how do you calculate rake and trail

[mart]

as the tittle says is it possible to work out rake & trail and how would you do this for a given bike

[Sid Squid]

Easiest to use makers quoted figures, failing that get the bike on a perfectly level surface, using a spirit level and a protractor measure the rake, unless you've got a Harley forks and steering axis will be parallel, if they're not it's complicated. Trail - measure from point directly below front spindle to extended steering axis point - keeping sttering perfectly square. For ease I'd probably make some measurements and produce a diagram.

[mart]

thanks squid

[21QUEST]

Are you trying to work out how different changes affect the rake and trail?

Cheers
Ben

[extreme3d]

This site explains what to measure:

http://www.sportrider.com/tech/146_0310_art/

[mart]

thats a handy site. no just want to see the difference between the gsxr forks conversion and the stock sv forks and to try and counter act any problems that may arise with it i know a steering damper helps but im not too pleased to have a 120/50 front tyre on

[21QUEST]

.......but im not too pleased to have a 120/50 front tyre on

You mean a 120/70 ?

Nice link extreme3d. Helped confirm a few bits for me.

Inch difference in fork length is equivalent about 1 degree reduction in rake. Personally I work with 0.03714 dgrees for every mm.

My calculations are these

Depending on how much shorter you make the GSXR forks(some say 20 mm but I make it about 25mm) , these are my figures

Forks 20mm Shorter
120/60/17( Dunlop 220) with rolling radius 288mm measured TRAIL=93.53
120/70/17(Pilot Road) with Rolling radius 299mm measured TRAIL=98.44

Forks 25mm Shorter
120/60/17(Tyre as above) TRAIL= 92.46
120/70/17(Tyre as above) TRAIL=97.33

Those figure are for the curvy with standard rake taken as 24.8 degrees/GSXR forks flush with top yoke. Yoke offset for the GSXR600/750/1000 up to K3 is 32mm.

The yoke offset for the SV650 Curvy is 29mm by the way. Don't know the offset for the Pointy.

Cheers
Ben

[xj/frosty]

Im racing a curvy with gixxer front end and some JHS internals
its effectively steepened the rake about 1 degree.
a lil advise dude --if youre thinking of doing it get the forks rebuilt using .95 springs --the difference is un believable

[21QUEST]

xj/frosty , if you don't mind me asking how much do you weigh (With gear or without).

Also did you have the forks lengthened? Personally don't think really required with a 120/70 but just curious.

Cheers
Ben

[xj/frosty]

I' 176cm and currently weigh in at 68 kg nekkid--scales are right by the shower
And nope diddnt have the forks changed externally--Ive actually got em pushed through the yokes 12mm (1/2 inch) to quicken up the steering.
Mind you -My setup isnt soposed to work -Im running an ohlins shock setup for a k3 gixxer 600 with 97mm doggies. Looks like is bums hanging down compared to other sv's. I've always used a lot of body english so it seems to suit my riding style .

[21QUEST]

Thanks.
I must say my initial thought was blimey .95? but if your setup works for you then it does.
There is a racer IIRC on here about your weight and he uses 0.80Kg/mm. All in the rider preference.

Front on mine is flush with a 120/70 tyre but rear shock is about 18mm longer than standard at lowest ride height setting.

I did think my shock(Technoflex)was 10mm longer at lowest setting but only recently had the chance to measure it proper with it off the bike. I was a little bit :shock: but looking forward to riding and setting bike up my way.

Cheers
Ben

ps:I don't race by the way.

[xj/frosty]

quest I hear ya dude --I think what you will find is the bike will seem a bit top heavy the first few times you read it-High feeling c of g and some times it feels like its gonna just fall over