Why are rear shocks longer than front shocks?

[Plaidfish]

but isn't the travel the same in front and rear shocks???therefore making the droop te same?

 

[olds97_lss]

What the hell is droop? Would a basher like me give a crap?

BTW, UE shocks are in between the length of OFNA 9.5 front and rear shocks. They are really neither. But, I'm using front shock shafts in the shocks as true rear 9.5 shock shafts were to long as I thought the same thing.

I'm using OFNA 9.5 fronts shafts because UE's site wasn't operating correctly at the time I needed a couple new shafts. I lost about 2mm of travel, but since I can buy them from tower whenever I feel like it, I don't really care.

Sorry guys for the long and drawn out thread. I just thought there was a simple answer. With me being new to 1/8 buggies, I just figured buggy guys knew it as common knowledge... apparently I was wrong.

Right now, I have the front shocks in almost the lowest position and the rear shocks in the highest position. The buggy sits level... just like it did with the stock shocks. The bottom of the arms almost touch the little droop (I think that's what it's called) part of the chassis that sticks out on both the front and rear. I don't have any droop set screws in it anywhere. I wasn't sure what the point was. To me, it just looked like a bad leverage point and might either cause my arms to break or the hinge pins to bend, so I left it without any screws.

 

[Plaidfish]

lift your buggy
the amount the wheels fall below ride height is droop

 

[CorradoPsi]

i dunno about you guys but i have about a half inch more total rear travel than front. the amount of droop you run controls how the buggy handles through weight distribution changes, and ruts in the track. droop does matter for a racer, and thats the reason for longer rear shocks. whether you use them or not is up to you.

 

[Diver6127]

I knew that. It's pretty critical on onroads but couldn't for the life of me, figure out why on buggies they're different lengths because on-roads are equal. 1:1's are different lengths as well and that's for weight transfer when loaded (along with spring rates). Oh well, as long as it works, it's good for me.

I still fiddle with the shocks more than I should

 

[Lessen]

converting off-road truck to off-road car

I got to thinking about this thread today.

Since I'm planning to convert my RC18T to a dirt oval car it got me thinking about the differences between on-road and off-road shocks. I think it has to do with jumping. With the exception of MT's we see this type of "shock stagger" in most off-road vehicles that are designed to jump... buggies, stadium trucks, now truggies.

My hypothesis is that rear shocks are longer to help vehicles stay level in flight without disrupting it's level ride height while on the ground.

Buggies (and other types) need a longer rear shock [more rear suspension travel] to kind of "kick up" the rear end when it takes to flight when coming off the top of a jump, otherwise they would always fly nose up untill you made some other input. People always talk about how well a buggy jumps or flies. Anyways, if the rear shocks were the same length as the fronts the only way to get this effect would be to run higher ride height in the back. That would allow more compression of the rear spring translating into more suspension travel for "kick up". Running a more firm spring in the rear doesn't help because it simply won't compress as much therefore won't rebound as much. I think travel is key here. But using this theory your normal ride height on the ground would be jacked up in the back... and that's certainly NOT desirable, especially for off power turning. This is where more rear droop comes in. This is only my hypothesis so if anybody would like to make an argument please do so.. this topic still interests me.

IMO, utilizing a longer shock in the back gets us the best of both worlds. Level flight and level height.

 

[Toolman]

There is a simple reason and I don’t know where I got this from but its to do with the universal joints. The front wheels have both up & down movement as well as left & right movement which limits the maximum angle on the universal before it can bind. On the rear you only have movement in one axis so you can move through a greater angle with no binding. You can see this if you try turning a spare drive shaft in your hand. The greater movement in the rear requires a longer stroke shock.

Now you may ask why give the rear more suspension movement, well its to do with handling landing from jumps. Generally there is a about 40:60 weight split front to rear and you land rear wheels first, so on a small/medium jump or jump with landing ramp you can actually land without bottoming out & it all evens out. If you look at Inferno series for example the latest 777 have a lot more shock travel than my original MP7.5, particularly in the rear. The explanations being that they found it improves the handling on jumps. I don’t think that oil volumes have any effect as such because for a given amount of shock movement the piston is moving through the same amount of oil irrespective of the length of the shock.

Tim.

 

[Lessen]

The front wheels have both up & down movement as well as left & right movement which limits the maximum angle on the universal before it can bind. On the rear you only have movement in one axis so you can move through a greater angle with no binding.

Hmmm.. I don't think that's right.

If you have a joint and bend it at a given point along axis X by a measure of 30 degress you will have an angle of 30 deg along plane A. If you then turn one segment of that joint along another Axis (Y) by 30deg along plane B you still have an overall angle of 30 degrees on plane C. The angle does not compound. I don't think the angle of the universal when turning would limit the maximum angle creating with suspension movement. I think the limits are equal

 

[olds97_lss]

Both the front and rear of the chassis typically are set to be the same height off the ground. So, they can both only travel so far before the chassis hits.

I guess I'd understand it a bit more if you set the suspension up so the rear of the chassis was 1/4 inch higher from the ground than the front. Then that's where the extra length would be required.

Regardless, I no longer have a buggy so it's mute for me.

 

[Toolman]

Hmmm.. I don't think that's right.

If you have a joint and bend it at a given point along axis X by a measure of 30 degress you will have an angle of 30 deg along plane A. If you then turn one segment of that joint along another Axis (Y) by 30deg along plane B you still have an overall angle of 30 degrees on plane C. The angle does not compound. I don't think the angle of the universal when turning would limit the maximum angle creating with suspension movement. I think the limits are equal

I do understand the point you are making and in theory this is true however,
the geometry is a little more complicated in that you have caster angles and steering akerman which steers one side more than the other. If you play with a front end with no droop/upstop limits (ie off the car) you will see that you can't get anything like as much travel as the rear without binding the driveshafts when steering lock is on.

On some universals you actually get extra rebates to allow a greater angle before binding just on the front end.

Tim.

 

[Lessen]

the geometry is a little more complicated in that you have caster angles and steering akerman which steers one side more than the other.

ok, I can see how caster can change the angle of the joint. However, these changes seem very miniscule to me. I just can't see how drivetrain binding is the reason for the shorter front suspension...

allow me to throw another scenario into the equation..

what about 2WD stadium trucks and buggies? They also have stagger style shocks, but they don't have front drivetrain to contend with.

 

[Toolman]

what about 2WD stadium trucks and buggies? They also have stagger style shocks, but they don't have front drivetrain to contend with.

I am sure I have seen this question asked before (a long time ago in a Galaxy far far away) and thought the driveshaft reason was the answer, and I do think it is a factor. However it can’t be the reason why 2WD buggies have smaller shocks!

I am wondering if it’s the weight distribution that’s the key. Looking at a picture of a Losi 2WD buggy as an example.

The battery is quite far back & the motor behind the wheels, let’s guess it has a 30:70 weight split front to back. Now if you put the same shocks front & back (ignoring the suspension travel movement for the moment) the springs on the rear would need to be different (stiffer) and the piston holes different to give the same damping as the front.
When you buy spring sets, the wire used is usually the same thickness front to rear, & piston holes are usually the same (I know these can & people do change these for tuning). However assuming you are trying keep to one piston design & spring coil rate ( I’ll come back to reasons why this is desirable in a minute) the only way to get the same damping performance under the different weight load is to have quite different geometry. By that I mean the angle of the shock & the moment arm distance from the wheel.

Looking at the picture of the 2WD car We can see that the rear shocks are attached closer to the wheel giving the shock more mechanical advantage & making it in effect stiffer that the front shock. This allows it to perform the same while still having the same spring rate & damping rate. The result of having an attachment point closer to the wheel is that it has a longer motion arc & has to be longer. See I was coming to a point!
The reason why it would be desirable to have the same piston & spring rate is that for you basic starting point setup you would expect to have the same shock oil & springs front to back & its cheaper to make. You can then tune from there depending on what feel you are after. I think the issues are the same for a 1/8 buggy though the weight difference isn't as much as for a 2WD.

As to the question of why the rear has more travel I do think this helps on landing or take of from jumps.

What we need is a car designer or Pro driver to answer this question eh!

Tim.

 

[phx123]

And here I thought it just looked cool.. Oh well

 

[Lessen]

It may be that simple.. What I find is that every answer seems to pose another question.

 

[Plaidfish]

It may be that simple.. What I find is that every answer seems to pose another question.

it's an enigma wrapped in a conundrum (sp?)....

 

[Toolman]

Has anyone looked in the Tamiya RC guide book!?

Tim.

 

[Lessen]

I don't have one of those... did a google... wouldn't mind having one though

 

[Toolman]

I asked this question to Jamie Booth who is the distributor for Hong Nor (Jammin) in the UK and is a really really good driver!
His reply was as follows:-


Hi Tim,

I think you are on the trail, but I think the reason is much, much simpler.
Because the front wheels turn left and right it's often not possible to have the shocks mounted so far out on the wishbone as on the rear. If the shocks are moved in on the wishbone they need less movement for the same amount of travel, therefore having the same length of shocks on the front would A) make the car ugly and vulnerable to damage and B) it would be totally unnecessary.

Maybe I am wrong but I think it's as simple as that.

JB


So I think I pronounce that Myth Busted! – Tim.

 

[Robinator]

why not send an e-mail to ofna asking this question?

 

[olds97_lss]

I asked this question to Jamie Booth who is the distributor for Hong Nor (Jammin) in the UK and is a really really good driver!
His reply was as follows:-


Hi Tim,

I think you are on the trail, but I think the reason is much, much simpler.
Because the front wheels turn left and right it's often not possible to have the shocks mounted so far out on the wishbone as on the rear. If the shocks are moved in on the wishbone they need less movement for the same amount of travel, therefore having the same length of shocks on the front would A) make the car ugly and vulnerable to damage and B) it would be totally unnecessary.

Then I wonder why they wouldn't just shorten the rear tower and move the connection point of the shock on the rear arm further in...