much more strongly evident than the acceleration decrease. And WOW! Real braking! Plus-sizing turned the RSX into a different car.