Tyres different sizes

[caz_manc]

I just brought a car and yes I didn’t notice that the front tyres are bigger than the back tyres on a read wheel drive car. I find it odd, but the collective might be able to explain why?

So I have 225/50 16 on the front and 205/50 16 on the back on a 320d e46. Is this weird? Is there a good reason for it?

Would just like an explanation if anyone can let me know?

[kambites]

I'm not sure what sizes it's meant to have, but I suspect someone has rotated the wheels to even out tyre wear without realising they're different sizes. Are the wheels themselves the same width?

Edited by kambites on Friday 25th April 18:01

[r11co]

No good reason. Plenty of bad ones though. Previous owner probably didn't check when they were replaced, or bunged some incorrectly sized ones that they happened to have lying around on.

[caz_manc]

As the ones are at half way, would it be best to go back to the same size on all four?

[kambites]

caz_manc said:

As the ones are at half way, would it be best to go back to the same size on all four?

I suppose the instruction manual should say what size it should have at each end. It's not impossible that they're meant to be different, but if they are they're the wrong way around.

[esuuv]

I'd go with what Kambites says above - someone has swapped the tyres / wheels, front / rear without realising there is a stagger.

[jamieduff1981]

A friend's old E46 325Ci had staggered sizes front-rear. Wider on the rear, obviously.

[Leins]

kambites said:

I suppose the instruction manual should say what size it should have at each end. It's not impossible that they're meant to be different, but if they are they're the wrong way around.

But even then the rolling circumference is different on these, despite both being on 16" wheels. I would have thought if the 205/50 was correct for the front and a staggered approach was desired, then the rears should be 225/45?

[kambites]

Leins said:

kambites said:

I suppose the instruction manual should say what size it should have at each end. It's not impossible that they're meant to be different, but if they are they're the wrong way around.

But even then the rolling circumference is different on these, despite both being on 16" wheels. I would have thought if the 205/50 was correct for the front and a staggered approach was desired, then the rears should be 225/45?

Many cars have a larger rolling circumference on the rear than the front. Mine even has larger diameter wheels on the back (although admittedly it's not a mainstream saloon car).

It does cause something of an issue with spare wheels, though.

[Leins]

^^^ Aha, OK

It'd be a first on a BMW that I know of though, as any with a staggered approach tend to have very similar circumferences. I suspect with 16s on an E46 these shouldn't be staggered anyway and all four wheels will turn out to be 7J

Don't recall any BMWs with a larger diameter rear either

What's a spare wheel? Really must get a new can of foam for my E46

[NPI]

Leins said:

kambites said:

I suppose the instruction manual should say what size it should have at each end. It's not impossible that they're meant to be different, but if they are they're the wrong way around.

But even then the rolling circumference is different on these, despite both being on 16" wheels. I would have thought if the 205/50 was correct for the front and a staggered approach was desired, then the rears should be 225/45?

Most Merc's have a staggered set up. Mine has 205/55R16 on 7J wheels on the front and 225/50R16 on 8J wheels on the back. Same rolling circumference within 1mm.

[kambites]

Leins said:

What's a spare wheel? Really must get a new can of foam for my E46

Something that wouldn't fit in my boot even if the wheels were the same size.

You may be right that BMW don't do it, but certainly some manufacturers do. I had a feeling that wider rears were an option on the E46, but I haven't a clue about diameters. As you say I'd probably expect them to have similar rolling radius, but I'm not certain of that.

I doubt any mainstream saloon cars have different diameters wheels front and rear, although some certainly do have different width rims. Certainly a lower profile rear would make more sense if they're going to be wider.

[Leins]

^^^ I have 6J/7J 16s on my E30, but generally I think 16s on the E46 seem to be the same front/rear, as were 7-Star 17s. I think it's only when you get into M-Sport 17s that they started to stagger them, e.g. the 225/245 setup on the Compact Sport IIRC

Can't think of a saloon that came standard with different diameter wheels f/r though. Wasn't it a Honda trick with the NSX? Wonder if any of their saloons had it too?

[NPI]

Leins said:

^^^ Aha, OK

It'd be a first on a BMW that I know of though, as any with a staggered approach tend to have very similar circumferences. I suspect with 16s on an E46 these shouldn't be staggered anyway and all four wheels will turn out to be 7J

Don't recall any BMWs with a larger diameter rear either

I'm not that familiar with BMWs but whenever the staggered setup is discussed on Mercs, it's often stated that BMW do it too.

Maybe even Merc don't do it much now - I had an E350CDi Sport courtesy car recently and that had the same size all round. It's certainly a right pain not being able to rotate them as the front tyres last forever and I'm running into the area where tyre age is a concern.

[Leins]

^^^ Yes, BMW do it with loads of their cars in more recent years, but generally only with the larger diameter wheels. Most (all?) of the M-Sports will have a staggered set-up, and the vast majority of //M-cars built have too

Edited by Leins on Friday 25th April 19:21

[classicc]

Oppa

Edited by classicc on Friday 25th April 20:42

[Censorious]

kambites said:

caz_manc said:

As the ones are at half way, would it be best to go back to the same size on all four?

I suppose the instruction manual should say what size it should have at each end. It's not impossible that they're meant to be different, but if they are they're the wrong way around.

Yes kambites is probably right here.

BMW commonly use larger tyres on the rear and the difference in width you have would be about right for staggered tyres sizes. You'll probably find that the wheel rim sizes are different too but it can be difficult to spot this unless you measure them.

[Mustard]

16" wheels should have the same size tyres front and rear on the E46

Should be either 205 55 16

Or the ES specification was fitted with 225 50 16

205 55 16' s are a fair bit cheaper than the 225 50 16's, is yours an ES that somebody's try to save some money on the tyres?

[kambites]

Mustard said:

16" wheels should have the same size tyres front and rear on the E46

Should be either 205 55 16

Or the ES specification was fitted with 225 50 16

In that case it sounds like some muppet just fitted the wrong tyres to it. Still if I was the OP I'd swap them over and put the bigger ones on the back (assuming he doesn't want to replace them).

[caz_manc]

Thanks for all the comments. I am going to swap them round again, as there is enough trend on them for the back.

I forgot to say it is a compact and has a sport steering wheel, but I think that has been changed for show.