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.