Oem Wheel upgrade.

[2one3E90]

I have 16 inch rims on my 2.5 e85. It is the OEM wheels that came with the car. Well upgrading to 17 inches or 18 inches ruin the handling or mpg? The OEM wheels already feel so light. I drive it hard in backroads and love the handling it already has. i'm debating if I should buy New tires for the OEM wheels or upgrade to bigger rim size.

[elerner61]

Usually, an increase in rim size is accompanied by an increase in overall wheel (tire and rim) weight, unless you go with a lighter weight rim. Increasing wheel weight beyond what the installed shock/spring pairing can control will result in adverse wheel movement when driving on bumpy surfaces (in particular). Ask anyone who has modded a Miata.

I think there are two ways to find an answer to your question:
1. Ask someone who has your model of Z4 that has increased from 16s to XX what the effect on handling was

2. For Z4s that come with 17" or 18" rims from the factory, is the stock shock part number the same as yours.

Going up 1" in rim diameter is probably negligible. Going up 2", not so confident.

[Huz-Z]

My buddy and I both have 3.0si roadsters. Mine has 18 inch rims and the car looks great. The streets in my town are subject to harsh winters so we end up with lots of rough pavement which causes me to swear like a longshoreman from time to time. Having said that though, I would not go to a smaller rim because I like the look of my car with the staggered 18s.

https://www.zpost.com/forums/showthr...t=Hyper+silver


But I have to admit that my buddy’s car with a square set up of 17s seems to ride much nicer over the rough pavement areas. So, go with what is important to you.

[Huz-Z]

Originally Posted by Piper1

Increasing wheel diameter will stiffen the feel ie. you feel more of the road more turn/cornering compliant pending tire selections as you’re reducing amount of rubber side wall on the +1/+2 of the wheels. Not to be confused with damper stiffness. If tires from 16 on up are the over all same diameter most mpg difference will be most noticeable by changing to less aggressive driving. You’ll get more compliant cornering going to least 17 compared to 16.

Also stock 16 are 7 wide stock 17 are 8 wide so you’ve got more foot print for more grip. From 17 to 18 tire selection and width will play a bit more in factoring in just how the handling will feel along with alignment. If you drive the same in the same tire diameter on the same model of tire just changing rim size don’t think you’ll see too much mpg difference as the tires have same rotation per mile driven driving exactly the same. Performance can mean different things to different people but there’s a reason the z4M never came with 16s so from an aggressive driving perspective, no compared to your current stance plus size won’t hurt performance.

As these cars came factory equipped with up to 18 inch rims, shouldn’t the suspension system on the car be able to accommodate a change from 16 inch to 18 inch rims?

[pungo]

If you like better handling, increase the wheel diameter while keeping the tire diameter the same.The only downside is the ride will be a little rougher over bumps, but the increased handling more than makes up for it. If your roads are smooth, all is good, if your roads are pretty rough, not so much. I wouldn't go any larger than 18".

[Piper1]

Originally Posted by Huz-Z

As these cars came factory equipped with up to 18 inch rims, shouldn’t the suspension system on the car be able to accommodate a change from 16 inch to 18 inch rims?

My comment from 16 to 18 is more along the affects of handling. Yes the car will be fine with both but reducing the sidewall that much pending tire comparison of the two tires the 18 will show certain imperfections in road but have crisper response vs the cushion the side wall on a 16 will give. Keeping in mind tire selection is a major factor. A 225/45/17 in say a continental oem run flat will be more forgiving than say a 235/40/17 falken azenis 615k+. I use those as examples because I’ve run those on 17s with mine prior to 18x9 255/35 square with Toyo r1r. The particular car in question with the OP is non sport 2.5 prefacelift so ride height is higher and on non sport springs, putting on oem 18s will still have more wheel gap than sport trim and will be softer than on sport. Also 16x7 vs 17x8, 18x8/9 you’re naturally gaining grip as well when comparing oem plus sizes.

[kaybat]

i put 107's on my 2.5i(came w/16's) with no problems whatsoever.It rode a little rougher, but no where near harsh.

[Piper1]

Originally Posted by kaybat

i put 107's on my 2.5i(came w/16's) with no problems whatsoever.It rode a little rougher, but no where near harsh.

Which suspension is that pic on stock non sport or sport springs.

This is of my coupe stock sport springs and my roady on eibach/koni combo

[2one3E90]

Originally Posted by Piper1

My comment from 16 to 18 is more along the affects of handling. Yes the car will be fine with both but reducing the sidewall that much pending tire comparison of the two tires the 18 will show certain imperfections in road but have crisper response vs the cushion the side wall on a 16 will give. Keeping in mind tire selection is a major factor. A 225/45/17 in say a continental oem run flat will be more forgiving than say a 235/40/17 falken azenis 615k+. I use those as examples because I’ve run those on 17s with mine prior to 18x9 255/35 square with Toyo r1r. The particular car in question with the OP is non sport 2.5 prefacelift so ride height is higher and on non sport springs, putting on oem 18s will still have more wheel gap than sport trim and will be softer than on sport. Also 16x7 vs 17x8, 18x8/9 you’re naturally gaining grip as well when comparing oem plus sizes.

Yes this is my build sheet. Didnt even option the autotrans. Its base model. I will be changing the suspension to bilstein b12s or its coil over setup soon. I just wonder if i will gain more grip with high performance 16 inch tires. I have Apex wheels that I can put on the car. 17x9 square and 18x9 18x8.5 staggered. Both Arc 8s

[Huz-Z]

Originally Posted by kaybat

i put 107's on my 2.5i(came w/16's) with no problems whatsoever.It rode a little rougher, but no where near harsh.

That rim looks spectacular on a Z in my opinion.

[pungo]

Originally Posted by 2one3E90

Yes this is my build sheet. Didnt even option the autotrans. Its base model. I will be changing the suspension to bilstein b12s or its coil over setup soon. I just wonder if i will gain more grip with high performance 16 inch tires. I have Apex wheels that I can put on the car. 17x9 square and 18x9 18x8.5 staggered. Both Arc 8s

Not sure what you're asking here.

• The wider the tire, the better the grip.
• The lower profile the tire, the better the grip.
• You're not going to get as good of a grip with a 16" as you will with a 18" if both tires are the same model and width.
• The taller the sidewall the more the tire squirms on turns providing less grip.

[kaybat]

[QUOTE=Piper1;29554090]Which suspension is that pic on stock non sport or sport springs.

That's a stock photo(cars long gone) it was a 2.5i with non-sport suspension.

[2one3E90]

[QUOTE=kaybat;29555825]

Originally Posted by Piper1

Which suspension is that pic on stock non sport or sport springs.

That's a stock photo(cars long gone) it was a 2.5i with non-sport suspension.

im on stock suspension but will soon upgrade them!