Torque Shop
Modifying a car with wider or larger tyres may affect performance
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Ensure that the wider tyres do not compromise the suspension and steering functions.
PHOTO: JASEN DELGADO/BROAD ARROW AUCTIONS
Shreejit Changaroth
Just how wide can wheels and tyres be upgraded to?
Most owners replace original wheels and tyres to enhance their car’s looks but there are some factors to consider other than the aesthetics.
It is common to swop the original wheels for a set that is an inch larger in diameter. With this, the tyres also have to be changed. The profile – which is the height from the road surface to the wheel rim – will be lower. This is to keep the overall outside diameter of the tyre within two per cent of the original specification.
Outside of this tolerance level, the car’s speedometer and odometer reading will be inaccurate.
It is possible to upsize the wheel diameter more. However, bear in mind that as the wheel diameter increases, the height of rubber has to be decreased to retain the rolling diameter. This will tend to give a sharper steering response and overall grip, but the trade-off is increased ride harshness and, often, road noise too.
Another important specification to consider is the wheel’s offset. This is the distance between the mounting face and the centre plane of the wheel.
When wider than original wheels are fitted, a slightly different offset is often necessary to maintain clearances with suspension parts such as the vertical struts. Adding wheel spacers could alter the offset, but this would effectively require longer wheel-mounting studs and, on some designs, cause excessive load on wheel bearings. Avoid spacers when upgrading wheels and tyres. Also, check for any interference during maximum suspension compression and full steering lock in both directions.
Offset is part of the suspension geometry and drastic deviation from the original will have mild to severe adverse effects on steering precision, feel, feedback, response and, in extreme cases, grip.
Fitting extremely wide tyres that actually protrude out of your wheel arch will cause a number of problems. Firstly, the wheel arches will interfere with the vertical suspension movements over humps and any uneven surface causing damage to the bodywork and tyres.
There is the possibility of modifying the bodywork by trimming the wheel arches and then fitting fender extensions that will provide sufficient clearance for the new wider wheels and tyres. Such modifications are expensive and while they may alleviate the physical constraints around the tyres, there is the question on the legality of altering the car’s exterior dimensions.
