Got some 19" M3 alloys - have a couple of tyre questions

G

glastoveteran

Active member
 Bristol
Hi all,

Got myself a nice set of 19" M3 alloys from ebay to replace the OEM ones on my Z4MC and have a few questions for the wheel and tyre gurus amongst you:

1) New wheels are 8 x 19 front and 9.5 x 19 rear, whereas I think the OEM ones are 9 x 19 rear. Does that mean the new wheels will stick out an extra half inch either side and will it look odd?

2) Since the fronts are the same width as OEM I figured I may as well get the same width tyres, obviously with the correct profile - 225/40/19. As the rears are half an inch wider I guess I should be going 265 or 275 instead of the current 255? And would a 225 front / 275 rear setup be ok?

3) Why on earth do they measure wheel widths in inches and tyre widths in mm?!

Thanks all,

Alex
 
1) Depends on the offset. If the offset is 12-13mm more than the OEM ones then they might sit the same on the outside, but stick inwards more, or they might have a 6mm different offset which means you'll get 1/4 inch in & out.

2) I'd probably put 235/40 or 245/40 on the front and 265/35 or 275/35 on the rear to give the wheels some protection from kerbing - don't know if those bigger options will foul on anything though.

3) Because they can, and due to some merging of the two systems some time back.
 
Thanks mmm-five, :thumbsup:

I'd always wondered exactly what the offset meant, but got a better grasp of it now, even if I don't know exactly what the numbers mean.

A quick bit of googling and I think the 19" M3 alloys are +47F and +27R. Do you know what the stock ones are, and is it easy to work out the difference it will make?
 
gannet said:
have a look here for all BMW wheels and offsets:

All BMW Wheels

19" M3 wheels (Style 67) show offsets of 47 front 27 Rear

as for what it all means :tumbleweed:
Click to expand...

Thanks gannet that's really useful, and confirms the offsets. I was wondering what weight they were compared to my OEM wheels but this should answer it.
 
FWIW I had checked with a few sources that the wheels would fit - I'm just curious as to whether it's going to look like a hot rod with the rear wheels sticking out :lol:
 
Original Z4M wheels:

8.0 x 18 ET 42 front
9.0 x 18 ET 30 rear

OEM 19" M3 wheels style 67:

8.0 x 19 ET 47 front
9.5 x 19 ET 27 rear

At the front , with respect to protrusion, the difference is due to offset alone. The front wheels will in fact be 5 mm further inboard than your original Z4M wheels, perhaps underfilling the arches a tad.

At the rear, the difference is due to both offset and the extra wheel width. The wheel width component increases protrusion by one quarter inch (c 6.5 mm), whilst the offset will increase protrusion by 3 mm.

The overall effect is that compared to your original Z4M wheels, your new wheels will actually stick out by 5 mm less at the front, and protrude more by 10 mm at the rear.

My CSLs protrude by an extra 10 mm at both the front and rear, and I have no rubbing issues (pictures will be posted when I have time... :driving: )


With respect to tyre size, I would recommend 225/40/19 for the front and 255/35/19 at the rear. This is the stock BMW M3 19" style 67 set up. At the front, this is a 0.4% change in your rolling circumference, whilst at the rear the overall rolling circumference will be identical to that of your original wheels. This set up will lead to absolutely no change in your speedometer readings.

If you did increase your tyre sizes to 235/35/19 at the front, this would lead to your speedometer over-reading by c 2% (ie it will read 60 mph at a true speed on 58.9 mph). Similarly, 265/30/19 tyres at the rear would lead to your speedometer over-reading by 3% (indicating 60 mph at a true 58.2 mph). This is the set up I use, but my front wheels are 1/2 inch wider than yours :D

For your homework, please study the following reference materials. There will be a test:

http://www.miata.net/garage/tirecalcold.html

http://www.driverstechnology.com/wheel-offset.htm

:D
 
I run my CSLs on 235/35 and 265/30 no worries but these are stock CSL size rather than standard M3. I don't see any advance in going fatter, 19" wheels are never going to be great at kerb protection on such a low riding car. I didn't do any speedo research but I tend to use the camera detector for my true speed anyways :)
 
Thanks BMWZ4MC that's really helpful! :thumbsup:

BMWZ4MC said:
The overall effect is that compared to your original Z4M wheels, your new wheels will actually stick out by 5 mm less at the front, and protrude more by 10 mm at the rear.

My CSLs protrude by an extra 10 mm at both the front and rear, and I have no rubbing issues (pictures will be posted when I have time... :driving: )
Click to expand...

Ok, so could I use a spacer at the front (say 10mm) so that they would protrude by 5mm at the front and 10mm at the rear? Is there any downside to this? Or even 15mm at the front so there is a more even stance front and back? I have no idea what size spacers you can typically use, but I shall indeed go and do my set homework.

BMWZ4MC said:
With respect to tyre size, I would recommend 225/40/19 for the front and 255/35/19 at the rear. This is the stock BMW M3 19" style 67 set up. At the front, this is a 0.4% change in your rolling circumference, whilst at the rear the overall rolling circumference will be identical to that of your original wheels. This set up will lead to absolutely no change in your speedometer readings.
Click to expand...

I certainly feel more comfortable going ith stock sizes, and I did use a tyre calculator which suggested that going up to 245/40/19 at the front would be a 2.8% increase and therefore a bad idea. I'm ultra careful with kerbs so I'm not too worried about extra rim protection.

So, it's just a question of whether spacers at the front are the way to go...
 
glastoveteran said:
Ok, so could I use a spacer at the front (say 10mm) so that they would protrude by 5mm at the front and 10mm at the rear? Is there any downside to this? Or even 15mm at the front so there is a more even stance front and back?
Click to expand...

I'd be a little cautious over-doing it with spacers as that way may lie rubbing issues.

I would expect that 10 mm spacers should be ok wrt rubbing as mine protrude still 5 mm more than that combination. That said though, I have no experience of spacers. You could try ali_b, if he's still on here. He sold a set of 19" style 67 wheels and a set of black CSL reps when he sold his ///M coupe, and his advertisment mentioned that he was using 10 mm spacers on the front.

What will you do with your original wheels? I'm keeping mine for track use so I don't shred the Vreds on my CSLs each time I want a little fun :driving:

Make sure you post some pics when you've got them on the car :thumbsup:
 
BMWZ4MC said:
I'd be a little cautious over-doing it with spacers as that way may lie rubbing issues.

I would expect that 10 mm spacers should be ok wrt rubbing as mine protrude still 5 mm more than that combination.
Click to expand...

That was my logic, figuring that if they were still 5mm less than the CSLs then there wouldn't be any probs in theory. I will indeed contact ali_b as suggested, though I didn't realise he had sold is car and I did PM him a couple of weeks asking if he had any photos but no reply as yet.

I'll probably keep the original wheels somewhere in case I sell the car back to BMW and they may want the standard wheels.

I had planned to go with Vred Ultrac Sessantas as well.

I will indeed get some phootos up :thumbsup:
 
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