Talk to me about B+

[Chew]

Ive been thinking of getting some B+ wheels for the winter to try out.
Kinda mini fat, for those wet moorland crossings where the extra footprint will hopefully offer more float.

[Mariner]

Published on Jan 23, 2015

After years of arguments and speculation as to which mountain bike wheel size is fastest, we tracked down someone who's trying to prove it... with actual science!

https://www.youtube.com/watch?v=vhS1HfvBeYA

[GregMay]

Published on Jan 23, 2015

After years of arguments and speculation as to which mountain bike wheel size is fastest, we tracked down someone who's trying to prove it... with actual science!

https://www.youtube.com/watch?v=vhS1HfvBeYA

I was one of the subjects for that study :)

They we're certain it would turn out differently, made me laugh when I came back 1.5mins ahead of the time they expected on the 29er :)

[ZeroDarkBivi]

Well, those results certainly surprised me. I would have expected the opposite from what they concluded for climbs & descents - I have found 29" feel slower on the ups and quicker on the downs. The in-the-middle wheel size (650b) being slowest makes me wonder how credible the science is...as Joe said, Nino Schurter has it all wrong!

I don't understand what Dr Howard meant when he stated that, “In scientific terms there was no difference whatsoever… but in practical terms the 29er was faster.” No mathematical difference from the statistical analysis software – what does that mean, other than they wasted a lot of money on all those hi-tech gadgets?

[Mariner]

I think in the end its up to you and what works best for you and what you are trying to achieve.
These tests all seem to be about 'performance' while I am just riding A-B with a load of gear on board for extra weight.
Devon Dirt a few weeks ago had 430ish starters. I saw 2 'odd' bikes in the form of two Gravel bikes on 'thin' tyres while the rest were all generic mountain bikes in one guise or another.
I rode in a group with one of the gravel bikes and was amazed at the grip he was getting up muddy climbs where I thought I would catch and overtake.
His tyres were rounded with a fine diamond pattern against proper knobblies in various forms.
The all round performance made me start to wonder next bike?.
I had just dumped the 650b wheels and tyres and switched to 29er but still had the rigid fork fitted.
In fact the only 650b tyred bikes I saw all day were on the Marin stand.
Perhaps 'we' are asking the wrong question and Gravel+ is the answer.
Be interested to see what turns up at the HT next week.

[GregMay]

I don't understand what Dr Howard meant when he stated that, “In scientific terms there was no difference whatsoever… but in practical terms the 29er was faster.” No mathematical difference from the statistical analysis software – what does that mean, other than they wasted a lot of money on all those hi-tech gadgets?

[sciencehat]
What he means it was not a statistically significant difference at a level of <p0.05, or even p<0.01 - or less than a 5%/1% difference between them. It's what we as academics need to have to declare something statistically significantly different.
Practicality has nothing to do with it in science, I'm even surprised he said it, you'd get slated in a paper if you put that in...but in terms of performance in a sporting context - ie racing - it has everything to do with it. a 2 second difference may not be statistically different, but it you watched todays XCO in Germany, 2 seconds would have very much won the race - it came down to a wheel length on the line.
The gadgets aren't that high tech they used, pretty normal lab equipment these days. Some of the stuff they are planning to use...that's different.
[/sciencehat]

I'll go back to pretending I'm an idiot again.

[DrMekon]

I don't understand what Dr Howard meant when he stated that, “In scientific terms there was no difference whatsoever… but in practical terms the 29er was faster.” No mathematical difference from the statistical analysis software – what does that mean, other than they wasted a lot of money on all those hi-tech gadgets?

[sciencehat]
What he means it was not a statistically significant difference at a level of <p0.05, or even p<0.01 - or less than a 5%/1% difference between them. It's what we as academics need to have to declare something statistically significantly different.
Practicality has nothing to do with it in science, I'm even surprised he said it, you'd get slated in a paper if you put that in...but in terms of performance in a sporting context - ie racing - it has everything to do with it. a 2 second difference may not be statistically different, but it you watched todays XCO in Germany, 2 seconds would have very much won the race - it came down to a wheel length on the line.
The gadgets aren't that high tech they used, pretty normal lab equipment these days. Some of the stuff they are planning to use...that's different.
[/sciencehat]

I'll go back to pretending I'm an idiot again.

I fear you're in danger of misrepresenting what p values mean there. It very much sounds like you are talking about effect sizes, whereas the 5%/1% you mention refers to probabilities of a rejecting a null hypothesis falsly (a torturous way of describing null hypothesis significance testing - NHST) - ie if you tested two different tyre sizes (say 29 versus 26) and the test you used didn't result in a p value of <.05, then you could say that you'd failed to falsify the hypothesis that there was no difference between the two sizes (the null hypothesis). If, instead, the test found p<.05, you could say that there's a less than 5% chance that rejecting the hypothesis that there was no difference was an error (ie a type 2 error). As an aside, it's routine to allow a 20% chance of a type 1 error.

NHST doesn't prove anything true, it just proves things false... and as Feyerabend would point out, valuing experimental hypotheses that have resisted falsification still relies on the metaphysical construct of consistency. ie what's the point of any of it - we could all turn in to <insert delicious fruit based spread here> tomorrow.

To look at effect sizes (how big the difference is of wheel size), properly, I'd like to see a meta-analysis, rather than any one trial. Much as I'd like to do more cycling research, my life is too short for that one - and 29+ is best anyway

[GregMay]

I will admit I was trying to not put my big science hat on :)

[benp1]

I rode in a group with one of the gravel bikes and was amazed at the grip he was getting up muddy climbs where I thought I would catch and overtake.
His tyres were rounded with a fine diamond pattern against proper knobblies in various forms.
The all round performance made me start to wonder next bike?

I've always thought that was dependant on the actual surface?

Mud over some solid or hard pack then thinner tyres cut through the mud and find grip below

Anything really slippery like wet grass or mud/mud/mud and you need a fairly aggressive tread

I still find it hard to understand how tread makes a difference on a gravel bike - see my STW thread where the question never got answered really - http://singletrackworld.com/forum/topic ... tyre-tread

[DrMekon]

I will admit I was trying to not put my big science hat on :)

I wish I had one of those. I don't even have a white coat.

[GregMay]

I will admit I was trying to not put my big science hat on :)

I wish I had one of those. I don't even have a white coat.

I can send you one of mine. It's mostly white. Some blood, but mostly white.

[benp1]

I will admit I was trying to not put my big science hat on :)

I wish I had one of those. I don't even have a white coat.

I can send you one of mine. It's mostly white. Some blood, but mostly white.

Sounds like an abattoir coat

[whitestone]

F*** me! When Stu mentioned that getting the WTB tyres *off* was hard work he wasn't kidding! Thought I'd put the tyres on to the Rumpus rims to help give them a bit of shape prior to getting some proper rim tape. After fifteen minutes and a good sweat I'd got one bead on to the rim Decided not to put the tyre on fully in case I never got the thing off. The rims are so shallow that there's very little "give" in the system as with normal rims.

I'm just hoping that the 3.0" Bridger will fit in my forks, otherwise I will have to take the thing off which might be an evening's job in itself Not putting any sealant in until I know that everything's going to work.

[Bearbonesnorm]

F*** me! When Stu mentioned that getting the WTB tyres *off* was hard work he wasn't kidding!

Aye, they're certainly 'secure' Bob

[ScotRoutes]

Fitting/removing the FBNs on the Scrapers was certainly easier once I'd fitted the recommended 50mm WTB rim tape. I reckon the shiny surface helps

[Bearbonesnorm]

I didn't have any trouble getting the tyres on or really getting them off. The problem was getting them to break from the bead when I needed to remove them but once the bead was broken, they behaved like any other.

[whitestone]

A bit of searching and watching a few videos (not that kind!) and the Trailblazer went on a lot easier so I suspect (lack of) technique was a lot to do with it. Fitting Bonty XR4 & 3 tyres to Hope rims is a doddle by example.

Will let the tyres "take shape" until the rim tape arrives and I can fit things properly.

[whitestone]

Couldn't wait for the tape Nipped down to B&Q and grabbed some. Taping and mounting the front tyre was done in about 15mins but a small leak meant adding more fluid. Did the rear in about ten since I now knew (allegedly) what I was doing but also used soapy water to ease the bead in. Used two full syringes of sealant on both tyres.

The Bridger comes up about 12mm narrower in diameter than a Bontrager XR4 on a Hope XC rim. The Trailblazer is about 23mm narrower overall, again on a Hope XC rim. The front weighs 2805g (with disk rotor) compared to the Bontrager XR4 weighing 1960g. The Trailblazer weighs 2580g (inc rotor but not the cassette). I checked the Bridger in the forks and there's about 4mm clearance, does add noticeable weight to the front of the bike.

Have pumped both up to 16psi. I'll leave them now for a while to let any leaks manifest themselves and hopefully have the sealant do its job. Not mounted the rotors yet just in case I need to have another tussle.

Not too bad given that these are only the second and third tubeless tyres I've ever done.

[littlegirlbunny]

Thanks Stu n Scotroutes for clarifying the 142/148 thing

The new frame will have a 142 spacing (and for now use my current 29er wheels) but will have room for B+ tyres too

Very useful thread this!

[whitestone]

I've now discovered that I can't read! Guess who found that he'd put the rear tyre on the wrong way round?

At least I found out that the tyre is a lot easier to take off and put back on the second time. Also it hadn't quite sealed properly so was slowly deflating overnight. Seem to have got it right this time as it was still up to pressure. Fitted the rotors (had grabbed some rotor shims just in case the rotors and callipers didn't line up), moved the cassette over and dropped the wheels in and went for a test spin round the yard.

Will head out for some steady rides this weekend to see how I get on with them. Once I've got used to them I'll head round my test loop again to see how they compare to standard 29er wheels and which, if any, types of ground are quicker or require less effort.

There doesn't seem to be any consistency in how tyres are measured, the WTB Trailblazer 2.8" isn't that much wider than my Bontrager XR4 2.35, it's more like a 2.5" rather than the 20% increase you'd expect. It's also very square in profile which is probably why ianpv suggested not to use them on the front. I'll measure them properly rather than judge them by eye. There's plenty of room for a bigger tyre in the back, a Schwalbe Rocket Ron 2.8" should fit I think. The Bridger on the front is absolutely massive BTW, only 2mm gap either side at the narrowest point in the forks but that's the side wall not the tread.

[whitestone]

OK, measured them with callipers and the results are rather surprising.

My original wheels were Bontrager XR4 2.35" on the front and XR3 2.2" on the rear.

XR4 (@ 25psi) measured 59mm at the tread
XR3 (@ 27psi) measured 56mm at the tread.

Given the quoted sizes this difference isn't too far from what's expected and are spot on (to within 0.5mm) of the stated width.

The Bridger (@12psi) is 74mm at the tread, the sidewall is very roughly the same, possibly slightly less.

The Trailblazer (@13psi) is 69mm at the sidewall and 58mm at the tread.

So despite being quoted as a 2.8" tyre, the Trailblazer only 2mm bigger than the XR3 and is narrower at the tread than the XR4! Of course it's a lot bigger in volume.

[Brothersmith]

As stu says rim width makes a huge difference and comparing a 2.35 with a 2.8 that has a narrow tread to allow retro fitting on rim under 40mm proberbaly doesnt tell the whole story. I found the table below to be quite accurate when deciding what rim to plumb for and would seem to fit with your measurments. I think tyres used are 2.8 TB, 3.0 and 3.25 vee trax fatty

[whitestone]

On an ever so slightly different track, someone is jealous. Does anyone know what wide rim and suitable tyre would be the maximum that could fit into a Cotic Soul frame (the 26" variety). I might build up a pair of wheels for her. There's no way a full on plus rim/tyre can get in there but there's quite a bit of room around a Bontrager XR3 on a Hope XC rim.

[Brothersmith]

Someone once told me that if you measure 330mm back from the centre axle (which is approximately where the center of the casing will be) and then measure the width between chain stays it should give you an idea of what you can fit.

[whitestone]

Well I didn't expect that!

Did a loop the other week as a base against which to compare 29er and B+ wheel/tyre combos. A mixture of surfaces, some long descents and a couple of long climbs, it's just under 23Km so a reasonable length and means I can easily nip round it in an evening.

So using Strava as the comparison tool and wearing a HRM so that there's a second metric to compare other than just speed this was the ride using the 29er wheels - https://www.strava.com/activities/583323126/ There was a strong SouthWesterly and due to recent heavy rain the ground was wet with lying water but underneath the surface dampness it was pretty solid, not muddy at all. I think most of the PRs are due to being on my own rather than in a group and having to wait at gates etc. I didn't really push it - at most times I would have been able to hold a conversation, but equally I wasn't dawdling.

This evening I headed out again, but this time with the B+ tyres. I'd had the bank holiday weekend to get a little familiar with them but I wouldn't say I'm completely up to speed with them, though ... In the intervening eleven days things have dried out completely, now rather than compliant damp turf you had rock hard ridged soil. This time the wind was from the NE so into my face on the early climbs. Again I was keeping things at about the same perceived level of exertion and the HR figures bear this out, some are slightly higher some a little lower. This is tonight's ride https://www.strava.com/activities/596495023/ and I'm somewhat shocked to get so many PRs. The B+ wheels and tyres make the bike over 1.5Kg heavier.

I expected it on one or two segments - "Boss Moor techy climb" is ideal for fatter tyres being stony with a few larger loose rocks lying on the surface leading to a rutted section for example. On the Mastiles Lane climb it was just a case of sitting down and spinning your legs, very little back wheel spin/slip. On the descent from Weets Top, there is a very short and steep climb up from a beck, slightly loose I have never managed to get up it. Tonight it just wasn't a problem (the parade of cows and their calves heading up the track shortly after was a different matter ). There is a similar loose section at the start of the last climb which since it got washed out I've never managed but nearly got it tonight. So the grip is amazing - keep your weight just forward of the back wheel and so long as you can pedal you'll get up things.

The tyres make the bike feel "plush" for want of a better word - on ground where with normal tyres you would get a lot of high frequency chatter it's just all smoothed out. Some of the descents that normally have my eyeballs shaking in their sockets were silky smooth.

So if those are the positives, what are the negatives? Well on the descent from the top of Mastiles I hit a rollercoaster of bumps and hollows and the undamped suspension of the rear tyre set me pogoing and threatened to bounce me over the front. This made me a bit wary on some of the similar stuff later on. The little bit of road on the ride was again hard work - the largest section had the wind on my back and it felt harder than riding in to the wind on the 29er wheels.

It's early days. I haven't got the pressures dialed in yet, particularly the rear tyre, and when you are running at 12-15psi just one psi up or down can make a big difference. I think that for routes/rides that are predominantly off-road and composed of tracks of packed hardcore or a little rougher then they are well worth considering. For any route with a significant amount of road then normal tyres would be preferable. I've only done 100Km or so on the wheels to date so it's early days.