measuring a bike

[jellywrestler]

i've got a couple of bikes i want to measure rake trail wheelbase etc for a magazine article, thinking with all the laser measuring shit around that shouldn't be hard?
thoughts
also, is rake trail normally measured with no load on suspension, normal load etc

[Grumph]

Usually measured unladen.
I do it the old fashioned way. Tether the bike upright, straightedges and a marker pen. A spirit level helps - as does a clean floor.

[Crasherfromwayback]

also, is rake trail normally measured with no load on suspension,

Both are as from the factory, no load.

[Michael Moore]

as does a clean floor.

And a level floor helps too, otherwise you have to shim under the tires to level the bike.

[husaberg]

i've got a couple of bikes i want to measure rake trail wheelbase etc for a magazine article, thinking with all the laser measuring shit around that shouldn't be hard?


You can measure Rake with a Cellphone with a simple angle app
if you then get the tyre outside diameter and fork offset you can calculate the trail
Either that or plump bob and meter ruler builders protractor and old school maths
There are plenty of calculators on the net.
https://www.rbracing-rsr.com/rakeandtrail.html
these calculators are useful as you can calculate the effect of different off sets and tyre diameters etc

[malcy25]

You can measure Rake with a Cellphone with a simple angle app
if you then get the tyre outside diameter and fork offset you can calculate the trail
Either that or plump bob and meter ruler builders protractor and old school maths
There are plenty of calculators on the net.
https://www.rbracing-rsr.com/rakeandtrail.html
these calculators are useful as you can calculate the effect of different off sets and tyre diameters etc

Exactly what I have recently done.

On thing though, as you cannot guarantee the floor is flat. Mark wheel position. Measure fork rate, Turn bike around so the front wheel was where the back wheel was and vice versa. Remeasure fork rake. Take the average of the two. This will remove any variances that can be induced from a not flat floor. Think about it - could you see 1 degree of angle on the floor, but that would show in the head angle....

[malcy25]

Exactly what I have recently done.

On thing though, as you cannot guarantee the floor is flat. Mark wheel position. Measure fork rate, Turn bike around so the front wheel was where the back wheel was and vice versa. Remeasure fork rake. Take the average of the two. This will remove any variances that can be induced from a not flat floor. Think about it - could you see 1 degree of angle on the floor, but that would show in the head angle....


Also forgot to say, unless you have "raked" yokes, changing the fork length does not alter the result in the calculators (and is otherwise essentially irrelevant from a calculation perspective). Most bikes DO NOT HAVE RAKED Yokes. Reasonably common on Hardley's and some older bikes.

So if you are looking at fork position relative to rake/trail change. If you change the effective fork length of the bike you need to recheck the head angle and insert the new head angle into the calculator to recalculate the trail.... just changing the fork length will not alter the result. Took me a while to figure that one out.

I've learned a lot about rake and trail lately having just had new yokes made for one of the race bikes.

[husaberg]

Also forgot to say, unless you have "raked" yokes, changing the fork length does not alter the result in the calculators (and is otherwise essentially irrelevant from a calculation perspective). Most bikes DO NOT HAVE RAKED Yokes. Reasonably common on Hardley's and some older bikes.

So if you are looking at fork position relative to rake/trail change. If you change the effective fork length of the bike you need to recheck the head angle and insert the new head angle into the calculator to recalculate the trail.... just changing the fork length will not alter the result. Took me a while to figure that one out.

I've learned a lot about rake and trail lately having just had new yokes made for one of the race bikes.

Old Bimotas used to have a split rake with the yokes and the head angle.

In my experience you notice small difference in trail but not feel the effect of slight rake variation. But I guess if you were a pro you might
I think those calculators are more about building a chopper with extended forks.

Specking of race bikes who has the McIntosh TZ750.

[malcy25]

Specking of race bikes who has the McIntosh TZ750.

Which one. there were a couple built that I know of.
The ex Discombe, Alan Green Bike is with a private collector in Auckland.
The other one which at times was ridden by Norris Farrow in the early 80's is still owned by the same owner.

[husaberg]

Which one. there were a couple built that I know of.
The ex Discombe, Alan Green Bike is with a private collector in Auckland.
The other one which at times was ridden by Norris Farrow in the early 80's is still owned by the same owner.

The Discombe one was the one I meant, I never knew there were others.
I never thought of measuring the rake twice, but sure makes sense