Ozonation

I was at a urban cycle shop while visiting another city on business, and tried the Tern Link D8 and the BYB (8 speed). While I love my Brompton, it's one of the older models (not the greatest brakes) and I wish I had some more cushy tires for rougher roads and packed trails. The D8 had Big Apple tires - rode fairly well, but it was a bit more upright and I still kind of felt "over the front wheel". Since I was there, I figured I might was well try the BYB. To my surprise, I liked it more. It was solid, and very comfortable, almost like my full size bike. I couldn't figure out what the difference was between it and the D8, and then I realized the seat tube was angled just a bit more, so that translated into a longer "cockpit" for me to stretch out. But it has narrower tires, and we could not easily tell if larger tires could be mounted. Anybody know what the practical limit to larger tires on the BYB might be (with or without fenders)?

Leisesturm

I found a site comparing the two models you mentioned directly. It should have been pretty easy to tell whether larger tires could fit the BYB. The fact that it was difficult, and my own experience with folding bikes in general, says that pretty much the tire the bike comes stock with is about all that will work. No fenders might get you an additional 5mm. You might be able to increase the size of the cockpit by pushing the saddle back on the D8? You might also want to actually measure things to eliminate any implicit comparison bias due to other factors.

willydstyle

I really like my BYB, and I've looked into precisely this, and I think the biggest limitation to larger tires is that the stock fenders are quite narrow. I've got tentative plans to fit 60mm fenders (according to my measurements they should fit) and I think they would easily fit 1.75" tires, and *maybe* 2" tires with those wider fenders installed, although I think it might require altering some of the mounting hardware on the rear fender (or if you remove the fenders you can fit 2" tires).

Ozonation

I contacted another vendor who thinks Big Apple 20X2.0 should fit. Hmmm... we'll see!

Fentuz

and the weight; 14 something vs 12 is something you can feel. This is why I sold my Jetstream (14.5kg) and kept the helios (10.25kg).

Leisesturm

Quite right. This point is somehow often missed in the current craze to stuff the largest size tires possible into bikes that were never designed for them. Even in a 20" tire there is a noticeable difference in weight between a 1.5" tire and a 2.0" tire. At 700C (29'er) diameters the difference between 28mm and 50mm is measured in kilograms, and it is rotational mass!! If you NEED the big rubber, then you need, it but needing uber big rubber is not likely something the designers of the majority of folding bikes, especially the super trick ones like the BYB, ever planned for in their R&D. I like the BYB, but I'm having a very hard time seeing how 2" tires could possibly fit on one. But, of course, I haven't seen a BYB. I'm not understanding why someone that works in an LBS can't say definitively yes, or no. All they have to do is look. Or, if they don't trust their own eyes, get the calipers out and measure the clearances. As I understand it, 5mm minimum, and 7mm is better for clearance around a tire for safety. In reality these numbers can be fudged but Tern is subject to a higher authority. If you ask their opinion they will say "ixnay" and leave it there. Also, it must be said, I think: fenders are not 'optional equipment' for the vast majority of folding bikes.

Schwinnsta

I have two 20-inch folders currently. A Xootr Swift, and a Zizzo Liberte. Going to 406x50, Big Apples,made a big difference in comfort and stability to me. I had to modify the Swift to make that work. Both came with 1 1/2" tires. I have fenders on both bikes. The limitation on size in both my cases is the rear chain stays not the fenders.

If I were in the market for a twenty-inch folder clearance for 50 mm tires would be a requirement. For me, on the roads I ride, the comfort and stability, is worth the small extra mass.

Jipe

The Big Apple aren't heavy compared to comparable touring tires, the 50x406 Big Apple weight 495g, the 40x406 Schwalbe Marathon weight 530g (the Marathon 47x406 weight 640g and the Marathon Plus 47x406 weight 725g !).

Of course, comparing the Big Apple to road tires like the Pro-one 28x406 or One 28x406 makes a big weight difference but its a totally different type of tire and use.

I also like wide tires on small wheels bikes.

The same Big Apple are excellent on the Birdy they not only improve riding on roads but allow to ride off-road with the Birdy. I rode with them on trails, even with mud (not too much) and hard sand of a beach.

The Brompton upgraded with a Kinetics fork and rear triangle accepting 50x355 Big Apple tires is greatly improved vs. the original limited to 35mm wide tires.

Schwinnsta

Agreed, I wish Brompton would bring out that model. However, Andrew Ritchie was relentless in minimizing Brompton's folded size. That would add a couple of inches. It would make a more practical bike, IMO. I would not be able to stuff it above the seats in an airplane, but I don't do that anyway.

Jipe

Yes, its a drawback of the Brompton design with the rear wheel folding under de main tube: any wheel diameter increase, increases the folded length and height of the bike which is not the case for the Birdy (to some extent of course) due to the fact that the rear wheel fold on the left side of the main frame.

For the Kinetics upgrade that uses ETRTO355 wheels (because there are no 50mm wide tires in ETRTO349), the wheel diameter is increased of about 36mm.

Fentuz

1.5" or 2.0" of the same tyre is not that bad in weight difference (~28% diff between marathon 35-406 and 47-406) . The type of tyre is more of a concern: when I went from marathon 35-406 to kojak 35-406, I save 50% because Marathon is twice the weigh of kojak. It was important for me because I wanted a fast accelerating bike and l wanted to reduce the "carry" weight.

But, on my gravel, I run 700c wheel with 35-622 (353g) and 650b with 52-584 (670g). the later is much heavier and yet, it spins better because of the rotating mass. The bigger flywheel spins at "constant" velocity with less input but it required more torque to increase than velocity.
-> if you cruise on long consistent distance, bigger tyres are better as more comfortable and they spin nicely with less effort.
-> if you ride in a urban environment with loads of stop/start, fast accelerations or if you climb maany steep hill, the lighter tyre is best. But, lighter can compromise comfort. I like to use 35c tyres and adjust the pressure depending of the sidewall stiffness.

Clearance, 5-7mm is fine is urban environment. With off-road, I go 10 to 12mm especially with carbon and titanium frame.

Fentuz

I was looking at that when the "new at the time" brompton explore came out; I could not understand why they kept the 349. They could have made the explore with 305 and fit tyres like big apple 50-305 and it have been a peach. Kinetic offers that option.

Jipe

Its not possible to put ETRTO305 wheels on the Brompton with caliper rim brakes: it would require very long caliper arms to reach the smaller diameter rims.

Kinetics makes Brompton with ETRTO305 wheels and Big Apple but always with disc brake upgrade.

Fentuz

yes, 305 with 50-305 tyre would not work with classic bompton caliper but If Brompton had looked into another rim size, I would expert them to look into calipers too. 50-305 would work bit bmx type caliper like dia compe 806 or 833

Pahana

How do you like the Zizzo? There is someone near me that has a Liberte looking like new for $250. I really don't need it but the price is hard to resist. I like grip shifters and miss having one as they shift so well.

Jipe

The Brompton caliper need to have a reach of about 60mm front and 55mm rear with ETRTO349 rims.

With ETRTO305 rims, 44mm smaller in diameter, the caliper need to have 22m more reach, we can expect to need a reach of 82mm front and 77mm rear that's more than what the Dia-compe 806 have but the Dia-compe 833 should have enough reach.

But the Dia-compe 833 is an old school single pivot caliper with an ultra long reach, I wonder what is the braking power of such caliper ?

And how will the side pull fit with the Brompton folding ?

Schwinnsta

I like it. It's lightweight, good components and room for 50 mm wide tires. It folds small. It's a bit under geared even for an old guy like me, and I have arthritis in one knee. It comes with 28i to 81.5 gear range. When it is worn out, I will change it. The rims are narrow, but my tires work OK anyway. They were a little hard to install. I have changed several items on the bike touchpoints and few others. It is not as stiff as my Swift, but it is good enough for me. I purchased it new as return or refurbished for $320 shipped. I could not find any defects at all but I did have to adjust the chain keeper which as it is now is necessary, or it throws a chain. I have not looked into fixing this, as it works fine with the chain keeper adjusted.

Schwinnsta

Some years ago, at least five, there was a poster in the forum, who had modified his brompton to take 50-305 wheels, so he could ride knobby tires. I think he could switch back and forth. As I recollect the fit without modification. He did not use discs. I think he may have brazed on additional brake bosses or he may have made custom drop plates or U-brake set up. Even more remarkable, he had experience cold bending tubes and reshaped the back triangle to take a normal derailleur by making a series of vertical notches or crimps in the rear stays. I think said he did this with both steel and titanium. Maybe someone will remember how id his posts. He did have pics and videos.

Fentuz

So, I spoke with Kinetic as I am interested i getting a cheaper S1L and convert it to a 8gear hub like sturney/nexus/alfine. As it requires wheel building either way, I asked about 305. The reason the 305 conversion have disc brake is simplicity; the 305 requires need fork and rear triangle due to tyre clearance. As new frame components have to be made, it makes sense to add disc caliper tabs as it doesn't cost much more and it makes the conversion rather simple.