Rear Wheels

UK forum for general and technical discussion about the Z3 roadster
Post Reply
Luke2015
Joined: Fri 18 Jul, 2014 08:36
Posts: 26

  Z3 roadster 2.8

Rear Wheels

Post by Luke2015 »

Hello Guys!

My first post! I have recently just had my Z lowered on Apex springs really happy great handling. :)

Problem is i had the tires changed at the rear 245/40/R17 when i first had the car as they where low on tread.

Now that i have had it lowered the size of the wheels from the front is noticeably different - 225/45/R17

My question is could i put either 255/40/R17 on the rear or 225/45/R17 to match the front tire wall hight.

Because it looks really silly with a small tire at the rear and a big one at the front!

Thanks In Advance.
User avatar
lightning
Joined: Tue 27 Nov, 2007 08:15
Posts: 818

  Z3 roadster 3.0i
Location: Stockport

Re: Rear Wheels

Post by lightning »

Why not try changing the front and rear wheels over....it might look better with the larger tyres on the rear.

My 3.0 Sport has 17" wheels on the front and 18" at the rear, as standard fitment. So the rear wheels look larger anyway.
User avatar
BladeRunner919
Joined: Fri 17 Feb, 2012 20:18
Posts: 2225

  Z3 roadster 1.9

Re: Rear Wheels

Post by BladeRunner919 »

The difference in sidewall height between a 245/40/R17 and a 225/45/R17 is about 3mm. I can't believe that you can actually discern a difference.

It sounds more like you need to fine-tune the ride height (different spring pads) and maybe fit wheel spacers. Can you post a pic that demonstrates the problem.
gIzzE
Joined: Mon 06 Aug, 2007 21:32
Posts: 169

  Not specified

Re: Rear Wheels

Post by gIzzE »

There is no difference in tyre wall height between a 245.40.17 and a 225.45.17 tyre, the width is different but not the sidewall.

24.977" overall diameter for the 225 tyre and 24.724" for the 245 tyre.

The first measurement is the width, so 225 wide and 245 wide, the second measurement is the sidewall as a percentage of the width, so 40% in the case of the 245 and 45% in the case of the 225.

I take it you have had new springs all round? However...
If you have lowered the rear and not the front of course it will look odd, you will now have a whacky racers look going on with the front being some 30-40mm higher than the rear, the gap between tope of the tyre and the wheel arch will look a bit silly. :D

You need to consider changing the front suspension to match really.
Luke2015
Joined: Fri 18 Jul, 2014 08:36
Posts: 26

  Z3 roadster 2.8

Re: Rear Wheels

Post by Luke2015 »

Cheers for the reply's guys but it is defiantly the wheel it was like it before i had it lowered although now its lowered it is so much more noticeable. I will upload a picture and you can see the diameter of the wheel with a 245 tire is a lot smaller than my front 225 tires
User avatar
Robert T
Site Admin
Joined: Mon 12 Jun, 2006 10:35
Posts: 10170

  Z3 roadster 1.9
Location: Cheshire

Re: Rear Wheels

Post by Robert T »

245/40R17 anf 225/45R17 would have been the standard sizes for a staggered setup from the factory! The 40 and 45 are not sidewall heights in mm but rather percentages of the tyre width. 40% of 245 is approximately the same as 45% of 225 (98 vs. 101.25). Bearing in mind that a tyre normally has about 8-9mm of tread on it, you will be pushed to see a 3mm difference. What you are seeing is an optical illusion. You can get your tape measure out and measure it if you like.

You can swap front to rear to prove the point, but don't drive it with wider tyres on the front that the rear!!

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
Image
Luke2015
Joined: Fri 18 Jul, 2014 08:36
Posts: 26

  Z3 roadster 2.8

Re: Rear Wheels

Post by Luke2015 »

Now see I was thinking the same as that but I'm puzzled as iv seen another z with the same wheels and tires and they don't look the same as mine. Is it possible to put the same tyres as the front on the rear?
gIzzE
Joined: Mon 06 Aug, 2007 21:32
Posts: 169

  Not specified

Re: Rear Wheels

Post by gIzzE »

It will make no difference.

The diameter is the same for both.
User avatar
Robert T
Site Admin
Joined: Mon 12 Jun, 2006 10:35
Posts: 10170

  Z3 roadster 1.9
Location: Cheshire

Re: Rear Wheels

Post by Robert T »

Are they the same wheel rims front and back? If they are, then the wider rear tyres will overlap the rim more, possibly making them look bigger. You would be able to reduce the rears down to the same 225s as the front. If the rear rims are wider (which they will be on a proper staggered setup), then you need to have the wider tyres on them. If they have a deeper dish on them, then this may account for the visual difference in profile.

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
Image
gIzzE
Joined: Mon 06 Aug, 2007 21:32
Posts: 169

  Not specified

Re: Rear Wheels

Post by gIzzE »

lightning wrote: My 3.0 Sport has 17" wheels on the front and 18" at the rear, as standard fitment. So the rear wheels look larger anyway.
What??!! :shock:

You serious?
Luke2015
Joined: Fri 18 Jul, 2014 08:36
Posts: 26

  Z3 roadster 2.8

Re: Rear Wheels

Post by Luke2015 »

Acording to the handbook my style 18's rear is 8.5j x 17 and front is 7.5j x 17 I will get some pictures taken today so that it makes it clearer to see. The only thing I can think is the rear alloy is 16 and not 17
Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2136

  Z3 roadster 1.9

Re: Rear Wheels

Post by Del »

According to my handbook that was the typical (and BMW correct), staggered wheel size for the 2.8. The wheel size i.e. 7.5J X 17 (front) and 8.5J X 17 (rear) will be stamped on the wheel and is clearly visible on the style 18 wheel. Ignoring the emergency wheel, I am not aware that BMW ever approved different diameter wheels between front/back axles on the Z3.
Rafolian
Joined: Wed 27 Feb, 2013 08:41
Posts: 547

  Z3 roadster 2.8

Re: Rear Wheels

Post by Rafolian »

That's what is fitted to my 1998 2.8 also.
gIzzE
Joined: Mon 06 Aug, 2007 21:32
Posts: 169

  Not specified

Re: Rear Wheels

Post by gIzzE »

Del wrote:I am not aware that BMW ever approved different diameter wheels between front/back axles on the Z3.

Of course they haven't, that is why I was so surprised he said his had 17s up front and 18s at the rear.
User avatar
BladeRunner919
Joined: Fri 17 Feb, 2012 20:18
Posts: 2225

  Z3 roadster 1.9

Re: Rear Wheels

Post by BladeRunner919 »

Luke2015 wrote: The only thing I can think is the rear alloy is 16 and not 17
If that was the case, your 245/40/R17 tyres would leak somewhat! :D
Mike Fishwick
Joined: Fri 19 Jun, 2009 10:27
Posts: 2093

  Z3 roadster 2.8
Location: Daglan, France

Re: Rear Wheels

Post by Mike Fishwick »

Why don't you check the sizes of the front and rear wheels before convincing yourself that something is odd - if you have the 8.5 inch rims with 245-40 tyres on the back, and 7.5 inch rims with 225-45 tyres on the front, then that is the way things should be - if otherwise, decide what is wrong - just look at the wheels:

Image

Z3 front wheel, carrying information of rim profile - J, rim width X diameter of 7.5 inch X 17 with number of raised safety rings - H2, offset (IS) of 41 mm, made by Chromodora Wheels (CDW) and carrying the BMW part number

When you had the suspension lowered, did they fit the 7.5 inch rims on the back? That would certainly make things look odd . . .
A Z3 is not just for Christmas - it's for life!
Luke2015
Joined: Fri 18 Jul, 2014 08:36
Posts: 26

  Z3 roadster 2.8

Re: Rear Wheels

Post by Luke2015 »

Excellent information ^^^ As regards to lowering the issue was there before it was lowered it's now just a whole lot more obvious. :( I am puzzled. I will be taking her out today as it's sunny!! So ill get some pictures.
Post Reply