Steering offset - triple clamps and e-axles

[numroe]

Q1) Anyone found anything like the Rekluse e-Axle for pitbikes?
See Rekluse Motor Sports - e-Axle

Q2) Anyone know of some fork triple clamps for 48mm fork tubes with an offset much lower than 37mm?

See the diagram below.

I want to increase the steering trail on my bike pitbike. Reason is to get slower initial steering response in soft terrain. In soft terrain, the bike often steers in much too fast, which can cause front tyre to eventually push, or bite and then knife, or just general loss of control. In other words I want to remove the twitchy "shopping trolley" feeling.

I've tried increasing rear sag (only to increase steering rake), but that kills normal corner handling. I try standing and hanging off the back and keeping the power on harder, but that's way too difficult for me to do accurately, and impossible if I trying to wash off speed.

The bike doesn't get headshake at speed. Which surprises me.

My fork lower ends have the axle hard against the front chrome tubes. I'd go for 25mm clamp offset if I could get it. Which is a massive change in trail I know.

I don't fancy installing an $800 steering damper just so I can ride soft or sandy corners on my pitbike.

Thanks for any help.

 

[jovian]

The Axle is a brilliant Idea.

37MM seems like a massive offset when standard MX is between 20-24mm. I when from 24mm to 20mm on crf supermoto and the different was amazing. I am know thinking of going to an adjustable 14/16mm set. I have thought of changing the offset on the mini. I doubt any thought went into this in the china factories.

 

[numroe]

37MM seems like a massive offset

It's hard to say. The ideal amount of trail depends on a few things. Wheel size included. Perhaps the clamps are a copy off some mini bike which has the front axle on the bottom of the fork tubes and not much thought went into it. But maybe the clamps were designed for a frame with more steering stem rake and/or designed for good steering on hard packed tight BMX style tracks. Who knows the history.

I know I want to try more trail. A change like 8 or 10mm which would be a huge change on a mini. Modifying some clamps will probably be the go. I think the outcome will be interesting and possibly unreal. I've no doubt it'll be better in the soft dirt. But it's a compromise thing.

 

[jovian]

Like i said i doubt they china factories thought about offsets. I will measure mine up tonight to let you know.

To me it sounds like ur alittle confused on wat u want to do. A small offset will speed up your steering but give more feel and control on the front. The more aggressive offset will decrease the trail. I would say the excessive offset and trail you have now will make ur bike feel horrible in those conditions in particular, much like trying to ride a harley in the dirt, very vague front end.

Change ur rear sag back to want u had. A steering dampner would be a massive waist of money, usually all they do is mask a bad suspension setup - which would def apply in this case.

My advice would be hunt around for a smaller offset, move the rear wheel back as far as possible in the swing arm and check your tyre pressures.

 

[numroe]

I will measure mine up tonight to let you know.

Thanks for that. Appreciated.

My advice would be hunt around for a smaller offset, move the rear wheel back as far as possible in the swing arm and check your tyre pressures.

Onto to it. Already searching. Rear wheel went way back a long time ago. Tyres always as low as I am game to run em. Sag always setup for general cornering.

A small offset will speed up your steering but give more feel and control on the front. The more aggressive offset will decrease the trail.

Take another look at the diagram. Imagine the steering axis stays where it is. Then reduce the offset only and bring the whole wheel aft. You can see how the trail increases. This why people always get more stability and comment on "more feel and control" with reduced offset clamps. Now some people say their bikes also steer quicker. But technically speaking, they sure don't. OK, this is bit of a terminology thing with the words steering (arms and bars) versus turning (chassis and ground). With the ideal amount of steering trail, a bike will achieve the best combination of countersteer response, lean in, and turn in. This sets the bike up with the right lean and front wheel loading, which then permits faster chassis turning.

A more "choppered out" steering setup is exactly what's needed in sand. Because softer ground has the effect of moving the drag/contact point forward on the front tyre, which means that steering trail is reduced or even goes negative in soft sand. The resulting tendency to "knife" in sand is why we naturally sit back. I'd not be surprised if the AMA and FIM pro teams use super low offsets for sand tracks.

 

[jovian]

measured up the offsets - MSO140S 36mm & Pitpro 125R 37mm.

Makes me think i should get a smaller offset to imporve the turn in on my minitard like i did with the big bike.

My crf450 supermoto runs a 20mm offset (24mm standard) however i am thinkin of going to an adjustable 14-16mm offset.

 

[numroe]

I've given my clamps to a machinist to get the offset reduced. I'm going for a big change, from 37mm to 30mm.

A 2mm change (24 to 22) on my big bike was easy to feel and slow down the steering a lot and in most conditions improved my turning.

So 7mm seems like heaps on my mini, but I don't want to do it half measure, and as it was the steering was way too sensitive. I wont be able to test it until a couple of weeks from now. Keen to try it.

 

[jovian]

sweet let me know the results could be a good mod for the minitard. how is the offset being chnaged?

 

[numroe]

how is the offset being chnaged?

Not my idea, but apparently this is how it's "always" done when moving in the direction I want the stem to go. ie. more toward the middle where there is plenty of metal.

Each clamp: Oversize mill a circle hole around the old hole centered more fwd. Then press an billet alum disc into that circle cut out. Then mill new stem holes in the desired position, which is within the new pressed in piece. Lastly, press stem into the bottom clamp, and press the lower bearing down onto the stem.

Make sense?

I think I've got a real good chance my midsized mini will be a lot more cooperative in most turns, especially on soft ground. With more steering trail, via setup and technique, I hope to be able to put a lot more weight on the front wheel in corners with good results.

I was thinking of getting an offset front axle made up (Rekluse e-axle copy), but that'd only get me about a 3mm change.

 

[jovian]

i know some guys who get thier triples modified on thier aprilia supermoto's but never bothered to ask how its done

 

[numroe]

After what feels like 6 months, today I finally rode my pit bike again.

Firstly must mention that the punchy throttle response of the Lifan 150 with the Akunar A1 bottom end cam is just unreal. With the Lifan wide spaced gear ratios (meant for road riding I assume and stupid for MX), the A1 bottom end cam and resulting good torque spread over a wide range of RPMs is just the ticket. With an occasional clutch fan at low speed, I get a huge speed range out of 3rd gear (15:39 sprockets I think). Also nice for reliability not needing to shift the china gearbox too often.

Anyway my reason for posting here is that I rode with 25mm offset triple clamps. The whole bike is so much better to ride than with the old 37mm clamps. 12mm change is massive but it needed it. The steering is way slower now, so the turning can be way more aggressive with more power used. I can lean the bike easier and steer with the throttle much easier. Also easier to put weight on the front wheel over bumpy corners. Now I can ride is deep soft sand ruts and berms and in the sand the front does not uncontrollably knife out from under me.

The stock 37mm clamps worked okay on hard backed bermed BMX style tracks. But on soft dirt, or sand, or flat slippery tracks, or ruts, the new slower steering = much sharper/faster turning. In high speed hard pack power slides, you can steer around a fiar bit, and the bike now has much less chance of throwing me over the high side.

Must say the Pirelli Scorp MX Extra 12" rear tyre does pretty good in the sand too.