How high does the road holder fork compress?

Captain B

Captain B

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Jan 21, 2009
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I have a 75 850 Commando roadster. I put a zip tie on the fork to see how much travel I use while riding. It is maxing out with a 3 inch gap above it. Is that where the fork normally tops out?
 
It all depends on what oil/grade you use, springs installed etc etc and the road conditions, hit a big pot hole and can bottom out the forks easy, also weight of the rider and how heavy of a load you are carrying all plays a part in how far the forks will travel or bottom out as well the condition of the forks.
 
Commando forks have a max travel of 6". The distance you should be looking at is that between the zip tie and the top of the slider (at the dust seal). If you measure that with the bike on the center stand and weighted at the back so the front fork is fully extended, you can see how close to the 6" full travel you are getting. As ashman said, with stock fork setup you can certainly bottom them out in some situations, particularly on the '75 e-start model, the heaviest of the Commandos.

Ken
 
There's actually 3 mechanisms that could determin the limit of travel. Damper travel length, Spring travel length, or fork slider travel length. The OEM damper travel length is 7" so it's not the damper cartridge limiting travel. The springs total amount of travel before it's coil bound factors out to be about 4.875" so that might be the shortest element of the three. The fork slider travel I can't actually measure at the moment without taking stuff apart but I would guess it's at least 4.875".

When you calculate in the amount of rider sag in the spring from rider weight, which reduces the compression travel distance by nearly an inch, the maximum safe travel distance without bottoming or topping out the spring is probably about 4" (LAB is generally right about stuff) If you are measuring your slider travel with a zip tie and you are getting 4" of travel without clunking on compression or rebound, you probably have a good spring rate for your weight and are close to the correct oil viscosity too if you have acceptable low speed damping performance.
 
o0norton0o said:
The fork slider travel I can't actually measure at the moment without taking stuff apart but I would guess it's at least 4.875".
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Approximately 4.15 inches. It can't be more than the distance the springs become coil-bound and the forks should become fully compressed before that happens.
 
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L.A.B. said:
Approximately 4.15 inches. It can't be more than the distance the springs become coil-bound and the forks should become fully compressed before that happens.
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Thanks for that info, I'm doing some damper mod testing and I've swapped dampers 3 times in the last 2 months and never once did I remember to measure that... It's a pretty important to know the travel limit if you're trying to use as much of the available travel possible without bottoming, or topping, out. The other 2 travel distances I measured off of parts that are out of the bike.
 
L.A.B. said:
However, the damper assemblies reduce the fork movement to just over 4 inches.
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Oops. My bad. 6" was the amount given in the service manual specifications, but I should have remembered from past experience with the forks that actual travel in use was a lot less. Just another senior moment.

Ken
 
jan nelder said:
what testing are you doing?
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I modified 20mm showa dampers to fit in my commando. They are similar to the one's that Cosentino engineering makes for commandos. Individual compression and rebound valves in each fork with shim stack secondary circuits for separating the high speed and low speed damping responses...

I made a few sets to try a few options. One damper cartridge with an internal top out spring, one with no internal spring, but with a progressive suspension spring, and one with a softer suspension spring. I'll be doing viscosity testing this coming riding season just so I learn a little more about that...

commando dampers2.jpg
 
Thanks everyone! I'm trying to ride pretty hard on country roads to test it. I don't feel it bottoming out, but I'm wondering if I could be getting more compression out of the setup. It won't compress further, so I know I'm using all I have, but it seems like there's a good bit of fork showing above the seals and I'm wondering if I should be investigating if there's something prematurely binding it up or something.
 
You realise that the spring rate and damping in the front forks and the rear shocks affect the steering as you brake and accelerate ? - The rake on the steering head changes - altering spring rate and damping changes the rate at which that happens.
 
Captain B said:
Thanks everyone! I'm trying to ride pretty hard on country roads to test it. I don't feel it bottoming out, but I'm wondering if I could be getting more compression out of the setup. It won't compress further, so I know I'm using all I have, but it seems like there's a good bit of fork showing above the seals and I'm wondering if I should be investigating if there's something prematurely binding it up or something.
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I think what you might mean to say is, "get more travel out of the set up". The maximum travel is 4-1/8" as LAB pointed out. After your fork slider moves 4-1/8" there will be a clunk as hard parts of your slider bushings collide with the slider or fork tube. Tuning for the maximum length of travel with the OEM fork dampers is only a single aspect of suspension that isn't the most significant one for road riding...

In the case of the OEM suspension, just go for a feel that is in between , the best tire grip without feeling harsh or feel like the tire is skipping (heavier fork oil), and being so soft that the handling is sloppy (lighter fork oil). The OEM parts kind of suck (but work in a rudimentary way). If you are going to stick with OEM dampers at least upgrade them to Jim Schmitt's damper upgrade parts kit. You still will be tuning performance with only your oil viscosity choice, but at least your damper parts tolerances will let those different viscosity choices actually change the response more accurately... (Just my opinion..)
 
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Back when Noah built the Arc , they used ATF with STP , which was stiffer . So more STP more stiffness , to toon .

The Prog. rate springs are intresting . My 1000 year old Triton forks , short road roadholders , had external prog. rate springing .
On the Road , it'd let the move . Whereas on the Track , they didnt . in comparison . Under ' Full ' brakeing & combat .

Actually , they threw about 2 1/2 inch . Eraly Commando guard just tapped the steering dampener lower threaded wotsit ,
the ding in the guard made it apparent that occasionally they used the full available travel . Like where the put FLAT bridges
on steep declines . Seemed to be some ' quicker - stiffer ' factor somewhere . The Dampner assys were semi polished & Id say
custom race built , somewhere . In the early 60's . The Olde ' attention to detail ' and precise fit & operation , being noted .

SO ; might be worth establishing a primary ' soft ' rate , then throwing the ' supersonic landing ' rate over that .
likely the 2/3 rd travel ' rally ' set up , where the last third ( or quater ) travel is say fully laden , dropped 6 foot . :eek: to bottom out .

Presumeably thye damping was semi progressive & speed sensitive too . Was no slack & no binding , we wont mention the mouldy stauchions tho .
 
o0norton0o said:
I think what you might mean to say is, "get more travel out of the set up". The maximum travel is 4-1/8" as LAB pointed out. After your fork slider moves 4-1/8" there will be a clunk as hard parts of your slider bushings collide with the slider or fork tube. Tuning for the maximum length of travel with the OEM fork dampers is only a single aspect of suspension that isn't the most significant one for road riding...

In the case of the OEM suspension, just go for a feel that is in between , the best tire grip without feeling harsh or feel like the tire is skipping (heavier fork oil), and being so soft that the handling is sloppy (lighter fork oil). The OEM parts kind of suck. If you are going to stick with OEM dampers at least upgrade them to Jim Schmitt's damper upgrade parts kit. You still will only be tuning performance with only oil viscosity choice, but at least your parts tolerances will let those different viscosity choices actually change the response more accurately... (Just my opinion..)
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I really just want to know if it is stopping short of full compression. One time I didn’t get the front axle straight and the fork was binding, and I’ve been paranoid about the fork since. I don’t ride it for high performance. I have a Ducati 999s if I want to go too fast for my own good. 😊
I ride it just hard enough to have fun.
 
Captain B said:
I really just want to know if it is stopping short of full compression. One time I didn’t get the front axle straight and the fork was binding, and I’ve been paranoid about the fork since. I don’t ride it for high performance. I have a Ducati 999s if I want to go too fast for my own good. 😊
I ride it just hard enough to have fun.
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I should specify, that it was binding on compression before and that's what I'm looking to measure.
 
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