SP1 Fork/shock questions - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 4 (permalink) Old 02-10-2012, 09:05 PM Thread Starter
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SP1 Fork/shock questions

I have owned and absolutely loved my 2000 RC for 2 years. I do occasional track days, but mostly spirited street riding and commuting (Hey, I know it's not a commuter, but I love this thing, sound, power, etc...). It has stock suspension. May even still have stock fork oil. Previous owner owned it from 2001 until 2010 and he gave me pretty meticulous service info (oil changes, brakes, tires, battery etc..) but come to think of it, he never mentioned having the forks serviced. From the research I have done, the stock suspension is set for a 180lb rider. I want to set the suspension up more for my weight. Slightly more. 270lbs. I consulted Racetech's website and spring calculator for springrates.

Recommended Fork Spring Rate: 1.096 kg/mm (use closest available)
Stock Fork Spring Rate: .959 kg/mm(stock)

Recommended Shock Spring Rate: 10.875 kg/mm (use closest available)
Stock Shock Spring Rate: 9.8 kg/mm (stock)

I have picked up a 10.7 kg/mm spring (not from them, but the closest they listed). It was quite a bit of difference over stock compared to the front.

My questions are.

1. Their website lists a 1.0 kg/mm fork spring as the highest rate. Will a 1.0 really make that much difference over stock (.959)?

2. What weight fork oil would be recommended?

3. Will I notice any handling issues with just changing the fork oil and replacing the rear spring with the higher rate spring?

4. How thick of a shim would be recommended on the rear shock?

I know an Ohlins or other aftermarket suspension would be great, but I would just like to bring my stock up to snuff for my "larger than Honda's ideal rider" size. I am fairly pleased with the bike's handling as is, but I know it can be better.

The bike has 23,000 miles.

Last edited by 87Hurricane; 02-10-2012 at 09:30 PM.
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post #2 of 4 (permalink) Old 02-10-2012, 10:48 PM
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Originally Posted by 87Hurricane View Post
1. Their website lists a 1.0 kg/mm fork spring as the highest rate.
If you look at the alt spring model, They go stiffer.

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post #3 of 4 (permalink) Old 02-10-2012, 11:27 PM
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The service manual lists Honda SS-8 fork oil, which is 10 wt, or 39.7 Centistokes (cST) at 40 deg C.
You could try 7 or 5 wt oil if you find the forks too harsh.

You'll notice a difference in handling when you install springs to match your weight.
You'll shouldn't notice as much squat under heavy throttle, or as much dive under braking.
Some riders have installed a 3mm or 5mm shim at the upper shock mount, which raises the rear and makes the bike turn quicker.

If you're running a 190/50 tire, a change to 190/55 can also change the handling as well.
The 190/55 tire is slightly taller than the 190/50, which also raises the rear, but the 190/55 is also a more pointy (similar to a 180/55) in profile rather than round as the 190/50.
This really makes a nice change in handling.

Besides installing springs for your weight, I would try the 190/55 tire first, the decide if you want to pursue adding a shim under the shock mount.
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post #4 of 4 (permalink) Old 02-11-2012, 10:25 AM Thread Starter
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Thanks Waldo and SubSailor.

Sub- I do notice some excessive brake dive (used the zip tie on the fork slider as a visual and feel from riding) and some squat under heavy acceleration. I was thinking it was from stock springs and maybe from the fork oil. Has been that way since I bought the bike with less than 10,000 miles on it. I am running the 190/50 rear tire. I have thought about going to the 190/55, but will the more "pointy" profile result in more rapid tread wear in the center? I do commute to work on it some (50 mile round trip) and I have been generally getting 3000-3500 miles out of a Pilot Power or Pilot Power 2CT. Doesn't matter which, If I remember right, I got a little more mileage out my last PP than I did on the 2CT I ran right before it. As far as harshness, I cannot complain. Maybe a little too soft. But it does have at least 13,000 miles on the fork oil, and maybe 23,000. So you would recommend staying with the stock weight oil, and not a heavier.

I have now located fork springs from Racetech and Ohlins.

The Racetechs are 1.10 kg/mm which is almost exact rate. (thanks again Waldo)

The Ohlins are 10.5 N/mm (which according to my springrate converter is 1.07 kg/mm), a littlle lower.

So with this information, the Racetech springs would be my best option, correct? Silly question, I know.

I have also read some on here about cutting down the "top out" springs. Would this benefit me any? And where would you get the spacers after the cut? I know I could just send them to Dan Kyle Racing, but I am a hands on guy that wouild like to sharpen the handling some.
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