GSX1100G rake fix?

[GregT]

Well aren't you clever, I'll let you keep that technic in Australia.

The brits developed many ways of changing steering head angle. Usually for trials use. From jacking the bike up in the air and heating the top tubes until the frame sagged - to, yes, running it into a wall...
Personally I'd have no problem cutting, jigging and rewelding to achieve the desired head angle. But y'know, if good old Amurrican technology can't do it, well, go find a suitable wall....

 

[Buffalo Bill]

Don't be so worried about cutting and welding Rick, won't cost much, far less than buying the wrong forks.
"Any job worth doing, is worth doing right."

 

[Guest]

In that case jack up the rear 3/4"-1", drop the front 1/4"-3/8" and call it a day. Changing the forks is a waste of time and won't do anything useful for you. All of the sport bike forks have minimal offset to work with 23 degree rake angles and will result in way too much trail on a 32 degree steering head.


Mark

I've been thinking about that. I still have the rear shocks for the '07 750 and an 04 R6. I may take some measurements an see if they may be a little taller. I have the feeling that my bike may be lowered a little. I have to lean it a little to the right to swing the kick stand out. I recently change the rear tire with a slightly taller profile, but it didn't feel like any change was made in the steering. I'll look at the front end tonight and see if there is any room to drop the front in the trees. I can always change the fork spring spacer to some PVC that is a little shorter.

 

[Guest]

The brits developed many ways of changing steering head angle. Usually for trials use. From jacking the bike up in the air and heating the top tubes until the frame sagged - to, yes, running it into a wall...
Personally I'd have no problem cutting, jigging and rewelding to achieve the desired head angle. But y'know, if good old Amurrican technology can't do it, well, go find a suitable wall....

There are plenty of chopper builders around that I could have that done. As far as me doing that, I don't have the welding skills good enough to trust on something as critical as the steering head. I don't weld enough to have that skill set, but I'm sure I could do it if I did. We have no problem building things on this side of the pond, plus our wall isn't up yet.

 

[RichDesmond]

In that case jack up the rear 3/4"-1", drop the front 1/4"-3/8" and call it a day. Changing the forks is a waste of time and won't do anything useful for you. All of the sport bike forks have minimal offset to work with 23 degree rake angles and will result in way too much trail on a 32 degree steering head.


Mark

Yep. Especially the bit about modern offsets. Slapping a modern front end on is going to make things worse, not better.

Rick:
To summarize, when starting with a given bike there are 4 things that affect trail. Rear height, front height, steering head angle and triple offset.
If you're looking for easy and/or low cost mods the ride heights are the place to start. Slide the forks up in triples as far as you can without causing interference (pull the springs to check at full compression) Look at the rear dogbones. If they are just flat pieces of steel you can make new ones out of steel stock with a saw and a drill. Typically, shorter dogbones raise the rear. It helps to have some idea about the linkage ratio, but 2.5:1-3:1 range is common, so if your new hole centers are 10mm closer together the rear will rise 25-30mm.
You have to be very careful about shock swaps, you need to consider both length and spring rate. It's unlikely that a shock from a significantly lighter bike is going to be both longer than what you have now and have a suitable spring rate.

On the SV 650 it takes about a 3mm change in ride height to get 1mm change in trail. I haven't done the math on a bike with significantly more rake, but I think the ride height changes would have a bigger effect. If you raise the rear 30mm and lower the front 15mm you might get a 20mm reduction in trail, which you'll be able to feel.

As I said earlier, it really helps to calculate what you have now, and if you do that you'll be able to tell how much changes in ride heights are going to change trail. A sheet of graph paper, some good measurements and a little high school trig are all you need.