why wider tires on rear of x5?
 

Seen some 'older' pre-facelift x5's about and have wondered why they have smaller tires and narrower rear tires?anyone know?

not sure what the question is :)

Narrower tires (then the 315's found on the rear of most X5's) can be there for several reasons:

1) matched tires mean you can rotate them
2) smaller tires grab less "road" and thus less "road pull" when driving
3) the ride is generally smoother
4) in the winter, narrow is preferred over wide
5) smaller tires are cheaper
6) better fuel economy
7) most E53's (4.8/4.6 aside) came with matched wheels and tires, not staggered

cheers wagner, question is my e53 04 3.0d has rears 285/45 r19 and front 255/50 r19 bridgestone turanzas,are the rears wider for a reason? and where could I find for example if I can fit a 255/55 as opposed to 255/50 tire up fron't just curious as to whether there is a defintive list of the tire sizes one can use or not?

Ahh.

The X5 is rear drive bias, which means the rear is doing the majority of the work. More rubber in the back gives better traction and better handling in a curve. That is why some models come staggered (i.e. the performance variants for sure).

A definitive list? Not sure. I'm sure some of the regs on here can come up with something. :)

BTW: a 255/50 vs 255/55 is simply a change in overall diameter and sidewall height via the aspect ratio. The tire is no wider tread wise :) If you ran 255/55/19's on your X5 it would sit a little higher in the front.

thanks, that is the reason I wanted a list is to make sure I can stick a tire in the front that sits higher without compromising the cars ability or safety etc...hmmmm just wondering now how the drive distribution is on the x5, 50/50 or 40 front 60 percent rear

The pre-face lifts were a 62 rear 38 front distribution.

The primary reason why our rear tires are wider is appearance. It just looks cooler.

:thud:

neh.

Ok, well that response is hard to refute.

But let me try to flesh the point out a bit.

Look at heavy duty vehicles that are more industrial fleet oriented then consumer oriented. Many trucks and vans fit in this category. Look at the width of their tires, are they as wide as our tires? No, they are not. That's because wide tires don't have utilitarian advantages, they only have an advantage in that wide tires appeal to consumers. In fact, there are some disadvantages of wide tires. They are heavy, expensive, have poor hydroplaning characteristics and also do poorly in mud/snow.

If the wide tires had a functional advantage then you would see them on fleet vehicles of similar weight.

Re. our rear tires are wider because they do most of the work. Look again at the fleet oriented vehicles, do they have wider tires in the rear? No they don't. That tells us that it's a consumer issue, not a functional issue. And if this theory was correct, most front drive cars would have wider tires in front. Name a single one that does.

In fact, it's the front tires that do the most work because they support more weight, and they control turning the vehicle.

Consider this from a perspective of tire wear. Tire wear on street vehicles is a goat screw because they run an alignment intended to create understeer, that is to say if you take a corner too fast the front tires will slip and you will go off straight. So OEM alignment settings are deliberately unbalanced. That makes tire wear a little confusing because the tires alignment is deliberately unbalanced. By unbalanced I mean front vs. rear.

But in a race car the alignment is fine tuned to be as optimal as possible, so it's a pretty good measure of how much strain are on the tires. And front engine rear drive race cars always wear out their front tires first.

So the reason we have big fat tires, and the reason that our rear tires are fatter then our fronts, is all consumer preferences. Otherwise we would have the same narrow tires that fleet vehicles of similar weight use.

I think you are 1/2 right.

I don't agree with your points that it's only for looks.

Performance vehicles have wider wheels and tires. Not every day vehicles or fleet vehicles.

Fleet vehicles priorities are about fuel consumption, not increased handling characteristics. Narrow tires and ones made to have a lower rolling resistance are used to lower fuel consumption. You won't find wider tires in the rear there for performance reasons. You might find dual wheels in the back, then again, it's not for performance but for a wider base to support the weight of the load.

In my opinion, front wheel drive cars are not performance vehicles from a handling perspective, other than the potential argument for straight line racing. But not for me in any case. Even all wheel drive vehicles that have roots as front wheel drives have a different bias towards the front and wouldn't benefit from wider tires - front or rear. In fact, wider tires in the front would be an issue.

Performance handling cars like a Porsche Carrera have the weight in the rear and certainly perform better with wider tires.

I have several vehicles with wider tires in the rear, they are all performance oriented. In one of them, it came stock with equal width tires and I switched to staggered wheels/tires and gained better handling.

Plus they look better. Much better.