Track width

[BipDBo]

Here's something that has bugged me a bit since this contest started. The front track width is 58.5", just slightly wide than the rear, at 58.3". We have had a lot of debate about what the F?R weight distribution will be, but i know that most of the weight will be on the rear. It will probably be 60-65%, but likely closer to 60%. Anyway, the trend seems to be that the more weight that is on the rear of a car, the wider the rear track is as compared to the front. This makes perfect sense that this would be optimal. I assume that they are planning to use stock WRX wheels, which are all the same width, so I don't think that this is a matter of wider tires in the rear.

Here's an example: Porsche 911
Track Width, Front 61.6"
Track Width, Rear 63.8"
Weight distribution: 39/61
5737

Here's an extreme example, but it relies a lot on torque vectoring:
Deltawing concept
Weight distribution: 27.5/72.5
5738

I am not well educated on the nuances of suspension systems. maybe the 911 is just wide in the rear to accomodate a flat 6 and some wide rubber, but I think there's more to it. Can someone enlighten me as to why Factory 5 made the rear track on the 818 slightly more narrow than the front?

[vozproto]

I'm not sure I know why either... but at least this may be a clue as to one of the biggest reasons...
The WRX has similar dimensions.

2005 WRX track width
Track Front 1,485 mm (58.5 in)
Track Rear 1,480 mm (58.3 in)

Otherwise a quick googling turned up this discussion that I think may answer many of your questions...
http://www.f1technical.net/forum/viewtopic.php?f=4&t=6311

[BipDBo]

I'm not sure I know why either... but at least this may be a clue as to one of the biggest reasons...
The WRX has similar dimensions.

2005 WRX track width
Track Front 1,485 mm (58.5 in)
Track Rear 1,480 mm (58.3 in)


That answers the question as to why they did it.

The 818 will have new suspension arms and there was some speculation that Factory 5 may need to provide new driveshafts, so they should be free to play with the track widths. So that leaves the question, would the 818 be better with different track widths, theoretically. Costs aside, would it be better with front tires that are more narrow than the rear like the 911?

[Draco-REX]

You can always widen the rear track with wider rims/tires and lower offsets. Unlike the AWD WRX the 818 can run different wheels front to back. I'm planning to do this as I should be making over 300whp with my build. So wider rears with possibly a low 30s offset will give a few more inches of width. I'll likely have to run fender flares.

[Nelff]

I really don't mind if the track is a bit different front to rear. I wouldn't mind the ability of deeper wheels in the back. I was planning on going aftermarket with the wheels anyway...

The only thing that would concern me if the track is more than an inch or so different. If the track is very different the car 'points' differently when the suspension is loaded on a banked surface.

[flytosail]

Anyways, would the track difference be changeable depending on tire width or is that accounted for?

[PhyrraM]

Strictly on a technical level...

Front track is limited by the range of adjustment in the Subaru steering rack. I'm guessing that Jim picked a front track very close to stock to keep the tie-rod adjusments close to stock. There are also some suspension geometry reasons to stay close to stock, but only Jim can say how and why he chose his camber curves, toe curves and such.

Rear track is limited by how FFR decides to interface the front inner CV joint (transmission) to the rear outter CV joint (hub/knuckle). The easiest way is to fabricate a CV shaft of any length chosen. However, it may be cheaper for FFR to use either a front or rear existing shaft and have just a custom splinded inner race made. We know that some of the OEM rear links are being re-used, so there are a few geometry reason to stay close to stock also.

Best guess? Jim chose to stay close to OEM to eliminate as many variables off the top as possible. Lord knows that there is enough other work to do without purposely adding more without a really good reason to do so.

[Draco-REX]

Best guess? Jim chose to stay close to OEM to eliminate as many variables off the top as possible. Lord knows that there is enough other work to do without purposely adding more without a really good reason to do so.
This.

They are already redesigning the suspension. Keeping the variables down makes things easier. The track width already works with the transmission and steering rack as-is.

Also, keep in mind: The 818 will have a lower CG than the WRX, and a wheelbase 7-9" shorter. Maintaining the same track width would be like widening the track on the WRX. The 818 is going to be VERY stable just on a basic numbers standpoint. That's not even considering the better suspension design.

And to toss another couple numbers out there: The Miata has a track width of 55.5 F / 56.2 R. The 818's footprint will be 3" wider in the front and 2" wider in the rear than the Miata, while weighing 300+ lbs less.

[BrandonDrums]

You can always widen the rear track with wider rims/tires and lower offsets. Unlike the AWD WRX the 818 can run different wheels front to back. I'm planning to do this as I should be making over 300whp with my build. So wider rears with possibly a low 30s offset will give a few more inches of width. I'll likely have to run fender flares.

And this. All that matters is that there's room for wider wheels in the back and it shall be done. I'd rather have an easy build and big offset wheels than the other way around.