For about half a year now I have the Logitech G27. I love it. H-shifter feels kinda cheap, but the pedals are okay and the wheel itself gives great feedback and I've even improved a bit. Before this I had a Logitech MOMO Racing. The thing about the G27 is that the steering wheel itself is so thin. It also has a pretty big diameter. If you look at a real racing wheel or a custom G27 wheel, you can see how thick the grip is (or what's the proper name for it?).

Instead of buying a custom wheel I'd really like to make the grip thicker, myself without making the wheel bigger. So a bit more grip on the inside/front. Maybe some kind of thick foam or something? How could I go about doing this?

You could try somewhere like ebay to see if you can get a small steering wheel cover, although due to the small diameter of the G25/G27 wheel, might be difficult.

Better alternative might be to get some badminton/squash/tennis racquet anti slip/sweat tape and either wrap that straight onto the wheel or use it to hold foam sheeting in place.

The tape is about 25mm wide x at least a metre, and comes in various colours and textures.

You'll probably need to also buy some coloured electrical tape to match racquet tape colour, as this is needed to very hold end of racquet tape in place.

Probably lots of quides on youtube on how to re-tape a racquet but maybe struggling to find one on how to do a steering wheel

The alternative to racquet tape is bicycle handlebar tape - likely the same sort of stuff as used on racquets, but groovier styles. Have a look HERE on something I found on ebay.

Maybe you can be the guinea-pig on modding your wheel and let us know how you get on and give tips.

Ah, great suggestions, thanks! I'll try that.

Thought I'd try my own suggestion for using bicycle handlebar tape on my G25 to try thicken the grip, but its far too thick to use, and because its so thick, bit inflexible.