Subaru axle lengths

[DesignByDesign]

I am building a mid-engine sports car with an EJ20 / 6 speed man. transmission from a 2007 STI donor.
The track width of the STI (front) is 58.9" which is not enough for the setupof the rear track in the new build.
I see that all subaru models share the same front track dimension except the Tribeca which has 62.2" front track.
does anyone know if the Tribeca axles would fit the Impreza hub, and how much longer the axles are?

 

[patprimmer]

The extra track might be extra wheel offset rather than longer axles.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[DesignByDesign]

Thanks Pat.
You are right, of course!
Since you prompted me I checked the geometry of both cars & combined them (on the attachment) - I knew that the STI has 8.5" rims & the Tribeca 8", so did not expect these results!
The WRX has 7" rims but on the Subaru websites they quote the same track width for STI & WRX. That's what threw me.
I have always been told the centre of the wheel should be within the extents of the bearings & preferably biased over the larger inner bearing. The only Subaru that complies is the STI.
Question now is, if I put a 10.5" rim with only 10mm offset on this bearing will it still have an 'acceptable' lifespan?
Car weight is +/- 1100kg. (STI 1550kg, Tribeca 1880kg)
I dould really value your opinion.

 

[Bribyk]

You could ballpark the result of changing your bearing loads by placing a load "x" at the contact patch center plane, modeling the hub or spindle as a beam and the bearings as the supports (you'd change the relative distances for different wheel offsets).

Your bearing life is typically exponentially inversely proportional the the load with an exponent of between 3 and 4 (Juvinall, Machine Component Design). That is to say, if you double the load on a rolling element bearing you will only get 1/8th to 1/16th the lifespan out of it.

Then all you'd need is one of the experts on here to give you a typical design life for a wheel bearing (100,000 miles of street use?).

 

[patprimmer]

Many cars survive with extra track via wheel offset. How long the bearings last and if the stubs, knuckles and ball joints will survive depends on the reserve capacity of the original design. I have no idea how much safety factor is built into the parts you are considering.

If the Tribeca parts are the same, I would suggest there is some margin there when used on the lighter lower car.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[DesignByDesign]

Many thanks guys, this is really helpful feedback.
I appreciate your time.