New forks

Nathan_S

Likes Bikes and Dirt
So I’m in need of a new set of forks. I currently have a set of Fox 36 180mm forks on my bike, fairly sure they’re what came with the Transition TR250. And they’ve just about had their day. The stanchions have sever wear on them, the CSU creaks (was purchased in that condition). So here’s the dilemma.

Bikes currently still 26”, but is 27.5 compatible. I do want to go 27.5. I’d also have to more then likely run a boost fork and boost hub.

If I was to drop down to a 160mm fork ( 180 is abit excessive for the riding I do now days) and go 27.5, would that retain the same geometry as the bike currently sits? This is my working out,

27.5” (698.5)
-26” (660.4)
=38.1

38.1 \ 2
=19.05

Is there anything I’ve forgotten or not taken into account?
 

Nathan_S

Likes Bikes and Dirt
That would be greatly appreciated if you could, thank you!

I’ve just measured the OD of my current wheels, 26”with a 2.5 - 685mm
 

Dales Cannon

The Olden Dazed
Staff member
710mm OD, 2.35 NobbyNic on 30 internal width rims. Sorry forgot I changed to 2.35 front and rear...
 

Dales Cannon

The Olden Dazed
Staff member
Depends on tyre size. Based on the numbers posted yes but go for a bigger tyre and it changes. You going 27.5 rear too?
 

Nathan_S

Likes Bikes and Dirt
Yeah would like to have 27.5 all round. The transition has 3 different locations for the rear wheel, so can either lengthen or shorten the chain stay
 

Dales Cannon

The Olden Dazed
Staff member
Potentially longer wheelbase but geo will only be the same with 180 fork, front and rear go up together...
 

The Duckmeister

Has stumpy thumbs, Speciaized are so weird
Potentially longer wheelbase but geo will only be the same with 180 fork, front and rear go up together...
Wheelbase can't increase, but will either remain the same if fork travel is unchanged, or slightly reduce if travel is cut.

Everything else being equal, increasing rim size from 559 to 584 will lift the bike 12.5mm. All the angles will remain constant, however there will be a slight increase in front trail, which will affect steering a bit. Subsequently dropping the front (by reducing fork travel) will tip the whole bike forward, and that will affect all your frame angles relative to the ground, as well as the front end triangulation. Someone with better maths than me can fill in the details. :p
 

Dales Cannon

The Olden Dazed
Staff member
Wheelbase can't increase, but will either remain the same if fork travel is unchanged, or slightly reduce if travel is cut.

Everything else being equal, increasing rim size from 559 to 584 will lift the bike 12.5mm. All the angles will remain constant, however there will be a slight increase in front trail, which will affect steering a bit. Subsequently dropping the front (by reducing fork travel) will tip the whole bike forward, and that will affect all your frame angles relative to the ground, as well as the front end triangulation. Someone with better maths than me can fill in the details. :p
Yeah would like to have 27.5 all round. The transition has 3 different locations for the rear wheel, so can either lengthen or shorten the chain stay
It fucking can if the chainstay is adjustable.
 
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