Greg Bender
http://www.thisoldtractor.com/gtbender
Tires
Good rubber is a necessity. I once read that the combined contact patch for the both the front and rear tires is the size of the palm of your hand (David L. Hough - Proficient Motorcycling). That being said, just about any tire you purchase today will be better than the tires available 30 years ago.
I think it is a usually a very good idea to purchase tires as close to the manufactures original specifications as possible. Modifying tire sizes can have a dramatic effect on the handling of the motorcycle. That's not to say you can't make modifications, just that the consequences may or may not be desirable. Here are the Moto Guzzi specifications for all V7, Ambassador, and Eldorado models:
- Rim width (inside dimension): 2.15 inches
- Rim width (outside dimension): 3 inches
- Rim diameter: 18 inches
- Tire size: 4 inch x 18 inches
Here would be my choices. In making these selections, I chose touring or cruising tires because that's what I do with my Ambassador and I like to get as many miles out of my tires as is safely permissible. If you choose sport rated tires, you can expect greatly decreased tire life (but all that gooey traction will let you ride the bike up a wall).
When viewing these selections, keep in mind that I tried to find the tires I think would be best for the style of riding I do with my Ambassador. I chose to include some brands below for which the tires they currently offer don't really meet my needs. I included these selections so that individuals who choose to be loyal to a particular brand would see it listed here. In the end, the tires you choose to put on your motorcycle are your own business.
- Avon (from their "Performance X-Ply" line):
- Front: AM20 SuperVenom [100/90-18]
- Rear: AM21 Roadrunner [110/90-18]
- Note: This was my first set of tires on my Ambassador, only in the wider 120 width on both the front and rear. I was pleased with the traction, but I personally felt the handling suffered due solely to the width. I switched to the Dunlops because I wanted to get a longer wearing tire. The rear tire lasted about 8,000 miles. Not bad, but I'm seeing if I can get one to last longer.
- Bridgestone/Firestone (from their "Sport Touring" line):
- Front: Battlax BT45 [100/90-18]
- Rear: Battlax BT45 [110/90-18]
- Cheng Shin:
- Front: Marquis Sport/Touring [100/90-18]
- Rear: Marquis Sport/Touring [110/90-18]
- Note: I just purchased these for my Eldorado project. We'll see.
- Continental (from their "Classic" line):
- Front: TK 22 RC [100/90-18]
- Rear: TK 44 RC [4.00-18]
- Dunlop (from their "Sport Bias/Cruiser/Touring" line):
- Front: 491 Elite II [100/90-18]; 6/32" tread depth when new
- Rear: 491 Elite II [110/90B18]; 9/32" tread depth when new
- Note: I got 16,522 miles out of the first rear tire. I am still running the front tire. I am very happy with them.
- Metzeler (from their "Sport Touring" line):
- Front: Lasertec [100/90-18]
- Rear: Lasertec [110/90V18]
- Michelin (from their "Road Sport" line):
- Front: Macadam 50E [100/90-18]
- Rear: Macadam 50E [110/90-18]
- Pirelli (from their "Road" line):
- Front: MT66 [100/90-18]
- Rear: MT66 [110/90-18]
What tire size should I use?
Width: Most modern tires are now specified in metric widths. However, the Guzzi documentation specifies 4 inches as the appropriate tire width. A little math will tell you that 4 inches is equal to 101.6 mm. So, a 100 tire is the closest you can get to the factory specification. It is possible to fit a 110 or a 120 on a loop and still clear the fenders.
Height: Most modern tires specify the height as a percentage of the width. As near as I can tell, back in the day when Guzzi specified a 4 inch wide tire, the tire was also 4 inches high. That is, the height was 100% of the width. Finding a tire that is the same in both height and width is not easy with many modern tires. Instead, most tires applicable to loop frames will have a height that is 90% of the width.
My first set of tires were 120/90-18 front and rear. I thought they were fine until I put on my second set of tires, 110/90-18 in the rear and a 100/90-18 up front. Wow, what a difference! My skill level in the twisties went way up immediately. The bike turns much more quickly and I love it. No more 120/90-18s for me.
That being said, some very well respected owners like to run the wider 120s.
- One reason to run the wider tires is that it fills the fenders more and looks better. If you are really interested in running a 130 or 140 wide tire in the rear, contact Mark Etheridge of Moto Guzzi Classics as he can provide you with the modified components to make the switch easy.
- Another reason is to gain a little extra cornering clearance. A 100/90-18 would give a height of 90 mm. A 110/90-18 would give a height of 99 mm. A 120/90-18 would give a height of 108 mm. So, to compare these figures, subtract the height difference between the tire sizes and multiple the result by 2 (for the top and bottom of the tire). Using a 100/90-18 as a reference point, a 110/90-18 would be 18 mm taller and a 120/90-18 would be 36 mm taller. These calculations are simplistic and don't take into consideration all factors...but the main point is that the height differences are real.
Can an inner tube be fitted to a tubeless tire?
Yes. I'm not currently aware of any tubeless tire that will damage inner tubes.
Metric size information
The common format for these numbers is AAA/BBC-DD (e.g., 110/90H-18). Explanation:
- AAA: This number refers to the width of the tire in millimeters (see tire width conversions table below). A quick conversion from inches to millimeters (4" x 25.4 = 101.6 mm) gives us a value of 101.6 mm. Using metric sizes, either a 100 mm, 110 mm, or 120 mm wide tire would work on the 2.15" wide loop frame rims.
- BB: This number refers to the height (aka: profile or aspect ratio) of the tire as a percentage of the width of the tire.
- C: This letter refers to the speed rating (see speed ratings table below).
- DD: This number refers to the diameter of the rim in inches.
Inch / American size information
The common format for these numbers is A.AA/BBC-DD (e.g., 4.00/90H-18). Explanation:
- A.AA: This number refers to the width of the tire in inches (see tire width conversions table below).
- BB: This number refers to the height (aka: profile or aspect ratio) of the tire as a percentage of the width of the tire.
- C: This letter refers to the speed rating (see speed ratings table below).
- DD: This number refers to the diameter of the rim in inches.
Alphabetic / British size information
The common format for these numbers is ABCCD-EE (e.g., MT90H-18). Explanation:
- A: This character is always an "M" and is an abbreviation for "Motorcycle".
- B: This character refers to the width of the tire as a code (see tire width conversions table below). Using the alpha codes, either an "M", "N", "P", "R", or "S" would work on the 2.15" wide loop frame rims.
- CC: This number refers to the height (aka: profile or aspect ratio) of the tire as a percentage of the width of the tire.
- D: This letter refers to the speed rating (see speed ratings table below).
- EE: This number refers to the diameter of the rim in inches.
Speed ratings
| Code |
Speed rating
(in miles per hour) |
| Unrated |
95 |
| S |
112 |
| T |
118 |
| H |
130 |
| V |
149 |
| Z |
above 149 |
Tire width conversions
Permissible Rim Widths
(in.) |
Metric Width
(mm.) |
Standard Width
(in.) |
Standard Low Profile
(in.) |
Alpha Numeric Codes |
| Examples |
###/90-18 |
#.##/90-18 |
#.##/90-18 |
M#90-18 |
1.60
1.85 |
70 |
2.75 |
- |
G |
1.60
1.85 |
80 |
3.00 |
3.60 |
H |
1.60
1.85 |
80 |
3.00 |
3.60 |
H |
1.85
2.15 |
90 |
3.25 |
3.60 |
J |
1.85
2.15 |
90 |
3.50 |
4.10 |
L |
2.15
2.50 |
100 |
3.75 |
4.10 |
M |
2.15
2.50
2.75 |
110 |
4.00 |
4.60 |
N |
2.15
2.50
2.75 |
110 |
4.25 |
4.25/85 |
P |
2.15
2.50
2.75 |
120 |
4.50 |
4.25/85 |
R |
2.15
2.50
2.75 |
120 |
4.75 |
5.10 |
S |
2.50
2.75
3.00 |
130 |
5.00 |
5.10 |
T |
2.75
3.00
3.50 |
140 |
5.50 |
- |
U |
3.00
3.50 |
150 |
6.00 |
- |
W |
3.00
3.50
4.00 |
160 |
- |
- |
- |