Lowering forks in triple trees 3/4"

I have the Works 1 1/4" lower shock, and a 170/60/17 rear tire that lowers about 1/4". Initially, I raised the forks 1/2". Last weekend I raised the forks an additional 1/4 inch. I took it for a ride yesterday. All I can say is WOW. The bike feels like it lost 100 pounds. The height is right, and the bike is much easier to maneuver. I had it on the interstate at 80 and it felt rock solid.

I've read that raising the front forks 3/4" lowers the bike 1 1/2". The rear is lowered 1 1/2". I'm guessing it feels so nice because it is balanced; each end is lowered the same amount.

I just bought a 160/60/17 rear tire that I'm going to exchange for a 170/60/17. I'm afraid if I lower the rear another 1/4 inch I'll upset the balance.

jspringator said:

I've read that raising the front forks 3/4" lowers the bike 1 1/2".

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Unless you take good measurements and are a wiz at geometry and/or trig you should break out the tape measure or ruler and make your own measurements

Someone will explain it to me but I don't see how raising the forks .75" will lower the bike 1.5". I think it would lower the bike less than .75".

I'm assuming 'balance' refers to weight distribution. I'd think that with small changes in height the trail of the steering geometry is the bigger consideration and is more affected than weight distribution. The weight/mass of the tire might change handling via gyroscopic forces.

You might want to measure the trail now and compute how changes in ride height front and rear might change that.

That would give me a headache!

ST Gui said:

Someone will explain it to me but I don't see how raising the forks .75" will lower the bike 1.5". I think it would lower the bike less than .75".

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You are right. Raising the forks in the triple trees by one inch lowers the bike .887 inch, the cosine of the fork angle. No, I didn't figure it out. An engineer on the UJM forum did.

According to this, I've lowered the rear an inch and a half, but only lowered the front a half an inch. What do I do now? Should I get shorter fork springs that will lower it a like amount?

jspringator said:

What do I do now? Should I get shorter fork springs that will lower it a like amount?

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you said you liked the way it feels, so why not just ride it?

I'm an engineer and when it involves handling, I'd go with seat-of-the-pants over numerical analysis. Unless it was so out of whack to begin with that what lowering you did recently made it seem great by comparison, then you may want to ride it a while to see if its really as great as it first seemed. Any more lowering is going to reduce cornering clearance, which isn't a good thing, so I'd leave it alone for a while and see how you like the current setup.

I think it was so bad before it seemed like a huge improvement. I'll measure the distance between the top of the fender and an impact point above to verify there is enough space for the forks to compress fully, then I'll probably ride it as is. If shorter springs can help without raising the possibility of the fender hitting the tire, I may go that route.

Thanks for your input.

jspringator said:

What do I do now?

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Hard to say. Maybe nothing. First by lowering the back end 1.5" you increased trail from stock which slows down handling but usually give better straight line stability. From what I've read the ST1100 had more trail than the 1300 and the 1300's trail was decreased to give it more sport-like handling.

Lowering your front end .75" with the raising of the tubes decreases your trail somewhat giving back some quicker handling but probably slower than stock.

If you were to raise your tubes enough (clearance permitting) you'd be back at the factory spec. Raise them more than that and and now the handling is quicker than stock. That could be more fun you want at speed. (There are additional variables at play: tire brand/air pressure/suspension adjustment or wear etc.)

At this point it's all hypothetical. Seat of the pants riding can be a good enough barometer but without a fairly well-tuned tush you could fall prey to the placebo affect. To this day after every 3K mi oil change my bike always runs better. So knowing your numbers doesn't have to be the final deciding factor but it can help keep your head on straight.

If you're happy with the way it is now and there are no odd or dangerous quirks (ground/foot peg clearance): sure why not just ride it until you feel like a change.

jspringator said:

You are right. Raising the forks in the triple trees by one inch lowers the bike .887 inch, the cosine of the fork angle. No, I didn't figure it out. An engineer on the UJM forum did.

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LOL... I thought this topic seemed familiar! Ha

ST Gui said:

...no odd or dangerous quirks (ground/foot peg clearance)...

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Those are the issues that would concern me the most there...
Most might say "...I'm not an aggressive rider to begin with...", but during evasive manoeuvres or after a minor judgement error at a turn entrance, the avail max leaning angle can quickly grow very important...

Traxxion can rebuild the forks, put it where I want it height wise and replace the springs for $500. I would have to get the bike to Atlanta. If I remove the forks and ship them it would only be $400. I would rather them have the whole bike and test ride it. I'm thinking I should shoot for an inch to 1 1/4 inch lowering. That way if I have clearance problems, I can go back to a 70 series tire on the rear and raise it up a little bit.

I'm going to ride it like it is until the end of the season. It is 16 years old with 45,000 miles, so the front will need to be freshened anyway. They can leave it like it is (3/4 inch up or more) freshen everything but limit travel so there is no way the fender will contact the bottom of the triple trees. This wouldn't really be any cheaper. I can schedule a Friday, trailer down Thursday night and drive home Friday night.