Thursday, December 17, 2009

Beyond the Pipes!

If I’m going to build a cruiser frame, I’m going to need some tubing . . . Lets Go Shopping!

From what I’ve seen Truetemper Superthem (TTST) tubing is a popular choice for BMX frames.

So for my first frame it’s only natural that I build it from TTST so when I experiment down the line I have something to reference.

So where do you go to get TTST?…Henry James!

Henry can also tell you everything you need or what to know about tubing, as well as anything involved with metal working.

Below is my Parts List. TTST tubing is double-butted. That means it’s thicker are the ends, and thinner in the middle to save weight. For instance take the Top Tube for example. The tube they ship me is 675mm long or 26-1/2 inchs long. For the first 100mm its 1.0mm thick, then transitions for 75mm, from 1mm to 0.7mm thick, then for the 225mm mid section it’s 0.7mm thick, then transitions for 75mm from 0.7 to 1.0 thick, then for the last 200mm it’s 1.0mm thick.

If you notice the tube is not symmetric. One end/butt is 100mm longer than the other. This is where the magic comes in. If you spec a 22” (559mm) top tube for your frame, then you have to shorten the tube 116mm. If you take it all off the 200mm side, then (1.0x100mm)-75-(0.7x225mm)-75-(1.0x84mm) 559mm, -…or you can take 8mm off one side and 108 off together to make it symmetric, (1.0x 92mm)-75-(0.7x225mm)-75-(1.0x92mm) 559mm. It’s all up to the builder. Also not all tubing is the same. Some tubing manufactures have longer transitions. So some builder will blend different manufactures of tubing

Seat Tube (1-1/8”, 28.6mm)True Temper Supertherm, BMXST-ST01; Straight (0.7 x 290), 290mm

Top Tube (1-1/4”, 31.8mm)True Temper Supertherm; BMXST-DT01; Double Butted (1.0x100)-75-(0.7x225)-75-(1.0x200), 675mm

Down Tube (1-1/2”, 38.1mm)True Temper Supertherm; BMXST-DT03; (1.0x100)-50-(0.7x285)-50-(1.0x265), 750mm

Head Tube (37mm)True Temper's VERUS Heat Treated; MHT; (1.6x250), 250 mm

Seat Stay (16mm, 19mm, 12.4mm)True Temper OX; OX3SS; (0.66x537), 537mm

Chain Stay (22mm)True Temper Supertherm; BMXST-STAY04; (1.25x360); 360mm-Lugless Botom Bracket Shell (38.1mm)68mm; ISO THREAD

The rest are parts I have hanging around. DropoutsSurly Track Horizontal Dropouts

. . . Cantilever Bosses, and Cable Stops.

I thought about going with a 1.25mm thick Head tube instead of the 1.60mm, but with a 4” Head Tube what weight are you really saving? The tube they send you is about 9-1/5 inchs long, and the difference is about 90 grams between the two 9-1/2” tubes, so it’s about 45g or about 3 oz. It’s like my old saying. It doesn’t do you any good to save 45grams, but find 10 places to save 45g, now you’ve saved about 1Lbs.

I did change Seat Stays. I changed out the TTST 19mm stays in favor of the Platinum OX 19mm double taped for a couple of reasons.

First: Since I’m using Surly’s, Breezer style dropout, I’ll have to ovalize the end of the tube, so it can be mitered to mate to the dropout from 19mm wide to about 16mm.

Second: The cantilever bosses have to be spaced 92mm apart, plus don’t forget to add the offset. I’m going to have to bend them. The TTST Seat Stays are heat treated, where as the OX are not. So they will be easier to bend. I will note that TT does make heat treated seat stays (HOX), but since the stays on a BMX bikes are so short, I’m sure it’s not going to make a noticeable difference, other than ease of assembly.

What Now? We make a drawing.

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