Frame modification

[Chadvdw67]

Hey guys, I am pretty sure I know what the answer to this question is going to be, but I want to ask just to be sure....

 

I have an old 26" mtb frame that I have converted into a MX bike, but I would like to try fit fatter rubber on it, but the braces on the seat stays and chain stays limit it quite a lot, would removing them be a really bad idea? I see lots of newer gravel bikes that dont have those braces in place, but maybe their construction is different to this old frame? What would be your suggestion?

 

Pics of the mentioned braces....

[TheoG]

Yes, I think that what be a bad idea.  Those add a crapload of stiffness to the frame.  It might be strong enough without them but you frame will flex a lot without them.

If you don't mind to write off the frame, maybe give it a shot and see just how flexible it is, just maybe you can get away with it.

[DIPSLICK]

as above, you may as well just throw the frame away if touch any of those braces. Other frames may not have them but the design of those frames have support built into them in different areas  

[Chadvdw67]

Thought as much, but always worth asking

[JA-Q001]

The top one is only there to support the seatstays when using V-Brakes. It stops the stays from flexing open under braking. Removing it wont do anything to the strength of the frame.

The bottom one helps support the chainstays. They help reduce the flex at the BB junction and prevents the chainstay/BB weld from cracking. you can however cut part of it out and make it thinner, just fill in the open tube section with a small plate.

[droo]

If you want bigger tyres, fit 650 rims. You'll have clearance for 45c gravel tyres with room to spare.

[Chadvdw67]

9 minutes ago, droo said:

If you want bigger tyres, fit 650 rims. You'll have clearance for 45c gravel tyres with room to spare.

This was my other option, I just have a set of 700c rims, so wanted to use what I have...

[droo]

1 hour ago, Chadvdw67 said:

This was my other option, I just have a set of 700c rims, so wanted to use what I have...

Spares box is always first prize...

[Jewbacca]

2 hours ago, JA-Q001 said:

The top one is only there to support the seatstays when using V-Brakes. It stops the stays from flexing open under braking. Removing it wont do anything to the strength of the frame.

The bottom one helps support the chainstays. They help reduce the flex at the BB junction and prevents the chainstay/BB weld from cracking. you can however cut part of it out and make it thinner, just fill in the open tube section with a small plate.

I'm with JA on this. 

Cut out the seat stay one and cut the BB one with a hole saw or file out a tire profile.

It's made as a MTB, so it's over engineered to take the stresses of the rough and tumble of the trails.

 

[Nuffy]

I would be very scared of introducing extra flex into an aluminium frame. My understanding is that it has far lower fatigue resistance than a material like steel, so even though it might be “strong enough” without the braces to begin with, some time spent flexing it repeatedly will probably weaken it pretty quickly.

[Mamil]

What an interesting mix of risk orientation profiles there is on the hub. 

[Puncture Kid]

Don't modify it. You risk life and limb if it fails at the most inopportune moment. Years ago there was a guy at the Knysna race that modified /  welded his fork. It failed during a descent and the bottom part took half of his face away. He died en-route to the hospital

[Stretched@Birth]

I had the same issue on my build.  I took a file to it and filed out sufficient material to get the tire to fit, without filing through the piece of pipe.  Not sure what he wall thickness is of that piece, but it is thick enough that I didn't go through it.  I could do with another couple of mm, but am a little scared to take it any further.

I managed to get 35c rubber in there.

Edit: Giant XTC 26er frame

Edited April 19, 2022 by Stretched@Birth

[RobertWhitehead]

My opinion: shorten the supports and re-fit them. Have a look at my very rough sketch 😁. If you take off say 5mm in total you will be able to move the supports away from the wheels enough to give you some more clearance. But you will need the services of an alu welder 😢

[Jewbacca]

I'm definitely not going to show some of you how I've cut up carbon frames and made inserts, adjusted size, geometry and all sorts and stuck it back together with epoxy and carbon wrap and subsequently thrown it down trails and off drops and jumps with reckless abandon.....

[MORNE]

2 hours ago, Jewbacca said:

I'm definitely not going to show some of you how I've cut up carbon frames and made inserts, adjusted size, geometry and all sorts and stuck it back together with epoxy and carbon wrap and subsequently thrown it down trails and off drops and jumps with reckless abandon.....

Awesomeness can only exist outside the boundaries of conformity’s box.

🤘