Random Tech: STi Weight Distribution vs. Fuel Load

About a week ago I asked Dan to do some comparisons on the weight distribution of his Subaru Impreza WRX STi after he was corner balanced. Specifically regarding how a larger fuel load will effect the F/R bias. Sure a formula could’ve figured it out but some real world hard data is better.

Here’s the data Dan (CGMDan on IWSTI) collected.

Methodology car was weighed, without driver, starting at slightly less than 1/4 tank indicated. Once on the scales, the car was not moved or shaken. Fuel was added 2.5 gallons at a time and data was collected. Sways were not disconnected as I was only concerned about front to rear weight bias. I did record corner weights at 1/4 tank and again once full. Once full, I reverse calculated the fuel load at each measurement.

1/4 tank starting weights without driver

928.5 | 924.5
660.4 | 650.4 Cross weights were 50.1% LR to RF

Fuel ___fuel load ___total wt. ___Fr wt. ___R wt. ____F/R bias in %
1/4 tank 3.5gal _____3163.5 ____1852 ____1311.5 ____58.5/41.5
+2.5 Gal 6gal _______3179.0 ____1854 ____1325.0 ____58.3/41.7
+2.5 Gal 8.5gal _____3194.5 ____1856 _____1337.5 ___58.1/41.9
+2.5 Gal 11gal ______3210.0 ____1858 ____1352.0 ____57.9/42.1
+2.5 Gal 13.5gal ____3225.5 _____1859 ____1366.5 ___57.6/42.4
+1.5 Gal 15gal ______3234.0 _____1859.5___1374.5 ___57.5/42.5

Full fuel corner weights without driver.

931.4 | 927.4
691.4 | 682.4

For comparison, here is Colin Feidler’s corner weights.
It also shows the F/R weight bias is a bit different.

“My STI with me in it weighed 3294 last time I corner balanced it. I weighed probably about 160 which means the car was 3134. I was able to get it to get a 50/50 cross balance fairly easily with me in the car. We ended up with LF- 997, RF- 958, LR-690, RR-649. I think after I set the ride height we had to adjust the RR spring perch like half a turn so we got really lucky. My ride heights were lower than most people at 13.5″ front and 13″ rear.”

It’s good to see that the overall % isn’t changed too much. I normally suggest people get corner balanced at the fuel load they plan on competing with most often. This shows that you could get balanced with 1/2 tank and be pretty well balanced with 1/4 or full.

We are kind of stating the obvious here, but its still some fun data. The key is still to get corner balanced once you put on a new coilover suspension.


Big thanks to Dan and the guys at Flat Out Racing

2 thoughts on “Random Tech: STi Weight Distribution vs. Fuel Load”

  1. Wow, that is some really cool data to see. I guess my hunch that fuel load didn’t effect corner balancing too much was more accurate than I thought. Thanks for sharing!

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