split in rear tyre ...

[XmisterIS]

And the damn thing's nearly brand new ... I replaced it after getting a puncture in the previous tyre

It's right in the middle of the tyre, about 2 cm across and as far as I can make out, it's at least the same depth as the tread. It's not losing pressure, so it's not a full puncture.

how to repair it?

I've found something called Xtra Seal and a website that sells various sealants, but it says "for professional use only" and I can't for the life of me find any instructions on how to use it!

Is such a big split repairable?

[mealexme]

maybe it says on the tin?

You know the annoying thing aout that product? I have found a few instructions, but they are all for roofing waterproofing which is also called xtra seal lol

[mealexme]

http://www.tisa.com.do/catalogos/Xtra-seal.pdf a rather long PDF, sorry but page 23 has the product your on about (not sure which one you are on about, but it has aout 6 products on that page), but most of them say it has to be used in conjunction with a patch

[eastanglianbiker]

of the split in the tyre

[satnavsatnav]

This should do it apply plenty in the split

http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_173106_langId_-1_categoryId_165691

[Guest Hodgy]

I'd take it along to a reputable bike tyre shop, get it checked properly, if it goes bang while your riding....

[whitedevil]

Id change it if i was worried about it, is saving a 100 odd quid worth it?

[XmisterIS]

Well, the chap at the garage said it was ok, plus it's not leaking, so he says it will be ok for the life of the tyre.

That being said, after my last rear-tyre blowout (I get all the luck!), I'm going to keep a tin of that emergency tyre inflation goop strapped to the frame so that I could at least limp home if I get another puncture.