bikeforumKEN

Is a new all ALU Brompton coming? https://www.linkedin.com/posts/bromp...573767168-pqVq
CEO was on a podcast 7 months ago , he mentioned he’s not happy with the price of the T - line because he feels it’s too high and they actually don’t make money on it because titanium is not cheap and people wanted a Brompton but lighter, I know they are bringing out a new tubeless wheel soon , and he said more things on the way? interesting link

tcs

At the 2015 Eurobike, Brompton showed a model with LumiLor paint that glowed when a small current was applied.


Yeah, never hit retail. Moral: I'll believe Brompton is going to use aluminum frames when they offer them for sale.

Duragrouch

Aluminum can be a great frame material. I have a late 1980s Cannondale from 6061-T6. Newer aluminum bikes use 7005 aluminum as it does not require post-weld heat-treating like 6061-T6.

In general, aluminum frames need to be designed for greater rigidity, as aluminum being flexed a lot is bad for fatigue strength. But for many bikes, like my old race bike, this works out well, with both great rigidity and lower frame weight.

Next, if highly stressed weld areas, "dressing" (filing or sanding) the welds to a smooth concave transition with the tubes, also helps greatly in improving fatigue life, as more "bulbous" (convex) welds will have a stress concentration where they meet the tubes. My Cannondale had wonderfully dressed welds, that was a real calling card of the bike.

Titanium is great stuff, half the weight of steel and much better fatigue resistance than aluminum for the same geometry. But expensive material, and processing.

That said, really good quality (like 4130 chrome-moly) steel is also still a really great frame material, and relatively low cost, however to achieve low weight, by increasing the tube diameter and reducing the tube wall thickness, there reaches a point where that thin a material is really difficult to weld. Double-butted tubes with thicker wall at the ends, have been used for many decades on steel road race bikes, most especially brazed into lugs rather than welded.

Video: When they said "low carbon aluminum", my first thought was, aluminum is already very low carbon content. They meant how it is produced.

tcs

Bromptons have a non-inconsequential amount of aluminum now: the cranks, rims, bars, brake calipers, hubshells, Pentaclip, folding pedal. I think Brompton is alone* in recommending the owner/rider swap out some of these aluminum parts for new on a scheduled basis: "As with all bicycles, aluminium parts such as crank arms and handlebars are subject to material fatigue. Aluminium is a great choice for these components for a number of reasons: it’s lightweight, stiff, and cost-effective. However, it is also less resilient than steel, and for this reason, we recommend aluminium parts, particularly safety-critical components, are replaced within 5000 miles - sooner for vigorous riders, and especially after an accident or significant impact. To give an indication of time; assuming you commute 10 miles per day in total, and use your bike 3 times a week for 48 weeks of the year; your aluminium parts will need replacing approximately every 3.5 years."

I never see any used Brompton ads that mention the aluminum parts have been replaced or discounted prices because the parts are (over)due for replacement. Shrug. Anyway, a Brompton aluminum frame with a 3.5 year life is a non-starter in the marketplace.

1) In present discussion, welding is a non-issue. For reasons unknown to me, Brompton has stuck with the old high labor content torch brazing method of joining the frame tubes.
B) Folding bike designers usually consider an additional frame design parameter: denting from being knocked about. For this reason, you don't see many folding bikes fabricated with relatively thin wall tubing.
iii) Exactly what the Brompton frame is fabricated from today is unknown outside the company. They used to advertise the frame was "hi ten steel" without specifying any particular alloy. WB-A recently wrote that the Brompton used many different steel alloys for the various frame parts but did not elaborate as to what any of them were.



*Hmm. Do I remember Birdy recommends replacing the fork assembly on a scheduled basis?

Jipe

What is sure is that currently, Brompton factory has no in house aluminum frame manufacturing capabilities (nor in house aluminum frame design knowledge), unless they build up a brand new production unit for aluminum frames (welded, hydroformed or any other frame building) they will have to sub-contract the manufacturing of an aluminum Brompton frame just like they do for the frame of the T-line and titanium parts of the P-line what will increase the costs and be a problem to sell a cheaper lightweight Brompton.

If they sub-contract outside UK, their marketing image of a British bike will be lost.

For the weight, moving to aluminum doesn't mean that the bike will weight less, the Dahon Curl (the most similar aluminum folding bike) doesn't weight less.

Making a really lightweight bike like the T-line, whatever the material used for the frame, costs more money and end up eventually in an expensive bike.

tcs

Which they might well be doing.

https://www.theguardian.com/lifeands...tory-on-stilts

https://road.cc/content/news/new-car...-delays-306637



FWIW, the Curl has a higher max rider weight.

Jipe

This announcement of a new plant was made early 2022 before the T-line was released, it had nothing to do with an aluminum frame Brompton intended to solve the problem of the too high price of the T-line!

I do not believe that its possible to build a ultra lightweight cheap aluminum Brompton in the UK.

Even a company like Riese & Müller that sells expensive high end ebikes is making the aluminum frames for these ebikes in Portugal to reduce the costs and not in Germany.

Actually, an ultra lightweight aluminum folding bike with a weight similar to the T-line will be cheaper than the T-line but will never be really cheap since it will always require expensive components to reach the weight of the T-line.
The Curl is relatively cheap but its heavy because of its low end components.

tcs

They say this new facility will double their production capacity. I've seen no announcement from the company that they absolutely will not use any of the additional space to fabricate other models.