steering off-set

**Mr. Ron** · #1 11 Jul 2005

Hello. Could someone please explain to me what effect steering off-set has on the handling of a motorcycle. The KTM triple-clamp i'm mounting on my R100gs has an off-set of 14mm, and a 20mm version is available. The stock unit has a 36mm off-set, and for curiosity i measured the off-set on my Yamaha R-6 racebike, an enormous 42mm! Forgetting the clearance for the fuel-tank the larger off-set gives me, what can i expect from the 14mm clamp?

**Frank Warner** · #2 11 Jul 2005

The offset between the fork tubes and the steering head?

Well it is the resultant trail that effects the steering. The trail will change as you change teh offset .. but is also effected by the place where teh axel mounts and the tyre size. Not forgetting the distance to the steering head.

So do a google on trail, handeling, motorcycle and see.

**Mr. Ron** · #3 13 Jul 2005

Thanx Frank. The outcome was very informative.

**Mr. Ron** · #4 14 Aug 2005

Okay, back from holidays and back to my project. I plan on copying the HPN design, but things would be easier if i had some specs. Could someone tell me the off-set of the HPN triple-clamp for the WP forks. I've searched the internet for hours and can't find the answer. Tomorrow i'll try to measure the stock trail and start a discussion on weather this can be improved.
Thanx to all.

**Mr. Ron** · #5 22 Aug 2005

Update: Ive measured the steering geometry on my '89R100gs/pd. The numbers are as follows:
Steering offset-37mm
fork rake-27 degrees
fork length-32 inches
floor to axel-13.625 inches (90-90/21 tire)
resulting trail-3.5 inches
I hope this information becomes as useful to others as it has to me. Today i began machining a new set of triple-clamps from solid blocks of aluminium to copy the current geometry for my new WP4860 forks. More later...

**Grant Johnson** · #6 22 Aug 2005

If you're going to that much troube, and not to make life complicated or anything,

but why not make them adjustable?

The stock steering is a little heavy, could perhaps do with slightly steeper rake - but that might not be good at speed... but isn't that what experiments are for?

Wish I oculd join the fun, but I'm closing up shop Tuesday and the movers come Wednessday to ship everything to the UK, where I'll have a lovely parking garage open to the weather for a workshop...

have fun

by the way, I have a Conti Tour brand new rear for your bike, real steal...

------------------
Grant Johnson

Seek, and ye shall find.
------------------------

One world, Two wheels.
www.HorizonsUnlimited.com

**Frank Warner** · #7 23 Aug 2005

Fork rake ... you mean steering head angle...
If you vary the fork rake from the steering head angle (i.e. they are usually the same) then as the suspension moves you get different trail .. and so different handling .. much rather have consistency?

Changing the steering head angle requires modification of the frame...

I hope your measurements take into account any offset between the wheel axis and the fork axis.

**Mr. Ron** · #8 23 Aug 2005

Thanx for the input guys, but at this time i feel changing the rake properly involve frame mods, not an option at this time. I could do this to the triple-clamp, but something seems fundamentally wrong about the forks and the steering head not being paralell. I bored the holes for the forks on Sunday, and only dilled a locating hole for the spindle, which i'll cut this coming weekend on the lathe. I do have an opertunity to change the steering off-set, which will increase or decrease trail. Actually, now that i think about it, i can only increase the off-set by about 2mm.which would decrease trail about the same amount, or i could significantly increase the trail by reducing the off-set, but then i get into clearence issues with the PD tank. Unless someone can convince me there is a better geometry, i think i'll stay with the original geometry.
Grant, my goal is to finish my project in time for the meeting Sept.11th weekend, which also happens to be my birthday

Hopefully i'll see you all then.
Ron...

**gsworkshop** · #9 23 Aug 2005

Mr Ron why don't you e-mial Klause at HPN direct. He is very helpfull and they have more work than they can handle so they do not feel threatned by guys doing their own thing.

**AndyT** · #10 24 Aug 2005

I know this is a bike with a different purpose, but the Harley V-Rod has a triple clamp set up that rakes the forks out more than the steering head angle, so I don't think there is anything inherently evil about that. I don't know the specs, but I think that the steering head is 32 degrees off vertical and the triple clamps add 4 degres to that or something close.

**Frank Warner** · #11 24 Aug 2005

How much travel does a Vrod have ? Lots less than 8 inches I'd say. The more travel - the mosre that change in angle will change the trail - the more effect on stablity of the bike.

**Mr. Ron** · #12 24 Aug 2005

Quote:

Originally posted by gsworkshop:
Mr Ron why don't you e-mial Klause at HPN direct. He is very helpfull and they have more work than they can handle so they do not feel threatned by guys doing their own thing.

Thanx for the info, but i've e-mailed HPN four times over the last year or so asking questions and requesting input, never received an answer. I figured they were just too busy...

"the Harley V-Rod has a triple clamp set up that rakes the forks out more than the steering head angle, so I don't think there is anything inherently evil about that."

Andy, you are right. You could probably do this on any roadster thats made to go in a strait line or lean deep into corners. Its when the wheel is turned to some degree, like in off-roading,this difference in angle will have more of a swooping or scalloping affect on the front end.From what i can tell this would have a negative impact on handling overall. Anyways, i'm happy with how the GS handles now and plan to keep it this way, unless someone out there can give me some numbers on changes they've made, and the effect it had on their ride.Oh, one thing i will change is bar position, back and up 1/2-3/4 inch. When standing on the pegs, i always have this feeling of getting too intimate with my front fender. Even with my new Fastway footpegs on low-mode, i't still too tall on the bike, and i'm less than 5'8".

BTW, thanx everyone, it's nice to see a few others have shown interest in this thread!

**Mr. Ron** · #13 19 Sep 2005

Hello. Just here to give you guy's an up-date on my front end. I decided to machine a new set of triple-clamps out of billet aluminum, maintaining the stock geometry. This also required having the new WP4860 forks shortened by 3.5", re-sprung and re-valved (thanx to Mike at Holeshot Racing

). I'm almost done the clamp, it fits well! Just have to deal with some clearence issues. My biggest problem now is the Akront wheel and hub. The hub doesnot provide enough clearence for a brake-rotor not hitting the fork housing upon compression, without some radical alteration. I'm researching my alternatives right now and am focusing on getting an Excel 1.85x21 rim laced onto a KTM dirtbike hub (eg. 520EXC...) Then i can go with the super-trick super-moto 320mm floating wave-rotor and four-piston caliper from Braking, available from KTM Hardparts. These items would be simple bolt-on replacements, readily available through the internet. You can see some current photo's at
www.mrron.smugmug.com