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Unsprung Weight

 
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legalr



Joined: 30 Jan 2005
Posts: 163
Location: Wallingford, Vermont

PostPosted: Sun Feb 27, 2005 11:04 pm    Post subject: Unsprung Weight Reply with quote

What effect does unsprung weight of a sidecar have on handling? Are there limits of acceptable unsprung weight?
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Wallingford, Vermont
BMW K1200RS/EZS RX-5
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Mon Feb 28, 2005 1:01 am    Post subject: Reply with quote

Unsprung weight is any weight that is not supported by the suspension. Yes, there is contention concerning some items such as suspension parts and how much of them is actually supported etc. There is also a factor that concerns the spring effect that a tire itself has. But ignoring those topics we can still be correct in saying that unsprung weight is not our friend. It does nothing good for the handling of any vehicle.
With less unsprung weight the chances of maintaining a more consistant contact patch between the tire and the ground is much better.
With all of that being said we can still argue that rtacing sidecars have a rigid sidecar wheel on them. This is due to the rules and is related to the saftey of the passenger as well as probably cost concerns. Yes, the go fast.
I have often wondered if the idea of unsprung weight when we are talking about a sidecar wheel is that big of an issue. I am convinced it surely isn't as important as it is on the front end of the bike.
Just my thoughts. Come on guys what's everyone's take on this?
Claude.
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zentime



Joined: 22 Jan 2005
Posts: 832
Location: Massachusetts USA

PostPosted: Mon Feb 28, 2005 1:34 pm    Post subject: Re: Unsprung Weight Reply with quote

legalr wrote:
What effect does unsprung weight of a sidecar have on handling? Are there limits of acceptable unsprung weight?


same as what Claude said.....

I've always thought of anything attatched to the bottom side of the shock as unsprung. The wheels hubs shocks etc.
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will August ever come............
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Mon Feb 28, 2005 9:59 pm    Post subject: Re: Unsprung Weight Reply with quote

zentime wrote:
legalr wrote:
What effect does unsprung weight of a sidecar have on handling? Are there limits of acceptable unsprung weight?


same as what Claude said.....

I've always thought of anything attatched to the bottom side of the shock as unsprung. The wheels hubs shocks etc.


Right Bill..the 'discussion' comes in whether half the shock, half the swingarm etc is unsprung or not. To me it isn't worth a big discussion as what we would build would be more focused on proper strength over and above minute (mineut?) weight savings. In racing it is all about weight savings above anything else.
What may be seen as compromises in this area for the street are a necessity IMHO. It has been mentioned that designing a fast rig for the street is more diffcult than for the track and I beleive that has a lot of truth in it.
Good topic Larry Smile
Claude
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zentime



Joined: 22 Jan 2005
Posts: 832
Location: Massachusetts USA

PostPosted: Mon Feb 28, 2005 10:57 pm    Post subject: Re: Unsprung Weight Reply with quote

swaybar2002 wrote:
zentime wrote:
legalr wrote:
What effect does unsprung weight of a sidecar have on handling? Are there limits of acceptable unsprung weight?


same as what Claude said.....

I've always thought of anything attatched to the bottom side of the shock as unsprung. The wheels hubs shocks etc.


Right Bill..the 'discussion' comes in whether half the shock, half the swingarm etc is unsprung or not. To me it isn't worth a big discussion as what we would build would be more focused on proper strength over and above minute (mineut?) weight savings. In racing it is all about weight savings above anything else.
What may be seen as compromises in this area for the street are a necessity IMHO. It has been mentioned that designing a fast rig for the street is more diffcult than for the track and I beleive that has a lot of truth in it.
Good topic Larry Smile
Claude


on the street, I think safety is a priorty over saving a pound or two here or there.

not to hijack this topic but Claude when are we going to see prelim pictures of your project Impatient
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will August ever come............
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Mon Feb 28, 2005 11:18 pm    Post subject: Re: Unsprung Weight Reply with quote

Bill wrote:
on the street, I think safety is a priorty over saving a pound or two here or there.

not to hijack this topic but Claude when are we going to see prelim pictures of your project Impatient
............. ...................... ........................

Agree that saftey is the priority..no doubt. Maybe followed by durabilty if they are not one and the same. Some racers may feel okay replacing heim end every few races but on the street I'd rather be riding than messing with stuf like that.
Pictures of the project? I tried to send you some yesterday but the disc in my camera was not formatted it said. Embarassed I 'll see about getting some soon.
Claude
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Paul



Joined: 27 Jan 2005
Posts: 182
Location: Utah

PostPosted: Tue Mar 01, 2005 3:50 am    Post subject: Safety not the same as reliability Reply with quote

Safety can be quite different from reliability. For instance, take some stock BMW wheels (either bike or car). They're made of a very soft aluminum alloy - so that if you hit something major (like a 6 inch deep sharp edged pothole in the middle of an on-ramp at night) the wheel will bend - but it won't break, and usually won't lose air. Sure, the wheel is now damaged - but the rider and the rest of the bike is okay.

Admittedly this works great in Germany, and California, or anywhere they pave their roads more than once a century - but in new england it can get expensive (ask any M3 owner).

As far as unsprung weight goes - it is evil. Reducing it improves handling (assuming that you change suspension settings to match). A light wheel can follow the road better, and get much better traction, than a heavy wheel.

Nice super lightweight automotive wheels are available, but they're expensive ($400 each for a 15 pound wheel) and wouldn't show much difference unless the rest of the suspension (adapter, axle, swingarm, shock, brake disk, brake calipers, tire) was also light weight.
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bmcsheehy



Joined: 22 Jan 2005
Posts: 981
Location: Massachusetts USA

PostPosted: Tue Mar 01, 2005 11:55 am    Post subject: Re: Safety not the same as reliability Reply with quote

Paul wrote:
... so that if you hit something major (like a 6 inch deep sharp edged pothole in the middle of an on-ramp at night) the wheel will bend - but it won't break, and usually won't lose air. Sure, the wheel is now damaged - but the rider and the rest of the bike is okay.


Hey Paul, is there a story behind this? Smile
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High Performance Sidecaring... ...There is nothing "HACKED" about it.
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bmcsheehy



Joined: 22 Jan 2005
Posts: 981
Location: Massachusetts USA

PostPosted: Tue Mar 01, 2005 12:01 pm    Post subject: Reply with quote

Sprung or un-sprung weight? I add weight to the sidecar to help keep it down. Maybe un-sprung or sprung weight in the right place, to the right or to the right and back would help keep the sidecar tire on the ground?
Motorcycle Happy
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Bill
High Performance Sidecaring... ...There is nothing "HACKED" about it.
2006 ZX-14 / HANNIGAN HP.
2011 Concourse / California Friendship III.
1936 Ford Fordoor Humpback
www.Yankee-Engineering.com
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Tue Mar 01, 2005 12:06 pm    Post subject: Reply with quote

Paul nailed it when he wrote:
>>As far as unsprung weight goes - it is evil. Reducing it improves handling (assuming that you change suspension settings to match). A light wheel can follow the road better, and get much better traction, than a heavy wheel. <<
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Tue Mar 01, 2005 12:10 pm    Post subject: Reply with quote

swaybar2002 wrote:
Paul nailed it when he wrote:
>>As far as unsprung weight goes - it is evil. Reducing it improves handling (assuming that you change suspension settings to match). A light wheel can follow the road better, and get much better traction, than a heavy wheel. <<


Witht that being said ...too light a wheel , or any suspension part, that is not up to the task at hand will embarrass you, create a lot of hassle at the side of the road, put you in the weeds, put you in the crash house staring at the ceiling or kill you.
A little overkill, especially on a street machine with all the variations in the road conditions is not a bad way to go.
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Tue Mar 01, 2005 12:24 pm    Post subject: Reply with quote

While on this topic of weight has anyone here ever weighed their rig? How heavy was it?
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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docmike



Joined: 27 Jan 2005
Posts: 630
Location: Eastern NC

PostPosted: Tue Mar 01, 2005 3:57 pm    Post subject: Reply with quote

I tried cut and paste from Excel spread sheet, but the columns didn't line up to well. I'll put * to separate the numbers

Weighed the rig a few weeks ago, used the scales we use at work to weigh instrumentation. Got some help to set the scales under the wheels.

Everything was weighed empty, with just a rider, with 100 pounds of lead shot in the sidecar, and again with both.

Weights are given for front wheel, rear wheel, sidecar wheel, then total. As a check the rider weight and weight of the lead shot were calculated. ( I had my heavy boots on.)

Also measured sag, some of the sag numbers seem a little strange to me, I plan to check them again a little more carefully.




K11RS / EML Speed 2000

Weight on wheels
*Front *Rear *Sidecar *Total *Calculate weights

Unloaded *361 *396 *192 *949 Rider 218
Rider *423 *554 *190 *1167 Weight 103
Weight *380 *402 *270 *1052 Both 318
Both *440 *559 *268 *1267

Height Measurements
*Front *Rear *Sidecar
Unloaded *31.5 *31.2 *24.8
Rider *31.1 *30.2 *24.5
Weight *31.5 *31.1 *24.3
Both *30.1 *31.1 *24.3

Sag
*Front *Rear *Sidecar
Rider *0.4 *1 *0.3
Weight *0 *0.1 *0.5
Both *1.4 *0.1 *0.5



Rider was seated upright on drivers seat. Bike had about 1/2 tank of gas, all other fluids full
Wet weight in period road tests 635 (w bags?)
592 tank empty
623 tank full
564 claimed dry
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93 BMW K1100RS / EML Speed 2000
89 Honda GB 500 (6,700 miles, all original except tires)
67 Triumph 650 chopper
92 Suzuki GS500 (eldest son)
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Paul



Joined: 27 Jan 2005
Posts: 182
Location: Utah

PostPosted: Wed Mar 02, 2005 2:41 pm    Post subject: Re: Safety not the same as reliability Reply with quote

bmcsheehy wrote:
Hey Paul, is there a story behind this? :)


Yeah... picked up the bike from having a wiring fault found and fixed (heated handlebar grips wire had worn through it's insulation, was grounding on the fuel tank, and blowing fuses once in a while - couldn't find it myself so there goes 3 hours labor at shop rate). Finally everything is working - driving home, nice evening, hit the cloverleaf at the 237/680 junction at a good rate of speed, footpeg just skimming the pavement... and WHAM WHAM there go two perfectly good rims. I rode home without stopping - didn't even know the rims were dented. So the bike was in perfect running order for about 15 minutes total.

They're still on the bike, but on the other hand I haven't ridden that one for several years now. I'm sure they could be straightened, but I'm also sure they wouldn't pass a safety inspection.

On the bright side, my car rims are still round, despite driving in New England...
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