[Closed] Cotic Rocket 650b home baked

Good work! Tinkering is fun.
Looks nice

Crests? Either you're mega lightweight or a rider with massive finesse to not mince those rims with what rocket is designed for 🙂

But its been a great way to compare wheel sizes with pretty much the same set up just small adjustments in travel to compensate for the wheels.

And your conclusions?

matther - Yes maybe not the best choice but it was more a bit of experimenting with bits I had/could scrape together easily and they work ok for what Im doing right now, I'm waiting on shoulder surgery so I'm not hammering it right now.

As for conclusions - I think its a great fun bike in 26" mode 650b changes it a bit but not that much, tweaking the geometry showed me that little changes there make as much of a difference. I do like the extra acceleration you can seemingly get out of 26" wheels and it suits my style of riding but maybe thats just because its what I'm used to riding.

Had crests on my fuel ex for a few years, their weight belies their strength imo

Crests are strong - if you ride smooth ...

I'm lightweight but I have had my Crests for ages now and ridden all kinds of rocky and fast jumpy terrain with not a slight change in their perfect performance.

Fantastic wheels

I found Flow Exes barely strong enough for my big bike 😯 And it's made of lightweight aluminium so god knows what all that steel would do to them * Also that was naturally stronger 26 inch not your half-clown stuff.

*Yes I know the frame's actually pretty much the same weight as the alu competitors.

I found Flow Exes barely strong enough for my big bike

Were you doing a Gwin with them? Tyres help! 😉

Crests are strong - if you ride [s]smooth ...[/s] never pinch flat.
The wheel containing a crest as a whole can be strong (ie is still true and roundish after a lot of miles) but the rim does not like rock strikes at all (IME YMMV etc etc)

Perspective on that pic is wonky, looks like you've got a 26" front wheel.

One does wonder with so many companies doing 650b upgrade merely by offering different dropouts and maybe faffing with the shock how much difference there actually is between a fully thought out and properly designed 650b frame and a 26er bodged to fit slightly bigger more [s]expensive[/s] enduro wheels.

D0NK - Member

how much difference there actually is between a fully thought out and properly designed 650b frame and a 26er bodged to fit slightly bigger more expensive enduro wheel

Proper 650 frames tend to have BB below the axles, don't they? Whereas 26" frames wouldn't - and fitting 650s makes that BB higher still.

Proper 650 frames tend to have BB below the axles, don't they? Whereas 26" frames wouldn't

Most 26 inch frames have the BB well below the axle when sagged (and whenever it counts, it'll always be sagged, you don't care if the BB's above the axles when you're unweighted)

I've adjusted the geometry using a smaller shock and offset bushes, and using a shorter travel front fork with a low axle to crown dimensions, so although the travel ends up being less you get the same geometry, the only other difference is the drop link will be slightly further into it's rate, so you would get a slightly different stroke. I think this is negligible though, so the upshot is you end up with a more direct comparison between wheels.

Northwind - Member

Most 26 inch frames have the BB well below the axle when sagged (and whenever it counts, it'll always be sagged, you don't care if the BB's above the axles when you're unweighted)

All true, but the point remains - BB will end up significantly higher on a bodged 26"

Comparing my own bike to the 27.5 equivalent (Ion 16 26 vs Ion 16 27.5) - the BB (low setting) on the 26" bike is +6mm, on the 27.5 bike it's -15mm.

So 21mm in difference - more than 3/4 of an inch - add the additional half inch from the bigger wheels and you may well be above the axles

Putting 650b wheels on a 26" bike is only going to raise the BB by .55" surely? about 13mm.

No the BB is not higher, by adjusting things as I have it's the same

Nobeerinthefridge - Member
Putting 650b wheels on a 26" bike is only going to raise the BB by .55" surely? about 13mm.

Yes, but the question was:

how much difference there actually is between a fully thought out and properly designed 650b frame and a 26er bodged to fit slightly bigger more expensive enduro wheel

So I was talking about the difference between my 26" bike with 650s bunged on it, versus the proper, 650 version of same bike.

Just taking the back end in isolation for a moment, it normally runs a 200mm shock with 57mm shock strokel giving 6" travel, by putting a 190mm shock in with 50mm stroke you end up with approx 5" of travel with the bike being 1" already into the travel as its a shorter shock. With the use of offset bushes you can fine tune things to get it perfect so the BB is the same height off the ground.
Using a shorter travel fork you can sort out the front end the same way ie lose an inch or so to make up for the longer fork and wheel size.

i tried just putting 650's on ages ago for a bit of experimenting and it completely changed the ride, the BB felt way to high, but with these changes it brings the BB back down. Obviously you cant do the same with a hard tail and it depends on what length of shock you run and clearance you can get on any specific frame.

does the frame have a cage mount there or have you added some clever bottle mount solution?

does the frame have a cage mount there or have you added some clever bottle mount solution?

So I was talking about the difference between my 26" bike with 650s bunged on it, versus the proper, 650 version of same bike.