What is the maximum 18 inch profile I could fit?

[Blacknight05]

My ride is 320i E93, been changing my rims and tyres at SouthEast Kaki Bukit for a number of years now, but suddenly felt shortchanged when I looked at my tyres this evening.

Changed my first set of 4 tyres early this year on PSS 245/40 R18, they charged me $400 each.
Changed my second set of staggered in Sep, same size of PSS, but front only 225/40 and rear 255/40, they charged me the same price at $400 each. The boss even boasted he was not charging me extra for the upsized rear.

I only discovered this evening that the front is only 225/40, so he was just balancing the price of the front and rear. No wonder I keep feeling my tyres are so small and weak, while my 245/40 are looking big.

What Is the maximum profile of the tyre I could fit for my 18 front? Thanks in advance

 

[Baby1M]

Re: What is the maximum 18 inch profile I could fit?

My ride is 320i E93, been changing my rims and tyres at SouthEast Kaki Bukit for a number of years now, but suddenly felt shortchanged when I looked at my tyres this evening.

Changed my first set of 4 tyres early this year on PSS 245/40 R18, they charged me $400 each.
Changed my second set of staggered in Sep, same size of PSS, but front only 225/40 and rear 255/40, they charged me the same price at $400 each. The boss even boasted he was not charging me extra for the upsized rear.

I only discovered this evening that the front is only 225/40, so he was just balancing the price of the front and rear. No wonder I keep feeling my tyres are so small and weak, while my 245/40 are looking big.

What Is the maximum profile of the tyre I could fit for my 18 front? Thanks in advance

Hi Blacknight05,

Unsure if there's any typo errors... anyway no worries, being RWD, it is fine to use staggered. My E82 is staggered at 225/40R18 and 255/35R18.

More importantly is below...

I do not know your 'factory' tyre configuration so I shall based on your post's configuration is 225/45 R17 (front & back)...

However... being staggered, your setup is NOT QUITE RIGHT giving you an imbalanced speed difference between Front & back wheels plus higher error in your speedometer reading.

Your staggered setup should be 225/40R18 (front) with 255/35R18 (rear)... both upsized tyre has near idential errors (has to be) over 225/40R18 & 255/40R18 (both errors are differed by 1 to 2km/h) resulting in the best near correction speed reading on the speedometer.

The above is based on 225/40/R18 as standard 'factory' fit.

You should have used the free online 'upsize' calculator to check which is the proper sizing to minimise speedometer reading errors.

Cents worth.

 

[Blacknight05]

Re: What is the maximum 18 inch profile I could fit?

Typo here, my front is 225/40 and rear 255/35.

Will it help to increase size 235/40 or 245/40 for front? What are the limitations?

 

[Baby1M]

Re: What is the maximum 18 inch profile I could fit?

Typo here, my front is 225/40 and rear 255/35.

Will it help to increase size 235/40 or 245/40 for front? What are the limitations?

Just IMO, with staggered setup of front 225/40 and rear 255/35 is good to go... because this staggered setup has the least error and most compatible.

I will not advise swapping the front to 235/40 or 245/40 or 245/35 but final decision is yours... look at the below data for consideration... when your rear 255/35R18 is at 60 mph:

225/40 will be at 60.14 mph (diff of 0.14) - Your current front setup

235/40 will be at 60.9 mph (diff of 0.49)

245/40 will be at 61.65 mph (diff of 2.75)

245/35 will be at 59.34 mph (diff of 0.66)

Of course minimum difference will be advised.

 

[Blacknight05]

Re: What is the maximum 18 inch profile I could fit?

Thanks, but I thought the speed reading is affect by the profile thickness, 35 and 40 instead of the profile width? Correct me if I'm wrong. Cheers!

 

[Red_Bean_Bun]

Re: What is the maximum 18 inch profile I could fit?

Tire profile is a percentage of tyre sidewall versus width ........

Main impact .....

- speed readings (Overall diameter)
- Rotational mass (affects acceleration)
- braking (patch shape changes due to tyre width increase)

Usually one would plus size 1 or 2 levels above stock based on what is prescribed on the cards by the side of the door .....

 

[esis311]

Re: What is the maximum 18 inch profile I could fit?

RBB is very correct, width(225 front) and 255(rear) are the correct size for speedometer reading, only the front width rim size is usually 8", combining with 225 size will have a situation where the surface of the side wall tyre and the rim being at flat surface, rim being scratched to concrete wall during parking, fitting 235 size will eliminate this issue and not affecting the speed reading as 320i is rear wheel drive.
The other negative affect fitting an extra wide tyre in the front will create larger force to turn the wheel, all the bushing steering arm rubber will wear off faster.
For rear fit, 8.5" rim with 255 width will eliminate the scratched issue, this size is more than sufficient to handle the 2.0 liter engine.
Availability of tyre width, height profile, rim width selection are limited to fit all your expectation.
Its a matter of personal preference, have fun.

 

[Blacknight05]

Re: What is the maximum 18 inch profile I could fit?

I'm on 8.5" front with 225/40 R18 and 9.5" rear with 255/35 R18.
Rear looks ok, but my front got big gap, very eye sore.

View attachment 65561

 

[Red_Bean_Bun]

Re: What is the maximum 18 inch profile I could fit?

One of the reasons many switched to coilovers ...... get complete control over height and dampening needs ........

I'm on 8.5" front with 225/40 R18 and 9.5" rear with 255/35 R18.
Rear looks ok, but my front got big gap, very eye sore.

View attachment 65561

 

[louisliu]

Re: What is the maximum 18 inch profile I could fit?

Hi... juz a side question.. i have a set of 19 inch bbs rims+conti tyres.. like to change to 17 inch.. any recommemdation hw much i can trade in n where to trade in?