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  • making progress on deep shingle/pebble beaches fatbike rim/tyre advice pls
  • kaiser
    Free Member

    A year ago I finished a full refurbishment of a 2015 surly Pugsley but after a couple of rides found my knees couldn’t cope with the increased Q factor and the bike remained in the garage until recently when I found a solution so hopefully I will soon be riding the local beaches down here in Devon (which are mostly shingle/pebble and often loose and deep) . I am aware it’ll be hard work but thought I’d ask about best tyre/rim choice and whether it would make much difference .
    I currently have 65mm Marge lites with 4.8 jj’s . Clearance is tight at the back but up front the moonlander fork can accept pretty much anything . I am presuming that crawling at a very low pressure is the recommended approach but find that the 4.8/65mm combo is rather squishy/wobbly at low figures so am considering putting a 90 or 100mm rim up front to give more stability and float over the deep loose areas. I may leave the rear as I would be concerned about whether it would fit /rub and am presuming the larger /wider tyre up front will flatten and compress the stones and leave a more dense surface for the rear to pass over .
    I’d appreciate any feedback re these ideas and whether a change to a considerably wider rim up front is likely to be worthwhile and make a noticeable difference . I will probably add a Bud up front and possibly change to a Nate at the rear as well . I am not too bothered about the weight increase as going fast is not a priority . Thanks in advance , Bill

    Full Member

    I find 4.8 on 80mm rims a sweet spot. The good, high TPI version of the tyres, setup tubeless.
    If I know I’m riding a long stretch of very soft, loose stuff such as you describe, with no danger of high speed rim slamming, then pressure can be dropped down to a few psi above atmospheric.
    Ultimately, 100mm rims and some of the huge 5″+ tyres will be even better, but frame choice is limited and it becomes more limited as an all rounder.

    Full Member

    As Bedmaker suggests low low pressure as you’re unlikely to smash a rim onto something.

    My experience is around Brighton with a trip over to Dungness to find the sound mirrors. ICAN carbon 90mm rims with 4.8 JJ’s of the 120tpi supple sidewalls tubeless variety. Also if I remember and it was fine with 30t up front and 10/50 out back.

    The area around Dungness is super pebbley but flat. Progress was fine, just slow and it needed work. On the Brighton beaches again, along the beach was fine but any slope uphill, the pebbles just rolled out from the tyre. Game over. Downhill from the prom to the sea edge was easy. Back up was a push. It’s possible to get traction on the pebbles but they move amongst themselves.

    Re the 4.0 4.8 issue. If you are relatively light in kilos then I assume the potential float would be similar to 4.8 but the surface the tyre is covering will be a bit smaller. The Veetire 5.0 is a monster but only a few frames will take them.

    Pictures on Google pics

    Full Member

    I have 4.8 on 80mm but I can’t say I’ve tried anything else. IME the JJ 4.8 is superb- the 4.0 wasn’t so hot but the big one on a decent size rim works as well as anything I’ve used

    Free Member

    As mentioned .. I have 4.8 JJ’s on 65mm rims .
    I have little riding experience with fatbikes but as many have noted ( not all though) the front end felt downright dangerous over even fairly light mud . The first patch I crossed at fairly low speed nearly had me off and I became wary of using them unless on firm ground.
    Would changing the front rim to something like a “blizzerk” 90 ( 84mm ID ) ..currently only £55 on eBay ..make a huge difference or is the cost/ rebuild not really worth it ?
    I would love to have wheel/ tyre combo that would allow very low pressure but without the associated wobble/squirm/ unstable feeling. I love a soft ride and had previously believed a fatty would offer that but quickly found it not to be the case unless I accepted the squirm from sideways tyre movement.
    People talk of ploughing over anything and magic carpet type ride but that’s not my experience at all at least not rigid .Does a 100mm rim stop much of the squirm and sideways movement when running soft? If yes I may well go for it!

    Full Member

    The eternal self steer front dilemma. IMHO its a combination of tyre type and pressure between the front and rear. Same tyres that self steer will run true on my bike if I change the pressure. Too low and it’s terrible. Have a play around with pressure. Some swear on 6psi in general but I’m using more than that.

    What to use is a bit of “it depends” and I have had 15 – 3 psi depending on the surface. Jumbo Jims are fast but disastrous in mud. The knobs are spaced far apart and not very tall. Its basically a bumpy slick tyre. Great on the beach but snow, mud or similar and again IMHO its very sketchy. Nate / Bud super grippy in mud but like velcro on some surfaces.

    4.8 tyres on narrow rims give a very round profile, less so on 100mm rims where they are squarer. for more float. Your 4.8 on 65 rims will make for a very round profile methinks.

    The sweet spot is around 80mm to run 4 – 4.8 tyres nicely where pressure variations can be made without too much compromise. Personally I use 4.8 Minion DHF and DHR for winter and 4.0 JJ in drier times when a fatter tyre is just a waste of extra rubber.

    Full Member

    I have both 65 and 90mm rims for my fatbike. I run the 65s for most of my riding – the 90s were built for running Snowshoe XXLs in the arctic where at 1-2psi they can be the difference between riding or pushing on soft snow, or where you get overflow (water between the snow and ice on frozen rivers and lakes). I’ve not ridden on Devon beaches like Branscombe with large pebbles which I imagine would be near impossible although have ridden on some Sussex shingle at Bognor and Shoreham.
    IME With most soft surfaces, it’s usually just down to low gears and smooth pedalling and experimenting with tyre pressure to see if it helps. Certainly a bigger front wheel helps on soft conditions as it helps lift the front end and provided you can maintain forward momentum/drive then help with progress. I’ve never run a fatbike tyre above single digits psi.

    Full Member

    I had a moonlander with 100mm rims and bud/lou tubeless with a max of 5psi. Some sections of shingle are just impossible. Riding between Benacre and Orford Ness here on the East Coast was fine apart from a stretch at Dunwich that was purgatory whatever I did. Only way to stay pedalling was to buzz the tide where it’s sandy. Might not be an answer to your problem!

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