Outer Limits 4x4 Board

g'day people, this question might sound stupid to you 4x4 gurus on this site but why do most 4x4 ers change there rim size to from 16 to 15 inch

cheers

Generally tyre cost and availability. Also gives slightly taaler side wall allowing more tyre flex. Although most vehicles fitted with 16" rims won't fit 15" due to the size of the brake rotors and callipers.

hill billy wrote:g'day people, this question might sound stupid to you 4x4 gurus on this site but why do most 4x4 ers change there rim size to from 16 to 15 inch

cheers

cost of tires, more sizes available in different tires. But that gap is closing now

does it change low down power etc

hill billy wrote:does it change low down power etc

how can it?

Its the tire that makes the difference no the rim.

31inch tire is a 31inch tire contacting the ground.

yes but by having 15in rims abd using 31in tyres compared to the size for 16 would thee be any difference

If you want to do it, just look for the overall diameter or circumference of the tyre.
Like bogged said, a 31" tyre is just that and wouldn't matter if it had a 20" rim inside of it.
A 33" tyre however would have the car revving lower, but would feel a bit less powerful.
A lot of the tyres to suit 16" rims are measured in metric 265/75/16 where 265 is the tyre width, 75 is the percentage of that width which equals the sidewall height and 16 is the rim size.
Most tyres to suit 15" rims are measured like 31x10.5x15 31" overall diameter, 10.5" width 15" rim.

Tyre websites should have info

if you are considering doing this make sure 15" rims fit first, for the reasons I mentioned above.

hill billy wrote:yes but by having 15in rims abd using 31in tyres compared to the size for 16 would thee be any difference

15inch rim with a 31in tire,
is same as a 16,17,18,19 or 20in rim with a 31in tire.

the outside diameter is always the same.

YMMV

http://www.outerlimits4x4.com/PHP_Modul ... =rim+sizes

Cheers,
Ryano

Yes bogged they are the same overall diametre.
Look deeper
But has anyone consided the weight differences.
One has more rubeer making up the 31 inches and one has a higher percentage of steal rim.

Now when I went form 32's to 35's on my cruiser I lost a hell of a lot of power, and I dont take this crap about my gearing beaing to high as 1st gear is still frigging low and even if I keep revs high power is still not there.

I assume it must be the weight. So this being true

Would 15's not help with power as I would assume they would be a lighter combination.

On the downside I believe they are not as good for touring as they have a larger and weaker side wall more prone to staking.
Burnsy

no mate it is ur gearing, nothing to do with weight .

So turning a tyre that ways a shit load more changes nothing

bruiser wrote:Yes bogged they are the same overall diametre.
Look deeper
But has anyone consided the weight differences.
One has more rubeer making up the 31 inches and one has a higher percentage of steal rim.

Now when I went form 32's to 35's on my cruiser I lost a hell of a lot of power, and I dont take this crap about my gearing beaing to high as 1st gear is still frigging low and even if I keep revs high power is still not there.

I assume it must be the weight. So this being true

Would 15's not help with power as I would assume they would be a lighter combination.

On the downside I believe they are not as good for touring as they have a larger and weaker side wall more prone to staking.
Burnsy

I cant see weight being that much different..

The other thing with larger rims is less sidewall to flex, which gives better ride on the road, main reason most road cars are comin out with bigger rims. Go for a ride in an EH with 13inch rims

bruiser wrote:So turning a tyre that ways a shit load more changes nothing

the weight diff aint that much more and going to a 15" rim might save u a kilo

now whats sucking up all ur power is the increased rolling diameter of the tyre. You have he same power et,c as before but the truck has to push the bigger tire around means it uses up the power u have quicker, so it u change ur gearing from say 4.3:1 to 4.88:1 you will find it drives like it did before.

you will prolly also realise about now your speedo is out, this is becuase the tire size has affected the final drive ratio.

http://www.4lo.com/calc/geartire.htm

The difference between a 32 and 35 at a glance......

OD difference - 76mm
Rolling Circumference Difference - 240mm
35's do 33.57 revolutions/km less than 32's.
When your speedo reads 100k/h, your actual ground speed will be 109.38.

It's going to sap some power out to turn the extra tyre.

Cheers,
Ryano

Not just the speedo but the odometer as well.
Untill recently forgot to take this into account when working out my fuel economy. Economy does not seem quite as bad now.

Not sure how much extra weight there is when you go up in tyre size, but if significantly the case then extra weight also taxes the brakes. More inertia to slow down.