Recognizing Wheel Offset
Offset on both front and rear motorcycle wheels is something that becomes unnoticed and pushed under the rug but plays a crucial role in how your motorcycle will perform and handle. Today's blog post I will show you how to check wheel offset using a Triumph dual leading shoe front wheel. You can also use all the information below to help you with any motorcycle wheel, not just British.
Those that fail to check wheel offset are putting themselves at risk. Whenever you have to replace a rim or relace your wheel I would recommend that you check the offset before you disassemble the wheel. If in doubt refer to your workshop manual or contact a specialist.
The chart below shows most Triumph and BSA models that where equipped with the correct wheel that we are specifically referring to in this blog. "Dual leading shoe" a.k.a. "single leading shoe" with the cast iron flanged hub.
|Brand||Model||Year||Engine Size||Hub Size|
|Triumph||Bonneville / Tiger / Trophy (All)||1966-1970||650CC||8"|
|BSA||Lightning / Thunderbolt / Firebird / Royal Star||1969-1970||500CC / 650CC||8"|
|BSA||Star Fire / Barracuda||1969-1970||250CC||7"|
What is a Dual leading shoe front wheel?
Before we get into detail let's discuss what a dual leading shoe wheel is. In 1967 the Triumph racing department designed and used a new prototype of brake which would later be referred to as the dual leading shoe or twin leading shoe brake.
This new brake features 2 brake shoes and 2 brake pivot cams which operate interdependently. Each cam has there own lever tied together. When the front brake is activated each shoe is evenly applied inside the hub - when properly adjusted.
As we now know the dual leading shoe was first seen in 1967 but in 1968 most Triumph and BSA models where equipped with this new brake set-up. This included both export and home market models.
The dual leading shoe brake uses the same hub as found on 1966-1967 Triumph 650 twins but at that time the brake was single leading shoe. This hub is also referred to as the cast iron flanged hub. In 1969 both Triumph and BSA had to widen there top and bottom fork yokes by 1/4" to accept the new wider brake plates.
What is wheel offset?
There are many definitions of what wheel offset means. Here is a brief definition of what wheel offset means according to "TSW Alloy Wheels".
"The offset of a wheel is the distance from the hub mounting surface to the center line of the wheel. The wheel offset is measured in millimeters and results in a positive, negative, or zero offset. Positive offset is when the hub mounting surface is toward the front or wheel side of the wheel. It is common to find a positive offset in newer and front wheel drive vehicles. Negative offset is when the hub mounting surface is toward the back or brake side of the wheels centerline. A negative offset wheel usually has a "deep lip" Zero offset. The hub mounting surface is even with the centerline of the wheel."
Obtain a straight edge
To measure the wheel offset you will need a straight edge long enough to cover opposite ends of the rim. You can measure the offset of the wheel with the tire on - just make sure your straight edge covers both sides of the rim without interfering with the tire wall giving you a false reading.
I used some steel bar that I had laying around the shop that I used to check the offset. I measured the distance of the rim (straight across) and cut my steel to the proper length required.
You can use any straight edge as you please - yard stick, meter stick, level gauge, etc. Get creative!
Here are the specs on my steel bar that I used on my 19" front rim.
Put the wheel on a flat surface
If the wheel that your measuring has the tires and axle still in place, I would recommend that you put the wheel in a vice and lay it flat (use a soft cloth towel to wrap the axle to prevent damage). You can also use the shoulder part on the hub cap to rest the wheel. If your tire and axle has been removed from the rim simply lay the wheel assembly on a flat surface.
Measuring the offset
Using the front wheel we must measure the offset on the brake drum side. This means you will have to remove the brake plate. Once the plate is removed you can lay your measuring stick over the shoulder of the rim and over the brake hub. The stick should run diagonal down from one side of the rim to the other.
Once your measuring stick is in the correct position check and see if your hub is sitting lower or higher than the shoulder of your rim. This would indicate the offset of the hub in relation to the rim shoulder. If your hub is sitting lower than the shoulder of the rim that would be a negative offset - if your hub is protruding over the rim shoulder that would be a positive offset.
According to a Triumph workshop manual the offset on a dual leading shoe wheel should be -1/64" (negative). That means the brake hub should sit -1/64" lower than the shoulder of the rim - you should be able to fit a .015" feeler gauge between your measuring stick and the brake drum surface.
Another wise way to measure offset is to mount the rim on the front and or rear section of the motorcycle without the tire on. Get your ruler out and measure using the fork legs or the swing arm as a guide. For this dual leading shoe on a BSA the rim shoulder must be centered between the two fork legs.
If the rim is pulled more one side, your offset may be the culprit. With the wheels mounted (front and rear) without the tire on, now would be a good time to check and measure that the front and rear wheels are running true together in a straight line.
Example #1 - the good
Notice that the hub is sitting lower than the shoulder of the rim?
Here is an example of a wheel that we laced here at shop years ago. The offset is not exactly -1/64” as show in the book but it very close! This offset would not cause any troubles as it falls in the precviable margin.
Example #2 - the bad
Here is an example of a wheel that has the incorrect offset. Notice that the brake hub sits higher then the shoulder of the rim? This type of offset would be considered a positive offset which is incorrect for our application.
Side note... The flange on the dual leading shoe hubs are very fragile. When lacing a wheel do not over torque the nipples as that can cause damaged. The cast iron flange hubs are known for cracking and breaking due to an excessive amount of torque.
Symptoms of incorrect wheel offset
Recently, I was working on a customers 1970 BSA Lightning and noticed that the front wheel was not sitting in the center of the forks! After checking and double-checking I noticed that the offset on the rim was not correct. The person who laced the front wheel had a positive offset which was pushing the wheel too far to the left (as if you were sitting on the motorcycle). At that point the front and rear wheels were not aligned.
The symptoms of a wheel that has the incorrect offset is subject to bad stability and handling. It is crucial that you check in observe your wheels to see if they have the proper offset.
There you have it lads - checking wheel offset is a task that shouldn't be over looked. Triumph and BSA wheels all have a certain type of offset whether it is a front or rear rim. A great source to have if you are experiencing difficulties is to try Buchanan's Spoke & Rim located in Azusa, California.
If you have any questions or if you would to drop us a comment please do so using the comment section below. Don't forget to read our other useful blog posts and tips.