United Trifold: Front Single Crankset

The stock crankset on the United Trifold is a square taper crankset, with a 52T chain ring. You can see a picture of it in the first post.

I am not a fan of oil-slick bicycle components, although some people love it. In any case I will change it out to a Hollowtech II bottom bracket and crankset, similar to how I did it on the Brompton.

In this case, I will use a cheaper FC-RS510 crankset, which is a non-series crankset that has the 4 arm, 110 mm BCD. The main difference with the other 4 arm cranksets is that this non-series crankset does not use a hollow forged construction. Instead, it uses a solid crankarm with material cut out at the back to save some weight. 

RS510 crankset vs R8000 crankset. The RS510 crankarm is much slimmer.

RS510 left crankarm + crank arm fixing bolt weighs 258 grams, noticeably heavier than Ultegra R8000 crankarm which weighs about 189 grams.

The drive side crankarm is also much heavier than the Ultegra R8000 version, which is just 325 grams.

In all, the RS510 crankset (without chain rings) weighs 664 grams, which is quite a lot more than the R8000 version, which is 519 grams. That's a difference of 145 grams just from the crankset, excluding chain rings.

Next, I needed to get a new chain ring to match this RS510 crankset. Recently I have been using Stone narrow-wide chain rings, since it is half the price of Wolf Tooth, and yet the quality feels the same. Previously I have used the 52T Stone chain ring on the Fnhon Gust.

This time, I chose the more lightweight version, which is designed to be used with the older generation of 4 arm cranksets (9100, 6800, 5800). It can also be used with the RS510 crankset as there is no extra wide crankarm.

Stone 52T chain ring! I like the many cutouts which makes it look more lightweight.

Weighs 123 grams, not so lightweight though. Only a bit lighter than the other version which is 128 grams.

Installed with my signature Infinity Stones chain ring bolts! I like how this looks.

536 grams for the drive side crankset, including the chain ring and chain ring bolts.

Whole crankset weighs 794 grams. An Ultegra version would be about 654 grams (794 - 145 + 5).

I chose the MT500 MTB Hollowtech BB, as the adapter cups are narrower than the road type (such as BBR60).

For detailed info on the difference between Road and MTB Hollowtech BB adapter cups, check out this modification and study that I did some time ago on the Avanti Inc 3.

Basically, I need to add more spacers at the drive side BB, so that I can push out the chain ring and crankarm for frame clearance. If I use a normal road BB, I can only add a maximum of 1-1.5 mm, before the spindle at the non-drive side becomes too short.

Therefore, using the MTB BB will give me an additional 2 mm for the spacer. From experience, at least 3 mm of spacer is needed on the drive side.

For a start, I added 4.3 mm (1.8 + 2.5) of spacers at the drive side BB.

There is good clearance between the chain ring bolt (blue colour) and the frame. This is at folded condition.

There is about 3.5 mm of clearance, so there is room to reduce it slightly if required. About 2 mm of clearance should be enough, since this is only at folded condition.

Another view of the bottom bracket area, with 4.3 mm of spacer at the drive side, and no spacer at the non-drive side.

When folded, the crank arms will hit the non-drive side seat stay.

The crank arm will also interfere with the drive side chain stay.

I noticed that due to the narrow Q-factor of Shimano road crank arms, the crank arms will hit the seat stay and chain stay of the rear triangle, if you try to spin the cranks when the bike is folded. This occurs on both the drive and non-drive side.

There is no way to solve this issue, other than to get a crankset with a longer spindle and wider Q-factor. The stock crankset has a wider Q-factor, which is why there is no interference.

Since this only occurs when folded, I think it is acceptable. Just that there are already some scratches on the frame due to this interference issue.

Installing a Hollowtech crankset on this United Trifold frame was not an issue for me, mainly because I already had prior experience from modifying the Brompton.