Contributed by SubaruCO at NASIOC (http://forums.nasioc.com)

----------------------------------------------


I hope this information will be of some use to fellow Forester folks…

As an engineer I tend to over analyze every aftermarket purchase for my FXT. This leads to inevitable ruler swinging and calculator punching. However, this at least gives me comfort before making purchases so here is some of my preliminary findings in the wheel and tire department. Please let me know if anybody finds any errors or has any other suggestions.

I have been formulating a wheel tire combo for some time now. I would like it to complement my suspension upgrades and serve my purposes in my everyday pursuits. It is for these reasons that I have chosen to stay with a 16” wheel on the FXT. I have also decided to go with a 225/60/16 tire to knock down the gearing a tad and get more tread width on the ground. The research below can however be easily replicated for 17” or 18” wheel/tire combos if so desired. I have sat down and mocked up a 2-d layout of the wheel and suspension relationship. From there I have introduced various wheel and tire combinations comparing against the limiting fitment requirements. Hopefully I have come to a meaningful conclusion.

All information was pulled from manufacturer specifications on tirerack.com so if the actual production tires don’t conform then YMMV.

The limiting factor as I see it on the FXT is the rear strut clearance. There is about 5/8” between the stock tire sidewall and the strut housing. With camber adjustments in alignment I believe the absolute maximum tire section width for the rear is 9 ¾ inch. At the bottom of this post I included a snippet from TireRack tech data on tire section width. Therefore, with a 16x8” rim w/ 48mm backspacing the maximum tire section width I feel comfortable with is about 9.5”. Below is the resulting data. Enjoy!

Original Equipment:

Tires – 215/60/16 Yoko Geolander H/T G900
· Specs:
o Rim Width = 6.5
o Section Width = 8.6
o Tread Width = 5.7
o Overall Diam = 26.2
o Revs/Mile = 792

Wheels – 16x6.5

Aftermarket Possibilities:

1. Rota Slipstream – 16x8.0

· Tire Possibilities:

1. 225/60/16 Bridgestone Potenza RE750 (Ultra High Perf Summer - $100.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 8.9 on 6.5 rim OR 9.5 on 8.0 rim
§ Tread Width = 7.3
§ Overall Diam = 26.6
§ Revs/Mile = 783

2. 225/60/16 Firestone Firehawk SZ50 EP (Ultra High Perf Summer - $113.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.0 on 6.5 rim OR 9.6 on 8.0 rim
§ Tread Width = 7.0
§ Overall Diam = 26.6
§ Revs/Mile = 783

3. 225/60/16 Continental ContiExtremeContact (Ultra High Perf All Season - $84.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.0 on 6.5 rim OR 9.6 on 8.0 rim
§ Tread Width = N/A
§ Overall Diam = 26.6
§ Revs/Mile = 784

4. 225/60/16 Dunlop SP Sport 5000 Symmetrical (Ultra High Perf All Season - $94.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.1 on 7.0 rim OR 9.5 on 8.0 rim
§ Tread Width = 6.9
§ Overall Diam = 26.6
§ Revs/Mile = 788

5. 225/60/16 Yokohama AVS dB S2 (Ultra High Perf All Season - $98.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.0 on 6.5 rim OR 9.6 on 8.0 rim
§ Tread Width = 7.2
§ Overall Diam = 26.7
§ Revs/Mile = 779

6. 225/60/16 BFGoodrich Traction T/A V (High Perf All Season - $77.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.0 on 6.5 rim OR 9.6 on 8.0 rim
§ Tread Width = N/A
§ Overall Diam = 26.6
§ Revs/Mile = 782

7. 225/60/16 Bridgestone Potenza G009 (High Perf All Season - $71.00)
o Specs:
§ Rim Width = 6-8
§ Section Width = 9.0 on 6.5 rim OR 9.6 on 8.0 rim
§ Tread Width = 7.8
§ Overall Diam = 26.6
§ Revs/Mile = 783

Notes:
Section Width
A tire's section width (also called "cross section width") is the measurement of the tire's width from its inner sidewall to its outer sidewall (excluding any protective ribs, decorations or raised letters) at the widest point. This measurement is made without any load placed upon the tire and after the tire has been properly mounted on its industry assigned measuring rim and has been inflated and reset to its test pressure after 24 hours.
Because a tire's section width is influenced by the width of the rim upon which the tire is mounted, the correct industry assigned measuring rim width for the tire size being measured must be used.
The width of a tire mounted on a narrow rim would be "narrower" than if the same tire was mounted on a wide rim. NOTE: because the overall diameter of a steel belted radial is determined by the steel belts, there is little, if any, change to the overall diameter of the tire due to differences in rim width.
The industry rule of thumb is that for every 1/2" change in rim width, the tire's section width will correspondingly change by approximately 2/10".