short bb30 crankset and new Rotor aldhu direct mount design

Discuss light weight issues concerning road bikes & parts.
Post Reply
sleep
Posts: 15
Joined: Tue Feb 05, 2019 9:16 pm

by sleep

I am looking for experiment a short arm crank like 155mm or 160mm on my tri bike (BB30). Firstly I considered use cheap square taper crank, but then I realized I need knock out my bb30 bearing, get and press fit a adapt, get and install square taper BB as well as crank, seems a lot of touble.
Then I start to look for BB30 crankset, it seems that I almost do not have any option other than rotor ... ... (I know there is another way to modify the exisiting metal crankarm, but I don't want that router)
After investigate the new rotor aldhu, I have mainly have two questions:
1. Rotor has a longer spindle which require 2 11.5 spacer, but I found what strange is, the "real" BB30 crank such as sram red22 has a 145mm q-factor, while rotor aldhu claimed q-factor is 147mm. Only 2mm difference. However rotor require 23mm space while Sram red do not have any spacer, only a small preload, it just not add up right. Feels wrong, unless rotor crank is far thin than sram red.
2. Anyone worried about the new direct mount could easily wear out (creaks) because of the small teeth? All past direct mount chainring that I can found are all larger size and directly mount on drive side crank arm not on spindle.

by Weenie


AZR3
Posts: 775
Joined: Wed Sep 12, 2012 9:00 pm
Location: Az USA

by AZR3

You have to look at the arms of each to understand how they can have similar Q factors. The Red arms are “bent” while the Rotor arms are straight.

Not the crank arms you’re talking about but you can see the difference between BB30 with a short spindle and BB30 with a long spindle
Image

sleep
Posts: 15
Joined: Tue Feb 05, 2019 9:16 pm

by sleep

AZR3 wrote: ↑
Sat Feb 09, 2019 3:54 am
You have to look at the arms of each to understand how they can have similar Q factors. The Red arms are “bent” while the Rotor arms are straight.

Not the crank arms you’re talking about but you can see the difference between BB30 with a short spindle and BB30 with a long spindle
Image
oh yes, this make perfect sense! In this case, rotor crank not a full "bb30" won't be a big problem to me, I know longer spindle means a bit more weight, but I mostly care q-factor than weight.

2lo8
Posts: 539
Joined: Thu Mar 31, 2016 10:32 am

by 2lo8

I would caution you if you use cleats with float, the U-factor on Rotors is not very good, you you tend to ride toe out, heel in, you might find you get excessive shoe rub. If you use no float cleats straight ahead, no problems.
[6.6kg of no carbon fiber]
[2lo8.wordpress.com]
Your one-stop source for information and reviews on cheap eBay bike junk.

User avatar
C36
Posts: 582
Joined: Fri Mar 03, 2017 3:24 am

by C36

Spécialité TA Horizon, exist as small as 155mm, compatible BSC 68/73, BB30, PF30, PF89/92, BB Right (but TREK BB95).
The qfactor evolves with the length (155-185mm) but I haven’t been able to find the values.


Envoyé de mon iPhone en utilisant Tapatalk

sleep
Posts: 15
Joined: Tue Feb 05, 2019 9:16 pm

by sleep

2lo8 wrote: ↑
Sat Feb 09, 2019 5:04 am
I would caution you if you use cleats with float, the U-factor on Rotors is not very good, you you tend to ride toe out, heel in, you might find you get excessive shoe rub. If you use no float cleats straight ahead, no problems.
Thanks for the advice. but it is true for all small q-factor crank, right? Sram red also has this problem since q-factor is even smaller, I normally restrict the float to be toe in and heel out to avoid this.

It seems that no one worried about the small direct mount teeth? Not a problem?

2lo8
Posts: 539
Joined: Thu Mar 31, 2016 10:32 am

by 2lo8

sleep wrote: ↑
Sat Feb 09, 2019 9:11 pm
Thanks for the advice. but it is true for all small q-factor crank, right? Sram red also has this problem since q-factor is even smaller, I normally restrict the float to be toe in and heel out to avoid this.
No, this is one of the reasons for true BB30, it reduces the U-factor because the bearings are inboard like a traditional square taper crank. I remember Rotor cranks as being especially susceptable to shoe rub.
[6.6kg of no carbon fiber]
[2lo8.wordpress.com]
Your one-stop source for information and reviews on cheap eBay bike junk.

sleep
Posts: 15
Joined: Tue Feb 05, 2019 9:16 pm

by sleep

2lo8 wrote: ↑
Sun Feb 10, 2019 1:23 am
sleep wrote: ↑
Sat Feb 09, 2019 9:11 pm
Thanks for the advice. but it is true for all small q-factor crank, right? Sram red also has this problem since q-factor is even smaller, I normally restrict the float to be toe in and heel out to avoid this.
No, this is one of the reasons for true BB30, it reduces the U-factor because the bearings are inboard like a traditional square taper crank. I remember Rotor cranks as being especially susceptable to shoe rub.
oh, I see, you are talking about shoes rub crankarm, while I thought rub chainstay (with my current sram red, shoes could potentially rub chainstay if I point heel inwards)
In this case, you are right, since rotor provide a straight arm, it is easiler to rub crankarm than curved one such like sram red.

by Weenie


Post Reply
  • Similar Topics
    Replies
    Views
    Last post