Shortening an FXR swingarm

[Wil_K]

Hi all,

I am interested in shortening the swingarm on my FXR. Has anyone here done this modification that can offer some advice?

Mainly I want to know:
1) How much can it be shortened by? I don't want to take too much off and ruin the handing. I don't mind moving the shock mount back if needed to keep the suspension ratio and ride height similar to stock.
2) Are the handling improvements noticeable and significant enough to reduce lap times?
3) Does anyone have a spare swingarm they want to sell?

Cheers

[Askor]

Just ride the damn thing. The time, effort, and money you spend attempting to shorten the swingarm would be better spent on more track time.

More laps = more better

[Wil_K]

I am an engineer and I enjoy making improvement to the bike as much as riding it. Cutting and welding the swingarm isn't going to cost me a cent. I am a quick rider and get as much track time as I can, never miss a practice or race day. The four weeks between meets can go to improving the bike.

[Grumph]

I am an engineer and I enjoy making improvement to the bike as much as riding it. Cutting and welding the swingarm isn't going to cost me a cent. I am a quick rider and get as much track time as I can, never miss a practice or race day. The four weeks between meets can go to improving the bike.

While the above is admirable, think about what you want to do a little longer...
Shortening the arm puts more weight on the rear wheel - taking it off the front...
The class leaders in NZ using FXR engines are undoubtedly the GPR boys - and those frames have more front end weight bias than OE - not less.
And a more radical steering geometry to go with the weight bias.
If you want a project for your FXR, look at doing an adjustable geometry steering head bearing setup, the rewards are potentially much better.

[chrisc]

Wil, chat to Rick Ford. He did it on the FXR he used to have.

[chrisc]

Come on guys, shortening a swing arm and trying it out will mean he learns something. Instead of saying don't do it, maybe share some insight into what might happen so he can give it a shot. It's only a FXR.

Wil, I have a spare FXR swing arm I don't need that you can modify.

[Bert]

Nice words Grump.

A long time ago I managed to shoehorn a TF100 into a FXR frame (prior to the rule change allowing FXRs).
I chased around handling for a long time until I found some fork modification suggestions. I found that getting the weight forward and getting those slicks working (closer to their intended operational loading the temperature yielded the best results).
Drop the forks through 30mm, add 8mm of preload, 10 weight oil. Stage2 changes to the damping holes (this is actually covered in the FXR forum).
but I am slow...

[Henk]

Wil

I have two spare swing arms if you want to have a go at chopping one up.
On the plus side if you modify one and hate it swapping it back is a fifteen minute job as long as you have a spare chain the right length on hand.

[Wil_K]

Grumph:
Thanks for your input. That is just the sort of information I was hoping to extract from the experienced folk. So if the swingarm is shortened, then would a solution to the rear wheel weight transfer be to increase the rear ride height to shift more weight to the front wheel and at the same time making the steering geometry more aggressive?

Chris:
Thanks for the swingarm, I will most likely take you up on that offer. Will get in touch via FB if I do. Yes I have heard of Rick Ford having done it, and know Terrene's FXR had a shortened swingarm. I had a look on Saturday and it didn't look like much length was removed. It was carted off by its new Wellington owners before I could get the tape measure out. She said she could feel the difference compared to a stock FXR, didn't get a chance to talk to Rod about it.

Bert:
When you say drop the forks 30mm do you mean 30mm from the triple clamp to the top of the fork tube? FXR manual says 50mm, but this seems like too much. Most FXRs i have seen don't have it that high. Mine is 45mm. I have cartridge emulators fitted. Too early to tell if they have been a worthwhile investment. Have done one meeting since fitting them with the recommended baseline settings. Front end feels good, I had no problems with the front over the weekend. Rear was sliding lots, especially on the Saturday with the cooler track. I would like to be able to turn the bike tighter and faster without feeling like I am close to losing control which led me to the whole shorten the wheelbase thing.

[MrMarko]

I would simply slot out the axle adjusment slot further first... get it as far forward as you can without the middle of the tyre hitting the swingarm, shorten the chain to suit and trial it.

[Wil_K]

Wil

I have two spare swing arms if you want to have a go at chopping one up.
On the plus side if you modify one and hate it swapping it back is a fifteen minute job as long as you have a spare chain the right length on hand.

Thanks Henk, as always you are one helpful and generous bastard. I will probably grab that one off Chris. Unlikely he will ever get on one of those Malaysian commuter bikes again now that he has moved on to his GP framed machines.

[Grumph]

Grumph:
Thanks for your input. That is just the sort of information I was hoping to extract from the experienced folk. So if the swingarm is shortened, then would a solution to the rear wheel weight transfer be to increase the rear ride height to shift more weight to the front wheel and at the same time making the steering geometry more aggressive?

That's a short cut, yes. It can work well enough too.
To get weight forward on the basically stock chassis the easiest way is to move you...Clipons with a forward extension, a seat hump - taped as a trial.
My suggestion of adjustable steering head would be worth pursuing. have a look on the chassis thread for the RS125 geometry and compare. Measure, adjust and try.

[Wil_K]

I would simply slot out the axle adjusment slot further first... get it as far forward as you can without the middle of the tyre hitting the swingarm, shorten the chain to suit and trial it.

I like your thinking. That is a pretty good idea. Could go 15-20mm further forward by the looks. Guess I would have to modify the brake carrier too.

[MrMarko]

I like your thinking. That is a pretty good idea. Could go 15-20mm further forward by the looks. Guess I would have to modify the brake carrier too.

The brake carrier should slide forward with the axle? can't recall its about 6 or 7 years since i had my fxr bucket. i sold it to the club and its used as the bike for people to try out buckets on at mt wellington. still around apparently.

[Wil_K]

The brake carrier should slide forward with the axle? can't recall its about 6 or 7 years since i had my fxr bucket. i sold it to the club and its used as the bike for people to try out buckets on at mt wellington. still around apparently.

Would have to have a closer look at it but, I thought the retaining protrusion on the swingarm would hit the back of the slot on the carrier it moved further forward than it was designed. Anyway no big deal.

Unfortunately the old Mt Wellington club hack was stolen a few months back. Henk Zeeven has fronted up with a new one.