How do you measure rake and trail?

[TonyB]

I've had my race bike for a few years now, and through a combination of not taking notes and losing some that I did take, (coupled with a poor memory), I lost track of how the bike was setup as stock. I measured a stock version of my bike the other day (thanks Casbolts) and now realise that I have made some fairly radical changes to the ride height at both ends of the bike.

So what I want to do now is measure the rake and trail and compare it with modern sports bikes. I know how to take the measurements and calculate things thanks to this article, but what I'm not sure of is whether you measure the bike unloaded, with static sag, or even with the rider on board.

Can some one offer some advice please?

[Motu]

The specs in my riders handbook gives trail loaded and unloaded - but it is normally taken unloaded.

[t3mp0r4ry nzr]

The specs in my riders handbook gives trail loaded and unloaded - but it is normally taken unloaded.

unloaded, as in suspension unloaded ie, extended?

[Motu]

My BMW manual says unladen weight is ready for road with tank full,normal load is with 75kg rider - buts that's honest Germans,other manufacturers might have different theories.

[TonyB]

Thanks Motu, thats a good start.

To be honest I would have thought that rake/trail should be measured with the bike on its wheels, as measuring with the suspension is a bit pointless- you can't ride it like that. Then again it does give a fixed starting point...

[lostinflyz]

modern sportsbikes are setup to be easy to ride something with significant amount of horsepower, for the average rider to be able to handle. Matching to that may not be a great idea.

[Robert Taylor]

I've had my race bike for a few years now, and through a combination of not taking notes and losing some that I did take, (coupled with a poor memory), I lost track of how the bike was setup as stock. I measured a stock version of my bike the other day (thanks Casbolts) and now realise that I have made some fairly radical changes to the ride height at both ends of the bike.

So what I want to do now is measure the rake and trail and compare it with modern sports bikes. I know how to take the measurements and calculate things thanks to this article, but what I'm not sure of is whether you measure the bike unloaded, with static sag, or even with the rider on board.

Can some one offer some advice please?

In my world unladen, but also in effect both as it tells you whether you have the spring rate and preload somewhere within the correct ''window''.

[TonyB]

modern sportsbikes are setup to be easy to ride something with significant amount of horsepower, for the average rider to be able to handle. Matching to that may not be a great idea.

AT the risk of confirming that I am an idiot, allow me to explain why I am doing this little exercise.

My bike was running wide in the corners (pushing the front). So I raised the rear by installing new ball joints on the ‘hoop’- the smallest gain I could get was another 15mm. This fixed the problem, which was probably caused by my old Sachs shock squatting down/ packing down. I now have a shiney new shock (AT LONG LAST- sorry RT if you're reading this, but I got a WP from RCMP....it all came down to $$$ and the WP also had a better range of adjustments. I still feel guilty…). So I figure the NEW shock is going to behave very differently, and the adjustments I made may make the bike as twitchy as all hell once it stops squatting. I also considered that my habit of being tentative in the corner entry may not be entirely caused by my lack of testicular fortitude- i.e. maybe the bike is twitchy as all hell, and it needs to wait until I'm driving out of the corner to squat down and settle again.

SO. Not knowing what my bikes standard ride heights were any more, I went into Casbolts and measured a couple of early Monsters. This lead to the discovery that I had lowered the front by 30mm, and raised the rear by 25mm. “Crikey…that seems like a lot” I thought. Mind you, a Monster is more of a cruiser….so maybe its not that bad…

So I put the original ‘hoop’ ball joints back in, and set the shiney WP shock to 336mm length. The theory being that the nice people at WP probably have some idea what they are doing, and this will give an idea of what is sensible. This means that the bike is now 30mm lower in the front and 19mm higher in the rear. If I want to raise the front again, I have to either buy some different clipons, or put them back under the top triple clamp.

SO. Yesterday after setting the rear ride height as described above, I measured the rake and trail with the bike on its wheels and came up with 22.3° rake, and 93.5mm trail. Scary numbers? They don’t seem too bad when compared with a modern 600…..which has a stiffer frame….better forks…

[TonyB]

In my world unladen, but also in effect both as it tells you whether you have the spring rate and preload somewhere within the correct ''window''.

Oh look, you ARE reading this...

Thanks Robert

[t3mp0r4ry nzr]

Hi Tony.
How did you go about measuring the rake and getting an exact figure (to one decimal place)? Keen to measure my geometry to measure any subsequant changes.

As I have learnt, small adjustments are the key. Large adjustments away from factory settings arent neccessarily a step forward.

An interesting subject - geometry - was just reading that gearing changes can effect swingarm geometry and squat characteristics. Will definitely be doing as much further reading as possible.

Great link you provided.

[TonyB]

Hi Tony.
How did you go about measuring the rake and getting an exact figure (to one decimal place)? Keen to measure my geometry to measure any subsequant changes.

As I have learnt, small adjustments are the key. Large adjustments away from factory settings arent neccessarily a step forward.

erm, think of it as 22 to 23° and 93 to 94 I used a good level and the ruler on a square to calculate the rake using trigonometry, and then the trig calculations on the web page in my first post to get the trail. It can't be too far out though, because when I measured the trail manually I got between 93 and 94mm.

[Blackflagged]

If you can try more trail, you must have less than stock.After pitching the bike forward, that much.Standard triples? 30 or 34mm offset.

[TonyB]

They are standard tripples with 1" (25.4mm) offset.

[Shaun]

They are standard tripples with 1" (25.4mm) offset.

Good luck with your little exercise Tony. If Robert from CKT could NOT help you enough in the past, how is this place going to help

Numbers are only numbers

If the rider cannot say what ther bike is doing that they do not like, NO ONE on earth can fix it

[Blackflagged]

SS900ie stock is 30mm, 916/Rsv is 34mm. 25mm seems low, i`ll measure one.

Ducuti Racing used numbers close to what was on your web link.888 was basically the same frame,with some goggling you should be able to find out what the customer kit bikes used.They know a thing or two.

Here`s a quote from John Robinsons book Motorcycle Tuning.. Chassis "Trail is probably the most significant dimension,once a bike is constructed and ready for testing,along with weight distribution."

It`s an interesting topic,and an open public forum, I believe.