Car allowance - reduce tax liability?

Hi

I have a car allowance from my company of say €20000 per annum, paid monthly in my salary at the rate of €1666 per month gross.
I do not get paid a mileage rate or other motoring expenses and use my own car for business trips.
While I understand this is fully taxable, I believe there is some way of reducing my tax liability by providing a log of my business journeys assigning a portion of my miles and benefit to business related trips.

Can anyone shed any light on this?

Thanks

If you go down this page to part headed "Expenses claims submitted to Revenue". There is a Revenue claim form for what you refer to.

Many thanks