Foot hitting rear derailleur

[AndyAll73]

I have a problem with my heel hitting the rear durailier(I'm size 12).
The bike has a 170mm crank arm so not long at all. It's a 21" frame.
If I go to a larger frame e.g 23" will the distance between the crank and rear hub be greater or is it just the height that changes?
Pedal spacers are not enough and my feet are correctly positioned on the pedal.

[axel_knutt]

My frame's a 64cm (~25"), with 445mm chainstays. There's about 15mm clearance with 170mm cranks and fairly bulky size 12 trainers.

[AndyAll73]

Even without shoes on I still need half an inch minimum. So would a bigger frame give this? The pedal arm did seem very close to the chain too so I wonder if it's faulty design/assembly as it's a brand new bike.

[Mick F]

I ride a 23.5" frame with short dropouts and my heels are an inch or so away from the rear mech.
I'm 5ft 9ins tall with size 9 shoes.
I'm Mr Average .................. if clothes shopping and shoe shopping are taken into account.

I would be hunched up on a 21" frame, so you can't be as tall as me, or if you are, your frame is too small.

As for frame geometry, you need to look at the frames. Some can be taller, but the same length as shorter ones. It seems to me that you need a frame that is taller and longer.

[531colin]

Even without shoes on I still need half an inch minimum. So would a bigger frame give this? The pedal arm did seem very close to the chain too so I wonder if it's faulty design/assembly as it's a brand new bike.

So what do they say where you bought it?
You need longer chainstays (or rear centre) in the geometry chart/table.
If its a race bike lookalike, its unlikely that a bigger size will have longer chainstays. If its a tourer, then it might.
Try before you buy is always a plan.

[AndyAll73]

It was mail order. Ive sent it back and will order a completely different make and model and see if I have any joy. It was a road bike. Weird thing though unless it was bad manufacture/assembly. The pedal arm drive side had hardly any clearance from the frame or chain either (literally 3-5mm it actually rubbed the chain in the lowest rear cog) but non drive side there was easily an inch or more. Could have been BB installed wrong way round at the factory?

[Psamathe]

(I don't have the experience to comment on frame sizes or geometry but ...) maybe have a look and go for a few trial rides in bike shops. See what bikes fit (and why). Some bike retail chains are also online and can be very price competitive (same pricing in-store and online). As an example (no recommendation nor criticism) I tried my bike before purchase in Evans. They got me in the bike I wanted in the size they thought would be right (I had to pay a £50 deposit, returnable as long as you turn-up to look at the bike - you don't have to buy it to get the deposit back). I actually made sure they had the two possible sizes when I visited. Left my card with them in-store and took it out for a test ride. Then didn't buy it there (because I noticed some cosmetic damage and they were not happy to lower the price appropriately).

But there are ways you can try before you buy.

Ian

[reohn2]

It was mail order. Ive sent it back and will order a completely different make and model and see if I have any joy. It was a road bike. Weird thing though unless it was bad manufacture/assembly. The pedal arm drive side had hardly any clearance from the frame or chain either (literally 3-5mm it actually rubbed the chain in the lowest rear cog) but non drive side there was easily an inch or more. Could have been BB installed wrong way round at the factory?

There should be a geometry table to the bike giving you the problems,as Colin says that's your first port of call,check the chainstay length.
You need longer chainstays on the next bike you buy.
Colin's also right in pointing out that unless you know exactly what your requirements are,it's better to go to a good bike shop,try some different bikes and take some advice from them.
It may cost more but in the long run it's money well spent.

[NATURAL ANKLING]

Hi,
IGH

[iandriver]

Odd. I'm a 12 and have never had anything like this problem. Are you sure the ball of your foot is over the peddle axle. I'm a bit concerned you may have your foot too far back on the pedal.

[Cyril Haearn]

Maybe you were not ankling properly, you could try pulling your heel up sooner as the pedal comes up. One soon learns to do this without thinking. The difference between 21" & 23" frames is substantial, maybe 22" would be right.
..

How do you cycle so fast, Mr Blower?

Every time a pedal comes up I push it down again!

[Mick F]

Size 12 is a big foot.
Actually, it's about a foot long.
https://www.clarks.eu/fitguide

If we consider that the ball of the foot is about 25% from the toe tips, it means that there's 9" of foot behind the pedal spindle.
170mm cranks are 6.5" long, so that means the heel of a size 12 foot extends 15.5" behind the BB at its furthest.

My chainstays are 17" long.
My size 9 feet are 27.2cm = 10.5" ............ 75% of that is just less than 8"
As my cranks are 6.5" long, my heel extends 14.5" rearwards.
I therefore have a couple of inches spare to the rear axle, and by the time you consider that the rear mech is 1.5" forward of that, I have only one inch clearance.

For a 12" foot ............... on my bike .............. it means that the the heel hits the rear mech.
No question of it.

[AndyAll73]

I just opened the returning parcel as its being collected tomorrow and measured the chainstay length at 16 inches (41cm), my MTB is 17 (44cm) obviously a different kind of bike but still I know I need a chainstay of at least 17inches now.. does this sound about right? Is 16" (41cm) quite short for a road bike?

[531colin]

You need a frame with longer chainstays, much longer chainstays..."E" in the diagram here.....



That actually shows shorter chainstays for bigger frames,, but its just something I borrowed off the internet.

[RodWatts]

Bottom line is 'don't buy a bike by mail order'
If you want to get a decent bike spend a £100 on a bike fit first off!
Rod