I'll be using my Genesis Longitude for the Borders 350 but she's a heavy beast. The cheapest way to cut weight and increase speed is to put thinner non+ tyres on but how skinny a tyre would work on a 33mm internal width rim before causing problems?

Difficult to say really Ray as real world sizes will vary between makes / models regardless of what it says on the side. Seeing as that's not at all helpful, I'll now say that the 'average' 2.3" should be fine. The tyre might square off a touch but you shouldn't really notice.

Ray, have a search for ETRTO tables - basically a compatibility grid of rim and tyre sizes. They do err on the side of caution so a couple of mm less is probably OK.

You will probably only get to a 2.3 or 2.4 tyre before things get impractical. What weight saving would that get you? Maybe 200- 300g. Even if it’s more think about what you will loose in comfort.
Having swapped from exclusively riding 29+ to a choice including standard 29er recently I am certainly feeling the difference. Without the plus tyres I feel the need for suspension forks. I don’t know the Borders course at all but if it rough with a bunch of tussocky section as I guess it may be, sticking with plus maybe of more benefit than loosing a bit of weight.
This is coming from someone who has made some poor decisions in the past about weight saving!
IMO you should look at your kit and try and loose a bit of weight there first.

How about a 2.6 vittoria mezcal?

Somewhere in the middle. A bit lighter perhaps, very very fast rolling, some of the comfort retained.

lune ranger wrote: ↑Tue May 14, 2019 6:56 pm You will probably only get to a 2.3 or 2.4 tyre before things get impractical. What weight saving would that get you? Maybe 200- 300g. Even if it’s more think about what you will loose in comfort.
Having swapped from exclusively riding 29+ to a choice including standard 29er recently I am certainly feeling the difference. Without the plus tyres I feel the need for suspension forks. I don’t know the Borders course at all but if it rough with a bunch of tussocky section as I guess it may be, sticking with plus maybe of more benefit than loosing a bit of weight.
This is coming from someone who has made some poor decisions in the past about weight saving!
IMO you should look at your kit and try and loose a bit of weight there first.

I think you may be right. Comfort over slight weight loss means you can put more hours in. I doubt I could cut my kit much more than from what I had last year, it was minimal to say the least.

Too skinny will make the tyre profile entirely weird and make cornering sketchy as well. Probably not a good thing.

29 er wheels fit so a set of those with the tyres of your choice - if you really want i can tell you the weight saving [tomorrow night] if i weigh the wheels
you gain speed you dont lose that much comfort [though i use suspension forks so not sure about if fully rigid,]
those rims dont look suitable to anything below 2.5 though i have never tried.

Please say you are tubeless as the inner tubes weighed over 300 g - get rid of them.

Lazarus wrote: ↑Tue May 14, 2019 10:18 pm Please say you are tubeless as the inner tubes weighed over 300 g - get rid of them.

Good point, tube weight never occurred to me, doh!

I have 29er wheels but not in boost spacing for the front.

I think I'll just go tubeless as it's the cheapest way to lose weight.

Absolutely. Never even thought anyone would run plus with tubes. If it’s 29+ a standard tube can be as much as 400g.

I've a 2.6" Vittoria Mezcal on the front of my Solaris, which has rigid carbon forks, on a 35mm rim. I fitted it for last year's French Divide to give a bit more cushioning. Rolls really fast, decent grip in the dry but the compound feels pretty hard so I'm not sure how good the grip will be in proper wet conditions. Tread is in the Bontrager XR2/Maxxis Ikon sort of range.

As above - go tubeless. It lets you run lower pressures so you don't get bounced around so much anyway and it's that vertical motion that's one cause of loss of rolling efficiency: the energy you put in to the pedals should be propelling you forward, if you are bouncing up and down then some of it's being used for that.

I have 29er wheels but not in boost spacing for the front.

Ebay do conversion kits - basically a spacer for the disc mount and 5 mm for the hub - less than a tenner

i have never used them as my wheelset is a BOOST front QR rear version

Ray... dont forget that if you go too narrow on a wide rim, trying to mount/unmount the tyre can become a bit of a nightmare...

FWIW on a 33mm internal (I think I remember original post stating that) I dont think I'd wanna go less than 2.35. I've got (goes to check to makw sure he's not talk8ng rubbish) some 35mm internal M1700 wheels and have been as low as 2.4 (Mavic something Tubeless) which were a tight fit but not too tight...

Mavic also do a chart with what they feel are optimal/max/min tyre widths on equivalent rim widths...

Still looking but this one's more about pressures which could live here I suppose

https://engineerstalk.mavic.com/en/the- ... rim-width/

Basically... what they're saying is (and I'm extrapolating here) that on a 33mm internal you need something around what Bob said (a 2.6 inch... remembering that all tires not being true to size/widths on a given rim)...

Also, the tyre/rim interface should look like this middle thing



Remembering (IMO) that if it looks like the pic to the right then popping tyre on and off is gonna be a nightmare (but you should get a lovely seal for tubeless without much extra rim tape ) and if you get a sideways naughty rock, it'll probably knacker the rim as well as the tyre...

Then the image on the left (the one with too much a lightbulb shape): the tyre is probably so big for the rim that even though it (probably) went on really easy. Getting a tubeless seal is probably gonna be a nightmare; its gonna be so loose on the rim that once the tyre has stretched from being run tubelessed, it might be prone to popping of the rim; running too low pressures (and I'm trying to make this bit up on the spot but have thought it through previously and really do believe it myself ) will mean the side carcass isn't supported properly with air pushing it taught ans sooner or later there's gonna be a side gash/slash/wear...

Hope I got all my paragraphs right and hope it makes sense (and feels of value)...