tire suggestions for '77 GS400

[tkent02]

Whatever the metric size tube was for 90/90-18 and 100/90-18.

[bwringer]

Buying tubes online is a giant pain in the rear because tubes are made of rubber, a substance famous for being stretchy. That means that any given tube will fit a range of tire sizes, not one specific size. Mix in the fact that tubes may be sold under old-style inch sizes, letter sizes, or metric designations, or even all the above, and there are really no e-commerce systems that can cope very well. (This is one product where an old fashioned shop shelf has a lot of advantages over a web site.)

On the plus side, as long as you get the right wheel diameter and you're in the ballpark as to size, you'll be fine.


Anyway, to buy tubes:

- Start with your wheel diameter -- 16", 18", 17", 19", or whatever.

- Then look at your tire width. Don't worry about the aspect ratio. (If you're looking for a 130/90, don't worry about the /90.)

- Then figure out what the closest inch size old-school conversions are for that width. There are charts everywhere. Here's one:

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

Notice that just to make this crap even more confusing, front and rear letter and inch size conversions can be slightly different... Further, notice that most conversions aren't exact.

- Using this information, sift through the available tubes to find a match. For example, on a '77 GS400, the original tire sizes are 3.00-18 and 3.50-18. This translates to 90/90-18 up front and 100/90-18 out back.

American Moto Tire is probably the clearest in their descriptions, so we'll use them as an example (they're a great vendor):

Notice that the correct tube for the front supposedly covers widths from 2.75 to 3.60.
IRC TUBE 2.75/3.60-18, 90/90-18, TR-4

http://www.americanmototire.com/catalog/product_info.php?cPath=610_615&products_id=2349

This tube would stretch to work for the rear as well. This would be a good choice for a spare tube to carry on the bike, since it would fit either end.

However, there are two other IRC tubes available that could also work for the 3.50-18 rear:


This one is listed as covering 3.25 to 4.10: http://www.americanmototire.com/cata...oducts_id=2350
This is the one I would buy, since 100/90-18 is just a teensy smidge smaller than 3.50

This one just lists 3.50 - 4.00: http://www.americanmototire.com/cata...oducts_id=2352

[dyslexic]

i just picked up a 1977 GS400 that has a 100/90 R18 on the front and a 120/90 R18 on the back....Bridgestone Spitfires....

[tkent02]

It will ride like crap with those sizes especially with old design tires like those.
.

[Runeight]

bwringer >

I have ordered from AMT and agree. Thank you for the detailed reply. Sums it up for me and anyone else.

Since I lean towards originality I'm still on the fence. Plenty of time to decide.