2.5mm - Will I notice a difference?

Just think if you moved your saddle 2.5mm forward.It feels like a foot.I have long legs and went from 170 to 180 and when climbing can push a higher gear with ease for the same heartrate.I think it's down to length of your legs I'm 6ft4ins if I was 5ft 165mm cranks would be better.

Like many others here. I have run crank lengths from 170 to 175mm and can't say I notice any difference.
You might want to adjust your saddle height slightly if you did go from 70-75 but 2.5mm is about like a thick pair of socks, as mentioned. Have to say I do adjust my saddle height between wearing approach boots, sandles or bare feet though.

I read an article recently where they tested crank lengths to see if there was a performance difference, there wasnt any. The crank is only one part of the lever along with the gears themselves, the only difference was noted at real extremes, like 200mm cranks.
You might notice for the first hour, just because its different, but after that you'll be fine.

You could try running one side at 172.5 and the other at 175, on the basis that most people's legs are different lengths.

Just to add to the chorus of no answers. I switched and no, I did not notice the difference. But then I did compensate by wearing four pairs of padded shorts.

Your hip joints are articulated less on shorter cranks. If you are getting on a bit you might want to think about that. They do wear out in the end.

I had 175mm cranks on one bike 172.5mm on another and I did notice a difference injury wise, but I think I had my saddle too high; so whilst on the 172.5mm cranked bike my seat height was almost ideal the same saddle height on the other (175mm cranked bike) was fractionally too high. Gradually it felt like my calf was being pulled too much; I moved the seat down 2.5mm and forward 2.5mm and the feeling went away and I can't say I noticed a difference after that.

More recently I run 172.5mm cranks on my two bikes and 170mm on the fixie and I cant say I notice a diference there either.

I have 172.5 on one bike and 175 on another. Can't say I ever notice a difference.

2.5mm about the same as a pair of thick winter socks!

Why not just get the thread in the crank arm repaired..? or ebay it (LH ones should be easy and cheap to obtain if that's the side in question).

Isn't crank length supposed to be related to shin length?

You wont be able to get your knee down so much during those 100mph Crit races. Other than that...you'll probably not notice after the first minute.

I knackered my 175 mm cranks on the penultimate day of a trip to Spain. So I could ride on the last day I managed to borrow some 172.5 mm ones off our host. I noticed 2 differences.

First, if I was riding hard then my quads seemed to be working in a slightly different area of the muscle so I was getting pain further up my legs than usual. Not a big deal and I'm sure you'll quickly adjust.

Second was on steep sections (>15%) I felt like I had less leverage (to be expected) and had to work harder at a lower cadence. So the opposite going the other way I guess.

Probably worth mentioning, if you do make the change, don't forger to adjust your saddle height slightly as the change in crank length will change the distance from the bottom of the pedal stroke to the saddle.

I doubt you will notice, I have 170 on my track bike and occasionally use a 165. My road and MTB have 175, and my wife's bike has 172.5 and the only time a feel any difference is if I dont drop my seat a little on the track bike

You'll probably not notice, I have both - that said I *think* I prefer 172.5 to 175 on my road bikes but it may be psychological. 85cm inside leg for what it's worth.

I feel a big difference between my 175mm and 180mm cranks (BMX). Not sure if this helps as its twice the difference you are talking about.

I've used 165mm and 170mm on the road and can feel the difference although its certainly not enough to throw me off my stride. 155mm felt odd.

I think that there's probably a comforatable maximum length depending on your build and leg length and anything up to this length will feel OK even if its not the most efficient. For fixed gear bikes shorter cranks help to avoid pedal stike too.

I run 170 + 172.5 cranks on different bikes and don't really notice a difference, obviously the saddle is slight;y higher relative to the handlebars so does depend whether you are at the extremes of your bike's position. There are some schools of thought that think that a smaller crank size is more efficient. Worth a search on google. Personally I wouldn't spend the money changing the crank size. Think how small 2.5 mm are, although it makes a significant difference on circumference, i wouldn't worry about it terms of leverage as some people discuss.