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Proper Coil DH Forks Tire Clearance

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
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So I'm thinking long-term I want to ditch this Mastodon on the Foes, the air-spring is asinine in the cold and the equalization gets all fucked up and you have to connect a pump to the bottom, etc. I'd settle for a coil kit for it, but they have no plans. There isn't much else, except the single crown inverted Wren.

I did see someone with a red mutz with a red 2004 marzocchi Monster T. Not interested in trying to dig up that kind of crap, but it did give me the idea.

I figure I'd need the arch clearance starting at the arch and then maybe every 10mm down until the legs are straight. I can probably do the rest, as most list their A to C. I just measured my tire and it's about 14" axle to the top of the tire, normal 27.5x2.5 is about 14.5, 29x2.5 is about 15.5.

So by those numbers, it appears a 27.5 fork would work for vertical clearance, also the fact that the fat tire is a little lower buys me a little extra clearance in the arch...but that's what it would come down to. And I'd probably want a 29er fork, because my summer wheelset is 29er for the bike, so preferably, 29er DH fork numbers. I see *most* are making them now, but mainly I want to stick to coil and probably 180 travel.
So anyone got a current coil DH fork they can take the measurements on?

I figure there's a good chance of this working with the right fork...Kinda interested in the Ohlins...but there are others.

clearance.jpg
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
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My Zeb looks close, maybe even work with a 4" tire instead of my 4.6, but I'm thinking DC legs may be spaced out a little more for turning radius than this. Also, it's not 29 though.
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
I got a nice PDF from Ohlins, showing the exact dimensions. it's about 10mm too narrow...but close
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
A Manitou Dorado Comp seems like it would suit your purpose.
Yes, but so far, they are being idiotic. I keep explaining that I'm asking what the width of the legs is just below the crown, and they keep saying the vertical limit is this...here's a chart from the website saying the max tire size. I keep explaining that 26x4.5 is LESS TALL as in SHORTER than a 27.5x2.5 (I've got them both here on the floor) so the limiting factor is that width...but they just don't seem to get it. Have explained it 3 times now. Hell, even sent a picture.
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
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Ok, I'm stupid, it is a little taller than a 29 and definitely taller than a 27.5. Comes out to 374.65mm axle to top of the tire. That seems to be within the normal 29er height though, but width is definitely the problem. Manitou dorado is 103mm wide, the tire is 110mm at the widest point. Ohlins is between 98.6, 102 at the arch and 105 legs. Obviously not enough room. Maybe with a "4 inch" tire, but I don't want to run those skinny-fat tires.
 

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,273
149
Vancouver
Anyway you could just disable the air spring and ghetto-rig a coil in there from a different fork? (coil from either Push or Vorsprung)
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
Anyway you could just disable the air spring and ghetto-rig a coil in there from a different fork? (coil from either Push or Vorsprung)
34mm stanchions makes it really difficult. I've raided the local shops, I have multiple Push coils from my Lyrik, but they are a bit too long for one (the Masturbon is 150mm), and for two, they only fit if you take the plastic shrink-wrap off (34mm problem). I've already raided the local shops for the pre-cheapening-forks-with-air-spring days but the 34mm issue becomes the main problem, springs are either way too skinny for old 32mm chassis or for 35mm forks. Then I think I'd also have to fashion up some kind of coil negative spring for top-out?

So like a really wide-spaced DC would work...old Monster chassis looks like possibly they would, except the vertical clearance definitely wouldn't work with the Pre-2003 models and no one wants a 12lb fork anyway. Dorado is close, but still a bit too narrow. I've heard of people getting custom crowns made for it, but that's a hell of a longshot.
 

Lelandjt

Turbo Monkey
Apr 4, 2008
2,264
615
Breckenridge, CO/Lahaina,HI
Yes, but so far, they are being idiotic. I keep explaining that I'm asking what the width of the legs is just below the crown, and they keep saying the vertical limit is this...here's a chart from the website saying the max tire size. I keep explaining that 26x4.5 is LESS TALL as in SHORTER than a 27.5x2.5 (I've got them both here on the floor) so the limiting factor is that width...but they just don't seem to get it. Have explained it 3 times now. Hell, even sent a picture.
Measuring mine I'm getting 95-97mm between outer legs.
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
I've found a few pictures:
SDIM1263.jpg
FullSizeRender-5.jpg
42059096_2333625786712487_5534566300111601664_n.jpg
45406693251_c66cb4b068_b.jpg





Both a DC and coil conversion seem equally longshot right now...
 
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Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
For hardtail fat bikes, a headshock/action-tec setup would be tits. One the biggest issues with suspension on fat is having to have like a foot-wide crown, massively heavy any way you do it.
 

iRider

Turbo Monkey
Apr 5, 2008
5,094
2,526
Can you not buy some spring and ghetto fit it?
Make spacers/seat on the lathe, put a roadie inner tube around it, old elastomer as bottom out bumper. I did that back in the day when I needed a different spring rate for a Dorado and Manitou could not provide anything.
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
Can you not buy some spring and ghetto fit it?
Make spacers/seat on the lathe, put a roadie inner tube around it, old elastomer as bottom out bumper. I did that back in the day when I needed a different spring rate for a Dorado and Manitou could not provide anything.
What lathe?

But yeah, trying to do some sort of coil conversion is possibly the deal, just have to find the right spring, which so far has been fruitless. There were lots of 150mm dual-coil spring forks, but not many single coil ones and then they were usually tiny stanchions, but 34 is just kind of "in between", which makes it difficult. The only thing that "spring finder" brings up in the range of length, width and force is a 100mm travel spring :( I can probably figure out some "hats" for buffering the ends of the spring.
 
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Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,589
906
SWE
Doesn't seem easy... another long shot: maybe you could fit an old u-turn coil in the Mastodon? I manage to fit one in my son's suntour. Off course you would have to convert first the threading in the casting that is so dear to Manitou to something more plain and conventional. Then find the proper rate for the coil. Length of the coil is easily adjusted with a grinder if the u-turn adjustment is not enough
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
Doesn't seem easy... another long shot: maybe you could fit an old u-turn coil in the Mastodon? I manage to fit one in my son's suntour. Off course you would have to convert first the threading in the casting that is so dear to Manitou to something more plain and conventional. Then find the proper rate for the coil. Length of the coil is easily adjusted with a grinder if the u-turn adjustment is not enough
I have an old U-turn pike coil, I haven't been able to get that bottom U-turn thing off though and I think I was having other issues with it being too long or something.
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
Maybe I'm not thinking about this right though. I was thinking of having the spring sit on top of the air piston, using some sort of plastic spacer/hat, but all current springs like Push or Vorsprung are basically too long for this. Push is only just barely too long, so that makes me think if it's just a 150-160mm travel spring it would work, vs. the one-size-fits-all springs that Push and Vorsprung make for forks up to 180mm of travel. But if I were to junk the air piston, then I'd have basically unlimited space. I'd have to find a way to seat the spring though. That also seems to imply no top-out spring.
 

iRider

Turbo Monkey
Apr 5, 2008
5,094
2,526
I think just putting in on top of the air piston is not giving the spring enough room. The available travel of the spring is the sum of the gaps between the coils, then they bottom out. The chambers in air forks usually are too short from what I have seen.
 

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,589
906
SWE
I was thinking of having the spring sit on top of the air piston
From my limited understanding of the u-turn spring, it seems that it is only fixed to the crown and to the bottom of the lowers without any guide at the bottom of the stanchion. Top out seems to be covered by the spring extending or maybe by a top out spring in the damper?
If it works in a pike it could work in a manitou if you manage somehow to avoid the rotation of the spring.

By the way, did you ask Dougal at shockcraft if he has a solution for you?
 

Jm_

sled dog's bollocks
Jan 14, 2002
16,629
7,592
AK
From my limited understanding of the u-turn spring, it seems that it is only fixed to the crown and to the bottom of the lowers without any guide at the bottom of the stanchion. Top out seems to be covered by the spring extending or maybe by a top out spring in the damper?
If it works in a pike it could work in a manitou if you manage somehow to avoid the rotation of the spring.

By the way, did you ask Dougal at shockcraft if he has a solution for you?
From perusing his site, it actually does look like Manitou might have the closest spring I've found so far, Nixon coil spring intended for 145mm travel fork. 27mm OD, which is probably good, Push is around 29.8, but doesn't fit without taking the shrinkwrap off, so 27 would be fairly optimal likely. Correct/close rates too.
 

Leafy

Monkey
Sep 13, 2019
308
217
why not a cut to length die spring for a 1-1/6" hole, those have about a 27mm OD. Mcmaster sells them in to rates, you'll probably want the higher rate I would think. You could also use some 6-8" long springs with couplers, just remember when you put 2 springs in series you half their rate.
 

Cerberus75

Monkey
Feb 18, 2017
507
190
Maybe I'm not thinking about this right though. I was thinking of having the spring sit on top of the air piston, using some sort of plastic spacer/hat, but all current springs like Push or Vorsprung are basically too long for this. Push is only just barely too long, so that makes me think if it's just a 150-160mm travel spring it would work, vs. the one-size-fits-all springs that Push and Vorsprung make for forks up to 180mm of travel. But if I were to junk the air piston, then I'd have basically unlimited space. I'd have to find a way to seat the spring though. That also seems to imply no top-out spring.
How much too long? Ream out the top of the airspring. Put a metal washer to support bottom of spring.