A rally car set up for gravel and a circuit track prepped race car look strikingly different. One sitting high off the ground on chunky thick tires and the other sitting low to the ground on a thin veneer of rubber.
Despite the visual differences, both cars share similar philosophies: maximize grip and inspire driver confidence, but how they realize that goal requires different strategies.
For this topic, I asked DirtFish instructor Michelle Miller to give some advice. She has extensive experience in both realms as a three-time SCCA SOLO National Champion and as a rally driver/co-driver in over 50 events, including finishing third place overall in the US co-driver standings in 2018.
Whether it’s racing on asphalt or in the forest, for Michelle, car set-up always comes down to what gives the car the best grip by adjusting it to the conditions.
What does this mean for gravel vs asphalt?
She says that “in general, drivers will want a semi-soft suspension setting for gravel.” Gravel is malleable and slippy. This is why you’ll see a gravel rally car sit higher off the ground and run with softer suspension.
It allows the car to transfer more weight which pushes the tires through the loose dirt to find grip on the hard packed surface underneath. Gravel forest roads are full of potholes, rocks, and jumps, so this type of set-up helps the car absorb the abusive conditions.
By contrast, asphalt is generally extremely consistent and grippy. You’ll rarely see rocks and jumps on a race track. Thus, road racing cars can sit very low to the ground.
Michelle notes that “because of the inherently grippy asphalt, they are normally set up very stiff to keep them as level as possible maximizing the amount of tire on the ground for grip.”
This difference in surface types also explains the differences in race tires and rally tires. Rally tires have a tall profile with chunky tread patterns made for gripping the dirt and withstanding rock impacts. Race tires are low profile and minimal tread patterns made for sticking to the asphalt like glue.
It can boil down to “the harder and grippier the surface, the stiffer you can run the set up. The rougher and slippier the surface, the softer you’ll want to run the set up.”
Aside from suspension, ride height, and tires there are other differences to consider. In rally, alignment tends to be fairly simple. The conditions change so frequently that aggressive alignment settings rarely help.
This could make the car extra twitchy, especially under braking. Plus, Michelle jokingly warns there is a very high chance your alignment will get knocked out of place anyway by the bumps and impacts in rally. By contrast, asphalt is smooth and consistent lending itself to aggressive alignment settings. Lots of camber and toe adjustments can make the car quicker to respond.
The car’s gearing also varies between the two disciplines. It is quite common for rally drivers to shorten their gear ratios giving them more low-end torque that is well suited for the slower technical sections of rallying.
Race tracks tend to see much higher speeds than forest gravel racing. So, track drivers may choose longer gear ratios to give the car the legs to reach high top speeds.
The last main point Michelle highlights is the quality of parts used. Many folks just starting out will either go for the cheapest option or the lightest, depending on their budget. While for smooth asphalt racing the cheapest or lightest options might work just fine, that isn’t always the case in rally.
Rally cars take a ton of abuse. Having strong, robust parts, wheels, and skid plates will help you survive difficult terrain and keep your car on the road for the entire rally. She remarks: “It’s great to be light, but don’t compromise dependability for lightness.”
These are general differences between gravel and asphalt set-ups, but remember it all lies on a spectrum.
Michelle recalls an example from her autocross days. Even though it was always on asphalt, she would change her Mini Cooper’s set-up quite drastically between her wet home courses in the Pacific Northwest and the dry rougher courses in the Midwest for the national competitions.
When it comes down to it, continuous testing and documentation are the only way to zero in on what works best for the driver’s style, vehicle characteristics, and road conditions. A perfect set-up will give the driver confidence that they can perform consistently in any condition with a predictable and stable car.