Lalato

I wonder how much rider weight the Titanium frame is rated for vs the Brompton steel?

tmac100

It is a wedding anniversary GIFT for his lovely wife. You have an issue with giving your wife an expensive gift? If so, get her a small and inexpensive bag of "lollies" (sugar-free) as a gift. I personally like the idea of giving an expensive nice gift - and do follow my own advice

chagzuki

The big question for me is whether there's more overall flex than with the standard steel brompton. From my investigations flex felt when pulling on the handlebars becomes an issue at bar heights around that of th M-type. S-type riders don't tend to notice much flex, so perhaps you won't really feel any on this ti model. But I wonder how it would feel with higher bars. I believe the majority of the flex comes from the ridiculous wedge stem 1970s technology, so if titanium is less strong than steel at the same volume then the stem will flex more, and that wouldn't be good.

fietsbob

That Qatar pumps money out of the ground certainly helps..

Stephenjeffrey

Raxel

I am not really sure, but other guys who've been riding full ti Brompton clones say they feel just the same. All titanium parts are made by Ti3Al2.5V titanium alloy with ~600MPa yield strength, where 4140 cromoly has 415MPa yield strength. And as Brompton is not even made with cro-mo steel to begin with, the titanium parts should be (in theory) stronger than original steel parts (assuming the same volume!!!)

And the carbon seatpost and handlepost (which is hand made in small quantity by a carbon specialist guy) are actually quite flexy compared to steel ones. Some people like them because it smooths the ride, some people prefer more stiffer titanium ones.

dahoneezz

bikingbill

Do you need this tested by a strong heavy (107kg) rider on some absurd climbs?



If so, I'm your man.

(Note: I had to re-tension the rear wheel after a few of these :-) )

chagzuki

Schwinnsta

Yes

dahoneezz

Raxel

Titanium Brompton frames (both UK and third party ones) are claimed to be made of grade 9 titanium alloy (Ti-3Al-2.5V) Brompton said their frames are made of hi-tensile steel. Let's assme it is AISI 4340 steel alloy. As ti alloy is roughly 1.74x lighter than steel alloy. if one directly copy steel frame (~2000gr) with titanium it will only weigh 1150gr. Mine is roughly 10% heavier than that, which means it uses slightly thicker tubing than steel ones.

And here are two properties:
- Yield Strength: how much force can a material withstand before permanent deformation. Or how unlikely the frame will snap under pressure. 4340 steel has yield strength of 470MPa, and grade 9 titanium alloy has yield strength of 724MPa. As they are measured by volume, I can say that grade 9 titanium frame is 724/470=1.54 times stronger if built identically. And as my frame has 1.1x more material, it will be 1.54*1.1 = 1.7x stronger than original frame.

-Modulus of Elasticity: how much does a material undergo elastic deformation under a small load. Or how springly/supple will it be. 4340 steel has MoE of 27~30M psi. Grade 9 ti alloy has 15~17M psi. So titanium is roughly twice more flexy if built identically (same volume, 1.7x lower weight).

tl;dr The titanium parts will be 1.5x stronger, 1.7x lighter but 2x supple compared to steel parts of EQUAL thickness.

BromptonINrio

hey raxel!
amazing feat in archiving those wheight.
even they factory cannot sell bikes that light.
they are selling full brompton copycat now too with grade 9 and grade 5 titanium aloy internal hub derrailer(srf3), rack(titanium) and mudguards(plastic).
they archieve 10.4 kg.


​
​​​​​​
​​​​so, i assume that if i want to chop off more 5kg from theyr build to archieve your i must:
1) swap wheels(to carbon ones,2 speed) - 800g
2) take rack and mudguards off- 700g
3) swapp prowheel crankset/botton bracket to a carbon one-700g
4) swapp seat? -
3) swap chain tensioner to a carbon one -146g
5) ???

i have to idea how to go

Jakey27

Brompton_X

I have ridden my full titanium bike for more than two years. It is a 4-speed (11T~13T-17T-21T). The weight is about 7kg. I ride the bike in the hilly San Francisco about once a week. Never have any issue if you don't count flat tyre as one.

However, I don't recommend people to buy one. The Brompton OEM main frame is really not that heavy. If you want, you can still build a 2-speed Brompton below 8kg.
The biggest problem with those 3rd party main frame is you might experience some compatibility issue when building your bike. Some of them are easy to be fixed but some of them are not. If you really want to buy one, just remember to build the bike as soon as you get it. If you find any problem, just return it. Buy from ebay, not Alibaba so if there is any problem, eBay can still protect you and help you to get your money back.

Raxel

Steel main frame + post set is roughly 1kg heaver than full titanium set, and two sets cost almost the same. Titanium is lighter, easier to maintain and personally looks better.

And I know >20 people who has built full titanium Bromptons and they seem to be mostly fine, if built by skillful mechanic with proper tools.
My frame has very slightly oval headtube and the BB shell threads were bit too tight (couldn't hand tighten the bottom bracket). Using tools solved both issues just fine.
A brand new UK frame needs BB tapping and headtube / seatpost collar / rear hinge reaming anyway.

Nightdiver

Wow! That is the best looking faux Brompton I've seen yet. Except those mismatched tires... How's the 4-speed work? What are you using for your shifting system? Have you already made a separate thread where you detail your build? Nice work there. Classy.

Brompton_X

3/5 of the people I know who purchased the titanium main frame they returned. I know the sample size is very small but still I think that's a very high ratio. Anyway, like I said, you can definitely build one if you want. Just make sure you buy from the right place. I purchased the main frame, rear frame, fork, and stem all together. When I found out I had issues with the fork, and rear frame and tried to replace with Brompton OEM parts, they just didn't work. So right now, I can't fold properly if the chainring I use is bigger than 52T.
I have probably one of the best mechanic in Taiwan built the bike for me. It is just the product issue, not whom built the bike. That's my 2 cents.

Brompton_X

I bought the 4-speed kits from a Korean guy. You can find more info by searching Brombacher 4 speed kits on Facebook. It works fine when I ride in the hilly San Francisco but could be better if I can get a better shifter.

I know the tyres are different but they both are Kojak. It happens when you got too many flat tires. lol

Raxel

Do you know EXACTLY WHAT are the issues? "They just didn't work" doesn't sound very convincing to me.
Also what does it mean that you can't fold properly if the chainring is bigger than 52T? Does the chainring interfere with the frame? Then why it matters only for folding?

BromptonINrio

so, the original and faux frame parts isnt interchangeable?

Raxel

a) They are NOT faux parts as they never market their parts as original ones.
b) They are fully interchangeable.

BromptonINrio

thanks for reply.

how did you solve oval headset? can a titanium frame be coldset?

Raxel

Mine was VERY slight oval, and headset press worked just fine. Worse frames may need reaming and facing.

tcs

Or maybe it's AISI 1040. Almost all bike companies in the world trumpet the metal alloy they use in their frames. Why is Brompton so coy?