I want to upgrade my first generation Larry vs. Harry Bullitt to 180mm rotors from their current 160mm (this is the largest size they said I could use when I emailed them). I want to keep my current calipers for now.
To do this I need to know what kind of a mounting system I have so that I can identify which adapter to buy. This is what I have come up with. If possible, could someone take a look and let me know if I am wildly off (mostly in my understanding of how these adapters work – I can't and won't expect anyone to know the actual measurements of my bike. That is on me to get correct.)
I have a few questions (actual questions are in bold italic):
— Based on what I can tell, my frame has IS mounts. The calipers look like they have post mounts. So, assuming I got that right, what I need would be an IS to Post adapter for 180 mm rotors, correct?
From what I understand, IS mounts come in a few discrete sizes. From using a basic (imperial) ruler and converting to metric, I get a rough measurement of about 51mm (which is one of the IS mount sizes I think). Using the same, imprecise imperial ruler held up to the calipers, it looks like the distance between mounting holes on the calipers is 74mm.
— Do I need to measure the mounting hole dimensions (distance they are apart) super accurately? Or are the standards discrete enough that if I roughly measure about 51mm I know it will be 51mm (and same for 74mm measurement)?
— Assuming I measured the distance between holes on the frame correctly at 51mm and distance between holes on the calipers at 74mm, I would need an: IS to Post adapter with a 51mm frame interface and 74mm caliper interface for 180mm rotors, correct?
— Here are two products that I found. Do you think (assuming I got the measurements and mounting types correct above) that these are what I am looking for?
Front IS to Post 180mm adapter with a 51mm frame interface and 74mm caliper mounting hole dimensions.
Back IS to Post 180mm adapter with a 51mm frame interface and 74mm caliper mounting hole dimensions:
— Anything else I should be considering (besides needing new rotors and pads)?
Thanks so much! Learning how to work on my own bike is pretty rewarding.
by bvz2001
2 Comments
Yes you just need a 180mm IS adapter, should be a pretty straight forward swap.
Those are crazy small brakes for that bike. I had full DH brakes with 203mm rotors on my cargo bike and it wasn’t too much. If I built one again I would do double front rotors.