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Old 02-27-2013, 09:28 AM   #1
ironjack63 OP
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fork oil

Okay, I find I need help once again. I went out to buy fork oil today so I can put my r100rt back together, and I could not find any 7.5 weight fork oil in this town. The few bike shops here are Jap crotch rockets or HD and they both appear to use heavy weight oil in their forks. Does anyone have a good alternative short of ordering online?
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Old 02-27-2013, 09:42 AM   #2
kaput13
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You could use ATF fluid until you send out for proper fork oil. It will work but you might have difficulty determining its true viscocity.
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Old 02-27-2013, 09:48 AM   #3
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Quote:
Originally Posted by ironjack63 View Post
Okay, I find I need help once again. I went out to buy fork oil today so I can put my r100rt back together, and I could not find any 7.5 weight fork oil in this town. The few bike shops here are Jap crotch rockets or HD and they both appear to use heavy weight oil in their forks. Does anyone have a good alternative short of ordering online?
10 weight would be fine in an RT.
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Old 02-27-2013, 09:56 AM   #4
One Less Harley
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order the weight you want, or hove one of the local shops order some for you.
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Old 02-27-2013, 11:56 AM   #5
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IMO, heavier than 7.5 Spectro gets you too much compression damping in '84 and earlier forks. The choice is usually between 5 and 7.5. The later forks? Picking between 7.5 and 10 usually works.
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Old 02-27-2013, 12:00 PM   #6
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I have bought 10 and 5 weight oils and mixed them 50/50. Unscientific but it works out to a 7.5 to me.
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Old 02-27-2013, 12:06 PM   #7
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I use Bel Ray Fork oil. 10 weight, but have been know to mix 10 weight and 15 weight for a stiffer ride. You can also use 10 weight and increase the oil volume a little bit until the ride is comfortable. There are lots of variations, but remember, it is always easier to add oil than to pull it out.

With the RT fairing you can stand to run it a little stiffer than recommended. I always do.
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Old 02-27-2013, 12:26 PM   #8
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Originally Posted by boxerkuh View Post
I use Bel Ray Fork oil. 10 weight, but have been know to mix 10 weight and 15 weight for a stiffer ride. You can also use 10 weight and increase the oil volume a little bit until the ride is comfortable. There are lots of variations, but remember, it is always easier to add oil than to pull it out.

With the RT fairing you can stand to run it a little stiffer than recommended. I always do.
I am just trying to help a common misconception but you probably do not need or really want 12.5 wt oil versus 10wt. I highly suspect what would make your bike work even better is more spring preload versus heavier oil. Trying to set the spring up with oil isn't the answer.

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Old 02-27-2013, 06:41 PM   #9
ironjack63 OP
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I bought Yama lube 10 weight oil today, because that is all that is available around here. I don't mind a little more compression, as I am a bit heavier rider than probably the majority of the r100 riders today. I put 1 inch pvc spacers in my 2012 Bonneville, and that worked out great. The front end is way better than stock with that little addition. So, I am good to go with trying 10 weight oil.
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Old 02-27-2013, 08:06 PM   #10
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Here's something of interest.http://www.bmbikes.org.uk/Forum/view...ork+oil#p89718

Read the attached spreadsheet in one of the replies, comparing fork oil W between brands..


Motul 10W seems to operate equivalent to BMW 7.5w.

The W can be different between brands, so if you're keen to be exact...

http://widman.biz/English/Calculators/Mixtures.html

Otherwise, it all gets down to what feels best for you for the type of riding you do.
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Old 02-27-2013, 08:18 PM   #11
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Originally Posted by boxerboy81 View Post
Here's something of interest.http://www.bmbikes.org.uk/Forum/view...ork+oil#p89718

Read the attached spreadsheet in one of the replies, comparing fork oil W between brands..


Motul 10W seems to operate equivalent to BMW 7.5w.

The W can be different between brands, so if you're keen to be exact...

http://widman.biz/English/Calculators/Mixtures.html

Otherwise, it all gets down to what feels best for you for the type of riding you do.
+1 For some reason, I have used Spectro fork oil my entire life. It's what we had at my dad's shop and what I have used every since. Spectro dino oil and Blendzall bean oil. Both good stuff to this day!!! BMW fork oil is Spectro oil
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Old 02-28-2013, 09:28 AM   #12
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I recall reading some where that fork oil in the older BMW (presuming non cartridge) forks controls rebound, primarily. I did experiment with this a bit when I was setting up my forks. If it feels like it's bouncing down the road, then that is probably a rebound issue (assuming the sag and what not is correct, as supershaft was saying). I noticed this with 7.5 wt oil. I put synthetic ATF in and it cured the bouncing.

Keep in mind that there is no set standard between fork oil manufacturers.
One company's 10wt may be another's 7.5 wt.. So try to stick with one brand if you are looking to experiment.

A lot of suspension guys like using ATF because its always a certain wt. So they have a constant base line. I used it because none of the shops around me carry multiple weights from the same manufacturer.

So, what does the the bike feel like?
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Old 02-28-2013, 11:05 AM   #13
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ATF is nominally 7 cSt at 100 deg C so not too far away from 7.5 fork oil but then 100 Deg C is a crazy way to rate fork oil. I always do the comparisons at 40 C which is what the previously mentioned charts are really about. If an oil manufacturer doesn't provide the viscosity at 40 C I won't even consider it. I shoot for approx. 28 cSt at 40C which is a little thinner than ATF at 36 cSt.


Strangely mixing 5 and 10 weight oil 50:50 doesn't result in exactly 7.5 but the difference isn't worth worrying about when compared to the differences between brands. As a rough guide the oil will come out approx. 6% thinner than you expect. if you really want half way between two oils mixing 60% of the heavier oil with 40% of the lighter will get you closer. For a more precise figure there are online calculators to be found.

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Old 02-28-2013, 01:21 PM   #14
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Quote:
Originally Posted by supershaft View Post
I am just trying to help a common misconception but you probably do not need or really want 12.5 wt oil versus 10wt. I highly suspect what would make your bike work even better is more spring preload versus heavier oil. Trying to set the spring up with oil isn't the answer.
SS is right. Seems like I regularly see guys posting about using heavy weight fork oils. How much better their suspension would perform with correct spring rates and a lighter oil (correct preload, sag, etc., etc,). Heavy oil gives too much damping for these old bikes! Another common problem I see with the late model adjustable forks (and rear shocks, too) is that guys crank UP the compression and rebound damping. I would rather go with springs slightly too stiff and damping slightly too soft. There are articles and books written on suspension set-up (educate yourself), and plenty of guys who know how to set up these old Beemers correctly.
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Old 02-28-2013, 01:52 PM   #15
supershaft
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Quote:
Originally Posted by batoutoflahonda View Post
I recall reading some where that fork oil in the older BMW (presuming non cartridge) forks controls rebound, primarily. I did experiment with this a bit when I was setting up my forks. If it feels like it's bouncing down the road, then that is probably a rebound issue (assuming the sag and what not is correct, as supershaft was saying). I noticed this with 7.5 wt oil. I put synthetic ATF in and it cured the bouncing.

Keep in mind that there is no set standard between fork oil manufacturers.
One company's 10wt may be another's 7.5 wt.. So try to stick with one brand if you are looking to experiment.

A lot of suspension guys like using ATF because its always a certain wt. So they have a constant base line. I used it because none of the shops around me carry multiple weights from the same manufacturer.

So, what does the the bike feel like?
I wish oil in our forks effected primarily rebound. That would be awesome. I would throw some 25wt in mine and get my rebound around where I want it. The problem with going that route is that you end up with way too much compression damping. Too much compression damping gets you chatter and your front tire losing grip for the suspensions reaction time being slowed too much. It's the whole point of going the emulator route. To finally separate compression and damping so that you can finally get enough rebound without too much compression. Then people with emulators start changing fork oil weight when they should be adjusting the valve. Most people are determined not to win!

To me one of the funny things about setting fork preload is that most people re-adjust there preload on there shock like it was nobody's business and then never think to do up front. Maybe because it is a lot more work? Preload doesn't change the springs rate, it changes the fork and shock's rate from one end of its travel to the other.

Most of you guys know I am just trying to help. It seems as if I have got some people thinking about fork preload and sag. Like I always say and don't forget once you get started: Sag is THE place to start. BUT! It is only the beginning! You can change preload just enough to not even effect sag and still make a big difference in how your bike rides. Get your sag in what I call your 'zone' wherever that is (most of it depends on your rear shock setup!) and then a washer's thickness more or less preload can make all the difference.

Someone mentioned people jacking up all the damping. I agree! Don't go there. Nevertheless, I run my shock rebound to the max and my shock compression on 0. I run 15wt oil in my Mono forks and would run 25wt if it weren't for that getting me too much compression. But I ride with a lot of 'spirit'.

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