July 17, 2018
The Bitmap was designed as an aggressive hardtail, intended to be as fast and as fun as possible. With that in mind, we built it around the new generation of wide rims and tyres. But can it be run with a plus sized tyre?
The last couple of years have seen a proliferation of new options for wheel, rim and tyre sizes, and this has created a bunch of new niches for bikes to plug into. So when we set out to design the Bitmap one of the first things we had to do was work out where it would fit into this brave new world. You can read about the Bitmap's development here but the short version is that we decided on a 27.5x2.6" tyre with loads of mud clearance. For us, that meant we could run short (420mm) chain stays and get the benefits of the latest aggressive tyres without having to make any compromises.
Since we launched the Bitmap a few weeks ago, we've had a lot of questions about what tyres you can fit, and it turns out there are a bunch of people out there who probably would want to run their hardtail with a 2.8" tyre. So we decided to give it a go:
I know that plus tyres can be a bit marmite when it comes to aesthetics but to me at any rate, the Bitmap looks sick with these tyres on. Maybe that's because there's a lot of tread on this particular combo. But the big tyres passed the first test.
To really make sure we were testing this out properly, we went for an full-on combination; the Minion DHRII 2.8" front, which has arguably the most aggressive tread pattern of all the Maxxis 2.8's, and a High Roller II 2.8" rear, which is what you'd probably run in combination. There are other 2.8" tyres such as the Rekon which would roll a lot faster, but since we were trying to work out clearances, there didn't seem much point in going for a half-measure.
This new generation of tyres is designed around a wider rim, and this was essentially a clearance test, so we went for a Hope Tech 35w rim - that's a 35mm internal, 40mm external rim. When you fit a smaller tyre on a rim like that it squares off the profile a bit, changing the ride character. That can be a good thing with a lot of tyres, but you have to exercise a bit of caution. In this case though, it makes the tyre sit exactly as intended.
The High Roller II 27.5x2.8" goes in just fine, with ISO clearance (6mm) all round, so no problems there. We'll take a closer look at that a little later on, but it gives us confidence that you could run any of the new Maxxis 2.8" tyres in the Bitmap and still have enough clearance for the inevitable mud when the weather reverts to normal.
All our bikes are fitted with Boost compatible forks now, with a 15x110mm front axle spacing. That means there's a good amount of clearance for a 2.8" tyre up front and we still managed to fit our Airdrop Marshguard with plenty of space.
No clearance issues on the seat stays, but that was never really a concern. The Bitmap's seat angle is relatively steep at 74° so there's plenty of room for manoeuvre. And mud.
As you might expect, things are a bit tighter around the chain stay yoke. This is where we put a load of design effort into keeping the chain stays nice and short, good mud clearance and ISO clearance both for the tyre and chainring (you can run a 36t ring no problem). As you can see, the 2.8" tyre fits with enough clearance but it's pretty obvious that this is about as big as you'd want to go. Having said that, 2.8" really is as big as I'd want to go anyway.
In this side-by-side comparison you can see a range of tyres in ascending (nominal) size starting with the WTB Vigilante 27.5x2.3" which is by no means a small tyre. From there we have the Convict 2.5" which is a seriously aggressive, heavy duty tyre, the new Trail Boss 2.6" (this is a sample) and then onto the Maxxis High Roller II 2.8" and finally the Maxxis Minion DHR II 2.8" which is arguably the most aggressive of the new Maxxis 2.8's.
It's worth noting that tyre manufacturers all measure tyre width in different ways, so one brand's 2.6" is not the same as another brand's 2.6", and to make matters worse, they might not actually measure 2.6" at all depending on the rim and the pressure. What's more, nobody mentions the external diameter (tread tip diameter) which all helps you to understand how big a tyre really is.
The Bitmap was designed around a tyre that has a tread width of 69mm and a tread-tip diameter of 723mm. That's exactly what you get with the new WTB Vigilante 2.6" tyre, which our good friends at WTB were good enough to tell us about in advance. What's interesting is that's also almost exactly what you get from a Maxxis Minion DHRII 27.5x2.8" tyre. So the WTB 2.6" and the Maxxis 2.8" are very similar size in real terms.
We state that the Bitmap's max tyre clearance is 2.6" and that's what got people asking questions, but it turns out that running a Maxxis 2.8" is more or less the same thing.
So yes, you can run a 2.8" tyre, if your brand preference is Maxxis. If you prefer WTB or Schwalbe, 2.6" is the way to go, but that doesn't mean it's a smaller tyre. And obviously we're happy to supply and fit them to your Bitmap if that's how you want to run your bike.
The other question we're getting asked a fair bit is whether you can run a 29" wheel in the Bitmap. It's understandable given that so many companies have released bikes that you can run either as 27.5+ or 29". But those bikes basically were designed as 29ers, with enough clearance on width that you can run the smaller wheel with a higher volume tyre if you choose. And to make it work, you have to run a 29er fork.
The Bitmap has been designed as a 27.5" wheeled bike, to run 27.5" forks. Yes it has plenty of tyre clearance and that enables you to run a big 2.8" tyre, but that's very different to a bike that was intended to be a 29er originally.
To express that in terms of actual tyre sizes, even a fairly modest 29er tyre such as a WTB Ranger 29.x2.4" has a tread-tip diameter of 746mm. That's fully 23mm bigger than the Bitmap allows for. If you wanted to run a decent volume tyre such as a WTB Vigilante 29x2.5", it's 755mm. Sure, we could design a bike around that tyre, but the Bitmap isn't it. And if it was, the Chainstays might have to be a good 20mm longer. That's not a compromise that we were willing to make when we designed the Bitmap, nor is it a compromise that we'd be comfortable foisting on our customers. It's an alluring thought - to have a frame that you can fit any wheel or tyre to - but you have to consider if all that versatility is really worth the inevitable compromise.
If we were to do a 29er, it would be designed from the ground up to be just that. But maybe that's a debate for another day...
At time of writing, we've got Bitmaps in stock in all sizes and colours. You can buy it as a frame only option, and we chuck in our new CNC seat clamp and rear axle for free. or you could take a look at our three standard build options; the Bitmap Trail, Bitmap Pro and Bitmap Works. But if you're reading this because you're plus-curious or you want to run a bigger volume tyre, probably the best thing to do is give us a shout and we can talk through what options you're interested in. We can source pretty much whatever tyre you like and we're happy to advise.
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Ed is the owner of Airdrop Bikes. A former web and graphic designer, he sacked off his job one day and decided to start up a bike brand.
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We're always working on stuff behind the scenes, and we'd like to share some of those stories with you. Some things work out, some things don't - but it's always interesting.
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