What tires did a '78 R100 roll out of the factory on?

It's time for new tires on the R100. If I remember correctly, my dad (the previous owner) put on an oversized rear tire. That's great and all, but I want 100% factory size when it comes to tires and tubes. The problem is everything I find in the manual is in inches, but shopping online, everything is metric.

I can't seem to figure out the conversion, so any help would be appreciated. Any brand recommendations?

My bike: 1978 R100/7T. Build date 10/77

Wheels: Stock spoked 1.85X19 fronts and 2.15X18 rear.

Tubes: Unknown?



Here's what the manual says, but, of course, it's in inches again! argh..

Bridgestone S-11 Spitfires are a great all round tire that stick well, last respectably, offer good ride quality and steer nicely on an airhead. They're cheap, too. Whatever.

You need a 100/90-19" front and a 110/80-18" rear.

You're just not shopping hard enough, as there are still inch-size tires available in the correct sizes.

Tubes must be fitted.

BTW, there are ZERO metric equivalents to these sizes.

yep, I agree with what lornce says, those bridgestones are great tires for the money, and those are the proper sizes. lots of folks put a 120 in the rear, but you have to let the air out of it to get it between the swingarm and the brake shoes, the 110 will slip through with a minimal of fuss.
trust me, NONE of those bikes will overpower a 110 rear. I thinks its the "big rear tire syndrome", makes folks think they can ride faster.
if you hunt around, you can still find the original equipment style continentals or dunlops, in the proper inch sizes, but they are getting harder and harder to get, and you'll probably pay dearly for them.

I remember most of them coming with Continentals and some with Metzlers. I don't remember them coming with Dunlops right off hand.

Most conversion charts convert a 3.25 to a 90/90 and a 4.00 to a 110/90. I don't think a S11 comes in 90/90. 90/90 and 110/90 are usually a little smaller than 3.25 and 4.00 and 100/90 and 120/90 are usually a little larger but all that ultimately depends on the specific tires in question since they all vary in size.

they do come in a 90/90, I have one in the garage as I type this.
my bad, your right, some did come with metzlers, not dunlops.
I just always order the 100 for the front and the 110 for the rear, been using that combo for years and have no problems. bike is ridden two up and loaded most of the time.

I just spooned a set of those on my airhead last weekend.

Good to hear Lornce


Mike

That may be a bit of an overstatement, since the tire's listed size, whether it's metric or imperial, isn't exactly what the tire ends up being in terms of width after being mounted. A 4.00 tire will be close to its' metric equivalent, but it's probably not exactly 101.6 mm wide. It's close enough, and your implication that there are "ZERO" metric equivalents is a bit misleading. In addition, each tire has a range of approved widths, and that will have a little bit to do with the final mounted dimensions.

The tire sizes themselves are nominal, ie: the size on the sidewall is a group size, and the tire fits somewhere within that group's limits. It may be at the high end of spec, (wider/taller), possibly dead-on in the middle of the range, or it may be at the small end...but it's still the same listed size on the tire sidewall. Whether it's sized in millimeters or inches, all that really matters is- does the tire fit your wheels, and does the rider like it?.

Getting back to the OP's question, I have a bike of the same era, with the same skinny rim sizes. Spec tires are a 3.25X19" front & 120/18" rear, and the few current 120's that I've tried are just too wide. The manufacturer's tire spec pages also seem to agree, as the smallest approved rim with for a modern bias-ply 120 is a 2.5" rim.

My best combo so far in terms of overall ride & handling was a 100 or 3.25 front, and a 110 or 4.00 rear Metzler Lazertech pair. Downsides to that approach is that it's an expensive choice, so I've switched to a BT45 rear in the same 4.00 inch size and kept the ME33 front. The Bridgestone rear is ~$35 cheaper, handles just as well, but it's noticeably smaller in diameter than the Metzler, to the tune of about 200 rpm at freeway speeds. The pegs also touch down a wee bit sooner.

I tried a BT45 front once, and didn't like it one bit. Your results may be different, so feel free to try one, as it's about $30 bucks cheaper than the Metzler.

I've got a set of Michelin Pilot Activs, 3.25H19 front and 4.00H18 rear; they're going on next, and fwiw the rear Michelin is noticeably both wider and taller than the Metzler rear. It's design rim width is a 2.15, and it was $172.98 for the pair, delivered.

Whatever you choose to go with, get the "H" speed-rating flavor instead of the "V" variety, and you'll save about $10 up front per tire as well as lose a bit of unsprung weight. My guess is that the lower speed-rating's lighter tire might also be a bit more compliant, but the money difference made the choice for me. I only get about 3.5K miles to each set, and that adds up in a hurry. :eek1

Have fun, and when in doubt, skinnier's better.

Where does BMW spec the rear tire at 120/90? I have only seen 4.00. Most 120's (probably not BT45's since they run pretty small) are too wide with the stock axle spacer.

I find that usually the 90/90's handle better than the 100/90's. Many a conversion chart recommends 90/90's for our bikes. Speaking of approved rim sizes for 120's. Most 100/90 front tires are not approved for 1.85 rims, just 90/90's. It seem like a lot of people make fun of some running a fat 120 rear tire when they themselves are often running a fat front tire? What gives?

I am curious why you think V rated tires are heavier?

i have spitfires on my rs, 100/90-19 front and 110/90-18 rear. they fit well and one can remove the rear wheel from the swingarm.. you can find 4.00in in most manufactures line up for bias tires. the 120/80-18 or 120/90-18 is too big for the dual spring bikes. it is however spec for the single side swing arm bikes, like the g/s and 88 rs/rt

just based on looks, the 100 front looks closer to the original size when mounted than the 90, the 90 fronts just seem very small, but maybe that's me. you will get quicker steering with a 90 front.
perhaps it all depends on the brand you choose.
don't make fun of my fat front and skinny rear!!LOL!

It likely came with continentals, something like a RB2 front and K112 rear. You can still buy conti twins in the inch sizes, I run them on my /5, and buy them from American Motorcycle tire or southwest moto tire.

I agree - Conti's seemed to be the standard for most US bikes. Like many others, I run the S11's on my R80/7. When I first got the bike it had some sort of Conti on the rear that was a 120. Even with the air out, I had quite a time getting the thing off the bike. The 110 rubs on install, but not much, and clears everything just fine after that.

I once considered the BT45's (looked to be the next up the chart for "stickiness") but after running the S11 for a while, I don't see the use. I can drag hard parts on the R80 with S11's so traction isn't an issue, and I get much better mileage than I would on the BT45's.

The Conti twins were the most common here (RB2 & K112) and like a lot of folks I went over sized. The 120 is a bitch to install past a rear brake drum but I recently went back to the stock size and noticed better handling. Looks like bicycles tires though but she's definitely old school at this point.

Those RB2s didn't like the rain grooves in California and I was glad to get away from both of those.

The Avon Roadriders are available in inch sizes, they are by most reports a very good tire. Never tried the inch-sized Michelin Pilot Activ's but they look to be similar to the Avons.

I have had S11's and Conti's on as well. The S11's were also a good tire, see Lornce's post for the sizing. Wasn't as fond of the Conti's but tires are a personal thing.

I haven't totally made up my mind on the Avons yet. I don't feel completely comfortable at deep lean angles and I am playing with tire pressures a bit to see.

dc

Getting ready to bolt up Battle Axes on my R100RS/beater/super mottad Das Beast.

Most of the time the major difference between an H and V version of the same tire, is initial tread depth.

The V will have less tread depth in order to somewhat eliminate the tire squirm that causes the heat that causes the tire to fail the "V" test.

Given this, I'd expect the H tire to be heavier, as it has more rubber.

H is, in fact the better buy, as no Airhead needs a V tire.

It's pretty academic in any event.

Academic events?

On an airhead?

That's what I thought about tire weight too Ikchris.

I wish I could recommend Avon Roadriders. Avon bias ply rubber is much stickier than any other street tire I have used and they last as long or a lot longer than other tires that don't have near the grip. Then they quit making their good tires for our bikes.

The Roadriders make my bike weave badly. Others have reported the same. I have replaced my Roadriders with Avon race tires and the problem is instantly gone and then I can put new Roadriders back on and the problem instantly re-appears. Currently I am running Avon race rubber in front and a Roadrider in back. Just the rear Roadrider brings back quite a bit of the weave but most of it is from the front Roadrider on my bike. I could get the rear Avon race rubber to last 2000 miles versus 3000 or a little more out of most of their street tires. I rarely get more than a bit over 3000 miles out of long wearing rear tires. I am LUCKY to get 1500 miles out of Metzlers and some other brands.

I have installed Roadriders on my own SWB slash 5 and a buddy's LWB slash 5. Both bikes are rock solid stable at 90+ mph, absolutely no weave at all. They are like freight trains. The last person to ride my SWB was convinced I'd converted it to LWB.

Just a data point, not saying that it doesn't happen for supershaft, but it definitely DOESN'T happen for me.

dc