Hi - just a slight point of confusion regarding some literature on the Husky site. They say that the triple clamp offset was reduced from 25mm to 18mm to quicken the steering. I thought reducing the offset increased the trail, making the steering slower but more stable (CR Huskies now have 18mm offset, WR's have 15mm: which would have the quicker steering?) Thanks for shedding any light on this for me...
offset triple clamp properties
- Thread starter robj
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dirt bike dave
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- May 3, 2000
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You are right, reducing the offset does increase trail. However, it does shorten the wheelbase, so if the bike's are quicker turning that would probably be the reason.
If you search the internet, there are some good pages that address these issues (sorry, I don't have any bookmarked).
If you search the internet, there are some good pages that address these issues (sorry, I don't have any bookmarked).
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
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Um guys.. I don't think so.. IT reduces both the bike trail and real trail.. This effectively shortens the forces that act to make the wheel go straight.. This allows for quicker wheel changes, but poorer stablity...
One other really important consideration.. Axle mounting postion allso impacts effective offset.. So just because one bike has 15mm clamps and one has 23mm the effective offset may be equal..
BR,
Jer
One other really important consideration.. Axle mounting postion allso impacts effective offset.. So just because one bike has 15mm clamps and one has 23mm the effective offset may be equal..
BR,
Jer
dirt bike dave
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Thank you svi. To the non-beleivers, here is a quote from the following page:
http://www.bankeperformance.com/catalog_dtu_tripleclamps.html
QUOTE As a general rule, less fork tube to steering stem offset yields more trail and hence, up to a point, more stability. More fork tube to steering offset yields less trail and less stability. These changes also change the wheelbase. ENDQUOTE
If you draw a quick diagram, it is easy to see why this is. Here is a link from Tony Foale discussing geometry; some interesting stuff.
http://www.ctv.es/USERS/softtech/motos/Articles/RakeEx/RakeEx.htm
http://www.bankeperformance.com/catalog_dtu_tripleclamps.html
QUOTE As a general rule, less fork tube to steering stem offset yields more trail and hence, up to a point, more stability. More fork tube to steering offset yields less trail and less stability. These changes also change the wheelbase. ENDQUOTE
If you draw a quick diagram, it is easy to see why this is. Here is a link from Tony Foale discussing geometry; some interesting stuff.
http://www.ctv.es/USERS/softtech/motos/Articles/RakeEx/RakeEx.htm
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
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Ok so we all have those momets when suddenly no matter what we thought we where doing we ae over in the meadian asleep in our boxvan at over 80MPH.... What thats never happened tou you? :p
This is one of those for me.. While I was out this sumer I had all kinds of revolations, and whilst board, dateless, and tired of drinking this last weekend, I was surfing around for fun things to look at from the time I was away.. When I came across what I had said, and what had been said back, I was getting all fired up over the verbal slaying I was gonna deliver and then It started to setle in like the sound of entire contents of your box van getting juggled as you casually come to from the vivid dream to realize your going 80MPH down the highway medain in your box van..
Lecture classes allways made good sence whilst i was in school, beacuse you could elimninate all your stupid ntions before you could embrass yourself in public.. I got real serious about chassis stuff some time back after doing some road race testing with Muddy in Austrilia. I know alot about valving but I was fairly ignorant to basic gemeorty stufff so I made it a point to learn more. I got Tonys book and continue to study it.. However I made the tragic error of cusnfusing what I know from exspereince with what I learned in the book and while if you can teach you know it, you may not really no it coorectly.
There should be a really obvious question poping up here... why do offroa bikes with less offset turn better? I can tell you that I know for a fact that they do. So why the heck is that posible when yes when you think about it correctly it increases trail with less offset? That should as SVI and DBD noted make the bike more stable, and harder to intiate a turn.. Really firging werid..
Well not able to come up with a answer I e-mailed Tony, I have gotten to know him a little over the last year talking about diferent things.. While I was waiting I also asked some other freinds, and I've not heard back yet.. Well heres Tony's answer...
Firstly, I assume that top and bottom yokes both have the same changed
dimension. If not for example, if the bottom yoke keeps the same offset
and the top one is increased then the trail will increase not decrease.
Secondly, assuming that the first comment doesn't apply. Reducing the offset does two things that work in opposition insofar as
steering resonse is concerned.
1. It increases trail which slows steering, but this takes a little time to
take effect.
2. It reduces the steering inertia which quickens steering during the
initial part of the turn-in. (It also shortens the wheelbase)
I imagine that you are talking about riding on dirt, in which case the
effect of a given trail is less than on tarmac in this regard and so the
second point begins to assume a greater proportional importance. Look at fig. 4.12 in the book. In particular the initial 0.05 secs (about
the first 3 or 4 mm. of the plot)
What is termed the "tyre induced torque" is the torque from the trail. The
"resultant" torque is what's left when all of the separate torques on the
steering are added together, and it is this resultant that accelerates the
steered assembly about the steering axis. The actual acceleration depends
on the steered inertia as well as this torque.
Note how during the initial 0.02 - 0.03 secs. The resultant torque just
follows the rider's applied torque until the feedback torque from the
effect of trail starts to build up.
So reducing the steered inertia will either require less effort during that
short initial period to achieve the same performance or else will perform
faster with the same rider input. This initial period is very short but
maybe it's enough to give the feeling that you are experiencing. Also the
data in fig.4.12 is only for that particular example which was a fairly
aggressive lean-in on tarmac. On dirt I would expect the build up of tyre
force to be slower which would extend that initial period.
I would be very interested to hear about these effects if you repeated the
same tests on tarmac.
Keep me informed on this, it's quite interesting. I'm fairly busy right
now but when I get a moment, I'll input some test parameters into the
simulation programme that I used to produce the curves in Chapter 4. and
see if it throws up results similar to yours. I'll let you know what I find.
Regards,
Tony
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I have read Tony's books and admire him greatly however in over ten years of setting offset with different riders on different machinery I have never once heard of less offset making the initial turn in easier and John Bradley in his book would definately agree with that.
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
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SVI,
I want to say I don't understand it either, but KTMs for instance are a prime example and where my "notions" come from.. JC and I have been thinking about doing a CRF clamp, beacuse I've heard many riders praising ofset change on those bikes as well. However I've done ZERO testing on what offsets or changes are impacting things. Things sure do get intresting in our sport sometimes..
BR,
Jer
I want to say I don't understand it either, but KTMs for instance are a prime example and where my "notions" come from.. JC and I have been thinking about doing a CRF clamp, beacuse I've heard many riders praising ofset change on those bikes as well. However I've done ZERO testing on what offsets or changes are impacting things. Things sure do get intresting in our sport sometimes..
BR,
Jer
dirt bike dave
Sponsoring Member
- May 3, 2000
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I've got a couple of theories about why less triple clamp offset may make a bike feel like it turns better.
To illustrate, get a ruler, a pen and a pad of paper. Make a dot at the bottom of the paper, use this as the steering head pivot at 0" on the ruler. Place a pen at 2" on the ruler, and rotate the ruler 45 degrees off center to the left and then the right. Use the pen to draw an arc on the paper.
Now place the pen at 4" from the pivot point and repeat. Note the arc drawn is much larger.
The 2" line is simulating a lesser offset clamp, while the 4" line represent a clamp with more offset.
The line drawn by the pen effectively represents how the contact patch of the tire moves with handlebar moevement. Less offset = smaller arc, preusmably less effort/force required by the rider.
Maybe the decreased offset/steering effort gives the rider more 'feel', while the increased trail also adds to the rider confidence. The result is a bike that is perceived to handle better by the rider, having quicker initial turn in but with more stability & holds the line better.
To illustrate, get a ruler, a pen and a pad of paper. Make a dot at the bottom of the paper, use this as the steering head pivot at 0" on the ruler. Place a pen at 2" on the ruler, and rotate the ruler 45 degrees off center to the left and then the right. Use the pen to draw an arc on the paper.
Now place the pen at 4" from the pivot point and repeat. Note the arc drawn is much larger.
The 2" line is simulating a lesser offset clamp, while the 4" line represent a clamp with more offset.
The line drawn by the pen effectively represents how the contact patch of the tire moves with handlebar moevement. Less offset = smaller arc, preusmably less effort/force required by the rider.
Maybe the decreased offset/steering effort gives the rider more 'feel', while the increased trail also adds to the rider confidence. The result is a bike that is perceived to handle better by the rider, having quicker initial turn in but with more stability & holds the line better.
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I think one relevent point that has not been discussed above, is that less offset results in the front wheel being closer to the mass of the bike and rider, thereby causing more weight on the front end which reduces the bikes tendency to push or understeer. FWIW
sigar....BINGO...you get the prize.....unforutunately the prize is a 87 Can-Am... :uh: :moon: ;)
I think you hit on the reason it works....just like trying to ride a dyno....sometimes all the data in the world doesn't add up to the perceived end result.... :yeehaw:
I think you hit on the reason it works....just like trying to ride a dyno....sometimes all the data in the world doesn't add up to the perceived end result.... :yeehaw:
db dave,
I think your idea would make more sense if you look at the other end of the fork. The little dot is in front of the contact patch on the ground. (where the steering axis meets the ground) Then draw the 2" and 4" arcs behind the dot (which would be the arc of the contact patch). The 2" being stock and the 4" as a result of reduced offset clamps.
This would increase self centering effect more and also require more effort. Which seems backwards of the example you used. weird huh?
My CRF has the 20mm offset (stock is 24mm). I have a damper on my bike so I can't feel the quickness of the initial turn in that Tony was explaining. I would guess this is why so many people say that they reduce stability (thats the part of the equation I don't understand). I can definately feel the self centering effect of the reduced offset once I am in a turn an have the bars cranked even with the damper. This is a good feeling to me. If anything happens to the front end while turning It is that much easier to adjust to a wider arc in my turn and keep myself from washing out. (Its almost automatic) In fact I haven't crashed in a turn since I installed the reduced offset clamps.
The other aspect is the extra weight on the front wheel. 4mm may not seem like much but I definately feel like I am noticably farther over the front wheel when riding. (even going straight) So we all now this will help the front wheel stick better when cornering.
What confuses me the most is the 03 CRF has less trail (self centering affect) but more weight on the front wheel because of the steeper rake (raised rear).
It must be good enough to win the 250 shootout.....
I think your idea would make more sense if you look at the other end of the fork. The little dot is in front of the contact patch on the ground. (where the steering axis meets the ground) Then draw the 2" and 4" arcs behind the dot (which would be the arc of the contact patch). The 2" being stock and the 4" as a result of reduced offset clamps.
This would increase self centering effect more and also require more effort. Which seems backwards of the example you used. weird huh?
My CRF has the 20mm offset (stock is 24mm). I have a damper on my bike so I can't feel the quickness of the initial turn in that Tony was explaining. I would guess this is why so many people say that they reduce stability (thats the part of the equation I don't understand). I can definately feel the self centering effect of the reduced offset once I am in a turn an have the bars cranked even with the damper. This is a good feeling to me. If anything happens to the front end while turning It is that much easier to adjust to a wider arc in my turn and keep myself from washing out. (Its almost automatic) In fact I haven't crashed in a turn since I installed the reduced offset clamps.
The other aspect is the extra weight on the front wheel. 4mm may not seem like much but I definately feel like I am noticably farther over the front wheel when riding. (even going straight) So we all now this will help the front wheel stick better when cornering.
What confuses me the most is the 03 CRF has less trail (self centering affect) but more weight on the front wheel because of the steeper rake (raised rear).
It must be good enough to win the 250 shootout.....
Guys,
i'm the owner of a 450exc03, and find the bike really doesn't want to turn (compare to my 400 02) as anyone tried the 14mm offset on it? or is it to much? should i use the 18mm?
i'm of course, using a wer steering damper, so headshake is not realy the problem....
thanks for your advices
Lionel
www.wereurope..com
i'm the owner of a 450exc03, and find the bike really doesn't want to turn (compare to my 400 02) as anyone tried the 14mm offset on it? or is it to much? should i use the 18mm?
i'm of course, using a wer steering damper, so headshake is not realy the problem....
thanks for your advices
Lionel
www.wereurope..com
