OzVMX Forum
Clubroom => Tech Talk => Topic started by: caps 999 on February 09, 2009, 09:28:57 pm
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of the front end on the 480 has allot to be desired so im wondering if any one knows of ways to harden it up with out replacing springs as im only 89kg with gear so mabye spacers and hevier oil might do it any suggestion would be good
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you have just about answered the question your self ;D try some air maybe.
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i was thinking if anyone could think of any valving but that seems ok
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from reports i have heard, emulators do stiffen up the forks. i have known people that have fitted them and then no longer need to run air.
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Perhaps half a cup of cement or a viagra in each?? ;) Caps have a chat to Yss I believe replacement springs/Damping valves are a fairly cost effective item.
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Capps
Have you set up your sag ?
both static and race sag are the first places to start.
Static sag should be around 15mm and race sag about 100 to 110mm.
Static sag is measured with bike on stand, find two points to measure between, then take bike off stand, bounce the rear end up and down a couple of times then measure the same points. do this a couple of times and the difference should be about 15mm.
Then do the same thing but this time with you and your gear on the bike, the difference shopuld be about 100mm.
Now here is the tricky bit, you will need to adjust the spribng preload collar on the shock, if when you have adjusted it to get 100mm race sag you remeasure your static sag it is LESS than 15mm you will need a STIFFER spring, if it measures MORE than 15 mm you will need a softer spring.
You will need to get your spring weights right first, nothing else will work properly until this is sorted.
Ahhhh this has got to do with your shock, so all these measurements are done on the rear end.
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I've stuffed around with all sorts of combinations in my forks and reached the following conclusions, right or wrong.
Use heavier springs, heavy enough to hold the bike up. Total weight of bike and rider /20 is a good starting point.
Adding spacers will give a stiffer/harsher ride initially but the forks will still be too soft.
Air, to me is just another way to compensate for incorrect spring rates and poor damping
Going to too heavier oil will just make the forks sluggish.
PD valves/ emulators will give you low speed damping but be much softer during high speed movement.
The right springs and damping valves are the way to go, my three cents worth (allowing for inflation!)
Brent
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well ive now purchased some hevier pogressive rate s[rings these should solve my woes
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Hi Brent J,
When you say "Total weight of bike and rider /20 is a good starting point"
Do you mean to add 20 kilos or divided by 20?
This was a great tech posting well done. I think it may have been worth 5 cents.
Ji
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evo I you have it arse about in your summary, to realise static sag you have to have a full extention figure(with not weight on the spring) and increasing the pre-load will always reduce the free length of the spring,it won't be a true indication of the spring rate. A far easier gerneral rule is a Sag= Total travel divided by 10%/30% rule say you have 100mm total travel, 10% of the travel is taken up with the weight of the bike(static sag) and 30% of the available travel used with the rider on board. A cable tie on the shaft is the easiest way to measure this.Brent is 100% on the fact that air and preload adjustment is no a substitute for the correct spring rate. Also chopping coils off springs doesn't just make it shorter it increases the spring rate ;D
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That's what I said lozza
Static sag is measured by first having bike on stand(with rear wheel off the ground) measure between axle and seat bolt, then take bike off stand and again measure between first two points, this should measure about 15mm difference from the first measurement.(give or take a few mill, it's best to do this a coulpe of times and average out the measurement)
Then do race sag settings (with gear on and on bike) at about 100mm, again give or take a few mill.
If you can't acheive both of these settings at once then you will need to change spring rates.
If race sag is then set at 100mm and static sag is LESS than 15mm you will need a STIFFER spring
If race sag is then set at 100mm and static sag is more than 15mm you will need a SOFTER spring.
Some people make the mistake of assuming to little static sag requires a softer spring, when in actual fact it's the other way around.
Think about it and get back to me. ;)
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He was, the reason i mentioned the rear was that if sag hadn't been checked and was currently 70mm then it would give and unbalanced weight bias to the front of the bike, giving the sensation of a soft front end, when in fact it was a hard rear that was the problem. That's all ;)
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rear is fine for the minute just the front is hopeless
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I'll really stick my neck out here, this is something I wrote up a while ago.
I don't mean to hijack your post CAPPS but it might give you some ideas.
Wasp, thanks for your comments, just don't tell Walter I'm trying to give suspension advice ::) And I do agree with the comments in your email!
Front suspension.
You needed to separate the two suspension functions, load carrying (springs) and control (damping).
Spring selection. ( This is from Works Performance) You need the total weight of you with your riding gear (in lbs). Be honest as any false modesty here will result in the wrong spring rate!!
Weight your bike (again in lbs), add your weight to the bike and divide the total by 20.
This will give you a very good STARTING POINT for the spring rate for your fork springs in pounds/inch.
For a road bike or 10-12” travel MX multiply by 1
For 8-10” travel MX multiply by 1.1
For 6-8” travel MX multiply by 1.2
Once you have found the required spring rate fit the springs with 0-5mm pre load NO MORE!!!!
With the bike sitting upright on it’s suspension the forks (and rear end) should sag between 6-10%. I prefer 10%
Now sit on the bike with your gear and it should sag 25-30%. I prefer 30%.
Pre-loading springs.
This is a definite no no.
If you have a bike that needs a 30lbs/in spring and you have a 20 you may think “oh well I’ll just pack the spring up a bit”. Bad move.
Assuming the bike will sag 1” on a 30lbs/in spring. The spring is under 30 lbs pressure as it sits.
Using a 20 with preload in this case would need about ½” then the bike would make it sag a little over and inch because the spring rate is lower.
Start moving the suspension through its stroke and the 30lbs spring takes 30lbs more to move each extra inch.
1” is taken up with static sag (30lbs) then 60lbs, 90, 120, 150, 180, 210, 240, 270, and finally 300lbs for the last in, assuming 10” travel.
Do the same with a 20lbs spring with preload. 1” sag takes it to 30lbs (20lbs spring and ½” preload) then 2” 50lbs, 70, 90, 110, 130, 150, 170, 190, 210lbs for the last inch.
This spring will ride about as a 30 initially but will bottom very easily. Simple you say, preload it a bit more. OK we’ll add 1 inch more preload and try again
With 1.5” of preload the 20 pound spring now sits static at about 50lbs. so no sag in the front at all. Move it 1” and it pressure is now 70lbs then 90lbs, 110, 130, 150, 170, 190, 210, 230, 250, 270.
Where the 30 only took 30lbs to move it initially the preloaded 20 now take 70 so you have a harsh ride but it will still bottom out as the fully compressed rate is still less than the 30.
GET THE RIGHT SPRINGS
Standard damping
Most of our bikes have damper rod forks with fixed damping orifices. These can be made to work at either high or low shaft speeds (not related to bike speed) but not both!
If these forks have enough restriction to provide low speed damping they will rip your arms off on sharp edged bumps which generate a high shaft speed. The forks just will not move fast enough.
If they are set for high speed damping then they will wallow on slow bumps and dive under brakes.
The manufacturers made the damping a compromise which really means they don’t have enough low speed but too much high speed damping.
If they used the correct spring rates then the forks would be even harsher as the high speed damping would add too much resistance.
As well as compromising on damping they went a bit soft on spring rates to remove the harshness.
I’ve seen air assisted springs, negative springs, low spring rates with lots of preload but like most compromises they seem to address most things badly.
I am using Race-Tech cartridge emulators in my current bike but do have a set of YSS PD valves in a second but unfinished bike. I have not tried these yet but I believe the YSS valve will work at least as well as the Race-Tech product.
Both units use a small hole in the spring loaded top plate to control low speed damping and small movements.
The spring loaded plate controls mid and high speed damping.
There are different rate springs available for this and the spring preload can be altered.
Rebound damping is controlled by the oil weight.
Oil height is important. As the forks compress the air space reduces and the compressed air assists the spring. By increasing or decreasing the oil height you can soften or increase spring pressure in mid stroke and above and increase bottoming resistance. Low speed damping can also be used to increase bottoming resistance.
I use two online spring calculators to measure my spring rates. This was I can find springs at wreckers etc and find their rates.
http://www.pontiacracing.net/js_coil_spring_rate.htm
and this one to find rates with two springs
http://www.proshocks.com/calcs/2spgrate.htm
I’m not saying this is gospel but I’ve talked to people with suspension knowledge and researched everything I can find. Then I’ve gone out and played with settings for hours at a time.
My suspension settings will probably never be finalised as I keep finding improvements. I’m probably the slowest rider out there but one of the most comfortable.
I’ll try to copy and maybe post a few seconds of film from Conondale last year. Four bikes come over the main straight drop off. Three hit the deck and wobble around, one just lands so softly, that one’s mine
Brent
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Thanks Brent J.
That is just magic.
Thank you for sharing one of your lifes work.
Do you have the video footage of Conondale listed somewhere like You Tube.
Thanks again
Ji
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Brilliant Brent! Cheers Tim
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Its a serios good read Brent , but it will take some time to absorb. The good thing is as time goes by , I can fall back on it , and use it . Thanks Brent . There you go again , there is also usefull information on this forum
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Thanks for the kind words guys :-[
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i have found these which claim to contol low/mid/high speed damping and anti dive circuit
made in Australia
Promecha provalve damping control unit for conventional forks.
http://www.promecha.com.au/featured_products.htm
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Hi Brent J,
I am now talking rear shocks.
What is the factor that you multply by if your travel is 86mm or 3 and a half inches?
Thanks Ji
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Well explained Brent. You answered a couple of questions I was too embarrassed to ask publicly! I'm about to attack a set of 34mm YZA forks and a set of 38mm Cerianis and will use your spring theory as well as YSS PD valves.
For what it's worth, I have no qualms with Promecha or their products but prefer to support Walter and YSS because he's one of us and supports vintage racing even though the real focus of his business lies in other more lucrative markets.
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Leith , Brent has done a good job of explaining the whole issue in a non biast way and the correct fix. (And he probably has to do this many more times , as probly not a month will go by before somebody else will ask the same question again. ) If I remember correctly, you started a thread about that product not so long ago , with no replies. So why throw that in again?????. Sometimes I can not be bothred anymore to reply serios to some of your postings . Are they worth replying ? Yes , but only in a humerous way :D :D :D.
How would you feel when someone throws in a post about enhancing rear light bulbes, into your detailed thread ofSuzuki footpegs?
Are you being serious walter ? Why post that ? its a Poor effort in dragging down a perfectly good thread.
Just because leith is not refering to your lame PD valve rip offs you cut him down for adding another product or brand into the mix which is part of this thread, where your response is totally out of left feild, i thought you got rid of your YSS account so you wouldnt continue with this kind of crap, wouldnt even take too much to guess then who your bagging out in your email to Brent as well, same spots differant leopod im seeing here.
HAving said that, it was a Great post Brent, some good stuff in there and good to here its all tested info, be good to see the vid too, and sorry for the side line , but that stuff shits me
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Just because leith is not refering to your lame PD valve rip offs ...
Why are they lame? Aren't they as good as the Gold Valve Emulators?
How are the ProMechA valves better?
Have you tried and compared any of these products?
What are you basing you opinion on?
I have been using Gold Valve Emulators in my bikes for years and they are one of the best things you can do to a bike.
I also tried the YSS PDD valves with YSS shocks on Dave's Superlight when I partnered him in the 2008 One Hour. It was a huge improvement.
I bought YSS PDD valves which I haven't fitted yet. They look like they should work the same as the Gold Valve but are two thirds of the cost.
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Freaky , I dont even take you serios enough to pic an argument . Full stop.
so join the club no one takes you seriously either. You dont have an arguement. ps great thread hijack Walter.
Freaky , I dont even take you serios enough to pic an argument . If I rember right the thread is called " Soft Forks " not "Soft Cocks" Full stop.
Bias is a 2 way thing.......ohh and doing your usual back post edit work means nothing, it still dont make sense and is still highly derogitory to your fellow vmxer's, you really need to pick up your game and grow up fella.
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Just because leith is not refering to your lame PD valve rip offs ...
Why are they lame? Aren't they as good as the Gold Valve Emulators?
How are the ProMechA valves better?
Have you tried and compared any of these products?
What are you basing you opinion on?
I have been using Gold Valve Emulators in my bikes for years and they are one of the best things you can do to a bike.
I bought a YSS PDD valve which I haven't fitted yet. But it looks like it should work the same as the Gold Valve but it is two thirds of the cost.
Mboddy i know nothing about PromachA valves, my point about lame was simply why it needed 2 consecutive posts on Leith being bagged out just cause he mentioned somthing else.
I have PD's in mine and walter has personally showed me his, they look like straight copies so they "look like they should work". Fitting though might be somthing to consider, you really need to speak to Oldfart directly for his opinion as he fitted some a while back.
and Before we get the usual legal email threats "let me clarify i have no opinion on this, as i havent fitted that brand"
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As you should have noticed over the past few weeks, I have not posted . Why because I feel that some have axes to grind and others egos to stroke.
To answer the question YES I purchased a set of PD valves from YSS ( model 310 ) and there was correspondence and phone conversations approx 26- 10-2007
The rest is history.......
Brent, Thanks for all the help and tips .....a brilliant post
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Ji Gantor,
I don't have any vids posted on utube, I'm not really sure how to yet. I'm just up to converting my tapes to disc. I do have some footage from Conondale and Proserpine but it's only of my mate Muz going fast and me going slow.
As far as rear suspension (twin shocks) goes I still work on the same %'s of sag but have not yet worked out how to determine the spring rate from the weight. I'm trying to work this out but it has to allow for shock position and angle.
Freaky, re your reference to to my reply to Walters email. It had nothing to do with anyone on this site or even VMX. I posted the comment here as I can not access my personal email from work. Won't make that mistake again.
When I first fitted the emulators to my bike I noticed an improvement in my forks. The next time I rode it I wasn't so impressed. I started to play around with the settings, some changes helped and some went backwards. I quickly realised that the manufacturers put these things to an "average" setting. They should show an improvement but they are adjustable. It takes time to try these things and for most of us time is hard to come by.
It's just like jumping in someone elses car and the seat and steering column is in the wrong place, you've got to change it to suit yourself.
Brent
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Hi Brent,
The factor for 6-8" of travel is 1.2 or an increase of 20%
So may be for 3-4" of travel an increase of say 30% may be correct
Weight your bike (again in lbs), add your weight to the bike and divide the total by 20.
This will give you a very good STARTING POINT for the spring rate for your fork springs in pounds/inch.
For a road bike or 10-12” travel MX multiply by 1
For 8-10” travel MX multiply by 1.1
For 6-8” travel MX multiply by 1.2
Works Performance sent me similar data when I purchased a set of their shocks last year. Your explaination is much simpler to understand.
When you work it out let me know.
Thanks Ji
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Ji Gantor you're right, that info came from Works performance. I've mentioned that when I've posted the info in the past.
I've found the formula works pretty well but doesn't allow for different weight bias on different bikes. The guy I dealt with rides a TT500 and uses 23lb springs. My 500 carries a lot more weight on the front wheel so needs 25's so it still pays to play a bit if you have time.
I like the idea of allowing a percentage for different travel in the rear. I'd like to try and work out a formula for selecting rear springs simillar to the one for fronts. You would then have to allow for the shock position ie forward of the axle and angled.
I figure if the shock had 4" travel and was mounted to give 8" at the axle then you'd need double the spring rate.
Something else for a rainy day
Cheers
Brent
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Hi Brent J,
I hope you don't think I tried to water down your efforts by mentioning Works Performance, as that was not my intention.
Besides you have taken it a few leaps forward from what they have written and as I said made it simpler to understand.
I will try and work out a formula to suite small travel rear shocks and send it through for you to cast your eye over.
Thanks again for sharing your experiences.
Ji
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No problems Ji Gantor :)
I'd be very interested in what you can work out.
Tell me, does your online name come from the 60's cartoon "Gigantor"?
I can't get the theme song out of my head every time I see your name :D
Brent
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This is going to play on my mind forever!
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I had to do it!
I Googled it
Jimmy Sparks
Now I can sleep!
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I'm pretty sure "Speed Racer" came out about that time.
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Can't think of anything but I'm a kiwi so we might not have had it over there.
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Hi Brent J,
I have been working on the problem this morning.
I should have something to share soon.
Ji