CBR front end swap?

[Guest]

So a buddy of mine lowsided his 2004 cbr1000rr off a small cliff. He's fine but the bike isn't and he decided to part it out. I can pick up the front end for a good price and the forks are still straight. Anyone ever seen this swap before? My only real worry is the aggressive angle and fork length.

[rwnielsen]

The aggressive angle is in the steering head of the frame.

[John Kat]

I believe the fork legs will be too short?
Here's some info on different fork lengths I gathered some time ago:

http://www.thegsresources.com/_forum/showthread.php?t=186805

[mmattockx]

I expect the fork legs will be too short, but that is easily confirmed with a tape measure. Another concern is if you use the complete CBR front end you will end up with way more trail than stock and heavy steering that is more bump and rut sensitive than original.


Mark

[John Kat]

I expect the fork legs will be too short, but that is easily confirmed with a tape measure. Another concern is if you use the complete CBR front end you will end up with way more trail than stock and heavy steering that is more bump and rut sensitive than original.


Mark

The trail will increase ONLY if the bike stays level.
Given that the fork legs are much shorter the caster angle will decrease bringing the trail back to a more normal value.
Roughly speaking for every 2.5 cm decrease of the front height ( or increase of the rear) the caster angle will decrease by 1°.

[mmattockx]

The trail will increase ONLY if the bike stays level.
Given that the fork legs are much shorter the caster angle will decrease bringing the trail back to a more normal value.
Roughly speaking for every 2.5 cm decrease of the front height ( or increase of the rear) the caster angle will decrease by 1°.

OP will run out of ground clearance before he gets enough rake reduction to keep the trail reasonable. The 17" front radial will help with reducing the steering effort but there is simply no way to not gain a bunch of trail when swapping in a modern front end. I have a set of forks from a 2003 GSXR600 in my basement, they have just over 32mm of offset. The CBR front end will be similar. My '82 1100E has close to 50mm (based on a quick measurement in the garage).

One of the big reasons the early 90's GSXR1100 front ends work so well as a swap onto the GS bikes is that they ran fairly conservative rake angles and small trail amounts, which means they end up with pretty decent steering geometry numbers when combined with the more raked out GS chassis.

A question for OP: do you plan on swapping in a wide 17" rear wheel to mount the matching rear radial to go with the front 120 you will get with the CBR front end? Or are you planning on making the skinny GS front wheel work in the CBR fork?


Mark

[Sci85]

You could also go with different triple clamps with more offset. Each mm of triple clamp offset is roughly the same trail change all else being equal. But that's one of the most expensive ways to make that change unless you can find some that are adjustable used maybe. Emulators and fork braces can make a significant difference for a whole lot cheaper btw.