Tires - back to original intent?

[Altritter]

I still have the manufacturer's tire size decal posted on the top of my rear fender. MY '81 supposedly arrived with 3.25x18 front, and 4.00x18 rear. It now wears 100/90 front, and 120/90 rear. (That's how I bought it.)

Query: does anyone currently using English sizes (e.g., 4.00) know what their tires' aspect (width of tire, divided by height of the tire sidewall) is? Without that knowledge, I can't estimate how much I can lower my bike by merely going back to an approximation of the original tire sizes.

I estimate that replacing the 120/90 rear with a 110/90 would lower the rear of the bike slightly <0.35 inches; going down to 100/90 would lower about 0.3 more, for a total of ~0.65 inches. What I'm interested in knowing is what would happen if I installed a 4.00x18 on the rear and as close to a 3.25x18 as I can find for a front.

My action plan is to see how the bike handles at approximately its original height, then consider installing shorter shocks if I want to lower it further.

I'd appreciate thoughts.

John

[Motu]

As far as I can tell,the 4.00 is the same height as the 120/90,but narrower.I have 2 sets of wheels,so swap fairly regularly.

[Ed Miller]

I've put a  4.00 x 18 on the rear, and didn't really notice any difference from the 110 I usually use, though it only lasted about 4600 miles.  That was a Conti-Go.  I didn't measure them to compare, though.  I've never found a  3.25x18 which makes me wonder what the heck BMW was using on our bikes when new.

[Altritter]

Thanks for the input, everyone.

As far as I can tell,the 4.00 is the same height as the 120/90,but narrower.

Thanks especially for that. It makes sense, for I have a 560x15 spare in the boot of my '66 VW (modern tire profiles won't fit), and the 560x15 sides give the tire profile a "square" look. All of this suggests: For my purposes, should I look for a 110x90 (or 100X90, which is almost the original size) rear and a 90x90 front? They should have a lower aspect (thus reducing the bike's seat height slightly), if the formula is valid.

To follow up with stream-of-consciousness questions: what about mixing brands (within the same category, such as Touring or Street tires, of course)? Also, it used to be a deadly sin with automobile tires to mix radials and bias-ply tires. Is it OK with bikes? (I was surprised to see bias-ply tires still in the motorcycle market in 4.00x18 size. I thought they were extinct.)

[The Conti-Go 4.00x18] only lasted about 4600 miles.

Point well taken. I recall someone reporting getting 16K-plus with an Avon 4.00X18, so I guess YMMV.

[Semper Gumby]

HI John,

I have used the 4.00-18, and the 120/90-18 Michelin Macadam.  I currently have a 110/90-18 Dunlop 491 Elite II on the back that I got used from a local shop while I wait for Michelin to decide whether they are going to make a 110/90-18 or 4.00-18 Pilot Activ.  (It seems that they are not going to do it after all).

I prefer the 4.00-18 and the 110/90-18 as they are easy to put on and pull off the bike and don't interfere with the swing arm.

As for the front.  The only company that makes a stock sized front is Heidenau http://www.moto-amore.com/heidenau/new/productsnew_b.html in Germany.  They are quickly building a reputation in the Adventure rider community for tough tires.  Whether that translates into street tires remains to be seen.

[Barry]

Query: does anyone currently using English sizes (e.g., 4.00)

I'm dubious about metric sizes unless the manufacturer publishes actual dimensions of width and diameter for comparison with the correct English sizes.

Pirelli City Demons come in 4.00 x 18  and 3.25 x 18 sizes. Another silly name aimed at the commuting market like Conti go, other than that they seem decent enough tires. Probably not a patch on the Avons although much cheaper and I'm no racer. The rear is quite narrow and therefore very much easier to fit than the previous Metzeler. Beads popped on reasonably easy too. Wear rate so far suggests min life of 9000 miles.  

Note they are S rated tires (112 MPH) which BMW specified for the R45 while R65's were H rated. Still how many of you exceed 112 MPH.

http://www.pirelli.co.uk/web/fitment/selectSearchTyresForm.do?mySelectActived=goToMotoFull&myEntryPoint=%2Ffitment%2FhomeMotoFull&brandVehicle=5300&modelVehicle=119627&versionVehicle=227853

[DeeG]

My 45 has the 'original sized' tires on it and its needing new ones.  I looked at the City Demons, but the 3.25x18 is only offered for the rear.  Can I put a rear tire on the front?  I'd really like to keep the bike as original as possible, down to the old style looking tires.  It'd look kinda dorky with Sport Demons on it.  

[Ed Miller]

DeeG, it shows the 3.25 x 18 for the front for your bike, and a 4.00 x 18 for the rear.  Oddly it says they don't have any for my bike, even though we use the same size tires.

Oh, I see now.  When you look up City Demons, it doesn't show the size they recommend.  That's weird.

[bjamesw]

HI John,

I have used the 4.00-18, and the 120/90-18 Michelin Macadam.  I currently have a 110/90-18 Dunlop 491 Elite II on the back that I got used from a local shop while I wait for Michelin to decide whether they are going to make a 110/90-18 or 4.00-18 Pilot Activ.  (It seems that they are not going to do it after all).

Here's a link...
http://www.americanmototire.com/catalog/product_info.php?cPath=33_176_184&products_id=4655
http://www.americanmototire.com/catalog/index.php?cPath=33_176_184

[Semper Gumby]

HI John,

I have used the 4.00-18, and the 120/90-18 Michelin Macadam.  I currently have a 110/90-18 Dunlop 491 Elite II on the back that I got used from a local shop while I wait for Michelin to decide whether they are going to make a 110/90-18 or 4.00-18 Pilot Activ.  (It seems that they are not going to do it after all).

Here's a link...
http://www.americanmototire.com/catalog/product_info.php?cPath=33_176_184&products_id=4655
http://www.americanmototire.com/catalog/index.php?cPath=33_176_184

Thanks.  Seems too good to be true so I sent them an e-mail.    :-?

[Semper Gumby]

Got this e-mail from AMT this morning:

"Thank you very much for your inquiry!!  No, unfortunately, the backorder has
affected us all.  The Avon RoadRider is the tire we recommend above any
other in this class.  Please let me know if I can assist in any other way at
all.


Thanks again!


Vaughn"

(drat drat drat Holy Moose and Squirrel -- its time for another phone call to Michelin....)  

Wow.  I just got blown off by Michelin.  I just talked to Diane in Greensboro SC where I guess Michelin USA is located.  She wouldn't or couldn't give me a Michelin contact in France so I could find out if they are going to make the Pilot Activs.  She was clueless.  I guess I'm going to have to go with the Bridgestones or the Metzlers or perhaps the Heidenau's.

What a shame.   :-/

[jay]

metzeler 22 3.25/18 front
metzeler 77 4.00/18 rear

still current models,and once i'd scrubbed 'em in,along with Hagon rear shocks and Hagon progressive fork springs.....i had a ball.