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-   -   Crit bike geometry? (http://www.bikeforums.net/framebuilders/573048-crit-bike-geometry.html)

acer910 08-11-09 08:15 PM

Crit bike geometry?
 
I'm looking to build a "crit bike" frame. Basically, a crit bike is almost like a track bike but made for criteriums. Shorter chainstay, higher bb, sharper headset angle ETC. Sadly, nobody makes these bikes anymore so I don't have a bike to base my geometry off of. I do not know anyone with one of these bikes and I would really like to own one as would alot of people I know.

If anyone actually knows what i mean by a crit bike and knows some general dimensions off the top of their head I'd greatly appreciate the help.


Thanks,
Ben

Rosso Corsa 08-11-09 08:18 PM

I would start with a cheap aluminum Leader road or even track frame.
Or
CAAD9

NoReg 08-11-09 08:50 PM

Try the search function. There have been previous threads. One went on for 111 posts. Tends to get nasty. :)


At least one thread had some dimensions.

merlin55 08-11-09 08:52 PM

assuming you are say 5'10 to 6' tall: 73.5 to 74 degree head tube, 73 to 74 degree seat tube, b/b height of 10.65 inches, wheelbase of 39 inches. This will give a quickly handling crit bike than is very easy to pick lines through corners. I've ridden for many years, and my after work ride is on a virtual crit course, about 20 very tight radius corners taken at 20 to 25 mph per 7 miles....which I ride 3 to 5 laps every afternoon....and after doing this ride 1000's of times on dozens of bikes, the above specs seem to work the best for me

tuz 08-12-09 07:02 AM

Yes there was a rather heated discussion on the crit geometry :)

I have a Gios compact, which has a geometry something close to what you're looking for. 74* parallel angles and short 39.5cm chainstays (the dropouts are sliding and have some 1cm of fore/aft movement). The BB height however is rather standard at 26.6cm, and so is the rake at 45mm. This puts the trail at around 50mm.

Trakhak 08-12-09 11:24 AM

Quote:

Originally Posted by tuz (Post 9469174)
Yes there was a rather heated discussion on the crit geometry :)

I have a Gios compact, which has a geometry something close to what you're looking for. 74* parallel angles and short 39.5cm chainstays (the dropouts are sliding and have some 1cm of fore/aft movement). The BB height however is rather standard at 26.6cm, and so is the rake at 45mm. This puts the trail at around 50mm.

Thanks for the link. That was a wild ride. Wonder if that thread would have gone on for 5 pages if the OP had avoided that upsetting "crit geometry" term, as in, for instance, "Does anyone still build a road bike with steep, nearly track-bike-like angles"? And parts of the discussion remind me of a story about Kris Kristofferson, I think it was, who once told a music business executive, "You don't have 20 years of experience in music. You've had 1 year of experience 20 times."

merlin55 08-12-09 01:22 PM

Quote:

Originally Posted by tuz (Post 9469174)
Yes there was a rather heated discussion on the crit geometry :)

I have a Gios compact, which has a geometry something close to what you're looking for. 74* parallel angles and short 39.5cm chainstays (the dropouts are sliding and have some 1cm of fore/aft movement). The BB height however is rather standard at 26.6cm, and so is the rake at 45mm. This puts the trail at around 50mm.

Higher bottom brackets reduce the chance of striking a pedal in a corner. You have to be riding fast and have some serious lean going on while pedaling to touch a pedal, which I do about once a year....so far just a light touch and no crashing. (KOW) It seems to happen when I hit a corner hard with lots of lean, and start pedaling again too soon out of the corner....much less exiciting than trying to pedal through a corner and hitting a pedal at the apex

26.6 cm is only 0.45 cm less than my 10.65 inch suggestion. Depending on the length of your crankarms and choice of pedals can influence the max lean angle more than the slight BB difference we are talking about.

zzzwillzzz 08-12-09 05:36 PM

go to vintagecannondale.com and look at the pdfs of old catalogs from 1990 when they first came out the the 3.0 model. they had a crit frame and a road frame at one point, in '90 they might have just had the crit frame. i had one and it was awesome, super stiff and very quick handling especially for that time.

Six jours 08-12-09 10:35 PM

I raced a bunch of "crit" frames in the eighties when that was the hot ticket. Typically 75 head angle, 74 seat, and the generic 4 cm. of rake, all on my 58-59 cm. frames. BB was generally a tad higher than standard, maybe 27 cm. or so.

I was really into that geometry as a young hotshot. Then I had my first stage race frame built up and discovered that twitchy bikes suck under all circumstances. I won just as many crits with the stage race geometry, and my shoulders didn't hurt anymore from having to fight with an unstable bike.

Everyone seems to have to figure that out for themselves, though...

acer910 08-13-09 10:57 AM

well, the person who told me about crit frames lead me to believe nobody talks about them anymore because its a "forbidden" topic (and i can see why is it started an 11 page argument). I've seen people hit their pedals during alleycat races in historic downtown, it makes you cringe but its also kinda funny until it happens to you.

but thanks for all the suggestions. and one last thing, 4130 chromoly would be a decent steel to start with right...

Six jours 08-13-09 05:57 PM

If you really want, you can build a bike with "standard" geometry and a high bottom bracket. I personally think a low bottom bracket feels more stable than a high one, but it's very slight -- and as you've seen, a lot of folks argue that it's imaginary.

Then again, we could also start a spirited fight over the supposed value of pedaling through corners... :D

4130 is the only place to start for a beginning framebuilder, IMO.

acer910 08-13-09 06:40 PM

i just need a bike, dont have the cash for a highend bike (my ability to ride fast is growing faster then my ability to make money), love making stuff and already have all the tools. That and i can get up to 15 feet of any tubing for free through my work. i reckon that should be enough for a bike? haha

Road Fan 08-15-09 03:18 PM

Quote:

Originally Posted by Six jours (Post 9481223)
If you really want, you can build a bike with "standard" geometry and a high bottom bracket. I personally think a low bottom bracket feels more stable than a high one, but it's very slight -- and as you've seen, a lot of folks argue that it's imaginary.

Then again, we could also start a spirited fight over the supposed value of pedaling through corners... :D

4130 is the only place to start for a beginning framebuilder, IMO.

I think my Woodrup is a good example of that! Only non-standard thing is teh 44 cm chainstays. But BB drop is only 6.5 cm. Other than that it's a road bike.

acer910 08-15-09 07:33 PM

i have another question and i dont want to start a whole new thread.
but whats a good wall thickness for 4130 chromoly tubing for road frames? and should it be thicker for mtb frames?

JohnDThompson 08-15-09 09:41 PM

Quote:

Originally Posted by acer910 (Post 9493734)
i have another question and i dont want to start a whole new thread.
but whats a good wall thickness for 4130 chromoly tubing for road frames? and should it be thicker for mtb frames?

How heavy are you? How tall are you? What type of riding?

Yes, an off-road frame should in general use thicker tubing than e.g. a crit frame.

acer910 08-16-09 07:16 PM

im 6 foot, 150lbs.
XC racing. il be putting a front suspension fork on it but im going to leave it hardtail. i think il wait until i get the hang of this before i attempt a road frame. id rather it fall apart in the woods going 15mph then on asphalt going 35mph


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