How big is too big?

[brettski]

At some point I will need to put some new rubber on my 2000 740iL, it has the standard 16" alloys on it, and I am wondering what size tyres will go onto this vehicle before I will strike issues with either too much sidewall flex or scrubbing. I am only considering going from the factory 235/60/16 to 245/55/16 or 255/50/16. Does anyone have experience with these size tyres on their E38?

[marti5]

My front are 8j on which I have 235/50 ZR

My rear are 9j on which I have 285/40 ZR

[brettski]

Originally Posted by marti5

My front are 8j on which I have 235/50 ZR

My rear are 9j on which I have 285/40 ZR

Excuse my ignorance of these codes, are the 8j & 9j referring to the Rim width?

Are you still running 16" wheels, or am I correct in assuming that you have gone up to 17" or 18" rims given the 50 profile on the front?

What is your brand of preference for tyres?
Are Toyo Proxes T1-R considered an acceptable tyre, or do I need to look elsewhere for a better product?

Would you continue with 100W series even if you are limited to 130km/h, and never likely to exceed 150km/h?

These are the rims I am running now, I don't know the specifics of them other than the 235/60/16 tyres on them now show very little indication of being oversized on them, that is little or no sidewall deflection.


Thanks for your predictably punctual response.

[marti5]

Sorry Im running on 18" fitted at production, 8 & 9j are the widths of the wheels.

I run on Toyo proxes T1 S...which a brilliant wet or dry, Ive had them on approx 2 years and they have hardly worn at all.

As for limits...sometimes Im doing 130 MPH....approx 210 KMH, but normally 95-105 MPH.

IMHO if I had 16" rims on, I would have to change them for 18" or 20" it just gives the car such a stance....

[brettski]

Do the standard BMW rims have the size information makred on them anywhere?

Is the ride on the 40 profile tyres pretty firm? Sometimes I am driving on unsealed and badly corrugated roads, so I'd like to keep a bit of sidewall flex to soften out the larger bumps.

Is there an adjustment within the speedometer mechanism to cater for the 18" rim, or is the effective rolling diameter the same between the rim sizes with the correct tyre sizes?

[Torque]

Here's a good website for you to play around with: Wheel / tire size calculator / comparer - WHEELSMASTER

To answer your original question, both of the tire sizes you're considering have less sidewall (smaller overall diameter). 255/55/16 is 2mm smaller sidewall and should still fit as far as the width ... at least on the back. Front ... check before you do anything, you might need spacers to keep from rubbing suspension components.

[brettski]

Originally Posted by Torque

Here's a good website for you to play around with: Wheel / tire size calculator / comparer - WHEELSMASTER

Torque, you are 100% right. That is a really good web site. I have saved that for later reference. Can anyone tell me what the standard offset is on the E38 rims?

It looks like I can go from the stock 235/60-16 to a 255/55-16 tyre without dramatically altering the speedometer calibration or undue distortion of the sidewalls.

[marti5]

BMW 7 Series (E38) 2000 5x120


Make: BMW
Year: 2000
Model: 7 Series (E38)
Bolt Pattern: 5x120
Offset Range: 10 to 25
Wheel Size Range: 16x7.5 to 20x9.0
OEM Tire Size: 235/60-16 (235x688 mm)

[Torque]

Originally Posted by brettski

Torque, you are 100% right. That is a really good web site. I have saved that for later reference. Can anyone tell me what the standard offset is on the E38 rims?

It looks like I can go from the stock 235/60-16 to a 255/55-16 tyre without dramatically altering the speedometer calibration or undue distortion of the sidewalls.

I believe the offset for the stock 16 inch basketweaves is 23. I think.

[marti5]

Correct Torque it is 23mm, I did but that down 1st but its for 97/98 but I dont suppose they changed it for the 2000.

[nukeduster]

I am running 275's in the front on my 8... the 7 runs the same size and offset rims and has the same front suspension, I'd suspect you should be able to run something similar if you have the correct offset. +5 MM in my case.

[brettski]

So at what point does a difference in the rolling diameter of the front and rear wheels cause the DSC to become less than effective?

[marti5]

Basically if you start putting 17" or 18" rims on your speedo will read higher than what your actually doing +/- will vary dependent on what rim size you put on, example 100mph will be 97mph on the clock, as your car has been calibrated for 16" so if you require the correct reading on your speedo for 18" its off to BMW dealer for re-calibration or a sat nav with speed monitor. But to be honest most people dont bother....so you buy a car with 18" rims on without knowing theyve been changed from 16" so your speedo is out, but you wouldnt know, so imagine if you went to 21".....but I wouldnt really worry....as for the DSC this will not be affected..

[brettski]

Originally Posted by marti5

Basically if you start putting 17" or 18" rims on your speedo will read higher than what your actually doing +/- will vary dependent on what rim size you put on, example 100mph will be 97mph on the clock, as your car has been calibrated for 16" so if you require the correct reading on your speedo for 18" its off to BMW dealer for re-calibration or a sat nav with speed monitor. But to be honest most people dont bother....so you buy a car with 18" rims on without knowing theyve been changed from 16" so your speedo is out, but you wouldnt know, so imagine if you went to 21".....but I wouldnt really worry....as for the DSC this will not be affected..

I am not sure if I am asking the question correctly. I'll rephrase it at the risk of having you say, see previous response

If for example you have 275/40-18 on the rear and 245/40-18 on the front, will the difference (~24mm) between the two rolling diameters having any impact on the operation or effectiveness of the DSC?

Sorry if this is what you have answered above.

[marti5]

Originally Posted by brettski

I am not sure if I am asking the question correctly. I'll rephrase it at the risk of having you say, see previous response

If for example you have 275/40-18 on the rear and 245/40-18 on the front, will the difference (~24mm) between the two rolling diameters having any impact on the operation or effectiveness of the DSC?

Sorry if this is what you have answered above.

Nope, the DSC is run by the ECU which will adapt...