Background:
I’ve used a set of the SSR Competition wheels for a long time across car models and have been a fan of their lightweight design.
When Apex announced that they were developing a wheel for the Mk7 GTI, I was excited to join the group buy for these track-focused wheels.
It took almost two years from Apex announcing their interest in developing a Mk7 suitable wheel to when I took delivery of a set.
Along the way, I had added a TTRS brake setup to the GTI, which would complicate a switchover to the Apex wheels.
When the Apex wheels arrived, I decided to conduct an acceleration test with them and the SSRs to see how the different weight wheels and tires would affect the vehicle acceleration.
Test Process:
The first step of the test involves weighing the wheel and tire combinations.
- Apex / Firehawk Indy (235/45R17) – 43.4 lbs
- SSR / Conti (225/45R17) – 34.4 lbs
Three test cases were run:
- July 15, 2022 – Apex Wheels / < Quarter tank of gas
- July 22, 2022 – SSR Comp Wheels / < Quarter tank of gas
- July 29, 2022 – SSR Comp / Full tank of gas
Note: The dates are accurate; it has taken a while to write up the test report.
The acceleration is made in third gear at full throttle, starting around 2,000 RPM and finishing around 6,500 RPM.
Test Results:
First, the intake air temperature (IAT) is checked for consistency to rule out being a cause of differences in the acceleration times.
Then the acceleration times from 47 to 84 miles per hour are compared.
The Apex wheel runs are consistently slower than the SSR wheel runs, even after the fuel tank is filled and the SSR wheel run is repeated.
Note: The added weight of the fuel is ~50-70 lbs.
The following chart shows the data points and the average acceleration times.
Next, the acceleration data is processed using Virtual Dyno to estimate the peak wheel horsepower.
Note: To estimate the power difference equivalent to the wheel weight difference, the power calculation is performed while holding the vehicle weight constant, despite its variation when the wheels are changed and fuel is added. Put another way, the change in acceleration time due to the change in vehicle weight is equivalent to what amount of HP change.
Plotting each of the peak wheel horsepower values over the series of pulls.
Finally, summarizing the peak WHP values and comparing the data points and means.
| Configuration | Average Peak WHP |
|---|---|
| Apex Wheels & 235/45R17 Tires | 337 |
| SSR Comp Wheels & 225/45R17 Tires | 353 |
| SSR Comp Wheels & 225/45R17 Tires + Full fuel tank | 345 |
Conclusions:
A test was conducted to compare the acceleration times of a Mk7 GTI using different wheel and tire combinations. The wheels and tires tested had a weight difference of 9 lbs per combination, resulting in a total weight difference of 36 lbs.
The heavier wheel and tire pair had slower acceleration times, estimated to be equivalent to a 15 whp peak difference in wheel horsepower.
After filling the vehicle’s fuel tank, which added between 50 and 70 pounds to the lighter vehicle configuration, the vehicle’s acceleration rate decreased, but not to a slower rate than the heavier wheel tire combination, which was a 36-pound difference.
The peak WHP difference between this full tank configuration and the heavier wheel tire pair was approximately 8 WHP peak.
This test demonstrated that the difference in unsprung weight of the tested wheel and tire combinations could affect vehicle acceleration rate to a degree equivalent to a 15 whp difference.
Ultimately, the paper-thin clearance between the Apex wheels and the GTI’s TTRS brake calipers necessitated their installation on my wife’s Golf R.