Is a stock Tri Z 250 really that slow????

[MR ATC]

top speed yes its correct...how fast they acheive that top speed is differant.

[ATCs Reborn]

oh alright, i always get confused when you guys use top speed to compare machines!!!! LOL
sorry bout that,
steve

[Jeb]

Concerning the Tri-Z Frames,

I think those rake angle numbers are wrong. Unless I'm mistaken rake of a motorcycle frame is measured by the angle of a line through the center of the steering head off of a line perpendicular to the ground as the complete unit sets on a flat surface. If the rake of a tri-z frame was .22, the forks would be nearly verticle???? I think that should be 22 degrees of rake. Also a change of .05 degrees would mean very small difference on the actual trail. surely they meant 1/2 degree or .5 degrees. I guess I shouldn't say they are wrong, but I question the location of the decimal.

Correct me if I'm wrong, but I thought you could change the rake of a motorcycle (or 3 wheeler) front fork by raising or lowering the front and rear ends, either by changing tire sizes, suspension heights (slide forks in tubes or lower rear shock), or any way that changes the angle of the forks as the machine sets on flat ground. Changing the rake effects the trail which is what effects handling. The more trail the better the straight line stability and the less trail the better the cornering. Now the actual steering head angle is a fixed dimension from some point on the frame. If I'm right, the 86 Z RAKE could have been changed 1/2 degree by the differences in the Tire sizes meaning the actual STEERING HEAD ANGLE could have been left the same as the 85. Based on stock tire sizes the rear axle on the 86 got 1/2" closer to the ground and the front axle got 1" closer. In other words as a bone stock 85 Z with 22" rear tires and 25" front tire sets next to a bone stock 86 Z with 21" rear tires and a 23" inch front tire they could have the same steering head angle but different rake angles do to the way each sets on the ground. The 86 axles are lower in the front 1" and lower in the rear 1/2" which changes the angle of the rake of the forks and reduces the trail without changing steering head angle.

OMG, i've gone cross-eyed....

Anyway I hope that makes a little bit o' sense! I guess my real question is could Yamaha have changed the claimed factory rake between the 85 & 86 Tri-Z with out changing the actual steering head angle of the frame???? Only way to tell is measure the steering head angle of a bare 86 tri-z frame and then measure a bare 85 frame the same way and compare ( a 1/2 degree difference will not be obvious upon visual inspection). If the frames end up being identicle except for coolant tank placement then an 85 can be easily modified to have the same rake by changing the wheels, tires, shock and forks to the 86 variety and should handle just like it. :-D

[denn]

Alright this is dragging on way to far. I own a MINT stock 85 tri-z 250 and a MINT stock 86 tri-z 250. All the parts a factory (shock, forks wheels tires etc.) The specs that darius gave are 100% correct. They did change the rake to excatly those numbers and the rest of it is also true. How they changed it I don't know. I've looked closely at both frames and never really saw a difference myself, but how can you accurately tell a degree by looking. The 2 bikes sit totally different and they feel totally different. They handle totally different and the motor is totally different. If you look at an 85 cylinder the part number is 38W and an 86 is 38W01. The powerband is longer and it pulls harder and has more top end to the powerband. The suspension is 10 times better and you can jump a hell of alot higher without bottoming out. I recommend everyone who has an 85 tri-z or any other bike and is curious about the difference try and find someone to let you ride there 86 or build one if you have the time and access to the parts.

Thanks Denn

[J.D.]

One of the improvements Yamaha needed to do was change the gas tank and air filter to traditional spots, that would have improved the Tri-Z exactly 86.98252 percent. Plus it would be less of a hassle having to remove the seat just to fill up on gas, that's bs. People like me who go riding and want to fill up at the pump have a harder time than just removing a cap, you gotta take off the seat, blah blah. BORING. I do love my Tri-Z though, and for 360 bucks in running cond. you cannot complain a bit. LONG LIVE TRI-Z's!!

[Darius1502]

Jeb...great analysis. I am in Houston, Texas...where are you at?

The dunes I was talking about are not Monahans.....but are just North of Monahans. Its basically the same sand. They reside in town called Kermit Texas. A ton of fun and very little restrictions as its a city park.

[Darius1502]

Denn,

I am also rebuilding my 86...I guess that's why I started this troublesome issue.

I would love to see your MINT '86. Please, Please post a pic of both!!!!!

Welcome to the board....

As far as mine I am waiting on an axle and some chrome from the shop. One thing I did do is get some Banshee Raptor hubs and swap my rear wheels and tires for Banshee 20 inchers.

Would love to see your Tri Z!! Here is a pic of mine

[Wickedfinger]

I don't think this thread has gone on too long in the least ... I think its very interesting and informative and its quickly becoming one of the all time great ones - worthy of trophy status - I might go out and buy another '86 Z now. Again though, I really think (for the umteenth time now) that this arguments basic core centers around the difference between fast vs quick. All three trikes had just about the same horsepower numbers, it was all in the stock gearing and to a lesser extent their piping - ATC250R 13/39 gearing, Tecate-3 13/37 and suprise suprise the Tri-Z 13/44! - thats why your top speeds are so different. This is the same discussion everyone gets into involving T-4's, TRX250R's and LT-R's - yes we all know the LT-R's were geared way too low at the output shaft and ran out of grunt on the top end when compared to the others, so what - they are great woods machines and a lousy $12 sprocket will change that top speed number real quick (assuming the chain and rear sprocket are in good shape). I think this holds true for the Z as well. ... I think Tim has a great point too in that "What the hell really is stock anymore anyway".

[TimSr]

Im thrilled that a discussion has lasted this long and still remained civil and intelligent. You folks have restored my faith that intelligent life does exist here!

I started thinking about it, and realized that since 1990 when I got my Z, the only things left of my original Z (which was not original then) are the frame, forks, front wheel and front brake assembly, carb and intake, gas tank, fuel pump, flywheel and cylinder which is on its 8th bore (after resleeving, of course). I just take for granted that I have an 85 Z with an 86 motor, when in fact I only have a giant cluster of parts from everybody elses aborted projects!

[200xer]

My 86 Z is stock except for the pipe. And I hung right with a brand new Banshee with FMF pipes in a short drag race. I also have BIG 22" tires on back, so acceleration was limited more than it should have been. I wouldn't call it slow by any means, but I haven't ridden a tecate or R, so they might be faster. It doesn't matter though as long as you're having fun. 8)

[Darius1502]

Tim,

You are right it has been a very interesting discussion...between this and my debates with MR ATC in the thread "Would you trade"...I wonder how I get myself into these situations.

Oh...I also promise I will stop posting pics of my project...I am just sick of waiting on my axle.

I would like see that ATV News Test. Also let me know if you guys want me to scan in any tests from the 80's on the Tri Z. I have both Dirt Wheels tests of the 85 and 86, plus the ATV News Tests...which are pretty detailed.

Maybe when I get my 86 running and can ride it for the 1st time I can give some real feedback.

Looking forward to more debate!

[Jeb]

I've been reading what little I could find on the internet about rake. Once again it's defined as the angle of the steering head off a line perpendicular to the ground. On most everything, the forks are held in an attitude parallel to the steering head, but moved forward a couple inches for more available steering lock. Some triple clamps increase rake by having a slight twist actually in the triple clamp. I don't believe this to be the case with the Z.

Take a look at my CAD sketch. I don't care what yamaha printed or dirtwheels printed. The 86 Tri-Z cannot have a .22 degree rake. It has to be 22 degrees. Unless yamaha measures rake differently. I also did some other sketchs that show the different tire combos change the rake .5 degree with out changing steering head angle. I used same wheelbase and some other assumptions which may not be the case. It does prove my own personal 85 Tri-Z has even MORE rake because I went to 18" tires out back. No wonder it doesnt corner as well. The added 2 inches on the W.C. Swingarm helped some. I need to try a 23" front Tire. And I still think the beefy 86 forks would help because of the flex of the skinny 85 forks. The 84/85 Tecate is the same way in the fork flex department.

Tri-Z Weight distribution is another issue in my opinion.

I agree 100% that the 86 tri-z is an improvement over 85. I just think you could set up an 85 to handle as good as an 86. But either or will never handle as good as an 86 Tecate or an 86 ATC 250R.

I know, useless info but it's been interesting research.

Darius, So your Houston area. I live west of Ft.Worth.

[TimSr]

Excellent research Jeb! I see this kind of stuff keeps you awake at night! "Rake" is almost self explanitary as to what it is, but that was a great catch on how its measured. It kind of reenforces my own personal belief that no earth shattering engineering design changes were made on the 86 model over the 85. Im still open minded, but am not convinced otherwise.

I concur with your observation about the 18" rear tires, though I believe you mean reducing rake (less of an angle) to cause worse handling. Last year at the fairs, I raced with 22" All Trax (which suck on the track) because the 18" Turf Tamers were even harder to corner with.

If you are correct in your method measurements, its no wonder I cant see any improvements in the 86. I run 22" rears, and slid the forks up over 2" so my Z probably has a lot more rake than a stock 86.

[Jeb]

Yes, I've wasted too much thought time on this! :-D In the grand scheme of things does it make a rats-@$$, no. :-D The engineering behind it is interesting to me.

I hope what I've come up with is right. I went to Kawasaki's web site and they list the different KX rakes in the 27 degree range. that's quite different from 22. I couldn't find rake measurement in the specs at yamaha's web site.
I wish someone could accurately measure the steering head angle between the 85 & 86 Frames. I could, but I don't have an 86. I'd just like to know if they really changed it or not.

[MR ATC]

one thing you may want to consider. triple clamps and steering stems can be changed to alter your rake without changing the steering neck on the frame. it's cheaper to manufacture these changes then to build a new frame jig.