Fork Preload and Travel?

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Dan1950

Dan1950

1974 MK II Roadster
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After replacing my long gators with the short American type, my fork seems to not have the same spring rates as before. I am bottoming out far too often. Given that I am pushing 280#, I think increasing the spring rate might be advisable. Also with the Old Britt's oil pressure gauge I am hitting the front fender when the fork bottoms out. I have shortened the tube until the banjo is pulled up tight against the stem, but the fitting still contacts the fender. I have just over 4 1/2" of travel clearance.
 
There was a guy in Michigan who did a bunch of work in this area about 20 years ago. He lengthened the damper rods by an inch and added short springs to the top of the existing coil springs (I think they were Ford 8N tractor valve springs) to give you an additional 1" of front suspension travel. Might help - not sure...

Other Option: I have had good luck with the Keto Diet - lost 28 lbs since the beginning of March.... much more energy as well :)
 
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Dan1950 said:
Also with the Old Britt's oil pressure gauge I am hitting the front fender when the fork bottoms out. I have shortened the tube until the banjo is pulled up tight against the stem, but the fitting still contacts the fender. I have just over 4 1/2" of travel clearance.
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I don't think you'll be the first one with a dimple in your fender from that. I'll let somebody else with more savvy than me try and answer you other issues, but I have progressive rate springs and alloy dampers and rods in otherwise stock forks. I weigh just shy of 200 and still bottom out, and top out, on occasion. Something I've learned to live with.
 
I have the same oil pressure gauge with a hex banjo bolt, same issue with a completely stock front fork setup. They did change to a different banjo bolt that may have a lower profile that was an allen head. I doubt that changes the issue, maybe just a smaller dimple on the fender.
I'm going to do an entire front end upgrade with Lansdowne internals and turcite bushings along with the CNW seals. I'll convert the banjo bolt too.
I'll post the results later next month.
 
I had always thought the OEM Commando front end was too mushy. Yeah, thicker oil would help some....but still.
So, I installed Landsdowne Dampers. Whoa! What a transformation! Now I can dial in compression and rebound
to my preferences with a hex key at the top. I also fooled around with 3 different fork oil weights until I found
the weight that worked best for me with these dampers. My setting is fairly stiff and I have no doubt it would
solve the issue presented at the expense of a rougher ride (potholes not good) but much better handling (No more
wallowing)..
 
Dan1950 said:
After replacing my long gators with the short American type, my fork seems to not have the same spring rates as before. I am bottoming out far too often. Given that I am pushing 280#, I think increasing the spring rate might be advisable. Also with the Old Britt's oil pressure gauge I am hitting the front fender when the fork bottoms out. I have shortened the tube until the banjo is pulled up tight against the stem, but the fitting still contacts the fender. I have just over 4 1/2" of travel clearance.
Click to expand...
Interesting. I weight more than you and I have a completely stock front end. My fork tubes, bushings, and seals are new - the dampers, springs, and other components have never been changed. I sit upright and I use SAE 30 oil. I've never noticed bottoming out other than taking speed bumps too fast. I don't have the oil pressure gauge so the only indicator I have of bottoming out is the shock/noise.

I did have a customer bike onetime that bottomed out a lot - the springs were shot (about 2" shorter than the used stock springs I had) and he was using ATF. I put the used set of springs and SAE 30 in, and it was fine then. He was also heavy - probably around 260.
 
lazyeye6 said:
I had always thought the OEM Commando front end was too mushy. Yeah, thicker oil would help some..
Click to expand...
When I changed out the gators, I drained the oil from the lower legs and put in 5oz of ATF type F. That is when I noticed the difference.
 
Dan1950 said:
When I changed out the gators, I drained the oil from the lower legs and put in 5oz of ATF type F. That is when I noticed the difference.
Click to expand...
When I could get it and I weighed less, I used SAE 20. Today SAE 30 (conventional). I even do that for light customers and tell them if it is too stiff to use a lighter conventional, non-detergent (if possible) oil but recommend that they get used to it - much better damping.
 
Derek Wilson said:
There was a guy in Michigan who did a bunch of work in this area about 20 years ago. He lengthened the damper rods by an inch and added short springs to the top of the existing coil springs (I think they were Ford 8N tractor valve springs) to give you an additional 1" of front suspension travel. Might help - not sure...

Other Option: I have had good luck with the Keto Diet - lost 28 lbs since the beginning of March.... much more energy as well :)
Click to expand...
Decent Cycles, http://www.decentcycles.com/the-decent-store but it looks like they are out of stock. This kit, along with drilling and capping the drain holes to stop the top out problem made a huge difference.

@Dan1950 The progressive fork springs are good as well, I run them with the kit above.
 
Dan1950 said:
When I changed out the gators, I drained the oil from the lower legs and put in 5oz of ATF type F. That is when I noticed the difference.
Click to expand...
If you had been running oil before, go back to fork oil. I never bottomed out with my forks - either stock, progressives, or Lansdownes - using fork oil. And I am 200# + gear.
 
An old school preload botch is to put spacers twixt fork top nut and springs to preload them.
 
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The standard fork springs are already close to becoming coil-bound when the forks are fully compressed so anyone thinking of fitting additional preload spacers that reduce the fitted length of the springs is likely to result in them becoming coil-bound before the forks are fully compressed thus reducing fork travel and why the Greg Fauth/Decent Cycles modification has longer damper rods.
 
L.A.B. said:
The standard fork springs are already close to becoming coil-bound when the forks are fully compressed so anyone thinking of fitting additional preload spacers that reduce the fitted length of the springs is likely to result in them becoming coil-bound before the forks are fully compressed thus reducing fork travel and why the Greg Fauth/Decent Cycles modification has longer damper rods.
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Good point, well put.

I should emphasise the word BOTCH in post #12 !
 
Fast Eddie said:
An old school botch is to put spacers twixt fork top nut and springs to preload them.
Click to expand...
Ride height and spring rate are two different things, A usual trick, if you don't have gaiters, is to fit an electrical tie to the staunchion above the slider. After you ride the bike, the tie will show where the travel ends . If the tie is high above the staunchion, either fit a spacer or a stronger spring
 
I did the Fauth fork mod to my Commando some years ago and have very pleased with it/ATF. I weigh around 170 lbs with gear (never understood why the abbreviation for pounds in weight is 'lbs"). No topping, and the only bottoming that ever occurred was when I was trying to get around traffic and dropped into a culvert I didn't see 'till I got there! But no damage to me or the bike - just rode up out of the culvert and got around the traffic! No, I don't recommend that maneuver.

Fauth mod handles great. Of course, unlike the Lansdown mod, there is no adjustment so what worked well for me/my weight, might not work well for someone much heavier.
 
acotrel said:
Ride height and spring rate are two different things, A usual trick, if you don't have gaiters, is to fit an electrical tie to the staunchion above the slider. After you ride the bike, the tie will show where the travel ends . If the tie is high above the staunchion, either fit a spacer or a stronger spring
Click to expand...
And preload is a third!

Which is the OPs question…
 
Derek Wilson said:
Other Option: I have had good luck with the Keto Diet - lost 28 lbs since the beginning of March.... much more energy as well :)
Click to expand...
In 2019 I lost 125# with Weight Watchers (and exercise) in a little less than 1 year. With the pandemic closing down the live meetings and going through a divorce, i put about 60# back on over 2 years. I'm hoping that the live meetings resume. I need the support for motivation.
 
Dan1950 said:
In 2019 I lost 125# with Weight Watchers (and exercise) in a little less than 1 year. With the pandemic closing down the live meetings and going through a divorce, i put about 60# back on over 2 years. I'm hoping that the live meetings resume. I need the support for motivation.
Click to expand...
What better motivation do you need than the price of gas these days ;)
 
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