Where are we going to for lightweight brake rotors these days?

None in stock at XC racer and I’m not paying £175 total to get them shipped from Germany so….

I’d usually go for Quaxar Axims based on past experience, does anyone know of an equivalent 180mm Xc/Trail rotor available from UK with a good reputation?  They would be replacing SRAM centreline 6 bolt.

Thanks

Swap with the ones on the old bike?

Mate..  you have a problem..

Galfer seem to be well received or just get some more centreline ones?

you have a problem

And what’s that then?  Or can’t a person even ask for some rotor recommendations without receiving judgement anymore?

What has the better braking friction to weight ratio – a standard 160mm or a lacy lightweight 180mm?

I went down that rabbit hole and concluded that despite what GCSE physics says about friction and surface area, there is a loss of braking power when the rotors are more air than metal, and it was better to go down a size with solid rotors than try and make a 180mm rotor weigh as little as a 160 one.

If you really want some I’ve got a drawer full of lightly used ones in various designs.

Rotors like the magura SL.2 are lighter than standard, but still ok for xc bikes. Not sure if they work with a sram caliper though due to thickness. ? Anyway, they would only save 28g I think.

I used to run a very skeletal alligator something rotor, but it really was rubbish and would get cooked very quickly. Also would bend easily so transporting the bike with wheels off usually resulted in some straightening when I got somewhere.  Swapped them for some centrelines I think.

Snake oil, top 10 at the last world cup xc won’t have been running running anything other than what shimano/sram/magura/etc supply.

Or can’t a person even ask for some rotor recommendations without receiving judgement anymore?

Not on here no, sorry 🙂

Back when I was a serious weight weenie, Clee Cycles is where I went to get my fix https://clee-cycles.co.uk/grp/brakes.disc_rotors/products

Oh, I really shouldn’t have looked at that…

Or can’t a person even ask for some rotor recommendations without receiving judgement anymore?

You’re asking about lightweight rotors – which TBF is very firmly on the weight-weenie-skinny-assed-racer end of the spectrum, and you weren’t expecting some-one to point that out to you?

You’ll go quicker if you brakes work better 🙂

is it an “I like riding a light bike” or “light bikes are faster” motivation?

better to go down a size with solid rotors than try and make a 180mm rotor weigh as little as a 160 one.

Agreed. Had a think about it before posting the Q, there’s 12% rotor size and material difference vs around 25% reduction in weight needed from the 180mm rotor to match the 160, if you account for the PM180 adapter (vs a 160 direct PM). So you’ll probably get better braking at the same overall weight from a stock design in 160mm.

But for an average domestic XC race .. buy whatever you like the look and weight of, it’ll be fine (as long as it doesn’t fold up into the calliper)

and you weren’t expecting some-one to point that out to you?

Especially considering that most people know I roll that way (XC Race) I didn’t know what he was pointing out exactly. 🤷‍♂️

Cynical-al it’s light bikes are faster, especially up hills with me on them.   And before anyone mentions that 80g on the rotors is an immeasurable difference at my disappointing level of performance, it’s not about the rotors themselves but the savings from the some of all parts – over 450g with the rotors  which does make a difference.

Re performance, I never had a stopping, bending folding or other issues with those Quaxars, hence mentioning them.

As much as I appreciate marginal gains, what overall percentage of your system weight will dropping a few grammes off your rotors make?  And will that really make any difference compared with the negative effects on your braking performance?

how much do you weigh? How much does your current bike weigh? I suspect this is a vanity exercise more than anything else, but then again I have a ceramic speed ospw on my tt bike which clearly makes zero difference so I can’t criticize

If you genuinely want to sit on the start line thinking you’ve done absolutely everything you can to give yourself a performance advantage, and can afford then, then go for it

but I can guarantee it’ll make the sweet sum of f’all difference in reality

For the road bike I got XT 160mm rotors for the MTB I’ve got 203 and 223mm discs. lightweight is silly on MTBs

Surely sum of all parts would still be in the region of 400g without the rotor change.

Edit: Actually checks back, I weighed centreline at 145g (180mm) and 113g (160mm) so more like 100g saving in the rotors assuming 180 F+R currently fitted (QUAXAR claimed 92g for 180mm).

It would never be a place I went for weight savings.
I always remember >>bigdugsbaws?<< from on here, having a lucky escape when a light rotor crisped/failed.

You can also save a few grammes by only using three bolts instead of six, or just removing the brakes entirely and dragging your feet on the ground to slow down. Will it actually get you round a course any faster though?

Leave the poor guy alone. Some people just like light bikes, and building a light bike is fun. This used to be the majority position, and then for some reason it became fashionable to ride hardtails that weighed 5kg more than my 140mm trail bike.

Airotor are pretty light, and actually function well as rotors too. I don’t find any downside to ’em, wouldn’t put them on the big bike though

(they work best with a brake with fairly large pads, though)

kryton have you done the maths vs how distant the next fastest guy is in your races?

The Quaxar Axims are available from the mt zoom eBay shop.

Should be available at xcracer then too if mt zoom are selling them…

Fibrax Lightweight 160 are 85g  180 are 105g

Been using them for years without any issues.

They are available at xcracer just in limited colours.

If there’s a minimum thickness stamped on them, treat is a target. Sandpaper out, onto the lathe.

Ashima rotors were always the lightweight rotors of choice a few years ago, although there were always photos knocking about with mangled spiders where they had collapsed.
I think some of the time this was due to them being installed back to front.

dragging your feet on the ground to slow down

This way the OP’s shoes would get gradually lighter through the race as well, which would be good as you tire!

I would go for a custom build bike with V Brakes

As much as I appreciate marginal gains, what overall percentage of your system weight will dropping a few grammes off your rotors make?

In fairness, it’s not just the rotors – as was pointed out, if you want a light bike, you don’t spend money on one thing, you have to spend it on everything if you want a 10kg bike instead of a 14kg one.

Ashima rotors were always the lightweight rotors of choice a few years ago, although there were always photos knocking about with mangled spiders where they had collapsed.
I think some of the time this was due to them being installed back to front.

One of mine no doubt, luckily it was the rear and the ‘disc’ sheared off at the spokes – when I measured the thickness it was at 50%…

Incidentally just had to change the rotors on my eBike, 2.0mm ones had reduced to 1.5mm in under 1,800 miles – admittedly pretty much all enduro type descending.  Also caused lots of piston corrosion as they were never fully retracting back into the calliper – new callipers too…

Cynical-al it’s light bikes are faster, especially up hills with me on them.   And before anyone mentions that 80g on the rotors is an immeasurable difference at my disappointing level of performance, it’s not about the rotors themselves but the savings from the some of all parts – over 450g with the rotors  which does make a difference.

Yes, but have you compared the time saving of dragging 80g to the top of the hill Vs the time saving coming down the hill.

My experience was I was having to almost constantly brake the whole way down technical descents because they were just so rubbish at braking later into corners.  Trading single digit Watts on the way up for hundreds on the way down.

You can also save a few grammes by only using three bolts instead of six, or just removing the brakes entirely and dragging your feet on the ground to slow down. Will it actually get you round a course any faster though?

I got my track accreditation last night so I’m going to suggest he also saves the weight of freehub and gears.

It’s a good example though, you wouldn’t race singlespeed because you know that the 1500g or so of drivetrain bits is actually faster than the theoretical weight saving.  Same applies to brakes.

In fairness, it’s not just the rotors – as was pointed out, if you want a light bike, you don’t spend money on one thing, you have to spend it on everything if you want a 10kg bike instead of a 14kg one.

Yeah I know that, it’s the very definition of marginal gains!

stumpy01
Full Member

Ashima rotors were always the lightweight rotors of choice a few years ago, although there were always photos knocking about with mangled spiders where they had collapsed.
I think some of the time this was due to them being installed back to front.

Yeah, they ****ed up and made them the wrong way round so they collapsed under strain. They were really obviously the opposite way round from most rotors, Ashima claimed it was better for a while then they “revised” them which literally just meant having the arrows point in the other direction! So there was a while when you could buy 2 different sizes and they’d say to fit them in opposite directions because they never recalled the wrong ones.

(there was someone on here who was really insistant that rotors must always be fitted as directed and if you didn’t you’d die, so they had their rotors “facing” different directions front and back and insisted it was the best way to do it)

Really very shoddy but, in the end, once you had them on the right way they were OK, just shortlived. The Airotors they do now are a descendent and tbh, they’re really good.