Coldsetting and 36er hub widths

Any of you guys have experience coldsetting frames to fit a different hub width?

I’m considering relacing my 125mm 36er hub with a 100mm hub and would need to bend the frame to fit. Would my LBS be able to do this with a regular frame bender?

Also, would I lose that much integrity in my wheel going from 125 to 100 on a 36 spoke wheel? It’s road only.


Also, could bending the frame that much weaken it?


Where would you bend it?

I’d imagine in the frame legs.

I was reading a bit about it on Sheldon Brown’s website. I figure you’d just pull at the bearing holders and the frame would bend where it bends. :thinking: I’ve seen frame benders, and would feel a bit more comfortable if someone with experience bending frames were to do it.

I would be concerned that the bearing caps of the frame would be at angle after bending inward, possibly causing a bearing “seating” issue, and also the bearing holder bolts might not thread properly into the frame caps.

Pardon my bad ms paint rendering!


Terry is correct. The only way to properly achieve this is with two bends – one bend at the top to pull the legs in, then one a little further down, to make the legs parallel again. Not an easy operation! (I have seen some frames made this way on purpose to create greater tire clearance at the top.)

Similar to the old Surly frames. I still don’t see it as being that difficult for an accomplished frame bender. I worry more about weakening the frame…

Like this:

If it’s a steel frame, cold setting it shouldn’t be a problem.

The wheel will be a good bit more prone to taco’ing at 100mm. Why do you want to go narrower?

Is heating and bending not an option?
if cold looks to risk deforming the tube or worry about stressing/ cracking something

obviously you will need to re finish your paintwork afterwards other than this i see no issues taking a frame in with heat, maybe even no heat. We are talking 12.5mm each fork leg arent we?

Steel i would have a go at bending but cutting and re welding alloy will be lighter and nicer. Stiffer too? Are stiff frames better for a uni?

You can do this yourself with blocks of wood and bar clamps.

I’m contemplating the same thing, though there is a certain “weakness” that will be added with this modification because you are adding bends to straight tubes.

You should plan it out, mark the spots you want to bend, use a bare hub to brace the bearing holders.

It’ll probably be fine, steel is very resilient, just don’t bend to near the welds.

Are you going to use a 100mm hub and Spirits? That’s my plan for the 36/32 wheels, mostly doing it to cut weight and reduce profile.

The frame is steel.

So even though the wheel would be more prone to taco, what is the likelihood of that actually happening?

Here’s a little Sheldon Brown:

I wouldn’t build a 36" wheel with the narrower (100mm spaced) Oracle hub, the disc side spokes would be very steep and would probably fold with significant side load.

A standard wide symetrical hub (100mm) with Spirits is just fine, that’s what I’m going to build after bending the frame. If you can’t affrod Spirits, then run Moments and Maguras.

You could also spend a few $$ and have the frame pro bent, add a disc brake mount, and then get it powder coated :slight_smile:

So I can stick this in it.

Can you expand a bit on using blocks of wood and bar clamps? Looking at Sheldon Browns article, he used a 2x4, but braced it against the seat post. I’m not sure where I’d brace on a uni frame.

Which bare hub would you use to brace the bearing holders, the 125mm one or the 100mm one?

If I put the coaster in it, I’ll be using ventures and venture II’s.

Depends on what you do with it. Tacoing happens when the wheel gets more sideways force than it can handle. Typically that happens when you land awkwardly on a drop or a crash, or step on the wheel coming off, or something like that. It could happen at any time, but it might never happen.

To bend the frame narrower, you will need to squeeze the legs together in one spot and spread them apart in another, so think about how you would make the frame legs into an double curve (S shape).

Keep in mind that you have to slightly overbend the frame to make it stay, but don’t go so far that you have to bend it back.

Tools needed: Two sliding bar clamps with rubber clamp protectors, two blocks ~100mm wide. Blocks should be made of hard wood, metal, or plastic so it won’t deform. The block will need to be ~100mm, you need to determine the exact width needed by measuring your frame, but it needs to hold you frame at 100mm while you bend the frame. Adding a little curve to the block may help prevent tube kinking.

Start by marking your frame for the lower bend, say 1/3 the distance from the bearing holders to the existing leg bend, place a block at that point between the legs and tape it in place. This bend will take place BELOW the block to restore bearing cap alignment.

For the second bend, place a block in the existing leg bend, for this bend you will not be adding a new bend, but increasing the existing bend; this makes it a little easier as the bend is already there and should make it easier to add a little more curve.

Once the blocks are in place, try to visualize the two bends:
The upper bend “narrows” the frame
The lower bend “restores” bearing alignment

You can block and bend the upper and lower frame at the same time, working both sets of clamps simultaneously, just be carefull the clamps and blocks don’t slip. You don’t have to use a hub to maintain the bearing holder width, but you will need the hub to determine final alignment.

The key issue is to make the two legs bend equally, so you don’t end up with a crooked frame. If one leg bends more than the other, you may need to modify you blocking technique to hold one leg steady as you bend the other to match.

Don’t sweat it, it’s not that hard.

Once you get the frame fit to your new hub, build the wheel and go party!

The frame will probably be a little crooked, so you’ll end up having to align the rim to center, so build your wheel facing the direction you plan to run it.

Give it a try, the best thing that can happen is you fail and get to buy a nice frame. :sunglasses:

THANK YOU BEN! That was a reply and a half and exactly what I needed.

Quick question: What would you be using to bend the bottom section of frame out to fit the hub? All of my bar clamps only squeeze stuff, I’d be looking to spread them apart once the upper frame is clamped in, correct?

I’m going to run it into the bike shop as well and see what they have to say about it, but it’s looking like I may just do it myself.

Shmolagin, it’s a $70 frame, so if I screw it up, I’ll be pissed, but it’s not the end of the world. In my mind, it’ll be worth it to try the first free wheel 36er.

My biggest worry right now, is wheel integrity going to the narrower hub.

Tholub, this will be a road only unicycle, so I won’t be doing drops or anything like that, but I will need to mount and dismount the thing, hopefully that wouldn’t taco it?

From my calculations, even if I didn’t put the ‘S’ bend in the frame legs, they’re only moving 1.85 degrees, which I imagine would probably be fine, though could cause premature bearing failure.

It won’t taco in normal use; it’ll taco when you hit something, or land awkwardly on it.


Bar clamps are not expensive, you can get a couple at Home Dept for $20-30, they mount on pieces of pipe, pipe clamps are the technical name. You could get a couple clamps, two pieces of pipe 2’ long, then when you’re done, as long as the clamps aren’t damaged, well you know what I’m suggesting…

Okay, so you are sqeezing the upper frame legs inward, increasing the existing bend, which will make the full length of the leg move inward, so the lower blocks keep the lower frame static as the upper legs bend. To bend the lower legs back so they are straight again, you block the upper frame and bend the lower frame above the lower block.

I hope that makes sense :slight_smile:

And yeah, it’s not a ton of bending, so it shouldn’t be that hard to get close. You could use the frame with the upper bend tweaked, leaving the bearing holders "out of alignment, but you would wear bearings fast, and you would lie awake at night wondering if you could have done it right :wink:

Just do it! I’ll do mine next week and we can compare notes :slight_smile:

I have bar clamps, I was just having trouble seeing how you’d ‘flare’ out the lower section of frame by clamping inward, but I think I get what you’re saying now.

I’d have (likely) a larger block in the upper section of frame, and a smaller block on the lower section, and clamp in between the two. If the upper block was larger, it’d allow for the legs to bend inward enough, and then the lower block would put enough pressure on the lower section, to ‘flare’ them out a bit. Hopefully I’d end up with something ‘Conundrumesque’.

I’m gonna wait till I have the hub in hand before I do it, probably order it this weekend. If I don’t like it, it’s going in my 29er. So I’d probably start bending end of next week or sometime the week after.

Definitely let me know how your’s goes, I’m thoroughly interested. :stuck_out_tongue:

Both my parents will be in my ear about how upset I’ll be when I screw it up, but how hard can it be? :roll_eyes:

Thanks guys!