I been looking for a replacement for my B75 Chainring, it come in size 44T and I been riding like a hamster on a flat road. I need a bigger chainring to optimize my drivetrain efficiency. Oval chainrings had become very popular lately, the design increase pedalling effectiveness thus lesser force waste means more energy saved which allow longer ride. But oval chainring is not for everyone and not all size can fit onto a Brompton, here’s 3 key things I learned before changing into an Oval Chainring.
Chainstay length and Chain length
Sizing for Oval Chainring is same as normal chainring, it go by number of teeth, but since is oval in shape the length of the chainring will not be consistent when it rotate. The longest side of the chainring it’s known as the Recovery Zone and when it’s parallel to your chainstay it might hit your front hook. So we need to be sure to pick the right chainring size. I cannot find any standard sizing guide for oval chainring, every brand come with different sizing guide but the maximum teeth we can fit onto a Brompton without hitting the hook is 56T so whatever brand of chainring we just need to make sure the maximum Teeth is 56T (about 12cm from center of bottom bracket). I realise the longest axis of an Oval Chainring is usually size + 4T , example if the size indicate 52T the longest axis is usually +4T = 56T.
Bold Circle Diameter (BCD)
BCD is the diameter of the circle within the chainring, it’s important to select the right BCD that fit your crankset. I’m using the original Brompton crankset so I will need a 5 bolt 130 BCD chainring.
The orientation of Oval chainring is extremely important, when position right we will be able to transmit more power to our pedal but if position wrongly will cause it harder to pedal and not able to transmit power to pedal effectively. The logic of Oval chainring is to position crankarm at about 110 ° to the longest axis of the chainring so when we are pedalling downwards and pushing the longest axis forward generating higher power outputs with same effort, this is call the power zone. It’s a brilliant design and because of the irregular rotation, there’s always a powerzone (hard to pedal) and recovery zone (easy to pedal) making it ideal for climbing steep slope.
AbsoluteBlack vs Stone vs Ridea
Once I got all the facts right, I start searching for one that fit my requirement. I need a size 52T-56T, 5 bolt, 130BCD Oval chainring. There are few different brands and I narrow down to these 3 brands, AbsoluteBlack, Stone and Ridea.
|52T||$160 ~ $173||$78||$155|
AbsoluteBlack is the premium brand amount the rest, the 53T is available at their official website at $173 excluding shipping fee or $160 from CANNASIA website. AbsoluteBlack claim that their oval chainrings are designed with optimum percentage of ovality and shape, allow optimum angle of the crank arm to achieve most effective pedalling power. They provide a lot of great explanation and research in their website but the price is on the high side and not within my budget.
Ridea is another popular option, the 52T is available on Shopee at $155 and come in 5 different colours. According to Ridea’s website the hollow design create a laminar flow to reduce drag which help to keep momentum. not sure how much does it really contribute to momentum but I like the look of the hollow design.
Stone is the most affordable option I can find in the market, the 52T is available on shopee at $78 only. It comes in hollow and non-hollow style, the 52T weigh only at 112g. Pretty good deal at half of the price of rest of the brands, so I decided to go with Stone.
It fit nicely onto my Brompton, the hollow design look great and the black blend in well. I did a short 50km test ride with slight elevation and I must say it really helps in term of climbing and on flat road the bigger chainring definitely allow me to pedal harder and generate more power but I do not feel the different intern of the shape. It still roll smoothly and I realise it exactly allow me to be more consistent on my pedalling. Given the price, it’s very worth it and definitely a good upgrade that I will recommend.