Found a new alternative brake disc that fits

[highboy_coupe]

TLDR edit: I have purchased and fitted one and this disc fits perfectly with the original caliper, it weighs 4.5 lbs (2.04KG).
https://www.chinesemotorcyclepartsonline.co.uk/partno_BDSC005


Hello,
First of all, I am new so this is my introduction. I'm in the UK and have imported a 1980 special a few months ago, nearly ready to put back on the road.
I have been looking at brake discs, and the alternatives; I was going to go with a modern floating disc and spacer setup after studying this thread: http://www.xs650.com/threads/replacement-front-disc-rotor-thoughts-offsets-dimensions-compatibility.48664/

I started looking at other 298mm discs, and eventually discovered that there are a couple of Chinese bikes that have an almost identical setup, the offset appears be 2mm different (but then they are 2mm thinner).
Here are the specs:

Outside Diameter: 298mm
Inner Diameter: 65mm
Thickness: 5mm
Minimum Thickness: 4mm
Qty of fixing holes: 6
Distance between fixing holes (centre to centre): 40mm - 80mm BCD
Is the fixing hole countersunk: No
Standard or Wavy Disc: Standard
Dished or Flat:: Dished
Offset: 14mm


The bikes in question are The Lifan thunder (LF400) and the Skygo Thunder, both 400cc twins.
I will buy one and weigh it, I think it will be under 7lbs!

I was under the impression that Chinese stuff, on the whole, was getting better in quality, and I have read plenty of first hand accounts of small Chinese bikes surviving being left outside and ridden through winter (here in the UK), the only way I will know about the quality is to buy one and fit it!

 

[gggGary]

I'd be interested in how this goes.
I am running 3 FZ floating rotors with about 7mm spacers 2 on madness, 1 on period piece, quite happy. The clearance from the rotor rivets to the caliper carrier is "snug".

 

[highboy_coupe]

I'd be interested in how this goes.

Hi, it was from your thread I got most of my info (so thank you!) about the standard discs. I'll get one and measure it up.
One question - On a car disc, offset seems to be measured from the outer face with the bolts to the inner face of the braking surface, I think you had a photograph that showed offset, but I couldn't reconcile the ~12mm figure given in the thread with the photograph.
I have no idea how the Chinese disc offset is measured, I will know when I buy it!

 

[highboy_coupe]

Ok, bought one and got it fitted:

 

[Paul Sutton]

My God, that disc is damn heavy!!

I will be interested to see if it slots straight into your Special. Was it an Ebay purchase??

Edit: It seems you need the following search words to find it on Ebay UK - LF400 Skygo Thunder Lifan, or

https://www.chinesemotorcyclepartsonline.co.uk/partno_BDSC005

 

[highboy_coupe]

Ha, you can get them on eBay, I got it direct from a Chinese bike part online store. It actually worked out cheaper!
As soon as my wife gets back I'm going in the garage, I'll post some pics with the standard caliper too

 

[gggGary]

Spill a url? What's it weigh, after the 10 tons are removed?

 

[gggGary]

Very good sleuthing! Have you mounted it in the fork yet?

 

[highboy_coupe]

URL: https://www.chinesemotorcyclepartsonline.co.uk/partno_BDSC005

They were on Amazon.com at some point too.

 

[aldo5468]

Very nice work! Thanx for sharing!

 

[Paul Sutton]

Do you think this rotor would fit comfortably into the stock caliper? I was thinking it may be an easier option to drilling the stock rotor at home.

 

[highboy_coupe]

Do you think this rotor would fit comfortably into the stock caliper? I was thinking it may be an easier option to drilling the stock rotor at home.

The caliper I used fit right over the stock disc in the same arrangement, i hadn't spaced out the stock disc at all. I could put the old one back on to show you so you could be 100% sure.
It is essentially exactly the same as if you skimmed 2mm off the back face of the original disc.

 

[Paul Sutton]

Thank you highboy_coupe. That is good enough for me. Will be nice to hear in the future how well the brakes work when you have finished all your work. Some will be interested to know what size master cylinder piston you are using also.

 

[highboy_coupe]

Thank you highboy_coupe. That is good enough for me. Will be nice to hear in the future how well the brakes work when you have finished all your work. Some will be interested to know what size master cylinder piston you are using also.

It's a12mm AJP trials bike MC, seems ok, a pig to bleed though.

 

[Paul Sutton]

Excellent - Thank you.

 

[highboy_coupe]

For the sake of completeness, here is a standard caliper, fit on the new Lifan disc.

 

[aldo5468]

Do you think this rotor would fit comfortably into the stock caliper? I was thinking it may be an easier option to drilling the stock rotor at home.

Right hand disc off a Yamaha XS1100 fits the stock caliper - it’s slotted, 5mm thick if I remember correctly, so would be another option easier than drilling your stock disc at home.

 

[highboy_coupe]

Right hand disc off a Yamaha XS1100 fits the stock caliper - it’s slotted, 5mm thick if I remember correctly, so would be another option easier than drilling your stock disc at home.

The issue I had is that on eBay in the UK they all seem to be 7mm thick, and often not slotted. This was my first choice but I literally couldn't find a 5mm slotted one! Still, shipping from the us would be about £50, so if it was cheap enough...

 

[5twins]

I use a 5mm SR500 disc. I had to drill it, it had no slots or holes stock. Can't say I notice any difference between it and the original 7mm disc. Even though it weighs less, there are no handling differences I can perceive. Seems to stop no better or worse than the 7mm too. Only difference I found was it heats up more/quicker. I suppose that could be an issue if heavily used but I haven't encountered any problems because of it yet.

Near as I can tell from comparing the 5 and 7mm Yamaha discs, they took 1mm off each side of the 7mm braking surface to make it 5mm. It wouldn't surprise me if both discs started out as the same blank and were just machined differently.

 

[Paul Sutton]

Once again, thank you high-boy coupe. I wonder if the modern rotor will give better performance compared to the 40 year old XS rotors due to improved metallurgy?? It will certainly look nice on your bike. Sure hope you get some riding in before the drought breaks in the UK. Rumour has it the fine weather will continue for another month. All the grass is now dying back in Cardiff.