Pipe dreams and conjecture.

[nice2day]

Ok. Not much happening on this forum currently so I thought I'd air some long held thoughts regarding the Saxon range of two strokes.

I own a 301 Tour and bought this new in around 1994 I think. One thing I did not really like was the 16" rear wheel, it just did not look right and made the bike look too short in the wheelbase which, in my opinion, makes the steering a little too light as well.
I always considered IF ONLY the designers had made the new "box section" swinging arm about 50mm (2") longer and also used an 18" diameter wheel or even a 17" ...but certainly NOT a 16" one which makes tyre choice difficult and looks puny. The longer swing arm would have needed longer chain run and protectors but not difficult to change. Also the rear section mudguard could have been made slightly longer. I'm sure this would have made the bike look and feel better though.

By the way, I wonder if anyone has ever fitted an 18" rim on the rear of the ETZ 251 range? I'm sure that would also look better. Shorter shocks would keep the seat height the same...Just some thoughts that always drift through my mind when I look at my Saxon Model...

What changes would you have made? Please keep to sensible but practical, relatively low cost mods...
Look forward to your ideas.
Les

[Puffs]

Les, interestingly I addressed the very same issue in my first thread: viewtopic.php?f=5&t=9127. Have a look there. Yes, people have fitted an 18" rear, but IMO it would require longer shocks (by 1"), to fit the wheel at the end of the shocks's stroke.

Personally I have not fitted an 18" wheel, for me fitting a bigger 110mm/90% x 16" sufficed (matched with a 90/100x18 at the front). It gives a bit more ground clearance & handling is fair. It remains a very agile little bike. Obviously the speedo underestimates if you increase the circumference of the rear wheel. I also fitted a 1T smaller front sprocket.

My biggest gripe with the 251 (was that the first to have that geometry?) is the seating position, with the seat a bit low & your feet to far forward. I raised the seat (probably close to 1") and with the tips of my boots on the footrests it'll work. Maybe once I'll make rear sets around the pillion footrests, as for instance shown in a pic breakwellmz showed recently.

[Blurredman]

You know, I think this is something that I could actually do now..

I have both a 251 and 250. And I do believe I have an 18" spare rear wheel (I must check though that it isn't a 16" because I'm silly and I have lots of 'stock' for lots of different bikes). It also happens I have a spare 3x18 tyre that I could put on said spare wheel.. Maybe I should see if it fits when I get some time...

I do recall Puff's inaugural thread, and I recall the discussions that bounced.


I myself wonder why MZ went back to their origins in regards to civilian bikes, the ETZ250 is the only one native with an 18" at the rear - why did they change back..? It means you have to carry two different sized tubes whilst touring! I agree with the above. I feel the longer (and sleeker) 250 gives the bike a more stable feel, esp in higher speeds- the 251 can tend to have an underlying wobble and become sensetive. But is that rectified with a larger wheel? I don't think so.. I think the length has a good deal to do with the stability there.

I must admit I've never used anything other than a 3.5x16 on the rear of my 251..

There are benefits to either. The rear wheel on the 251 is nice to remove..

But as I say I have both bikes so I don't see the point to modify one. I take them for what they are and have done very little in the way of modifications to either. All bikes have different feels to me, like everyone has a different personality..

I don't think that answers any questions though- but my 251 is physically accessible, so I may indeed put a tape measure to it and maybe offer up the 18" rear wheel..

[Puffs]

IMO the main difference between the 250 & 250 is in the frame, I think the part below the tank is quite a bit longer on the 250. Thus placing engine & footrests farther back.

[nice2day]

Some really great points on your replies Puffs and Blurredman, I'll come back on these a little later. Just for now, before I take my dog out or his daily walk, I've knocked out a very quick alteration on an MuZ showing original and lengthened bike with bigger rear wheel. OK it was done in about 5 mins so it's very rough but maybe enough for you to see the "Improvement?..or ruination? For me I'd take the longer bike if factory made that is: CU later.

Les

[DAVID THOMPSON]

the rotax bike pictured
i have one it handles good but needs your attention its fork does not rotate as far as some
i had been riding a BMW R50S before i got it.. i turned into the driveway and almost hit the
mail box when it hit the stops

do not go girl watching on it it will bite you if your not paying attention

bike is a good runner

just pay attention to what your doing when riding it
and if an old /2 BMW handles funny check the forks to make sure its not set up for a sidecar
and not been changed back to solo
dave

[nice2day]

Right I have a little more time now...I have always considered the ETZ 250 to be the better looking bike simply because it has both wheels of 18" size, but hadn't realised the 250 version also featured a longer frame, so I'm really looking forward to finishing the bike and riding it. I bought it as a non runner and I guess I'm spending too much on it trying to get it back to virtually a new machine. Will I ever sell the Saxon 301? Well it looks immaculate as I have always kept it well but there was always the fact that I never felt confident laying it over much on bends as I was just not getting any feedback from the front. I fitted racing front springs, different tyres which helped just a touch but the most peculiar thing was riding straight lines in between slow cars moving on motorway slow downs and hold ups....I kept getting this un-nerving feeling that I had to concentrate just to avoid wandering left or right rather than just travel confidently in a straight line between the cars, so much so, I had to stop as it was making me feel giddy. This was caused by the bikes lack of self-centering, it was just far too light at the front or not enough trail on the steering made worse by the fact it has quite a heavy half-fairing attached to the forks/handlebars which I reckon amplifies any lightness by adding to the inertia of movement and thus exaggerates the effect. Anyway that was the worst thing about it and hopefully the ETZ 250 will be much better steering wise. I'll check the specs for the wheelbase of the models mentioned above just to see if they are different. All the best and thanks again....Nighty night....Les

[Blurredman]

I took my spare rear wheel out- it is an 18", so can test. Need to buy new bearings for it first though. They're already in the post.
I don't think it will fit though, or if it does it will be merely mm from the swingarm cross member. Might be able to get away with using the 3" tyre as opposed to a 3.5".... As it stands, it is pretty much an inch, maybe one or two 16ths over, space between the crossmember and the 3.5"x16 wheel that is currently on there..


I hear you regarding the fairing.. I ride this:

Of course, it's a bigger machine than your 301, and also a lot uglier.. But it is straight and stable at speed, and actually, very confidence inspiring in the corners, HOWEVER I experience what you do regarding low speed riding between two sets of cars. The white lines, the tarmac joins, influences the fairing and the gravity of the bike largely and can cause some sticky and close situations in that scenario. Now your fairing is a heck of a lot smaller and lighter so might not be the same situation.

Is it possible you can remove yours to test? Also.. These MZ's use single piece caged wheel bearings, so it is not really possible to tighten up the head bearings?

[Puffs]

Les, yes I think I read Guesi write that somewhere; the spine of the frame (which runs below the tank) being longer on the 250. And it makes sense, comparing the tanks of the 250 & the 251. I've also considered buying another 250 frame (yes, you can buy those, new), but there is an awful lot you'd have to replace then. More than just the rear wheel. In fact just about everything except the engine & the front end.

Insofar as road holding is concerned, for normal commuting/road use, I don't think there is all that much wrong with the 251 geometry (which I presume is identical to the 301). Yes, it's a bit twitchy, but you can work with that. Bigger, good quality tyres help. But indeed, the bike is a bit small. Too short is what others think too (also of the 250), see https://www.returnofthecaferacers.com/s ... -mzetz250/.

However, one can ride/tour satisfactorily with a 251 (/301); from what you describe: are you sure the steering head isn't too tight? Has the steering head angle changed over the years?

BM: no, I remember from that earlier thread: you can fit an 18" wheel, but only with a very small tyre and you'll loose chain adjustment range. You also need another swingarm. + shocks + mudguard + something else...

At low speeds wind is not much of an issue & a fairing should not impact riding??? I don't know, you saw my fairing...

[nice2day]

Really interesting replies again. As far as the Saxon fairing affecting the handling, the point I'm making is that on my Model Tour, it is fixed to the handlebars NOT the frame as your bigger bike has Blurredman. So as said above, the slightest wobble, breeze or surface change causes all that weight to gently pull on the bars, and as you know, the very slightest pull on any one side causes an immediate reaction in the opposite direction. I'm not saying I feel it zig zagging all the way along the road but the strange feel it has takes away all my confidence from the front and road surface. There is the other model (was it the Saxon Fun?) where it wears a different style fairing and this is fixed rigidly to the frame and not the handlebars thus leaving them free of the extra inertial weight. Unfortunately I find this bike extremely ugly but I reckon it will steer better. I feel sure the ETZ 250 is going to be so much better....well it had better be as I'm spending a small fortune doing it up.
Hi Puffs, that ETZ in the photo looks really good. Checked all the steering bearings etc...I'm just left with no confidence in really cornering fast or even leaning over much when taking in town corners, I just get zero feedback from the front so take no chances.
Les

[Puffs]

Looking in the manuals, wheelbase is not specified, but I measured my 251 at about 134cm. Of course it depends on how the rear wheel / chain is adjusted.
For steering angle (Lenkungswinkel, rake) they specify 63° for both the 251 and the 250.
Surprisingly they do however specify a different trail (Nachlauf): for the 251 = 112mm (and 105mm for the 125/150), vs. just 95mm for the 250. So apparently the fork offset is different??? I always thought the forks were identical, but apparently the yokes are not.

If you put a bigger rear wheel in, the rear end comes up, the rake gets steeper & trail reduces, making it more twitchy & less stable going straight. Maybe a bigger front tyre would help you?

I presume the 301 has the same geometry as the 251, but I'm not sure. Maybe it has the 250 yokes with less offset.

[nice2day]

Very interesting Puffs. Yes, less trail will result in faster steering with less straight line stability....we would need to find out what the trail was for the Saxon models.

By the way, previously I used the term INERTIA when talking about the handlebar fairing. What I meant in that example was "KINETIC ENERGY" not inertia.
By that I meant that any movement of the steering would cause a greater (longer) turning action of the bars due to the extra stored energy (extra mass) of the fairing.

Then again the actual INERTIA of the fairing (reluctance to move due to its mass) might dampen the natural CASTOR action of the steering set up thus "delaying" the self centering correction that naturally occurs. Any minute delay will encourage a slight weaving effect. Both theories seem to be at odds with each other but I feel confident that the fairing does effect the steering in a negative way. One way to prove it would be to remove the fairing and do a comparison ride of course.

All the best. Les

[Blurredman]

So, In my restless pondering state I've decided to test this out.

I did buy bearings but they have yet to come, but after fitting a tube and tyre to my spare 18" wheel, I couldn't help myself but have a look.

Here are my findings, keep in mind without bearings there maybe some changes to clearances, but they're large enough in my conclusion for this not to be a factor. I moved the wheel about to try and ascertain any issues but found none. Of course it helps that the right hand side of the wheel mates into the cush drive fairly squarely, wheel bearings or not. I am also sorry for the poor photos, it's not a nice day and I also couldn't be bothered to get things out of the way in order to wheel the bikes around for better camera angles..

Foremost:

The chain on the 251 is new. The adjustment in the tension is approximately in the middle, not extreme to either direction.
The new tyre is a 3x18" Mitas H-03 with only a few hundred miles worth of use.

- Gap between swingarm brace and tyre = 1/2".
- Gap between bottom of tyre and ground = 3/4".

I think it doesn't look too bad in my opinion... I would wonder what a 3.5" mitas would look like instead, but I think that might be touching it a bit fine with the gap with the swingarm brace. Of course, the tyre itself wouldn't look like a bicycle tyre if it was 3.5" but I don't think it's worth messing around with my two bikes just to see what it looks like and then swap back.. Clearance IE mudguard all look fine. It's quite a deep and wide mudguard on these 89-90 251's (as you can probably tell by the rear facing pic)... But the front side still looks like it would clear without an issue.

By the way, distance on 251 front axle to rear axle approximately 52.5".
Distance of 250 front axle to rear axle approximately 54.75"

Of this, the 251 is from front axle to swingarm spindle: est 35" and swingarm to rear axle 17.5"
And the 250 is est 36.5 from front axle to swingarm spindle and swingarm rear axle 18 and 1/4"
Not scientifically done, but - it emphasises that there are length differences in both swingarm length, and also swingarm spindle forward.. It's not all about the swingarm length and subframe, as puffs says.


When I get my bearings I will re-install the wheel and have a little pootle and see how it runs/rides.. Might be fun..! All in all, it really doesn't look too much taller than my 3.5"x16" wheel in reality..

[nice2day]

Oh Blurredman, what a tremendous effort you've made! I really applaud you on this one, especially doing all that measuring and then actually swapping over the wheels. Really well done and so interesting actually finding out the different lengths and distances.

As Puffs says, the steering trail will be reduced very slightly so this will minutely quicken the steering so it will be interesting to compare how it handles. New rear shocks of 1" shorter would return the original geometry and seat height as long as you had sufficient clearance under the rear mudguard for the tyre and fitting the longer 250 swing arm would also load the front end more and increase stability too.
I would be very interested to see how it looks too (does it look better as I had imagined?). Perhaps not so much on the centre stand (which is probably a little wobbly now?) but propped up on the side stand so the suspension is loaded ....Once again many thanks for taking this up.

By the way I notice the number plate has the supplier of "DC Butler" . I knew that shop in Stanstead Abbots (is it still there?) , I wonder if you live in that area? I was going to buy a new Enfield Bullet from him back in the 80's, he was a friendly bloke, but I never did.

All the best

Les

[Puffs]

Gents,

firstly Les, I'm not sure I quite follow your 27 Jun 2020, 12:35 post, but if I remember correctly, sir Isaac taught us that kinetic energy = ½mv², and that F = ma. Anyway, if you cannot find specs, the geometry could also be measured. And specs appear to be not always completely accurate or correct. And finally, yes, try it without to feel the difference (if any).

Then indeed, ta Blurredman for all that effort to confirm that indeed an 18" wheel will only fit properly with a very small tyre size. You fitted a 3.00" tyre, which gave you 0.5" clearance to the front brace, with the wheel in the middle of the adjustment range.

Tyres in imperial sizes are normally 100% in height, meaning they are as high as they are wide. This is particularly so for the relatively small sizes, but for bigger sizes (>5") not so much, those are less high. Anyway, it means that if you would fit a 3.50" tyre, it would sort of rub that brace, with the wheel mid-way in the adjustment. And would give about 0.25" clearance below the wheel, when on the centre stand. But: a 18"x3.00" tyre will fit & work well, with some possible limitation on the adjustment range. Note that Eric Frith fitted a similar tire after moving that brace forward:

21.08.17 003.jpg (59.81 KiB) Viewed 1698 times

The standard tyre is a 16"x3.25", so a 18"x3.00" will raise the back by 0.75", given the wheelbase, the difference in steering angle & trail is easily calculated.

One thing I'm not sure you tested is what happens when the shocks reach the end of their travel. The top of the tyre will then also come 0.75" further up. It may fit, they probably gave it quite some clearance, it may not, certainly not if a bigger tyre were used, like so: Image
See the wood below the centre stand & that the tyre is not quite properly centred around the wheel axle, as it can't go farther forward. OK, it's an 18"x4.50".

Anyway, that is something that also needs to be tested (by taking off the springs & bump rubber). At the time I eyeballed it, and I didn't think it would fit with a meaningful tyre (and no, that is not the 4.5" one). Also, I believe the shocks for the 250 are 20mm longer (in fully compressed length) than those for the 251. So you may have to fit those taller shocks, and add their extra height (x the linkage ratio) to the previous 0.75" for the new geometry.

Ta for your measurements of wheelbase & where the swingarm spindle sits. Your wheelbase for the 251 = 52.5" = 133.5cm = pretty close to my 134cm with the wheel nearer the end of the range.
So the 250 = 54.75" = 139cm is some 5.5cm longer. Of which 1.5" = 3.8cm in the frame, and 0.75" = 1.9cm in the swingarm - great measurements, very useful! But I can't remember having said that 'it's all about the swingarm length and subframe', I think I said "the spine of the frame (which runs below the tank) being longer on the 250". And indeed, apparently 3.8cm.

One question I would still have, wrt the comparison 250/251, is if it is indeed correct that the yokes / triple clamps are different? Only that could explain the difference in trail. According to their specs, the stanchions on the 251 should be 17mm further forward... Or just an error in the specs?

Finally Les, no, I do not think you can/should fit shorter shocks, I think if anything you'd need taller shocks for reasons outlined above. Also, note that if you would fit a longer 250 swingarm, the bottom shock mounting point would be further back (probably by about 1.9cm), changing the shock's angle & linkage ratio. A bit, not much, but I think it would require calculation. Of course the upper mounting point on the 250 frame might also be different. And with the wheel 1.9cm back, and 0.75" bigger in radius, it might no longer fit inside the standard mudguard.