[Closed] Alloy mtb frame modification, seat tube and brace trim

You could put the post down a bit?

shorter cranks would be a better idea. That saddle isn't super slim either.

As for cutting the frame, do it yourself.

It's a dropper post, it won't go any lower.

Agreed, that seat isn't the slimmest. I've taken the specialized phenom off as its an instrument of pain. It's got my 170mm cranks on it too.

As for cutting it myself, it's something I'm considering. Grind down the welds to the brace and then send it away to be refinished?

Why not run it slightly "dropped"?

It's a dropper post, it won't go any lower.

Agreed, that seat isn't the slimmest. I've taken the specialized phenom off as its an instrument of pain. It's got my 170mm cranks on it too.

As for cutting it myself, it's something I'm considering. Grind down the welds to the brace and then send it away to be refinished?

Selle SLR or a Pro Turnix a pretty slim saddles. 165mm cranks are another option (and seem popular these days). Or get some thicker socks!

As for cutting it myself, it's something I'm considering. Grind down the welds to the brace and then send it away to be refinished?

I don't think it'd be too much trauma to cut the brace off. Then just file the welded areas flush. It looks like it's anodized? I'd probably just put some toiuch up paint on it and leave it at that.

Shorter drop dropper? I've always wondered how small a persons frame must be if they can run a 170mm dropper.

Pic didn't show for me, I have tried to put it up here :

[img] [/img]

Doesn't look like much to cut off, the brace is there for a reason...

The other issue is that even when the seat is dropped, I don't feel it's giving me enough room to move around. It's too high compared to my other bikes.

I agree, the brace is there to support a moment on the long seat tube, but if the tube is sufficiently trimmed it should not need to be there as its braced by the top tube.

David, it is ano finish. I'm more minded to DIY it. I might do some measuring and planning. I'll lose the end of the decals on the post, but as its really a winter hack, I'm fine with that.

I agree, the brace is there to support a moment on the long seat tube, but if the tube is sufficiently trimmed it should not need to be there as its braced by the top tube.

But the top tube likely hasn't been designed to handle the load on its own

Can't you go for one of the droppers with the shorter collars? Was it the Bikeyoke dropper that had a slim top collar?

I know exactly how you feel with it, most bikes I like the look of have seat tubes too big for my stubby legs.

I have a leftfield suggestion for you, based on owning the same bike...
http://unduro.co.uk/mtb/behold-the-frankenthumper-aka-project-279/

If you favour technical trails over covering miles, there's not much of a downside at all.

I've always wondered how small a persons frame must be if they can run a 170mm dropper.

My frame's enormous, but you should see the length of my legs 😉

I've done something similar in the past and the one piece of advice I would give you is - make sure the seat tube is the same diameter all the way down...

Just get a dropper with a 100mm instead of 125mm drop??

I have essentially the same frame and before buying it considered a similar modification to get a longer front end but decided against it because...

Seat tube could be slightly different internal dia.
Grinding could cause heat problems in the alu frame.
Toptube seat tube joint may not be strong enough.
Seat could be so low the wheel gets in the way when post is dropped.
You may not be able to insert the post much further because of the seatube bend.
Didn't want to generally fubar a perfectly good frame.

1) You'll weaken the frame (whether it breaks there as a result depends on a lot of things).
2) When your suspension bottoms out it will hit the saddle if you lower it too much.

I'd guess different frame/shorter dropper post/put up with it are your best options.

chakaping - Member
I know exactly how you feel with it, most bikes I like the look of have seat tubes too big for my stubby legs.

I have a leftfield suggestion for you, based on owning the same bike...
http://unduro.co.uk/mtb/behold-the-frankenthumper-aka-project-279/

If you favour technical trails over covering miles, there's not much of a downside at all.

But fitting a smaller rear wheel won't change the saddle height, so the OP's problem willstill be the same.

How much too high is the saddle at present - or did I miss that?
I wouldn't even entertain the idea of removing that brace - simply because you'll ruin a perfectly good frame and the seat tube will probably end up fracturing anyway.

Ok - I did miss it. Another inch off it.

So, cut the seat tube as short as possible without cutting into the weld area - that should get you 20mm by the looks of it.
Drill two 5mm holes in the back of the seat tube in the area between the top tube and the brace and then slot between them, say 2mm wide. Find, or get made up, a split clamp to suit the frame dia and clamp the seatpost with that.
Unorthodox maybe, but it's a better solution from an engineering point of view than removing the brace.

Don't do it. Keep it and make do or sell it and fund something that fits IMHO.

I had the same issue with a Lapierre spicy,

I cut what I could off the seat tower and fitted a reverb which is the lowest clamp to rail height I could at the time.

In the end I conceded and bought a Saracen Ariel and its a dream.

I get a much lower seat height when it is down and feels like it is out of the way now when i'm throwing shapes.

But fitting a smaller rear wheel won't change the saddle height, so the OP's problem willstill be the same.

It will drop the rear of the bike by 2cm, so the saddle and BB should be at least 1cm lower - combined with the slacker HA it will make the bike MUCH more confident on steep stuff, which I assume is where the OP is having trouble.

As hes running a dropper, I dont think it's an issue with the steep stuff, just his legs arnt long enough when the dropper is at full extension.

I see what you mean and I take the point about wheel size not changing distance from pedal to top of saddle, I was focusing on this bit...

even when the seat is dropped, I don't feel it's giving me enough room to move around. It's too high compared to my other bikes.

I have a 150mm dropper that came on my enduro bike - and at full extension it's 5 or 10mm too high. I've got very good at micro-dropping the saddle or stopping it at the right height with my bum.

Just get thick pedals innit... 😀

It's a two-fold problem of my legs not quite being long enough to use a preferred saddle and pedal combination, and I'd like the seat a touch lower on the 'gnarrrr'

I'm minded to think if I were chopping the seat tube to near the top tube (25mm or so) I would not be concerned about losing the brace. However, I'm listening to the advise above and post dia and insert length (to the bend) need checking first.

You may think I'm ignoring the other comments on the potential to snap the seat tube, but if it's shortened enough, I can't see it breaking as the moment on the welds from my seat load is dramatically reduced. I'm also 11st, and the frame cost me very little.

I've taken the seat post tube down as much as I can, whilst still leaving enough room for a small clamp above the brace weld. I don't quote follow what was mentioned about the split clamp and the holes.

The 650 rear wheel might be an option, but I fear it will be a bit extreme and lose the roll over characteristics (it's got a minus 2 degree headset and 140 fork already, and pedal strikes are easily instigated). I think I've read some of your blogs previously, chakaping. The wheel supplier you mention in your blog, was the owner I spoke with who removed his brace entirely (who purchased my canfield yelli frame too-small world)

I've made do by using old v12 dmrs and a thin saddle, but I'm not enjoying that saddle, and the pedals don't help with strikes either.

Time for some more measuring before I crack open the tools.

The 650 rear wheel might be an option, but I fear it will be a bit extreme and lose the roll over characteristics

It didn't lose much (if any) rollover ability downhill, but on flat bumpy stuff it was noticeably harder work.

it's got a minus 2 degree headset and 140 fork already, and pedal strikes are easily instigated

OK, you've talked me out of it!

Have you thought about 165mm cranks? Zees are fairly cheap, if you're single ringing it.

Just a thought if you go ahead. Are three any bottle bolts on the steattube? These often protrude into the steattube and prevent dropping long (400mm) seatposts. If so they would need reaming out. It would be the same if there are any welded junctions further down the steattube that your current post doesn't reach..

The zee cranks are flipping heavy though. I am going to try the yari fork with a 150 air spring. I have bottomed the fork on the local dh trails. This should remove my low bb /pedal issues.

No cage bolts to worry about, just that bend by the mech mount.

Well, no going back now.

I had the angle grinder out to fix the wife's exhaust.

So here it is

https://imgur.com/c36YAOO

I'll update the post if it snaps.

That looks spot on - well done!

Will the saddle not catch the wheel when it's dropped and you hit something big?!

Ps fair play for having the cajones to just do it!

Will the saddle not catch the wheel when it's dropped and you hit something big?

I also wonder how that seat tube will get on. I'd keep an eye on it.

The small Hammerhead Thumper frame is pretty much the same as the OP's now so there shouldn't be an issue with the rear wheel / saddle clearance.

Easy to check by letting the air out of the shock.

First dibs on the frame if / when it dies or you get rid. It'd be good to have spares for mine

Theporge, noted.

Clearance is fine with a flat shock.

Load path on big hits is up the stays and to the shock mount. I just need to be mindful how much I load the seat tube when seated.

Most of my riding is up fire roads and then down trails.

Time will tell if it survives.

Couldn't you have just modified the dropper stanchion, ie: remove the head, shorten & re-attach ? Its probably just pressed on.

But fair play for a tidy job in taking the brace off.

I don't think you can trim the reverb collar.

This way I can drop the saddle beyond the ideal pedaling position, for when I'm playing.

I'll take it to the local dh trails tomorrow and see how it goes.

I did have to use a smear of filler to remove some of the angle grinder marks. Also, there was a hole in the tt to fill

Done this mod a few times over the years.. Doesn't throw up any issues whatsoever. I've got it done on my current bike too.

Good job op

Cheers!

I was going to recommend cutting down to the level of the brace tube, then cutting a slot at the back and getting a bolt clamp welded on. Anyway, you've gone further than that 😉

Reverbs have a very long outer section/tube, and they're also very stiff, so you'll probably be OK. Frames do sometimes fail at the top-tube/seat-tube weld area, but that can be due to leverage caused by long seatposts when there isn't much inserted into frame. Again, with your Reverb, there's as much material inside the frame as outside, so it's not putting much stress on the region of seat-tube near that weld, or at least not bending the seat-tube at that point.

Agreed,I've gone a bit lower than the ideal height but I'm up for sacrificing pedalling efficiency for a lower seat, and reducing any potential moment on the seat tube.

What could be a factor is the reverb is a 30.9 and I have a 100mm Sleve in the seat tube to the correct dia..

In any case, it's a cheap winter build from a 29" ht I could not sell for a good price

Nice job.

If it was a regular cutting disc you used to [s]chop **** outta[/s] carefully modify your frame I'd chuck it in the bin now. They aren't suppose to be used on aluminium, it may clog and explode!

Fair play having the balls to get choppy choppy.

Holy crap!

Thank goodness I didn't get the wheel wet, as I subsequently used it to cut a couple of steel bolts. I should really know this. Thermite isn't to be messed with!

Binning that wheel and maybe I'll invest in some alloy specific wheels.

I'd bet a few people suffer badly from this, as it's not something I'd considered.

http://www.finishing.com/317/17.shtml

Well, couple of months have passed. It's still in one piece and it took a rather large drop to flat on Sunday. Rides so much better with the seat lower. I've also dropped out the 140 yari and put a 160 pike in (running a bit more sag than normal as ideally I'd prefer it to be a 150).