Can You Use Mountain Bike Forks For Rear Suspension? | Ask GMBN Tech

Can You Use Mountain Bike Forks For Rear Suspension?  | Ask GMBN Tech

(technical noises) – Welcome to Ask GMBN Tech. It’s our weekly Q and A show. If you want to get some
questions into ask us, there’s an email address at the bottom of the screen right there or you can add them in the comments below. Just make sure if you’re asking questions, use the hashtag #askgmbntech and the same goes for the email and you put it in the
subject line header there. So this week, we’ve got a lot of suspension related questions. So I thought I’d group them all together. So first up is from JJ Wood. “Hi Doddy and the GMBN Tech crew, I recently bought an older
model Rockshox Domain coil from around 2010/2011. It has had a U turn unit fitted.” U turn, in case you don’t
know, is Rockshox’s old system for winding down the travel without affecting the spring rate. Recoil systems, you could
literally pick up anything from say 140 to 110, just by
winding a dial on the top. It was very cool at the time. “I measured my sag to be around 30% and I would like to
lower this to 20 to 25%.” So basically meaning the fork’s
gonna be a little stiffer. “How can I do this? I don’t think any preload
spacers can be added to the U turn unit or that
the spring can be replaced. What would adding a larger
volume of oil do to the fork? Would this have the right effect? Sorry I have sent so many questions. I’m 15 and looking at using for downhill racing if that helps.” Okay, so as far as I know, I don’t think you can change the preload on the U turn system. You can change the fork springs, but getting that much difference, only like 5% difference in the sag, I’m not sure if there’s gonna
be enough variety of springs in order to do that. Now, I think there’s two
options you can really do and one of them would be to have the U turn unit removed from the fork, so you lose the ability
to adjust that travel. It will remain at the
full travel of that fork. I guess that wouldn’t be too much of a problem for you though, because you’re using the
fork for downhill racing, so you want all the travel on there. And what that would enable
is under the top cap which would not have the U turn system, it would mean you could
fit preload spacers. Now, preload spacers will not affect the spring rate of the fork. They won’t make it a harder fork, but what they do mean is
you’ll basically resist the amount of the fork will move initially with your body weight. So you can actually affect
the sag on there slightly, so that might be what you want to do. The other option is to remove
the coil unit full stop and have an air unit
fitted into that fork, which is quite a common process for people to do with coil shocks and vice versa actually, depending on your preference and what you want out of the fork. Rockshox are quite good, they’ve got a lot of
interchangeable components between forks like the lyric, the domain, the revelation, the pike, stuff like that. So definitely something worth checking out with your local or your
national suspension tuners, depends on where you’re based. If that’s in the UK, someone like TF Tuned will be
able to help you with Rockshox failing that, you should be
able to find a local person near you that will be able to help. “Hi guys, great videos,
keep up the great work.” Thank you. “I’ve recently got back
into mountain biking and I’ve bought myself a Vitus bike. I’ve found that I’m still the
aggressive rider I used to be and I find I can bottom
out my fork quite easily, with some runs at Bike Park Wales. I have a Rockshox recon
silver RL 27.5, 120 mil fork, and I want to make it more progressive. I’ve reached out to Rockshox, who confirm they do not
produce air volume tokens for my specific fork. Are you aware of any third party token that I might be able to use or any way that I can
make it more progressive? Thanks in advance.” No, unfortunately I
think there’s no options. That was the fork I used to
have on my Nukeproof Scout here. Now it is possible to put
volume spacers in that fork, but you would have to make them yourself and the reason for that is you can’t get any way of volume spacers fitting into the top cap system there. So it’s possible that you could make some that could slide in or perhaps
you could bond them in, but of course would definitely
invalidate your warranty if you did do that. It was something that
I was gonna do myself, but I never actually got that far, a million other things all racked up. I can still look at doing that, although I wouldn’t want to recommend it if you were going to do
something like that yourself ’cause it would definitely
invalidate your warranty. If you do want to do something like that and reach out to a suspension tuner, give Sprung Suspension over
at the Forest of Dean a shout. If you speak to Jake, he’s your man there and he’ll tell you if it’s something that they would be happy to do for you. Of course, they might
not want to interfere because of warranty issues, but it is definitely
something they could do if they wanted to help you. Okay, next up is from Christopher Walden. “Now, I really enjoy your
channels and appreciate all the work you guys
put into each episode. I’ve been researching mountain
bike rear suspension designs and I feel like I’ve got
pretty good understanding of the goals and issues
inherent to common designs. My question is, why don’t we see bikes with a simple fork on the rear? Is there a structural
problem with such a design? I included a photoshopped
picture of what I mean. Basically, the frame
would have another fork that is mounted to another
rear triangle of kinds. Let me know if I’m way
off target with my summary of what I think would be good.” so he thinks frames would be simpler, more standardized, no pivot servicing. Okay, so this is with your own design. First up, I just want
to call you out Chris, it’s a great idea, but
your particular design wouldn’t work for various reason. But I’m just gonna show
you a really old design on the screen there now. So the bike in question is a
Manitou full suspension frame. This particular one is actually manufactured by Marin Cycles and conventionally, they used
to have a pair of Manitou’s, front and back. And this bike in question
was raced by the late Earthquake Jake Watson. So he was a huge dude, as
you could probably see by the size of the frame on his bike. He was sponsored by Rockshox. So we’ve got a pair of
Rockshox forks on the front. The fork in question was
actually one of the early DH, which came before the box zone, who’s known as the Diablo. So quite a cool and rare fork on it. And on the rear, as you
might be able to see there, looks like a pair of what looks to me like a pair of Mac 21s
that have been modified to fit it on the rear of the bike. So, it’s a great idea
because you’ve got a nice low pivot behind the bottom bracket there. So it’s not really gonna interfere with your chain line too
much with chain tension. It’s got a horse link
over the bottom there, so your braking’s not really
gonna affect the suspension and of course, you’ve got the
suspension design built in. But of course, it is quite
a lot going on there. There’s a lot of extra weight
that you don’t really need. Of course, you’ve got two legs there. The legs have got air and oil
inside them, it’s expensive, it’s everything about it costs
more money to manufacturer, where there’s no reason to do it. You think how much a pair of
suspension forks can cost, it can be £1000 these days. So of course, rear shock
absorbers are very expensive, but they’re also a lot
smaller, they’re a lot lighter, they can do a lot more
with the design of them and also allows manufacturers to tune the feel of a bike a lot more and change the frame
design and frame layout by using a single shock absorber, as opposed to having a twin
legged fork on the back. Now that design concept came
originally from Manitou, so that’s Doug Bradbury. He was the maker of the
original Manitou suspension fork and the Manitou suspension bike, the FS, which you can see in this picture. That’s from 1991. So, it’s been there,
it’s been done before, but as you can see, it
just didn’t quite work out to be the best solution in the long term. However, I do think it’s one of the coolest looking bikes of all time. What do you guys think? Okay, next up is from Ewain Johns. “What is the best air
fork for 27.5 wheels, with a straight inch
and an eighth steer tube or is there any way I can
adapt anything from tapered? Any help appreciated.” As far as I know, I looked on the Rockshox
site, I looked on a Fox site, and I looked around a bit, you can get some X Fusion forks, but a bit sketchy on the details
on which particular model. So Rockshox have got the Reverb available in a straight inch and eight steer tube, which is a great fork. 27.5 inch wheels and it’s got various different travel options in
10 millimeter increments, from 100 millimeters up to 150. So it didn’t say which travel you wanted, so I’m guessing something
between 100 and 150 will hopefully suit you and the Reverb is a great fork too. Okay, next up is from
Christopher De Santis. “Watched all the tech shows, awesome.” Thanks, Christopher. “My Monarch Plus shock
always has oil on the shaft, is it a leak and how can I fix it? I’ve watched your service videos, but what should I be looking for? Cheers, Chris from Morro Bay, California.” It kind of depends how much you’ve got on the actual shock itself. So you’ve got to bear in mind that shocks do kind of
ooze a little bit out because there’s lubrication
oil on the inside, much like the lower leg
lube you get on forks and the whole idea is to
keep the bushes on the fork nice and lubricated so
everything’s sliding nicely with no friction on there. And of course, to help the
seals slide and not get caught or binded in any way. Now also part of that
job is preventing water and other muck getting in there. You’ve got lubrication there, obviously water doesn’t like oil. It tends to sort of move away from it. At least that’s part of the theory. So it does tend to be that. However, how long was it since you last had your shocks serviced? It might just simply
need a bit of a service and a fresh seal on there. It’s unlikely that it’s gonna
be any other kind of leak other than just a bit of lubricant
coming out via that seal. Otherwise, you would
definitely have noticed severe lack of performance, lack of damping, or even the
air spring failing on there, if there’s any of the
main seal on that shock. So I’m hoping it might, if anything, just be a new wiper seal needed or perhaps it’s just
leaking a bit of that oil that lubricates the
shock in the first place. Next up is from Kristian Farrujua. “Hey Doddy, love you show
and all the GMBN shows. I’ve got a Mondraker Dune.” Great choice, dude, love Mondrakers. “And would love to mount the shock in reverse order, if it clears. It’s a Monarch Plus RCT3. Would the shock work well
or could it get damaged? My main reason for doing this
is that I never use the switch and would rather have
the shaft more reachable for easier cleanup access.” To be honest, I don’t see why
you would put it upside down. Effectively because it
doesn’t limit any adjustments that you do want to make, even though you said you
don’t make adjustments. I still think it’s nice to
have that stuff to hand. Generally, people do frown the shocks that are mounted upside down. But as you can see on my Scott here, as part of the design to
have cables internally rooted on the frame and keep it looking neat, the shock is actually upside down. It has no affect on the
performance on the shock whatsoever despite what people will say. People will look at you and be oh, your seal’s gonna get dirty isn’t it. Look at the seals on the fork. They’re exposed in the exact same way as the shock is upside down. There’s no problem, especially
if you look after your bike and suggest you do look after it by sending on axis for cleaning. However, it does mean by having the end of the shock up that way, the suspension is a bit more exposed. So by tucking them away down
the bottom end of the shock there on the Mondraker, you’ve got the little mudflap that tries to keep it
sheltered away from wet stuff, it does mean it’s a bit
more prone to scratching, if you say you put your
bike on the bike rack, uplift wagon, anything like that. So from that point of view, it’s actually not the best idea, but I don’t think it’s really
gonna affect your performance. So if that’s what makes you tick and it doesn’t affect how the
back end of the bike works, go for it. So there we go, that’s another
Q and A session in the bag. Hopefully you enjoyed Ask GMBN Tech. Get your questions in below
in the comments and email us, we love getting your questions. For a couple more videos, click down here, if you want to see how
to change an inner cable, as part of our essential series, and if you want something
more suspension related, click down here to see what some of those tuning differences do when
you’re actually out on the trails so you can see the
suspension working there. As always, click on the globe
to subscribe to GMBN Tech and if you love mountain
bikes and working on them, give us a thumbs up.

About the Author: Michael Flood


  1. @askGMBNTech Hey doody ive got 27,5 wheels on my 2014 santa cruz Nickle which can with 26" . will i have any issues with this? i also want to put a 150mm fork on it but it is a 140mm travel. love the info and all of gmbn cheers Pommy fella living in Australia.

  2. Good video as usual. It’s amazing how many times I have had a question that someone else has asked on here. Cheers Doddy. ✌🏻

  3. #askgmbntech Hi Doddy! Love the channel! I have a Novatec D462SB-B12 rear hub and I have noticed that there is a side to side movement on my cassette. I have removed my cassette and as it turns out the movement comes from the cassette body. Is it normal for cassette bodies to have such movement and if not what can I do to fix the problem? Cheers!!

  4. The old Manitou FS was my dream bike when I used to bounce down rough hills on my Saracen Trekker, such a great looking design. I spent hours working out the parts list for my dream bike and that frame was always at the heart. Shame the reality of finances never came anywhere near to the dream of such a bike.

    Wonder if there are any still around, it would look sweet hung up in a bike cave. Or living room……..

  5. I remember seeing one of those manitou forks hanging in Harry halls bike shop in Manchester when I was a kid and just bring blown away.

  6. 3:07 @Dean You want: Formula's Neopos Volume Spacers. You can just chuck them into the chamber without the need to mount them, but You could try to glue them to the cap without blocking the valve

  7. About the tapered steerer fork into 1 1/8 steerer tube… why didn't you tell the guy about an option to use external cup instead of semi-integrated (zero-stack) lower headset bearing… (in case if that is a semi integrated HT frame of course…) those straight steerer forks are hard to find and limits your options to get a real bargain…)) I have done this my self and works great.

  8. Wow that photoshopped rear fork pic is hilarious. I think the guy should build it and send it at rampage. Problem solved….

  9. Hey Doddy I love the show and have a question for you. I’ve been looking at entry level full suspension trail bikes and have narrowed down to 2 bikes in general. One I can’t find a lot of reviews on but it does have a lifetime warranty on the frame and the components look decent. Have you ever heard of Fezzari and what is your opinion on them? I have my eye on the Wiki Peak.

  10. 2:15 i don't think that, that will work because i have a domain dualcrown on my donwhill bike and the stancions are not aluminium, they are stell or so. (Because the domain is a cheaper fork) I was thinking to do the same, throw out the coil and convert to air but many people told me that the inner diamater isn't the same as the aluminium forks and i haven't found an conversion kit for the domain or domain dualcrown. If it works and there is an conversion kit, please tell me.
    Thank you so much and greetings from Austria!

  11. Hi, love the vidoes. I am upgrading me front fork on my bike. Want either a good coil fork or a good air fork. Are there any good coil/air forks for under £200.

    I ride trails and want to get into a bit more downhill. Probably want around a 120mm travel.


  12. Howdy boys! #askgmbntech I'd love to hear your opinion on how far might the wheel size battle go. For a good few years 26'' was the thing in mountainbiking. Then a 27,5'' showed up and now after around 5 ish years 29'' seems to take over – seems like 29'' now is the big thing in enduro and dh as well. How do you see this evolvement of wheel sizes? Are bigger wheels coming in the nearest future?

  13. #askgmbntech I want to get a nice tool kit for maintenance at home. I can’t afford Parktools at the moment and the wife would probably kill me since I just bought a Giant Reign SX. Can you recommend a decent tool kit for a home bike mechanic? Thanks! Love the show!

  14. Absolutely, you could use a fork stanchion to dampen the rear. The dampen and rebound action are the same principle. Look at F1/Prototypes, etc. 4 corners of the same type of dampers. It's just a matter of design and application of a fork stanchion(s) mated to the rear of the machine.
    And this guy apparently thinks a stanchion is a go as well!

  15. #askgmbntech Hey Doddy, I use mirrored lens on my goggles; i have gone through a few lens now due to scratches from trying to clean off mud and rain on the trail by using the micro fibre on my gloves. Any tips on cleaning mud and water off my lens on the trail so I don't get anymore scratches? Thanks a lot.

  16. #askgmbntech Hey doddy ! I have a Monarch Plus Debonair on my Specialized enduro. And it's making a big "clonk" and it's vibrating the whole bike, when I'm in the open position. But doesn't in the trail or lift position. I've heard it can be a production issue. It sounds like a seal problem. Will rockshox send me a new one if I send this one in repair ? Cheers from France !

  17. You should make some service videos on unique brand tech. Like the Switch Infinity for Yeti! The old system and the new!

  18. #askgmbntech If the fork(Rock Shox XC 30 TK Coil 100mm) has a set limit for disc size (eg 185mm) why can't you fit a bigger one, I mean what are the issues that are going to or can happen. Cheers.

  19. 3:15 For Tokens a special Tipp =)
    Use the on that Formula sell like these:
    I use some self made similar and the feeling is very nice now.
    Fit´s in every Fork, because it is spongy.

  20. How strong do you think Carreras frames are? I’m looking at getting the fury, which has a good price and spec, but I’ve seen too many halfords horror storys

  21. #askgmbntech Hi and thanks for all the great content! I am currently building a hardtail from scratch using a Vitus Sentier frame and I was wondering if there would be any pros to modifying the cable housing stoppers on the frame to make the cable housing go through it rather than to have to cut it and have exposed wire in several places. Seems like I would want to avoid exposed wire if I can (riding in sweden can get wet and muddy). Any ideas as to how to proceed with this? Should I drill up the holes in the stoppers in the frame to make the housing fit through it and go all the way from the rear mech to the shifter or just go with cable ties along the frame? Or maybe just go with the exposed wire as the manufacturer intended… Thanks! /Henrik

  22. #askgmbntech Hi mate, I have a carrera subway 2015 model and as of right now, i shiamo gears and brake however they are joined together. I wanted to know if it was possible to change it to be seperated gears and brakes without damaging anything, my mate has done it on his bike but now his gears dont work or his brakes.

  23. Suntour Epixon & Epixon-TR are great forks with internally adjustable travel from 100 to 140mm depending which fork you have and if you have right tools you can adjust travel without voiding warranty. I've done this personally as advised by Suntour.

  24. Great show GMBN team…. So I'm looking at buying a second hand 100mm rear travel 29er full sus frame. Would putting my 27.5 wheels effectively increase the amount by which the rear wheel could travel by the difference in wheel size÷2 eg (38/2=19mm)? The bb drop is fine and fork will slacken the head angle to 68°. I'd like some first hand input nit just thoughts or opinions

  25. Hey Doddy, my gf and I were watching this video and could not stop laughing on segment 6:26!!! It looks like bike porn mate.

  26. The Manitou full suspension bike (Marin) talked about it was Uber cool still to this day (even if explained design was flawed + most of them cracked), always going to be a timeless design iconic image from my days involved with Mountain Bike XC (mostly XC racing) 1991 – presant.

  27. #askgmbn
    Hi Doddy and GMBN love all the channels I was wondering if I can put a tapered fork on a non tapered steerer tube? I am keen to upgrade my fork. Thanks for the help 🙂

  28. #askgmbntech ,,,,,,,,,I now have a two by 10 but if I would make it to a 1 I would also change my casette to a bigger one? and I put a dropper post on my hard tail (cube attention 2018 sl), what more could I upgrade ,the tires?

  29. #askgmbntech How far should the rear derailleur be from the largest sprocket? I have an M6000 rear derailleur with an 11-42 10 speed cassette. I already have the b-tension screw all the way in and I only have around 4-5mm clearance for the chain. I'm considering to install a goatlink for my setup because I'm having difficulty shifting to the largest sprocket. BTW, I have a single 34T chain ring up front. Love the show! Thanks! – Marc

  30. For the question wanting an air fork for a 27.5 straight 1-1/8 steering tube. You can put forks with tapered steering tubes in a straight head tube frame. Cane Creek makes headsets specifically for this. Link: Hope this helps.

  31. I think the fork for rear sus guy was either high af or he was trolling Doddy. Either way it's the funniest thing I've seen in a q/a video.

  32. Hey guys, i've recently bought an specialized stumpjumper 29 ht from 2012. I've got a Shimano Deore rear brake and the caliper leaks mineral oil. I know there are no repair kits for Shimano, but is there Any other way of fixing this problem?

  33. If you need a 27.5 fork you can also use a 29er fork and account for a 30mm difference in distance stanchion to bottom headset

  34. Dean, I had exactly the same fork on my previous bike and never managed to find any spacers. I had to resort to designing and 3D printing some spacers and then simply gluing them into the top cap of the fork.

  35. #askgmbntech I was out biking in -7 degree C weather on my local frozen but dry trails. My tires felt incredibly slower than normal, running normal pressure. Wonder if you could do a video about how temperature affects rolling resistance and if different compounds change this?

  36. My monarch rt3 dabonair has to be upside down because the air inlet valve is in the way of my linkage should of got fox instead

  37. #askgmbntech I just recieved a Canyon Exceed wms 8.0 cf sl. Much to my surprice it arrived with a “dork disc” fitted. Now I am wondering if I should remove it? If I remove it, I will have to remove it by destroying it, as I do not own the correct tools to remove the eagle cassete of the xd driver… ( my old bike was shimano equipped).

  38. #askgmbntech Doddy, winter riding where I live can be extremely cold and dry. I often find myself venturing out in anything up to -8°C. Are softer compounds such as the side knobs on Maxxis 3C tyres more adversely affected by the cold than say a dual compound? Much appreciated.

  39. #gmbntech Hi there, loving the tech videos and learning about all things MTB again, I am 53 and after loosing 4 and a half stone I'm wanting to get back into mountain biking after a 20+ years break, next year after I've built my bike cave I want to buy a Whyte T-130 s as I want to keep my bike in top condition I need to get a full set of tools, the trouble is I don't know what to buy, can you help please, thanks in advance.


  40. Hi doddy, just wondering why my gears have gone rubbish. I’ve got Sram GX 11 speed. My gears were working rubbishy-new inner and outer. Work great again. Then next muddy ride then don’t shift down into highest 3 gears. Any ideas. Cheers #askgmbn

  41. #askgmbntech Hi Doddy, I am going to build a dirt jump bike and I chose rear hub with 10 teeth as I dont have many options. I think of buying Shimano Zee crancks. So my question is should i stuck with the stock chainring or should i buy smaller one so its gonna be more easier for me to pedal? Or should I buy bmx cranks? Can you explain if the single speed works like normal drivetrain? Thank you!

  42. #askgmbntech I wanted to build myself a trail hardtail, but the frame I bought couldn´t be delivered. I was looking at the Nukeproof Scout 275 2019 but can´t find it anywhere in my size in grey and also at the Commencal Meta HT, but they recomend using a 29 fork with 555mm axel to crown, but I already got a 27,5 fork with 532mm axle to crown. Would that difference be to big?

  43. #askgmbntech I have a newer Fox Float X2. When I slowly put my weight on the bike (as if I'm checking sag) about 1/3 of the way into the travel there is slight resistance, then it gets softer again. At the same time I hear a really faint squish. Any ideas of what might be causing this?

  44. Great video, thank you very much! I leave you a review of the latest technology for your biking trips I hope you are interested, otherwise, I apologize

  45. 3:20 Formula neopos spacers might work for that fork. They just drop into a fork… not sure if it would work with the recon.

  46. #askgmbntech Hi I ride a Cannondale trail 4 and was wondering about the axels on it. They are thinner in diameter than the axels on the bikes you guys ride and they are not through axels. Are there any advantages or disadvantages of this and would I be able to jump this bike.

  47. Manitou FS. Ya, I'd gladly have one today. That and the Mountain Cycle SAN ANDREAS were my dream bikes back in the day. I would love to be able to build one up today. And yes,, I would ride them!

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