My rationale is that it will form a physical barrier to ozone, and also react sacrificially with it. It seems to work, but it did seem to be absorbed by the rubber to some extent. Since I can't really predict the effect of an unstable oil inside the tyre structure, I'm trying canola oil (which is more stable) on the rear tyres, though I'll be surprised if I can tell the difference.
The cracks have....er....gone.
(well almost)
OK obviously they can't have gone. They must just have been hidden/closed up, either because there's been some swelling of the surrounding rubber, and/or because the cracks have filled up with a sticky mixture of veg oil and degraded rubber/carbon black.
Maybe if I'd been driving more they'd have stayed open.
I didn't really expect cosmetic improvement and have to regard it as a bad thing, since it could hide a problem.
OTOH, if the cracks are filled/closed up, it seems reasonable to suppose they are to some extent protected from further ozone attack.
I've seen a US Army ref to SFO as a rubber protectant, and an (unreferenced) recommendation of castor oil as a tyre treatment. Latter is a lot more stable, but expensive.
I've posted this in the tyre section here and was told (politely and quite reasonably) to stop it.
I also posted it (along with some speculation on N fill) on the UK Honest John website (where be pompous arseholes) and it got quite nasty, but I realise that being criticised by pompous arseholes doesn't make you right.
This procedure is speculative, experimental and not necessarily safe.
After I did this I read that one of the big tyre producers was using SO to enhance grip, but I think that's irrelevant either way, since they'll incorporate it into the compound.
Front OS untreated
http://www.flickr.com/photos/31043052@N06/6900646920/
IMG_0113 by
ed_lithgow, on Flickr
Front OS untreated detail
http://www.flickr.com/photos/31043052@N06/7046744391/
IMG_0114 by
ed_lithgow, on Flickr
Front NS tyrewall 10 mins after the sixth daily treatment with sunflower oil
http://www.flickr.com/photos/31043052@N06/6900651372/
IMG_0115 by
ed_lithgow, on Flickr
Front Nearside treated detail
http://www.flickr.com/photos/31043052@N06/6900653460/
IMG_0110 by
ed_lithgow, on Flickr
These pictures are from a couple of years ago (thought it was longer). After the initial week of treatment I went to a top up every 2-3 months. They look better now.