Original subtitles

so this is an interesting one I I get a

lot of feedback from the people that

I've fitted about the changes that we've

made to their position and how it's

affected their writing now the obvious

ones are the sense of like the pedal

stroke and how symmetrical it is and the

less weight on the hands and all that

good stuff interestingly years and years

ago I noticed this a lot of people would

get back to me after after we've altered

their position and they would say mate

the bike handles way better and they and

I I always thought this was kind of

unusual that what the changes that we

were making to their position were

having a really marked effect on their

perception of particularly the cornering

stability of the bike so this was a

really common feedback that I was

getting so I'll tell you my experience

with this and we're talking again

specifically about road bikes here so

we're not talking about mountain bikes

or gravel or track bikes or anything

road bikes specifically so I've fitted a

lot of people over the last 14 years and

this is the feedback I often get so we

I'm not going to go into detail about

the nuances of frame geometry here this

is the these are the three big things

with actually frame geometry like the

tiny little things about frame geometry

are probably down at number four and

five but the three big ones the single

biggest factor that I've ever found

which affects the handling of the bike

is what I would call the location of

your center of mass so what the heck is

Center of mass now if you imagine for

example on this bike behind me here if

you're looking at a bike from the side

there is an imaginary point at which if

we flip the bike 90° onto its side and

we put a pin there you and the you and

the bike would balance like a spinning

top the C CER of mass as viewed from the

side bikes are all built with a certain

center of mass in mind so this is this

sort of affects your weight distribution

more weight towards the front more

weight towards the rear higher or lower

Center of mass or some variation of all

of that the center of mass is the big

handling sort of uh determinant I guess

you would say so the further they're

they're all built with an ideal Center

of mass involved in in in mind so the

further your your center of mass tends

to deviate away from this ideal Center

Point

the worse the handling gets in different

ways so you imagine if the center of

mass deviates forward too far you have

too much weight on the front not enough

weight on the rear the handling goes all

out of whack the steering doesn't feel

right people might have experienced this

running like 150 mm stems and stuff on

bikes and similarly if the center of

mass goes too far back if you've got for

example a person who's got really long

femur and a really high seat height and

they have to push the seat way back on

the rails and have to run a short stem

they will often feel that on a given

bike that the handling is way more

Twitchy and the front end is too light

and it doesn't feel stable at high speed

so the center of mass is the big one and

this is what happens is when we change

people's position around their Center of

mass changes and this explains the

massive sort of discrepancies which you

will see in bike handling like reviews

if you like from people with different

body types and you and I are great

examples of this because we get quite

different impressions of two different

frames and the big reason we get that is

because of the difference in where our

Center of mass is mine is higher and

further forward yours is lower and

further back so we feel the the ride

feel really differently to others so we

tend to I well I tend to take this into

account if I if I'm fitting a person and

I see a person with huge amounts of seat

set back for example because they've got

really long FAS I will do stuff like run

the click position further back on the

shoe to allow their foot to move further

forwards towards the front of the bike

so that we can move their pelvis forward

to basically improve the hand of the

bike and the weight distribution so you

know Center of you you can do a lot of

tricky things with the position to alter

their Center of Mass to make the bike

faster through the corners because

they're more confident on it and also

just to improve their General feel of

the frame and so this is a big one I've

had huge amounts of feedback from people

you know we do a fit and then they they

email me a week later and say m i what

what's going on it's faster downhill and

the frame feels completely different

because we've altered their position so

the position of the rider which affects

their Center of mass is front and center

in terms of bike handling the second

biggest Factor number two the wheelbase

of the bike and you you've experienced

this you've ridden some bikes with

really long wheelbases and some really

short wheelbases you can further break

this down into what we call the front

center which is the distance between the

crank and the front axle and the rear

center which is the distance between the

crank and the rear axle most bikes have

got a pretty similar rear center it's

it's usually 405 to 410 mm but the front

center is very quite a lot due to the

different head angles and all this sort

of stuff so that is the main determinant

of wheelbases is front center changes on

most modern road bikes the the front

center like if you if you make a bike

with a really short wheel base as a

reference point 54 cm bike with a

wheelbase of say 970 mm which is fairly

short this will dramatically sharpen up

the steering the bike will feel very

very Nimble a tiny little bit of input

from the bar will change will make the

frame change Direction it will feel

extremely Nimble and it can sometimes

make them feel a little bit

disconcertingly sharp in the steering

right if the wheelbase is really long

you'll find that it's much more stable

at high speed it doesn't tend to change

direction without you noticing you can

do things like take your hands off the

bar without it kind of wandering all

over the place and you can turn behind

you in a bunch and look and you turn

your head back and you're still going in

the same direction so longer wheelbases

tend to create more stability at the ex

expense of sharper handling and for me I

actually much prefer bikes with a longer

wheelbase those 54 cm frames that you

and I are often reviewing wheelbases

above about 980 9 985 for me feel way

better than a shorter sharper wheelbase

but if you've got a shorter Rider with a

lower Center of mass and a longer stem

they actually often prefer the shorter

wheelbase bike so this is number two is

the wheelbase which is mainly on Modern

road bikes a function of the front

center length so that's that's the two

big ones now lastly the third one I've

got is the frame stiffness and the

weight which sort of often go together

heavier frames being stiffer although we

have had a a very lightweight bike which

we've been reviewing recently which is

very stiff but really stiff frames in

the bottom bracket they tend to handle

better when they're on the limit because

they don't wander around as much you can

load your foot and move it around and it

just it's a more direct feel in the

corners and the frame doesn't feel like

it's it's wobbling in the bottom bracket

so super stiff frames um with typically

with um with a a fair bit of bottom

bracket stiffness in particular and head

tube stiffness really stiff frames do

tend to make the frame feel much more

planted I've had a lot of experience

with quite whippy frames and they feel

great going uphill but downhill they're

kind of not quite as stable so yeah a

really stiff frame bottom bracket and

head and head headset makes a big

difference yeah the big one that we've

sort of left out here which is probably

going to get an honorable mention is the

tire size and the pressure yeah so this

and again these these things are all not

not necessarily geometry considerations

in the frame but the tire size and

pressure if you're running a 30 mil tire

at 50 psi tubeless versus a 25 at 85 PSI

with a tube in it the frame is going to

feel way more planted in the corners due

to the much larger contact patch of that

tire it can be two or three times the

size the contact patch and so when you

tip it into a corner the TIR is going to

deflect onto the road and grip better so

bigger tires make a huge difference so

if you've got a bike that's a little bit

nervous in the handling which you don't

love get the biggest tire on it that you

can and it's going to make a massive

difference to the confidence in the

corners in particular on rough terrain

yeah so those are the big three with a

notable notable number four there being

the tie pressure but Center of mass is

the big one mate and uh it's just my

experience from fitting thousands of

people and the feedback I get that they

often when we fix their position they

notice that the handling of the frame is

way better and it's partly because we've

solved any issues that they had with

where their Center of mass was whether

the seat was too high or too far forward

or back or whatever it was optimizing

the center of mass can make a big

difference to your perception of how the

frame feels makes logical sense does

make logical sense I I do make logical

sense every now and again yes you do it

doesn't happen very often but this is a

notable

exception cheers