Long Haul Trucker and Disc Trucker fork comparison

[andyh2]

Has anyone ridden both the canti / V brake Long Haul Trucker and the Disc Trucker? If so did you notice any difference in how the forks feel?

[robc02]

I haven't ridden them but I emailed Surly about the same thing and was told something along the lines that both forks are the same but with the addition of a disc mounting. I'll try to find the email, if it hasn't been deleted, and quote the exact wording.

I suppose there could still be a difference in compliance as the disc mount would stiffen the bottom part of one of the fork blades - depending on where the blade flexes on the non-disc fork. This might all be academic if using wide tyres.

EDIT: The email from Surly was actually about the frame, not just the fork. However, it said:

"Both frames are made of the same tubing, so they'll ride very similarly to each other.

The non disc frame weighs about 5lbs 8oz and the disc version weighs about 5lbs 11oz. The forks weigh about the same too - just a touch more for the disc at about 2.8lbs each."

[reohn2]

I've not ridden both but I have a DT fork on my Kona Dew Drop(for extra tyre clearance).There's not much spring/compliance in it but I don't think the LHT will be any different.
TBH comfort comes from big section,supple tyres run at the correct pressure for load with touring forks built to take front panniers.

[Brucey]

here

http://surlybikes.com/parts/forks/long_haul_trucker_fork

it says that the standard LHT fork is 2.3lbs; this would make it a medium-to-heavy weight steel fork for road use ( for comparison a 531DB fork with a 1" steerer is around 1.5lbs)

If the DT fork is 2.8lbs as indicated then that is 0.5lbs heavier than the LHT.

I've not had the chance to compare the DT with the LHT back to back but IME that kind of weight difference will invariably make for a correspondingly stiffer fork and that won't go unnoticed.

cheers

[stewartpratt]

My Disc Trucker frameset turned up a couple of days ago - haven't built it up yet and it's a few years now since I got rid of my LHT, but the DT fork certainly has heft. Not unreasonably so, but noticeable. For me that's no bad thing - I ride 62cm Surlys and have always found their forks too flexible if anything - so I don't personally anticipate an overly-harsh ride (we'll see); but for smaller folk maybe it'd be an issue.

[samsbike]

I find it interesting that the disc fork isnt significantly heavier.

[samsbike]

Sorry double post

[Brucey]

I find it interesting that the disc fork isnt significantly heavier.

well 2.8lbs vs 2.3lbs is over 20% heavier. If you repeated that exercise with a whole touring bike it would be about 3kg heavier.

20% in a fork is quite a lot; note that, because not all the fork flexes normally, you can (nay should) put nearly all the extra weight into the part that does flex, and suddenly a 20% increase in weight can be more like a 50% increase in stiffness or something.

cheers

[andyh2]

Interesting info as always. My experience with rigid mtb forks is that the Salsa Cromotos at 1100g feel significantly less rigid and more comfortable than On-one rigid steel forks which are about 100g heavier. Different design though too, with the Salsa forks having much more taper.
I'd be running Pasela 26" x 1.75" tyres, which I prefer the feel of, despite significantly less volume than 55mm Big Apples.

[Brucey]

you obviously can't tell by looking from the outside, but traditionally, fork blades are made by starting in two distinct ways.

Cheap forks are made from a starting tube that is plain gauge, or a form that is approximately constant weight per unit length.

Posher fork blades are made using a form that is butted from the start. E.g. typical Reynolds 531 blades are thicker-walled in the top 2-3" or so, where the bending stresses are normally highest, but plain gauge below that.

In either case the tube can be worked to yield an externally tapered form, but might well remain approximately constant weight per unit length wherever it started as a plain gauge tube. If so, the external diameter gives a good idea of how stiff that part of the fork is, but tapering at the tip (with rim brakes) is the icing on the cake, not the main deal that determines the fork stiffness, because the loads are lower wherever the fork is tapered.

[BTW A comparable product is a golf club shaft; these go double or more in external diameter, but remain similar weight per unit length; unless the tube is deliberately butted, the forming operations tend to retain constant weight per unit length because the diameter of the tube is easily varied, but the length dimension is not so easily changed.]

So in fork blades, the springiness is primarily determined by the wall thickness near the fork crown and then secondarily by the wall thickness and external taper in the rest of the fork. Some older patterns of 531DB fork have a really nice flex to them because they have both quite light gauge walls near the crown, and then a thinner walled blade that is externally tapered near the tip.

1" steerers flex significantly too (more so in larger frames where the steerer can flex more); pretty much all are butted internally, and if not they would not be strong enough. I have occasionally seen forks that were made where too much was trimmed from the butted portion and the steerer was weakened; I have also seen the converse where the stem won't go all the way in because the butt is left too high.

1-1/8" steerers are not usually butted but they can be; they are pretty stiff without additional butting. You can take it as read that any 1-1/8" steerer will be pretty stiff to the point that on most road frames (even ones for touring with a fair load) the flex in the fork will be mostly in the fork blades rather than the steerer.

Unlike rim brake forks, disc brake forks see exceptionally high bending loads local to the disc mount and one fork leg sees most of the gross bending load too. If you start with a design for a nice springy rim brake fork with gauge that is adequate near the crown, you will normally need to thicken it there (because of the gross loading) and in addition thicken the wall (and/or increase the diameter) near the disc mount too (because of the local loading). Obviously the disc mount stiffens the fork tip directly, but this alone usually doesn't have a big effect on the fork flex.

0.5lbs of extra steel seems about right to beef up a fork to take a disc brake, and it should make the fork a fair bit stiffer.

So I would suppose that in the example above where a 100g lighter fork with a significant taper is a deal springier than another with blades of more uniform diameter, it is likely that most of the difference arises from the tube gauge near the crown (and hence the weight difference) and a much smaller proportion from the difference in the taper of the blades.

cheers

[andyh2]

Thanks for all that detail Brucey.

As an aside from the original query, but related to forks... all other things being equal eg forks designed for particular level of load carrying and either road or off road would the order of potential fork 'springyness' be;
Caliper (because the braking forces go through the fork crown rather than fork leg?)
Canti
Disc or other eg internal hub brake (because the braking force is amplified by being applied at the end of the fork leg which then produces a lever effect and is applied unevenly on just one side?)

My 30 year old 531 caliper braked Galaxy feels quite a lot nicer than later 531ST canti versions. Though I suspect the latter are better load carriers.





do caliper brakes which

[Brucey]

I think that is about right but with the following comments;

- I think there are very few fork blades which are so lightly made that they won't take a traditional brazed-on canti boss. However I'd fight shy of using full V brakes on some unless I was sure that the bosses were definitely on the thicker part of the butt (this can vary with the trim that the framebuilder used, as well as the fork blade design).

- Disc brakes and other hub brakes don't all exert the same loads on the fork. Disc brakes apply a torsion loading to the fork blade as well as a bending load, and other hub brakes usually do not. Most hub brakes are not as powerful as many discs are. In addition the reaction arm on a hub brake (in contrast to most disc mounts) reaches about half way up the fork leg. The simple, apparently crude, clip fitting that is commonly used to mount the end of a hub brake reaction arm obviously doesn't involve any heating or welding of the fork blade, so there is no possibility of a softened HAZ or whatever where the clip mounts, and greatly reduced prospect of (say) fatigue damage. SA hub brakes (by accident) normally also share the torque loading through the axle to some extent too. Between these things and the typical usage of such brakes, hub brakes are commonly fitted to forks that otherwise use caliper brakes with no problems. I've seen quite a few SA hub brakes fitted to lightweight 531 forks with no reports of trouble in normal use, but then again aggressive use of an XL model brake might be a different kettle of fish.

cheers

[reohn2]

Can someone tell me where they're getting the fork weights?
I've looked on Surly's website and can't find anything

[robc02]

Can someone tell me where they're getting the fork weights?
I've looked on Surly's website and can't find anything

The weights I quoted (in italics) were emailed to me by Surly. Also, somewhere on Surly's website is a pdf on the LHT which includes the following:

Weight: 58cm frame = 5.15 lbs. (2.34 kg) Fork - uncut = 2.25 lbs. (1.02 kg)


EDIT: http://surlybikes.com/files/SURLYLongHaul.pdf

[reohn2]

Can someone tell me where they're getting the fork weights?
I've looked on Surly's website and can't find anything

The weights I quoted (in italics) were emailed to me by Surly. Also, somewhere on Surly's website is a pdf on the LHT which includes the following:

Weight: 58cm frame = 5.15 lbs. (2.34 kg) Fork - uncut = 2.25 lbs. (1.02 kg)


EDIT: http://surlybikes.com/files/SURLYLongHaul.pdf

Thanks for that.
On a slight tangent,interestingly the 58cm Salsa Vaya frame weighs 2.42kg and fork is 1,01kg which slightly heavier overall.