1 (edited by Huskar 2018-09-16 05:39 AM)

Topic: Get Low

Our mini truck has a larger than desired rake and we would like to lower the back.  Has anyone here used lowering blocks during a race?  Where there any undesired effects from using these?


EDIT.   My use of the term mini truck is misplaced.  I believe the official term is compact truck, ie s10, ranger, frontier.  If we have leaf springs, a panhard bar is not of concern.  leaf springs should have a roll center in plane with the axle connection points.  assuming the rear has a fairly high CG raising the axle should bring the roll center closer to to CG.  It sounds good, but not if it adds too much liability in the stability of the connection points.

1975 Chevy LUV.  1 Corinthians 13:7
1999 Chevy Blazer

2 (edited by cheseroo 2018-09-16 11:34 AM)

Re: Get Low

Been a while but i believe that raises the axle above the roll center.  Is that bad in a mini truck?  Hell if I know.  You are road racing a mini truck.  Run it.  I *think* if you wanted to do it "properly", you'd raise the front shackles.

1990 RX7 "Mazdarita"  1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)  1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)

Re: Get Low

You may just have to adjust the panhard bar mounting.  We have rear coils on a live axle and clamped them. 

As long as the Panhard bar's level with the truck at ride height you should be fine.

Tunachuckers: 15 Years of Effluency
'08 - '10: 1966 Volvo 122, "Charlie"
'10 - '18: 1975 Ford LTD Landau --> 2018 - current: Converted into 1950 "Plymford"
'22 - current: 1967 Volvo 122, "Charlie ]["

Re: Get Low

You could also get shorter shocks

Mistake By The Lake Racing (MBTL)
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Re: Get Low

mechimike wrote:


……..As long as the Panhard bar's level with the truck at ride height you should be fine.

Yes, it needs to be level. 

Please note that the panhard bar is your roll center.  If you have the panhard bar lower than the axle center line you will induce greater body roll.  Lowering blocks will induce roll steer, to what degree will be determined by your roll center, spring rate, and the size of the blocks.  You can also remove leafs to lower the truck (the shortest ones have the most effect on lowering), but that can also have a negative effect on your pinion angle and can increase understeer. 

Remember, lowering is not 'always' the path to better handling.



Bill

2020 I.O.E. CT #36 The Rootes Of All Evil,1958 Sunbeam Rapier Convertible (YES 1958!!) & 2019 Judges Choice NJMP
2016 Thompson Speedway #36 Sabrina Duncan's Revenge, IOE Trophy, 5th Place 'C' Class 1977 Ford Pinto
2009 Stafford Motor Speedway #16 Team Teflon, 11th Place (overall) 1997 Saturn SL2

Re: Get Low

Does it even have a panhard bar?

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Re: Get Low

No reason for a leaf spring car to have a panhard and OP edited post to say it doesnt have one.  IIRC, roll center on leaf spring axle is set by shackle bolt locations.  If I had to make an uneducated guess, I'd say rear CG in truck is lower than a car.

1990 RX7 "Mazdarita"  1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)  1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)

8 (edited by -SDR- 2018-09-16 09:20 PM)

Re: Get Low

cheseroo wrote:

No reason for a leaf spring car to have a panhard and OP edited post to say it doesnt have one.  IIRC, roll center on leaf spring axle is set by shackle bolt locations.  If I had to make an uneducated guess, I'd say rear CG in truck is lower than a car.


I have added panhard bars to all my leaf spring auto-x and race cars, they help immensely with keeping the rear of the car where you want it, and make it predictable.   Those that have driven my cars will tell you how well they handle, but please note that I do lots of other things too.

Even with a panhard bar, leaf springs WILL twist and flex, and that flex WILL change the geometry of the rear suspension of the vehicle (roll-over steer and roll-understeer), however it will be significantly reduced with a properly installed panhard bar.  Flex will be amplified with lowering blocks and/or longer shackles.

Question: Why do people swap to poly (bearings) in the front end?  Answer: To help keep the geometry correct.  Why should the rear of the vehicle any different??

If there is no panhard bar the centerline of the axle is the roll center, if you add a panhard bar, where the panhard bar IS becomes the roll center.  Ideally the panhard bar needs to be as long as you can make it, as level as you can make it, as centered as you can make it, and its distance above or below the centerline of the axle will effect the handling; you can use this to help tune the suspension.

Watts links are better...…..


Bill

2020 I.O.E. CT #36 The Rootes Of All Evil,1958 Sunbeam Rapier Convertible (YES 1958!!) & 2019 Judges Choice NJMP
2016 Thompson Speedway #36 Sabrina Duncan's Revenge, IOE Trophy, 5th Place 'C' Class 1977 Ford Pinto
2009 Stafford Motor Speedway #16 Team Teflon, 11th Place (overall) 1997 Saturn SL2

Re: Get Low

Do you guys have any recommended reading or references for suspension design?

1975 Chevy LUV.  1 Corinthians 13:7
1999 Chevy Blazer

Re: Get Low

I use 1" lowering blocks on our leaf-spring Imperial.

Did it improve handling?  Hell if I know, but it sure looks better! 

It does handle great it the wet/rain though, and we can pass many cars in the wet that we should have no business passing.

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Re: Get Low

Books:

"How to Make Your Car Handle" - Fred Puhn
"Chassis Engineering: Chassis Design, Building and Tuning for High Performance Handling" - Herb Adams
"Tune to Win" - Carroll Smith

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