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Old 04-09-2013, 10:23 AM   #1
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Default normal front tire bounce ?

One question from a novice in crawling : i have a Losi Comp crawler with 21.5 brushless, 3s lipo , dig ,... HB rover tire with stock foam , added weight 8oz front, 2oz rear. pink springs, 40wt oil in shocks.
Now I'm working on tire and foam setup and noticed that if i drop the car on the floor i have some bounce , most on front wheels. I changed foam, when using proline memory foam the bouncing is reduced but still present. Shock oil and spring don't have aby effect on it. I noticed that such bounce was absent when the car was stock, stock wheels (not soft) , no weights. I guess that this is normal and it's not a problem for crawling. Somehow the shocks can't work as on a buggy since all tha weight is on the axle instead of the car body ... please let me know what you think and if your crawler have some bounce when dropped too , so that i can stop trying to remove it buying different foams. (By the way , i like rovers with stock memory foam ... lot of traction...)
thanks !
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Old 04-09-2013, 08:16 PM   #2
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Default Re: normal front tire bounce ?

Im assuming you didnt vent the tires or wheels? The rovers should not have come with memory foam stock. Try venting the wheels or tires and it should take alot of bounce outta it. I like several vent holes in the sidewall of my tires
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Old 04-09-2013, 11:48 PM   #3
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Default Re: normal front tire bounce ?

Thanks.
well, The wheels are vented while the rover tires are not .
And you're right, they don't have memory stock .
But i have the same bounce effect with vented Chisel tire too (again, without memory foam yet, i'm waiting for it to arrive).
Anyway i'll try to vent them as you suggest.

But again , i'd really like to know ... is it normal ? does a 6lb. rock crawler with minimum unsprung weight (that is ... most in the wheels) bounce or not ? By the way ... I'm talking about a couple of inches rebound falling from almost one foot ...
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Old 04-09-2013, 11:52 PM   #4
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Default Re: normal front tire bounce ?

correction for my previous post ... i wanted to say ... minimum 'sprung' weight ... again ... most of the weight in the wheels , so not easy for the shock to work when falling ...
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Old 04-10-2013, 02:59 PM   #5
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Default Re: normal front tire bounce ?

NO, bounce is NOT normal and you do not want it. If you set the rig down gently, what kind of pre-load sag do you have up front?
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Old 04-10-2013, 03:09 PM   #6
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Default Re: normal front tire bounce ?

the front sag is about a third of the entire range for the shock , rear is less . If i change it by adjusting the preload front bounce for the 'fall test' doesn't change ...
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Old 04-10-2013, 03:11 PM   #7
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Default Re: normal front tire bounce ?

will soft memory foam solve everything ? why ? ... please help ...
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Old 04-10-2013, 03:32 PM   #8
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Default Re: normal front tire bounce ?

When you say "Shock oil and spring don't have any effect on it" please tell us why you feel this is the case.
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Old 04-10-2013, 03:34 PM   #9
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Default Re: normal front tire bounce ?

Quote:
Originally Posted by lorespix View Post
will soft memory foam solve everything ? why ? ... please help ...
I doubt it...
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Old 04-10-2013, 07:43 PM   #10
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My guess is you set your crawler shocks up with rebound like you would on an offroad truck. Most don't run any rebound in the shock.
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Old 04-10-2013, 11:32 PM   #11
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Default Re: normal front tire bounce ?

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Originally Posted by RcBro View Post
My guess is you set your crawler shocks up with rebound like you would on an offroad truck. Most don't run any rebound in the shock.
Can you explain this a bit more?
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Old 04-11-2013, 12:02 AM   #12
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Default Re: normal front tire bounce ?

Guys thanks a lot for your suggestions , they're really important.
Now i'll tell you what i did :
i take my Losi Comp Crawler and 'copy' Jake Wright setup ... so : a lot of weight in front wheels (8-9oz. each) , very hard oil in springs (50wt front , 40wt rear) and minimum unsprung weight (move battery on front top arms). So i guess that what's happening is that shocks don't work much since most of the weight is below them ... so if damping is most in the wheels they can't eliminate bounce completely . If i put a couple of battery on top of the car , the bounce is completely eliminated 'cos the shocks are working , but that more weight on top is bad for crawling ...
But maybe RcBro is right ... i didn't know that most crawlers don't put oil in shocks ... maybe if i do that the shocks come back to work and crawling is still good ...
let me know more what you think ...
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Old 04-11-2013, 01:59 PM   #13
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Default Re: normal front tire bounce ?

OK , problem solved , with the following steps :

1) vent tires (even if wheels were already vented) : bounce only slightly reduced
2) change shock oil and springs : remove 50wt and put 25wt , remove losi pink and put back stock losi white springs (softer) : bounce much reduced
3) finally i have the proline dual stage oversized memory foam : put them in the rovers : bounce completely removed

and crawling is even better ...
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Old 04-11-2013, 07:19 PM   #14
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I wasn't saying not to run oil, oil is a could thing, im sorry if i was misunderstood. rebound is when after the shock is built with no spring, if you push the shock shaft into the shock body the amount the shock shaft comes back out is Your rebound. Ideally, if you push the shaft in, you want to stay in. Your springs will do the work to push it back out. An improperly built shock will cause all the issues you are describing, but of course, sometimes the keyboard gets in the way of truly understanding the issue.

If all else fails, I'd suggest looking for a club in your area and learning from those who are in it. Getting face to face help always helps. Sounds like you are making progress
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Old 04-11-2013, 11:43 PM   #15
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Default Re: normal front tire bounce ?

Quote:
Originally Posted by lorespix View Post
OK , problem solved , with the following steps :

1) vent tires (even if wheels were already vented) : bounce only slightly reduced
2) change shock oil and springs : remove 50wt and put 25wt , remove losi pink and put back stock losi white springs (softer) : bounce much reduced
3) finally i have the proline dual stage oversized memory foam : put them in the rovers : bounce completely removed

and crawling is even better ...

That's great! I'm a fan of Crawler Innovations Double Deuce Foams, you should give them a try next time around
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Old 04-12-2013, 12:30 AM   #16
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Default Re: normal front tire bounce ?

Thanks a lot for the explanation RcBro : now it's clear . That's an important info and i didn't know that , in fact i thought rebound was a 'good' thing and built the shocks with as much as possible when i put heavy oil in them. Luckily , even if i didn't read your post yet, when yesterday i built the shocks with lighter oil, there was no rebound , so maybe that was really the cure . But also Memory foam plays an important role . Now the car is fine , there's no more bounce . I'll may try a bit heavier oil (but in small step this time) , but even with 25wt it's crawling well on the rocks . As for crawling club and races ... in Italy it's not that easy ... i was not able to find anything yet ... i'm always crawling alone ... but i'll ask again at the shop where i bought the car even if i think that they meet to run monster truck or buggies (maybe some scaler) .
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Old 04-12-2013, 12:34 AM   #17
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Default Re: normal front tire bounce ?

Yes Crawl-o-matic : i'll try the CI foams too ... Thanks .
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Old 04-16-2013, 11:48 PM   #18
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Default Re: normal front tire bounce ?

you sorta answered your own question up above; "very little sprung weight"

Since all your weight is in the tires and axles, the shock have nothing to do to "dampen" the bounce. Only thing to absorb it are the tires so tuning the foams are your only option. It would be opposite if you had more sprung weight; shock will help absorb the bounce and keep the rig from bouncing. it helps absorbs forces from both direction; sprung weight coming down, unsprung going up. thus creating an effect where the rig "sticks" to the ground.

IMO, I would tune the tires for traction as you'll most likely be going so slow, bouncing should not be a factor. assuming this is what you are trying to achieve. different story if you are building rock racer.
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