why wider tires on rear of x5?

[Ranger]

Originally Posted by X5rolls

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.

Your fuel consumption arguement is reasonable as a factor, but it doesn't alter the validity of the point.

Referring to our truck as "performance oriented" from a tire handling perspective is optimistic. For all practical purposes, Tire's don't really "handle" until they start to slip. This assumes a quality tire and a suspension in good order. Max traction is acheived at 4-8deg of slip, depending on the tire. It's the interplay of suspension, weight distro, tire geometry and tire compound that determines the degree of slip on all 4 corners of the car, millisecond to millisecond. That varying degree of slip at all 4 corners is what tire "handling" is all about.

Note that I'm not talking about the car's handling, because that adds all the suspension components and car's static weight distro, into the equation. I'm only talking about the handling of the tire itself.

How often does the X5 owner take a corner so fast that the tires develop a slip angle? I see "performance oriented" trucks and SUVs on the track occasionally, but it's still pretty rare. We drive our X5's well within the limits of the tires, which is to say, no slip. So talking about the handling of our tires is almost a moot point. Not entirely so, because there are some handling characteristics that occur below the slip threshold, but they are pretty inconsequential.

Yes, performance vehicles do have wider wheels and tires. But why? On an ideal surface the force of friction is independent of surface area. And although roads aren't an ideal surface, it's not a strong arguement to say that fleet vehicles have accepted risk in reduced traction in order to optimize gas mileage. They have accepted very little risk because traction isn't reduced much under normal (meaning no slip angle) conditions.

And since we don't drive our trucks so hard that they acheive slip angle, "normal conditions" pretty much applies to us too.

Re. front wheel drive cars are not performance oriented. There's a lot of folks that would be surprised to hear that. There's numerous race series' devoted to front wheel drive car's. I can probably come up with a dozen just off of the top of my head. A couple Pro ones are Mini Challenge and Volkswagon TDI Challenge. NASA (North American SportsCar Assoc), the guys I race with have Honda Challenge 1-4, and numerous front wheel drive cars in GTS1-3.

Your Porsche example doesn't fly. 911 based cars are rear weight biased, and our X5's are front weight biased. I spent a couple yrs on the track in 911's and they are great cars. But they demand a lot from the rear tires and they wear quickly. In contrast, we don't demand much from our rear tires.


Re. You bought bigger rear tires for your car and it handled better. No offense, but whenever we spend money on our cars we're always convinced of the resulting improvement. But "feeling" it and having dyno or data logger records from the track are two different things.

[X5rolls]

Originally Posted by Ranger

Your fuel consumption arguement is reasonable as a factor, but it doesn't alter the validity of the point.

Referring to our truck as "performance oriented" from a tire handling perspective is optimistic. For all practical purposes, Tire's don't really "handle" until they start to slip. This assumes a quality tire and a suspension in good order. Max traction is acheived at 4-8deg of slip, depending on the tire. It's the interplay of suspension, weight distro, tire geometry and tire compound that determines the degree of slip on all 4 corners of the car, millisecond to millisecond. That varying degree of slip at all 4 corners is what tire "handling" is all about.

Note that I'm not talking about the car's handling, because that adds all the suspension components and car's static weight distro, into the equation. I'm only talking about the handling of the tire itself.

How often does the X5 owner take a corner so fast that the tires develop a slip angle. I see "performance oriented" trucks and SUVs on the track occasionally, but it's still pretty rare. We drive our X5's well within the limits of the tires, which is to say, no slip. So talking about the handling of our tires is almost a moot point. Not entirely so, because there are some handling characteristics that occur below the slip threshold, but they are pretty inconsequential.

Yes, performance vehicles do have wider wheels and tires. But why? On an ideal surface the force of friction is independent of surface area. And although roads aren't an ideal surface, it's not a strong arguement to say that fleet vehicles have accepted risk in reduced traction in order to optimize gas mileage. They have accepted very little risk because traction isn't reduced much under normal (meaning no slip angle) conditions.

And since we don't drive our trucks so hard that they acheive slip angle, "normal conditions" pretty much applies to us too.

Re. front wheel drive cars are not performance oriented. There's a lot of folks that would be surprised to hear that. There's numerous race series' devoted to front wheel drive car's. I can probably come up with a dozen just off of the top of my head. A couple Pro ones are Mini Challenge and Volkswagon TDI Challenge. NASA (North American SportsCar Assoc), the guys I race with have Honda Challenge 1-4, and numerous front wheel drive cars in GTS1-3.

Your Porsche example doesn't fly. 911 based cars are rear weight biased, and our X5's are front weight biased. I spent a couple yrs on the track in 911's and they are great cars. But they demand a lot from the rear tires and they wear quickly. In contrast, we don't demand much from our rear tires.


Re. You bought bigger rear tires for your car and it handled better. No offense, but whenever we spend money on our cars we're always convinced of the resulting improvement. But "feeling" it and having dyno or data logger records from the track are two different things.

I understand your points – I think we can agree to disagree on some of them though. First, I should qualify that my answers were from a street perspective. You have a much better base of knowledge on the track than I do so I would defer to your experience.

My 4.8is is performance oriented - I'd not suggest it's because of the tires but because of the sum of it's parts. I'd have to go and check other tire and wheel sizes for other X5's but I'd bet (not a big $ number) my set up has a bigger footprint, shorter sidewalls and compounds (in the summer versions) oriented to more performance oriented street driving.

My buying bigger rear tires for one of my cars did make the car handle better - the sidewalls are shorter. It just holds the road better in turns and takes more power to swing the back end out, therefore I can come out of turns with more power/speed. I couldn't get the same tire size on the previous wheel used and these would not fit on the front of the car – so staggered is the only option.

Not sure I'd ever like the way even a performance front wheel drive car drives no less races. It's preference. Although I’ve not owned a performance front driver, I’ve had a few 200 + HP ones and I didn’t like them after a short time. I'm strictly rear or all wheel drive biased. Front, mid or rear engine based. Front wheel issues with torque steer, overloading the tires in the front and push all are not favorable characteristics in a car trying to race, take corners quickly etc. IMHO. I’m sure that is were the science, R&D and driver expertise combine to make these cars very competitive.

I have pushed my X5 pretty hard on the street, ABS engaging on dry pavement and hearing the great sound of Michelins howling on occasion. Having said all that however, I’d still enjoy the opportunity to drive one of these front wheel cars that been purpose built for racing. I have an open mind, especially if it involves going fast J

[Ranger]

Originally Posted by X5rolls

I understand your points – I think we can agree to disagree on some of them though. First, I should qualify that my answers were from a street perspective. You have a much better base of knowledge on the track than I do so I would defer to your experience.

My 4.8is is performance oriented - I'd not suggest it's because of the tires but because of the sum of it's parts. I'd have to go and check other tire and wheel sizes for other X5's but I'd bet (not a big $ number) my set up has a bigger footprint, shorter sidewalls and compounds (in the summer versions) oriented to more performance oriented street driving.

My buying bigger rear tires for one of my cars did make the car handle better - the sidewalls are shorter. It just holds the road better in turns and takes more power to swing the back end out, therefore I can come out of turns with more power/speed. I couldn't get the same tire size on the previous wheel used and these would not fit on the front of the car – so staggered is the only option.

Not sure I'd ever like the way even a performance front wheel drive car drives no less races. It's preference. Although I’ve not owned a performance front driver, I’ve had a few 200 + HP ones and I didn’t like them after a short time. I'm strictly rear or all wheel drive biased. Front, mid or rear engine based. Front wheel issues with torque steer, overloading the tires in the front and push all are not favorable characteristics in a car trying to race, take corners quickly etc. IMHO. I’m sure that is were the science, R&D and driver expertise combine to make these cars very competitive.

I have pushed my X5 pretty hard on the street, ABS engaging on dry pavement and hearing the great sound of Michelins howling on occasion. Having said all that however, I’d still enjoy the opportunity to drive one of these front wheel cars that been purpose built for racing. I have an open mind, especially if it involves going fast J

Your response is fair and reasonable. Like you I've owned a couple FWD cars but they don't strike me as ideal for performance driving either.

I see that you live in Maryland. There's a number of great tracks in your area that host "Driver's Education" events all the time. You show up with your sedan, are handed an instructor for the day, and have the greatest time of your life. It will almost make you swear off chicks and beer.

Next year's schedules will be posted soon. So in a couple weeks check out
www.MotorsportsReg.com
www.TrackSchedule.com

[X5rolls]

Originally Posted by Ranger

Your response is fair and reasonable. Like you I've owned a couple FWD cars but they don't strike me as ideal for performance driving either.

I see that you live in Maryland. There's a number of great tracks in your area that host "Driver's Education" events all the time. You show up with your sedan, are handed an instructor for the day, and have the greatest time of your life. It will almost make you swear off chicks and beer.

Next year's schedules will be posted soon. So in a couple weeks check out
www.MotorsportsReg.com
www.TrackSchedule.com

Thanks for the heads up - I have been thinking about doing this for a while.

[omodos]

You guys are lucky, out here in cyprus the most exciting ride would be wehn you squash the odd snake or avoid the odd sheep that has deserted the flock, apart from that it is pretty cool come to thinkof it, got the highest number of cars per head of popluation in europe and not a very densley populated place so you can push the car nicely...and enjoy it....ok so fat tires at the back look better is the conclusion plus more traction due to larger surface area in contact with road...cool

[X5rolls]

Originally Posted by omodos

You guys are lucky, out here in cyprus the most exciting ride would be wehn you squash the odd snake or avoid the odd sheep that has deserted the flock, apart from that it is pretty cool come to thinkof it, got the highest number of cars per head of popluation in europe and not a very densley populated place so you can push the car nicely...and enjoy it....ok so fat tires at the back look better is the conclusion plus more traction due to larger surface area in contact with road...cool

Sounds pretty cool - do you know Greek by the way? If so can you translate?

There is a cool M6 video where it's going 340km/hr.


http://www.metacafe.com/watch/190910...ching_340km_h/

[omodos]

Originally Posted by X5rolls

Sounds pretty cool - do you know Greek by the way? If so can you translate?

There is a cool M6 video where it's going 340km/hr.


http://www.metacafe.com/watch/190910...ching_340km_h/

Yup speak Greek, thanks, and for you to know that is quite impressive as when I visited the states a couple of times nobody knew where Cyprus was let alone know what the native language was .Here is the translation but not sure your laptop/p/c will display the greek text properly :

Υπάρχει ένα πρώτο Μ6 βίντεο που το δείχνει να φτάνει 340km/hr

[X5rolls]

Thanks, geography and history are a few of the subjects I enjoy. Did you get a chance to hear what the guys in the video are saying? I bet one of them is saying, "ok already, slow down!"

[lo_jack]

I would have to agree with Ranger as applies to X5s. Now, If you are trying to launch a RWD sports car at the track, and have the motor, going from a 245 to a 315 will make a huge difference, but you would only want to add as much wheel as it takes to accommodate the extra width without making the sidewall deflect beyond design. Ranger is right because X5s a)don't really go to the track that much and b)do not have the motor to really break the rears loose in a dry 'performance' environment, like a quartermile launch.