Hi newbie here with a stupid question

[z4newbie2021]

Hi thank you for letting me join.

i just bought a Z4 2007 2.5si i and i really like it but i work on an estate covered in speed bumps.
so i want to calm the ride down and increase the ground clearance.
i was wondering if i could fit 17/255/ 55 all round from a 5 series G30/G31
The car is running 18s at the moment 225 fronts and 255 rears.


Thank you

 

[brillomaster]

thats probably a bit far.... the speedo will be well out, the handling would be all wrong and those wheels probably wouldn't fit under the arches anyway.

there are some thing you can do to improve the ride...
1) swap run flat tyres for non run flats
2) increase the profile of the tyres slightly - perhaps 235/40/R18 front, and 245/40/R18 on the rear
3) decrease the wheel sizes to 17", then you can fit 225/50/R17, and 245/45/R17

 

[brillomaster]

oh also before you go swapping any wheels over, make sure you understand offsets. Wheels off a G30 5 series probably have a completely different offset to the standard ones on a Z4.

 

[TheDan]

You wont be able to run G30/G31 wheels as they have a bolt spacing of 5x112. The Z4 uses 5x120. Also the speedo error with that size tyre would be around 10% (way too high).

If you're looking for a better ride via smaller wheels (and more sidewall) then you can fit stock 16" or 17" Z4 wheels such as these: http://www.bmwstylewheels.com/bmw/104 or http://www.bmwstylewheels.com/bmw/103.

In terms of ride height, there are a couple of options. Depending on how worn your suspension is, simply changing shocks/springs can increase ride height. Another option is to go for slightly higher springs (ie non m-sport) which gives ~15mm raise. Finally, you could go to coilovers with ride height adjustability, but these tend to give a harsher ride and are by far the more expensive option.

 

[enuff_zed]

The wife's car has 245/40/18 front and back and gives quite a comfortable ride.
Personally I'd like the fronts back to 225/40/18 when the tyres wear out.
Hers is on standard suspension.
What springs and shocks are on yours? They can make as much, or more, difference than the tyres do.

 

[Mr Tidy]

Well it looks like your question about wheels has been answered, so welcome to the forum.

And we'd love to see a photo or two of your car!

 

[buzyg]

I'll keep it simple. Welcome on board.

 

[Ole gits rule]

Hello and welcome to the forum

 

[z4newbie2021]

Thank you so much for all the replies that was very helpful. i think my car is lower than standard as i passed a 2.5 si yesterday and it looked a lot higher unfortunately i could not stop and measure i think someone in the forum may have had my car before me i enclose a couple of pictures

 

[enuff_zed]

Very nice. Very shiny too.
It does look a bit lower yes. It also highlights (to me at any rate) just how far in the rear wheels sit.

 

[brillomaster]

nice car! definitely looks lower than standard, so first port of call would be springs, and then ditch runflats if there are any on there still. I just carry around a 12v tyre inflator instead, if you have a puncture that can't be remedied by simply topping up the air every half an hour until you get to a garage, then runflats probably wouldn't have helped anyway.

 

[True-Blue]

They look lower than Eibachs to me, I’d take a guess at H&R springs, but have you had a look to check it’s not on coilovers?

 

[z4newbie2021]

My god you guys are good from just a picture.
The front bumper is 4.5 inches off the ground or about 11 cm
i will be changing out the springs for standard ones hopefully this weekend.
Is it worth upgrading the shocks they seem a bit old ?
i am in Essex does any one have a garage they would recommend?
Thanks so much for the help its really appreciated.

 

[enuff_zed]

I'd say if you have the dosh, then change the dampers while you're in there as it'll save one lot of labour.
That spring in your photo looks at least half coil-bound to me. I don't see how it can be achieving much shock absorption at all?

However, it also looks relatively new, so maybe someone on here would be interested, which would help your wallet a little?