Bike review: Tern BYB S11 folding bike

Published by Andrew on 30 July 2020

The Tern BYB S11 folding bike is ideal for combining cycling and public transport. Richard Peace takes it for a road test.

Tern BYB folding bike review

See also our review of the Tern Verge P10 folding bike.

Tern BYB S11 folding bike
£2200
Tern Bicycles

Putting a folding bike on Eurostar and hopping off for a spot of French cycling might sound like a great idea (and it is!) but you must be aware there are size restrictions on the dimensions of the folded bike package and it has to be in a bag. Eurostar stipulate that if you own a folding bike, it can be taken on any Eurostar train as long as it's smaller than 85cm when fully folded, and as long as it's in a protective bag that covers the whole bike. Don’t think you can get away with a few centimetres, either: Eurostar can and do check. If you get your folded bike’s longest dimension to be shorter than the magic 85cm and satisfactorily covered, then you can simply take it on Eurostar as an item of hand luggage.

This information is especially relevant at the minute as, though services are starting to run again during the COVID-19 pandemic (see here for our COVID/France cycling page), Eurostar have still suspended their usual EuroDespatch luggage service which includes their ‘bike on board’ service. This means it will be difficult if not impossible to take a full size bike via Eurostar, leaving you with folding bikes or hiring bikes in France as the two remaining options (or the ferry). 

To get a bike to fold under 85cm often means having to choose pretty small 16” wheels – this is about as small as is acceptable for a folder to go. However, some riders don’t like the quicker handling of smaller wheels and its certainly true that, all other factors being equal, smaller wheels are more inefficient than larger ones, so long distance tourers will have an eye on conserving as much energy as they can by using the largest wheels possible.   

The BYB tri-fold – compact and quick

Enter the Tern BYB (short for Bring Your Bike), a design that uses larger 20” wheels and folds together securely for train travel and, critically for Eurostar purposes, has a longest folding dimension of 81cm.

Tern BYB folded review

The key to the quick, compact fold is Tern’s unique tri-fold design that takes only a few seconds to fold and produces a pretty compact and secure folded package. You drop the seatpost, undo both frame hinges and concertina the bike back on itself to lock everything place using the anchor bolt. Leaving the handlebar post extended means you can stand the bike upright on the rear of the rack and use the bars as a ‘trolley handle’. Alternatively you can unlock the bar’s Andros stem mechanism and align it vertically before folding the bars down. On the outside of the folded package the protruding pedal can be quickly removed by hand and locked away on the frame.

While the folded bike still has a longest dimension similar to other 20” wheel folders, the package is very narrow so that it is in fact around 30 per cent smaller than traditional 20" folding bikes when folded (sometimes quite a bit more). This means it is small and slim enough to fit conveniently into lockers, closets, or any narrow space.

The chain sits neatly in the middle of the folded package, protecting clothes and other luggage from oil and dirt. The anchor bolt fixing system is also a big plus as it really does lock everything together securely; many other fold in half bikes I have tried use a magnet but this never seems sufficient to keep the two halves together in all situations, no matter how strong it is. The fact it can sit lengthways or vertically gives it flexibility to fit into a variety of spaces and the clever design means you can also place it on the floor without it toppling over.

Tern BYB folding bike brakes

The final folded size of 81cm x 51cm x 33cm has to make it the most compact 20” folder there is and one that is very easily portable, being reasonably light to carry and lift. Moreover, the rear rack incorporates trolley luggage style wheels for wheeling longer distances where you just don’t to carry it, though as the wheels are small the surfaces will have to be reasonably smooth.  

At 12.7kg, the BYB S11 is a respectable weight for a fully equipped folder with 20” wheels – especially when you consider it includes items you don’t often get with folders such as a rear rack, full length mudguards and kickstand.

While the BYB’s design is optimised for hopping on an off trains and buses, tourers will be pleased to hear there is a rear rack and also a front attachment point that will allow various KLICKfix additions.

How did it ride?

I like bike designs that can be altered to fit a variety of body shapes and sizes and the BYB is just that. Being in the riding position that you want means you are half way to a comfortable and efficient ride before you even pedal.

Telescopic seatpost design gives plenty of height adjustment whilst the Andros stem gives a good amount of fore and aft bar adjustment simply by pulling open a couple of levers.

Tern BYB folding bike review

This means you can enjoy a sporty leant-forward position or a comfy upright ride. Tern say it suits riders from 147 to 195 cm (4’10”–6’5”).  

This is a nippy little bike for sure. It accelerates quickly thanks to the stiff frame and the very solidly locked together hinges. You can snap through the 11 Shimano Ultrega Shadow RD derailler gears very quickly and precisely. The RD element of the design means a more compact derailleur with more direct cable routing and a more consistent direction from derailleur to gears throughout the gear range – all aimed at quicker more precise changing than previous designs. High quality Tektro V brakes have plenty of stopping power too. Schwalbe Marathon Racer tyres are a good compromise between speed, puncture protection and a decent width for comfort. 

My main niggle was that the road-oriented gear range that felt a little narrow (or at least too highly geared) for a not particularly fit rider like me, confronted with a steep hill. Conversely, the relatively small-spaced rear cassette allied with the large tooth front chain ring should give very impressive speed on the flat and over moderate terrain. A dealer might be able to alter the gear range for easier pedalling.

The S11 comes in at £2200 as against £1200 for the P8 version of the BYB. This is simply because of the use of much lighter and higher quality parts meaning the S11 is some 1.6kg lighter than the P8. 

The BYB range undoubtedly takes 20” folding bike design to a new level of compactness and portability. If you are looking for something with even bigger wheels for longer tours and a lower gearing for very steep hills you might want to check out my review of the Verge P10

See more detail hereand find dealer links.

About our reviewer
Richard Peace 
is the author of the official English-language guidebook to the Veloscenie Paris-Mont-Saint Michel bike route and the Sustrans guide to the London-Paris Avenue Verte. He also contributes to A to B magazineBike Europe and Eurobike Show DailyYou can see all Richard's books here.

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