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-   -   Fork effect on Wheelbase/Geomtery? (https://www.bikeforums.net/singlespeed-fixed-gear/725995-fork-effect-wheelbase-geomtery.html)

RoadJerk 04-07-11 03:55 PM

Fork effect on Wheelbase/Geomtery?
 
Can somebody tell me the names of some forks that make your wheelbase shorter and make your bike have a tighter geo? (If this is even possible?) I don't even know if different forks affect geometry much on the same frame, but I kind of feel like they do, considering the distance from the top of the wheel to the crown of the fork seems to vary on certain forks.

Do forks come in different lengths for track bikes? Or does only the rake vary?

The fork I currently have I feel is rather large and makes a huge gap (about 1.5in) between the circumference of the front tire and the downtube. I feel like if I had a shorter fork with the same or less rake I could bring the wheel in closer and have a tighter, twitchy-er handling. Advice please

Squirrelli 04-07-11 04:05 PM

less rake, more trail, more stable, less twitchier.

Track forks are relatively short rake, usually in the neighbourhood of 28-32mm. Paired with a headtube angle of 74-75, it will result in a relatively shorter trail which makes the bike relatively twitchy at a low speed but very stable at high speed.

RoadJerk 04-07-11 04:10 PM


Originally Posted by Squirrelli (Post 12474114)
less rake, more trail, more stable, less twitchier.

Track forks are relatively short rake, usually in the neighbourhood of 28-32mm. Paired with a headtube angle of 74-75, it will result in a relatively shorter trail which makes the bike relatively twitchy at a low speed but very stable at high speed.

Hmmm... I'm a bit confused. So less rake makes a shorter wheelbase which makes for twitchier low-speed handling but more stable high speed handling? What about fork length, does that ever vary?

Squirrelli 04-07-11 04:17 PM

they are generally about the same length, give or take 3-5mm.

Yup, short rake is more stable but you also have to take into chainstays account because shorter stays will have a faster acceleration than longer ones.

Rob Glatfelter 04-07-11 04:34 PM

Just get one of these.
http://leagueofbikepolo.com/sites/lo...93c0c928b4.jpg
26"s, but oooh dat headtube angle.
You want twitchy!

lz4005 04-07-11 07:11 PM

Some forks are a little longer to allow space for fenders and/or larger tires, but that isn't going to do what you want it to do. Reduced rake will get you twitchier steering.

http://farm5.static.flickr.com/4005/...1ab528a3c2.jpg

dookie 04-07-11 08:07 PM

^^

that's what i was gonna say. just turn it backwards!

(real answer: consider that the whole bike is a system. you don't just slap a new fork on a frame not designed for it, in order to make it 'tighter'. you want a short-wheelbase, instant-response track bike? buy one. don't put a track fork on your tourer.)

lz4005 04-07-11 08:33 PM

For the record, that's a motopace bike. They were designed to draft behind a motorcycle. The tradeoff of the crazy twitchy steering is being able to ride closer to the motorcycle for lower wind resistance. Plus the badassery of the giant chainring.

RoadJerk 04-07-11 09:48 PM

1 Attachment(s)
Observe:
http://i54.tinypic.com/wbuuzm.jpg

Above is an image showing the Kilo TT fork's dimensions superimposed onto a photo of my bike's frame and stock fork, both scaled equally. One can see clearly that the Kilo TT's fork not only has less rake than mine, but it ALSO appears to be shorter from axle to headset! Look at the the distance between the top of the tire and the top of the fork crown/bottom of the headset. My fork definitely adds at least a half inch of height there above the crown.

I know you can't really measure accurately from photographs, but these are taken pretty much perpendicular to both bikes, and the difference is big enough to see easily. I posit to the scientific community, that, If I put the TT's fork on my frame, it would make for a significantly tighter geometry than with the stock fork.

Does anybody know where Mercier gets the TT forks from, or what they are called? Or ones like them?

yummygooey 04-07-11 09:58 PM

You can buy a Mercier Kilo fork from the BikeIsland website.

xkillemallx16 04-07-11 10:05 PM

the crosslakesales is 1.125" while the kilos is 1", it wont work. dont worry about your geometry being tight or not, if you get a fork with less rake or axle to crown you will alter the geometry to the point where its uncomfortable and handles like crap. also consider trail, which determines your steering - the less rake, the more trail, thats why steep angles are paired with tight forks and 72.5deg. headtubes are paired with road forks.

also consider if you have too little space between dt/wheel, fenders will be difficult if not possible. my sks raceblades barely fit on my rush, i'd actually prefer a bit more space.

if you want track geometry/look, get a track frame.

EpicSchwinn 04-08-11 01:30 AM

I'm interested in this too. Surely someone on here has tried it?

Squirrelli 04-08-11 01:49 AM

Articles about fork rakes, steering and headtube angles.

http://davesbikeblog.blogspot.com/20...le-bit-of.html

http://davesbikeblog.blogspot.com/20...-steering.html

http://davesbikeblog.blogspot.com/2006/06/squirrelly_30.html'

Highly recommended to read all of them.


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