I'd really like to put some 1.9 Racing Ralphs on my Hybrid to help down muddy canal paths and woodland singletrack. Could I fit some 1.9 RR's on? If not what 700c tyres should I be looking at for commuting and off road riding? The current tyres are 700x28c.
Depends on rim width, I ran some 45c (I think) Smart Sams on some 23mm H plus sons rims.
700c and 29'er wheels are the same size but the rims widths vary a lot. It's the inside rim measurement that counts - the bit the tyre edges sit in, not the outside overall rim width. So you can put mountain bike 29'er tyres on if your wheel rims are wide enough (if not they may roll off when cornering hard etc).
If your rims are only 15mm wide (like most road bike and many commuter rims) I'd opt for safety and get a cyclocross tyre. If your rims are wider, say 19mm you'll be fine with the racing ralphs or anything up to around 2.3" so long as they fit in your frame of course. If you have 17mm wide rims then a thin mountain bike tyre will fit or a cyclocross one.
Something like a continental cylocross or a schwalbe cx pro would be a good CX choice with a decent amount of grip.
When you say 15mm, do you mean internal width?
yes, it's the internal width. I personally think its a bit of an old wives tale that the tyre will come off, I've used big tyre on Open Pro (17mm) and on another bike I currently have 26x2.5" on a Mavic 717 working very well in the Brecon Beacons. I have one bike with it the other way round, 622-25mm rims with 30c tyres and that works just fine too, so pretty much anything goes within reason.
I've ridden plenty of the SDW on 2.0 race kings on Mavic open pros (14.5mm internal, according to [url= http://www.justridingalong.com/news/2012/01/notubes-alpha-velocity-a23-mavic-open-pro-rims-internal-measurements/ ]JRA[/url]). Was "not hanging about" on the rutted, rubbly descents.
Currently not dead.
I've heard of 24hr solos run on 2.1" SB8s on Open Pros too. Don't think he's dead eitehr.
The main question is, will they actually fit in the frame & fork?
I've had 2.2" Nevegals on Mavic MA3 rims (the old name for Open Pro, I think (or Sport?)). I didn't die either.
Yeah I'm sure 99 percent of people can ride a 2.5" tyre on a 17mm rim and have no problems with it rolling off especially if it's not inflated too hard.
For sure there is far more chance you'll burst an inner tube if you ride hard rather than roll a tyre off but you don't want to run a 2.5 on 15mm road rim, the profile would be daft.
I ran 2.35 Nevs, on 717's (17mm). Worked fine. According to lore of old I should be in the afterlife for an act of such wanton tomfoolery. But, much to the Wifes disdain, I'm still around.