Slowtwitch Forums: Triathlon Forum: Building own tri bike... I have a few questions..

Calendar Retailers Stack & Reach Custom Geometry Calculator (beta) More To Come...
		MAIN INDEX	RULES & LEGEND	LOG IN

Search for (options)

Newsletter Signup

Slowtwitch Forums: Triathlon Forum:
Building own tri bike... I have a few questions..

wildstar

Aug 26, 08 8:24

Post #1 of 6 (259 views)

Building own tri bike... I have a few questions..	Can't Post

With free time on my break from grad school and a newly acquired Orbea Ordu, I'm going to mess around with building up my own bike. I have put together some bikes before, but never anything this complex. Obviously if I feel I'm in over my head, I'll let my LBS put it together, but with some negative experiences up here in Boston, I'd like to put that off. I would atleast like to scour the web and buy the pieces. So here are a few questions I have: (yes I searched, would still like clarification on some things)

1) Any advantage of braze on vs clamp front derailleur?

2) How do you pick crank arm length and ratio?

3) I'm guessing 10 speed over 9?

4) How do you pick cassette ratio and chain length?

5) THANKS

*if it helps I'm looking at SRAM red

DocVijay

Aug 26, 08 8:51

Post #2 of 6 (222 views)

Re: Building own tri bike... I have a few questions.. [wildstar] [In reply to]	Can't Post

In Reply To

I'm not an expert, but I have built a fair number of bikes. These are just my opinions, not necessarily right, though.

1) It's more a matter of what your frame is set up for. The Ordu is a braze on, simply because it'd be a bitch to find a clamp that would fit. If the bike had the standard round seat tube, there are adapter clamps to use a braze derailleur. With most tri bikes these days you are going to use a braze on.

2) For me it's a matter of preference. You need to factor in things like height and length of your legs. If your'e 6'5" you certainly wouldn't use a 170mm crank. Likewise, if you're 5'2" you wouldn't use a 180mm crank. Thinking back to my physics classes, I guess your leg strength would also play a part, with a longer crank giving greater advantage from the longer lever arm. I'm 5'8" and I use a 172.5mm crank. Is it right? Don't know, but it works for me.

3) Well, if you're considering SRAM Red, you have no choice over 9 or 10 speed. Older groups used 9 speed, todays groups use 10, and the new Campy uses an 11 speed cassette. Plenty of people still use 9 speed groups and like it just fine. You get the same overall gearing, just fewer choices inbetween. It's like cars these days, Lexus and Mercedes have a new 7 speed tranny, Most others have a six. Does that mean a car with a four speed tansmission is crap? No, but the seven speed will be able to keep it in the sweet spot (peak hp, or peak efficiency) more. With more gears on your bike, you will be able to maintain your ideal cadence at a greater range of speeds and terrain. Is it necessarily better? Depends. I'm sure some will dive headfirst into the new Campy 11 speed. Others say why would you need that many. With each additional gear ratio any advantage gets less and less. My first bike had 2 gears up front and 5 in the back. There is a huge gain from that to the current 2/10. Movign up to 2/11 is not so much of an improvement.

4) The cassette ratio you use depends on what type of riding and what type of terrain. Here in Florida we don't have much in the way of elevation change, so you could run lower numbers. Tri's here are fast, so a low range like an 11-21 or an 11-23 would work. If you live in aplace with a lot of hills, then you need a wider range. The 11 tooth cog would be great on the downhill side, but the 21 (or 23) would suck on the uphill side. So you obviously get a cassette with a wider range. You also need to keep in mind that the rear derraileur has a maximum range that it will work with. Keep that in mind. So just think about the terrain you'll be riding over. Your chainring size also plays a part, so mid that too.

5) Don't thank me until you read my post. You may regret it! ;)

* SRAM Red is a great group. Nice and light (and pricey).

(This post was edited by DocVijay on Aug 26, 08 8:52)

wildstar

Aug 26, 08 8:57

Post #3 of 6 (203 views)

Re: Building own tri bike... I have a few questions.. [DocVijay] [In reply to]	Can't Post

Thanks for your response, your post was very helpful. I am 5'10, 30-31" inseam, so I've been leaning towards the 172.5 crank. I've seen on this board that it may come down to trial and error as many people will have 2 crank lengths (ie 172.5 and a 175). Here in Boston it isn't extremely hilly, however I wouldn't want to be limited to not being able to do a hilly race.

Ti T'war

Aug 26, 08 9:19

Post #4 of 6 (174 views)

Re: Building own tri bike... I have a few questions.. [wildstar] [In reply to]	Can't Post

REmember that changing a cassette is pretty easy, so you could run an 11-23 for flat areas and switch over to a 12-27 for hilly stuff. Someone your height ususally runs 172.5s. I'm 6'2 and run 175 on my tri bike and 172.5 on the roadie - I can't really tell the difference.
__________________________________________________
It's T'war like 'car'
http://www.tritwar.blogspot.com
This is your life, and it's ending one minute at a time. - Fight Club

slowhokie

Aug 26, 08 9:19

Post #5 of 6 (172 views)

Re: Building own tri bike... I have a few questions.. [wildstar] [In reply to]	Can't Post

Experts correct me if I'm wrong, but do aero (non-round) seat tubes support clamp-on derailleurs? Something tells me clamp on is only for round tubes. There's no performance difference though, although I think I've heard the location of the braze may affect your FD decision if you want a compact crank.
Crank arm length is probably trial and error. My road bike was a 170, my new tri bike is 175. I don't even think I can tell the difference.
10 speed for sure!
Cassette ratio is up to the terrain and your ability. I'm a pretty weak cyclist so I've got a compact front and a 12-25 cassette, and with that setup I've never needed more gears in either direction. Chain length is specified by your derailleur manufacturers.

Good luck with your build, let us know how it goes!

Rokko

Aug 26, 08 9:26

Post #6 of 6 (160 views)

Re: Building own tri bike... I have a few questions.. [DocVijay] [In reply to]	Can't Post

Competitive Cyclist has a pretty good triathlon / TT fit calculator. They take a bunch of measurements into consideration, then spit out what they feel the ideal sizes are for you, including things like cranklength. Of course, it's an online generic calculator and does not factor in things like your persaonal flexability or comfort, but it still gives you a pretty good base to build your bike on.

http://www.competitivecyclist.com/...FIT_CALCULATOR_INTRO
-----

Blazeman Warrior
Wildflower Long, Big Kahuna, maybe Vineman, hopefully Alcatraz