Problem with suspension

[Vargas]

I bought a nice front suspension fork for my CB. After grounding the disk brake supports I installed it and then found it doesn't pass under the frame - I can not turn the front wheel 180 degrees because a knob on top of the crown hits the frame. See picture below.

This was easy to solve. Using my dremel I ground part of the knob and now the wheel turns 180.

Then I went out for the first ride and found my leg touches the same knob when pedalling.

This is a picture of myself at riding position and my leg touching the kinob.

Again my leg touching the knob from a different perspective.

I really didn't know what to do. The fork was quite expensive.

What I tried was moving the seat support all the way back in order to bring the pedal closer, raising it. That didn't solve the problem. These previous pictures were taken with the seat support all the way back.

Any suggestions different from "Buy another fork without any knobs"?

What I also tried was raising the seat with a 20mm hard blue EVA foam I had at home. This solved the problem. In case I don't get a better solution I might buy a black piece of EVA, a little bit softer than the one I have and use it.

 

[Charles.Plager]

A couple of (probaby not very

A couple of (probaby not very useful) thoughts:

(1) Can you add a spacer underneath so there's more clearance?
(2) For riding the bike, one generally doesn't turn the wheel that much. I can't tell how far it can turn, but maybe it's enough
(3) The offset of the fork isn't much, you could try running it forward and see how badly the bike handles (the offset of the fork is not large, but I it may still be large enough to make this idea a bad idea).

Good luck!
Charles

 

[floridabike]

Put Spacers on the bottom

As Charles suggested, put the spacers that you have on top on the underside of the frame and it will increase the trail slightly and it looks like the fork doesn't have much of an offset so if you put the spacers under the frame and turn the fork around you may still have a positive trail and plenty of clearance for your leg.

Phil

 

[John Tolhurst]

The lower cone sits

The lower cone sits on a slight sholder at the base of the fork steering tube. It cannot be spaced up.

 

[floridabike]

This should work

I forgot to mention that you would need the 'crown race' to place on the top of the spacers and that should work. I used a plastic spacer for the picture demonstration.

Phil

 

[floridabike]

This should work

I forgot to mention that you would need the 'crown race' to place on the top of the spacers and that should work. I used a plastic spacer for the picture demonstration.

Phil

 

[John Tolhurst]

cone fits on 30.0 +.05-.0

@floridabike,
I believe the cone will not be tight against the steerer, because the steerer OD is too small for it. Steerer is 28.6, while the sholder that the cone fits on is 30.0 +.05-.0

 

[Vargas]

Three options to solve it

Spacers underneath was a brilliant idea - until I read what JT wrote

But I still like very much CPLAGER idea of adding clearance underneath. What I could do is find a 1 1/4 steerer tube and have it machined to 1 1/8 from where the spacers would end. Then I would need no spacers. The sholder would be machined between the 1 1/4 and 1 1/8 interface. It would need to be machined to fit into the crown too.

So I see three options to solve the problem:
1 - Machine a 1 1/4 steerer tube (have to find it first) to 1 1/8 leaving 1 1/4 where the spacers would be.
2 - Purchase a SR original fork. @JT are they already available?
3 - Add a spacer underneath my ass - the 20mm EVA foam.

Option 3 is in place at the moment. Is it worth going for option 1 or 2? Which pros would they have compared to option 3?

Comments on CPLAGER thoughts:
(1) Can you add a spacer underneath so there's more clearance?
Answer: This at first sounded like a brilliant suggestion.
(2) For riding the bike, one generally doesn't turn the wheel that much. I can't tell how far it can turn, but maybe it's enough
Answer: True. But to carry it in my car etc I need to turn the front wheel 180 degrees.
(3) The offset of the fork isn't much, you could try running it forward and see how badly the bike handles (the offset of the fork is not large, but I it may still be large enough to make this idea a bad idea)
Answer: The offset you see in the pictures above is A, but the total offset is B, which is large. I'd rather not try this suggestion.
But let me tell you I really appreciated your sugestions.

 

[John Tolhurst]

The foam is your simplest

The foam is your simplest answer.
SR forks are not available seperately. Difficult to get them made and they all sell wtih the complete bike.
Machining down a 1 1/4 steerer will leave inadequate wall thickness. However, if y ou took the steering tube out and went to a machine shop asking for a copy with a longer base .. possible .. or asked them to machine a new sholder for you to slide on before adding the cone, also possible.

 

[Vargas]

Yes, the foam is the simplest

Yes, the foam is the simplest solution and adds confort to a very important body part

Thinking a little bit more about it, I can put the spacers I have on top, underneath. And machine the top one, or part of the top one to 30.0 +.05-.0 so the cone will be tight against the spacer which has almost no slack to the steerer.

Does this make sense? Do you see any problems using aluminum spacers below the crown race and the top one machined to 30.0 +.05-.0?

 

[John Tolhurst]

The top one cannot be a

The top one cannot be a regular spacer machined down, it should begin as a collar of steel tube 1 3/8 x 1/8. Dont' make it too tall, or you'll lose projection of the fork steer out the other side where the steering extension attaches.

 

[Vargas]

Thanks John - good

Thanks John - good suggestion!

Have you got any drawings showing the sholder shape/dimensions? Then I can have the collar/sholder machined on the 1 3/8 x 1/8 steel tube without having to take the fork to the shop.

I won't make it long; something between 20 and 50 mm. I'll sit on the bike and play with PVC pipe spacers to find the right size before having it machined.

 

[John Tolhurst]

I suppose it would look

I suppose it would look something like this:

 

[Tarmac Terrorist]

My front suspension has

My front suspension has clamps the hold the down tubes, it is possible to extend or shorten the fork by 1/2 a centimeter without compromising the strength. As you can see in this photo I have the downtube extended so the knob is just visible. From your photos I can't see if yours has a clamp and maybe the downtubs are fixed into the yoke.

 

[Vargas]

@John
Perfect, thanks.  One

@John
Perfect, thanks. One little detail; the 31.8 should be 35.
@TT
thanks for the suggestion but 5 mm won't help much.

 

[1happyreader]

R U sure your not 180°

Riding the trail today I could NOT find a bike with the front brake caliper behind the fork.
Are you sure you should not have positioned the fork the other way ???

 

[Charles.Plager]

@1happyreader:
When you use a

@1happyreader:

When you use a conversion kit, you flip the fork around 180 degrees.

 

[John Tolhurst]

31.8 was enough

@John
Perfect, thanks. One little detail; the 31.8 should be 35.
yes, that's what I wrote, but when I drew it, 31.8 was enough.

 

[KrautKontrol]

Suntour Swing

Here, have a look at the Suntour Swing suspension fork.

http://www.amazon.com/SR-Suntour-Swing-Shock-Steerer/dp/B004TN2C6E

Note: You will need to reverse the fork like all others at which point the "swing"
suspension mechanism will point forwardm which should work fine with the rest
of your setup.

 

[Vargas]

I like that one!

The suspension mechanism was probably designed taking into account the wheel curvature. When I reverse it, because of the triangle brackets the wheel will move towards the mechanism and might touch it. I'd need to try it before buying it or hear of someone who uses it with the kit.
But I really like the design!
And it weights exactly the same as the suspension I have installed.
Additional comment: a suspension makes a huge difference in confort - it is another bike.