Chainset mod options.

[Milzy]

I currently have 6800 Ultegra crankset in 172.5.
I need 170 to complete my bike fit correctly.
I’d also love to upgrade to the 8000 chainset.
What’s the most cost effective ways? Can I just buy the arms only in 170 & bolt my chain rings to them?
Wiggle, CRC etc only seem to do the full chainsets. Or I could try eBay for second hand 6800 or 8000 set depending on price point.

 

[Vapin' Joe]

I doubt you'd even begin to notice the difference between 172.5 and 170.

 

[Milzy]

I doubt you'd even begin to notice the difference between 172.5 and 170.

Maybe not, but I’ve paid for a professional bike fit, so I’m going to do as advised.

 

[twentysix by twentyfive]

Buy new and fit old chainrings. You'll then have new rings for a rainy day when things wear out.

 

[Milzy]

I might just buy the 4iiii power meter & a right hand side 6800.

 

[Blue Hills]

I doubt you'd even begin to notice the difference between 172.5 and 170.

Maybe not, but I’ve paid for a professional bike fit, so I’m going to do as advised.

Mm, there's a phrase for that isn't there milzy? Forget the exact phrase but first bit "buyer's"?

I have bikes with both 170 and 175 but didn't even know until I got the tape out.

Is this fitting something to do with "power output" or just comfort? Latter can be sorted yourself I think.

 

[fossyant]

Maybe not, but I’ve paid for a professional bike fit, so I’m going to do as advised.

Not worth it on cranks, sorry. General fit, yes.

I ran 170 on my road bikes, and 175 on my MTB's - only 175 because both happened to have them. Reach, saddle height etc is more important. You'll splash a load on a new chainset for nowt.

I set my bikes up using Bernard Hinault's 'Racing and Training' book - and I carry this forward to current bikes. Measure, check, measure, check....

 

[fossyant]

PS couldn't tell the difference when my old retro 90's MTB's crankset was knackered, so switched to a newer set (same level Deore LX) but 5mm longer. No issues.

 

[Milzy]

Mountain bikes usually are longer. I will run 170 for the rest of my life now. It’s only a few quid to change.

 

[themosquitoking]

I realise that 2.5mm is next to nothing but a bike fit is essentially based around the riders position on the bike and after the cleat position on the shoes the cranks/bb position is the starting point for it all. Saddle/bar position are adjusted to suit your legs, carry on and buy your new cranks and do whatever else in life that makes you happy.

 

[Milzy]

I realise that 2.5mm is next to nothing but a bike fit is essentially based around the riders position on the bike and after the cleat position on the shoes the cranks/bb position is the starting point for it all. Saddle/bar position are adjusted to suit your legs, carry on and buy your new cranks and do whatever else in life that makes you happy.

Cheers, I want to watch my wife go down a big slide into a paddling pool full of custard.
Regards.

 

[MiK1138]

Cheers, I want to watch my wife go down a big slide into a paddling pool full of custard.
Regards.

Make sure she's not holding your new cranks, you'll never get the custard out the threads

 

[themosquitoking]

Cheers, I want to watch my wife go down a big slide into a paddling pool full of custard.
Regards.

Who doesn't?

 

[FishFright]

I have cranks that are; 152, 160, 165, 170, 172.5 and 175 . Only the the first two sizes on the trikes were crucial .

Don't get hung up on 2.5 mm just because it's cost you money.

 

[Blue Hills]

I realise that 2.5mm is next to nothing but a bike fit is essentially based around the riders position on the bike and after the cleat position on the shoes the cranks/bb position is the starting point for it all. Saddle/bar position are adjusted to suit your legs, carry on and buy your new cranks and do whatever else in life that makes you happy.

Or make the professional bike fitter happy.
And in order to follow this guru the OP is considering swapping his new bits for second hand bits (not that second hand is bad in itself)
I applaud the straight practical responders with their practical answers.