Truth or BS? Rear Wheel Swap

[morbidelli17]

So I'm back in the MZ racing game. I really, really want to mount a new rear wheel onto the thing.

Who has actually done the rear wheel swap? What wheel did you use? What did you have to machine, cut, space, etc.?

Thanks - M

[edfmaniac]

I just contacted HPS to see if they still distribute wheels for the Skorpion and they do. The problem is the price. Here's the email that I received. Good luck finding the right wheels at the right price and I look forward to seeing what you end up doing.

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Hi Victor,

Thank you for your email.

We can still specially order the Dymag Cast Magnesium Wheels for this model (these are the 3 spoke design).

Price would be £2,250 plus shipping (£154.89) - these take approximately 4-6 weeks to produce.

Hope this helps?

Regards

Ben

[basser23]

So you're back eh? Cool!!!
I've heard tz250 3ma wheels work...Bill J knows for sure...Suzuki Gs 500e are supposed to work also,which means Gen 1 sv wheels should also work.
Bill J put out a list of weights of wheels on the mzog@yahoo.com I think.I'll look...
Did ya get your old Skorpion back,or are ya doing from fresh?
Chip

[basser23]

just happen to think...the swingarm is essentially an Fzr 600/R6 so....maybe an R6 wheel?

[Bill Jurgenson]

It should actually be well known that I have done the swap several times, as often as I have written on the topic.

where so you think I got this data? Made it up?
For street use, I have fit the Brembo wheels from the SZR (3.00 & 4.00)

http://home.arcor.de/w.jurgenson/pdfs/Distanzhuelsen.CAD%20(Brembo%20spacers).pdf
several times and twice TZR (3.00 & 3.50)

I use this set on the road myself with a 130/70 rear tire, just like the original Skorpion prototypes did.

The front wheel is the same for the TZR, SZR and FZR400. For real racing the 3" and 4" wheels are too narrow as there are no tires that fit them.
I have also explained this more than I care to think about. One could of course go for the narrower TZR set and use GP125 slicks. This would be the best bet, if you can get the weight well down. I know someone going this route. The 3,5" rear wheel is very light.
And once PVM 3 spoke (3.50 & 4.50).
And I have fit both the 4.50


and 5.00 Brembo rear wheels (TZ250RR) and use both for rain tires and SuperCorsas on the track.
To go with the wider Brembo wheels, I fit a 3,5" FZR front wheel but that is not so simple since the wheel hub itself must be machined down so that the rotor matches the caliper.
But for racing I fit Marvic magnesium wheels, in 3,5 and 5.00"


and used Bridgestone slicks.
All of these with the stock swing arm but in every case with the brake plate from the SZR/TZR/FZR and Brembo caliper. At the front always a Brembo P34 except for the last season on the track where I fit an ABM billet caliper and radial pump.
Pretty much regardless of wheel, you will have to replace the front axle. For the Brembo wheels, the 17mm Yamaha axle that goes with them is ideal. For my racer which had a Paioli USD fork, I made my own stepped, hollow 17mm axle.

At the back, it all depends on which wheel is chosen. I stayed with a 17mm axle for the racer and for most of the rebuilds. Nowadays I prefer to use a 15mm axle for the Brembo wheels like the Yamahas have.
That is all I can verify from my own experience.
Chris Hunsicker also fit the TZ250RR wheels to his Skorpion, long since sold.

A number of riders over here are using the wheel from the SUZI GS500 and one or two use(D?) wheels from the RGV. Again in the stock fork and swing arm.

For the front, I would get the RSU fork from the first R6 complete with wheel and brakes; it is 41mm like the stock fork and fits right into the clamps.
The R6 swing arm is not the same but it can be made to fit, given a basic machine shop. There is some data on this over at the Yahoo MZ owners group.

[basser23]

there ya go Michael...he knoweth....
The weight info is over at mzog at yahoogroups.com under the files section

[Bill Jurgenson]

BTW, Dymag went bankrupt, the rights and apparently some technique was acquired 2010 from the liquidation and a few sizes are again offered, all large and only usable for SBK.
the smallest rear wheel is 5,5". At the quoted price, I would definitely add a bit to that and buy BST carbon fiber wheels in those sizes. If the present source offers smaller sizes, they will be old stock. Old stock is bad news with mag wheels which have a short shelf life; they deteriorate (oxidize) fast.

Like I said and knowing what I do today, I would go for narrower and reduce the weight radically. It is possible to grt the weight down to 125kg ready to race and without CF fairings.
CF body work and tank would reduce further.
The 3,5" Brembo rear wheel is only slightly heavier than a similar cast mag wheel,

[morbidelli17]

Thanks for the info. I've read a lot of Bill's stuff over the years, so I had hoped you would weigh in!

I want to retain the stock swingarm, and I already have a plan for the front. I'll need at least a 4.0/4.5 inch rear wheel to fit the 160 DOT race rubber from Michelin, which is what I want to use. I was interested in the 125cc wheel route, but I'm not sure I've got the $$$ to get the thing down to 125kg range, and I'm a geezer so I leave the starters on my race bikes, thank you very much! With aluminum subframe and SV650 race tail, the thing weighs 361 lbs with some fuel in it.

I had hoped that a production wheel would fit, as I don't know if I've got the $$$ for the Dymag/Marvic/PVM route. I also have the option of getting a production wheel in 3.5-inch width and having it widened by Kosman. I've had them do an SV wheel for me when I was experimenting with a 5.5 inch tire on the SV and they did nice work, and for $475 it's still less than half the cost of a full race wheel (and actually weighs a bit less than the stocker when they're done).

So ... Let's start here. Does anyone have measurements and a step-by-step for mounting a GS500 wheel?

Interesting sidenote: My friend (who bought my Mz, worked on it, then sold it back to me) is having KTM 640 wheels fitted to his bike. And yeah, I missed my Mz more than I knew I would. Long story about the last race of the season that really drove the point home.

[Bill Jurgenson]

$$$$?
Who said racing was a budget proposition? Don't delude yourself.
you need a lot of elbow grease, some ingenuity, an angle grinder and hand tools.
And you need a start machine. A main culprit weight-wise is the heavy motor. removing starter, flywheel etc. gets it down to about 40kg from nearly 50 and doesn't cost much at all. A LiFePo battery for the ignition takes off another 3-4lbs.
The other culprit is the seat frame but you mention tackling that. Don't forget the fairing cage. And throw out those horrible clipons and rearsets. You can make your own rearsets with little more than a drill press, saws and files. I did; look at the one on Hunsicker's bike, those are mine.
Of course the Grimeca wheels alone amount to 29kg compared to the SZR's 23 let alone the TZR's 21kg, always complete with tire and rotor and chainwheel.
You would have still not spent any real money.
Barker's exhaust weighed next to nothing and while we are not talking about peanuts, you need a decent exhaust one way or the other.
then there ae all those nuts and bolts, mort of which can be subsitute with aluminum if the quality is good. A few need to be titanium: the 6 in the cam cover either side of the cam for instance. All the rest can be alu. Ditto seat frame bolts, fairing cage bolts, clipon bolts, banjo bolts, hugger screws front and back. All caliper bolts and those fastening the calipers to the bike need to be titanium. All three axles must be steel by regulation but they can be drilled out.
The mag wheels were my last resort, not my first.


sizes:
for the 160 tire you definitely need a 5" rim.
4" is far too narrow and only viable up to 140. The stock 150 needs 4,5"

wha'dya mean by Michelin race rubber?
From bad experience, I would not touch Michelin with a ten foot pole but that was with PiPo road tires.
At the moment, the only racing tire they offer is the Power one which is available in 150 as treaded (sculpté) tire (only 17"), slick and rain tire (only 16,5") for which at least the 4,5" rim would be necessary. I have no experience with this tire myself, since it is new. I found the SuperCorsa SC (front SC2 at 1,9AT,rear SC1 at 1,7AT) to be as good as I would ever need in a treaded tire. The 150 Pirelli is actually only 143mm wide so it can be used in a pinch on the 4" rim; Pirelli's reference rim is 4,25".
As mentioned above, I used Bridgestone slicks. Today I would at least try the BT003 racing:

There is even a 140 version of this tire which fits ideally on the 4" Brembo rim.

b

[morbidelli17]

Thanks for the suggestions and encouragement. You're right, there are some major bolts that can be swapped and/or drilled and cut. Definitely going to one of the superlightweight batteries, and new fairing mount and rearsets are in order, too. (I've just come into some Ducati race plastic, I'll see if that fits).

We get different tires over here in bigger-is-better U.S.A. Dunlop makes a 160 treaded rear that fits a 4.0 rim, according to its website, and we don't get the BT-003 in the 140-17 size.

More later. Thanks for the info.

Oh, and believe me, after 17 years of racing, I know even budget racing isn't cheap. I'm terrified to total up the receipts at the end of the year ...

[ejunker]

Has anyone tried using the 3.5, 5.0 x 17 Marchesini wheelset from a KTM640/690? What do those weigh?

I'm not racing, but that wheelset looks likely for a good street setup as an improvement over the OEM Grimeca's.

I figure for a 120 front and 140 or 150 rear tire.

Look forward to responses!

E.

[morbidelli17]

A friend just did that swap on his Skorp. Says the 690 wheel is about a pound lighter than the 640 wheel. Tricky spacer work, but it looks nice.

[morbidelli17]

I just got the SV front end onto mine.

[basser23]

M , looks great, how much of a bear is it? Ever figure out the rear wheel swap

[morbidelli17]

I'm told the SV front end installation wasn't too difficult. My guy machined the steering stem to fit the bearings, shortened it and cut new threads into the top. After that, obviously, everything else bolted right in. Understand that I went this route because I had a straight, newly reconditioned SV front end with Traxxion Dynamics damper rods and Gold Valve emulators and ti bolts just sitting in the garage, along with two SV front wheels of the same color. The goal is to get a lighter, wider front wheel for racing rubber, and hopefully that will also offset the additional weight of an extra (but smaller) rotor and caliper. The other advantage is in parts availability; instead of looking for MZ parts, I can just use SV stuff.

Rear wheel looks like we'll be trying spacer/sleeves to adapt the SV wheel to the smaller MZ axle. Will keep you posted.