Tire sizes. Battlax BT45

[Tarantulahed504]

Hey guys. So after a long and exhausting journey, my 750 finally arrived in New Orleans. I'm very excited to start up a mild brat/ cafe build. But before any of those parts go on, I am doing safety/maintenance/reliability stuff.

Battery
Brakes
tires
wheel bearings
plugs and plug caps
pionts clean and check
valve clearances
eletricial system, mostly charging system checks and upgrades

anyway. I think I have decided on the Bridgestone battlax bt45 tires. I know a lot of the GS community seems to be on the Avon train, but I'm not sure i want to deal with sidewall cracking issues,

front tire options are 100/90-19
rear tire are 120/80-18 or 120/90-18

my question is, should i go with the taller tire. Seeing that it's a smaller diameter rim and would bring the overall height closer to that of the front wheel?



thanks for your time and input guys
andrew R

[Tarantulahed504]

In addition. I saw that Bridgestone is doing a rebate on some of their tire lines but is didn't seem like the bt45s were included. Does anyone know if there are any other promotions/coupons on the sites out there

best price I've found is $208 shipped so far

[bwringer]

Yes, you'll want the 120/90 tire -- the 120/80 is intended for a much wider rim, so it'll sort of squash into a suboptimal hamburger shape cross-section instead of a nice smooth predictable round shape.

Just FYI, the original tire size was 4.00-18 rear, 3.25-19 front. You can actually get the Continental Go! or Michelin Pilot Activ in these exact sizes -- these are great modern tires in vintage sizes.

The front is pretty clearly 100/90-19 in modern sizes, and the rear could be either 110/90-18 or 120/90-18. IIRC, most folks with that bike are using the 120/90-18 rear.

And yep, the BT-45s are fine tires. Far beyond anything available in the '70s, that's for sure! I would avoid the Bridgestone S11 -- it's a much older design, and they wear or handle nearly as well as the BT45.

You might also check the Shinko 712 or Shinko 230 -- both are great, sticky tires at bargain prices.

That pricing sounds pretty normal -- I always check American Moto Tire. They seem to consistently be the lowest prices or within a few bucks. Don't forget to order up new tubes and rim strips as well.

http://www.americanmototire.com/catalog/

I've taken advantage of rebates a couple of times this summer, but I haven't seen a Bridgestone rebate that includes the BT45.

[Nessism]

I've got Conti Go's on my KZ and like them. They are a very supple tire and rides well.

[Stuarth]

You may want to consider Conti Classic Attack tires. They're radial tires for older bikes with narrow rims. I have them on my '77 GS550 and they'll go on my '76 XS650 soon (replacing the BT45's). They felt good from the start and within 10 miles they felt fully broken in on the winding roads of the coastal mountains around Alice's Restaurant. Not cheap but excellent tires if you're looking for good, sticky rubber. I have 2500 miles on them and the rear has maybe another 1000 miles left on it.

[smilinbrad]

I put BT45s on my Bonneville. I think they are the OE for it. I have no complaints. Ride well, grip decent, don't wiggle in the rain groves. Anything sold today is a better tire than anything available back in the day. I had excellent service from the Bridgestones I used on my BMWs over the years. I don't think you can go wrong with anything currently offered. 2 cents.

[Reddog78]

I recently removed Avon Roaders from my 750. Low mileage tires with front and rear cracking in the valleys of the rain groves. 2012 date stamp, which from reading various internet posts was the last year usually cited for cracking.

Avon size were metric 100/90-19 and 120/90-18. I installed Metzeler Sport Klassiks in the Suzuki OEM inch sizes mentioned above by Mr. Wringer.

The difference in handling is night and day. With the 120/90 rear it felt like I was dragging a boat anchor when cornering. Now the bike feels 100 lbs. lighter with lots of "flickibilty". Is it the tire brand or the tire size? I'm thinking it's more due to stock inch sizing.

So my 2 cents is whatever brand you select, go with inch sizes.

[John Park]

I recently removed Avon Roaders from my 750. Low mileage tires with front and rear cracking in the valleys of the rain groves. 2012 date stamp, which from reading various internet posts was the last year usually cited for cracking.

Avon size were metric 100/90-19 and 120/90-18. I installed Metzeler Sport Klassiks in the Suzuki OEM inch sizes mentioned above by Mr. Wringer.

The difference in handling is night and day. With the 120/90 rear it felt like I was dragging a boat anchor when cornering. Now the bike feels 100 lbs. lighter with lots of "flickibilty". Is it the tire brand or the tire size? I'm thinking it's more due to stock inch sizing.

So my 2 cents is whatever brand you select, go with inch sizes.

I've always found that a 100/90 on a 1.85 rim is a bad idea; at the rear it's what you often have to do and it works, but at the front there's no advantage and some downside over a 90/90 - or a 3.25 which maintains the original diameter. The 100/90 is not 'pretty clearly' the modern size equivalent for a 3.25 X 19. It's the same diameter but wider by about 10mm and should be on a 2.15 rim. That's not only my opinion but a minimum recommendation from several manufacturers.

I put a 90/90 19 Roadrider on a 1.85 spoked rim recently and it works just fine. Hard to fault. I put a 90/90 18 Roadrider on a 1.60 X 18 twin front rim last week and it isn't the happy thing that the 3.00 18 Pirelli it replaced was. Yes, it's a 'better' tire and all that but it rides kinda bouncy being pinched up in the middle, and the angle of the bead at the rim is not only awkward but not wanting to really seat properly. Just might be why the minimum recommended rim width for a 90/90 is 1.85…….

[Nessism]

This tire size business largely opinion based. Not even the OEM's agree on what is the "proper size" tire for a given rim width.

For example, Kawasaki commonly used a 1.85 X 19" front and 2.15 X 18" rear rim sizes on a bunch of their KZ bikes and they used a 100 front and 120 rear tires on most of them.

[John Park]

This tire size business largely opinion based. Not even the OEM's agree on what is the "proper size" tire for a given rim width.

For example, Kawasaki commonly used a 1.85 X 19" front and 2.15 X 18" rear rim sizes on a bunch of their KZ bikes and they used a 100 front and 120 rear tires on most of them.

And they would have been better off with a proper sized rim. The tire manufacturers agree; the manufacturers do what sells. I'm currently doing exactly the same thing with a 90/90 on a 1.60 rim. Yes, it works. Yes, it would work better if the rim were the manufacturer's minimum size or better yet the recommended 2.15.

Tire size isn't 'largely' a matter of opinion; its a matter of engineering. The manufacturers were delinquently slow to react to the 'advance' in tire profiles and the trend toward wider tires. The cycling press berated them on this mercilessly in the early '80s. It's not like the bike manufacturers haven't done a lot of stupid stuff over the years - much of it completely obvious at the design stage.

A 100/90 tire should optimally be on a 2.50 rim, with the acceptable range being 2.15 to 2.75. You can lever it onto whatever you have, but don't try to tell me that you wouldn't have been better off with a wider rim to put it on.

[Nessism]

I WISH my KZ had wider wheels, but it doesn't. I haven't noticed any handling issues using the stock tire sizes though.

[John Park]

I WISH my KZ had wider wheels, but it doesn't. I haven't noticed any handling issues using the stock tire sizes though.

Have you ever used the sizes commensurate with the stock rims? Of course not. It's a 'wider is better' world.

But then maybe you have. ??

I'm not exactly suffering with a too wide tire either, but it isn't as linear and smooth as the previous 'proper' size was, and I wouldn't have known that otherwise. Which is what the OP was about.

By the time you get around to the edge of those pinched up treads the engine won't say Kawasaki anymore. Just funnin' of course.

[Nessism]

The wider tires look better to me and they are the stock size. That's where I stop. If you check fitment on some of the tire mfg websites they recommend the stock sizes too.

[John Park]

The wider tires look better to me and they are the stock size. That's where I stop. If you check fitment on some of the tire mfg websites they recommend the stock sizes too.

I got you to say it; they look better to you. And the marketing guys at Kawi agreed. And you don't lie awake at night wondering if a more rim appropriate size might work better.

Disregard me and stay happy.

[Tarantulahed504]

I really appreciate all the input guy

i went with metzeler sport klassics from Dennis Kirk. $90 and $106. 3.25 x 19 and 4.00 x 18, V rated.
even though there are metric tubeless tires on the bike now, it looks like the valve is a tube valve. So I purchased new tubes and rub strips