Topic: Trying to convert front tire size on original Bridgestone from 1973

[drj434343]

I am putting two new tires on my '73 CB500.  The rear tire size is in a format I can understand and convert, a Dunlop MP90H18.  However, the front tire is original, a Bridgestone (says made in Japan).  The only size designation I can find is 32.5-19.  19 no doubt denotes the diameter, but what is 32.5?  I can't seem to find this style of size format on any conversion charts.

Cheers,
Jason

[CycleRanger]

I think you may be misreading that. Should be 3.25x19

[drj434343]

I'll double check tonight.  I may have fat fingered that decimal on my phone.

[MCRider]

I think you may be misreading that. Should be 3.25x19

That's my guess. Once confirmed its a 3.25x19, the closest metric is going to be a 90/ which is really 3.50x19, which will work fine.  3.25 = 82.5mm which doesn't exist. I think.


Don't know if there is a 3.25 available from a repro tire maker.

[brycegp]

Is it just a matter of finding a 3.25 x 19 front? 

here is a quick ebay search on "3.25 x 19 tire"

http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=3.25+x+19+tire&_sacat=0

[drj434343]

I've been looking at converters, and agree, it must be a 3.25, in which case a 100/90-19 looks to be the closest fit.

It seems like the Dunlop D404's are popular, well received, and a reasonable price, so I may start with those.

I called a local bike shop that will install tires, and they quoted an additional $60/tire charge if the wheel was on the bike, and $30/tire charge if the wheel was off the bike.  It initially seemed like a lot to me compared with the per tire install charge on cars.  I do understand there is more work to removing the wheels though.

Are those install prices reasonable?  Do most people remove their own wheels, or drive their bike in to the shop?

Cheers,
Jason

[MCRider]

I've been looking at converters, and agree, it must be a 3.25, in which case a 100/90-19 looks to be the closest fit.

It seems like the Dunlop D404's are popular, well received, and a reasonable price, so I may start with those.

I called a local bike shop that will install tires, and they quoted an additional $60/tire charge if the wheel was on the bike, and $30/tire charge if the wheel was off the bike.  It initially seemed like a lot to me compared with the per tire install charge on cars.  I do understand there is more work to removing the wheels though.

Are those install prices reasonable?  Do most people remove their own wheels, or drive their bike in to the shop?

Cheers,
Jason

A 100/90 will probably fit. But 100mm = 3.93 in. You may find this to be a bit cumbersome on a 500.

The prices you see are reasonable. Especially since the front is original and may have to be cut off. Its probably as hard as iron. Having removed old tires in the past, I'd pass that job onto someone else in a heartbeat.

[TwoTired]

My 1972 Cb500 Owners manual list 3.25x19 for front and 3.50x18 rear.

Metzeler and Continental  (Maybe more) still make inch size tires.
I put 3.25x19 on the front and 4.00x18 on the rear of my CB550's.  I see no reason why they wouldn't work as well on the CB500.
Local dealer don't stock these sizes.  But, they will order them if they can't coerce you from using a metric conversion.

[drj434343]

A 100/90 will probably fit. But 100mm = 3.93 in. You may find this to be a bit cumbersome on a 500.

The prices you see are reasonable. Especially since the front is original and may have to be cut off. Its probably as hard as iron. Having removed old tires in the past, I'd pass that job onto someone else in a heartbeat.
[/quote]

Great point on that front tire.  I picked that size because that's about the narrowest 19" tire I can find in reasonably common sizes.  Presumably a 90/90 would be next down, but I haven't even seen that size listed anywhere.

I called another local place, smaller shop and reputable.  They sell Shinko's, which apparently is a Korean outfit that bought out Yokohama.  Never heard of them, but Googling reveals generally good reviews.  They quoted $75 for install and balance with wheels on bike.  Much better!

[MCRider]

I thought it might be an availability issue. 90/90s are out there, but admittedly i haven't looked. The whole 3.25 market is limited in size. I think the repro/premium guys may have some nice tires but likely at $100+ for purists.

Just spec on my part.

Like this:
http://www.bikebandit.com/bridgestone-spitfire-s11-motorcycle-tire
About the cheapest i could find.

[HondaMan]

I've had good luck with the 90/90x19 front size combined with 100/90x18 rear size combo on those bikes.
The 100/90x19 front BARELY fits, and if the tire picks up a stone in the tread, can jam it into the fender and bend it a little.

[Chachi]

I got a new set of IRC GS-11's put on my 500 a few months ago. I ordered them from denniskirk.com with new tubes. They come in stock 500 sizes - 3.25x19 F and 3.5x18 R. You can also get Metzeler Lasertecs or Dunlop K70's, just note the rear is only available in 4.0x18 on both of those. There is another Metzeler line that has the rear in 3.5x18, but I think it is only available from Metzeler international dealers vs. US.

My mechanic did my tires and whereas they were not the original tires, they had been on for a good long while. He had a lot of cleaning up to do on the rims - rust, rough spots, etc. You may want to be selective of who deals with yours as it most likely won't be a straight forward job if the tires have been on for a long time (original stock tire).

[drj434343]

I've had good luck with the 90/90x19 front size combined with 100/90x18 rear size combo on those bikes.
The 100/90x19 front BARELY fits, and if the tire picks up a stone in the tread, can jam it into the fender and bend it a little.

This converter:

http://www.webbikeworld.com/Motorcycle-tires/tire-data.htm

Seems to indicate 100/90 is almost spot on with a width of 3.25-3.25" converted.  I'm not sure how they came up with that number though, 100mm is 3.93in width as previously stated.   

[drj434343]

I've looked at half a dozen converters now, and they all indicate 100/90 front is equivalent to 3.25-3.5", and 90/90 is 2.75-3.00".  If I knew nothing else other than the manual wanting 3.25-19 for the front, I'd choose 100/90.

What am I missing here?

[TwoTired]

Don't forget you are changing the aspect ratio, too.
Inch size tires, as what came originally, were 95% aspect or more.  Further, there is the pinch angle to consider when putting a wider tire on a narrow rim.

A 90/90 tire is 90% tall as its width (90mm).    A 3.25 inch tire stands very near 3.25 inches tall of the rim.  A 90/90 tire would stand about 3 1/8 inches tall off the rim.

Also a bigger tire is heavier than a smaller one.  Bigger tires usually need better shock absorber traits, and or spring rates.

Here is a chart made by Tower to illustrate.

[mjstone]

I put Shinko 712 tires on my '72 CB500

Front:  100/90-19

Rear  110/90-18

Bike ran great with these tires.  The aspect ratio is a key to look at if you want your speedo to work right.  With the 100/90-19 on the front the speedo was within 1 mph at 70 checked with my GPS.

You would have to have a huge rock to get it jammed in between the fender and the tire.

MJ

[Fritz]

Don't forget you are changing the aspect ratio, too.

Recently I had the chance to run the same tire model on my 550F with two different sizes:
a) 90/90-19 front, 100/90-18
b)3.25-19 front, 4.00-18 rear

Both are Bridgestone BT45 and without taking measures they look like having the same dimensions.

The metric front tire felt it little bit "spongy" when leaning over. The 3.25-19 feels much firmer and makes me more confident when leaning a lot. Also on highspeed runs on the Autobahn, with the 3-25-19 the bike felt more stable.

I also ran the combination 3.25-19 front, 100/90-18 rear

Could not feel any difference between both back tires.
Both tire sets were inflated to the same pressure (36 PSI front, 40 SPI rear)

-> I'd try to get a 3.25-19, there are still enough tire models to choose from.

[TwoTired]

I'll just mention that many tire makers stop making things when demand falls below expectations.

Personally, I'd like to see them keep making the inch sized tires.  But, if everyone stops buying them in favor of metric, they won't be available anymore in the future, and choices will be further restricted.

The same is true for Honda parts.  Low demand means no manufacture.  You might think about that when you look for the "Cheapest" solution.

Cheers,

[drj434343]

Actually, money isn't really the object here, I'll spend what is required for the right solution.  I was looking at metric because that's what the local guys stock.  The alternative is that I order a inch size online, strap them to the bike once delivered, and drive to someone happy to do the labor for me without the icing of a tire markup.

That said, the IIRC tires look pretty good...

[Stev-o]

Actually, money isn't really the object here...

Then buy the Avon Road Riders:

http://www.americanmototire.com/catalog/product_info.php?products_id=439

[drj434343]

Actually, money isn't really the object here...

Then buy the Avon Road Riders:

http://www.americanmototire.com/catalog/product_info.php?products_id=439

Sure, are the Avon's considered the clear winners?  I've certainly looked at a lot of $100/tire brands so far.  As a beginner, is there an advantage to these?

[Stev-o]

They are about the most expensive, and are good, but so are Bridgestone and Dunlops, my favs.  When it comes to tires, I don't buy the cheapest.

And get new tubes and rim strips too.

[TwoTired]

Actually, money isn't really the object here, I'll spend what is required for the right solution.  I was looking at metric because that's what the local guys stock.  The alternative is that I order a inch size online, strap them to the bike once delivered, and drive to someone happy to do the labor for me without the icing of a tire markup.

Your local tire dealer will order them for you if you insist on inch sizes.  Certainly, they would rather sell off their in-store stock.  But, if it's your way or the highway, they still make money on a "special order" and will cave.

And, if enough demand arises for inch sizes, they'll stock them!  (If they are any sort of businessmen at all.)

Cheers,

[Stev-o]

TT - FYI...not all of us have "local tire dealers".
I live in a small town, pop 6000, there is only 1 auto tire dealer and I'm certainly not buying tires from them! I do not know of a bike tire dealer within 15 miles.