An 18" Track Setup Question

[JCz04Bimmer]

I know this has likely been discussed extensively but I'm in the market to switch to 18" wheels from my current setup of 19" wheels. The wheels I'm looking at are the well known TRMotorsports MT1's and the sizes I'm interested in are:

18x9 +35 (FRONTS)
18x9.5 +35 (REARS) w/ 8mm spacer to make the offset +27

I want to run the following tire sizes:

255/40/18 (FRONTS)
275/35/18 (REARS)

According to the various calculators out there, this setup will yield the following changes versus stock...

FRONT: 6mm LESS clearance on the strut side, and the outside edge of the wheel will EXTEND an extra 20mm
REAR: 3mm LESS clearance on the strut side, and the outside edge of the wheel will EXTEND an extra 9mm (NOTE: This data is calculated using a +27 offset.)

So, the rear looks like it'll be perfect. No surprise there. As for the front, I think losing 6mm of clearance on the strut side is fine. Can someone verify? But on the fender side, adding an additional 20mm seems aggressive. I plan to run around -2.0 of camber up front on the street and will likely click to around -3.0 (or greater) on the track once camber plates go in. Should I be looking at a 255/40 front tire or a 255/35?

Thanks in advance.

PS - I know the TRMotorsport MT1's do come in 18x9.5 +25 which is very close to the +27 I'd be running with a spacer. My current setup with 19x9.5 +25 rears rub very slightly on the fender wall when the rear suspension is fully compressed. Granted, I am running an entirely stock alignment so even with the slightest bit of negative camber I'm sure rubbing wouldn't be an issue any longer. That said, I do prefer the great flexibility offered by the +35 rear wheel because I can run spacers to get things perfect. (And I've run spacers at the track for many years without issue. So long as they're of good quality and installed correctly, they'll present no problems.)

[onelove]

Which tires are you going to be running ? Looking at the sizes the roll out on the front tires will likely be quite a bit more than the rear.

[JCz04Bimmer]

I'm looking at tires now and it seems that 255/40/18 is comparatively uncommon in the performance category I'm interested. Perhaps a 255/35/18 tire in front is a better route.

From the Dunlop Star Specs, here's what I'd be looking at...
255/35/18 -- 25" Overall Diam
275/35/18 -- 25.6" Overall Diam

From the stock Continent tires, this is what the car came with...
225/45/18 -- 25.9" Overall Diam
255/40/18 -- 26" Overall Diam

[jmillet]

Originally Posted by JCz04Bimmer

I'm looking at tires now and it seems that 255/40/18 is comparatively uncommon in the performance category I'm interested. Perhaps a 255/35/18 tire in front is a better route.

From the Dunlop Star Specs, here's what I'd be looking at...
255/35/18 -- 25" Overall Diam
275/35/18 -- 25.6" Overall Diam

From the stock Continent tires, this is what the car came with...
225/45/18 -- 25.9" Overall Diam
255/40/18 -- 26" Overall Diam

If you're looking for track wheels why mount street tires?
Most Z4MC track junkies out here on the left coast run on either the Toyo R-888 or the Nitto NT-01.
I run the R-888 in 235/40-18 front and 265/35-18 rear with a stock suspension. I've seen 245/40-18 front and 255/35-18 rear used with the TC Kline DA coil over suspension.

[JCz04Bimmer]

Originally Posted by jmillet

If you're looking for track wheels why mount street tires?
Most Z4MC track junkies out here on the left coast run on either the Toyo R-888 or the Nitto NT-01.
I run the R-888 in 235/40-18 front and 265/35-18 rear with a stock suspension. I've seen 245/40-18 front and 255/35-18 rear used with the TC Kline DA coil over suspension.

Because even after 20 or so track days (7 in the Z4M), I'm not quite comfortable with going to an r-compound tire. I like the responsiveness of street tires squealing at the limit. I know I'm leaving grip on the table but I'm alright with that. Also, I don't really have the means to store 4 dedicated track wheels/tires since I live in the city. The arrive and drive model is almost a necessity. That and just this season alone I've gotten rained on HEAVILY for 4 of the 7 days I've done so street tires, to me, seems like the way to go. I'm also only considering street tires that are as close to r-compounds as you can get. I've run the RE-01R's for the past two seasons and am pleased with the results they give me... I've heard the Star Specs are quite comparable.

That said, thanks for the input on the various sizes people are running. I know that r-comps are usually much wider than their officials sizes suggest.

[onelove]

I'm about to order a set of the TR1 from Tire Rack as well.

18x8.5 +44mm / 18x9.5 +35mm ( after a ton of research and going back and forth no need to go crazy offsets IMO or extra width, these will accommodate the majority of the sizes that can fit under the Z4M)

Nitto 245-40-18 / 275-35-18

That being said I've heard good results on the Nitto NT-05 for a very sticky street tire just before switching to R-Compounds, I'm likely going to mount a set of these in 245/35/19 and 275/30/19 for street duty and rain days at the track. They're priced relatively affordable for the amount of dry and wet grip they provide. (I'm running 3+ degrees of negative camber on the street so fitment in the front shouldn't be an issue)

[JCz04Bimmer]

Nice! Well, I just really want to run a slightly wider front tire than the usual 245/40/18 tire. I understand that our cars don't behave as well with a square setup as the M3's do but I also found my current 245/35/19 and 275/30/19 tires to be a bit too drastic of a stagger on the track. Not by much, but a 255 up front would be perfect, I think. This is why I'm sort of pushing for the 18x9 front wheels which are available only with a +35 offset. If they had a +40 offset, I'd be golden...

[Eddy@ApexWheels]

is the 9" et35 the most optimal setup for the front? or would a higher offset be preferred? I don't know how the hub to strut tube spacing is on the Z4. On the E46 there is a lot of room, on the E90 non-m and E36 there isn't much room.

The APEX ARC-8 track wheels come in the following sizes and may be a better direct fitment:

18x8.5" et38, 18lbs~
18x9" et42, 18lbs~
18x9.5" et35, 19lbs~
18x10" et25, 20lbs~

E46 M3 guys find the 9.5" wheel in a square setup with 265's a popular track choice (camber plates needed). I don't know how much front clearance there is on the front of the Z4 though.

18x9" et42 front and 18x10" et25 seems like a light weight setup that wouldn't require any spacers at all.

example pics of the wheel

[tnsbruce]

Originally Posted by onelove

I'm about to order a set of the TR1 from Tire Rack as well.

18x8.5 +44mm / 18x9.5 +35mm ( after a ton of research and going back and forth no need to go crazy offsets IMO or extra width, these will accommodate the majority of the sizes that can fit under the Z4M)

Nitto 245-40-18 / 275-35-18

I will go with this same set up with NT-01's sometime next summer when I feel I am ready for R-Compounds. I believe RussRamz runs this set up on the Nurburgring.

Originally Posted by onelove

That being said I've heard good results on the Nitto NT-05 for a very sticky street tire just before switching to R-Compounds, I'm likely going to mount a set of these in 245/35/19 and 275/30/19 for street duty and rain days at the track. They're priced relatively affordable for the amount of dry and wet grip they provide. (I'm running 3+ degrees of negative camber on the street so fitment in the front shouldn't be an issue)

I have been using NT-05's all year and have been happy with the performance. The first couple outings I was so-so with the tires as I felt they were not delivering the advertised grip. After playing with pressures and a few heat cycles they work well. AND they are one of the only high performance tires available in 245/35/19 and 275/30/19 (PS2 and RE-011 being the others). I was able to get about 20 track days out of these tires. I will continue to get these as my street tire and use the 18' wheels and NT-01's for the track.

[jragan]

Originally Posted by jmillet

If you're looking for track wheels why mount street tires?
Most Z4MC track junkies out here on the left coast run on either the Toyo R-888 or the Nitto NT-01.
I run the R-888 in 235/40-18 front and 265/35-18 rear with a stock suspension. I've seen 245/40-18 front and 255/35-18 rear used with the TC Kline DA coil over suspension.

Choice between R-Comp or not is more one of driver skill and ability than it is wheel choice. R-Comps really should only be used by someone of a very advanced level who really knows how to drive because they impede learning since they stick when you would normally be off the track and therefore don't teach you proper car handling technique. To this point, the better HPDE associations don't allow drivers to run R-Comps unless they're in the advanced/red groups.

That being said, the current generation of ultra-performance summer tires (like the StarSpecs) are very nearly R-Comp territory. I switched from NT01s to the StarSpecs and found, beyond the StarSpecs needing a bit more warm up (or just more aggressive with them out of the pit), that I didn't seem to lose much speed or stick. I run with the advanced/red group on a very technical track.

[The HACK]

I would prefer 40+mm of offset on the front with that size wheel.

This chassis is also very sensitive to changes in track width. Running as close to stock-ish offset and stagger would yield the best result in my opinion. If you need grip up front, add negative camber, not track.

[O-cha]

If I remember correctly I was able to run a 30mm effective offset up front with 255 starspecs.

[silversprint]

Originally Posted by The HACK

I would prefer 40+mm of offset on the front with that size wheel.

This chassis is also very sensitive to changes in track width. Running as close to stock-ish offset and stagger would yield the best result in my opinion. If you need grip up front, add negative camber, not track.

I don't really have a choice. If you want to run wider tires and lots of camber then you have to space out the wheels slightly to add camber otherwise you rub the struts. I have to run a 5mm spacer on the front. That is the miminum needed to clear a 8.5+38 wheels with 255/35/18 tires and almost 3 degress of camber on my car.


I think the best way to find out what fits your car is to get under there and actually measure all the clearances on your car. Many of the wheel and tires suggestion on posts I have seen don't work on my car. Yea its a pain but so is returning wheels that don't fit.

The car seems to me more sensitive to increase in rear track width. I had 18x9.5+15 wheels on the rear for a while and there was quite a bit of increase in understeer specially in very slow corners.

[Eddy@ApexWheels]

Originally Posted by silversprint

If you want to run wider tires and lots of camber then you have to space out the wheels slightly to add camber otherwise you rub the struts.

You don't get negative camber by adding spacers.

Adding negative camber with plates does not take away inside tire to strut tube clearance either.

the 5mm spacer you need to clear 255's up front sounds extremely normal for most bmw's, not just the Z4. If you were at stock ride height or slammed all the way to the ground, you'd need the same spacer. Knowing this, a 9" wheel with the same tire would work up front with a 10mm spacer and negative camber, which is basically identical to the E90 front clearance.

[jragan]

Originally Posted by paintpro21

You don't get negative camber by adding spacers.

Adding negative camber with plates does not take away inside tire to strut tube clearance either.

the 5mm spacer you need to clear 255's up front sounds extremely normal for most bmw's, not just the Z4. If you were at stock ride height or slammed all the way to the ground, you'd need the same spacer. Knowing this, a 9" wheel with the same tire would work up front with a 10mm spacer and negative camber, which is basically identical to the E90 front clearance.

If you re-read, you'll see that he's not spacing for camber, he's spacing as a result of adding camber with wider wheel/tires.