Tire Suggestions for CMF 125 XC Bike

[Dale Fisher]

Pres. Paul forwarded this information.



Dale Fisher
Penton Owners Group - Memberships
Facebook - Cheney Twinshock Racing Group - Administrator

'70 Six-Day 125 - V2017
'71 Six-Day 125 (Dave Fisher's) - V5553
'72 Mudlark - W257
'73 Jackpiner - 175 21159727
'74 Berkshire 100 - 40171056
And some silly other bikes...

[Paul Danik]

My comments below are given with all due respect to those who do feel otherwise.

The spec. sheet above shows that the 125cc CMF Sachs powered Penton came with a 4:00 X 18 rear tire.  I am almost positive that we ran 400 X 18 rear tires at the 1973 and 1974 ISDT on the 125cc machines, and I know that I personally ran the 4:00 Metzler with 14 X 57 gearing in enduros, mud runs ISDT Qualifiers, ect, and loved the way that bike would get through the crappiest of conditions, well as high speed situations. There is another very important part of getting good results with that tire and gearing, proper carb setup. Not lean enough to hurt anything, but very clean running and crisp in the low to mid range, and the availability of plenty of fuel mix at fuller throttle openings.

Possibly in other parts of the country that size tire was not the hot setup. I know when we raced in Barstow I was not a happy camper and possibly a smaller rear tire would have been better for that event, but putting a mudrunner in a giant sand box was probably the problem:) For my money you just can't beat a 4:00 X 18, or what ever they call them today, on the back of a 125cc CMF Penton. For MX I always ran either 14 X 60 and sometimes 13 X 60 gearing, depending on the top speed needed and if a second gear start was desired.


Paul

[Dwight Rudder]

I do believe that Parts Unlimited (see your dealer)has the IRC VE33 in a 100/100X18 size which is a 400X18 Trelleborg copy. I have a Cheng Shin C183 400X18 (Barum Copy) on my Six Day 125 but they don't make it anymore. If you can get one on Ebay they only quit making them about a year ago.

[Dwight Rudder]

I believe the Duro 4.60X18 HF335 is about the same as a 400X18.

[pklinck]

Brian, Tonupchad,

I run a pair of MT16 Pirelli tires of my 73 penton 125.  The rear tire is 110-100x18 which is the same as a 4.00x18 tire.  I weight only 140 lbs. and so it is fine.  However, with the proper gearing and carberator adjustments as Paul says, heavier people also used the 4.00 rear tire on a 125.   Naturally, with lots of mud, maybe a 3.50 is ok too.

There are lots of good tire brands out there you can check in the the Dennis Kirk catalog such as Duro, Michelin, Pirelli (MT16), Metzler (unicross), etc.

peter klinck

[tonupchad]

Thanks all for the advice on my tires.  I ended up with the Duro HF335 rear for my CMF 125 and MT16 for the front.

The Duro looks a little small but it's big on traction.

I ran a 14/57 setup for White Lightning.

I picked mine up at Powersports Superstore for $47.38 FYI

http://www.powersportsuperstore.com/Duro-HF335-Cross-Country-Tire-Rear-4-10-18-Po-p/4155514.htm

Highly recommended.

'73 Six Day (CMF)
'68 Six Day Wasselump

[brian kirby]

Peter, that Pirelli is WAY too big for a 125, its too big even for some 175s. That 110/100-18 should be the same size as a 400-18, but it is not, its bigger. Your bike will respond and perform much, much better with a smaller tire.

Chad, the Duro might look small, but you are used to seeing modern tires, it is the correct size for a 16-18hp vintage 125.

As for gearing, I run 12/57 and I personally would not run anything taller. I ran 13/57 one time at the '08 ISDT Reunion Ride in Tulsa, but it was too tall. I went to 12/57 and have never run out of top end speed. In the real ISDTs and enduros of the time you needed really tall gearing to make up time on roads, we dont have that issue with Vintage racing. You should gear your bike to go only as fast as you will need it to go and no more. The lower you can gear it the better it will come out of corners, where it really counts.

Brian