midlife
Guru
Err, yes they do. Imagine a shoe with thickness 170mm and then the foot would only be 5mm from the centre of the axle for the OP. Sort of analogy with PMP cranks
Replacement chain set has longer crank arm - should the mechanic fix this?
- Thread starter Flossy
- Start date
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Err, yes they do. Imagine a shoe with thickness 170mm and then the foot would only be 5mm from the centre of the axle for the OP. Sort of analogy with PMP cranks
Justinitus
Warning: May Contain Pie
- Location
- Wiltshire
Err, yes they do. Imagine a shoe with thickness 170mm and then the foot would only be 5mm from the centre of the axle for the OP. Sort of analogy with PMP cranks
But wouldn’t the opposite side pedal then be 345mm from the axle?
I’d be inclined to take it back to the shop and ask them to swap it. It’s like them replacing a 90mm stem with 100mm stem - it might just be enough to make the bike uncomfortable for the owner.
the snail
Guru
- Location
- Chippenham
So if you have 175mm cranks 175mm platform shoes, your feet don't move at all?Err, yes they do. Imagine a shoe with thickness 170mm and then the foot would only be 5mm from the centre of the axle for the OP. Sort of analogy with PMP cranks
Fab Foodie
hanging-on in quiet desperation ...
- Location
- Kirton, Devon.
The shop should jave replaced with the same length cranks. Get them replaced.
- Location
- London
You should be fine. Pretty sure I have bikes with both 170 and 175 cranks.
And I think I had been riding several years before I realised.
If I was getting a new pair of cranks these days I don't think I would have any particular preference.
Extremely unlikely to be an issue.
And I think I had been riding several years before I realised.
If I was getting a new pair of cranks these days I don't think I would have any particular preference.
Extremely unlikely to be an issue.
Go back and ask them why they didn't change like for like. Be prepared for them to agree just to put the old crankset back on if you want to keep some goodwill for another time.
(I am assuming there was nothing wrong with the old crankset itself and the old crankset is compatible with the new bottom bracket.)
(I am assuming there was nothing wrong with the old crankset itself and the old crankset is compatible with the new bottom bracket.)
vickster
Legendary Member
If they still have the old one?
Just go have a chat with them
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
Personally I'd get it changed. All my road bikes and the old MTB were 170mm - I kept it like that. Old MTB got a new crankset a few years back, but it was in a bargain sale, and I could only get 175mm. I could tell, but soon got used to it. My next MTB also came with 175. I can't tell the difference now, although the longer cranksets are on a different type of bike. If the I had different lengths on my 3 road bikes, I'd probably not be happy as they are set up the same, same measurements etc. The MTB's are used differently, so I can't tell.
midlife
Guru
In my thought experiment the shoes were fixed to cranks, not sure why I thought that as its plainly not the case. Yep, you are right, the shoe itself rotates on the pedal spindle and also around in a circle.
Slopes off the the kitchen to count the number of empty tins of Fosters...
Bonefish Blues
Banging donk
- Location
- 52 Festive Road
That's simply what a decent LBS should do, ie replace like for like, or if not, ask you first. Get it changed and find another shop.
Heltor Chasca
Out-riding the Black Dog
If it’s any consolation: My tourer has 175mm and my Audax 170mm. Even on one of my most mindful days I can’t feel any discernible difference.
I have set the seat height up on both bikes using my turbo, starting first with the ‘foot just scrapes the pedal’ technique (pedal fully down) By sheer coincidence (or not) both bikes have exactly the same total distance from pedal to seat rail. I can ride all day on both.
Roll with it. You’ll be ok.
I have set the seat height up on both bikes using my turbo, starting first with the ‘foot just scrapes the pedal’ technique (pedal fully down) By sheer coincidence (or not) both bikes have exactly the same total distance from pedal to seat rail. I can ride all day on both.
Roll with it. You’ll be ok.
I wouldn't be happy if the 170 cranks on my road bikes were replaced with 175 I know what setup suits me so longer cranks would have to change the setup by lowering the seat, this changes the handlebar to seat relationship, so that would have to change, the distance from seat to ground would also change, no doubt all things I could get used to, but I I have been riding with my current setups for years and don't think a bike shop should determine when I change.
Levo-Lon
Guru
Would 172.5 be a good compromise?
I have 170-175 on different bikes, seat hight to pedal axle are all set the same 875 mm
The only thing that changes this is my shoes, so i have a few mm difference which i dont find a problem.
My legs notice the difference as my knees tend to hurt a bit on longer rides.
But this could also be the bike im riding on any given day
I have 170-175 on different bikes, seat hight to pedal axle are all set the same 875 mm
The only thing that changes this is my shoes, so i have a few mm difference which i dont find a problem.
My legs notice the difference as my knees tend to hurt a bit on longer rides.
But this could also be the bike im riding on any given day
sleuthey
Legendary Member
- Location
- South Gloucestershire
Totally agree with you and The Snail, thicker shoes will NOT affect the pedal diameter. However they will affect the knee angle at the top and bottom of the pedal stroke assuming no adjustments have been made to saddle height.
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Ajax Bay
Guru
- Location
- East Devon
Why compromise? And btw irrelevant to the OP who wants the same length cranks as were fitted before.
Crank length is disproportionately dictated by industry wishing to minimise the range offered for commercial advantage.
Continuing off topic.
175mm cranks are 3% longer than 170s so in moment terms for the same force on the pedal would need a large sprocket one tooth fewer.
5mm up or down in saddle height (and any corresponding adjustment to the bars) is small beer (unless your cranks are already too long). There are three main issues which help determine the optimum crank length for a rider:
1) Inside leg measure
2) Style of riding (spinning or honking up steep hills, in particular)
3) Physical issues regarding (including in particular) knee bend comfort
Think this Bike Dynamics article is a good and thought-provoking read with some useful graphs.
https://bikedynamics.co.uk/FitGuidecranks.htm
"your crank length can be the second most important dimension on a bike after saddle height. This may seem incredulous to some, especially if you can't tell the difference between 170mm and 175mm, which may well be true if you are around 1.83m (6') tall. The shorter you are, the more likely it will be that your cranks are too long and that you have been let down badly by the cycling industry.
change?
"inseam is not always the best means to define leg length. . . . , a deep pelvis means the leg starts much higher than the inseam suggests. An alternative leg length measure is to the top of the Greater Trochanter (GT)" [hip bone].
Leg Length Measurement
" . . . plot recommended crank length against . . . a simple addition of Inseam + GT height . . . . gives the plot below.
The BikeDynamics recommendation is always below the Industry Standard for everybody except the extremely tall and those of 180cm (5'11") where it matches exactly!"
Btw, Spa Cycles are the 'go to' boys for shorter cranksets.
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