Hi guys,
Today I got a flat up at stockton beach and when I got the spare out I noticed that it was larger than my other tyres.... 30" against 32"
What I'd like to know is if driving with 2 different tyres of different sizes on the same axel (rear drive axel) will damage anything?
Thanks.
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2 Different tyre sizes...?
Moderators: toaddog, TWISTY, V8Patrol, Moderators
Not quite true...
For rear axle applications:
If you have an LSD (any clutch pack type) you will burn the cluch pack out if driven on bitumen for any length of time, it will also tug like a bull on the froint end.
If you have an auto locker on that axle it will have very strange handling due to only one wheel being driven (larger of the two) until well into a turn to the same side as tha smallest wheel, when the smaller suddenly takes the drive.
The only time you will not get any grief is with an open rear diff. Even then the different sized wheel should ONLY go on the rear axle....
Simplest solution - buy a matching tyre. This will keep your insurance company onside too, as driving with dissimilar sized wheels on the one axle renders your vehicle technically unroadworthy = no insurance.
For rear axle applications:
If you have an LSD (any clutch pack type) you will burn the cluch pack out if driven on bitumen for any length of time, it will also tug like a bull on the froint end.
If you have an auto locker on that axle it will have very strange handling due to only one wheel being driven (larger of the two) until well into a turn to the same side as tha smallest wheel, when the smaller suddenly takes the drive.
The only time you will not get any grief is with an open rear diff. Even then the different sized wheel should ONLY go on the rear axle....
Simplest solution - buy a matching tyre. This will keep your insurance company onside too, as driving with dissimilar sized wheels on the one axle renders your vehicle technically unroadworthy = no insurance.
George Carlin, an American Comedian said; "Think of how stupid the average person is, and realise that half of them are stupider than that".
Also not True.DAMKIA wrote:The only time you will not get any grief is with an open rear diff. Even then the different sized wheel should ONLY go on the rear axle....
For Example at 100kph the axle gears,star gears and cross shaft get very little lubrication so if you are driving allong with 2 different size wheels at 100kph the star gears are spinning flat out and there is little lubrication on them. Usually you will find it will quickly seize the star gears to the cross shaft. Next the cross shaft breaks and the broken pieces make their way out and into the crown and pinion.
The exact same thing happens when you do a burn out with an open diff. Usually they spin one wheel untill the star gears start to lock onto the cross shaft then you get both wheels going.
If you need to fit a different size tyre then allways fit it to the front and reduce your speed as the steering will be a little out but there is bno way unless you have the hubs locked that you can cause any real harm in the short term.
Wouldn't the diff center be rotating with the ring gear, thereby dunking the dowel and side gears in the sump of oil in the housing, or at least gaining significant splash lubrication from the ring gear? We are only talking about a difference in axle speeds of ~6-7%. (I don't really think we are talking about single wheel burnouts, just the "getting home" scenario)RUFF wrote:Also not True.DAMKIA wrote:The only time you will not get any grief is with an open rear diff. Even then the different sized wheel should ONLY go on the rear axle....
For Example at 100kph the axle gears,star gears and cross shaft get very little lubrication so if you are driving allong with 2 different size wheels at 100kph the star gears are spinning flat out and there is little lubrication on them. Usually you will find it will quickly seize the star gears to the cross shaft. Next the cross shaft breaks and the broken pieces make their way out and into the crown and pinion.
The exact same thing happens when you do a burn out with an open diff. Usually they spin one wheel untill the star gears start to lock onto the cross shaft then you get both wheels going.
If you need to fit a different size tyre then allways fit it to the front and reduce your speed as the steering will be a little out but there is bno way unless you have the hubs locked that you can cause any real harm in the short term.
It is (absolutely) against the law to have different wheel sizes on the front for good reason, as there are too may handling compromises with steering and braking. (Like steering with a flat tyre)
George Carlin, an American Comedian said; "Think of how stupid the average person is, and realise that half of them are stupider than that".
It is just as absolutly illegal to have 2 different tyre sizes on the rear. For exactly the same reason.DAMKIA wrote:It is (absolutely) against the law to have different wheel sizes on the front for good reason, as there are too may handling compromises with steering and braking. (Like steering with a flat tyre)
And at 100kph the centrifical force inside the Hemisphere would force most of this oil out.
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