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UTV's Off Road ( RZR, YXZ, Mini Buggy, Carts,etc.) => UTV Chassis and Suspension => Topic started by: nagel on July 04, 2011, 09:00:51 AM
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Ok,
Here's my question. I know tires get "heavier" in feel the larger you go. Having no power steering eans you take all the hits..
I like the look / capability of the 26" bighorn tires that I have, but they are HEAVY mofo's to steer.. to turn from full left to full right (or vice versa) you feel like it starts easy, then gets harder and then easier. (imagine a bell curve).
I got the wheel adapters from Livewire here, modified them for my hubs, mounted up a pair of 21" tires I had from the ATV's, and they look WAY WAY too small.. I mean, hillariously small, like putting a mid-size car tire on a lifted / jacked truck.
So.. What tips can you offer to help eliminate a little bump steer / make the front end feel not so heavy with the 26" tires. I have a "stick type" (gibson) stabilizer from the YFZ's that I may try to mount up to the steering column. But that doesn't make it easier to turn the wheel, it will only help with some bump steer..
Thoughts on tire size vs. how "heavy" the steering feels?
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If the 26" tires are wider than the 21" tires that will change your scrub radius and could make your steering feel heavy........
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I don't see pictures. Did the inside edge of the tire move in or out? Outside? as vidio 1 said, extra scrub radius will make it turn harder. If either the inside or outside edge of the tire moves out, that moves the center out and increases scrub. Do you have a rack or bell crank style steering? Adjusting the steering for proper Ackermann will reduce steering effort at low to mid speeds.
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Control scrub,control scrub,control scrub,control scrub,control scrub,control scrub,control scrub,...................................just cannot be stressed enough.
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So, rumor has it it may be a scrub issue? ;D
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At least that's the rumor.
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Hey I was reading on another forum (traitor 9:) and they were dead set on bad steering being caused by poor ackerman and scrub radius. rofl rofl
All I know, once I corrected mine it turned 3 times as sharp. Get it right or get a bigger place to turn around.
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Well, since the 26's were the first tires on the buggy, I don't have something to compare to.. I just think the steering feels heavy..
As for scrub.. Both sets of rims (for 21's or 26's) are 3:2 offsets (3" back, 2" front). On the race quad I take off the stockers with a 3:2 spacing and change my offset to a 4:1 rim (wider a-arms keep my width there).
Can't be buying ANOTHER set of rims. LOL not in the budget.. And I've used the 3:2 offsets on my 4x4's forever with no issue (only thought on that is its a 4x4, and the front wheels pull too).
The plans are Stock piranha front single a-arm. Do I just have to deal with this until I this winter when I can swap in a double a-arm front end?
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If the backspacing of both rims are the same but one set of tires are a different width than the other the scrub radius will be different. Does it feel "lighter" with the 21" tires? Since the 26" tires were the first tires used was the KPI and scrub built to that wheel/tire combo? Is it heavy at slow speed like 5 mph or heavy everywhere? Slow speed maneuvering may be an Ackerman issue especially on hard pack. Going to larger tires won't make a car feel harder to steer if set up correctly. You should be able to move the scrub around to the point it feels so light it will be twitchy at speed.......
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scrub radius is set for 21" as per plans. I run 23" with minimum noticable difference.
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The diameter will have little to no influence on scrub. Differing wheel offsets do.
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If the backspacing of both rims are the same but one set of tires are a different width than the other the scrub radius will be different. Does it feel "lighter" with the 21" tires? Since the 26" tires were the first tires used was the KPI and scrub built to that wheel/tire combo? Is it heavy at slow speed like 5 mph or heavy everywhere? Slow speed maneuvering may be an Ackerman issue especially on hard pack. Going to larger tires won't make a car feel harder to steer if set up correctly. You should be able to move the scrub around to the point it feels so light it will be twitchy at speed.......
This is not correct. Tire width has nothing to do with scrub radius as scrub is determined at tire centerline.
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If it was built right for 21" and you put 26" the tire/wheel will need to move out, wider. Wheel spacers or bigger forearms? Pics, pics. Or did I miss them
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If built for 21 and using 26, with the same offset wheels, scrub radius will be ever so slightly less due to KPI. A heavier tire is harder to turn though.
Can you weld aluminum? 12" wheels? I have a set of 12" aluminum beadlocks, $90 for a pair. If you weld them on the inside of the wheel, you will reduce scrub by about 1/2"
Is it front or rear steer? Rack or bell crank steering?
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Not sure what the "planned" tire sizes was, think 21" like Doug mentioned.. But when I put 21's on, it looks like a monster truck with compact car tires. I didn't even bother to drive it with the 21's because they were so small. (I also knew there would be ground clearance issues in a few areas with them). They just dont look right (and I'm not fond of the ground clearance, lots of rocks and roots/stumps around). I used to have a pair of 23" Maxxis Razr II's but stupidly sold them about 8 months ago not even thinking about the buggy.. (Bought them for a rocky race in RI, and HATED how much flex they had and how they pushed in turns on the ATV, but they might have been a better option for the buggy)
For offset, I know I have 3:2 offsets.. Edge plans doesn't specify an offset. I am familiar with how offset will affect bumpsteer (hence the 4:1 offsets that I change the fronts to on the race quads). the 3:2 is a very common 4x4 quad offset for the front, hence why I used that offset (also because, well, I had a spare set of rims)
The front is your basic Piranha single a-arm setup. I bought Doug's old XRV rack from him and am using that for the steering. Front steer on the rack (scary for me with the amount of trees that can jump out at ya around here!)
In terms of tire sizes, fronts are both 8" (21x8-10 or 26x8-12). I usually run 8's on the front and 10's or 12's on the rear of my atv's, figured it would transfer over to the buggy.
As for what do I have to compare to? well, other than quads, a lawn tractor and my non-power-steering '79 chevy monza I had in HS, not much.. For all I know, this may be what you guys are used to.. But it just seems like when turning from full lock (L or R, doesnt matter) that you are riding a bicycle up a hill. When you reach the center (aka straight forward), you hit the peak and its easier to continue down the other side. Hmm, am I explaining the feeling correctly? Basically, its way easier to go from straight forward to L or R full lock, and its way harder to turn from lock to center.
Alignment is done, have about 1/4" or so of toe-in.. Perhaps I should play with toe a little more? I know on the quads if the tie rods are twisted wrong, or too long, that I get binding at full lock. And what I'm getting now is resistance (if I added to the tie rod length now I think it would bind like the quads).
The tires I am sure DO play a BIG part, you can not discount the affect of my tread patterns:
http://www.rockymountainatvmc.com/productDetail.do?navType=type&webTypeId=138&navTitle=Tires+and+Wheels&webCatId=8&keyword=trilobite&prodFamilyId=29207 (http://www.rockymountainatvmc.com/productDetail.do?navType=type&webTypeId=138&navTitle=Tires+and+Wheels&webCatId=8&keyword=trilobite&prodFamilyId=29207)
These are primarily for 4x4 quads and utes / SxS's.. Do ya think they may be pulling a bit on the steering? The pics don't do the lugs depth justice, these tires can really hook up, the rears are just trench diggers if I dump the clutch hehehe.. And I DO have a set (same sizes, front and rear) on a 2000 Wolverine 350 4x4 w/ a Warn 424 to make it 2WD, and the steering on that doesnt seem heavy in 2WD.
I saw in another thread that ITP has released the "Holeshot" series in SxS sizes, aka 25x10-12 and 25x8-12. When the checkbook allows I want to pick up a pair of the fronts from that line and try them. If Maxxis made the Razr II's in that size, I would jump on them as well... I also have a pair of Carlisle 489's in 23x8-12 size that I may mount up to see if they make a difference..
In terms of when it feels heavy.. Well, its hardest when you get to full lock. Slower is worse. Its almost like it falls in a groove when at full lock and you need to pull out of the groove..
Livewire - I can weld, but not aluminum :( And getting the 1 friend around here who CAN weld aluminum, TO weld for ya is tough.. He'll always agree to, but then takes forever / is never available even though ya see him at the local bar all the time. LOL
Pics of the build are here:
https://www.facebook.com/media/set/?set=a.402506271838.180745.552481838&l=5c8f0818cb (https://www.facebook.com/media/set/?set=a.402506271838.180745.552481838&l=5c8f0818cb)
about 1/2 to 2/3 the way down the page you can see some pretty good front end shots..
Thanks guys!
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Offsets do not affect bumpsteer. Do you know how to check bumpsteer? IMO your issue is entirely due to the steering geometry of the Edge single arm setup.
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Its quite common for the ATV racers to change from 3:2 to 4:1 to minimize the effects of bumpsteer as well as make the machine easier to steer. Everybody from B class on up has usually made the change. And we don't necessarily want to add width as its typically 48" limit.
See this link for an explanation:
http://www.exriders.com/archive/topic/300433-1.html (http://www.exriders.com/archive/topic/300433-1.html)
As for how to check, remove shock, lift front end and move the arm through its travel with tie rods connected and watch from above for change in toe. Correct??
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Yep.(bumpsteer check)
KPI is off, inside by 1-1.5" guessing
Hard to tell ackerman from photos.
large wide heavy tread tires multiply effort
Rack could be locking up at ends of turning, but with above list.
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+1. Carl hit it on the head IMO.
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Its quite common for the ATV racers to change from 3:2 to 4:1 to minimize the effects of bumpsteer as well as make the machine easier to steer. Everybody from B class on up has usually made the change. And we don't necessarily want to add width as its typically 48" limit.
See this link for an explanation:
http://www.exriders.com/archive/topic/300433-1.html (http://www.exriders.com/archive/topic/300433-1.html)
As for how to check, remove shock, lift front end and move the arm through its travel with tie rods connected and watch from above for change in toe. Correct??
I don't disagree with that in the least. At least not the thought. I maintain that wheel offset has no effect on bumpsteer. Bumpsteer is bumpsteer . What is being changed with an offset change is SCRUB.
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Scrub then causes wheel whip where you hit a bump and it yanks the wheel to that side hence why some people think that is what bump steer is. So when everyone is saying you have too much scrub, that is the same thing the quad guys are fixing. They are just not using the correct terminology.
;D
...that will change your scrub radius and could make your steering feel heavy........
..extra scrub radius will make it turn harder...
Control scrub,control scrub,control scrub,control scrub,control scrub,control scrub,control scrub,...................................just cannot be stressed enough.
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Ways to reduce scrub:
More offset wheels: 4+1 instead of 3+2
Hubs with mounting flange closer to center of buggy
Increase KPI by moving lower ball joint mount out on knuckle or upper ball joint mount in. What is important is the pivot point, not the mounting point. Depending on your knuckles, if the lower ball joint is below the mount and you can move it above, that will increase the angle. It will also decrease camber gain. Crap, I just remembered you have single A-arm so don't have ball joints. If you can tilt the knuckle pivot more, it will increase camber as well making the tire ride more toward the inside. You could angle the spindles down the same amount of the knuckles to change the camber back and then have higher KPI.
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Scrub then causes wheel whip where you hit a bump and it yanks the wheel to that side hence why some people think that is what bump steer is. So when everyone is saying you have too much scrub, that is the same thing the quad guys are fixing. They are just not using the correct terminology.
;D
YUP,YESSIR,CORRECTOMUNDO!!!!
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This is not correct. Tire width has nothing to do with scrub radius as scrub is determined at tire centerline.
Yep your right I wasn't thinking.
As for tire diameter, wouldn't a larger tire change the scrub? The KPI angle would be the same, but the difference in length from the spindle to the ground would move the center line of the tire to KPI imaginary spot on the ground relation. I would be minimal, but a 21" to a 26" might be noticeable....
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correct. Even the taller tires, the KPI looks as if its still too far inside. More KPI or 32" tires?
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Yes tire diameter will change the scrub but only slightly. Very slightly unless the KPI is radical. It MAY help with steering effort also. Honestly, I feel you should just live with it ,change wheel offset to help out for now and in the end get a "real" front suspension design in place in the future.
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correct. Even the taller tires, the KPI looks as if its still too far inside. More KPI or 32" tires?
Bigger tires. I run 31" fronts on My glass car with manual steering. No issues......
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Honestly, I feel you should just live with it ,change wheel offset to help out for now and in the end get a "real" front suspension design in place in the future.
Thats what I was figuring.. Just wanted to see if there was something simple and easy and obvious that I was missing... The KPI on the single a-arm though is not a quick fix :( And did I understand it correctly, that the top of my spindle should be angled in about 1 - 1.5" more to get a more correct KPI?
Thanks for the education too between scrub and bump-steer... I started educating my friends on that one.. Its amazing how two niches of off-road riding call the same thing something different..
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Thats what I was figuring.. Just wanted to see if there was something simple and easy and obvious that I was missing... The KPI on the single a-arm though is not a quick fix :( And did I understand it correctly, that the top of my spindle should be angled in about 1 - 1.5" more to get a more correct KPI?
Thanks for the education too between scrub and bump-steer... I started educating my friends on that one.. Its amazing how two niches of off-road riding call the same thing something different..
I don't know. I don't guess at these things. You will need to scale that out if you really want to know how much.
We are certainly a niche BUT WE use the CORRECT terminology. ;D ;D ;D ;D ;D ;D