I just posted the second part of my Cotic BFeMAX review and noted in it that I have a new frame and swapped the Cotic parts to it…more or less. This is the new frame! In this part of the review I’ll go over why I choose the Sirius, what parts I built it up with, and provide some initial ride impressions.
When I decided to get a new frame I wanted a few things in the new ride:
- The frame to be available to actually buy!
- Shorter CS.
- Adjustable dropouts for SS.
- Shorter Reach.
- Lower travel fork than the 160mm on the Cotic.
- Moderately slack HTA.
- 31.6mm dropper.
- Fit 29 x 2.6″ tires.
- High Stack.
- STA that wasn’t super steep.
- Flexible frame.
- Works Component headset compatible.
- Colour I didn’t hate.
- Steel.
If you go through this ^^ list you’ll see that I managed to get everything other than the high Stack in the Sirius. I debated getting the Moxie frame as the MRP fork I had on hand could be adjusted from 140-160mm which fits the design of the Moxie better, but in the end I decided the Sirius was the better frame for me.
Build Kit
- Sirius S5 frame in silver [Long size]
- 140mm MRP Ribbon Coil
- Hope hubs + Velocity Blunt 35 wheels
- Maxxis DXF/DHR 29 x 2.6″ tires with a Tannus Tubeless insert in the rear
- Shimano Deore 4 piston brakes 200mm/180mm rotors
- 30T x 22T SS drivetrain
- RF Next R 170mm cranks
- RF Chester pedals
- I9 35mm stem
- Ergotec 780 x 70mm rise bars with Ergon grips
- 9point8 150mm dropper
- WTB Pure saddle
- RRP front fender
- Mudhugger rear fender
- Rock Bros frame bags
- PDW DT splash guard
- Fabric bottle
Dealing with Pipedream was easy. Their website tells you what’s in stock and buying the frame for shipping to Canada was not a problem. The cost including shipping, taxes, and brokerage was $1315CAD or ~$1053USD. I ordered a SS dropout and a few small hardware spares so my bill was a bit higher than just a stock frame. I lucked out as they had a batch of frames landing right when I was ready to buy one.
It took 7 business days to get to me here in British Columbia, Canada. The frame was well packed and arrived undamaged. The fit and finish were excellent. This is clearly a quality product. The silver powder coat was particularly lovely and I am glad I went that route. The frame + dropouts + axle weighed ~6.3lbs.
I put the fork from the Cotic onto my GG Smash since it was running a 160mm MRP Ribbon Coil. The Ribbon can be internally adjusted down to 140mm travel. That didn’t take too long and allowed me to clean/lube the lowers so I know the fork is ready for battle. The Sirius was designed for a 100-120mm fork and I am over-forking it. That’s not ideal, but I didn’t have a better option that I could use on short notice…plus this option was free.
My first ride around the neighbourhood on the freshly built bike I thought the 140mm fork was too slack and didn’t like how the bike steered. As it turns out once actually on the trails that feeling went away in 5 seconds and it handles great. I suspect the aggressive weight forward riding style that SS demands sags the fork compared to seated pedaling such that the dynamic ride height is low enough to hit the design’s sweet spot. That said I wouldn’t hesitate to spec a 120mm fork on this bike if I was buying new parts.
Like all my bikes the Sirius got full MTB fenders and a bunch of frame bags so I can do a long ride with nothing on my back. The frame comes equipped with only 1 set of bottle mounts. However, it would be pretty easy for me to install a second cage inside the frame and a third under the downtube if I wanted all day riding hydration in the summer. For winter riding one bottle is enough as I rarely drink much in our cool moist weather.
The frame does fit a Maxxis 29 x 2.6″ DHRII, but with the dropouts slammed forward the clearance is less than what I would deem useable. The way the CS are shaped near the BB every mm you pull the rear wheel backwards you get a lot of additional tire clearance. So you can still have fairly short CS and a big tire. You could run a Maxxis 29 x 2.5″ tire with the dropouts all the way forward. I didn’t try any 27+ tires.
I took the Sirius to my local XC trails just down the road. Think rolling forest terrain with enough roots to be entertaining. I was really blown away by how well this bike performed there. The Pipedream carved tight corners well and was able to take flight off of every small feature. Getting the bike on its rear wheel was easy. The lack of any extended steep climbs meant that the SS drivetrain worked well and the experience was very engaging. I’m stoked about this because now that I have trails right by my house I want to ride them and really enjoy them. Having a bike that does that is great.
Next up was taking the Sirius to the “real” mountain bike trails in Cumberland. These are more techy and feature steeper climbs and faster longer descents. Thinking just about how the bike handled it did very very well there. What I may have lost in terms of riding a shorter less aggressive bike I got back because I felt really in control of the machine and could push it harder. The more active riding style on this bike was a ton of fun. I definitely liked the shorter CS on this bike. That just feels more natural to me and I can both corner and climb better with the rear wheel tucked in close to me. The steering felt very neutral….neither too fast nor too slow. I was all smiles on the bike.
I have to say riding SS on steeper techy trails was a lot harder than the rolling XC trails near my house. It’s clear I need to work on my SS fitness as I was tired and breathing heavily a lot more than I would have expected. I did a few laps on the same trails and my ability to climb tech sections got better with a bit of trail knowledge as I could get on the gas a second earlier for stuff coming around the corner and that translated into cleaning stuff I walked the first lap. 30 x 22T is not a bad gear, but I think I will try 28 x 22T or 30T x 24T for an easier gear…at least to start. I am enjoying learning the ins and outs of SS on the trails. It’s definitely something I want to get better at and to do a lot.
How a frame flexes matters a great deal to me. I hate overly stiff frames. They feel dead and they do not perform well for me. I have had frames that were too flexible and that causes handling issues when you are riding aggressively. Of course frame flex is hard to judge in advance. I’m happy to report the Sirius is a pleasure to ride. It’s more flexible than the BFeMAX and less flexible than my Daambuilt Mega Krampus. That’s just about ideal for the kind of riding I want to do on it. The frame feel plus the coil fork make me think this will be a very comfortable all day machine.
When I started this project I had three questions:
- Would I enjoy the Sirius frame enough to make it worth swapping in for the Cotic?
- Would I enjoy singlespeeding real mountain bike trails?
- Could I ride SS for all my trail riding?
I feel like I can already say yes the Sirius provides the ride experience I was missing from the BFeMAX and I am really happy to be on the smaller more agile bike attacking the terrain. I can also say yes I enjoy the SS trail riding experience a lot and it’s here to stay. What I don’t know yet is how much of my trail riding can I do SS and how much do I really want a geared bike for? I plan to use the Pipedream as my main and maybe only winter mountain bike to see what happens. I will report back next year!
Anything I don’t like? Sure. I’m a fan of taller head tubes and the resulting higher Stack so I wouldn’t say no to a 130mm or 140mm head tube. While we are at it let’s make the seattube 30mm longer as well. I’m running a 150mm dropper because I had it and I’d put a 175mm dropper on there if I was buying a new part. I don’t need more dropper than that on what is a Medium size trail bike and I’d enjoy more frame space inside the main triangle. I’d move the dropper cable routing to the top of the downtube. I’d add a second set of bottle mounts above the first and a third set under the downtube. I’d tweak the CS/BB area so a 29 x 2.6″ tire would fit with the dropouts slammed forward.
None of these items are deal breakers for me or I wouldn’t have bought the frame and you can’t buy a production frame without some compromises.
vikapproved MK2 
Hi Vik, I would love to hear more of your thoughts about frame flex on a trail bike. I ride a Rawland rSogn on gravel & road – it has very skinny & flexible “standard” gauge tubes & I love it! It really surges forward as you accelerate. I also ride a Jones Plus on technical trails & it is too stiff on anything but the gnarliest of trails (even though I am very used to rigid trail bikes). I love its handling, capability, fit & comfort, but there’s none of the surging acceleration of the rSogn. My solution is to get a custom frame built with the geometry & fit of the Jones, and the flex of the rSogn – built around 2.8” tyres. This will be for our typical local allroads riding – sealed roads, gravel, and some trails. I am also pondering a custom trail bike frame with a suspension fork. The question there is: how much flex? Your guidance is appreciated! I loved reading about your Daambuult. No-one is talking about the benefits of flex in a mountain bike, so I was thrilled to read that you are.
Cheers from Christchurch, New Zealand.
Marty Budd.
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Hi Marty,
I hate that dead feeling of an overly stiff bike. I demo’d a couple steel Jones bikes [Space and Diamond frames] they didn’t spark my interest so I never bought one despite liking some of the design ideas behind them. Your question about how much flex is too much is an important one and really hard to answer. I can say that for a trail MTB with a longish fork [say 140mm or longer] there is a lot of leverage on the front end of the bike. As the fork gets shorter that decreases. You are also riding a bike like that on rougher surfaces with stronger handling inputs. So the trail bike definitely needs to be stiffer than the road bike. One mitigating factor is that, typically, MTB frames are more compact than road frames for the same size rider.
The trouble of course is deciding what that means for tubing/bracing/etc… If you are going custom with an experienced builder you can show them/tell them what you enjoy about the Rawland and what you don’t like about the Jones. They should be able to use that plus you weight/size and the specs you give them for the custom bike to suggest what tubing to use and perhaps if any gussets/bracing is required. I don’t have any magic formula to use in this regard and nobody I know has this perfectly dialed. OTOH I do think there is a somewhat broad range of frame flex in a particular bike that you’d enjoy. So I don’t feel like it’s a tiny target you are trying to hit.
In a perfect, money is no object world, I’d say get a raw frame put together and don’t paint it. Ride it. Give your builder feedback and he/she will build you a 2nd bike [hopefully the final one] ride it raw again and see if a 3rd version is needed. Once you get the bike dialed paint the final frame and ride it. You could sell the protos and recover some $$, but it would be an expensive project. That said you’d a really great bike out the other end.
One way to short circuit/cheat this process is to find a builder who really “gets” frame flex and who has built many frames similar to what you are after. They’ll be able to use all that previous experience to get you fairly close to where you want to go the first time. Sometimes folks choose a builder who makes amazing bikes and then asks for something quite different than the builder normally makes. That’s fine, but in those cases they have to appreciate they are not getting as much benefit from the builder’s experience as they could.
With my Daambuilt I would say we landed on the flexy side of what would be acceptable. It shoots up climbs as you note with your Rawland and I love that feeling. I’d done a fair bit of real mountain biking with it and it handles that very well. That said I would not want to go any more flexible and I would not want to put a longer fork on it [thinking about the leverage here not the HTA]. I use my Daambuilt as my bikepacking/All Road machine mainly these days and the flex is welcome.
The new Pipedream Sirius S5 is not as flexible as the Daambuilt, but does have a compliant enjoyable ride. I think for a dedicated MTB it’s a very appropriate level of flex. Especially run as a SS because the climbing efforts are much more aggressive and I have over-forked it with a 140mm travel unit vs. the 100-120mm travel fork it was designed for.
I’m not sure if this ^^^ was helpful. Feel free to send me any more comments and questions. Let me know how the custom frame works for you.
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Hi Vik,
Thanks so much for your reply. It’s very helpful, and I’ll be drawing on your comments as I start working with a custom builder.
I’ve just been away for a week, doing some excellent trail riding. I was on my Jones Plus and was reminded of what an excellent-handling bike it is, especially at high speed on singletrack. But it does lack that “unseen hand pushing you from behind” when climbing – except when it’s fully loaded bikepacking, which is interesting. I guess the stiffness is overpowered a little by the load. Makes sense. Since my last loaded bikepacking tour I’ve lost 10kg, so I wonder if it’ll have “lost” some of that feeling next time I rode it loaded? It’ll be interesting to see. I overlooked mentioning that my Jones Plus is steel, as was my previous Jones – a 2011 SpaceFrame. I think the titanium Jones bikes probably have the right balance of flex I am looking for, but….$$$$$.
The Custom I’m going to get will have a non-suspension-corrected steel fork, so it’ll be optimised around the fork that’s on it, but I’d love to hear more of your experience mountain biking on your Daambuilt and its flex. At times when perhaps you felt the flex was bordeline-too-flexy, how did that reveal itself? What characteristics tell you that the flex is almost too much? If this Custom frameset works out really well for me, I would consider a hardtail trail MTB frame from the same builder. It would have a 120mm maximum fork, so not too long a fork. And it too would be all about the exhilerating ride of the bike.
Regarding too much flex, sometimes my Rawland rSogn will ghost-shift if I stand up and pedal too enthusiastically, so I have learnt to manage that (and use indexed shifting rather than friction). To be fair I was 98kg and am 6’3″ so the chainstays might have benefitted from being a bit stiffer.
I am still nutting out which tubes contribute most to the beneficial flex we are talking about. I have been reading up on Bicycle Quarterly, and Jan Heine’s new “blue” book, and it seems that flex in the top tube is the key thing, with the downtube being reasonably stiff and the chainstays being stiffer.
BTW, although I haven’t read your Cotic BeFe experiences yet (because I’m not drawn to “beefy” bikes), did you consider the Cotic SolarisMax? On their website they make quite a point of saying its top tube is flexible, embuing the bike with a lively ride. That certainly appeals to me, and in future if I do not go down the custom hardtail trailbike path, I can at least see myself getting one a SolarisMax.
Cheers, Marty.
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My Krampus rides amazingly with a load I wouldn’t say it’s overly stiff unloaded, but an extra 30lbs does make it ride better. I think that’s one of the reasons I enjoy it so much SS. The extra aggressive pedal inputs probably do some of the same things that the extra weight does in activating the bike’s flex.
The only times the Daambuilt has felt too flexy are on tour [so extra weight] and at higher speeds on rough roads. It’s happened 4 or 5 times and it hasn’t been terrible, but the way the inputs from the road come through the frame it just feels too “alive”. I don’t notice it at slower speeds or when riding unloaded. It’s happened enough times that I know it’s a “thing”, but not enough like I feel I have to do anything about it. My touring load is fairly light. I suspect that if I carried a lot more weight the issue would happen more, but that’s just a guess.
I have had overly stiff touring frames and I hated that. They rode very poorly unloaded and not great loaded. Lose – lose.
The BFeMAX is not an overly stiff frame although based on anecdotes the SolarisMAX would have been noticeably flexier. I preferred the geometry and frame features of the BFeMAX. I’m not a fan of the longer CS that are part of the Cotic hardtail design. Both models share that attribute so I didn’t see any point sizing down and/or trying the other model.
Jan’s work is very interesting to read. My one caveat is he’s basing his theories on road/all road/cyclocross riding and in those areas I have a high degree of confidence in him. When he has pushed this theories into mountain biking without that large data set/experience to back it up I have not agreed with some of the things he’s said. I wouldn’t hesitate to use ideas from BQ as inputs for designing a MTB, but I wouldn’t take them on faith in the same way I would if I was designing a rando bike.
Good luck with the custom build. I wish I had some sort of formula to specify the “right” amount of flex in a new frame. It’s a bit of a crapshoot. You just have to make some educated guesses and hope for the best. This is why finding a builder with a lot of experience in the sort of bike you are after is key. They’ll be a lot more likely to translate your requests into reality than someone who is used to building different bikes than the one you are after. If you are willing to build a prototype that would really help, but it’s $$$.
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Hi Vik,
So this is your first SS? I recently became interested in SS and decided to buy a Sirius frame (got from Steve – Hardtail Party YT channel), and build up SS, rather than put a tensioner on my Knolly Tyaughton, and run it SS. So this will be my first SS as well. Building up with a Sid 120mm fork and 29×2.6″ tires. I was hoping I’d be able to run the sliders all the way forward with these tires, and I don’t need much clearance riding here in the dry AZ climate, but we’ll see what happens. Taking frame and parts to LBS this afternoon, to have her built up. Can’t wait to see how I like her, just came across this review today, and am now even more stoked! Thx.
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Hi Jeff,
I’ve had a SS gravel bike and currently have a SS rigid MTB I use for everything from city riding to gravel, but not techy trail riding. The Sirius is my first dedicated SS trail bike. Something with small side knobs might work in 29 x 2.6″ with the sliders all the way forward. I’m running Maxxis 2.6″ tires and they are fairly small volume for their size.
Good luck with the new bike. I hope you enjoy it. 🙂
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