Optimal tyre profile / size on CSL alloys?

[funkdude]

Hi there chaps,

I am trying to order a new set of rear tyres for the CSLs on my Z.

The rear alloys are currently running on 265/35/19. I have been told that I can try maybe a slightly bigger tyre but I am not too sure since I am happy with my current size.

Reason why I am asking is because I am after a set of Eagle F1 Asy and they dont do the exact profile so I will have to go for either 265/30/19 or 275/30/19. Keen on the 35 height ratio tho cause it closes off the gap between the wheel and car nicely.

I am aware that stock profile for the CSLs are:

front: 235/35/19
back: 265/30/19

However I am keen to fit the largest possible tyres on the alloys to enhance protection on the alloys as well as closes gap between wheel and car.

Does anyone know what is the largest tyre profile / size that will fit on the CSL alloys (front and rear) without sacrificing performance?


Cheers.
FD

 

[Top pup]

I'm running 245/35/19 and 275/30/19 they fit fine with no rubbing. That's about as big as I'd want to go.

 

[mmm-five]

I'm running 245/35/19 and 275/30/19 they fit fine with no rubbing. That's about as big as I'd want to go.

That's the sizes I was going to put on mine...until I sold them and got standard Z4MC wheels instead (I'm a heretic, I know).

However I'm still thinking of going up in width when I need new tyres anyway.

 

[Top pup]

I'm running 245/35/19 and 275/30/19 they fit fine with no rubbing. That's about as big as I'd want to go.

That's the sizes I was going to put on mine...until I sold them and got standard Z4MC wheels instead (I'm a heretic, I know).

However I'm still thinking of going up in width when I need new tyres anyway.

I'm sure you could go up to 245/40/18 and 275/35/18 without any clearance problems, though I'm not too sure if they would be ok on the standard wheels.

Did the standard wheels help your handling problems?

 

[mmm-five]

I'm sure you could go up to 245/40/18 and 275/35/18 without any clearance problems, though I'm not too sure if they would be ok on the standard wheels.

Did the standard wheels help your handling problems?

That was my working out too - those sizes are about the closest to original overall circumference (265/40/18 are closer for the rear though).

For the front
245/40/18 are 1% under size - my choice
235/45/18 are 1.3% over size
235/40/18 are 2.2% under size
245/45/18 are 2.7% over size

For the rear
265/40/18 are 1.2% over size
275/35/18 are 1.7% undersize - my choice
275/40/18 are 2.4% over size
265/35/18 are 2.8% under size

None of those options above would affect the speedo enough to cause worry at speed cameras as they're all within 3% and the speedo under-reads by 5% in my recent test anyway. The only concern with going 'over size' would be dulling the acceleration a little, as I know from my time in marshalling that wider tyres equal more grip, but also increase rolling resistance and thus worsen fuel economy.

Whether they fit on the standard wheels is another matter which I'll have to investigate, but I can always settle for the 235/265 combo for now.

Just got to find both of these sizes in the same tyre - can get one size in Michelin PS2 and one in Continental SportContact2/3, but not all sizes in one.

As for the question on handling: yes the standard wheels and tyres have made all the difference. I've been blasting around the same roads I did over New Year and the car responds much better. Gone is the understeer I was getting on tight bends, gone is the skipping over cats eyes, gone is the all or nothing back end action. I've even done two track days on them and couldn't fault them. I've also manage to keep them completely mark-free, which is something I never managed to do with the CSLs.

I'm sure that there are some situations where the CSLs and 19's work better than the standard 18's, but I guess all of them involve a track/circuit of some kind, and not the public roads.

 

[GP20]

This thread should be moved to the M discussion forum so there's no confusion. All of this is talking about the sizes for the ///M.

For non-M's, stick with 235/35/19 & 265/30/19, or 225/35/19 & 255/30/19.

 

[WLH]

This thread should be moved to the M discussion forum so there's no confusion. All of this is talking about the sizes for the ///M.

Agree and moved...

 

[GP20]

 

[zippster]

I'm running 245/35/19 and 275/30/19 they fit fine with no rubbing. That's about as big as I'd want to go.

DING! no probs here either, except i can see the wear bars loomin'

 

[GP20]

Just got to find both of these sizes in the same tyre - can get one size in Michelin PS2 and one in Continental SportContact2/3, but not all sizes in one.

As for the question on handling: yes the standard wheels and tyres have made all the difference. I've been blasting around the same roads I did over New Year and the car responds much better. Gone is the understeer I was getting on tight bends, gone is the skipping over cats eyes, gone is the all or nothing back end action. I've even done two track days on them and couldn't fault them. I've also manage to keep them completely mark-free, which is something I never managed to do with the CSLs.

I absolutely agree with you. I'm also running 245/40/18 & 275/35/18 Michelin PS2's now and the grip is awesome! Ride comfort is also very good like you said. I came from 235/35/19 & 265/30/19 Goodyear Eagle F1 GS-D3's, which were very good street tires, but the PS2's are noticibly much better.

I'm sure that there are some situations where the CSLs and 19's work better than the standard 18's, but I guess all of them involve a track/circuit of some kind, and not the public roads.

Actually, there isn't. 18's are better than 19's in every way other than asthetic appearances. Which is the dilemman I'm in right now. My 18" BBS RGR's have the PS2's. My 19" BBS RGR's have the Eagle F1 GS-D3's. The 18" are lighter, handle better, and have better ride comfort than the 19's. But the 19's just look superb on the M.

 

[Z4Kevo]

I am running 245/35R19 on the front and 285/30R19 on the rear. Fit nicely.

 

[funkdude]

wow Kevo it is the first time I heard anyone fitting on a pair of 285/30R19 on the back. Most people would only go up to 275 and said it is probably the max they'd like to go! Good to hear theres no issues there with larger tyres. Except for potentially loosing a little on acceleration in real terms and slightly worse on mpg the difference is probably too little to be able to tell?

 

[Top pup]

I'm sure 285/30/19 will fit fine on the back, it's the fronts that are getting tight with the 245/35/19's.

 

[Z4Kevo]

wow Kevo it is the first time I heard anyone fitting on a pair of 285/30R19 on the back. Most people would only go up to 275 and said it is probably the max they'd like to go! Good to hear theres no issues there with larger tyres. Except for potentially loosing a little on acceleration in real terms and slightly worse on mpg the difference is probably too little to be able to tell?

Actually the 285s are much lighter than the stock OEM rears...and the difference from the 275s was really small overall. I chose the 285s over the 275s cuz it filled the wheel wells SO much better and had a closer undersize % to the 245s. Very happy with my choice.

I love how they look...

 

[GP20]

I wouldn't put 285's on my M for several reasons, but I gotta say I like how the 285's look on yours. Especially since the PS2's have bulkier side-walls that make the car look bad-ass and all-business.

 

[funkdude]

yea it surely looks good - provides great protection to the alloy too!

GP20 - what are issues you had in mind regard 285s?

 

[GP20]

yea it surely looks good - provides great protection to the alloy too!

GP20 - what are issues you had in mind regard 285s?

- extra unsprung weight
- more understeer
- more tramlining
- slower acceleration (both due to extra unsprung weight and slightly altered gearing due to tire diameters although not significant)
- worse gas mileage (again, due to unsprung weight and extra traction)
- potentially too much side-wall flex on a 9.5" wide rim (would work better on a 10" wide rim)

Stock Z4M's really don't benefit much from having 285's. The ESS Z4M with +500HP, on the other hand.......

But like I said though, 285 does look pretty sweet. I'm defying all the reasonings myself and will replace my 235/265 Goodyear Eagle F1 GS-D3's on my 19" BBS RGR's with 245/275 Michelin PS2's. They do grip better than the GS-D3's and I like the PS2's beefy side-walls.