Wednesday, September 24, 2008

Small Wheels + Big Rubber


Todd Fahrner of Clever Cycles in Portland posted the info below on Bike Forums and I thought it was worth capturing here for those of you with cargo bike builds on the go. I haven't tried using small wheels with large tires, but it's a concept which makes a lot of sense and Todd has loads of experience with cargo bikes. I'd be keen on hearing some feedback from anyone who tries it.

"For Xtracycles including Big Dummy, I greatly prefer 24" wheels with 2.35" Big Apples to 26" wheels with either high or low volume tires. High volume tires provide the only suspension to be had for the dead weight of your cargo, and improve braking and comfort. 24" lets you have it while still keeping the bottom bracket in the range of road bikes, so you can get a foot down to stabilize at stops, and mount/dismount easily without leaning the bike. This matters with a heavily loaded bike, particularly if your load is precious and mounted high, like a kid. You need disc or drum brakes to swap wheel sizes like this.

A similar trick is to start with a so-called "two-niner" frame (designed for 700c rims with poofy tires) and fit 26" wheels; e.g., http://clevercycles.com/?p=136 .


This advice doesn't apply if you intend actually to jump logs and so on with your cargo bike, or if you insist on pedaling through high speed sharp turns, such that you risk striking a pedal. Both Xtracycle and Surly do tend to promote the concept of these bikes being MTBs, and optimize ground clearance accordingly. I'm more urban/pavement oriented, excluding curb-hopping."

5 comments:

Clancy said...

I think it makes sense. I recently switch my Xtracycle from a really small frame w/low bottom bracket to a larger frame and higher BB. I miss the ease of putting a foot down. The geometry of the new frame is funny(short rear triangle) and I am thinking about a 24" wheel for the rear. This would lower the BB and level out the top tube.

nollij said...

It's interesting because while the folks at Surly don't negate the option mentioned, they seem to have many cons. Some apply and some seem overly worry-wartist. (Pedal Strike? Only neophytes and track riders pedal through corners, and most bike neophytes aren't going to buy a dummy... I think.) I would really like to ride a dummy set up w/ 24" wheels and Schwalbe Big Apple 2.35's (on an 18" frame) and see if it would be something I would want to do... kind of an expensive experiment b/c I'm running a Rohloff on mine.

I would have thought that Todd would have had some more influence on the marketing of the Dummy, since his Stokemonkey system is mentioned in the Surly Spew #19, as well as the fact that one of the surly guys had a broken leg, but rode the dummy w/ outrigger and stokemonkey system until he got better. I dunno... anyway, anyone got a Dummy set up this way live near the Bay Area (California) and willing to let me test ride?

Vic, you gonna do this to your dummy at some point?

Vik said...

"Vic, you gonna do this to your dummy at some point?"

It's unlikely as I have some decent 26" wheels and tires already. My other bikes are mostly 26" wheels so I can swap stuff around to some extent. I don't really want to invest in something that will only work with one bike.

I'm also quite tall and reasonably strong so dealing the loaded bike isn't much of an issue for me with 26" wheels.

Plus I do like to use my Big Dummy as a MTB so the BB clearance of a 26" wheel with a 2.0" tire is welcomed.

I'm sure Todd is onto something and I think it's an option worthy of consideration for someone building up a Big Dummy/Xtrarig. Like any idea there are pros and cons which will work out differently for each person.

Jeremy said...

24" Large Marge rims with 3.0 Maxxis Hookworms or 3.45" Hoggy-Gs from 3G bikes work really nicely and give you a magic carpet ride.

One of the crew here at Xtracycle has a dummy with 26" Large Marge's, a Rohloff, and Hookworms, and it's fast, smooth, pretty much perfect.

If anyone in the bay area needs help finding a dummy to test ride, talk to me. Jeremy at xtracycle dawt com

patmando said...

Vik,

Thanks for all your blogs.

I actually did something like this for my xtracycle conversion. I had a Surly CrossCheck frame that I used, but I wanted disc brakes. So I replaced the crosscheck fork with a 26" disc fork. With the drop in the bottom bracket, I felt really uncomfortable with how close my feet were to the ground while I was on the pedals. I put on some shortened cranks which solved that problem.

This was the second bike I had put together from a frameset. Some frustrations, but I learned alot.

Here's a link to some pics of the conversion process.
http://picasaweb.google.com/mcgeep12/Xtracycle#

I haven't taken any pics since I added the freeloaders.