Tom Posted October 4, 2021 Share Posted October 4, 2021 Service is coming up, bike's going to the shop. I'll be (well technically...they'll be :D) finally putting the new shock in the rear (Nitron), and I'm already running 10N/mm Hyperpro linear springs up front. Given that I'm planning on running my front fully stock - how do I set the sag, but more importantly, what should I say to the mechanics at the shop when it comes to fork oil, what should be the air gap, should they do the measurement with Hyperpro springs in, or out? I don't know the length of those Hyperpro ones. What's the length of stock 2002 EFI Bird springs? Quote Link to comment Share on other sites More sharing options...
blackhawkxx Posted October 4, 2021 Share Posted October 4, 2021 I think I would talk to the guys at Hyperpro to get the answers to your questions as they are the professionals. Quote Link to comment Share on other sites More sharing options...
fizzy Posted October 4, 2021 Share Posted October 4, 2021 Do you mean the front is stock except for the springs? These forks as delivered by Honda are not adjustable for sag. In order to adjust sag, the spring spacer length would have to be changed. As blackhawkxx states above, check with Hyperpro. FYI: oil air gap has no affect on sag. 1 Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 4, 2021 Share Posted October 4, 2021 46 minutes ago, fizzy said: FYI: oil air gap has no affect on sag. Wrong. 1 Quote Link to comment Share on other sites More sharing options...
Tom Posted October 4, 2021 Author Share Posted October 4, 2021 Just got the reply from Hyperpro, I gave them my bike's info and SKU for the springs I've purchased from them. They said the following; SAE 7,5 / 120 MM / measured without springs Quote Link to comment Share on other sites More sharing options...
SwampNut Posted October 4, 2021 Share Posted October 4, 2021 3 hours ago, fizzy said: FYI: oil air gap has no affect on sag. In which multiverse is the compressibility of air, and quantity of compressible air, not a factor? I would listen to Hyperpro. Quote Link to comment Share on other sites More sharing options...
Tom Posted October 4, 2021 Author Share Posted October 4, 2021 I'll go with their specs, they should know what they're talking about their own product. Although, if I'm not mistaken, this small air gap will stiffen up the front a lot, plus the stiff springs, I hope it doesn't end up acting like pogo, would like to avoid re-doing stuff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted October 4, 2021 Share Posted October 4, 2021 You can always fine-tune the level later by using a syringe and hose. Quote Link to comment Share on other sites More sharing options...
fizzy Posted October 4, 2021 Share Posted October 4, 2021 2 hours ago, SwampNut said: In which multiverse is the compressibility of air, and quantity of compressible air, not a factor? I would listen to Hyperpro. Compressible air gap only has a meaningful effect on fork action at the bottom roughly 25% of the stroke, giving a linear spring a progressive action. It has no measurable effect at the top where the sag is measured. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 4, 2021 Share Posted October 4, 2021 4 hours ago, fizzy said: Compressible air gap only has a meaningful effect on fork action at the bottom roughly 25% of the stroke, giving a linear spring a progressive action. It has no measurable effect at the top where the sag is measured. If the oil level is near normal a couple mm might not be noticeable, but "oil air gap has no affect on sag" isn't true because being far enough off can make a difference. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 4, 2021 Share Posted October 4, 2021 8 hours ago, FTM said: Just got the reply from Hyperpro, I gave them my bike's info and SKU for the springs I've purchased from them. They said the following; SAE 7,5 / 120 MM / measured without springs In case you don't know, fork oil labels don't always show the true viscosity. Way back I found a chart that showed different brands and labelled weights and what the actual viscosities were. Some were dead on, some were way the fuck off. Like 7.5 from brand XX was thicker than the 10 from brand Y. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted October 5, 2021 Share Posted October 5, 2021 I recall seeing that too. And I don't recall whether it was ever determined if "behaves like a 7.5" was a valid theory or not. Only way to know would be to buy a Ford cup. Quote Link to comment Share on other sites More sharing options...
fizzy Posted October 5, 2021 Share Posted October 5, 2021 1 hour ago, superhawk996 said: If the oil level is near normal a couple mm might not be noticeable, but "oil air gap has no affect on sag" isn't true because being far enough off can make a difference. How so? Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 5, 2021 Share Posted October 5, 2021 3 hours ago, fizzy said: How so? Think of it in extremes. If it's full to the top the fork won't compress at all, if it's an inch down it'll compress a little bit. If it's empty it'll compress a lot more than normal. Quote Link to comment Share on other sites More sharing options...
Tom Posted October 5, 2021 Author Share Posted October 5, 2021 9 hours ago, superhawk996 said: In case you don't know, fork oil labels don't always show the true viscosity. Way back I found a chart that showed different brands and labelled weights and what the actual viscosities were. Some were dead on, some were way the fuck off. Like 7.5 from brand XX was thicker than the 10 from brand Y. Yeah I saw those discussions but I couldn't find cSt rating of Hyperpro's oil, or whatever oil they use under their label. For my fork service I bought Motul's 5W light, which is around 18 cSt, Bird manual recommends Showa SS8, 36 cSt. Quote Link to comment Share on other sites More sharing options...
fizzy Posted October 5, 2021 Share Posted October 5, 2021 10 hours ago, superhawk996 said: Think of it in extremes. If it's full to the top the fork won't compress at all, if it's an inch down it'll compress a little bit. If it's empty it'll compress a lot more than normal. I obviously should have said "normal air gap". Didn't think that was necessary on a sophisticated motorcycle forum in the "garage". Quote Link to comment Share on other sites More sharing options...
tomek Posted October 5, 2021 Share Posted October 5, 2021 On 10/4/2021 at 9:36 AM, superhawk996 said: Wrong. Wrong. They are not pressurized, so when bike has been settling for while air pressure above oil equals outside atmospheric pressure. So the sag will be the same regardless of oli level. Let's not talk about bonehead move when someone fills oil to the top on fully extended fork. Now, the airgap above oil acts like progressive spring, higher the oil level more progressive it gets. Even with straight rate springs fork acts like it has progressive one. But that has nothing to do with "sag" Quote Link to comment Share on other sites More sharing options...
tomek Posted October 5, 2021 Share Posted October 5, 2021 7 hours ago, FTM said: Yeah I saw those discussions but I couldn't find cSt rating of Hyperpro's oil, or whatever oil they use under their label. For my fork service I bought Motul's 5W light, which is around 18 cSt, Bird manual recommends Showa SS8, 36 cSt. Go with 5W, it will reduce harshness from front end. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted October 5, 2021 Share Posted October 5, 2021 Here are my suspension upgrade notes from around 2004: https://web.archive.org/web/20040201212241/http://www.cbr1100xx.org/newhome.html And then tuning notes: https://web.archive.org/web/20040409163758if_/http://www.cbr1100xx.org/mods/suspension/tuning.html Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 5, 2021 Share Posted October 5, 2021 1 hour ago, tomek said: Wrong. They are not pressurized, so when bike has been settling for while air pressure above oil equals outside atmospheric pressure. So the sag will be the same regardless of oli level. Let's not talk about bonehead move when someone fills oil to the top on fully extended fork. Now, the airgap above oil acts like progressive spring, higher the oil level more progressive it gets. Even with straight rate springs fork acts like it has progressive one. But that has nothing to do with "sag" When doing the initial set-up it won't have 'settled'. Quote Link to comment Share on other sites More sharing options...
jon haney Posted October 5, 2021 Share Posted October 5, 2021 (edited) Large air gap vs. small air gap (reasonable), there would be slight difference in static sag. However, I would bet that the "stiction" range would be more than the sag difference. Edited October 5, 2021 by jon haney Quote Link to comment Share on other sites More sharing options...
tomek Posted October 5, 2021 Share Posted October 5, 2021 (edited) 1 hour ago, superhawk996 said: When doing the initial set-up it won't have 'settled'. Wut? Stiction? This measurement procedure takes it out of equation. Edited October 5, 2021 by tomek Quote Link to comment Share on other sites More sharing options...
fizzy Posted October 5, 2021 Share Posted October 5, 2021 1 hour ago, superhawk996 said: When doing the initial set-up it won't have 'settled'. If you believe the difference is measurable then prove it. Measure the sag both ways using method above (air settled vs air under compression) and report back. Quote Link to comment Share on other sites More sharing options...
superhawk996 Posted October 6, 2021 Share Posted October 6, 2021 6 hours ago, tomek said: Wut? Stiction? This measurement procedure takes it out of equation. Not stiction, the air pressure that you said would be the same as atmospheric after it 'settled'. Quote Link to comment Share on other sites More sharing options...
tomek Posted October 6, 2021 Share Posted October 6, 2021 58 minutes ago, superhawk996 said: Not stiction, the air pressure that you said would be the same as atmospheric after it 'settled'. Wut? My "stiction" comment was related to Jon's post, not yours. Anyway, your initial "wrong" comment was retarded but you being you will never admit you were wrong. Quote Link to comment Share on other sites More sharing options...
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