Dirtjumper as an urban commuter bike?

Author	Message

emdc

Posted: May 15, 2015 at 20:05

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strange as hell i know, but i ride a 20" bmx around the city as a courier, but I'm looking to switch to something bigger as my distances aren't as short anymore and its starting to kill my knees. everyone's telling me to go with a single speed or track bike, but I like the ruggedness and riding style of bmx. with that said, I'm looking into purchasing a mutant bikes EVO 2SIX dirt jumper with a solid fork, front disc brake, rear u-brake, but my only concerns are with drive ratio and seat height….
It currently has this SSC Pivotal seat post [ https://vimeo.com/5609678 ] that measures 24.5mm, but its way too low for the riding I'm doing. Is using a longer seat post and drilling a hole for this style of seat clamp in order to get better leg extension unreasonable?

Also,

Does any one have any suggested drive ratio for commuting? i think its like 22x12 right now, something around there

maybe I'm way out in right field with for even thinking about doing this kind of riding with this bike. idk. if you think i'm not doing this bike justice, that understandable. Just looking for honest opinions.

cmc4130

Posted: May 16, 2015 at 10:45

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emdc wrote:

It comes down to how tall you are and what you expect in terms of leg extension while sitting down. Coming from bmx, where people never sit down, or when you do, you're used to your knees coming up high.... then you'll probably find it just fine. But, people who come from a roadie or dirt-roadie (xc-mtb) background, demand to sit high--as a result they would find dirt jumpers impossible to sit and ride around--at least, taller riders would.

Last year, I bought my first road/commuter bike, a Fairdale Weekender, size Large. (Fairdale was started by ex-bmx-pro Taj Mihelich). You can see here, next to my Black Market Mob, that the seat height (center of bb up to top of the seat at the position where I have it) is vastly different. Basically 29.5" versus 17.5". I have a 34" inseam. But, if you'd be okay with having your seat at around 22"-ish . . . then a long post on a DJ-mtb could work just as well.

Although I rode bmx bikes (and later, mtb) for miles around cities all the time, when I finally got a road/commuter, I realized how much faster and efficient they are. It's just so easy to haul ass on the street. Pretty much blows away any bmx or mtb. Those narrow high pressure tires are FAST.

cmc4130

Posted: May 16, 2015 at 11:01

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Oh yeah... and for gear ratio.... You should look at some "gear inches" charts. 22/12 would not work at all. That's extremely spinny.

Are you in a flat city? I think most single speed commuters and fixed gear bikes are geared somewhere in the high 60's or low 70's gear inches.

You do the fraction, then multiply times wheel diameter to get "gear inches." Wheel diameter matters a lot when comparing gear ratio. If you put BMX's typical 25/9 on a bike with 26" (or 27.5") wheels, it would be way harder to pedal.

25 / 9 X 20 = 55.5 gear inches.

25 / 9 X 26 = 72.2 gear inches.

http://www.quora.com/What-is-the-best-gear-ratio-for-daily-city-commuting

cmc4130

Posted: May 16, 2015 at 11:13

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I don't know what your city's courier scene is like, but I know that some of the guys that were riding bmx-style street on fixed gear 700c track bikes a few years ago have now ditched 700c wheels and are riding mtb 26" wheels with mtb-urban style tires.

The weird thing about this scene to me is keeping the seat tube high enough to look road-bike-ish.... They're trying to blend two completely different styles of riding--one where you sit down and pedal, the other where the seat and frame is really low to allow for tricks. So, it's evolved to right in the middle. But, at some point I wouldn't be surprised if some of the FGFS start riding frames with slanted top tubes .... pretty much an mtb-urban/DJ bike.

Unsecure image, only https images allowed: http://phxbike.com/wp-content/uploads/2011/02/V2grind.jpg
Specialized took note of that trend and created the 26" wheel P.Fix:
http://www.specialized.com/us/en/bikes/archive/2012/p.series/p.fix

Black Market Mob, all rigid.

ricar

Posted: May 16, 2015 at 13:20

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I would look into a cruiser if you just want larger wheels. As CMC said, it's more about seat height than anything for knees, so BMX or road bike, you need to stretch the legs out at least a bit. If you want more, then the DJ style would still keep the BMX ruggedness and even the possibility of gears. Ive been toying with the idea of a 2 speed on a DJ bike with 135 spacing but still have not gotten to it.

Looking at the UNKNOWN CMC posted, it really is a 26" cruiser with a really high TT. Fork, head tube, BMX stem, cruiser bars, short chain stays all say BMX. Even the depression in the chain stay on the left side (you can see the one on the right) all say BMX to me.

cmc4130

Posted: May 16, 2015 at 13:32

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ricar wrote:

. . .

Looking at the UNKNOWN CMC posted, it really is a 26" cruiser with a really high TT. Fork, head tube, BMX stem, cruiser bars, short chain stays all say BMX. Even the depression in the chain stay on the left side (you can see the one on the right) all say BMX to me.

yeah exactly.

VOLUME did the same thing with the Hessian (which came after the Sledgehammer). However, if you notice, the Hessian still has some bb drop, whereas that Unknown has bb rise--so they were trying to make it even more nu-school bmx-ish for a fixed gear.

Hessian:

cmc4130

Posted: Mar 1, 2016 at 10:48

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emdc wrote:

well, what did you end up doing?

bikeman543

Posted: Jun 15, 2016 at 9:16

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I was having the same issue. Had a NS Capital and wasn't racing or going to the park much, so I decided to turn it into a cruiser. I'm only 5'9" and I couldn't get enough of a leg stretch to make it work. I cut the seat tube and got a Thompson post - I think they are the longest on the market - and to get a good leg extension the seat post was over extended (minimum line was above the frame" even though there was at least 2" in the frame. I thought it was going to be the perfect bike, but it was cramped and I feared the seat post would break.

I ended up with a PK Big Ripper. I got BMX geo, a decent gear (I think it could be harder) and she rides smooth. I have taken it to the park and can do everything I did on the NS (which isn't much) and have done 13 mile rides. I am eager to take her to the track and see how she handles.

Like CMC said, if you come from a road or XC background (which I did) then leg extension is mandatory. If ya come fro the BMX background you might accept standing up or less leg extension.

Just my 2 cents worth.

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