Hi
Is there any real difference with changing form 170mm lenght crank arms to 175mm lenght crank arms will I notice the change in lenght is there any benefits in the longer arms

Well, I'm 6'2 and really like the 175mm cranks – on my road bike and MTB's. All personal choice though!

yes

I know someone of similar height to Glenn who recently swapped to 170s and liked it.

no

my previous answer was facetious in response to a plain 'yes'. The real answer is that 175mm may be slightly better for riders who are 6' or taller (or have long legs), and some claim to be able to feel the difference, but I rode for ages with 2 different lengths left/right and couldn't tell which was which. For normal purposes it's not critical, unless perhaps you're very fussy or sensitive, and I wouldn't reject either length if available.

A short rider (5') tried 165s but told me they 'felt wrong' although that would be the recommeded length for her height.

Thanks for the feedback will try the 175mm see what it`s like