I currently have a Hilux diff in my Mk1 Escort that has a 4.88:1 ratio. At 8000rpm that gives a theoretical top speed of around 215km/h (from memory). During tarmac events the most i have seen in reality is 196km/h. The car usually struggles at high speeds especially if it is even slightly uphill.
I am considering whether i need to increase the diff ratio to 5.1 or even 5.3 for more punch out of corners, better pull up hills but at the expense of a little top speed.
What ratios are others using in their tarmac rally cars?
Is there any mechanical reason not to do this? Does the diff get weaker at higher ratios?
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