'92 600 tire issue!

[dcc5266]

Hey, my 1st post here, got a '92 600. Seen instructions to "upgrade" pre98" kat's with a 120/70ZR17 for the front and a 150/70ZR17 for the rear. I would love to use some pilot power's...but, that size is not available for the rear. The 150/60ZR17 is avail. but it is a 66W instead of a 69W, which would be a 160/60ZR17. I have searched threads here for a while and I get some mixed results. I want to get some tires quick! What do you know that works.....and is great for curves??

[streebs93]

Just put a Dunlop Qualifier 160/60/17 on my 93 kat 600 and she rides great! Ill let you know what i think after i take her on a long ride this weekend through some curvy forest roads.

[dcc5266]

Thanks stree.... first reply.....let me know!!

[The CyberPoet]

Do not run an under-weight-rating tire *ever*
It's a formula for delamination and calamity when you least expect it.

It's the same as building your new 2nd story deck out of balsa...

The Z6's still rule supreme!

Cheers,
=-= The CyberPoet

[loudnlow7484]

Actually, I have a question regarding this load rating issue. I wanted to run a particular tire up front, but it's a 54 load rating, and the factory runs with 57. The difference in actual load is 40 lbs. ( http://bikergarage101.com/tireloadindexchart.aspx ) Since I have likely removed a bit of weight from the front (fairings, headlight, fairing stay, idiot lights, etc) and I'm, shall we say, well below the weight of the average rider, would this really be an issue? Ok, I know the standard response is to always use appropriately rated tires, but from my logic, I can't see it being a real problem. (The load rating difference is 467lb vs 507lb)

Anybody have an opinion?

[Enjay386]

I'll plug Z6's til I die.

[The CyberPoet]

Actually, I have a question regarding this load rating issue. I wanted to run a particular tire up front, but it's a 54 load rating, and the factory runs with 57. The difference in actual load is 40 lbs. ( http://bikergarage101.com/tireloadindexchart.aspx ) Since I have likely removed a bit of weight from the front (fairings, headlight, fairing stay, idiot lights, etc) and I'm, shall we say, well below the weight of the average rider, would this really be an issue? Ok, I know the standard response is to always use appropriately rated tires, but from my logic, I can't see it being a real problem. (The load rating difference is 467lb vs 507lb)

Anybody have an opinion?

I have an opinion: don't do it. Find a different tire in their range that supports the right weight rating.

Here's the reasoning behind my advice:
The load weight of the front tire isn't the static load weight of the bike on that tire, but the mass-shifted load weight under maximum braking at speed. It represents both the static load weight and the effective-weight being pushed forward & down through the forks, and reflects the ability of the tire to handle this kind of stress without buckling, shearing belts, overheating or delaminating.

If you look at it another way: the 98+ Kat 600 weighs 512 lbs wet (or there-abouts); so unless you ride on one wheel, why would you possibly need a front tire with a 58W (520 lb) weight rating? Because it needs it to operate safely.

KNOW THIS:
Although the Kat can't do 149+ mph, the tires are Z-rated radials. Why? Because the heat factors and braking factors of stopping such a heavy bike dictate a Z-rated radial is appropriate, even if the tire will never see more speed than a V-rated tire could handle.

More:

http://www.motorcycleanchor.com/motorcycle/how_to/mc_tires.html

and

http://www.motorcycleanchor.com/Katana/kat_tires.html

Cheers,
=-= The CyberPoet

[loudnlow7484]

Here's the reasoning behind my advice:
The load weight of the front tire isn't the static load weight of the bike on that tire, but the mass-shifted load weight under maximum braking at speed. It represents both the static load weight and the effective-weight being pushed forward & down through the forks, and reflects the ability of the tire to handle this kind of stress without buckling, shearing belts, overheating or delaminating.

If you look at it another way: the 98+ Kat 600 weighs 512 lbs wet (or there-abouts); so unless you ride on one wheel, why would you possibly need a front tire with a 58W (520 lb) weight rating? Because it needs it to operate safely.

KNOW THIS:
Although the Kat can't do 149+ mph, the tires are Z-rated radials. Why? Because the heat factors and braking factors of stopping such a heavy bike dictate a Z-rated radial is appropriate, even if the tire will never see more speed than a V-rated tire could handle.

More:

http://www.motorcycleanchor.com/motorcycle/how_to/mc_tires.html

and

http://www.motorcycleanchor.com/Katana/kat_tires.html

Cheers,
=-= The CyberPoet

I understand the reasoning behind it...... but for me, it still stands to reason that if the difference in load rating is 40 lbs, and I'm likely 80 or even 100 lbs lighter than other riders on this very board, then I would figure I'd be ok.

I'd be more than happy to stick a properly rated 120/70 on there, but I didn't want to pull the sides of the tire in like that, changing the curvature of the tire, so it wouldn't match exactly with the rear. A 110/70 would be a better fit on the rim, keeping the curvature the same, but it's not weight rated for it. This is my dilemma. I suppose I could try to hunt down an early GSXR wheel, so I could keep the swept spokes, but fit a 120 on there without issue. We'll see. I've got, oh, about 7 months to figure it out.....

BTW- What do you mean a Kat won't do 149+? If only I owned a video camera 3 years ago. 160+ indicated, rev-limiter in top gear (-1 tooth in front, though), 2 AM on a dark, quiet country road....... A feat I will never try to repeat. (Isn't it funny how a mere 3 years can make you look back in amazement at how careless you really were?)

[The CyberPoet]

BTW- What do you mean a Kat won't do 149+? If only I owned a video camera 3 years ago. 160+ indicated, rev-limiter in top gear (-1 tooth in front, though), 2 AM on a dark, quiet country road....... A feat I will never try to repeat. (Isn't it funny how a mere 3 years can make you look back in amazement at how careless you really were?)

The HP numbers on an OEM Kat simply do not add up to 149 MPH in real world (we're not talking about odo discrepancies). You can do all sorts of engine mods to jack up the power to make 150 easily attainable (bandit 1200 engine comes immediately to mind), but the OEM engine as shipped from the factory won't do it.

Cheers,
=-= The CyberPoet

[loudnlow7484]

The HP numbers on an OEM Kat simply do not add up to 149 MPH in real world (we're not talking about odo discrepancies). You can do all sorts of engine mods to jack up the power to make 150 easily attainable (bandit 1200 engine comes immediately to mind), but the OEM engine as shipped from the factory won't do it.

Cheers,
=-= The CyberPoet

No, I agree that dead stock the 600's and 750's won't do 150 unless they're going down a steep hill with a tailwind.... I was just being a smarta$s. That said, there wasn't really much done to that one...... V&H 4-1, the aforementioned sprocket change, bigger main jets, and shims under the needles. (I may have taken the shims back out, I can't remember) I tried to figure out not too long ago, mathematically, how fast I would have actually been going....... if I'm not mistaken, it was somewhere in the 153-155mph range, assuming the bike cuts out at 13,000 RPM.

[The CyberPoet]

No, I agree that dead stock the 600's and 750's won't do 150 unless they're going down a steep hill with a tailwind.... I was just being a smarta$s. That said, there wasn't really much done to that one...... V&H 4-1, the aforementioned sprocket change, bigger main jets, and shims under the needles. (I may have taken the shims back out, I can't remember) I tried to figure out not too long ago, mathematically, how fast I would have actually been going....... if I'm not mistaken, it was somewhere in the 153-155mph range, assuming the bike cuts out at 13,000 RPM.

What's you're probably not factoring in is loss of perfect traction at high speed. At 130 mph, the wheels lose contact with normal roadway surfaces approximately 35%-50% of the time (simply time to reaquire road contact by the tires after hitting tiny bumps; the return time is static at any speed because the spring rates don't change, but the number of bumps hit in a given amount of time increases with speed).

But even ignoring the above....

The HP requirement is a cubic relationship to wind resistance. Thus, if 70 HP will net you 132 mph actual on a 98+ Kat 600, you would need to get to above 100 HP to hit 150 mph actual on the same bike without changing anything else (for reference, the Coefficient of Drag [Cd] of bikes is horrendous in general, because down-force and lack-of-lift is much more critical than Cg in designs; factors of .55 - .72 are common).

Wind Resistance:
F(wind) = (1/2 * Air Density * (velocity squared)) * Coefficient of drag * area

Power Required to overcome:
Power(drag) = F(wind) * velocity = (1/2 * air density * (velocity cubed) * Coefficient of drag * area

Cheers,
=-= The CyberPoet

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The Best Motorcycle Tire Valves in the World, plus lots of motorcycle & Katana (GSX600F / GSX750F) specific help files.

[loudnlow7484]

What's you're probably not factoring in is loss of perfect traction at high speed. At 130 mph, the wheels lose contact with normal roadway surfaces approximately 35%-50% of the time (simply time to reaquire road contact by the tires after hitting tiny bumps; the return time is static at any speed because the spring rates don't change, but the number of bumps hit in a given amount of time increases with speed).

But even ignoring the above....

The HP requirement is a cubic relationship to wind resistance. Thus, if 70 HP will net you 132 mph actual on a 98+ Kat 600, you would need to get to above 100 HP to hit 150 mph actual on the same bike without changing anything else (for reference, the Coefficient of Drag [Cd] of bikes is horrendous in general, because down-force and lack-of-lift is much more critical than Cg in designs; factors of .55 - .72 are common).

Wind Resistance:
F(wind) = (1/2 * Air Density * (velocity squared)) * Coefficient of drag * area

Power Required to overcome:
Power(drag) = F(wind) * velocity = (1/2 * air density * (velocity cubed) * Coefficient of drag * area

Cheers,
=-= The CyberPoet

______________________
CyberPoet's KR Specials
SuzukiStratosphere.com - 6 Cylinders, wet dreams...
The Best Motorcycle Tire Valves in the World, plus lots of motorcycle & Katana (GSX600F / GSX750F) specific help files.

This was all entirely too complicated! If you're saying that a pre98 needs at least 100hp to hit 150mph, then I'm a bit confused. I can't reasonably believe that that little 750 was cranking out 100+ hp....... but then it was obvious that it had no great struggle getting out of it's own way...... Maybe I'm missing something...... Maybe the motor really had more work done to it, since I got it basically without any info of it's former life, and with 19k miles already on it. Or maybe it was just some factory freak that dumped out all sorts of power with almost no work. I don't know, and never will, since the new owner pulled the motor, left it in storage, and then all of the stuff in storage got taken when the bill went unpaid.

Even with the momentary losses of traction at those speeds, I can't imagine that it would affect the actual ground speed by a huge amount. (Being that the speedo registers off of the front wheel, there would be no reason that it would read higher than it was spinning..... and as I said, it was indicating well beyond 160, which is the end of the speedo's line).

[The CyberPoet]

This was all entirely too complicated! If you're saying that a pre98 needs at least 100hp to hit 150mph, then I'm a bit confused. I can't reasonably believe that that little 750 was cranking out 100+ hp....... but then it was obvious that it had no great struggle getting out of it's own way...... Maybe I'm missing something...... Maybe the motor really had more work done to it, since I got it basically without any info of it's former life, and with 19k miles already on it.

My immediate suspicion would be a WiseCo overbore kit to 771cc or higher, which raises the compression ratio significantly (thus putting out more power, more by virtue of compression ratios than by virtue of displacement change). What kind of fuel was it partial to?

Even with the momentary losses of traction at those speeds, I can't imagine that it would affect the actual ground speed by a huge amount. (Being that the speedo registers off of the front wheel, there would be no reason that it would read higher than it was spinning..... and as I said, it was indicating well beyond 160, which is the end of the speedo's line).

Typically, an motorcycle speedo over-reports by 7 to 9% at low speeds by law & common practice (this is done to prevent the manufacturers from being liable for traffic tickets and for you driving beyond safe speeds at their liability; the variation for motorcycles is intentionally higher than car's speedo variations because of differences in the amount of typical tire-growth during the first heat/cooling cycles under pressure). At triple-digit speeds, normally an additional 10% error factor is added on rear-wheel measured bikes (as the tires spin up when in non-contact with the road due to that bump phenomena I spoke of earlier); on most front wheel sprocket-driven bikes, additional error is simply a factor of spring resistance on older bikes being no longer the same as new (the spring in the speedo).

The most accurate forms of speed measuring, like those used on MotoGP bikes is an actual short-range ground radar or sonar (or multiple ones); the second most accurate is some form of hall sensor in the front wheel.

Cheers,
=-= The CyberPoet

______________________
CyberPoet's KR Specials
SuzukiStratosphere.com - 6 Cylinders, wet dreams...
The Best Motorcycle Tire Valves in the World, plus lots of motorcycle & Katana (GSX600F / GSX750F) specific help files.

[loudnlow7484]

My immediate suspicion would be a WiseCo overbore kit to 771cc or higher, which raises the compression ratio significantly (thus putting out more power, more by virtue of compression ratios than by virtue of displacement change). What kind of fuel was it partial to?

It ran like pi*s on regular, so I always ran premium in it. I always just figured that it was because it was jetted so lean (112.5's across the board). Dammit I wish I still had access to that motor. I'd love to tear it down and find out.

If your suspicion is correct, it would explain a lot. (Too low ET's for stock internals, by many accounts. Ability to loft the front wheel slightly/spin the back tire under acceleration in 2nd, etc....)

I never figured it had any real work done to it, since I bought it so cheap ($700 if I remember correctly), and it was so ratty when I got it. It also had factory needles in it, and I figured that if anybody had really worked on it, then would have dropped a jet kit in it, instead of just changing the mains.

[The CyberPoet]

A thirst for something better than regular is a good indication that it was one of their overbore kits (all of which increase compression).

Cheers,
=-= The CyberPoet

______________________
CyberPoet's KR Specials
SuzukiStratosphere.com - 6 Cylinders, wet dreams...
The Best Motorcycle Tire Valves in the World, plus lots of motorcycle & Katana (GSX600F / GSX750F) specific help files.