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Discussion Starter · #1 ·
Ok. so here goes. I was just brain storming and wanted other minds to help.
1) Say 2 cars are sitting at 23 flat. one is on 17's with 215/40 and one is on 18's on 205/35.(or any ride heigh, or tire size, just throwing an example out there) would their axles be at different angles? i was just going over axle binding in my head in reference to tire size and wondered if running a smaller tire. like some people on here do. 16's or 17's would put the car's axles at less of an angle than 18's or 19's. or would it not matter enough to matter to anything since the over diameter of the tire will damn near be the same.
2) and question number two. Talking clearance on speed bumps. would oil pan and control arm clearance play a huge role? seeing as how both are in parallel with the tires and the car would raise as the oil pan and control arm was going across the speed bump. the roads around here are fairly good. But i have 2, 2 inch high, speed bumps to go across to get to my work.
figured i'd cram 2 questions in 1 post. thanks in advance..




Modified by korre07 at 3:58 PM 2-3-2010
 

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Discussion Starter · #3 ·
Re: theory that's probably wrong (Mk42003)

Quote, originally posted by Mk42003 »
I SAY GO LOWER and dont worry about it http://****************.com/smile/emthup.gif

http://****************.com/smile/emthup.gif anyone else?
 

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Re: theory that's probably wrong (korre07)

to aid in answering your first question, a 215/40R17 to a 205/35R18 would be close to rolling diameter height but... it would increase camber and change the geometry of the suspension w/ a smaller wheel. 16's to 19's would have a drastic rolling diameter difference in regards to each other. there are many factors to consider with this, wheel size, backspacing, type of suspension, motor size/weight, suspension load (cargo in vehicle or curb weight) also the alignment of the suspension. get's crazy technical man, trust me i have setup race suspensions on Porsches. but most in this forum could care less as long as it's low.
 

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Discussion Starter · #6 ·
Re: theory that's probably wrong (onelowdub82)

onelowdub82 http://****************.com/smile/emthup.gif

I just got to thinking about it b/c There was a silver gti on green sportmax's , and i know there's a red mk4 rolling around on gold Porsche phone dials(or bottlecaps, can't remember which they are). and they were both 16's and I thought there's no way their axle angles are the same as someone running 18's. B/c the general consensus is that around 23 axle binding occurs. give or take a bit. and that can't be for all tire sizes... thanks again man
 

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Re: theory that's probably wrong (korre07)

no prob, also have to account for the type of tire (brand really) not all 205/35r18's have the same tread depth and design. that will also effect rolling diameter, as well as alignment as they wear down (this has more to do with tire compound). as for your second question, for the oilpan height. 23in from fender to ground would be a constant regardless of wheel size. the chasis is mounted as is, unless the subframe is raised or lowered via spacers the oil pan height for a 1.8T on 16's or 19's w/ the fender at 23" will be the same due to chasis clearance.
 

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1) No, if you are keeping outside diameter of the tire the same (which most would do) it shouldn't change much (except for tread depth like stated above). For example, my 17" LB and 15" Beetle wheel I have for a spare have an equal total diameter. But, on a smaller wheel, you could put a smaller tire if you wanted to have a smaller outside diameter.
Now, the speed bump question...
If you had a ridged suspension then you wouldn't have to worry about your oil pan, but as you hit that speed bump, your springs will compress, making your oil pan lower to the ground. The faster you go the more force pushing your springs up. That's why really low people go slowly over speed bumps, because going slowly means your suspension wont compress as much so the clearance between the oil pan and ground remains more constant.
 

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Discussion Starter · #9 ·
Re: theory that's probably wrong (onelowdub82)

I wasn't talking about fender to ground.. I hear people on here say they can't go a certain height b/c their oilpan will hit on speed bumps... this doesn't make any sense to me as when your car raises to go over the speed bump the oil pan and control arms also move up.
 

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Re: theory that's probably wrong (korre07)

Quote, originally posted by korre07 »
I wasn't talking about fender to ground.. I hear people on here say they can't go a certain height b/c their oilpan will hit on speed bumps... this doesn't make any sense to me as when your car raises to go over the speed bump the oil pan and control arms also move up.

That's exactly what I explained. If you go slow, then your suspension doesn't compress and you should be fine, if you go fast then the suspension will compress and you'll bottom out. Most people I hear talk about things like pulling into driveways, their front lower valance will scrape, and that's because the bumper stick out further than the wheels..... and so on. Did that help?
 

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pretty sure the oilpan sits a tad infront of the wheels, atleast my vr pan does....Im suprised the bumps i have made it over though, at most all i get is a dogbone tap.
 
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