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Adjusting the ride height on the VTR250

Discussion in 'Modifications and Projects' at netrider.net.au started by sillygit, May 21, 2007.

  1. Hey All,
    I'm interested in raising the ride height on my VTR250. From what I can tell changing the pre-load will only make it stiffer and possibly lower it (how does the pre-load thing work anyway?) but I'm a 6'2" fat bastard so I'd like more height. The guy in the bike shop said I could possibly get a different spring; does that sound right?



    Cheers,
    Dan
     
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  2. Hi Dan,
    New spring is probably the go, although this won't neccesarily give you any difference in static height, just change the amount of sag under weight.
    If you are going to hang on to the bike you could look at getting a more flexible aftermarket shock installed (probably have to be custom).
     
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  3. try an RVF shock... might do the trick, or even an NSR with more adjustability... Let us know how you go, as i am looking into the same thing. You could always try and source a suspension link that will jack up the ride height... ask ur friendlt local wrecker.
     
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  4. depends whether you want the suspension to still work ok or not. spring may work, depends whether the actual shock has any more length. just talk to a suspension person and see what they say (usually exorbitantly priced so don't go asking for things done until you know.)
     
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  5. wedge a phone book between your arse and the seat.
    seriously though, i doubt there would be any aftermarket parts to rise the seat height, your preload should already be maxed, if not, youll need a crescent wrench to adjust, why the frick honda didnt include it in the VTR250s tool kit i dont know, you need it to adjust the preload on the shock and the head bearings.

    alternatively trade it in for a XR400, if thats not high enough for you nothing will be :LOL:

    cheers
    dom
     
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  6. you could drop the forks though the triple clamps a bit to give the feeling of rasied rear. also gives it faster turning...
    am thinking about doing it
     
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  7. Dan did I end up giving you the crescent wrench for the VTR when we handed it over?
    If not, I should still have it somewhere - it was only about 15 bucks and is crap basically.
    I doubt there is much left in upping the preload on that rear spring as I wound it up pretty tight when I had it.
     
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  8. Preload doesn't change the actual spring rate, it just pre-compresses the spring so that when the bike's static without you on it, the spring is already pushing up with X amount of force.

    Then when you sit down, it only has to compress a little bit more to support your weight, and the seat ends up at the correct ride height rather than sagging too low. (I can't remember the "correct" amount of seat sag. 30mm below the static height? 1/3 of the travel? Can't remember.)

    Preload only allows you to adjust the "loaded ride height" of the bike to suit your weight and your normal luggage/payload. It won't change the spring or damping rates to suit a heavier or lighter rider, nor will it increase the static unloaded seat height. :)
     
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  9. It's a simple mod for the non-adjustable VTR rear shock, but not easy for the average home handyman.

    After 25,000 km the rear shock on our '99 VTR250 had lost a lot of its damping - it just bounced up and down. Finally, at 33,000 km I sent it off in July to:

    RAD Motorcycle Shocky Repairs
    496 Sherwood Rd
    Sherwood QLD 4075 Ph: 07 3379 3302

    They quoted $180 for the rebuild (much cheaper than the others I phoned) which involves cutting the shock body open after removing the spring - it's a non-rebuildable shock, but that means nothing to a pro. :)

    They quoted 5 days turnaround, but mine took 3 weeks. However, when I got it back I only had to pay $80 plus freight. Amazing. It turns out that they only had to clean and refill with 15wt oil.

    I mentioned that the spring was sagging a little, especially with 2 up. They drilled extra holes for the circlip which retains the spring, to apply about 5mm extra preload. That worked very well.

    You do not need to replace the spring with a stiffer one - where would you get one, for a start?

    Cheers

    Trevor G
     
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  10. Has anyone adjusted the rear shock?

    I just had a look at it and its insanely hard to get to! Under the seat there is still a battery and cpu in the way. Would I have to yank all that out to get a c spanner onto it?

    Seems crazy....
     
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  11. You only need to take off the subframe and get in there. May sound like a lot of work but with the right tools (at very least a torque wrench) and the downloaded vtr250 workshop manual, it's a couple of hours of fun!

    They (honda) didn't include a C-spanner in the toolkit with the bike because the bike is a Japanese domestic bike only (it was a special import by honda australia for a bike not intended for other countries). With that the Japanese domestic vtrs did not have adjustable preload on the rear spring, so only the ones that came here needed the tool, but didn't get it.

    as for adjusting the preload on the rear spring, it will not change the height of the bike. It will just put too much load on the shock's damping, and the suspension will not work properly.
    Leave it as it is, unless you want to spend about $350 to have a suspension place rebuild the shock, incl tap it and weld on a connection for an external damping reservior (using an rgv250 reservior part etc). In the process you could get a heavier rate spring too.

    Other shocks from other bikes are designed for linked suspension, where the vtr's shock is mounted directly to the top of the swingarm bridge. So nsr, rfv, and all the rest will not suit.

    To increase the height of the rear will affect your steering geometry, but if you want to do it where are a couple of ways. take your shock to a suspension specialist, get them to cut off the top eyelet mount off, weld on an extension piece, and re-weld the mount you cut off. again, your geometry will be altered. Or you could extend the bottom rail of your subframe to lift your seat up.
     
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  12. What do you need the torque wrench for??? Not to adjust the shock preload!

    The 2 C-rings should only take 10 minutes or so to adjust. It's very awkward to get at, but I don't think the shock has to be removed.



    Whether you know it or not, the quote above is quite wrong.

    Of course adjusting the preload changes the ride height - that is what the adjustment is for! You can even see it happen as you do it.

    Some people think that it makes the spring "stiffer", but they are wrong. Whether the spring is straight or progressive wound does not matter - it compreses in a linear fashion.

    For instance, if it is a 200kg/inch spring it will compress 1 inch when a load of 200kg is applied. To compress it another inch you need to add another 200kg.

    Every modern bike has a certain amount of sag built in to the suspension before you even put the rider on it. Then with the rider seated the suspension should compress maybe 1/4 of its travel. If it compresses further, you increase the preload until the correct static sag is achieved. In this way a good suspension setup is able to quickly adjust for different rider weights.

    Since a steel coil spring (unlike air as used in air suspension) is a linear device with a fixed spring rate, the damping is designed in to match. Since you cannot alter the spring rate without changing the spring itself, when you adjust preload (or static height) you do not need to adjust damping - it does not change. The damping is not affected by the amouint of spring preload.

    Why do shocks have external damping reservoirs?

    One is not necessary in this case. Many bikes do not have them, or need them. It's just a design style, not an intrinsically different design for a different shock setup.

    Why do some designs use a suspension link?

    Only to change the progressive nature of the springing. The VTR250 system is an excellent, progressive design in its own right - it starts out soft and gets progressively firmer because the swingarm/linkage angles change.

    Yup, that's why people do it. When the sag is correct the geometry will be as designed. To quicken the steering you can then either drop the forks through the clamps a cm or so, or raise the back end. Even on the street the difference can be quite noticeable, and racers do it a lot to change handling characteristics. It is not a problem.

    Cheers

    Trevor G
     
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  13. Why are you being so belligerent? The torque wrench is for re-installing the sub frame, tightening bolts correctly. Please read thoroughly before posting

    You can't get to it with a C spanner without removing the subframe. You don't need to remove the shock. The vtr250 doesn't come with a C spanner in the tool kit, so you'll need one or a punch and hammer, it's really tight on the MC33!

    Actually, it's to allow more oil in the system to reduce the affects of oil heating up over longer stints. And also to give adjustability of the oil compression.

    So you're saying that shocks from other bikes will suit? I don't understand your response :?


    Maybe not a problem, but it could be for some and I stated it to be noted
     
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  15. Not a typical coil spring. You might be talking about some other type of spring with different characteristics...

    A coil spring with constant wire diameter, spring diameter and coil pitch is a linear device - if it takes 50 kg to compress the first cm it will only take another 50 kg to compress the second cm, and so on.

    Progressive rate suspension, such as on all properly designed monoshock bikes, uses either a linkage system (Kawasaki used to call it UniTrak on theirs) or the correct angle between the shock and the swingarm, to increase the amount of force required.

    On a progressive/rising rate suspension (VTR250 and so on) it might take 50kg to move the first cm on the shock, but 60 kg to move the next cm, and so on. (In actual fact, the rate rises progressively, not in fixed increments, but you have to describe it as if it went in fixed amounts.)


    No matter how tightly you squeeze the spring, it still deflects and extends at the same rate. That is controlled by the spring's own design, which is solely determined by its pitch, spring diameter and coil diameter, not the amount of preload.

    The speed of the rebound, for instance, will vary from the start to the finish of the cycle, but the damper greatly reduces these differences in speed.

    Here is a simple test of your idea, but it will only be easily visible on a non-linkage system. Alternatively a good spring works has the equipment to test (and compress springs) for spring rate and could demonstrate the practice and the theory at the same time...

    On a non-linkage bike - which would have to be a twin shock system without canted shocks (cruisers are quite UNsuitable) - reduce the spring preload to minimum, and measure the shock length. Then sit on the bike and measure how much it compresses.

    Adjust the preload to where the shocks no longer compress (but no further!) without the rider. Then sit on the bike again. You will notice that the shocks compress the same distance as before - the difference between the loaded and unloaded lengths will be the same in both scenarios.

    The shock will not compress as far as before (that's the reason for adding preload), but the amount of spring deflection will be exactly the same when you add the same load. It's simple, really. Try it.

    Cheers

    Trevor G

    PS The average cruiser with canted shocks has a falling rate suspension - the opposite of what is desirable, for appearance sake. On a falling rate system the spring rate effectively reduces the further it is compressed, which means that they have to be overly stiff to start with.
     
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  16. That's not belligerence, but incredulity. A torque wrench is usually used on engine components, but certainly is not important on subframe bolts, where you usually just apply considerable force! I don't mind if you use one in this area, but it's not necessary. :)

    It would be quicker to remove the shock, as we did recently, to adjust the preload, than to remove the rear subframe, surely?




    Oil aint compressible...

    You don't need a remote reservoir for adjustable damping, which reduces the oil flow to slow down either or both compression and rebound.


    Absolutely. No problem, as long as they have the same extended and compressed length, and appropriate mountings. Providing they are from something with similar weight (which means a similar spring rate) then the damping should also be appropriate, especially if adjustable.

    Even if it's from a much heavier bike a good shock rebuilder would then just use the appropriate weight/viscosity of oil to get the damping right for the spring you would use.

    Cheers

    Trevor G
     
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  17. turning up the preload will raise the ride height. if you max it out though, agressive changes in direction can cause the rear wheel to skip.
    i found it easier to remove the rear subframe. although if you could suspend the subframe i guess it would be easier just to undo the lower shock mount.
    trevor g, although you obviously have a sound mechanical knowledge. i use a torque wrench on just about every bolt on both bikes. this is after snapping too many bolts by over tightening. each to their own.
     
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  18. Hence the need to correctly set the static height and then the sag with rider on board. Approx 10% and 25%


    My son, who is 18 probably should too - I keep finding bolts and screws missing after he has worked on the bike. If he had to find/order the replacements he would soon get used to using the right torque!!

    Cheers

    Trevor G

    PS Using a torque wrench is fine if you know how to do it... :) but is far from essential, except on tricky things like cam towers on bikes where you have to pull the OHCs to adjust valve clearances.
     
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  19. yeah alot of the bolts are made from only mild steel, especially in the forks and brakes. i actually replaced them with high tensile steel bolts after snapping the replacement bolts again! :LOL: but after i took my bike in for its 24000kms service many eons ago sydney city replaced all the bunnings bolts with factory ones. and at no extra cost on the service i may add!
    yeah my torque wrench is in desperate need of calibration soon.
     
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