Fork bottoming - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 4 (permalink) Old 08-16-2016, 09:19 PM Thread Starter
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Fork bottoming

So...

I have an interesting challenge. I acquired a race RC51 over the winter; cheap and with some of the good bits, at least in theory. Or at least -- better bits than I am a rider, which isn't saying too much. Forks are at least in theory worked by Kyle Racing; not sure exactly when, however, or what weight they were set for and so on. Again, in theory I have the Ohlins 20mm kit in there, but haven't pulled it apart to check.

The local track has a couple of good old transitions over the edge of a banked oval. I'm ending up bottom the forks going over these; not hard, but enough that the zip-tie slider is all the way down. Did the obvious first, and had it re-sprung for my weight (200lbs without gear, these days, having porked up). Still bottoming, though i'm not getting to much from the front end on it.

The local guy had some 1.0's put in there. Same as stock, but again -- no idea what weight they were set for, and the new springs are apparently stiffer than the rest. Spacers were pretty beat up, so I figure I might need to replace those to get enough pre-load. Fresh oil at the start of the year, so not that.

Any other ideas? Appreciate the advice -- though I know the RIGHT answer (yank 'em, send 'em back to Kyle, get 'em sorted) I'm trying to do this on the cheap as an RC51 isn't exactly a dynamite bike for a small, rough, tight track. FUN -- but certainly not the fastest, so don't want to sink a tonne of money into it.
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post #2 of 4 (permalink) Old 08-17-2016, 10:31 AM
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Zip-tie is not a good indicator of what is really happening. Additionally if you really do bottom out a fork it is a HUGE hard smash that will not only get your attention, but usually cause a crash. If you are carrying any lean whatsoever coming off the banking and actually bottom the forks they will instantly wash the front end out from underneath you.

The first question is what are your current sag numbers & the second is how much preload did you have to use to get those numbers? Without knowing those 2 things the rest of this conversation is pointless.
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post #3 of 4 (permalink) Old 08-23-2016, 06:30 PM Thread Starter
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Quote:
Originally Posted by LDH® View Post
Zip-tie is not a good indicator of what is really happening. Additionally if you really do bottom out a fork it is a HUGE hard smash that will not only get your attention, but usually cause a crash. If you are carrying any lean whatsoever coming off the banking and actually bottom the forks they will instantly wash the front end out from underneath you.
Yeah. It doesn't feel like there's a HUGE smash, for sure. I wasn't convinced in the zip-tie, since I was /sure/ I'd feel it. And the
transitions aren't all straight up and down.

Reassuring.

Quote:
The first question is what are your current sag numbers & the second is how much preload did you have to use to get those numbers? Without knowing those 2 things the rest of this conversation is pointless.
THis is the part where I look like a right prat. I had 38mm or so with the old springs, and can dig out my notes on turns from my records. I haven't spent the time on the new ones to do the lift/drop -- just been too busy, so I took it out, rode it, and saw how it felt. *cough*

Luckily, I'm not the fast guy out there -- so I got away with a far less than optimal setup. Been meaning to get a mate over to shift the front around and set it up again, but just haven't had the bloody time!

Last edited by expatbrit; 08-23-2016 at 06:37 PM.
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post #4 of 4 (permalink) Old 11-03-2016, 10:36 PM
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The forks can be a little hard to extract reliable sag figures from due to their lack of internal preload and longer top out spring. Although having said that, most front sag figures are of little use.
Bring the oil level up a little and look at slightly heavier springs. 1.1s The big twins offer more compression braking and will benefit from the added stability the heavier spring offers.
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