Geometry, it matters

[Claviger]

Theres a lot of talk here on various tire sizes and the way they change steering feel.

I found a good calculator here:
RB Racing Professional Rake and Trail Calculator

I ran out and did some measurements.

Swing Arm Angle - ~13.2 degrees
Triple Clamp Offset - 2"
Fork Length - 31.75
Triple Tree Rake Angle - 0
Wheelbase 65"
Trail 4.5"
Calculated Rake Angle from measured trail using above calculator - 28.3 degrees
Swing arm pivot to rear axle 23”


Stock Geometry

Triple Clamp Offset - 2"
Fork Length - 31.75
Triple Tree Rake Angle - 0
Wheelbase 66.7"
Trail 5.8"
Calculated Rake Angle - 32 degrees

This all explains why my R3 is so easy to flick around and into turns, wheelbase is 1.7" shorter, trail is down from 5.8 to 4.5, plus the sharper Avon profile.

I put this up to advise people making changes, I would suggest NOT going at less trail than 4.5 or the 65 wheelbase. As setup the geometry I have is borderline "loose" for me (remember, I'm a sportbiker in a cruiser world not the other way around) and would certainly catch most cruiser riders off guard!!

For Comparison Sake:
2016 Goldwing F6B - Rake: 29.15 Trail: 4.3" Wheelbase: 66.5"
All Years Hayabusa - Rake: 24.2 Trail: 3.8" Wheelbase: 58.5"
2014 ZX-14R- Rake: 23 Trail: 3.7" Wheelbase: 58.3"
2014 Concours 14- Rake: 26.1 Trail: 4.4" Wheelbase: 59.8"
2014 Streetglide - - Rake: 26 Trail: 6.8" Wheelbase: 64"
2004 XL1200C - Rake: 30.1 Trail: 4.7" Wheelbase: 60.4"
2012 Victory Vision- Rake: 29 Trail: 5.6" Wheelbase: 65.7"
2012 Victory Kingpin - - Rake: 32.8 Trail: 5.4" Wheelbase: 65.6"

 

[Claviger]

Some examples with stock shocks and forks.
240/55R16 + 140/75R17 = 5.1 trail roughly
240/50R16 + 140/75R17 = 5.3 trail roughly

To get exact you'll have to measure your bike, they're all a bit different.

Edit: Thanks for the correction Nev!

 

[EasTexRIII]

Good info maestro!

 

[Claviger]

For those wondering why this stuff is important... if you ever have an itch to upgrade your front forks, you'll need these measurements to figure out if a certain set of forks are going to work...or not lol.

 

[Claviger]

Quote from another forum for possible swaps:

I thought i can share that with you, it can help a lot of people here..
Its the compilation of fork length i did this winter for my project bike.

Feel free to comment on it to add other bikes or correct informations. i'll update it as informations comes. i want to add tripple tree spec (up and low diameter, offset and spacing) as soon as i find away to convert my excel spreadsheet to txt without having to redo the layout...


Make/Model year Range Fork Length mm (inch) (axle center to fork cap top extended suspension)
Buell
M1 700mm (27,5'')
M2 730mm (28,75'')

Ducati
998s ohlins 720mm (28,374'')
monster 750ie 02 730mm (28,74'')
st3 04-05 725mm (28,54'')
st4s 02-03 697mm (27,44'')

Harley Davidson
most 812mm (32'')

Honda
CBR1000RR 692mm (27,25'')
CBR600F1 87-90 738mm (29,05'')
CBR929 00-01 724mm (28,5'')
CBR954 02-05 724mm (28,5'')
RC51 SP1 762MM (30'')
RC51 SP2 736MM (28,97'')
vfr 750 fl 791mm (31,15'')
VFR800 780mm (30,75'')
vtr1000f 778mm (30,62'')

kawasaki
fz1 2007 762mm (30'')
versys 774mm (30'')
ZRX1100 766mm (30,15'')
ZX10R 06-07 743mm (29,25'')
ZX10R 04-05 730mm (28,75'')
ZX14 742mm (29,25'')
ZX636 750mm (29,5'')
ZX9r B4 94-97 766mm (30,15'')

Suzuki
GSF 400 JDM 820mm (32'')
GSXR1000 01-02 726mm (28,54'')
GSXR1000 03-04 720mm (28,34'')
GSXR1000 05-06 720mm (28,34'')
GSXR1000 07-08 720mm (28,34'')
GSXR1100W 94 770mm mm (30,25)
Gsxr1300 Hayabusa 99-07 725mm (28,54'')
Gsxr1300 Hayabusa 08
GSXR600 00-03
GSXR600 04-05 720mm (28,34'')
GSXR600 06-07 738mm (29,05'')
GSXR750 90-95 750mm (29,5'') 257mm (10 1/8'')
GSXR750 00-03
GSXR750 04-05 720mm (28,34'')
GSXR750 06-07 738mm (29,05'')
GSXR750 SRAD 96-99 730mm (28,75'')
RF600 97 750mm (29,5'') 257mm (10 1/8'')
TL1000R all 717mm (28,22'')
TL1000S all 732mm (28,81'')
VZ800 Marauder 838mm (33'')

Yamaha
FZR400 790mm(31.1'')
FZ750 1986 825mm (32,5'')
FZR1000 87-88 770mm (30,3'')
FZR1000 exup 89 770mm (30,25'')
XV920 J virago 82-83 825mm (32,5'')

 

[Neville Lush]

240/55R16 + 140/75R17 = 5.1 rake roughly
240/50R16 + 140/75R17 = 5.3 take roughly

trail maybe ?

 

[Tripps]

Not sure what I'm missing, how would tires change the length of the wheelbase?

 

[mexican]

Good info maestro!

Way above my head, all i know about tires is that they are round

 

[Idaho Red Rocket 3]

Rob,

I understand rake to be the angle of the forks. Is that correct ?

Please explain Trail and its importance.

 

[mr hunt]

Trail is measured by imaging a line, perpendicular to the ground, extending up through the centre of the front axle. Now imagine another line extending from the headstock to the ground, drawn at the same angle as the headstock.

The headstock line will hit the ground in front of where the the line from the axle will hit the ground. The distance between these 2 points is the trail.

Theoretically a trail of 100mm (4") is ideal for optimal steering. Any shorter and the bikes propensity for tank slapping will increase markedly - more than 100mm it will 'slow' the turn in down making for a slower steering bike.