Measuring suspension travel and tire clearance.

papadapalis

papadapalis

New Member
I am in the process of finishing my frame, namely the rear hoop, and I need to make sure my rear wheel is not going to make an attempt to get too friendly with my rear end.

What method would one use measure the maximum travel of rear shocks to check the amount of frame/tire clearance?

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It is always good to say what year and model bike you are asking about.

Take one rear shock off, ratchet strap the swingarm to the frame and tighten it till the shock bottoms out.
 
I have a table so my method is more difficult for those who don't. But first I measure the space from the top of the shock body to the bottom of the rubber bump ring at the top of the shock shaft, using a set of inside calipers. I write that measurement down and call it "A". I then measure the distance between the bottom mounting bolt of the shock to the upper shock bolt on the frame, write it down and call it "B". Then I place a holding jack under the frame to support the bike on the table, then I remove both shocks off the bike. I go back to my measurements and subtract "A" from "B" and write down the result, call it "C". Now I start placing blocks of wood under the rear tire until the swingarm is lifted so that the lower shock mounting bolt is the distance "C" from the upper shock mounting bolt. At the point when the mounting points are "C" apart I check to see where the rear tire comes close to the rear frame hoop, and ensure that there is a minimum of 3/4" between the tire and the hoop as well as any pan I may want to place between the frame rail to hold electronics or the such. :o

Complicated I know but it never has failed me.
 
It's a 1976 cb550k.

So would I measure basically what is exposed of the shafts between the bump stop and shock body? Or do I need to account for some amount of squishing of the bump stop?

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papadapalis said:
It's a 1976 cb550k.

So would I measure basically what is exposed of the shafts between the bump stop and shock body? Or do I need to account for some amount of squishing of the bump stop?

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Click to expand...
You need to not follow the steps above because they will only give you an estimate, and the instructions are obviously over complicated. That might come off harsh but it is what it is. Use the ratchet method i posted to get an exact measurement of the neccessary clearance and be done. I don't see how using a table, lift or the ground would make the slightest difference. That's because it wouldn't.
 
After you take the time to post a pic of the results of the procedure I suggested, I'll take the time to explain what you do next. or if I'm lucky someone else will
 
Cars or bikes always the same. Run the suspension through its complete travel with the shock installed without the spring (assuming it is a coil over). The rubber bump stop can compress a LOT so add more than you think it will ever compress. The size of tires varies quite a lot, so add at least 1/2" from whatever tire you are using now. That will give you the point at which you can still actually have contact with the tire, so add a safety factor. Another 1/2" is what I use, but I like to live dangerously!
 
Before you focus on that though, mock up your bike with wheels and tires and front end - everything, and make sure you have the swing arm where it is supposed to be. With rider on the bike and full of fuel, you want the wheel and counter shaft sprockets and the swing arm pivot all on a straight line.
 
Okay so I put one shock on, and ratchet strapped it down until it was firmly on the bump stop.

With the wheel the whole way forward I had about 1 1/4" of clearance at the closest point.

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With the wheel all the way back I had about 1 5/8"

877eea8d00feec6c41adbc5582f0a504.jpg


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