Vintage Dirt Bike Q & A

this is more of a general question, but since my bike is a cr i figure i could post this here.

my wheels are: front 3x21; rear 3.5x18. i need metric conversions for tires/tubes for these, i believe they are both 80/100s. is this correct?

also, who makes rear tires/tubes with this small of a width? is this like a special order type thing or what?

im more concerned about the tubes, i need them now whereas the tires can wait.

thanks in advance!

Those sizes are standard. JC Whitney has a wide variety of brands to choose from. 3.00/21 up front and 4.10/18 in the rear would work fine. Good luck...Van

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1980 Honda CR125R

When you say your wheels are 3.00 X 21 and 3.50 X 18, I'm assuming you mean your tires are those sizes. And since you
said this was for a CR, I'll also assume you have a CR 125.

The metric equivalent for your front tire is an 80/100 X 21 and for your back tire a 100/100 X 18. Most tire manufacturers
make numerous versions of these sizes since the front one is standard equipment on about a gazillion MX bikes and the
rear one has been coming on 125 MX'rs forever. As for tubes, the tube manufacturer will list a range of tire widths the
tube will fit. Just look for the size that fits your application.

When you go to purchase your tires and tubes, Unless you have access to a "Cyclegear" or equivalent locally, I would go
with a mail order outfit. I use "Rocky Mountain" for my tires because even with shipping, I save between $30 and $40
per tire on my Dunlops from what the local dealers charge. I get tubes for my vintage bikes from "Dennis Kirk" because
they still stock tubes with the old style TR-6 stem.

Hope this helps.

dogger

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1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

thanks for the info.

yeah its a '74 cr125m, and i was wrong i was talking about the wheel sizes, and actually the front one is only 2.75x21...

the reason i asked was because my bike is stored elsewhere and because of winter weather it is a pain to go see. but, i had a chance to go see it and it has 80/100 and 100/100 dunlops, so ill just go with those sizes for the tubes.

i was just confused because i saw a chart which said the correct tire size for a front wheel of 2.75x21 in metric would be 60/70-100 and for the rear would be 80/90-100.

but, 80-100 for the front and 100-100 for the rear seems to be the tire norm for this bike so i guess ill just follow this.

hey dogger do you use the tr-6 stem because of functionality or does it just have a vintage look? thanks!

Redstripe,

You are absolutely right, I forgot that the early CR 125s came with a 2.75 vs 3.00 tire. The correct replacement is still
going to be an 80/100 metric because, as far as I know, that's all they make now. The OE rim size on your bike was a
1.4 X 21 front and 1.85 X 18 back.

I use the TR-6 valves for asthetics - they have the vintage look compared to the TR-4 valves used today - and I don't
have to drill out the valve stem hole on a vintage rim for it to fit.

dogger

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1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

ya i just read back through the thread and i even confused myself... every time i mentioned the words "wheel size" i really meant "tire size." although my bike is almost entirely original it is still a racer, so the stem isnt a big deal for me because i assume the wheel has probably already been drilled out. but, thanks dogger, ill keep this in mind if i ever decide to make my bike look "nice." i would have never realized the difference between stems by myself, lol. it was a good tip.