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California Scientific

California Scientific
1000 SW Powell Ct
Oak Grove, MO 64075

Motorcycle Tires & Wheels

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Different bikes respond differently to different tires, so it's impossible to make a generic recommendation. Generally I like Dunlops and Bridgestones.

Tires can be purchased mail-order at significant discounts. You can always find a dealer or shop who will change and balance your tires for about $25, if you bring in the wheel and the new tire. Generally it's more like $35 if they remove the wheel too. If you're going on the road, you can have the tires shipped to a friend or a motel, and then drop in to a local motorcycle dealer and get it done. With a little planning, you can be known and hated by Honda dealers all across the country. When these "Iron Butt" guys invent an award for the "Iron Wallet," I expect to be an early front-runner.

Good deals on tires can be found at:

Motorcycle Accessory Warehouse
Tires Unlimited
Tire Express

What the numbers mean: 120/70ZR18 120 means 120 mm or 4.75" wide. /70 means 70 percent as tall as it is wide, about 84mm or 3.375" tall. ZR means Z rated for continuous speeds up to 150 mph, R for Radial construction.18 means 18" diameter rim. The speed ratings are S for up to 112 mph, H for up to 130 mph, V for up to 150 mph, Z for 150 mph+.At high speeds, the tire can get very hot and the tread can separate from the belts. The speed ratings tell you how fast you can safely go. 170/60ZR17 is 170mm or 6.75" wide, 60% as tall is 102mm or 4" tall, speed rated for up to 150 mph continuous, radial belt construction, requires a 17" diameter rim.

You can tell the age of your tires by checking the date code on the sidewall. The date code will be three letters followed by e numbers. Ignore the letters, the build date is read as follows: VKD341 = 34th week of 2001. DEB403 = 40th week of2003.

Tire Size Conversion Chart

Street Front Tires

Street Rear Tires

MetricAlphaInch MetricAlphaInch
80/90MH902.50/2.75 110/90MP854.00/4.25
90/90MJ902.75/3.00 120/90MR904.50/4.75
100/90MM903.25/3.50 130/80 - 5.00/5.10
110/90MN903.75/4.00 130/90MT905.00/5.10
120/80 - 4.25/4.50 140/80 - 5.50/6.00
120/90MR904.25/4.50 140/90MU905.50/6.00
130/90MT905.00/5.10 150/80MV856.00/6.25

Dirt Front Tires

Dirt Rear Tires

MetricMetricInch Metric MetricInch
60/10090/80 2.50/2.75 80/100 80/90 2.50/3.60
70/10090/80 2.75/3.00 90/100 110/903.60/4.10
80/100100/803.00/3.25 100/100120/804.00/4.10

There's a lot of confusion about why we use such big tires. It's commonly believed that a bigger tire has a bigger contact patch. This is incorrect. An ST1300 fueled up weighs about 700 pounds; the rider is about another 200. The tires are at about40 psi. So, 900 pounds divided by 40 psi is 22 square inches. If the weight is equally distributed on the two tires, each tire has a contact patch of 11 square inches. That's it, tire width and diameter never entered into the calculation. A narrow tire will have an 11 square inch contact patch that's long and narrow; a wide tire will have an 11 square inch contact patch that's short and wide. If you drop the tire pressure to 20 psi (popular for on/off road bikes) then your contact patch doubles in size. If you find yourself in snow or rain, raising the tire pressure will shrink your contact patch and help you push through to the road.

Make your own Rear Tire Stand

pvc kickstand velcro parking brake
Get a section of 1½" PVC. Notch the end to fit your swing arm. Don't forget to lock your front brake first.Idea and photo by Paul Fox.

Tire Accessories

Ride-On Tire Protection System
Ride-On Tire Protection System fixes flats while you keep riding. Three 8oz bottles, $30. ST1300 requires 6oz in front tire, 9oz in back tire.

Digital Tire Pressure Gauge
Digital Tire Pressure Gauge$13. Be the envy of your Saturday morning breakfast crowd. Fits nicely at the bottom of the right glove box. Also available at Sears for $14, sometimes goes on sale for $8.

Digital pressure gauges are also available on-line from Measurement Specialties,and also at Target (pronounced Tar-Zhey). There's a neat pencil-sized combination pressure gauge / tire depth meter for $8.

The devices below are sold as tire pressure monitors. Unfortunately, the initial consensus seems to be that they don't work very well. They were reviewed in Motorcyclist, and got a poor review. Also, a rider at tried them on his ST and two cars, and wound up taking them off in frustration with their inconsistency. A warning device you can't trust is worse than no warning, IMHO. However, who can say, maybe they will improve in time.

Accu-PressureSafety Caps
Accu-PressureSafety Caps, four of the same pressure for $15, or buy them here,two for $7, one at 36 psi, one at 40 psi. These show yellow for 4 psi under, red for 10 psi under.

Tire Guard
Tire Guard four for $23.

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Make Your Own Portable Air Compressor

First, buy a compressor. Ok, this sounds pretty lame, but don't worry it will work out. Get a Campbell Hausfeld RP1200, about$10 at Wal-Mart or Harbor Freight. compressor
Take off the access door and pull the air hose and electrical wire out as if you were going to use them. There are now four screws visible on the back. Take them out. There's a sticker on the bottom still holding the case together. Cut it. Now pull the case halves apart and rip out the guts! All we want is the entire pump - switch - electrical cord - air hose unit.You can trash the case now, we won't be needing it again. compressor screw location
Here's what you're left with. The pump is about 6" long, 3" tall, 2" wide.

The arrow points to the fan that keeps the pump cool when it's in the case. I used a hacksaw to cut the shaft to remove this piece. Be careful if you do this, don't bend the internal part of the shaft.

 compressor insides

Photos by Rick Korchak.