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I have been training a lot on the turbo during lockdown using power and enjoying it (Elite Direto). Although I used the Turbo before I feel like I have a good understanding of what I am doing now.
I am now thinking of getting a crank based power meter. Ideally I would want to be able to fit this to my gravel/road bike and my MTB.
My gravel/road bike (which is on the turbo as well) has a Tiagra crankset fitted so I believe that I can fit the 105 left sided crank arm without issue.
https://www.wiggle.co.uk/4iiii-precision-105-r7000-powermeter/
Does a 105 arm also fit a MTB shimano crankset and therefore I would be able to swap? For the MTB I wouldn't be looking to swap it for every ride but there are some where I might want to fit and I would like to have that option.
My MTB is a Trek Roscoe with the following crankset and NX Eagle 12 Speed.
Truvativ Descendant 6k Eagle, GXP, 30T alloy ring, Boost, 170 mm length
Truvativ Powerspline, 73 mm, threaded cartridge, 118 mm spindle
I would be looking to swap this to a Shimano 12 speed crankset with HT2 bottom bracket. Which is the correct one for this bike? Any ideas!
You also need to check very carefully that the crank wont foul the chainstay. Make sure you have clerance. THe battery housing sticks out a few mm on the inside of the crank arm.
Just buy one mail order and check it all, post it back if it dosent fit.
I've got an Ultegra one on my road bike and use for zwifting. Do you want me to take a picture of the clearance to the chainstay - might give you a guide on compatibility?
There's a test mentioned on the 4iiii site that you can do to check if your crank/chainstay combo is suitable. You need around 4-5mm of clearance for the strain gauge/battery pod.
Do the Tiagra and 105 crank arms have the same profile and Q-factor?
I think it will be OK on the road bike as there is plenty of space for a cadence sensor. MTB might be more difficult as there isn't much clearance there at the moment.
Q Factor looks different on the two road cranksets as well so might be a non starter without upgrading to a 105 crankset on the road bike.
https://www.bike-components.de/en/Shimano/105-FC-5800-Hollowtech-II-Crankset-p40014/
https://www.bike-components.de/en/Shimano/Tiagra-FC-4700-Crankset-p43861/
Q factor on 12 speed SLX is 172mm so def not a option
FWIW my ultegra 6700 and R8000 LH cranks are the same depth from outer pedal face to inner Axle face.
My R7000 4IIII is the same depth also.
6700 q factor is 148mm and the R8000 is 146mm
The difference must be in the axle.
The axle interface on my road cranks are much smaller than any of my XT/SLX cranks - although all predate anything modern M780 being the newest i have - so i didnt try and fit my power meter there - although i thought it would be interesting to see what i do put out on the SS grunting up the hills.
I tried to put a 105 stages on an XT crank once and whilst the axle/arm interface seemed fine, mountain bike chainstays are a lot fatter so mountain bike cranks have a more pronounced bend to avoid a frame clash.
So I'd say it should be fine on a road bike orientated gravel or cc bike, you will likely struggle fitting it to an MTB.
You may also find that in use its hard enough maintaing a power output on a road bike, let alone a MTB.
When I did some proper training with a power meter its all set times at set power outputs, on the road thats pretty hard to do. Off road it would be pointless. Sure, you would see what your power is for an average on the ride, but you cant keep it to a zone off road.
Personally Id not bother off road with one. If you just are intersted in things like your max or average the Strava's estimation will do.
I've been pondering this too. Same as you, training on zwift through lock down and seeing the benefits that power based training is having. Again, thinking of getting a power meter for the gravel bike, and maybe the full sus bike.
Ideally I'd get a pair of pedal based power meters and swap between, but there seems to be an absolute dearth of 2 bolt spd compatible power meter pedals. SRM seem to be the only ones producing them, and £1000 for a pair of pedals is a painful concept, considering the hammering that they'll likely receive.