[-dustin]

assuming just the average frame, how does the geometry of a trials frame compare to that of a bmx frame?

i'm in the market for a bike to play around with, and was thinking bmx, but today, some dude told me he was selling his mod trials bike for 300$. i'm considering checking it out if the frame geometry would be similar to that of a street/dirt bmx frame. i figure i'll go up to 500$ (i'd rather buy a good frame with descent components), so think someone could reccomend something in the street/dirt department around that price? another guy i know is selling his K2 Mainline for 100$...my main ride is an On-One Inbred SS with a 23.7" TT if that makes a difference.

p.s. - i'm pretty anal about my bikes, and don't really enjoy having the same thing as 4 other kids on my block.

 

[shootr]

what are you going to use it for?

if you want a trials bike buy a trials bike.. If you want a BMX buy that , there is a tremendous diff in the geometry between a 24" trials and a 20" bmx, and even a 24" bmx...
the head angles on a BMX are way steeper.

decide what exactly you want to do with the bike, and then get one that suits your needs, otherwise you will be dissapointed in whatever you buy.

 

[-dustin]

i thought the mod trials frame was for 20" wheels?

 

[Toshi]

This is an interesting question. The geometry will be very different:

- the trials bike will run a long fork as compared to the bmx, for hooking over obstacles
- the trials bike will likely have a 19" rear wheel (so its brake mounts will not work with a 20" wheel), unless it is really cheap
- I'm not sure which of the two will have a steeper head angle, as my old mod felt very twitchy and downright scary at speed yet bmxs are steep, too
- the bottom bracket will likely be higher on the trials bike
- you will not be able to run a large chainring unless you are willing to allow it to extend beyond the bashguard. yes, the bashguard.

The verdict: unless you want a trials bike, don't buy one. It will make a horrible bmx, and with stock gearing (which is what you need for pure trials moves) it will be a lame street bike as well. There was talk about slapping together a mod with an internally geared rear hub on mtb-trials a few moons back to make it more suitable for street, but unless you're willing to go to that length just for the sake of being different, then stay away from the mod.

 

[shootr]

Toshi, the BMX will have a steeper head angle, but the reason that the trials feels twitchier is that it has FAR more negative caster
This is because of the fork design.

Caster is just what it sounds like, when you extend a line thru the king pin (the head tube in a bike) along it's prescribed angle it will intersect the ground at some point. If this point of intersection occurs in front of the tire, (or actually the spot of the tire which contacts the ground), the bike will have what is known as "positive caster" and if the intersection is behind the contact point it has "negative caster"..
to understand how this actually effects the wheel think of the caster wheels on your chair. the king pin is vertical so it's angle never changes, and it is placed to the extreme end of the wheel, so it intersects in front of the contact point (extreme positive caster), this is why the wheel ALWAYS wants to follow in a straight line behind the king pin...NOW try turning the wheel so that IT is in front of the king pin and push the chair...SEE the wheel IMMEDIATLY wants to turn and swivel around to the back..that is what happens with NEGATIVE CASTER, the wheel constantly wants to turn around..since there is sweep in the fork, the wheel feels "twitchy", because the intersection is well behind the contact patch, even with a shallower head angle..
ON a BMX even with it's steep head angle, the intersection is at or VERY near the contact patch, making it feel more stable, and with BMX race bikes (with shallow head angles) the intersection is well ahead of the contact patch, making them feel very stable at speed.

I hope that this explanation helps..

 

[Toshi]

Thanks for the explanation. That definitely explains the whole "feels-like-it's-going-to-flop-over" feeling.

 

[axel]

if youre going to spend 500$, you can get a pretty damn good new bmx. i got my s&m dirtbike classic for 500 with 3 pc. cranks, nice wheels and real nice components, i would recomend checking out one of your LBSs to see what they have, as it is much better to test ride a bike, than purchase it online. and whatever you do, dont get a trialss bike and try to use it for BMX or visa versa.

 

[-dustin]

yeah, the LBS would be a good idea, but during the summer i'm at least an hour away from any bike shops, and most of those just stock mtb and road stuff ('cause they're relatively small). i think the one here now has a couple Specialzied bmxs, not too sure, though.

did you get your S&M from a shop, or second hand? i couldn't find any prices on them over the net, but i was in hurry so i didn't look too much.

 

[axel]

i got it at danscomp.com

 

[NoseDiver666]

First off, there was a 20" trials bike a couple years ago. Real long top tube, short seat tube, hydraulic brakes, no seat. Worked extremely well for trials. Not good for BMX. If you want to do spins, dirt jumps, ramp riding, that kinda stuff, get a BMX. There are several companies out today, new ones who have completes for $350 to $400 that are amazing. Federal, WTP, Eastern, Macneil, S&M. Any local shop with any sort of BMX line will have access to order bikes, even if they don't stock them. Trust me, I used to work in one. Look for common parts to determine in they carry brands, Eastern can be secured from shops if the have QBP (which most do, very large distributor). WTP, MacNeil, and Federal all come from Tip Plus, you'll have to ask if they carry that one. They have a website you can see all their new stuff, its www.tipplusbmx.com. Any decent shop will carry one or more of these distributors. If you want you can go to manufactuars site, check who distributes, then go to that site for dealer locators. 24" bikes are way different, especially BMX vs trials. Steep head angle gives a different control factor. Not many companies out the offer good 24" crusiers. Shawdow has one, DK and Haro also make one. Pick what kind of riding you want to do and go with that. $500 will get an extremely good BMX bike (3-pc cranks, light frame, good wheels, etc).