Front static sag check

[CookMySock]

Ok, for something to do I measured up my front sag - can someone confirm this is in the ballpark ?

Bike is 2006 Hyosung GT650R.


|----- 125mm to lower seal lip, forks fully extended, no weight on front wheel
|
|
|
|----- 83.4mm top of static - lift up
| ---- average 80.7, stiction width 5.4mm (rider on, 91KG)
|----- 78mm bottom of static - push down
|
|
| stanchion all smooth and shiney in this area
|
|
|
|---- 50mm a few 'braking' lines evident below here
|
|---- 30mm more lines
|
|---- 8mm lowest line
|---- zero mm - bottom of stanchion.


Looks like these are cartridge forks! So they will take an aftermarket valve kit. http://www.racetech.com/evalving/eng...ngname=english

The rear suspension has to go. Looks like GSXR750 will fit with just a small mod. Does anyone know if the standard GSXR750 rear is a rebuildable cartridge type ?

Yeah yeah, I could sell it and get something nicer, but actually I'm beginning to like it, and it does nearly 400km on 17litres.


many thanks,
Steve

[Robert Taylor]

Ok, for something to do I measured up my front sag - can someone confirm this is in the ballpark ?

Bike is 2006 Hyosung GT650R.


|----- 125mm to lower seal lip, forks fully extended, no weight on front wheel
|
|
|
|----- 83.4mm top of static - lift up
| ---- average 80.7, stiction width 5.4mm (rider on, 91KG)
|----- 78mm bottom of static - push down
|
|
| stanchion all smooth and shiney in this area
|
|
|
|---- 50mm a few 'braking' lines evident below here
|
|---- 30mm more lines
|
|---- 8mm lowest line
|---- zero mm - bottom of stanchion.


Looks like these are cartridge forks! So they will take an aftermarket valve kit. http://www.racetech.com/evalving/eng...ngname=english

The rear suspension has to go. Looks like GSXR750 will fit with just a small mod. Does anyone know if the standard GSXR750 rear is a rebuildable cartridge type ?

Yeah yeah, I could sell it and get something nicer, but actually I'm beginning to like it, and it does nearly 400km on 17litres.


many thanks,
Steve

Static sag should be as close as possible to 30 mm for road going use, laden sag 40-45mm. The springs are too soft and yes a Race Tech valving kit will fit.
If the GSXR750 shock fits properly, is appropriate length and stroke and doesnt foul anything through its stroke then all well and good. But the spring rate is way too light and should you be able to sort that out the internal valving will have to be changed to match it.

[CookMySock]

Static sag should be as close as possible to 30 mm for road going use, laden sag 40-45mm. The springs are too soft and yes a Race Tech valving kit will fit.

Thanks Robert. ok I planned to lose some weight off my fat ass and guts, so that will be cheaper. Would you like to PM me a price to fit and set up the racetech valving kit ? I'm quite broke at the moment, but these things come right as other toys get sold etc.

If the GSXR750 shock fits properly, is appropriate length and stroke and doesnt foul anything through its stroke then all well and good. But the spring rate is way too light and should you be able to sort that out the internal valving will have to be changed to match it.

Right, so a shock from a GSXR750 is too light. Aside from whether it physically fits or not, would you care to speculate on its suitability for the GT250R ? edit: rider weighs 60KG.

I'll keep looking for something heavier for my GT650R. I might ride to town and see what junk is lying around just to check the fit, then find a low km's one on trademe - there seems to be lots about. I'm not hugely concerned about the rear as long as it's in the ballpark - anything has got to be better than what I have, later on I will gold-plate that too.


DB

[Number One]

I measured up my front sag

there are supportive undies you can get for that Steve

[CookMySock]

there are supportive undies you can get for that Steve

Hello miss, how are joo ? Miss ya heaps. Coming up to Taupo are ya ?

Steve

[Number One]

Hello miss, how are joo ? Miss ya heaps. Coming up to Taupo are ya ?

Yeah been a bit preoccupied with LIFE and stuff.

Taupo? Christmas bucket event? Yeah hopefully - just need to see if we can swing a mum and dad only trip for it.

[Robert Taylor]

Thanks Robert. ok I planned to lose some weight off my fat ass and guts, so that will be cheaper. Would you like to PM me a price to fit and set up the racetech valving kit ? I'm quite broke at the moment, but these things come right as other toys get sold etc.

Right, so a shock from a GSXR750 is too light. Aside from whether it physically fits or not, would you care to speculate on its suitability for the GT250R ? edit: rider weighs 60KG.

I'll keep looking for something heavier for my GT650R. I might ride to town and see what junk is lying around just to check the fit, then find a low km's one on trademe - there seems to be lots about. I'm not hugely concerned about the rear as long as it's in the ballpark - anything has got to be better than what I have, later on I will gold-plate that too.


DB

Will do, inevitably there are a few ''menu'' choices.

With respect to the rear shock I have misplaced my dilgent notes since I moved town and premises. But what I can reasonably recall is as follows:

1 ) I had assumed that the rear shock was similiar to an SV650 one, not so. Different length and stroke for starters and different end fittings. Massively different spring rate

2 ) As I best recall the spring rate measured within the range of 12 - 12.5 newtons. The SVs run at between 7 - 9.5 newtons and the GSXR shock you were looking at would have been around 8 to 8.5 newtons.

3 ) I am being brutally candid here..........when I dyno'd a stock GT650 shock it had a damping character very similiar to a budget passenger car shock. I.e essentially single acting in that it only had a very very tiny amount of compression damping, matched to a rebound curve that was very progressive in character, a true parabolic curve that is ''achieved'' by fixed orifice damping, either a single checkplate with a lift restrictor or indeed a fixed orifice of some sort. I didnt need to pull it apart to conclude that the internal construction is very very crude. So, essentially it is using a very firm spring, heavily preloaded to give some form of dynamic ride height control. ( In all fairness I might add that this low cost method of construction is used on many commuter bikes and with more stuff coming out of mainland Asia we need to brace ourselves for some very dodgy product )
The problem is when you ride over abrupt bumps ( that we have a good few of here in Helengrad ) the ride feels terrible.

This is where it gets difficult! If you do indeed find a higher quality shock off a Japanese bike that will fit properly with correct ride height etc it will likely not require a spring as firm as 12 - 12.5 newtons, unless your body mass is similiar to Buster Keaton. This is because a higher quality shock will have a proper compression damping force curve of a value approximately 8 - 17 times stronger than your GT650 shock at abrupt bump strike shaft velocities. The damping force stops the shock blowing so readily through its stroke meaning that there is rather less spring force required. A road going GT650 that we built a shock for 3 or so years back required a spring rate of 10 newtons.

4 ) As I also recall there is a frame tube ( crossways I think ) that is in very close proximity to the top of the shock when mounted. Look at that closely, it may be another niggling little factor.

Im sorry I have absolutely no data on the GT250 so cannot comment.

Hope this all helps....pm to follow tommorrow.

[CookMySock]

Thanks Robert. PM received. Now looking for 1988-1995 GSXR rear shocks.

[Robert Taylor]

Thanks Robert. PM received. Now looking for 1988-1995 GSXR rear shocks.

No worries, if you do find what you think is a suitable shock ''prospect'' pm or e-mail me and I should be able to adjudge its suitability. We offer this service to anyone who asks.