18" vs 19"

[philippelyp]

How does the diameter of the wheels affect the car. I'm not talking about look here. Obviously weight is going to be a factor. Would you have insight to share?

[ZStig]

other than weight, the ride is much rougher, the wheel is more prone to bending because there is less rubber to protect it, and the tires usually cost more. If you're considering going wider than 285mm, do research for availability in both diameters.

[philippelyp]

So, there's pretty much no good reason for going from 18" to 19" apart the look (which I don't care for).
Thanks

Originally Posted by Roffle Waffle

other than weight, the ride is much rougher, the wheel is more prone to bending because there is less rubber to protect it, and the tires usually cost more. If you're considering going wider than 285mm, do research for availability in both diameters.

[Twisted Six]

I've run both. It really depends on points like >>

a)-one piece cast ?
b)-two piece welded ?
c)-fully forged ?
d)-3-piece & forged center ?

Although my 18's had a slightly thicker sidewall...there were a few times it might have felt better than my 19's. But really not enough diff to tell. A hard transition on the Z's transfers quick and hard...end of story really.

I put 50K miles on 2 sets of 19's.....one set bent with the breeze and often...the other set is still perfect today. Both weighed in the same and were one piece cast.

My 3-piece wheels have seen much less road time....so I'll be finding out how they deal soon.

[nate96]

I have to say that the 19's are much harsher than the 18's. Wish I would have stuck with the 18's for the summer. I run 18's for the winter and 19's for the summer.

[Beedub]

i dont notice any difference, many 19s are now as light as 18s so i think its down to personal preference.... my 19s which were lighter than my stock 18s and have a thinner sidewall honestly??? could i tell the difference?? no way...

[dazed^]

Originally Posted by Beedub

i dont notice any difference, many 19s are now as light as 18s so i think its down to personal preference.... my 19s which were lighter than my stock 18s and have a thinner sidewall honestly??? could i tell the difference?? no way...

But there is always going to be more material needed in a larger diameter wheel, so assuming there is no specific reason to limit weight-saving fabrication techniques to the 19" class, then 18" will still always be lighter.

Having said that, I'm not sure how much difference one gets from going from the stock 18"s to, say, 18" TE-37's. That is, how much performance/fuel saving you get from that weight reduction. Anyone know?

[philippelyp]

From what I understand, the main benefit in weight reduction of the wheels is with the suspension (unspring mass).

Originally Posted by dazed^

But there is always going to be more material needed in a larger diameter wheel, so assuming there is no specific reason to limit weight-saving fabrication techniques to the 19" class, then 18" will still always be lighter.

Having said that, I'm not sure how much difference one gets from going from the stock 18"s to, say, 18" TE-37's. That is, how much performance/fuel saving you get from that weight reduction. Anyone know?

[ZStig]

I can tell a big difference in how the car reacts to throttle input, and general acceleration

[philippelyp]

Originally Posted by Roffle Waffle

I can tell a big difference in how the car reacts to throttle input, and general acceleration

So, 19" is better on that side?

[jophish17]

^ He's referring to the Volks being lighter. Lighter is better in the sense of overcoming inertia

[philippelyp]

Originally Posted by jophish17

^ He's referring to the Volks being lighter. Lighter is better in the sense of overcoming inertia

Make sense

[Beedub]

Originally Posted by Roffle Waffle

I can tell a big difference in how the car reacts to throttle input, and general acceleration

thing is with the tyres you run, add the spacers, in all honesty you not "THAT" much lighter imo.....

[pokeybritches]

The biggest difference is going to be the car's ability to stay glued to the road... like when putting power down on rough pavement, or midcorner bumps upsetting the car quite a bit less. Ride quality varies, because the more quickly the wheel responds the more movement is translated into the cabin, and the rougher the ride feels. Heavy 19's feel like they ride the same as stock because they respond so slowly that the lack of sidewall cushion is offset by the lack of responsiveness. On a sports car this is a terrible, horrible, no good, very bad thing.

Tire Rack conducted a test with wheels of different sizes and weights concluding the same thing I posted above. Another Euro tuner mag put lightweight wheels on their E36 M3 and saw a 7 hp increase on the dyno, although that will vary based on how quickly the car spins up the dyno. All I know is that I have never heard of anyone going to 19's on a Z4 non-M to increase performance- at least anyone who could back up their reasoning.

[ZStig]

Originally Posted by Beedub

thing is with the tyres you run, add the spacers, in all honesty you not "THAT" much lighter imo.....

lets compare my rears vs stock vs hypothetical aftermarket 19s. My fronts are about the same total weight as stock because they're much wider, but the weight of the rears is what affects acceleration most.

18x9 volk te-37 =17.7LBS
20mm ltw spacer = .5LBS max
265/35/18 RE-11 tire = 28LBS
total = 46.2lbs


stock z4m 18s =25.88 lbs
stock size 265/40/18 re-11 tire= 31lbs
total = 56.88lbs (10.68lbs over mine)


average aftermarket wheel 19x9 =24LBS (OEM CSL =25.5lbs)
265/35/19 re-11 tire =29LBS
total = 53LBS (6.8lbs more than mine)

to me, thats significant rotational mass

[philippelyp]

Originally Posted by jophish17

^ He's referring to the Volks being lighter. Lighter is better in the sense of overcoming inertia

Originally Posted by Roffle Waffle

lets compare my rears vs stock vs hypothetical aftermarket 19s. My fronts are about the same total weight as stock because they're much wider, but the weight of the rears is what affects acceleration most.

18x9 volk te-37 =17.7LBS
20mm ltw spacer = .5LBS max
265/35/18 RE-11 tire = 28LBS
total = 46.2lbs


stock z4m 18s =25.88 lbs
stock size 265/40/18 re-11 tire= 31lbs
total = 56.88lbs (10.68lbs over mine)


average aftermarket wheel 19x9 =24LBS (OEM CSL =25.5lbs)
265/35/19 re-11 tire =29LBS
total = 53LBS (6.8lbs more than mine)

to me, thats significant rotational mass

I like numbers. Put things in perspective. 10lbs has to make a difference on how the suspension behave.

[johanness]

Originally Posted by Beedub

thing is with the tyres you run, add the spacers, in all honesty you not "THAT" much lighter imo.....

The reason you're not feeling a difference is because your CSL's (19") are the same weight as our stocker 18's.

Edit - just read Roffle's post above. What he said.

[seank]

Tire sizes, and the availability of different tires is the biggest factor for me, which is why I choose the 18's. They also look more racey/performance, rather that cool.

[jophish17]

IMO 19s are just for looks. However, I've noticed tires play a huge role in ride comfort too, and can mitigate the 19 vs 18 effect. My 19s with Michelins tend to ride better than the Continentals I had on my OEM wheels - though a dip or bump in the road sucks on both of them

[Beedub]

Originally Posted by johanness

The reason you're not feeling a difference is because your CSL's (19") are the same weight as our stocker 18's.

Edit - just read Roffle's post above. What he said.

true.... good point.....

when i get my REALLY lightweight 18s maybe ill see a difference??? As of now i feel or felt nothing, i believe the stock CSLs were alittle lighter than the stockers but by a tiny amount, as were the studs and nuts, as is the AP BBK, by some margin compared to the stock items..... so factoring in the other losses, my CSL setup is quite abit lighter than my stock setup in terms of unspring mass.....

[Beedub]

Originally Posted by Roffle Waffle

lets compare my rears vs stock vs hypothetical aftermarket 19s. My fronts are about the same total weight as stock because they're much wider, but the weight of the rears is what affects acceleration most.

18x9 volk te-37 =17.7LBS
20mm ltw spacer = .5LBS max
265/35/18 RE-11 tire = 28LBS
total = 46.2lbs


stock z4m 18s =25.88 lbs
stock size 265/40/18 re-11 tire= 31lbs
total = 56.88lbs (10.68lbs over mine)


average aftermarket wheel 19x9 =24LBS (OEM CSL =25.5lbs)
265/35/19 re-11 tire =29LBS
total = 53LBS (6.8lbs more than mine)

to me, thats significant rotational mass

Solid info their tom........ ok...

my CSL is lighter than the stock 18" rim, Add in the studs and composite Kics nuts, The AP BBK which was considerably lighter that stock FR and Rear, i think my losses are a decent amount more.... still i notice no difference..... Rotational masses are bigger losses felt due to their nature.....

In all honesty??? i dont think we can Ever really start talking about weight loss benefits when we have 30lb of supercharger and cooling gear for the s/c up front..... Once we get into seat installs, now were talking, as were offsetting a good chunk of added weight...

[nate96]

Another difference between the M and the other cars were the factory tire sizes. The M came with 225/45/18 and 255/40/18. The Si came with 225/40/18 and 255/35/18. Going to a 19 means 235/35 and 265/30 which does not leave much of a sidewall. Might be why some of you with an M are not noticing at as much.