following a trip to spain I've got a couple of dents in the rims of my wheel. What's the best way of repairing these, can you / do you need any special tools

We'd need a picture to understand the direction and extent of the dent, the extent of metal damage and whether its flatspotted the rim or just moved local material. Generally most minor sidewall damage can be carefully rectified with an adjustable wrench and a cloth, but if it's stressed the metal too much you may have weakened the rim, or you may have flatspotted the rim which would need much more detailed reworking by a wheel builder, which would probably ultimately render it cheaper to buy a new rim.

Use a set of vice grips or pliers or an adjustable spanner and just lever them straight. Very easy to do

any tips to prevent damaging the lip that the bead hooks under?

Bear in mind that if youve kinked it right over, bending it back may shear it off.

Preventing damaging the lip? Use the right tyre pressure! There's only one real reason you're seeing that happening and thats because the tyre is too low and being crushed against the rim, letting the rim fold. In conditions like that you need to up your pressure, pick better lines or ride lighter. Or buy bombproof rims and use no skill at all 🙂

he means when bending the rim back not when riding smart arse

younggeoff Ive straightened a few sidewall dings using a big 12" adjustable spanner (with nice broad jaws), and never damaged the bead in doing it. If you used a skinny-jawed wrench or pliers then the extra local pressure on the bead might damage it, so as coffeeking says just stick a rag or something in between the rim and jaw.

he means when bending the rim back not when riding smart arse

? WTF? Did you read my post? What exactly were you replying to?

<edit>

Ah yes, now I follow 🙂 Sorry, my mistake there! I mis-read his post and assumed he meant damage while riding, as I'd covered the damage while fixing in my earlier post.

To be honest, if the tyre seats OK, leave the ding as it is. All spannering it out will do is weaken it yet further.

Rims are essentially a consumable, so it's not the end of the world to have an assortment of dinks in them. If you're not pinchflatting, then i'd suggest your tyre pressures are probably about right. (My DH rims currrently have several large dings in each and LOTS of flatspots. They just need to last until the end of this week and I'll rebuild them.)

I personally can't see how rims are consumables. Having not worn one out or broken one in 10 years (broken plenty of other things though!) I struggle to see the link. If you look at it that way, any part of your bike is a consumable as you'll break it eventually if you mistreat it enough!

rims were consumables when everyone used rim brakes which wore out through braking, but why is a rim on a disc braked wheel a consumable? I change my handlebars occasionally, after a couple of heavy crashes, but have yet to change a rim for anything other than a change in riding style, and even then Ive kept the old rim in case I want to change back (swapped 717's for 325DH rims a few years ago, have just swapped back to the 717's to rebuild them back as light XC wheels).

I do agree that there's less reason to need to straighten the dent out, if the tyre seats and the wheel doesnt feel unbalanced, than there was with rim brakes, and you could potentially weaken the rim wall. I still do it though.