Rear end bounce/hop

[Graham Odell]

Hi,
I have a 2006 Mx32 chassis.

I pretty much tried everything this weekend setup wise to stop it hopping but couldn't make it stop.
Was racing at a fast track with 3 very wide hairpins (track is very wide, more like 180deg turns than tight hairpins). On all 3 of these turns I had a very sever hop on the exit of the turn, I couldn't get back on the power without it geting very bouncy). Had the same problem all over the track, though.

The other few Mx32's at the circuit were running
3spacers on the front
1385mm~ rear width
front and side bar in
some had the rear bar in flat, others had it out.

These karts performed very weel over the weekend but I couldn't work out the bounce. it was very sever.. moving the track in or out a few spaces really wasn't enough of a change, seemed like an overall imbalance with the kart.

Not sure about seat position, I'm getting conflicting measurements. I have a Tillett T11 seat installed. Could my seat be in the wrong place? What would you recommend and more importantly when you measure, where are you measuring from/to as this seems to be a big factor in peoples measurements.

Not sure If I need to move it forward to take weight off the rear, or move it back to get weight over it and stop if binding up so much. I'm quite tall and fiarly heavy if that matters. Its difficult to get the seat much lower.

Any ideas? Cheers.

[Andy Seesemann]

Graham,

A couple of questions.

Where do you live, or better yet, which track are you racing at?

What tire are you using?

Where is your seat mounted?

In my experience there are a few types of rear end hop that are caused by different things. There is the rear end "chatter" that is caused by a setup that is too stiff in the rear. There is a rear end "roll hop" that is caused by a setup that is too soft in the rear. There is a rear "bounce hop" that is caused by input to the front end causing the wheel to lift and set back down.

Do any of these sound familiar?

Andy

P.S. Chris, you are welcome to jump in here any time you like. I won't be offended.

[Garry Lobaugh]

Chris is home today picking the sand and cactus particles out of his body and luggage. He will be in on Wednesday!

Good job to all of the MRP/Birel dealer network of drivers in Tuscon!

[Graham Odell]

Hmm.. sounds more like it was too soft.

However adding the rear bar often means having to use a LOT of steering input to get it turned in.

I'm not in the U.S. but I know a lot of you guys know your stuff so thought its worth asking here.
My seat is 58/59cm measured from the front bar as I was told. I was reccommended a T11 seat to aid me being a bigger driver.. it has a deeper flatter bottom to it, but the rear lip is quite low so its about 2-3cms lower than the measurements for the standard seat. Don't know if you guys are familiar with it.

For this problem though, could be Center of gravity be too high? I tried leaning forward coming off the turns and its felt like it helped (a little).

Cheers guys!

[Chris Lobaugh]

Andy pretty well nailed it there with the differences in hop. We struggled a bit with a soft hop in Tucson (mx32sc) while we were runing with the middle bearing loose and a short B . First we tightened the middle bearing and then went to a D and the problem was solved. The seat measurements sound close. Are you running one set of seat stays each side? Rear crash bar tight or loose? Side torsion bar in or out?