Bike sizes

General cycling advice ( NOT technical ! )
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Godzy89
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Joined: 10 Apr 2021, 3:00pm

Bike sizes

Post by Godzy89 »

Hello all
Iv been looking to get a hybrid bike but stock levels locally (Manchester/Bolton) are pretty dire
Being a bit vertically challenged i need a small
I have found the bike i want (Trek FX3 Disc) but its only in stock in a medium
Is there a big difference between a small and a medium and what would be the disadvantages if i got the medium?

Thanks for any replys

John
VinceLedge
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Re: Bike sizes

Post by VinceLedge »

I have found if you get a frame that is too big then you might not be able to move the saddle far enough forward to get a comfortable position on the bike.
Richard of York
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Re: Bike sizes

Post by Richard of York »

Without the cost of expensive bike fit t's really about comfort and preferred riding style. Saddle height adjustment means you can probably ride small or medium but the reach forward to the bars may be wrong. I can ride my sons large frames but feel too stretched out to bars and standover height is a little too tight for comfort. Be cautious about rushing to buy wrong size because of shortages. I bought a new bike recently from Spa Cycles and spent ages testing different sizes. A good shop should let you test before you buy.
Vorpal
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Re: Bike sizes

Post by Vorpal »

Godzy89 wrote: 30 Apr 2021, 11:01am Hello all
Iv been looking to get a hybrid bike but stock levels locally (Manchester/Bolton) are pretty dire
Being a bit vertically challenged i need a small
I have found the bike i want (Trek FX3 Disc) but its only in stock in a medium
Is there a big difference between a small and a medium and what would be the disadvantages if i got the medium?

Thanks for any replys

John
It depends...
How tall are you? Unless you are near the shorter end of the small range, or standover height is a problem, a medium is probably okay.

https://99spokes.com/bikes/trek/2021/fx-3-disc shows the geometry. There is not a big difference in reach between the two bikes. The seat tube length and angle are different, but with the longer head tube, this only results in a difference of a bit over 1 cm in top tube length.

That said, it's not ideal to buy a new bike in an incorrect size, so if you aren't sure, it's best to wait, or consider something else. Can you get it from a local shop & can they help you with fitting?
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
Godzy89
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Re: Bike sizes

Post by Godzy89 »

Vorpal wrote: 30 Apr 2021, 12:27pm
It depends...
How tall are you? Unless you are near the shorter end of the small range, or standover height is a problem, a medium is probably okay.

https://99spokes.com/bikes/trek/2021/fx-3-disc shows the geometry. There is not a big difference in reach between the two bikes. The seat tube length and angle are different, but with the longer head tube, this only results in a difference of a bit over 1 cm in top tube length.

That said, it's not ideal to buy a new bike in an incorrect size, so if you aren't sure, it's best to wait, or consider something else. Can you get it from a local shop & can they help you with fitting?
Im 5ft 5
None of the local independents have stock of anything really and am having to go to Evans Cycles for it
Ive looked around and think the Trek with its discs brakes and carbon fork is exactly what im after
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531colin
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Re: Bike sizes

Post by 531colin »

What size do Trek recommend?
The usual (inevitable) trade-off is that a small bike gives you short reach, but at the cost of low handlebars, whereas a bigger bike gives you higher bars at the expense of longer reach.
In this case, the Medium bike gives you much higher bars (stack 557 v.s 539) but with only 4mm longer reach (397 vs. 393)

I'm about 5'9" and 73 years old. I ride a bike with a 540mm seat tube BUT mine has 180mm head tube....my head tube is much longer than either bike you are looking at, the point is that head tube length is a good indicator of handlebar height.
I generally work on the rough rule that your legs are half your height, so your legs are likely to be 2" shorter than mine (50mm)
I would point you towards the Medium bike.

edit...it looks to me like the bike has a tapered head tube, ie a tapered carbon steerer, so you can't use a steerer extender. You can fit riser bars to get a bit more height. (although the specs. say inch and eighth headset)
Last edited by 531colin on 30 Apr 2021, 5:22pm, edited 2 times in total.
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531colin
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Re: Bike sizes

Post by 531colin »

VinceLedge wrote: 30 Apr 2021, 11:33am I have found if you get a frame that is too big then you might not be able to move the saddle far enough forward to get a comfortable position on the bike.
Vince, I think you have posted this before, and its a very odd thing to say.
In the case of the 2 bikes we are looking at here, the difference in seat tube angle is half a degree; this will give something like a 5mm difference in the range of positions you can get the saddle , front to back. (for me at about 5'9")
You aren't using saddle position to adjust reach to the bars, are you?
VinceLedge
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Re: Bike sizes

Post by VinceLedge »

531colin wrote: 30 Apr 2021, 5:19pm
VinceLedge wrote: 30 Apr 2021, 11:33am I have found if you get a frame that is too big then you might not be able to move the saddle far enough forward to get a comfortable position on the bike.
Vince, I think you have posted this before, and its a very odd thing to say.
In the case of the 2 bikes we are looking at here, the difference in seat tube angle is half a degree; this will give something like a 5mm difference in the range of positions you can get the saddle , front to back. (for me at about 5'9")
You aren't using saddle position to adjust reach to the bars, are you?
Not an odd thing to say at all, the 2 first things I would think .most people do to fit their bike to them is adjust the saddle height and the the saddle fore and aft, in order to get your knee over the pedal spindle with cranks at quarter to three position, whilst sitting on a normal position on the saddle. If you can get the saddle far enough forward to do this then you are likely to always be sliding forward on the saddle whatever angle it is at.
This not just affected by the length of the top tube and the seat tube angle but also by layback seatposts which most makes fit to their bike and don't allow enough 'fore' adjustment if the frame is on the big side.
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531colin
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Re: Bike sizes

Post by 531colin »

ImageKOPS by 531colin, on Flickr

KOPS....photo from my DIY bike fit guide, linked below.
VinceLedge wrote: 30 Apr 2021, 6:27pm ...... If you can get the saddle far enough forward to do this then you are likely to always be sliding forward on the saddle whatever angle it is at.....
If you can't get the saddle.....etc?
VinceLedge wrote: 30 Apr 2021, 6:27pm This not just affected by the length of the top tube and the seat tube angle but also by layback seatposts which most makes fit to their bike and don't allow enough 'fore' adjustment if the frame is on the big side.
If the seat tube angle is the same on 2 different size bikes, and the saddle height is the same, then the saddle is in the same position (fore and aft) because the seatpost is in the same straight line with the seat tube.
VinceLedge
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Re: Bike sizes

Post by VinceLedge »

Ooops, yes meant can't!
scottg
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Re: Bike sizes

Post by scottg »

What reason does the shop give for not setting up the bike to fit you as close as possible,
and letting you ride it ?

I've ridden bikes setup to fit me, that standing climb on the first little, were quite squirrelly (
american for marginal stability). The ways of British bikes shop sound very odd to us colonials. :)
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Godzy89
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Re: Bike sizes

Post by Godzy89 »

Thank you for all the replies
Tried the Trek in a medium but didnt feel comfy or right
Went for the Pinnacle Neon in small and its spot on
Picked up a pair of Look spuds for half price too so happy days 🙂

John
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Re: Bike sizes

Post by Vorpal »

Good result :)

Enjoy the bike!
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
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