An aluminum frame is typically 200-300g heavier than equivalent carbon.
Aluminum frames don’t become brittle or fatigue.
As long as the frame comes from a reputable manufacturer it’s very rare for a frame to fail, which would be at the welds or a high stress point where the tubing is too thin.
Any damage from crashing should be obvious.
Damage from crashing on carbon can be very hard to detect, as well as manufacturing defects and many extra failure modes such as debonding of inserts are common.
Yes, you cant really repair aluminum whereas most carbon tubes can be repaired.
I played around with this a few years ago, though I tried to get a uci illegal bike (6.8 kg) for the lowest possible price.
Off brand or used frame set. Make sure you know it’s light, so either a quoted weight by the seller or known quantity (ie caad, etc). Don’t forget a fork can get heavy, so don’t ignore it. Rim brakes.
SRAM has traditionally had the lightest group sets, so whatever can be found in budget (probably a mix of rival and force).
Aluminum handlebars and stem. Stems vary greatly in weight for seemingly no reason, so be choosey. Single bolt seat post, probably. Whatever saddle is comfortable (don’t save weight on your ass).
Knockoff hubs (ie bikehubstore), single butted wheel smith spokes, kinlin rims. Carbon rims could be lighter but hard to find cheap and reliable enough for a budget bike. Latex tubes. The thinnest tires you can ride without flatting.
In non COVID days it would be easy to get under 15 lbs without spending 2k, but prices were different in 2020.
I’ve bought several bikes off of eBay with no issues. Buy from a seller with 100% feedback who is obviously a rider/racer and who fastidiously documents the condition of the bike.
I got a BMC SLR02 Team Machine full carbon with Ultegra Di2 (and a lot of lightweight upgrades: ENVE seatpost, Arione carbon saddle, Dura Ace cassette, etc.) for under $1,800. Guy raced it for two seasons and was upgrading.
Also, remember that there are lots of places besides the frame to save weight cost effectively:
-Latex tubes and high quality tires (ex. GP5000)
-20g carbon bottle cages (amazon/ebay) and alloy bolts
-100g stems (UNO, $25 on eBay) save 50g+ over stock
-Giro Empire laceups are 100g/pair lighter than most BOA shoes.
-Lightweight jerseys (ex. Castelli climber’s jersey) can easily be 50-75g less than a standard jersey.
I have a 2002 CAAD5 I bought second hand in 2010 as my zwift bike now. Has been named lazerus by the bike club as thing just won’t die. Been in a couple of bunch crashes, a couple of significant mechanical failures. But frame is still fine.
I swapped to a Carbon synapse a couple of years ago, and on that, despite being a ‘big guy’ (6’4" and 86-89kg) then I am either first or second up all the hills for the group saturday centuries.
I know bike frame weight will make more of a difference for you, but honestly, the wheels and the right chainset will make the climbing much more enjoyable. I went to a mid compact on the synapse and that revolutionised my climbing. My FTP is 310-320 depending on the season, so not that high but I have a really flat fatigue curve. And the ability to climb seated and spin up almost all the climbs is fantastic.
And you don’t need to spend big money on the wheels either. Even some old zipp 101s (alloy) would be fantastic and should be cheap to pick up.
For example: I built a 6.8 kg “donkey” bike last fall for my daughter ( size 48 though) . Brand new Jamis Icon Elite frameset on Ebay for US$349. A used Sram Red group for CAN$400. I had a Rotor 3D crankset in the parts bin (that helps !). 5 year old carbon tubular wheels and voilà !!
I’d bet the Alez sprint frame will come lighter or as light as a budget carbon frame. They are 2200 new so a used one could knock a couple hundred off.
Also its a fantastic bike
I’m going to throw another vote for the CAAD.
The idea that aluminum fatigues or gets brittle overtime is simply untrue.
I have a CAAD 10 that I have been riding and racing hard for about 7-8 years and the thing is as good as day 1, buy a slightly cheaper frame (like the caad or the Emonda AL that someone alos mentioned) and spend some extra $$ on nice wheels.
Light and stiff wheels will contribute much more to climbing well then will saving a few grams on the frame.
That bike is way over priced. The MSRP for a brand new ALR 5, which has better components, is $2000 and that is coming with full warranted via any authorized Trek dealer in the country. Trek does still makes an ALR 4 disc which is <$1500 but isn’t listed in Treks US site however its a good price comparison. The bike Pro’s Closet is selling is a £1k bike give the damage on the down tube and the fact that the rim brake tiagra groupset is not a very desirable build. I have no problem recommending an ALR frameset for this type of build but you should be able to do a lot better than a damage Tiagra build in the sub $2k bracket.
It is actually not 100% clear to me that Pro’s Closet has listed the price correctly. They state the frame material as ‘Carbon fiber’ which it clearly isn’t and you wouldn’t want to touch a used carbon frame with that level of damage. That said the price they are requesting makes much more sense for an Emonda SL 4 (which would be carbon and the MSRP is of Domane SL 4 is $2400 so a used cosmetically damaged bike is in that 50-60% MSRP range) and so they may have gotten lines crossed in the listing pricing.
!). 5 year old carbon tubular wheels and voilà !!