Topic: Rear tire size

[longshanks]

I've been looking around the forum for threads or FAQ's about going to a larger tire but I can nothing. I currently am running a 18" with 120 width in the rear and would like to go to 130 or 140 in the future. Am I limited to a certain width with the stock rear swing arm? What is all involved in a swap?

[Bankerdanny]

The chain is as much of a limiting factor as the swingarm. The rim width too

[Roach]

you will rub all over the place if you go any bigger than a 120 you will also get weird wear on the tires faster...

First why do you want to go wider?

A) Looks
or
B) performance

120 is max for a stock rim
and probably even your swing arm
and gives you the best performace IMO

[longshanks]

Looks mostly. Are there any threads on here where people have successfully done a swap?

you will rub all over the place if you go any bigger than a 120 you will also get weird wear on the tires faster...

First why do you want to go wider?

A) Looks
or
B) performance

120 is max for a stock rim
and probably even your swing arm
and gives you the best performace IMO

[Retro Rocket]

I have a picture of a 750 with stock swingarm and a 170 on it, it is on a 17 inch rim and cleared the swingarm. I also used to run a 140 Michelin M48 {i think, long time ago} and used to ride the wheels of that bike, the only thing that didn't clear was the rear brake arm, a slight bend in it solved the problem. I am going to use a 160 on a 4.5x18 inch rim on my K2 and using a different swing arm, with an offset front sprocket it fits just fine....Anything is possible with enough time, skill and money.... On stock rims i would stick to stock tyre sizes....

[longshanks]

I have a picture of a 750 with stock swingarm and a 170 on it, it is on a 17 inch rim and cleared the swingarm. I also used to run a 140 Michelin M48 {i think, long time ago} and used to ride the wheels of that bike, the only thing that didn't clear was the rear brake arm, a slight bend in it solved the problem. I am going to use a 160 on a 4.5x18 inch rim on my K2 and using a different swing arm, with an offset front sprocket it fits just fine....Anything is possible with enough time, skill and money.... On stock rims i would stick to stock tyre sizes....

So a 140 would fit with the stock swing arm? I was inspecting my bike today and it didn't seem there'd be any room. Does changing out the sprocket and chain help solve this? Also, where would I get the correct rim if I decide to go to 140?

[Retro Rocket]

If you want to do it right i would buy one of Carpy's Dresda style swingarms in stock length, it will accept a much wider tyre. It all gets a bit tight but everything can be made to fit. Wider can rims can be bought {i think cycleX has them} for the stock hubs, in a variety of sizes as well, alloy rims can also be bought. I had a 140 in a stock swingarm on an 18 inch rear wheel on a K6 in the 1980's and only had to bend the break arm for clearance. The later model 750 K's {K77 K8} had a wider sprocket carrier, 10mm wider i think, and Cycle X have 10mm offset front and rear sprockets as well. So anything is possible..
Carpy Swingarm    http://www.cb750cafe.com/parts.php?id=84

Cycle X sprockets , Back and front, scroll down    http://www.cyclexchange.net/Cycle%20X%20Exclusive.htm 

[splitt]

If you are running a 630 chain, switching to a narrower 530 non-O-ring chain will allow the chain to clear a wider tire. Offset sprockets will also allow the chain to clear wider tires. Some have shaved the sides of the tread on wide tires to allow the chain to clear the tire.

What year and size of bike do you have? Some bikes (such as a '77-'78 cb750) have a different offset on the output shaft.

[longshanks]

If you want to do it right i would buy one of Carpy's Dresda style swingarms in stock length, it will accept a much wider tyre. It all gets a bit tight but everything can be made to fit. Wider can rims can be bought {i think cycleX has them} for the stock hubs, in a variety of sizes as well, alloy rims can also be bought. I had a 140 in a stock swingarm on an 18 inch rear wheel on a K6 in the 1980's and only had to bend the break arm for clearance. The later model 750 K's {K77 K8} had a wider sprocket carrier, 10mm wider i think, and Cycle X have 10mm offset front and rear sprockets as well. So anything is possible..
Carpy Swingarm    http://www.cb750cafe.com/parts.php?id=84

Cycle X sprockets , Back and front, scroll down    http://www.cyclexchange.net/Cycle%20X%20Exclusive.htm

Where is the break arm located and what is it? 

Do I have any other options than Carpy's swing arm? I've already looked at it and its very enticing but I'm not ready to spend that much money on it.

[longshanks]

If you are running a 630 chain, switching to a narrower 530 non-O-ring chain will allow the chain to clear a wider tire. Offset sprockets will also allow the chain to clear wider tires. Some have shaved the sides of the tread on wide tires to allow the chain to clear the tire.

What year and size of bike do you have? Some bikes (such as a '77-'78 cb750) have a different offset on the output shaft.

It's a 76 CB750K.

[TwoTired]

Where is the break arm located and what is it? 

The break arm is located either on your right or left, after Guido comes to visit, and you don't pay up the money owed.

Normally, both arms are flailed about while dodging things falling from the sky.  It helps alter prevailing winds.

Cheers,

[longshanks]

Where is the break arm located and what is it? 

The break arm is located either on your right or left, after Guido comes to visit, and you don't pay up the money owed.

Normally, both arms are flailed about while dodging things falling from the sky.  It helps alter prevailing winds.

Cheers,

Haha!    Not exactly helpful though!

[MCRider]

Kinda reply to many posts here, as i just did this on my K2. (Assuming proper rim width) The widest tire to fit is 150. It won't hit the chain but it will hit the chainGUARD, which will have to be notched or displaced. The popular harley 16" conversions are 150 widths, no problem, except for the guard.

Wider requires moving the mount point of the brake arm outwards. The brake arm is the stay that extends from the front right of the underneath of the swingarm and travels back to the brake plate, wher it keeps it from rotateing. You can simply pull the arm out of the U that it fits in, and put it on the outside of the U and run a proper spaced bolt in it. half arsed but it works. Or you can cut the inside leaf of the U off and reweld it to the outside, giving the brake arm a proper berth. This will allow out to 170, then you'll likely hit the chain.

I've settled on a 140/70-17 on a 3.50 rim. I'll likely go to 150 at first replacement. I moved my stay mount just in case.

You do not need Carpy's swingarm, IMO.

[MCRider]

The chain is as much of a limiting factor as the swingarm. The rim width too

Not the chain, but the chainguard. Good point on the rim width. Needs to be proper, I have one chart lisiting 110 as max, another 120, on a 2.15 rim.

[Lostboy Steve]

If you're going for look and the look is old school cafe, then stay 120. Its more about the aspect ratio that makes the look. Old school Harley's have narrow tires as well. I personally want to do a 16 x 4 front and rear on my project. A lot of past posts have reported terrible handling and tire wear with super wide tires. Whatever though its really only about what you like / want. Anything is possible.