Actually the GrC rules are Nick's (justme) territory, but..... as he's not frequently online I thought I'd join in and give you some more info. As usual the rule isn't so much about performance but more about the car looks
Front Wheel diameter: Clarification
The maximum difference between the inner –and outer diameter of the Tire/wheel was created to stop guys running extremely conical front wheels. The main reason for doing so is to create a small as possible contact patch...but some took it so far that their wheels lookes like diabolos which looks......
ugly! So we needed a rule to keep things under control.
Other series have rules that state that for example 5mm of the tyre should toutch the track, but as this was diffucult to measure the LMS chose to regulate this via the max difference rule.
A 1mm tolerance beeing more than enough to create a small contact patch and stil have have true scale looking wheel.
So why change the rule?
Well until now all standard chassis had one piece frontaxles. That is until the release of the new Plafit S24 chassis which has 2 seperate axle stubs. For this chassis there is now a tune-up set that allows you to mount the front wheels with camber (and even toe in or toe out)
I must say it looks great and it also helps getting a wider track under a narrow body.
The only problem is that you have to shape the tyres conical or otherwise the car will run on the inside of the tyre resulting in a even narrower track than without camber.
I think Nick imagined that the only option to counter this was to increase the max difference.
Other stuff to look into
Come to think of it...we might have to adjust an other rule as well
"3.1. Complete Body" states "In Top-View Parts and the Complete Chassis may not extend from under the Body".
With cambered wheels the whole purpose is to get a wider track than the body allows, and although the top of the wheel will be covered by the body the rest won't be.
Another thing is that although 3mm might be needed to run cambered wheels it wil also allow guys running cars with one piece axles to re mount their diabolo wheels
We'll have to look into this at the next rules update, wont be the first time that a well intended rule kind of
