|  | Topic : Fork preload spacer |  |
| | | drhach | | Set |  | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 26 Aug 2014 - 14:43 Post title : Fork preload spacer | | | Does anyone know offhand what the diameter of the fork preload spacer is? I'm trying ot add a little more preload and I don't want to disassemble the bike twice to do it. I know what lentgh to add bt I don't know diameter.
Thanks,
Dan
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| | | AleXL4 | | Chaac | |  | | Reg. Date | : | 17/09/2012 | | Posts | : | 571 | | Location | : | Gympie, Queensland, Australia |
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| | Posted : 27 Aug 2014 - 01:22 Post title : Re: Fork preload spacer (Re: drhach) | | | Hello Dan,
I use 40mm HD PVC orange conduit, electrical type.
Your local electrician or maybe your local hardware store should have some.
Cheers
Alex
| Enjoying the Journey
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| | | peteronkarra | | Chaac | | | | Reg. Date | : | 01/04/2012 | | Posts | : | 829 | | Location | : | Karragarra Island, Queensland, Australia |
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| | Posted : 27 Aug 2014 - 01:41 Post title : Re: Fork preload spacer (Re: AleXL4) | | | I use 1 1/2" exhaust tube.
Pete
| I sometimes wonder what I"ll do when I grow up.... but not very often 
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| | | daz | | Zeus | |  | | Reg. Date | : | 12/05/2009 | | Posts | : | 7,686 | | Location | : | United States |
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| | Posted : 27 Aug 2014 - 03:11 Post title : Re: Fork preload spacer How | | | How log a piece do you guys use, and is it really hard to get the fork cap back on?
| 2010 Blue/White Thunderbird, "Brutus". 1700 kit, short tors, gutted cat, UNI filter, filter seal off, custom tune. Brutus in his native habitat: Link
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| | | PapaSmurfMC | | Chaac | |  | | Reg. Date | : | 03/10/2013 | | Posts | : | 871 | | Location | : | Philadelphia, Pennsylvania, United States |
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| | Posted : 27 Aug 2014 - 04:14 Post title : Re: Fork preload spacer How (Re: daz) | | | daz wrote:
How log a piece do you guys use, and is it really hard to get the fork cap back on? |
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The spacer should be cut to give close to 30mm of static sag. If your sag is greater than 30mm, a longer spacer will increase your preload/reduce sag and of course a shorter spacer will reduce the preload/increase sag. There are lots of resources on the web with detailed instructions of how to do this; just google "static sag adjustment". There is some trial and error involved in cutting the spacers, checking sag between each cut; last time I did this it took about 3 trims of the spacers to home in on 30mm but it was well worth the effort.
To replace the fork caps, I found that using a palm ratchet with a short socket extension lets you rotate the cap with one hand while pushing down with the other (gripping the extension) enough to engage the threads pretty easily. Just be very careful not to cross-thread.
| 2013 Blue Marble Haze Thunderbird 1600 ABS
2009 Black Bonneville A1 ("Mag")
Buncha farkles
| | Post edited by PapaSmurfMC on 27 Aug 2014 - 04:15 |
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| | | daz | | Zeus | | | | Reg. Date | : | 12/05/2009 | | Posts | : | 7,686 | | Location | : | United States |
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| | Posted : 27 Aug 2014 - 04:52 Post title : Re: Fork preload spacer How (Re: PapaSmurfMC) | | | So not likely gonna be able to thread the cap w/o a "palm ratchet"? Never heard of that.
| 2010 Blue/White Thunderbird, "Brutus". 1700 kit, short tors, gutted cat, UNI filter, filter seal off, custom tune. Brutus in his native habitat: Link
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| | | drhach | | Set | | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 27 Aug 2014 - 14:55 Post title : Re: Fork preload spacer How (Re: daz) | | | Thanks guys. I measured my "Rider" sag, which is different from "Static" sag. Most accounts I've seen say that Rider sag should be about 1/3 of total fork travel. I know that the bike has 120mm of total travel, so, I'm shooting for 40mm of rider sag. Right now, it's set to 60mm (50% of total travel). I think in the end, I'm going to end up with a new spring, but I want to get my sag right first and then see how it does. I've been researching the hell out of this. I also bought RaceTech's Suspension Bible. In spite of all of that, it is still hard to find much good info.
I've had a lot of frustration trying to root information out of the "experts" about how best to choose a spring. I called Racetech and the salesguy immediately said I needed a heavier spring. I wasn't sure how he knew this given that I never told him anything about how the bike was acting or even what model it was. 
So, one thing at a time. Get the sag right and see how it performs. While the springs are out, I'm going to take some measurements so I can know exactly how much they're being compressed and how long they are uncompressed. The tuner I spoke with told me that his shop typically shoots for 10-15mm of spring compression for the bike to be at rest (static sag). This guideline coupled with a 40mm Rider sag should tell me what rate I need.
One of the things I'm also discovering is the notion of the air spring. The volume of air in the fork has a big affect on harshness. As the fork compresses, it reduces that air volume in the cylinder. The air in the cylinder acts like a spring. A smaller volume will stack up more quickly (harsher) a larger volume will compress more (Plusher). The air volume acts in conjunction with the spring to create a "progressive" spring system. You can use a straight rate spring and adjust the progressiveness with the air spring.
Naturally there is the back of the bike too, but doing the front is chepaer and I can do most of it myself, so I'm tackling that first.
Dan
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| | | peteronkarra | | Chaac | | | | Reg. Date | : | 01/04/2012 | | Posts | : | 829 | | Location | : | Karragarra Island, Queensland, Australia |
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| | Posted : 27 Aug 2014 - 21:07 Post title : Re: Fork preload spacer How (Re: drhach) | | | Dan
I also have been researching the bejesus out of this subject lately, several of the sources I came across suggest the oil level/air volume has an effect on the last third of travel. The idea of adding air pressure to the forks used to be popular with the dirt bike riders back when I started riding 40 years back. They would have a Schrader valve in the fork cap and add air pressure that way, I think they were only using a few PSI. The only issue with this or raising the oil level in the forks can be if you get too carried away the pressure in the forks on compression can be too great for the fork seals and blow them.
When refitting the fork caps I fit them first without the spacer to find the point of engagement of the threads, mark the cap and the fork tube. When I fit them with the spacer I start about 1/8 th turn back from that point. I then know when the thread should be engaged and how engaged it is.
Pete
| I sometimes wonder what I"ll do when I grow up.... but not very often
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| | | drhach | | Set | | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 27 Aug 2014 - 22:15 Post title : Re: Fork preload spacer How (Re: peteronkarra) | | | Thanks Pete. It was recommended to me to put a bleed valve in the system in order to bleed off excess air. I'm not a dirt bike guy but the tuner I was talking to is a dirt bike guy. He said that common practice is to fully extend the forks and release air pressure before riding. This minimizes the air spring effect. I doubt I'll be drilling and tapping any air bleed holes in my forks.
I put some zip ties on my forks in order to see where full compression takes place. It's quite a ways off from the full 120mm travel. I thought this was due to the spring beng too stiff but I hadn't considered the air mass' effect. First is preload and proper spring selection.
One more thing. The guy I spoke with suggested an experiment. To illustrate the true effect of the air spring, he suggested removing the fork springs and adding the quantity of oil that they displaced. After that, close the forks up without the springs. You should not be able to bottom the forks. The air volume is cushioning their travel (ideally the last 1/3 as you've said). He advocated removing oil in 5ml increments until you almost bottom the forks, then remove the spring volume and put the springs back in. This will be the plushest setup. Of course there would still need to be enough oil in the system for the forks to operate and you still will need the right spring.
I'll let you guys know how it goes.
Dan
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| | | AleXL4 | | Chaac | | | | Reg. Date | : | 17/09/2012 | | Posts | : | 571 | | Location | : | Gympie, Queensland, Australia |
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| | Posted : 28 Aug 2014 - 12:11 Post title : Re: Fork preload spacer How (Re: drhach) | | | Dan,
A guide to the calculation of your fork spring rate: Link
Good info in the Tech Articles in the above link. Under Information down left hand side.
Consider the use and effect of Linear Rate Springs as compared to Progressive Rate Springs on a Cruiser/Touring motorcycle.
Alex
| Enjoying the Journey
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| | | drhach | | Set | | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 02 Sep 2014 - 21:29 Post title : Re: Fork preload spacer How (Re: AleXL4) | | | Ok guys. I just wanted to post a quick follow up. I did some preliminary measurements. I'll post them here in case anyone else needs them or can speak to them. First is an observation. According to the factory specification, the front fork has 120 mm of travel. With the fork cap removed and the spacer and spring removed, I was only able to achieve 110 mm of travel. I'm guessing there's a top out spring that may be holding the other 10 mm in reserve.
So, for anyone's reference, I measured the fork spring to be 356 mm end to and and 41.35 mm wide. The preload spacer that the factory uses is 190 mm long. Theres also a washer (or spacer) between the spacer and the spring. I didn't think to measure it, but I would say it is at most 2 mm thick. I measured the compressed length of the spring to be 20 mm. This is the amount that the spring is compressed in the fork with the wheel off the ground. In other words, this is the amount that the fork cap comes up when you loosen it. So, there are 20 mm of compression before the wheel ever touches the ground. From the point the wheel touched the ground until the fork settled (static sag), I measured 40 mm of travel. That's without me on the bike. I also found from a post on this site that the front end weighs 339 (153 kg) lb and the rear weighs 379 (171 kg). I wonder if someone could confirm this, I don't have a good scale.
Based on a spring constant of 0.9 kg/mm I calculated for a spring that is compressed 60 mm to be 54 kg per leg, or about 118 kg spring force for the front end. This is obviously off from the amount I gave above. The only thing I can think to explain this is that total weight takes in to account unsprung mass, which the spring does not register. Is it possible that the wheel, brake and fender assembly wieghs close to 77 pounds?
So, assuming I'm in the ballpark with my estimations, I want 40 mm of travel for rider sag (not static sag). The force exerted on this would be equal to what I was getting for my static sag setting. I calculated that I need a 1.2 kg/mm spring. What's funny is most online calculators I've used say "1.1" So, however, they're arriving at their numbers, they're coming pretty clsoe to what I calculated. I may actually go to a 1.1 and call it a day.
Also, I removed 5 mL of oil from each fork tube hoping to increase my air spring a little. It didn't make a huge difference. I don't want to go too far until I have my new spring though.
Next steps, get a new spring and set rider sag.
Just to make it easier, here is a list of my measurements for a stock bird (2010 SE)
Spring compression with stock components: 20 mm
Fork spring stock uncompressed length: 356 mm
Fork Spring O.D.: 41.35 mm
Fork Preload Spacer length: 190 mm
Front Wheel weight [lb]: 339
Front Wheel Weight [kg]: 153
Rear Wheel Weight [lb]: 379
Rear Wheel Weight [kg]: 171
Measured Fork Travel: 110 mm
Static sag (front): 40mm
Dan
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| | | davetac1 | | Thunderbird | | | Reg. Date | : | 06/09/2010 | | Posts | : | 8,379 | | Location | : | Haverhill, Ma., United States |
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| | Posted : 02 Sep 2014 - 21:48 Post title : Re: Fork preload spacer How (Re: drhach) | | | If anyone is lookin for a picture [EXPLODED VIEW] of what's inside of somethin,like the front forks on a Tbird [in this case],and ya don't have a SM,go to the Bike Bandit website and punch in your make,model,and year, and you'll get an EXPLODED VIEW of any and all parts/pieces used in that application.That's what I do and have bought a few parts from them for different applications I've owned and or worked on. Dave!!!
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| | | drhach | | Set | | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 03 Sep 2014 - 15:56 Post title : Re: Fork preload spacer How (Re: davetac1) | | | That is a good resource. I used it a lot when I was rebuilding my 78 GS1000.
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| | | PapaSmurfMC | | Chaac | | | | Reg. Date | : | 03/10/2013 | | Posts | : | 871 | | Location | : | Philadelphia, Pennsylvania, United States |
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| | Posted : 19 Oct 2014 - 03:23 Post title : Re: Fork preload spacer How (Re: drhach) | | | drhach wrote:
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Next steps, get a new spring and set rider sag
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Hey Dan, did you ever get that spring (and where)? How'd it work out?
| 2013 Blue Marble Haze Thunderbird 1600 ABS
2009 Black Bonneville A1 ("Mag")
Buncha farkles
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| | | RichDesmond | | Set | | | Reg. Date | : | 19/10/2014 | | Posts | : | 1 | | Location | : | United States |
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| | Posted : 19 Oct 2014 - 14:53 Post title : Re: Fork preload spacer How (Re: drhach) | | | drhach wrote:
Ok guys. I just wanted to post a quick follow up. I did some preliminary measurements. I'll post them here in case anyone else needs them or can speak to them. First is an observation. According to the factory specification, the front fork has 120 mm of travel. With the fork cap removed and the spacer and spring removed, I was only able to achieve 110 mm of travel. I'm guessing there's a top out spring that may be holding the other 10 mm in reserve. |
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Exactly right, the spec'd travel includes compressing the topout spring completely. Real world travel is usually 10-15mm less than the spec.
So, for anyone's reference, I measured the fork spring to be 356 mm end to and and 41.35 mm wide. The preload spacer that the factory uses is 190 mm long. Theres also a washer (or spacer) between the spacer and the spring. I didn't think to measure it, but I would say it is at most 2 mm thick. I measured the compressed length of the spring to be 20 mm. This is the amount that the spring is compressed in the fork with the wheel off the ground. In other words, this is the amount that the fork cap comes up when you loosen it. So, there are 20 mm of compression before the wheel ever touches the ground. From the point the wheel touched the ground until the fork settled (static sag), I measured 40 mm of travel. That's without me on the bike. I also found from a post on this site that the front end weighs 339 (153 kg) lb and the rear weighs 379 (171 kg). I wonder if someone could confirm this, I don't have a good scale.
Based on a spring constant of 0.9 kg/mm I calculated for a spring that is compressed 60 mm to be 54 kg per leg, or about 118 kg spring force for the front end. This is obviously off from the amount I gave above. The only thing I can think to explain this is that total weight takes in to account unsprung mass, which the spring does not register. Is it possible that the wheel, brake and fender assembly wieghs close to 77 pounds? |
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Wouldn't surprise me if all that weighed 50lbs, so you're in the ballpark. There's also a contribution from the air spring component, although it's very small with the fork only compressed 40mm.
So, assuming I'm in the ballpark with my estimations, I want 40 mm of travel for rider sag (not static sag). The force exerted on this would be equal to what I was getting for my static sag setting. I calculated that I need a 1.2 kg/mm spring. What's funny is most online calculators I've used say "1.1" So, however, they're arriving at their numbers, they're coming pretty clsoe to what I calculated. I may actually go to a 1.1 and call it a day.
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The "1/3 of travel" rule for sag isn't really right, it's a holdover from the early days of dirt bike suspension tuning. For street bikes 28-30% is a better place to start. For most street bike that ends up in the 33-35mm range.
Also, I removed 5 mL of oil from each fork tube hoping to increase my air spring a little. It didn't make a huge difference. I don't want to go too far until I have my new spring though.
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Opposite way. :) Removing oil decreases the air spring effect, adding oil increases it.
Next steps, get a new spring and set rider sag.
Just to make it easier, here is a list of my measurements for a stock bird (2010 SE)
Spring compression with stock components: 20 mm
Fork spring stock uncompressed length: 356 mm
Fork Spring O.D.: 41.35 mm
Fork Preload Spacer length: 190 mm
Front Wheel weight [lb]: 339
Front Wheel Weight [kg]: 153
Rear Wheel Weight [lb]: 379
Rear Wheel Weight [kg]: 171
Measured Fork Travel: 110 mm
Static sag (front): 40mm
Dan
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Thanks for all the info, very helpful.
| | Post edited by RichDesmond on 19 Oct 2014 - 15:03 |
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| | | PapaSmurfMC | | Chaac | | | | Reg. Date | : | 03/10/2013 | | Posts | : | 871 | | Location | : | Philadelphia, Pennsylvania, United States |
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| | Posted : 20 Oct 2014 - 04:11 Post title : Re: Fork preload spacer How (Re: PapaSmurfMC) | | | Good news. After scouring the web for linear-rate springs, contacting a few vendors and coming up empty, I pestered Rich at Sonic Springs. I put in Sonic linear-rate springs and carefully set up sag in my previous bike and they transformed the front end. So, steered Rich to the stock spring measurements posted by drhach (Dan) and Rich found compatible Sonics at 1.00kg/mm and 1.10kg/mm and added them to their catalog. They're available here: Link
Ordered mine today. 
| 2013 Blue Marble Haze Thunderbird 1600 ABS
2009 Black Bonneville A1 ("Mag")
Buncha farkles
| | Post edited by PapaSmurfMC on 20 Oct 2014 - 04:12 |
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| | | drhach | | Set | | | Reg. Date | : | 18/10/2011 | | Posts | : | 250 | | Location | : | Waukegan, Illinois, United States |
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| | Posted : 20 Oct 2014 - 18:29 Post title : Re: Fork preload spacer How (Re: PapaSmurfMC) | | |
"Also, I removed 5 mL of oil from each fork tube hoping to increase my air spring a little. It didn't make a huge difference. I don't want to go too far until I have my new spring though.
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"Opposite way. :) Removing oil decreases the air spring effect, adding oil increases it."
Thanks for the correction Rich. I think what I meant to say was "I removed oil in the hopes of increasing air spring volume to reduce the spring effect".
PapaSmurf, that's great news. I gave up on finding alinear rate spring. I called a few places that specialized in springs and really couldn't get anyone to offer anything other than what they had in their catalogs. let me knwo how the installation goes. That will be one of my winter projects this year.
After that comes the rear end.
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| | | Slcharger | | Jupiter | |  | | Reg. Date | : | 18/02/2016 | | Posts | : | 1,661 | | Location | : | Denmark |
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| | Posted : 09 Mar 2016 - 15:35 Post title : Re: Fork preload spacer How (Re: drhach) | | | Reading this thread i observed that some of you use other than stock spacers. Please be aware that using spacers with different diameter or wall thickness, will change the volume it represents, and therefore in most cases will decrease total air volume, and so increase the air spring rate. The volume of the replacement part should be calculated and the difference to the stock spacer volume, the equivalent volume of oil should be removed.
May not apply in all cases, with thin wall tubes, but thicker wall tubes certainly do change the volume.
| Big Bird, Bordeaux with " Celtic theme " Airbrush, 2010, 1700CC, ABS, 65.000 km. Lowered with Nitros rear shocks, Linear front springs, Burchard forward footrest kit, Kuryakyn ISO grips, LOTS of chrome, SLcharger REV2+ tune, Modified Cee Baileys windshield, Oil pressure gauge, Air box elimination kit, Portet cylinderhead, Intake cam advanved 8 degree, Exhaust cam retarded 2 degree, 10.5 C/R, Knock sensor, Machined flywheel, DNA Chrome Spoke wheels, 18x8.5"- AVON AV72- 240/40/18, 21x3.5"- AVON AV71- 120/70/21, Corbin seat with backrest, 20W fork oil. Hiflo HF303RC oil filter, Penrite Racing 20-20W60 engine oil, Adjurl lights.
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