Rear tire size for 125 Six days

[jasonlamar]

I need a rear tire for my six days for racing.  I bought a Pirelli 110/100/18 and it looks way too big.  After searching the posts here, I see that Cheng Shin C755 4.10-18 is recommended.  Would someone mind confirming this? By the conversion charts I have looked at, it doesn't sound that different than the 110.  Is the Pirelli I bought too big as I suspect?  

Thank!

[Kip Kern]

3:50 x 18"

[jasonlamar]

I know that is the stock size.  Why can't I find an mx tire that size?  Sources anyone?  Much appreciated.

[Richard Colahan]

I have a 350 x 18 Barum on my 69 Steeltanker...but I do not race that bike...doubtful that a 400 section tire would clear the swing arm.
Perhaps a 400 will fit on a CMF...someone else will have to offer an opinion on that.
That 110/100 will surely be too big.

I do use a 100/100/18 Maxxis on a 73 Husky 125 WR that is used for CC races.
Works quite well.
Perhaps do a search for a good 100/100



Richard Colahan
1969 V1225
Upper Black Eddy PA

[Bill Ryburn]

Since you have not stated whether you have a Six Day Steeltanker or Six Day CMF, the tire answer can be different for each of these models. The Steeltanker has fewer choices.
Several of us have numerous times stated that the Duro H335 is an excellent choice for a rear tire. It fits the short swingarm on Steeltankers very well.
I have used both Cheng Shin and Duros and find the Duro far superior for my riding in both Cross Country and MX events on my Steeltanker.
The CMFs Pentons have a longer swingarm and can take a wider and higher profile tire, but I am not sure why you want anything bigger on a 125cc.
Also, Duros are much easier to find than Cheng Shins.
  Bill Ryburn
  V1893

[jasonlamar]

Thank you for replies. It is not so much that I want to put a large tire on my cmf framed bike. I tried to match what was on there which was a 4.00-18 not knowing this was not stock. The swing arm on my bike is from a later bike and not stock so fitment may not be my issue. I have gathered from this site that I don't want to put too large a tire on the smaller engined pentons.  My concern is changing the handling of the bike too far from design.  I am not familiar with Barum and Duros. I will keep them in mind. Thanks again for your time.

[jeff greenberg]

For what it's worth, used to run a 3.50 Metzler on the 100 & 125
The 4.00 always seemed like too much tire. Harder to "break loose" when you wanted it to,

[Dale Fisher]

I think it is important to note that one manufacturers 3.5 or 100 or 110 width is not the same as the next. Some have larger side lugs which make the overall profile wider.  Although the rim side is fixed the outside diameter also varies.  You really need to get that overall dimension(s) although at times it's not so easy to find published.  I run a Metzler 100/100 MC5 on my '74 Berkshire which has worked well in all conditions.

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...

[Richard Colahan]

Agree with the opinion that same sizes differ in reality per manufacturer.

And as a point of reference...my modern era Honda CRF250X...which has significantly more power then a 70's Sachs 125...specs a 100/100/18 tire. A 110/100 actually seems like too much tire for that bike.

Don't fear that a "smaller" tire will hurt...It's more likely to be just right!

Richard Colahan
1969 V1225
Upper Black Eddy PA

[brian kirby]

The Pirelli is WAY too big. The Cheng Shin and Duro 4.10-18 tires are much smaller than their number indicates, much closer to a Metzler 3.50-18. As far as I know the Cheng Shin is no longer available, and the Duro is now the only option that is small enough. The Duro HF335 is a much better tire than the C755 anyway.

Brian

[jeff greenberg]

My memory is a little foggy, but was there a Metzler 3.75 x 18 back in the 70's?  I thinks that was what we (at Piasecki's) were running on our 125's
Jeff

[Dwight Rudder]

Duro 4.10X18 with a Pirelli MT16 front.  
A Cheng Shin can be also used but is a bit smaller tire.

[454MRW]

Not trying to get off track on the subject, but has anyone tried the IRC Volcanduro VE33 tires? My RM restorer friend uses them and they have a 100/100-18, and look vintage. It is listed more for intermediate to hard terrain. Mike


Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R

[Denis Jeffries]

Try kings tires, I have 100/100/18 on my super rat. looks about to be a 3.75x18 in size

[brian kirby]

The VE33 is too big for a Steel Tanker or CMF Sachs Penton. That would be a great tire for a Jackpiner.

Brian