Motorcycle Suspension Gurus - Opinions Needed

I'm thinking about doing an upgrade to my motorcycle's suspension and have a question for you motorcycle suspension experts. The bike is a 2002 Suzuki Katana GSX750F and it only has about 10k miles on it. The rear seems fine, my issue is with the front. It seems to be very soft, dives under braking, you can feel it diving in corners and isn't pleasant on rough roads (this part I can deal with, I just want it to handle better).

I did one of those 'Calculate my Spring Rate' things on Racetech's website and it said I should be at .92kg/mm (stock is .62). I'm thinking about going with .90kg/mm springs since I don't race and heavier oils but here's the question. My current forks have adjustable rebound dampening only, no adjustment on the compression side. I can add cartridge emulators to add a compression adjustment (and actually give me some more dampening because stock is non-existant) but I need to know if it's worth it for the type of riding I do. I'm an aggressive street rider at best. I love a good set of twisties but the bike will never see a track day. It's more of an over-glorified sport tourer for me.

So, just go with stiffer springs and thicker/better oils and call it a day or go all out and get the emulators also (are they really worth the extra $$)?

 

Considering the bike you are on I would not go beyond the springs. I have had many bikes and ride tracks on a consistent basis. If it were a track bike, then there would be no question. But since you are only riding on street your money might be better spent elsewhere. I recommend checking with someone over at racetech to see what the costs would be while they are replacing the springs. We have a couple of race tech gurus that work our track events that I would be more than happy to put you in touch with.

 

Thanks for you input! I do have a contact that works with Racetech that I came into contact with through a motorcycle forum that I'm a member of. I will be doing all the work myself so my only cost will be the added parts. If I just do the springs and oils, it will run me about $100 for Racetech springs and $15 - 20 for oil. If I do a complete tear down and add the emulators also, it'll be $150ish for the emulators and another $45 in dust seals, oil seals and crush washers in addition to the springs and oils (plus a more lengthy tear down which means I'll have to do it over the winter or lose riding time).

I was honestly thinking along the same lines as your advice meaning, I don't race so the emulators are probably overkill for what I do. I think I'll go with spring and heavier oils for now and add the emulators later if I really feel they're needed.

 

Sounds like a good idea. Run the current setup and when it comes time to freshen up the suspension, consider valves then.

All the best,
Evan

 

I did straight-rate springs, heavier oil, and cartridge emulators on my SV650. It made a huge difference. I think the emulators mainly helped over the sharp-edged bumps.
I would suggest doing the springs and oil first and figure out if you want to go farther later.
Tires and suspension are the best investment you can make in your bike.

 

Thanks! I think that's what I'm going to do and forgo the cartridges for now. I believe the Racetech springs are straight rate, I couldn't find anything saying they're progressive.

 

One last question for you guys before I go ahead and order regarding spring rate. Apparently my stock spring rate is .62kg/mm, the Racetech Spring Calculator says I should be at .92kg/mm. To me, that seems like a huge jump and I'm wondering if it's because they intend people to push their bikes more than I will. I've modified my Katana to have motocross style handlebars so that pushed my weight slightly back but the front end does dive under braking and in corners. For road riding, should I stick with a lower spring rate such as .80 or .85 instead of .90 or .95? Some other spring rate calculators that have options to choose a more relaxed riding style say I could do with .85kg/mm.

I'm torn, heavier springs or softer springs for road riding?

 

+1

 

Bump, any input on spring rates?

 

http://www.tacomaworld.com/forum/motorcycles/216846-motorcycle-suspension-help.html

As far as the spring rate, if the Race-Tech site says .92, I'd probably see if they could send you a .90 and a .95, one for each fork-leg. I don't think the MX-style handlebar conversion is really going to affect too much, your weight is still on the motorcycle, different spot on the seat maybe but the springs still support the weight.

 

Damn, I completely forgot about that thread, I'm a dumbass... I'm going to pull the trigger on the suspension and I guess I'm having second thoughts or just got excited, it happens to the best of us.

Are you suggesting that I run different springs rates in each fork?!?! I'm admittingly not a suspension expert but that doesn't sound like a good idea. I understand that the springs still support the weight but the weight distribution is different with my weight sitting further back. The front end would be lighter than in stock riding position. Because of that, I'm actually considering dropping to .85 kg/mm for the front. My fear is the Racetech calculator is calculating for someone who pushes the bike and someone like me might not like the end result. Also the lower spring rate to compensate for the slightly altered weight distribution.

 

As far as running different springs, it's done all the time for trackday guys and racers alike. That axle running through the rim will make them both compress equally. You could drop the spring rate down, I don't think I would as I like mine set-up kinda stiffer for braking and trail-braking into corners, plus I hate nose-diving when on the brakes.

 

Interesting... I've never heard of such a thing (although I admittedly don't know a lot about motorcycle suspension).

I ordered .90 kg/mm Racetech springs yesterday with some fresh oil. They should be here next week and I'll install them whenever we get a stretch of crappy weather (either cold or rainy). I'm excited for no more nose diving! These springs are 50% heavier than stock and set up for my weight.

 

FYI new dirtbikes have a spring in one fork and the air and dampner in the other, talk about asymetrical.

 

Kawasaki are the ones who are doing it.

 

Trials bikes have been doing it for a long time

 

Now that makes sense, slow speed and a lot of dampening needed. For higher speed applications, that just sounds bizzare!

 

They're springy. That's how ya can bounce em around so easy. Makes front wheel hops really easy. Try balancing sometime and using the suspension to get the front wheel off the ground

 

they even do one fork compression and one fork for rebound now.