question about 18" RIM

[sewell]

i dont know how actually BMW engineer calculate tyre size to a car. car vs engine ? as we can see toyota vios, J spec, G spec, both using the same 1.5 engine but their profile is different.

can anyone told me which tyre profile suit my car most?

 

[bmw7833]

i dont know how actually BMW engineer calculate tyre size to a car. car vs engine ? as we can see toyota vios, J spec, G spec, both using the same 1.5 engine but their profile is different.

can anyone told me which tyre profile suit my car most?

U can refer to the sticker on the driver door body.

 

[xstatic]

Tire size has no effect on gear ratio; the gear ratio itself is a fixed mechanical constant determined by the number of teeth on the axles input (pinion) gear and output (ring) gear. However, tire size can, and does, affect the vehicle's "effective" gear ratio, which is a somewhat more complicated matter.
.Tire Cicumference
Effective ratio is all about how much ground the tire covers per revolution (a.k.a. "circumference"), which has everything to do with its diameter. Tire circumference is easy to calculate using that old grade-school formula "2 x Pi (3.14) x R (radius)." We'll use a 30-inch-tall (30-inch diameter) tire as an example. Two multiplied by 3.14 equals 6.28; since radius is equal to half of diameter, we'll next multiply 15 (30 divided by 2) by 6.28 to get 94.2 inches in circumference. You can actually just use the shortcut "Diameter x 3.14" in this particular instance, since you're multiplying by two and then dividing by it.
Size Difference
As in the above example, say you're switching from a 30-inch-tall tire to a 40-inch tire. The 40-inch tire covers 125.5 inches per revolution, which is 31.4 more than the 30-inch. Divide 31.4 by the original tire's circumference and you arrive at 0.333, which, when converted to percentage, comes out to 33.3 percent. That's the effective drop in gear ratio you'll experience when switching to the larger tire. The equation looks like this: "N" (circumference of new tire) minus "O" (circumference of old tire) equals "D" (difference). "D" divided by "O" equals the change in percentage.
New Effective Ratio
Effective ratio is vitally important since it's directly relative to your vehicle's torque output and acceleration. To get the effective ratio, multiply the percentage in change by the original gear ratio and then subtract from the axle ratio. We'll say 0.333 times a stock axle ratio of 4:1 (1.333), which nets you a new ratio of 2.7:1.
Restoring Stock Ratio
If you're running larger tire and want to return your vehicle to its stock effective gear ratio and acceleration, you'll need to change out the gearset in the differential. To find out what your new ideal gear ratio will be, simply add the percentage in change from the old ratio (1.333 in our example) to your existing ratio. In this example, that leaves you looking for a new gearset with a 5.333:1 ratio.
Dynamic Changes
Not all changes in performance due to tire diameter are necessarily bad. changing tires is a good way to make minor changes to your vehicle's acceleration and top speed without having to resort to a gearing change in the differential. For instance, if you're drag racing and your engine hits its red-line before you hit the end of the drag-strip, you can install larger tires to lower the effective gear ratio. The opposite also holds true. If, at the end of the drag strip, your tachometer reads 1,000 RPM below the engine's peak power RPM then you can see some serious gains in acceleration by simply switching to a smaller tire
.

 

[sewell]

For E39 is it the rim size offset has to be only 20 ?

 

[bmw7833]

15-20 to be exact if i am right.

 

[jaleeks23]

for 17 inch should pair with 225/45/17...235 is not suitable...245/45 is way out!
Not only will your speedo being not accurate, your gear ratios will be affected as well, as they are calibrated for a specific tyre diameter. In long run, not very good for the gearbox.
Just my humble opinion.

Bro,
Please help me understand why the size I'm using is way out... I used this site :- http://www.miata.net/garage/tirecalc.html to do a check on which closest tyre I should use. Below shows the readings. From the readings, it shows 245/45 R17 closest to 225/55 R16 in terms of speedo, revs/mile. Thanks.

Standard stock is 225/55 R16
Sidewall: 4.9in
Radius: 12.9in
Dia: 25.7in
Circumference: 80.9in
Revs/mile: 783

New tire is 225/45 R17 (3% too fast)
sidewall: 4.0in
Radius:12.5in
Dia:25.0in
Cir:78.5in
Revs/mile:808.0

New tire is 235/45 R17 (1.6% too fast)
sidewall:4.2in
Rad:12.7in
Dia:25.3in
Cir:79.6in
Revs/mile:796.0

New tire is 245/45 R17 (0.2% too fast)
sidewall:4.3in
Rad:12.8in
Dia:25.7in
Cir:80.7in
Revs/mile:785.0

 

[xstatic]

Bro,
Please help me understand why the size I'm using is way out... I used this site :- http://www.miata.net/garage/tirecalc.html to do a check on which closest tyre I should use. Below shows the readings. From the readings, it shows 245/45 R17 closest to 225/55 R16 in terms of speedo, revs/mile. Thanks.

Standard stock is 225/55 R16
Sidewall: 4.9in
Radius: 12.9in
Dia: 25.7in
Circumference: 80.9in
Revs/mile: 783

New tire is 225/45 R17 (3% too fast)
sidewall: 4.0in
Radius:12.5in
Dia:25.0in
Cir:78.5in
Revs/mile:808.0

New tire is 235/45 R17 (1.6% too fast)
sidewall:4.2in
Rad:12.7in
Dia:25.3in
Cir:79.6in
Revs/mile:796.0

New tire is 245/45 R17 (0.2% too fast)
sidewall:4.3in
Rad:12.8in
Dia:25.7in
Cir:80.7in
Revs/mile:785.0

Sorry bro, u were right...
Original rims was 225/55/16....not 225/55/15...my bad.
Cheers

 

[xstatic]

For E39 is it the rim size offset has to be only 20 ?

For the rear, most u can go 25 (if u lower your car)...subject to how low your car, u might need to roll your fender.
As for the front...like bmw 7833 said, 15-20. anything bigger, u need a widebody kit.
Best if you can get rims that are offset15 front and 20 rear...then it will be flush with the body

 

[xstatic]

For the rear, most u can go 25 (if u lower your car)...subject to how low your car, u might need to roll your fender.
As for the front...like bmw 7833 said, 15-20. anything bigger, u need a widebody kit.
Best if you can get rims that are offset15 front and 20 rear...then it will be flush with the body

Are you running on staggered rims? The above comparison is based on staggered setup with lowered springs. Rim width is F 8.5j and R 9.5 j...And changing offset to cater for wider rims does affect the handling, especially the braking com ponents.

 

[xstatic]

try using this to calculate...
http://www.1010tires.com/wheeloffsetcalculator.asp

 

[xstatic]

And some articles I came across...

OFFSET
Just because the wheel centers correctly doesn’t mean that it fits correctly. This means that the offset could be wrong. The offset is the location of the flat mounting surface of a wheel relative to the wheel’s centerline. A negative offset indicates that the mounting surface is toward the center of the car, and a positive offset that it is toward the outside of the car. It will appear that the wheel is pulled in toward the center. Offset will lead to more problems than just making the wheel appear to be sticking out of the fender. It can lead to rubbing problems when the suspension is compressed or the wheel is cut to turn. Offset also affects the steering geometry’s scrub radius, possibly leading to problems with the torque steer or the self-centering characteristics.

Offset can also affect the suspension’s motion ratio, which determines directly the effective spring and damper rates. In a heavily loaded vehicle, offset can potentially affect wheel bearing life. This problem though is seen more in trucks than in smaller cars. This is why using the proper offset wheels are essential.

Brake caliper clearance also comes into play when discussing offset. When choosing a set of wheels, it is important to make sure that the ones you choose do fit over the calipers. Spacers are available to alleviate this issue, but it is recommended to purchase a set of wheels that do cover the calipers and meet the offset specifications. You can be sure of this by contacting your wheel and brake manufacturers. Some aftermarket brake companies will provide you with a template of their brakes for you to check against your prospective wheels.

 

[sewell]

till now still not yet find my ideal rim. style 65 anyone selling?