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Pole say higher BB corners better with long bike geo -
Now only offered with 29″ wheels, bottom bracket height rises 17mm reducing BB drop to just 3mm. Pole says the higher BB makes the bike faster & easier to manage through turns, somewhat counterintuitively being the perfect complement to the long wheelbase.
Interesting. Certainly makes bunnyhops etc easier and Geoff Apps always made the case for higher BBs for agility in general, not just pedal clearances.
Interesting, not sure it would work on all LLS bikes - hardtails?
HT at cornering compression probably wants to be at a similar ride/BB height and angles as a FS? Higher BB HTs were more fun on the jumps from what I remember, was a long time ago though.
That's my thoughts, the pole would be good at fast cornering but feel rubbish at slow tech stuff. Interesting they've said it's specific to 29r and were reluctant to try it.
I don't like high bbs as it makes it hard for me to put my foot on the floor when I stop (it's probably the only thing that would make me consider a dropper!)
I like high BBs. When I got Brant to design my custom frame I specifically asked for less BB drop.
the pole would be good at fast cornering but feel rubbish at slow tech stuff.
I'm not so sure - Geoff Apps's Cleland bike is incredible over slow, tricky ground. He's from a motorbike trials background and makes a good case for higher BBs for that sort of riding. It's not a stable bike at speed but perhaps more to do with wheelbase and overall geo than just the BB position.
I don’t like high bbs as it makes it hard for me to put my foot on the floor when I stop (it’s probably the only thing that would make me consider a dropper!)
That was one of my thoughts on the Pole with 17mm higher BB and a 79 degree STA. That'll give you a high saddle for your normal saddle to BB dist, but droppers negate that problem (as long as you're fast, I can see some panic situations when dabbing on a tech climb)
But Geoff app's bikes is very much 'sit up and beg' positioning, enabling lost of control and easy trackstands etc - long and slack with a high BB would give a stretched position.
So the BB height has changed from 20mm drop, to 3mm drop.
What is high, middle and low? 20mm doesn't seem all that low in the first place on a 140mm travel bike.
Gut feel I would say drop greater than 30 is low. And less than 10 high.
Bb height is just one factor. Comparing a Pole and Cleland on one factor and one attribute alone kind of misses the point.
Yes true, though a higher BB seems to have advantages in balance as you move through slower trickier terrain, ease of weaving the bike side to side while your bodyweight stays central. Plus the ease of getting onto the back wheel. I don't see that being entirely lost as the reach or wheelbase goes out, though you'd probably not make a trials-y bike as long. Yet having seen how fast some riders get through closely linked corners and over drops/rocks etc in between, perhaps it's not that different to what an Apps bike is designed to ride at slower speeds.
With the BB higher, for how much the tyres move more side to side underneath you, your body weight has to move less. From the BB to the contact patch has increased radius. Gets complex with grip and balance as the speed goes up. Seems you could get weight inside in a corner a bit more easily at a lower lean angle - how/if a skilled rider uses that for speed, grip or agility I'm not so sure. There's a limit on all these things but in slalom-like turns or similar rapid edge to edge riding I can see a theoretical advantage to a higher BB bike.
Better overall, I don't know. Transferring to other bikes, not sure. I had a really low BB fat tyred road bike a while back. It would fail the EN pedal clearance test but was excellent on twisty fast descents. On road it's a far smoother edge to edge lean/flow and happens more slowly or more predictably than MTBing can be, plus my tyres don't slide on tarmac.
..also may just relate better to this particular suspension design. 17mm of BB height could be the difference between shocks and linkages across 2 bikes with the same static BB position.
Comparing a Pole and Cleland on one factor and one attribute alone kind of misses the point.
Sure, I get that they're very different. Was more the point that some of the positives of a high BB that a Cleland or a trials bike exaggerates or are known for will apply to some extent to any bike with a higher BB. The BB position has an effect on how the bike feels when it swings side to side pivoting on the contact patch and how the bike and rider c of g relate to the axles as fore/aft pivot points (endo or wheelie).
I just had to Google Geoff Apps.
Has he ever done a Megavalanche or an uplift day at a DH track? Because I'm not sure why you're even mentioning him in a thread about mtb's in 2021.
Just clicking the link, they don't appear to mention dropping the BB 17mm, just that the BB drop has been reduced by 17mm, so effectively they've moved the rear axle 17mm lower, the geometry chart states the BB is now 3mm lower, so not exactly earth shattering, especially considering your CofG on a bike is probably around your saddle or a little above that.
Because I’m not sure why you’re even mentioning him in a thread about mtb’s in 2021.
It's an example of what a higher BB can do for a bike, nothing to do with how relevant the Cleland or an Inspired trials bike is for MTB trails. In the same way you could say that some aspects of an Indian roadster's geometry is closer to modern MTB layout than the NORBA XC geo of 1991.
A lot of great design and creativity comes from seeing a benefit in a system and applying it to a different context. Pole may have made a dog of a bike or they may have looked at what was there already, questioned it and found an advantage.
Just clicking the link, they don’t appear to mention dropping the BB 17mm
Says they raised it 17mm (I assumed from wherever it was before), it has a static BB that's 3mm below a 29er axle line. I googled the old model and it's 20mm drop which isn't particularly low to start with for a 140mm 29er.
Raising the BB 17mm on a 140mm bike was just interesting at this stage from a brand who sells on how progressive/extreme their geometry is. Maybe that's some of why - to lead change.
The Pole bikes already had quite high bottom brackets - this model had only 20mm BB drop when 25-30mm is normal nowadays and 30+ is low.
What Pole have done with this “new model” is stick a metric shock on an old frame. The new shock is longer eye to eye. That raises the BB by 17mm to only 3mm drop. It steepens the seat angle to almost 80 deg. And then they’ve put a -2 deg angleset in to restore the old head angle.
Bodge + marketing = ?
SHS - short, high, steep! The future 😉🤔
Bodge + marketing = ?
Yeah I saw the bit about a conversion kit for the old model, you may be right that it's finding a positive in a result/effect they can't change. But if the bike handled worse wouldn't you just stick to a non-metric shock? Dunno, not really in tune with how important metric shock dims are now aside from assuming it's a little more future proof.
TBH it was just the challenge to current assumed wisdom on BB height that triggered my inner bike nerd. Edit to add, and isn't that at least some of what geometry changes are about in selling MTBs? While bikes generally get better, there's always an extreme example getting the most attention.
SHS – short, high, steep! The future
I have been riding track bikes off road for almost 20 years so I already know that future!
Of the various frames I have used the frames with a lower BB (something like a Surly Steamroller) feel a lot more stable and confidence inspiring versus the higher BB I am currently using which can feel more precarious.
However, my comparison of track bikes off road is about as relevant to this example as the Geoff Apps bikes.
“ But if the bike handled worse wouldn’t you just stick to a non-metric shock?”
At another time I’d agree but with lead times how they are, maybe the business survival depends on persuading people to buy frames with the shocks they can get hold of ASAP rather than the shock that is best but might takes many months to arrive?
What Pole have done with this “new model” is stick a metric shock on an old frame. The new shock is longer eye to eye. That raises the BB by 17mm to only 3mm drop. It steepens the seat angle to almost 80 deg. And then they’ve put a -2 deg angleset in to restore the old head angle.
Bodge + marketing = ?
I was think the same 😂
However, my comparison of track bikes off road is about as relevant to this example as the Geoff Apps bikes.
If you don't get how it is relevant, that's ok.
The next big thing
That tallbike looks worryingly good fun. Pedal strikes definitely not an issue.
Similarly, the Cleland could appeal when I'm old and just want to trug around in the woods.
I'd like prefer either to an 80 degree seat angle!
The bike industry is definitely a place where marketing spin and BS are used to obscure the real reason for certain design "features". Every bike book of my 80s youth said seatstays with top-eye inserts brazed to the side of the seat tube were the best thing ever and much stronger than a mitred joint. 30 years of mtbs suggests the mitred seatstay / seat tube joint is very strong. Having made a few frames, I now know the old style seatstay was just a quick lazy way of plonking on a straight tube with no mitre cutting.
Remember chatting to Dan Stanton about his opinions on geometry for 29ers a while back... He was of the same view about tall BB’s on 29ers. Interestingly, the Switch9er HT has quite a low BB height, but all the other 29ers he still makes have much higher BB’s...
It’s certainly a personal taste thing. I’m a “not quite in the weeds but getting there” kind of guy myself... Just prefer the confidence a low BB gives me, I run shorter cranks anyway and having been riding for 30 odd years I’ve had plenty of practice at timing my pedal strokes and learning to pump for speed rather than pedal wherever I can.
If you don’t get how it is relevant, that’s ok.
Gee, thanks.
A track bike and an Apps bike are irrelevant because they are not related to the requirements the Pole is made for. They may share higher bottom brackets but that is a small part of the story.
Just look at what terrain Apps is riding in clip above, nobody on a Pole would be riding at that slow speed or on that terrain.
Found the discussion interesting myself. I don't live in the kind of terrain where a Pole bike would make sense, and started trying to learn trials a couple of years ago. Think trying to ride trials has lead me to find the handlebar position on my MTB's too low like I'm leaning too much weight on the front so recently fitted a BBB BHS-25 high rise stem. Quite enjoying the upright position, and find it means I can more easily push the front wheel down without tipping my weight over it as well as pull it up easier. I've now concluded handlebars don't have any business being as low or lower than the raised saddle on an MTB. Now that's probably irrelevant.
The Pole bikes already had quite high bottom brackets – this model had only 20mm BB drop when 25-30mm is normal nowadays and 30+ is low.
What Pole have done with this “new model” is stick a metric shock on an old frame. The new shock is longer eye to eye. That raises the BB by 17mm to only 3mm drop. It steepens the seat angle to almost 80 deg. And then they’ve put a -2 deg angleset in to restore the old head angle.
Bodge + marketing = ?
****erteering at its finest, wonder if this one has been thoroughly tested, wouldn't want a repeat of the rear ends collapsing.
3mm bb drop, wonder if they've had someone on loan from cube, purveyors of shit handling bikes.
Gee, thanks.
Apologies, bit blunt.
A track bike and an Apps bike are irrelevant because they are not related to the requirements the Pole is made for. They may share higher bottom brackets but that is a small part of the story.
Just look at what terrain Apps is riding in clip above, nobody on a Pole would be riding at that slow speed or on that terrain.
Your fixed wheel bike is irrelevant here : )
but only because you can't ride or link corners with the pedals level or only moving 180 degrees on a fixed wheel.
I get that the Pole and Cleland are for different things, as said in an earlier post. Pretty obviously different bikes and uses. The Apps bike as an example is relevant since the point about your weight on the pedals and how it interacts with the BB to tyre contact patch 'radius' (from the end view) as you and the the bike move side to side or through corners is still there. The Apps bike makes a big thing of the high BB plus ride position and its rim+tyre set up to weave through corners or obstacles (it works) which is the only reason I mentioned it - nothing to do with what it's designed to ride and all about the reason a higher BB has a benefit there. The bike and terrain may vary and make it more or less important but it doesn't become irrelevant if you're looking at how it might have pros and cons.
3mm bb drop, wonder if they’ve had someone on loan from cube, purveyors of shit handling bikes.
I'll raise you.
To be fair it probably sags to a more normal 14" or so
I mostly ride short, high, steep, (SHS) bicycles designed by or based on the designs of Geoff Apps.
Occasionally, I take one of these bikes on a local MTB run. Geoff Apps' bikes are like large wheeled BMX bikes and to keep up you have to ride out of the saddle and throw your body-weight around a lot. Whilst a modern LLS Long-travel suspension bike rider can just bomb down a rock-garden section easily, I have to ride out of the saddle, and let the bike rotate under deliberately lifting the wheels to avoid wheel traps and bigger impacts. The idea is that the rider's body-mass moves as little as possible whilst the bike moves all over the place. I am of course slower than the modern bikes, but the other riders are usually surprised by what can be ridden on such a short tall bike. I do use dropper-posts and whilst a modern bike can handle a drop-off easily, I have to momentarily drop the saddle and move my body-weight well behind the rear wheel.
According to the the 'Inverted Pendulum Theory' in physics, a higher bottom-bracket height raises the center of gravity of the rider and causes the bike to unbalance more slowly. In reality this just buys the rider a little more reaction time. Not being able to put your feet on the ground is not a problem as you soon learn how to jump clear when things go wrong. Even when you are riding along a 45 degree camber pedal strike is not a problem.
I hope my explanation is helpful to the debate.
Muldoon talked a bit about this in the MBR Enduro/Firebird/Reign review.
Putting the Enduro in the high setting "destabilised" the bike to the point where he felt it was dynamic in handling and went from meh bike to superbike.
Perhaps Leo watched it too?
This is a quote from Geoff Apps that makes the argument that unstable vehicles are more maneuverable than stable ones.
"The difference between a helicopter and an aeroplane?"
"A 'copter can travel straight and fast, as can a plane, it is also highly maneouvrable and completely unstable."
The role that bicycle geometry plays in effecting the time a rider has to react in loss of control situations is also important. Apart from a higher rider's centre-of-mass buying more reaction time, the further away the riders weight is from the front-wheel contact patch the more time the rider has to make corrections when things go wrong.
I wouldn't factor too much into aircraft stability, there's so many factors to bring into this one, but one of the biggest ones is that even dropping the BB 17mm, it's not exactly earth shattering when you factor in the CofG being way above that anyway, so many folk aren't really running the BB height they think anyway, when you factor in longer travel forks, or more/less sag, tyre height, etc, etc.
I tend to think feel overrides a lot more than we think as well, feels a bit weird, we tweak the bike until it feels better, if it feels a little too twitchy then wider bars, higher stem and so on can be added, the LLS does allow a better starter for the current scenarios for trail/enduro style bikes though for me.
That tall bike looks great, I love how he's essentially steering by flicking the back wheel around with his hips.
The Apps bike - well, there's a time and a place for a pair of walking boots. It looks like it could do with some 5" tyres though?
“ Putting the Enduro in the high setting “destabilised” the bike to the point where he felt it was dynamic in handling and went from meh bike to superbike.”
But the Enduro has 28mm or 21mm of BB drop static and then about 175mm of suspension to sag (I know it’s more than the official 170mm rear travel). 3mm BB drop and 144mm travel is a LOT higher.
I have in the past described the original Geoff Apps' 650B Cleland Aventuras as the cycling equivalent of a comfortable old pair of walking boots. His more modern 700C bikes are more like the equivalent of the boots but with additional gaitors, crampons, and walking poles.
They are at there best when the terrain is soft, waterlogged or wet & muddy. Using excessively wide tyres in these conditions means that you have to push even more mud out of the way as you literally plough your own furrow. My experience is that in very wet and muddy conditions FatBikes tend to be much slower in mud than the thinner tyred Clelands. Also, claggy or freezing mud and clay can stick to the tyres and build up until 1.9 inch tyre soon looks like a five inch one.
The early part of this year where I live had been even wetter and more muddy than usual, and I have had a great time sliding around in the mud on a 29er Cleland. I have not even had to do any cleaning or maintenance between rides.
Due to the increased number of walkers out and about during lockdown the mud has been unavoidable and it's far easier to ride through than walk through. Now that everything has dried out the using the big Cleland is fast becoming the off-road cycling equivalent of using a sledgehammer to crack a nut. But this is Britain, so it's bound to rain again soon.
“ According to the the ‘Inverted Pendulum Theory’ in physics, a higher bottom-bracket height raises the center of gravity of the rider and causes the bike to unbalance more slowly.”
I don’t think the main effect of a higher bottom bracket is on raising the rider’s centre of mass, I think what’s dominating is that you increase the leverage of the BB around the contact patches. The higher the BB, the greater the horizontal displacement of the BB vs the contact patches for a given lean angle. It’s easier to initiate a change in direction with a higher and less stable BB, whilst a low BB means the bike is better at continuing on the same path.
Over the last 5 years or so I’ve had bikes with some pretty big differences in BB height and adjustable geometry and fork lengths etc that’s let me investigate how it changes the feel.
For general riding I’ve found I like a pretty low BB, just under 300mm at sag, but I think for racing a little bit higher helps with quicker turns as well as letting you getting pedal strokes in more often.
Hi chiefgrooveguru, Your suggestion that by applying a sideways force at the bottom bracket a rider could make the bike lean faster is very interesting. I can think of at least two ways that a rider could apply such a force, and if it were big enough it could in theory influence the angle of lean of the bike. Also, in such a case a higher bottom bracket could result in a larger lateral force then being applied to the tyre contact patches.
I think this is worthy of further investigation but is complicated because every force applied will have an equal and opposite reaction force. It is highly likely that in order to apply a force that leans the bike to the left the rider will need to apply an initial force to the right. It is also possible for a rider to apply a torque to the bottom bracket via the cranks. I need to try these ideas out on a bike so that I can better understand the possibilities better.
One thing that is overlooked in discussions about bicycle stability is the difference between
Longitudinal stability (front to back stability) and lateral stability (side to side stability).
The first is about the probability of going over the handlebars or doing a wheelie, the second is about how easily the rider to keep the bike from loosing equilibrium and falling over sideways.
These are two different things and it is possible for have a bike like a unicycle that is longitudinally less stable but more laterally more stable. Alternatively you can have a long wheelbase recumbent bicycle that is very longitudinally stable whilst also being laterally unstable at low speed. I don't believe you can simply comment about the stability of a bicycle without being specific about which sort of stability you are talking about.
A bicycle that is not moving is longitudinally stable, but rapid changes in velocity when moving can make a bicycle longitudinally unstable. A bicycle can become laterally unstable at any speed but lateral stability is more difficult to control at low speeds. The difference between the types of stability can produce counter-intuitive results. For instance an old Penny Farthing bicycle is more laterally stable than a safety bicycle, whilst also being very longitudinally unstable.
“Your suggestion that by applying a sideways force at the bottom bracket a rider could make the bike lean faster is very interesting.”
Sorry I think you’ve misunderstood me! I was referring to the downwards force caused by your weight on the pedals causing the BB to rotate around the contact patches, due to the torque generated by the weight multiplied by the horizontal offset between forces and fulcrum.
I know from experience that it’s easier to two-wheel drift a bike with a lower BB height. Longer wheelbases help too if the chainstays are also proportionally long. So does having the weight of a motor and battery down low. But nothing helps as much as that low BB.
My last full-sus bike had adjustable geometry and on the same trails it was better in the wet/mud when in the lower position and better in the dry in the higher position - when it’s dry and grippy the ability to change direction fast is critical whilst in the wet it’s about staying balanced when sliding.
Hi chiefgrooveguru, You said:
"I was referring to the downwards force caused by your weight on the pedals causing the BB to rotate around the contact patches, due to the torque generated by the weight multiplied by the horizontal offset between forces and fulcrum."
Are you referring to a situation where you are riding out of the saddle? I ask because there are three points where the riders weight can be applied to the bicycle; the handlebars, the saddle and the pedals.
Your scenario only makes sense when the rider is applying nearly all his weight via the pedals. In which case I would suggest that the handlebars are at one end of the second order lever, but effort in the form of the riders weight can also be applied to the bottom bracket via the pedals. You have already said the fulcrums are the tyre contact patches.
If this is correct it raises the question of what is the load that this lever is moving?
Would I be right in thinking that the load to which the mechanical advantage produced by the lever is mainly being applied against the rotational inertia of the bicycle? In saying that I am assuming that the rotation of the rider is caused by gravity acting downwards when the tilted bicycle is no longer directly underneath him or her. In other words, the function of the lever is only rotate/angle the bicycle and once the bicycle is leaning, gravity will do the rest.
If the above is correct it implies that there is a marked difference between the physics of how a bicycle corners when ridden in the saddle, compared to that of a skilled rider riding out of the saddle.
A far simpler example of this principle is that of someone balancing on a pogo-stick. If they unbalance to their right side they will slowly accelerate in that direction as gravity pulls them down. However, if someone balancing in the same way moves the top of the pogo-stick to their right, this will move their weight being applied to the footrests to the right of the foot of the stick. This will then introduce an additional leverage/torque that will cause them them fall over more quickly.
The further away the footrests are from the bottom of the pogo-stick the greater the resulting torque induced by angling the stick and so the more quickly the fall accelerates. In the case of a bicycle, the additional centripetal force generated by the turn should prevent the bike from crashing to the ground.
The principle that in the two situations are very similar in that; the higher the bottom-bracket relative to the ground the more torque will be generated, and the higher the pogo-stick's footrests the greater the resulting torque.
It would be interesting to find some video of bicycle slalom's to see what techniques the rider's use. I do know that Penny-farthing riders used to compete in slaloms and those bikes have very high bottom-brackets.
“ Are you referring to a situation where you are riding out of the saddle?”
Absolutely, I don’t ride anything downhill without the saddle dropped (usually by the max 185mm that my dropper allows). Likewise any flatter stuff with turns. Or technical uphills. To me, and many riders nowadays, the saddle is pretty much for pedalling in straight lines only.
There is absolutely no way that I could ride the trails I do at the speed I do with the skills I have whilst staying in the saddle.
“ It would be interesting to find some video of bicycle slalom’s to see what techniques the rider’s use.”
Dual slalom bikes tended to be full-sus 4X bikes, with very low BB heights.
Well here's another theory...
Doing really quick turns in the woods (slower and tighter than on a slalom track) the bike and rider don't behave like one thing. Initially the rider rotates the bike (about a longitudinal axis) and moves it under them, staying relatively still themself until the bike is set up for the corner and starts to bite. This is achieved by a combination of counter-steering, unweighting, jumping if you are that way inclined. Possibly preceeded by a Scandinavian flick. So approaching a right hand corner, the objective is to get the tyre contact patch off to the left of the line of travel (and the rider's cg) so that a turn can happen.
Let us assume that even the rider's feet don't move much in this process (probably they do move a bit more than the rider's bum does but let's just assume). The longitudinal axis of rotation (of the bike, not rider) I just mentioned will go through the bb (where the feet are). The more bike there is below the bb, the greater lateral displacement of the tyre contact patch for a given angle of rotation of the bike. This will make a higher bb bike feel easier to flick through this type of corner. Or to think of it another way, trailside trees permitting the rider's (higher) body can straighten out the curves more than with a lower bb bike.
You can see the technique that chiefgrooveguru is talking about between nine and fifteen seconds into this video. How to corner fast video
I tried my own method of leaning the bike into a turn on a Geoff Apps' bike with a fifteen and three quarter inch high bottom bracket. However, I was put off by the nose of the saddle hitting the back of my leg every time I lent the bike. I need to put on a short nosed saddle and try again.
With the dropper post down it was still possible to lean the bike a fair angle whilst remaining in the saddle. This cured the problem of the saddle hitting my legs and might be a lazy man's way of cornering faster.
^That demonstrates the thing I was trying to describe - the bike moves a lot, flicking from one lean angle to the opposite, the rider much less. Complete with little jumps.
I also agree with the @chief's point about controlling drift. Once relatively settled in a turn, altering the lean angle of the bike relative to the body can move the tyre contact patch more or less underneath the rider's cg, and bb height will affect how that works.
Slap in a normal headset and that Pole is ripe for a mullet.
Well here’s another theory…
Exactly, and what I was getting at with my poorly worded comment here earlier on,
Yet having seen how fast some riders get through closely linked corners ..
With the BB higher, for how much the tyres move more side to side underneath you, your body weight has to move less. From the BB to the contact patch has increased radius. Gets complex with grip and balance as the speed goes up. Seems you could get weight inside in a corner a bit more easily at a lower lean angle – how/if a skilled rider uses that for speed, grip or agility I’m not so sure. There’s a limit on all these things but in slalom-like turns or similar rapid edge to edge riding I can see a theoretical advantage to a higher BB bike.
But a lower does BB seem to help catching slides more quickly, both the MTB and gravel bike I have with low BBs are good in that situation.
Sorry I managed to miss your comment jameso. Exactly. I guess there are a number of things going on, some favouring higher some lower bbs.
I asked Geoff Apps about the cornering technique shown about nine seconds into this video.
Faster cornering video
He said that this was why from 1977 onward all his bike designs had had sloping top tubes. He said that it was essential that the rider can easily and quickly move their body-weight around. In comparison the early US mountain bikes had relatively high top tubes that were parallel to the ground.
He then went on to talk about the wide variety of cornering techniques that motocross, speedway and motorbike-trials riders use.
Geoff's designs are based on decades of experimentation with different geometries and what feels best. Give him any style of bicycle and he will take it off road to find out how it handles. By doing this for the best part of six decades, he came to the opinion that large wheels, high bottom bracket, steep-steering-angled and short wheelbase bikes work best for his purposes. He believes that shorter bikes are work best because it takes less time for the rider to move his body's centre-of gravity relative to the tyre contact, patches than with longer wheelbase designs. So his design's principly focuses on it being as easy and quick as possible for the rider to move his weight around in all directions. As I have said before, Apps bikes are fundamentally big wheeled BMX bikes. For him, speed is far less important than technical capability and machine reliability.