Rear Bumper Tight vs Loose

W5R

New member
A tight rear bumper will tighten up the chassis and slow down the way weight transfers, and can help fix a kart that is way too loose or drifting up the track. A looser rear bumper lets the chassis flex more and lets the kart be freer, lets weight transfer quicker. You can adjust the way the chassis flexes by loosening or tightening both bumpers, nerf bars, and the body. What most do is make everything as loose as possible to make the kart as free as possible to get the most speed out of the kart. A free kart is a fast kart
 

Charliemac115

New member
Weddle racing said it best..... I prefer loose personally. Let the frame do what it is designed to do and let the nerf bars and bumpers just be along for the ride
 

paulkish

old fart
What does having a loose rear bumper vs a tight one?

IMHO, a tight bumper will help transfer weight to the RR and right side front or back. Having it loose will mean more will be done mechanically transferring weight to the RR and right side front or back. Depending on where you have things to start with, weight outs, stagger etc., it can either tighten up or free things up. It can also either move you towards or away from either push or loose.

In general, what ever weight you have on the left is going to be easier to get to the right and return with the bumper tight. What you might do in making the bumper either tighter or looser, all depends on if an on track problem can be solved making it easier or harder to move weight. If you need to get weight off and on the LR easier then tighten it and if you want to make it harder to get weight on and off the LR loosen it.

And don't for get your also moving along the track when things happen. How fast your moving along the track is what determines if making it harder or easier to get weight off the LR, will relate to the over all process happening quicker or slower. If it makes weight leave and return too fast, then you might say it made it happen to quick. And the opposite it true. Some times making it a little harder mechanically for weight to leave, fixes a problem because it puts you at a point on the track when the mechanical action is completed or can be completed, that it's no longer an issue. And then you may need some mechanical action to take place quicker so it can change things at a specific place on the track. It relates to you can't start your turn in where you want your turn in to occur, because it takes time to make the turn in happen.

or not... ?

edit: In general anything you do to stiffen things up across the back will cause you to use the RR tire more and have access to it's use sooner or quicker. It will also put you closer to over using the RR and that may cause it to either slip or to eat more hp having to make the RR turn. It all just depends on everything else. And the other side of the coin is you will be able to get off the RR in general easier and quicker.


ps... What Wendle said explains it better then I could ever hope to be able to do.
 
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Just a touch looser than snug. The way I see it is, the rear of the kart will grip harder with the bumper tight because the rear end will be trying to bind up instead of flexing. The rear will not want to lift as much with a stiff bumper as the rear of kart will be trying to stay flat.
 

paulkish

old fart
When we started sprint racing Id adjust the rear bumper with an inch pound torque wrench, between 20 and 80 inch pounds. Id watch the inside rear to see how it unloaded and tighten or loosen accordingly.
 

Ltg

Member
If the bumper is tight it'll stiffen the back of the chassis and increase weight transfer at the back. Loose will do the opposite. I like my bumper snug (not flopping, not dogged down). I also don't like to adjust the chassis with the bumper - I set it and leave it alone.

Todd
www.dynamicsofspeed.com
 

paulkish

old fart
Sorry I should have been more clear. It was Sprint racing and for turning both left and right. And I said the amount was 20 to 80 inch pounds which may not be accurate because I do not correctly remember the exact amount. The adjustment was made in inch pounds and I did use an inch pound torque wrench. It was NOT a LTO chassis and I learned to adjust with the rear bumper because it was a factory adjustment. I remember not keeping the adjustment within what the factory recommended. The info was given in light of and thinking about the question posed of, "what does it do". Again sorry for referencing a Sprint chassis, to what I did understand to be a LTO question.
 

paulkish

old fart
wow, learn something every day. I DID use the rear bumper to control the use of the inside rear. BUTT, looks like I didn't understand it back then as well as I don't understand stuff now.

Here's what I found on the web just now:

7) Be sure to torque the rear bumper bolts at all times to 150-200 inch lbs.
You need to re-check the bumper bolts continuously as the rubber in the frame will
squish down a little every race (very important).

well, it worked for me as an adjustment. ... :)
 

Ltg

Member
In using torque take note of what type of bumper you have. For instance, the old Phantom style, the tighter the nuts the tighter the bumper. With the new wedge style it depends on where you start. If you start one way you can tighten it until the wedges break and never lock down the bumper.

Todd
www.dynamicsofspeed.com
 

paulkish

old fart
wow, learn something every day. I DID use the rear bumper to control the use of the inside rear. BUTT, looks like I didn't understand it back then as well as I don't understand stuff now.

Here's what I found on the web just now:

7) Be sure to torque the rear bumper bolts at all times to 150-200 inch lbs.
You need to re-check the bumper bolts continuously as the rubber in the frame will
squish down a little every race (very important).

well, it worked for me as an adjustment. ... :)


I have to repeat. I wrote about a Sprint Kart (Coyote) and it DID NOT apply to LTO, only to general thoughts about bumper tightness. Read what I wrote as you would anything else just to get ideas.

But if you want to learn something, pay attention to TODD... not me.
 
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