Thorn Nomad MK3 fork

[KDean]

Is it possible to fit a MK3 fork to a MK2 Nomad  ,enabling a disc break to be fitted ?
Thanks .

[Danneaux]

Is it possible to fit a MK3 fork to a MK2 Nomad  ,enabling a disc break to be fitted ?

This is likely a question best answered by Thorn's technical staff; I've found them to be responsive, providing answers to emails by the next day at the latest.

The steerer diameter won't be a problem, but you'll want to check the steerer length is adequately long for your head tube and preferred position if you don't plan to cut it down. Thorn's steerer lengths used to vary by model and might still do so.

There are two critical dimensions you'll need to know: 1) axle-to-crown distance and 2) fork rake. Variations in these dimensions compared to your stock fork can alter or affect the handling by changing the trail measurement. I think this may be a big factor for you because the Nomad Mk3 offers forks for a variety of wheel sizes.

I purchased a couple Sherpa Mk2 forks to fit to my Enduro-Allroad bike. These were the measurements I kept in mind and Thorn kindly supplied them, making the choices easy for me. Why two forks? One resulted in low-trail geometry, the other neutral-trail, so I could swap them back and forth as desire to best match the handling and load-carrying characteristics I preferred for different uses. So far, I've been happy with the low-trail geometry fork on this bike for most of my use and haven't tried the second one beyond several long test rides. I also ordered a third Sherpa Mk2 fork to fit to an elderly friend's bike in place of his heavy, thick-walled unicrown fork. He as seeking a more compliant ride to ease road shock to his arthritic hands and the Sherpa fork's Reynolds 531ST tapered blades filled the bill perfectly.

One final feature you may wish to check is whether the Mk3 rack mounting bosses are threaded for 5mm or 6mm. I know firsthand the Mk2 disc fork of one member came with 5mm bosses compared to his original v-brake fork. If that is important to you for load capacity, ask about it first.

Hopefully helpful, Dan.

[KDean]

Thanks for that I've just sent a email to SJS.

[PH]

Wasn't the Mk2 designed to accept suspension forks?  In which case I'd say the chances of a Mk3 (Which isn't) being a good swap would be highly unlikely.
As Dan says there's two critical dimensions you need to match, any variation has an effect, but a couple of mm either way is usually OK.  There's some variation between Thorn forks for the same frames. 
If a Thorn fork isn't a good match and you still want to go down this route (I wouldn't) there might be other suspension corrected options that work.  Or have something made, most framebuilders would do that for you, I haven't looked at prices recently, when I last did I was quoted about 50% over the cost of something OTP.

[WorldTourer]

Is it possible to fit a MK3 fork to a MK2 Nomad  ,enabling a disc break to be fitted ?
Thanks .

No, it is not possible. When Mk3 frames were still unavailable for months, I thought about buying the Mk3 fork and gradually upgrading that way. However, Thorn told me that the geometry does not match.

Thorn used to sell a disc-brake fork for specifically the Mk2, but it disappeared from the SJS website years ago already.

[PH]

The other alternative of course, because it's a disc ready geometry, is to fit a disc fork.  That won't help your weight saving agenda, though good quality disc forks (i.e. expensive ones) are not that much heavier than a steel one.  Though either option seems a lot of effort to change the brakes.

[mickeg]

Is it possible to fit a MK3 fork to a MK2 Nomad  ,enabling a disc break to be fitted ?
Thanks .

Because the frame of the Mk II is designed for a 100mm suspension fork, it has an unusually tall axle to crown race length for a 26 inch bike.  You might be able to fit a 700c fork from another brand.  As noted by Dan, the fork axle to crown race length and fork rake (or offset) are the numbers to compare.  The forks that have fork blades that curve inwards near the steerer tube and are welded directly to it are taller than the forks that have a separate crown between the fork blades and steerer.

I put a Surly fork on my Lynskey frame, the Surly fork had axle to crown length and rake dimensions that were only off by a few mm.  That saved me about $400 because I already owned the Surly fork when I bought the frame.  But in this case, both were designed for 700c.

I think the Mk II fork is much more heavy duty than many forks from other companies.  If you plan to load up a Mk II to capacity, I would not change the fork.

[Pavel]

The axle to crown is 10mm off between the two forks ... so I do not see why not.  The head angle will change by a minuscule amount but the offset should be able to effect a steering change more than the A/C distance is one wants a less reactive fork, as I do. 
That 10mm is about what one gets from changing from skinny to fat tires on the same bike - and nobody (that I know) freaks over that.
I think we are getting the Lawyer answers here and plan to go this route myself.  I may actually put a 26 on the back (no choice) and a 650B on the front, which again should even things out.  So it will look a bit weird, and perhaps I'll wind up in the ditch, but what small price for progress for bicycle kind, right? 

[PH]

The axle to crown is 10mm off between the two forks

Are you sure?  That doesn't sound much to accommodate up to 120mm of suspension.  If it is correct, then maybe it wouldn't make much difference.  There's 25mm A-C difference between Thorn's 853 V brake fork and the twin plate disc brake forks being offered for the same Mercury/Nomad models, with only a couple of mm difference in the offset.
853  385/46
Disc 410/48   

I'm not going to guess how much difference that would make, though I would expect to notice it. Neither am I going to suggest which anyone might prefer, which is entirely subjective. I am going to suggest that if Thorn are happy selling forks with such a difference, they must both offer handling within the norms of a touring bike. 

[UKTony]

You might want to have a look at this which SJSC say is an acceptable replacement for a Mk2 Nomad fork.

https://www.sjscycles.co.uk/forks/the-light-blue-darwin-mt-700c-disc-fork-1-18-inch-black-50mm-offset/

[Pavel]

This is where I got my information.  An earlier reply from thorn ... before they changed the tune.

What does the fork weigh? Can this be used with the Nomad Mk 2? If not, why not?
By Robert
11 May 2020
SJS Customer Service:
1.54kg but the - L1 Dimension (Axle to Crown Race Seat): is 410mm The Nomad mk2 needs an L1 of - 420mm with 48mm offset, reducing the L1 by 10mm will lower the head and slightly increase the head angle of a mk2 Nomad and lowering the b/b by perhaps 4mm (not much) RT

Source:   https://www.sjscycles.co.uk/forks/48-offset-a-700c-650b-26-inch-thorn-mk3-steel-disc-fork-gunmetal-imron/?geoc=US

[PH]

This is where I got my information.  An earlier reply from thorn ... before they changed the tune.

That's interesting, thanks.
10mm doesn't sound like it'd make much difference, but there's only one way to know.

[Pavel]

There is one other thought/question in my head.  All motorcycles except some race type dirt bikes and most scooters, have different wheels front and back.  It's a lot like having a 26" tyre on the back and a 700 on the front. The rear is normally fatter, and the front skinnier, but there is still a large difference in the diameter, with the front being larger.  My KLR has a 18" rear and a 21" front and the tire circumference difference on the outside is huge.  And the handling is highly predictable, just what a somewhat top heavy, overweight and under powered by thrives with.  I can pay attention to the scenery, and be relaxed at moderate pace. 

So I wonder what sort of ride a 26"x2.0 rear Nomad Mk2 would give with a 650B front?  That would raise the head up, lengthen the rake and change the trail the same way as going from skinny tires to fat tires does.

I don't have a 650B and am unlikely to get that size for the lack of choice in brakes.  But I do have a 700 front with a 38mm tyre, so I may do an experiment one of these days.  I live in a gated community with little traffic around the loop and it's perfectly flat so a few loops without front brakes don't worry me at all. 

If people didn't experiment, we would still be riding Penny Farthings. 

[PH]

There's plenty of example of bikes with different wheel sizes, the old style butchers bikes an early example, carried over to many current cargo bikes. Usually with a smaller wheel at the front, though also longtails with the smaller at the back to lower the load platform. It's also become a thing with MTB'ers, so much so that the UCI have authorised it for racing.  Usually referred to as a mullet after the hairstyle. 
These bikes are designed this way, the question becomes how much difference would such a change make to one not so designed. The numbers can be calculated, the result can be guessed, but only one way to find out.