Rim and tire education

[gsryder]

I need a little rim and tire education.
I have a set of spoked rims from a 77 GS750
I am looking to buy new tires but not sure what size I can put on them.

When I searched for the rim size online I get
Front - 3.25 x 19
Back - 4.00 x 18

But the rims are stamped
Front - Takasago 1.85 x 19 6G 102 Japan
Back - Takasago 2.15 x 18 6G 103 Japan

How do you know what width tire tire you can put on them?

What does the 6G 102 and the 6G 103 stand for?

Thanks in advance for the help.

[Steve]

Not sure about the 6G 102 and 103, but tire sizes you can look for would be either a 90/90-19 or 100/90-19 for the front and a 120/90-18 for the back. The stock size for the front would be closer to the 90/90, but putting the 100/90 on there will eliminate virtually all the speedometer error.

.

[Nessism]

100/120 are the largest tires you can use that are a reasonable match to the rims. Some people go even larger but this causes excessive curvature of the tread which is not recommended. Of course, you could go smaller but not many people want to go that way.

[trippivot]

3.25 inches multiplied by 25.4 = 82.55 millimeter so a 90/90 19 is as close as you can get to an american size. the 100/90-19 is wider by a smidgen. the speedo is fine with either size. width difference is 10mm height diff is 9mm there is MORE error with the bigger tire but 1 or 2 MPH at 60 MPH is not enough to worry about- if you are get a stop watch and time your self on the highway between mile markers, you can be exactly sure .


4.00 X 25.4 = 101.6mm so a 120 will probably not fit in your swing arm.

rule of thumb is 1 size wider is ok any bigger you better do a test fit

a 110 I'd bet will work not positive about a 120

the 25.4 is a multiplier to convert inches into millimeters for the width of tire
the inches in wheel diameter is always going to be in inches.

[Nessism]

3.25 inches multiplied by 25.4 = 82.55 millimeter so a 90/90 19 is as close as you can get to an american size. the 100/90-19 is wider by a smidgen. the speedo is fine with either size. width difference is 10mm height diff is 9mm there is MORE error with the bigger tire but 1 or 2 MPH at 60 MPH is not enough to worry about- if you are get a stop watch and time your self on the highway between mile markers, you can be exactly sure .


4.00 X 25.4 = 101.6mm so a 120 will probably not fit in your swing arm.

rule of thumb is 1 size wider is ok any bigger you better do a test fit

a 110 I'd bet will work not positive about a 120

the 25.4 is a multiplier to convert inches into millimeters for the width of tire
the inches in wheel diameter is always going to be in inches.

I'm about 99% certain that a 120 will fit between the swingarm just fine on a first generation 750. Hedging just a little since I haven't tried myself.

[gsryder]

The bike I am putting these on is a 81 GS 750. With the stock mags currently I have a 120 on the rear and a 110 on the front. With plenty of room.
On the spoked rims (off of the 77 750) I am planning to put on the 81 I want to run a 120 size tire both front and back.
I am not worried about the speedo I dont have one on the bike.
I am going for the cafe style and always see these cafe's with the same size tire front and back. I like that look but I dont want to get to crazy and sacrifice to much performance / safety.
Can I get a 120 tire on the 1.85 front rim?
I thought there was a tire manufacturer that specifically made wider tires for narrow rims. Does any one know of this??

[gsryder]

It doesn't seem like any manufactures make a 120x19 size front tire.

Has anyone ever run a rear tire on the front?

[Nessism]

It doesn't seem like any manufactures make a 120x19 size front tire.

Has anyone ever run a rear tire on the front?

120 is too big for that rim. Form follows function, not the other way around.

[waterman]

It doesn't seem like any manufactures make a 120x19 size front tire.

Has anyone ever run a rear tire on the front?

Some tires can be used on either end. I know Avon roadriders can be used with front in rear position but not sure about other way around.

In order to run wider front you will need to run a wider rim to keep the overall tire profile the same. This wouldn't be difficult if using spokes, just lace up a wider rim to stock hub.

[gsryder]

Sounds like thats what I need to do. Lace up a rear rim to the front hub. I need to count the spokes hopefully they are the same spoke count between front and back.

[Hammered]

This has been the best resouse for tire to rim info Ive ever found.

http://www.dropbears.com/u/utilities/tyrerim.htm

[trippivot]

on bias ply tires you turn them backwards for a rear to front tire application. radial type tire- run it in proper rotational direction.

re lacing will have you count the like to like spokes and the like to opposite spokes and that gives you the key spoke pattern. check it and tape a couple pairs of spokes before un-lacing take a good digital picture

[Big T]

Sounds like thats what I need to do. Lace up a rear rim to the front hub. I need to count the spokes hopefully they are the same spoke count between front and back.

Actually, you need wider front rim as the rear is an 18", the front is a 19"

Pretty easy to do if money is no object.

[76FJ55]

You could also lace a rear rim on the front and run 18" tires front and rear. You will need to get new spokes of the correct length for this conversion though. As for tire width to rim width I typically use the rim data from the tire manufacturer. you can usually go directly to the tire manufactureres website and they will supply the rim width range acceptable for each model and size tire. You may actually want to go with the 18 on the front any way. as a quick reference based on the Avon Venom AM41 the diameter of 100/90-19 is 26.10 inches and convertin to an 18" rim the 120/90-18 is 26.50 so the smaller 18 rim is actually larger in diameter when you take tire height into account.