Wide Body & Wheels Overview

After through testing, I have discovered there are several performance differences with different combinations of Wide Bodies and Wheel dimensions. To find performance differences I have conducted two tests. The first test is a Handling Test and the second test is an Acceleration and Top Speed Test. From the data gathered we can predict what each dimension change does according the performance pattern.

For both tests I chose the Toyota Supra 3.0GT Turbo A '88 with the following upgrades:

• All power increasing upgrades

• All weight upgrades

• Fully customisable racing transmission (Flipped)

• Sport soft tyres

All other upgrades remained stock during the duration of the tests.

The following settings were used for track conditions to keep the tests as repeatable as possible.

• Tyre wear rate: 0x

• Fuel consumption rate: 0x

• Equal conditions mode: ON

• Grip reduction off track: REAL

To reduce all results that do not correlate, all sets of data were gathered 10 times and each test was repeated in no less than 2 times.

I will compare my set of data with another reputable Gran Turismo setup builder, AMS_Dood.

Table showing the full data set of both tests

The primary goal is to measure the total amount of lateral g that can be pulled before going past the peak slip angle of the tyre. To do this, I used sector 2 of Blue Moon Bay for the test measurement.

To eliminate human deviation, I reduced the final drive to the point the top speed was only 15kph faster than the average apex of the corner. This is so that no brake input is needed.

As Blue Moon Bay has banked sectors, driving line and steering inputs will need to be near identical. Otherwise using a part of track where banking increases will increase lateral grip. The vertical angle of the tyre is reduced according to the banked road surface, reducing maximum slip angle compared to a flat surface. For these reasons I used the driving assist and did not deviate from this.

Theoretically, the faster the sector time the higher amount of lateral g pulled as a higher minimum speed is carried through the corner.

This table shows that the in game stats are somewhat reliable, although not 100% accurate you could use them as a rough guideline. Here we can see a considerable increase to cornering performance when applying the Wide Body upgrade and any custom wheel dimensions. Under these conditions, completely standard wheels and wheel dimensions is the slowest performance wise.

The primary goals are to find the acceleration thresholds and top speed thresholds. I completed both these tasks by using Special Stage Route X as the test circuit.

The only modification made was increasing the final drive to the point where at the 10,000 meter mark, the idle RPM's were at peak power ~RPM's. This is so there are no transmission limitations to vehicle top speed performance.

The test was a simple rolling start race to remove any possible traction loss variables, and to remove any RPM losses that will happen if the rev limiter is activated at different times when accelerating.

This table shows that the in game stats do vary a lot and do not show the true performance of the vehicle. Here we can see the that the Wide Body does slow the maximum velocity of the vehicle. With the Wide Body applied the wheel dimensions do not seem to effect acceleration or top speed. However, without the Wide Body applied different wheel dimensions effect acceleration and top speed.

What I expect is happening is the different rim diameter alters the output ratio slightly, allowing for better acceleration and lower top speed. I am leaning towards this being a factor rather than a inconsistent physics engine. 

• At maximum speed, using a smaller diameter rim -1" and -2" will increase engine running RPM at top speed. Top speed performance may be reduced as the engine running RPM maybe too high, out of the peak power RPM threshold.

• At maximum speed, using a larger diameter rim +1" and +2" will lower the engine running RPM at top speed. Top speed performance may be reduced as the engine running RPM maybe too low, out of the peak power RPM threshold.

Video showing AMS_Dood's wide body and wide tyre test

The first thing to take way from this test comparison is, the results obtained with no Wide Body upgrade come to the same conclusion. All standard wheel dimensions produced the worst cornering performance.

The second thing is the differences between the bottom 2 combinations of Wide Body and Offset. A Wide Body will allow you to increase the wheel offset even more compared to with out a Wide Body. This will give the sensation of a longer track width, improving stability. This is exactly what I believe is happening here. AMS_Dood is using racing soft tyres, maximum downforce and a fully customisable suspension for maximum cornering potential. This will mean the cornering force he will have will be far greater compared to mine. With a wider offset, he will have greater vehicle control over his increased cornering force allowing for faster cornering.

The vehicle I am using has majority stock parts that do not greatly increase cornering forces, with the biggest factor being sport medium tyres used. This means, at speed the vehicle will have a tendency to understeer and not oversteer. Using a wider offset will increase stability so in this scenario it will understeer more and the vehicle will not want to rotate.

The first thing to take away from this, is the in game stats are all incorrect compared to the in game results. It is safe to say not applying the wide body upgrade and using standard wheels are the fastest for top speed.

What i expect is causing the difference in the data sets is the fact AMS_Dood had downforce increasing parts compared to me. With the wide body upgrade I expect more drag is being generated because of this. the increased drag could also prove you may get more body downforce as a result of wide body and downforce increasing parts.