How to Corner Weight Guide
Not as complex as many think, but as not common practice in the automotive industry, many see it as being one of motorsports “black arts”. It’s one of the aspects of race car set up and is usually done alongside the suspension geometry. Here’s our guide to Corner Weighting.
What is it?
Corner weighting is where the distribution of the total weight of the vehicle is adjusted over the four wheels to effect its handling characteristics.
The car will need to be under race conditions. Meaning, tyres at correct pressures, correct fuel load, driver in position (or equal weights in driver position) etc. These can also be adjusted, such as the fuel load, to give maximum benefit at different stages of the race, for example, fuel level for mid way through the race, or tyre pressures to give maximum advantage at the start of a race, rather than midway or toward the end.
How it’s done
The vehicle is placed on 4scales, one under each wheel. The scales must be on a perfectly level surface so the measurements are accurate. Shimming under the scales to level the ground is common practice when needs must at the circuit or elsewhere. The readout from the scales will show the weights on each wheel (and usually the percentages). The suspension can be adjusted, or any ballast/movable components inside the car repositioned to adjust the balance. Adjusting the suspension can be done by many methods, changing the spring rates, or more commonly, adjusting the spring platforms using adjustable coilovers.
There are only so many things that can be adjusted.
The balance of weight front to rear cannot be altered without physically moving weight.
The balance of weight left to right cannot be adjusted without physically moving weight.
One would think that the ideal would be to have a perfect left to right 50%-50% balance. This isn’t always possible, and we wish it were that easy. Single seaters are much better balanced than your usual race car, but the most common clubman cars are converted road cars, where the driver being at one side plays a huge effect to the weight distribution. Regulations usually specify the minimum weights and location of any ballast too, but aim to get the static left/right balance as equal as possible before moving on.
Cross Corner Weight
Cross corners or Cross weight is the most important setting. This is the total of the front left plus the rear right, in comparison to that of the front right plus the rear left. Getting these equal will give a well balanced car with reasonably equal handling characteristics on both left and right hand corners. Decent Corner weighting scales will usually display a pre calculated percentage for these rather than you having to work it out yourself from the individual weights.
Having equal cross corners isn’t always ideal. If the vehicle is a circuit racer, then the track, be it a left or right hander circuit will have more corners in one direction. A converted road based car will benefit here, as this can help to keep weight on driven wheels, or the wheels that make the most cornering grip.
For example, on a circuit with tight left handed corners and open right handed corners, a front wheel drive car under cornering loads on the tight lefts may transfer too much weight to the outside wheel, causing understeer and allowing wheel spin on the inside wheel sacrificing the corner exit speed and overall lap time.
So “wedge” is the cross corner unbalance.
When the front right and rear left are above 50% of the car total weight, one would say the car has “Wedge” or “Positive Wedge”.
When the front right and rear left are below 50% of the car total weight, one would say the car had “Reverse Wedge” or “Negative Wedge”.
Generally, the loss of traction in one direction by altering wedge from the 50% mark, outweighs the benefits it gains in the other direction, but obviously this can alter significantly with the circuit. This is where analysing a circuit to find what gains you may get, then testing with various setting to get the optimal possible set up is the best way to get the maximum benefit.
Front wheel drive
An increase in wedge will reduce the weight on the front left wheel, so around left hand turns understeer will increase, as will the ability for acceleration traction on the inner wheel. Around right handed corners the car will have better grip for both turning (generating less understeer) and acceleration.
|Corner Direction||Effected area||Increase Wedge||Decrease Wedge|
Rear wheel drive
An increase in wedge will reduce the weight on the front left wheel, so increasing understeer around left hand bends. It will also increase the weight on the rear left wheel, so allowing more traction to the driven wheels for acceleration.
|Corner Direction||Effected area||Increase Wedge||Decrease Wedge|
Staggered, or to stagger wheels is where two different tyre sizes are used on the same axle. This is common in oval racing. It has many reasons at to why it can be beneficial, but with regards to corner weighting, it can effect the handling, and so the wedge can be adjusted to compensate.
With longitudinally engined, rear wheel drive drag cars, adjusting wedge to compensate for torque twist of the chassis/suspension can be beneficial to help keep one of the driven wheels from spinning. Usually this is the use of “reverse” or “negative wedge” to keep the rear right tyre in contact with the tarmac, but does depend on the direction of engine rotation.
Things To Consider
Changing the balance of weight on the wheels effects many things. When adjusting the ballast position or the springs/coilover platforms, it may be worth cconsidering the spring rates used on each individual corner, as well as the loaded, unloaded and static axle movement. Droop restriction or spring preloading may be beneficial.
It’s also worth considering the effects on braking performance, mainly the effects of your corner weighting on trail braking (where you are braking whilst the car is turning).
Coilover options including Avo, Tein, Tegiwa, Ohlin, Gaz gold, Bilstein, kw suspension, Eibach, Spax, Vogtland, H&R, Sachs, Koni.
Corner weight scales options including Intercomp, Longacre, B-G racing, STR, Proform.
Vehicles including Renault Clio, Clio Sport, Clio cup, Honda Civic type r, Intergra, Mazda MX5, Peugeot 206 106, 107, Citroen Saxo, Renault Megane sport, MGF, Caterham supersport, Lotus Elise, Lotus Exigue, BMW M3, E30 E36, E46, Ford Focus RS, ST, Mini, MG ZR ZS, Seat Leon, Ibiza, Ginetta , Ford Fiesta puma, Jaguar, Audi A3 S3, VW golf polo, Mitsubishi evo colt, Subaru impreza, Toyota celica MR2, Nissan. Formula ford, formula 3000.