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so this is an interesting one I I get a
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lot of feedback from the people that
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I've fitted about the changes that we've
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made to their position and how it's
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affected their writing now the obvious
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ones are the sense of like the pedal
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stroke and how symmetrical it is and the
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less weight on the hands and all that
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good stuff interestingly years and years
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ago I noticed this a lot of people would
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get back to me after after we've altered
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their position and they would say mate
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the bike handles way better and they and
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I I always thought this was kind of
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unusual that what the changes that we
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were making to their position were
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having a really marked effect on their
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perception of particularly the cornering
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stability of the bike so this was a
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really common feedback that I was
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getting so I'll tell you my experience
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with this and we're talking again
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specifically about road bikes here so
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we're not talking about mountain bikes
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or gravel or track bikes or anything
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road bikes specifically so I've fitted a
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lot of people over the last 14 years and
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this is the feedback I often get so we
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I'm not going to go into detail about
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the nuances of frame geometry here this
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is the these are the three big things
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with actually frame geometry like the
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tiny little things about frame geometry
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are probably down at number four and
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five but the three big ones the single
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biggest factor that I've ever found
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which affects the handling of the bike
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is what I would call the location of
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your center of mass so what the heck is
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Center of mass now if you imagine for
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example on this bike behind me here if
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you're looking at a bike from the side
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there is an imaginary point at which if
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we flip the bike 90° onto its side and
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we put a pin there you and the you and
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the bike would balance like a spinning
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top the C CER of mass as viewed from the
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side bikes are all built with a certain
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center of mass in mind so this is this
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sort of affects your weight distribution
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more weight towards the front more
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weight towards the rear higher or lower
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Center of mass or some variation of all
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of that the center of mass is the big
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handling sort of uh determinant I guess
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you would say so the further they're
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they're all built with an ideal Center
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of mass involved in in in mind so the
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further your your center of mass tends
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to deviate away from this ideal Center
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Point
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the worse the handling gets in different
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ways so you imagine if the center of
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mass deviates forward too far you have
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too much weight on the front not enough
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weight on the rear the handling goes all
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out of whack the steering doesn't feel
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right people might have experienced this
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running like 150 mm stems and stuff on
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bikes and similarly if the center of
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mass goes too far back if you've got for
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example a person who's got really long
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femur and a really high seat height and
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they have to push the seat way back on
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the rails and have to run a short stem
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they will often feel that on a given
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bike that the handling is way more
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Twitchy and the front end is too light
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and it doesn't feel stable at high speed
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so the center of mass is the big one and
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this is what happens is when we change
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people's position around their Center of
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mass changes and this explains the
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massive sort of discrepancies which you
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will see in bike handling like reviews
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if you like from people with different
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body types and you and I are great
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examples of this because we get quite
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different impressions of two different
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frames and the big reason we get that is
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because of the difference in where our
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Center of mass is mine is higher and
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further forward yours is lower and
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further back so we feel the the ride
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feel really differently to others so we
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tend to I well I tend to take this into
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account if I if I'm fitting a person and
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I see a person with huge amounts of seat
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set back for example because they've got
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really long FAS I will do stuff like run
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the click position further back on the
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shoe to allow their foot to move further
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forwards towards the front of the bike
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so that we can move their pelvis forward
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to basically improve the hand of the
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bike and the weight distribution so you
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know Center of you you can do a lot of
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tricky things with the position to alter
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their Center of Mass to make the bike
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faster through the corners because
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they're more confident on it and also
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just to improve their General feel of
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the frame and so this is a big one I've
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had huge amounts of feedback from people
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you know we do a fit and then they they
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email me a week later and say m i what
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what's going on it's faster downhill and
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the frame feels completely different
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because we've altered their position so
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the position of the rider which affects
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their Center of mass is front and center
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in terms of bike handling the second
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biggest Factor number two the wheelbase
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of the bike and you you've experienced
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this you've ridden some bikes with
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really long wheelbases and some really
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short wheelbases you can further break
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this down into what we call the front
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center which is the distance between the
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crank and the front axle and the rear
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center which is the distance between the
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crank and the rear axle most bikes have
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got a pretty similar rear center it's
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it's usually 405 to 410 mm but the front
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center is very quite a lot due to the
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different head angles and all this sort
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of stuff so that is the main determinant
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of wheelbases is front center changes on
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most modern road bikes the the front
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center like if you if you make a bike
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with a really short wheel base as a
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reference point 54 cm bike with a
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wheelbase of say 970 mm which is fairly
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short this will dramatically sharpen up
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the steering the bike will feel very
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very Nimble a tiny little bit of input
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from the bar will change will make the
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frame change Direction it will feel
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extremely Nimble and it can sometimes
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make them feel a little bit
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disconcertingly sharp in the steering
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right if the wheelbase is really long
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you'll find that it's much more stable
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at high speed it doesn't tend to change
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direction without you noticing you can
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do things like take your hands off the
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bar without it kind of wandering all
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over the place and you can turn behind
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you in a bunch and look and you turn
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your head back and you're still going in
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the same direction so longer wheelbases
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tend to create more stability at the ex
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expense of sharper handling and for me I
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actually much prefer bikes with a longer
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wheelbase those 54 cm frames that you
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and I are often reviewing wheelbases
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above about 980 9 985 for me feel way
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better than a shorter sharper wheelbase
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but if you've got a shorter Rider with a
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lower Center of mass and a longer stem
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they actually often prefer the shorter
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wheelbase bike so this is number two is
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the wheelbase which is mainly on Modern
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road bikes a function of the front
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center length so that's that's the two
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big ones now lastly the third one I've
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got is the frame stiffness and the
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weight which sort of often go together
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heavier frames being stiffer although we
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have had a a very lightweight bike which
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we've been reviewing recently which is
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very stiff but really stiff frames in
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the bottom bracket they tend to handle
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better when they're on the limit because
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they don't wander around as much you can
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load your foot and move it around and it
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just it's a more direct feel in the
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corners and the frame doesn't feel like
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it's it's wobbling in the bottom bracket
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so super stiff frames um with typically
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with um with a a fair bit of bottom
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bracket stiffness in particular and head
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tube stiffness really stiff frames do
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tend to make the frame feel much more
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planted I've had a lot of experience
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with quite whippy frames and they feel
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great going uphill but downhill they're
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kind of not quite as stable so yeah a
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really stiff frame bottom bracket and
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head and head headset makes a big
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difference yeah the big one that we've
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sort of left out here which is probably
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going to get an honorable mention is the
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tire size and the pressure yeah so this
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and again these these things are all not
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not necessarily geometry considerations
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in the frame but the tire size and
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pressure if you're running a 30 mil tire
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at 50 psi tubeless versus a 25 at 85 PSI
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with a tube in it the frame is going to
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feel way more planted in the corners due
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to the much larger contact patch of that
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tire it can be two or three times the
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size the contact patch and so when you
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tip it into a corner the TIR is going to
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deflect onto the road and grip better so
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bigger tires make a huge difference so
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if you've got a bike that's a little bit
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nervous in the handling which you don't
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love get the biggest tire on it that you
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can and it's going to make a massive
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difference to the confidence in the
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corners in particular on rough terrain
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yeah so those are the big three with a
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notable notable number four there being
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the tie pressure but Center of mass is
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the big one mate and uh it's just my
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experience from fitting thousands of
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people and the feedback I get that they
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often when we fix their position they
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notice that the handling of the frame is
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way better and it's partly because we've
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solved any issues that they had with
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where their Center of mass was whether
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the seat was too high or too far forward
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or back or whatever it was optimizing
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the center of mass can make a big
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difference to your perception of how the
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frame feels makes logical sense does
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make logical sense I I do make logical
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sense every now and again yes you do it
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doesn't happen very often but this is a
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notable
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exception cheers
17835
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