Ohlins Shock

[Tweety]

Have you checked the width of the mounts ?, you may need to modify then to fit. The stroke is imoportant if you look at your std shock you'll notice you use all the available travel to the bump stop, it may work but you really want the same stroke as std. The spacer you'll need is 56mm that's a big spacer and a short shock, Honda must've made them long for a reason. too much to modify on this shock I think.

I'd say part of the reason would be that there is no external canister... So with all parts in the shock body, along with a relatively long stroke means that the shock actually have to be pretty long...

A difference in stroke of 3 mm or in this case 4 mm doesn't make a huge difference if the other parts are correct... But give the wrong spring, and the fact that it's a fairly basic version... Yeah, sell it...

BTW, popcat... Would you know the stroke of the Hagon and other aftermarket shocks sold for the VTR? I'd say it's very likely that they are shorter than the OEM, since they rarely make a specific shock body for each model of bike...

[VTRDark]

Thanks for all the replies, that's given me some food for thought.

(:-})

[popkat]

BTW, popcat... Would you know the stroke of the Hagon and other aftermarket shocks sold for the VTR? I'd say it's very likely that they are shorter than the OEM, since they rarely make a specific shock body for each model of bike...

They'll go by the original specs for stroke, the shock bodies may be similar or the same but the rods are made different lengths easily. the firestorm spring is long so they may well go for a shorter spring but this won't effect stroke.

I have an Penske R6 shock on my XJ600, it has a slightly longer stroke but i'm happy that way as the damping does it's job, wouldn't have wanted to go with a shorter stroke, the linkage design has something to do with it too.

[Tweety]

BTW, popcat... Would you know the stroke of the Hagon and other aftermarket shocks sold for the VTR? I'd say it's very likely that they are shorter than the OEM, since they rarely make a specific shock body for each model of bike...

They'll go by the original specs for stroke, the shock bodies may be similar or the same but the rods are made different lengths easily. the firestorm spring is long so they may well go for a shorter spring but this won't effect stroke.

I have an Penske R6 shock on my XJ600, it has a slightly longer stroke but i'm happy that way as the damping does it's job, wouldn't have wanted to go with a shorter stroke, the linkage design has something to do with it too.

Actually, not to argue with you, but I have found this not to be the case at all... Not one aftermarket shock that I have found goes by the OEM numbers for stroke... They either vary a few mm either way, or simply leaves that number out from all their specifications...

Yeah, I know very well what that means in terms of linkage and such... I'm just saying that whatever variance you accept for the spring/shock length/whatever is just as significant as the stroke... And neither is exact to OEM spec when going aftermarket...

[popkat]

If they don't go by the std stroke then they will at least measure/know full suspension travel on a bike before making a shock, you'd need to know this or the suspension could bottom out too easily, if we knew the linkage ratio and rear wheel travel of a firestorm then it's easy to work out the minimum stroke needed. A 2-1 ratio with 120mm wheel travel would be 60mm stroke, if you had a shock with 55mm stroke it would bottom out at 110mm of wheel travel. A 2.5-1 ratio would have a 48mm stroke for 120mm wheel travel. (if I've got my maths right )


Spring length isn't as important as long as it's not so short it goes coilbound, I've added hydraulic preload adjusters before on shocks and gone from a long to a short spring to accommodate it with no difference in the performance of the shock. Spring length has to put the adjuster collar in the adjustability range on the threaded area, if it works that's all, and it looks better that way

[VTRDark]

I was laying awake thinking about this last night. So does the spring length make a difference according to the stroke. Say you have two springs the exact same weight in Nm or whatever. They are both designed to take that specific weight so would they compress down at the same speed or would the length of spring make a difference to the speed of travel. Or are the different lengths made just to accommodate different length shocks. Say 150mm spring for a 300mm shock and a 170mm spring for a 350mm shock.

On the Ohlins conversion chart what do the figures in the centre correspond to. I understand the top row and row down the right that gives the weight but I'm confused by the bunch of numbers in the middle that they line up with.



For those that may be following this thread the chart was first posted in the following thread. http://www.vtr1000.org/phpBB3/viewtopic ... 73#p232371

(:-})

[popkat]

see post above

[Tweety]

If they don't go by the std stroke then they will at least measure/know full suspension travel on a bike before making a shock, you'd need to know this or the suspension could bottom out too easily, if we knew the linkage ratio and rear wheel travel of a firestorm then it's easy to work out the minimum stroke needed. A 2-1 ratio with 120mm wheel travel would be 60mm stroke, if you had a shock with 55mm stroke it would bottom out at 110mm of wheel travel. A 2.5-1 ratio would have a 48mm stroke for 120mm wheel travel. (if I've got my maths right )

Actually, OEM rear linkage on the VTR is 3.88:1, and travel is 124 mm... So doing just that limited calculation, you then "need" a whopping 32 mm of stroke... Buuut... The linkage isn't that easy, really... It can pivot at a different angle, since it's a part suspended at three points... And as such, the actually needed stroke, (calculated using a suspension software, don't ask me to tell you the formula, since I wouldn't know how to even begin understanding it) for the measured parts, comes out at 48 mm... Still well within the limits of those 3-4 mm huh?

And as the OEM spec is 60, I'd say they just went for "safe" and added a little, or took a part in their bin of available stuff... Downside to that is simple... You can probably touch the rear wheel to the underside of the under seat tray, really if you work at it... Just like you can bang the oil cooler down hard enough to break the front fender, and actually touch the wheel (ask me how I know that!)... Neither of which is things I think should be possible... So Honda might not actually always be "right" when they make stuff...

So, again 56, or 57 or 60 mm makes no difference what-so-ever in terms of practical usage of the shock, really... Spring and valving does, as well as length to keep the geometry... And yes, stroke does have an impact, but not so much if it's longer than the minimum required...

[Tweety]

I was laying awake thinking about this last night. So does the spring length make a difference according to the stroke. Say you have two springs the exact same weight in Nm or whatever. They are both designed to take that specific weight so would they compress down at the same speed or would the length of spring make a difference to the speed of travel. Or are the different lengths made just to accommodate different length shocks. Say 150mm spring for a 300mm shock and a 170mm spring for a 350mm shock.

Actually, the actual definition of how the springs are rated for a specific weight answers that question... The length is entirely irrelevant to speed of travel... The 150 mm spring will compress the same length at the same speed for the same weight as the 170 mm spring... The only part where the length comes into the equation is the "allowed travel" of the spring... IE, at some point the shorter spring will reach the point where it can't compress further, and go solid, before the longer... But really, that should only happen if you are using a spring that is far outside the range specified for...

The point about that chart is, that it tells you what length's work at what compressed length too... IE, a if the spring is too long for a shock that compresses it too much on installation, changing the "pre-load" to a value it shouldn't be... But it isn't as easy as just the final shock length... It has to take into account how the pre-load is made, where it's fixed to the body, and stroke... Ie, "installed length" of the spring...

[VTRDark]

Wow all very interesting and just goes to show the complexity of it all. I do believe like Tweey said that Honda will make/design things on the conservative side and sometimes use parts that are available to other bikes. Also they need to take into consideration an average weight of a rider plus carrying a pillion from time to time. I don't think it's an exact science and there is room for some leeway.

So the numbers in the middle are the fully compressed lengths then.

(:-})

[popkat]

Actually, the actual definition of how the springs are rated for a specific weight answers that question... The length is entirely irrelevant to speed of travel... The 150 mm spring will compress the same length at the same speed for the same weight as the 170 mm spring... The only part where the length comes into the equation is the "allowed travel" of the spring... IE, at some point the shorter spring will reach the point where it can't compress further, and go solid, before the longer... But really, that should only happen if you are using a spring that is far outside the range specified for...

What I said in the post above


I don't believe the ratio from Honda, I've had a cable tie around the std shock and it bottoms out, therefore using close to the 60mm, there is a bump stop which may limit some of it, but the tie was buried deep in the bump stop. what this means is there's more than 48mm of travel. that 48mm by the calculation would be the point at which the suspension would lock up, or at least soon after.

[sirch345]

Hey this is getting interesting, I expect you're wondering Carl what have I started

Chris.

[Watty]

I have only gone and got myself an Ohlins Shock for a very good price

2nd hand and not even a years old and has only been on a bike for 3 months. The only thing is it's not a Firstorm shock and is for a Triumph Speed Triple. It's 290mm in length so I will need a new custom top shock mount made to make up the difference to bring it up to 346mm which is the Storm length. The only other difference is the Stroke which is 56mm and the Storm Ohlins is 60mm, I'm not sure how much of a difference the 4mm will make, but the piston diameter is the same. The spring weight I am not sure about yet, the guy I bought it off is a similar build to me but I shall check out the spring number and work out which weight it is made for. If the worst comes to the worst I could always buy a new spring as they are always popping up on eBay. The spring free length is 150mm, does anyone know what the Storm Ohlins Spring free length is

Some Pics.








(:-})

Nice one mate shiny

[VTRDark]

I expect you're wondering Carl what have I started

Not at all. A nice healthy heated technical debate is all good as it means I can learn something from it, have an understanding of the suspension, how it works and interacts with the bike. My challenge will be getting the right static sag and rider sag. Now that really will be interesting to see if I can achieve the desired amounts with what I have. I know the spring is probably a bit to heavy for me and I think I need to go with a 95Nm for my weight, possibly a 105Nm as the 95 may be too soft.

I'm staying in Guildford at the moment and there is a suspension guy down the road, Steve Jordan in Leatherhead that is supposed to be very good. So I think I shall pop down and have a chat with him. Maybe get him to work out and tell me the right weight spring that I need as I will be on the bike and kitted up http://www.stevejordanmotorcycles.co.uk/

(:-})

[popkat]

. I know the spring is probably a bit to heavy for me and I think I need to go with a 95Nm for my weight, possibly a 105Nm as the 95 may be too soft.
(:-})

No, stock spring in lb's is 916 the spring on that shock you have is 685, way too soft, going by the spring numbers on the Ohlins you have a 44 you need a 64.
In the thread with the ohlins chart going by racetec calculations the 950lb spring on my Penske should be perfect, but it's to stiff, even now as I seem to have put on half a stone since I wrote that I think I would have been better off going with something closer to a std spring rate.

Would be interested to know what spring comes fitted to a firestorm fitment ohlins, hasn't Wicky got one fitted ?

I don't think there's anything heated going on, just healthy discussion


*As it seems the racetec stuff appears more often to be inaccurate, I wonder if the std spring rate they list is right or not ?.