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94-06 Front Tire Fitment Issues

Disclaimer: The procedures and suggestions presented in this column are solely those of their authors. COG and Kawasaki Motors Corp. USA, neither recommends nor endorses any motorcycle modification, which might adversely affect rider safety.  Any modification that may be safety-related should only be done by, or under the supervision of, a qualified motorcycle mechanic.

Stock C10 Tire Sizes

The stock front tire for the 86-93 Concours is 110/80-18 and fits on a 2.5 inch wheel. The stock size front tire for the 94-06 Concours is 120/70-18 and fits on a 3.0 inch wheel. For both the stock rear tire is a 150/80-16 tire fit on a 3.5 inch wheel.

Fitment Observation

This article is about tire fitment observations for the 94-06 Concours using aftermarket 120/70-18 front tires. The stock Dunlop K700 series tires are radials tires, and the 120/70 front is designed for a 3.0 inch front wheel the Concours has. However this is somewhat unique. And the problem is no one really likes the stock tires very much. Many like to choose a more performance oriented tire. The problem with the performance oriented radial front tires available in the stock 120/70 size, is they are intended to be mounted on a 3.5 inch wheel. If you check the websites for Dunlop D205's, Avons and many other MFG's the 120/70 size is designed for 3.5 inch wheels, with 3.5 inches being the minimum width allowed and 3.75 or 4.0 being the widest.

In summary even though its the stock tire size of 120/70-18, the tires are not intended to be mounted on the Concours wheel. The wheel width is too narrow. That I can tell:

  • we can get front tires that are in the stock size and radials that fit the Concours, but not the cool high performance z rated radials
  • we can get front tires that are high performance Z rated radials that fit the Concours, but not in the stock size
  • basically we cannot get all 3, high performance Z rated radials, that fit the Concours 3.0 inch front wheel, in the stock size

Lawyers and Liability

Are lawyers getting involved? Its only a question, but I mention this because I have heard of a instance of a claim being denied because non-stock tires were installed on a motorcycle. Although in this case it was an automobile tire on a Goldwing. More to the point, I have also heard and had personal experience with a dealer not installing non-OEM sized tires on a motorcycle that is brought in for the install. This is for liability reasons. The tire manufacturer will not stand behind the dealer because the tires were not the OEM sized.

Ok...but high performance Z rated radials the OEM size tires do not fit properly on the Concours 3.0 inche wheel. What happens when claims get denied due to this. Or dealers figure this out and won't install anything but the Dunlop K700/701 series tires because they are the only ones that fit and are the OEM size.

Choices and Alternatives

I am not recommending a solution, the choice is up to you.

One choice would be to stick with the factory installed Dunlop K700/701 series front tire. This is a V rated radial tire that is the OEM 120/70-18 size AND is designed to fit a 3.0 inch wheel.

Stick with the high performance Z rated radial tires in the factory 120/70-18 size. While not designed to fit the Concours 3.0 inch front wheel, they are the recommended size in the fitment guides. And many Concours owners have been mounting them for years and years. This is what most do.  However see my pics below.

An alternative some are switching to is 110/80-18 front tire. Its not the factory size, but it does properly fit the Concours wheel. And it fits on the bike too, with no clearance issues. The 110/80 tires are designed for a 2.5 inch wheel minimum width, the stock wheel size for the 86-94 Concours. And designed for a 3.0 inch wheel for the maximum width, the stock wheel size for the 94-06 Concours. So they fit both C10 front wheels. This is what I am currently doing and it steers and handles great too.

There are also the GL1500 sizes which are also not the factory size, but do properly fit the Concours wheel. Wing Size tires are 130/70-18 front and 160/80-16 rear. On the front there is only a slight clearance issue clearing the front fender bolts when installing. Once installed these work with no clearance problems. These fit the Concours as the GL1500 has the same size wheels front and rear as the Connie. When you check the tires specs you will see these fit even for a larger tire. However this is because they are H rated bias ply tires.

Bias Ply Tires

I mention the GL1500 tires only to say they fit. To many mounting bias ply tires on a Motorcycle ( any vehicle for that matter ) that was designed for radial tires is simply unsafe and could result in someone getting hurt or killed. And that we should never be offering any advice, disclaimer or not, that is fundamentally unsafe.  I even found this quote right on Dunlop's website in the FAQ section.

"bias and radial tires have significantly different dynamic properties. They deflect differently, create different cornering forces, have different damping characteristics, as well as other differences. In order for radial tires to be introduced into the two-wheel market, it was necessary to change certain characteristics of the motorcycle. The introduction of the radial tire led to such things as modified frames, new steering geometries and suspensions. Therefore, it is recommended that a motorcycle be used with the type of tire construction that it came with originally."

Is the 120/70 size really that bad?

Once many moons ago a fellow COG member once posted in a forum the 120/70 deforms enough that they were not any wider than the 110/80 when mounted. According to the tire size calculators the 120/70 is supposed to be 4.72 inches wide. The 110/80 is supposed to be 4.33 inches wide. Just for reference the 130/70 Wing size front tire should be 5.12 inches wide.

I measured my D205 120/70 radial at 4.45 inches mounted on my wheel ( 2003 ). That's .27 inches deformation when mounted. Later when I removed the D205 and installed the BT45's I measured the unmounted D205 at 4.72 inches.

On the other hand the 110/80 is supposed to be 4.33 inches. My BT45 110/80 measured 4.33 both before and after mounting. No change in shape what so ever.

Here is my calipers set at 4.72 inches and then held up to the horribly cupped D205 about to be replaced. As you can see there is quite a gap there.

Here is my newly mounted BT45 still at 4.33 inches mounted

From a tire diameter point of view

120/70 should be 24.61 inches
110/80 should be 24.93 inches
130/70 should be 25.17 inches

Given this I was expecting some change in speedometer and odometer readings when switching from the D205's to the BT45's. However it didn't work out like that. I did not measure tire diameter like I did the width. But I suspect that squishing the 120/70 on the too narrow 3.0 inch wheel not only deformed it width wise, but also height wise as well.

Article By: Slybones

November 2010

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