PDA

View Full Version : Purpose of smaller diamater front wheels?


BlackBerry
2012.02.02, 09:00 PM
Is the only purpose of smaller than stock diameter front wheels for a lower ride height? Is there something I'm missing?

Thanks,

BlackBerry

GIHOSU
2012.02.02, 09:37 PM
They also reduce the size of the contact patch of the tire on thethe track and will take away a small degree of grip. I use them mostly in low power situations and sometimes on Mod cars to tame front bite.

The smaller size also reduces rotational mass of the wheel by moving the weight of the tire closer to the axle. This can increase spool up speed when used as a rear wheel and help acceleration. This can be an advantage in 70 turn Spec classes.

arch2b
2012.02.02, 10:34 PM
more clearance... the main reason i use atomic s6 wheels. less shaving i have to do to bodies.

BlackBerry
2012.02.02, 10:53 PM
So to sum it all up:

-lower ride height
-more body clearance
-less tire contact patch
-less rotational mass when used on rear axle

I could have sat here all day scratching my head and never come up with the "less tire contact patch". I'm assuming the reasoning behind this is when tires are less stretched the "roundness" of the tire increases? Thanks for that one GIHOSO.

Thanks for all the input, am I still missing anything?

BlackBerry

color01
2012.02.02, 11:23 PM
I think the contact patch argument is debatable, it depends on the way the tire is made and what composition it is. Generally, Mini-Z tires stretch thinner and harder on larger wheels, so I found that 19mm wheels allow for a wider and softer contact patch than 20mm, with the same tire. The rest of his points, though, are valid. :)

BlackBerry
2012.02.02, 11:49 PM
I think the contact patch argument is debatable, it depends on the way the tire is made and what composition it is. Generally, Mini-Z tires stretch thinner and harder on larger wheels, so I found that 19mm wheels allow for a wider and softer contact patch than 20mm, with the same tire. The rest of his points, though, are valid. :)

Interesting point of view as well. So lets update the summation:

Fact
-lower ride height
-more body clearance
-less rotational mass when used on rear axle

Debatable/Dependent on Tire:
-less tire contact patch due to less stretching of tire resulting in more "roundness"
-wider and softer tire tire due to less stretch

BlackBerry

chad508
2012.02.03, 12:03 AM
The only way to get 19mm on the rear is to run narrow rims. No one makes 19mm wide rears. I only run the 19s as I find myself not having to true the tire as much to get the overall thickness I want. If I ran 20s I would true most of the tire away

BlackBerry
2012.02.03, 01:28 AM
I only run the 19s as I find myself not having to true the tire as much to get the overall thickness I want.

When you say "thickness" are you running the 19s to primarily lower the ride height or to thin the tire sidewall? Or both?

Do mini-z tire sidewalls have a role in the car's handling (other than its effect on ride height)?

BlackBerry

color01
2012.02.03, 02:36 AM
Tire sidewalls affect the handling immensely. :) 19mm stretch the tire less, as we agree on, so the sidewall actually becomes softer to an extent -- this provides more grip. To top this off, at the same total diameter, tires mounted on 19mm rims will have a taller sidewall than tires mounted on 20mm rims, so the extra flex will provide even more grip. At the same sidewall height, the softer 19mm-mounted tires will still be a tiny bit grippier due to less stretch.

For the same sidewall height, the smaller total diameter of 19mm wheels makes the front bearings spin faster for the same car speed, so there's going to be a tiny bit more drag brake -- it's debatable whether people can feel this difference or not, but it is physically existent.

BlackBerry
2012.02.03, 05:45 PM
Good point, so what I took away from that is there would be more tire flex/car slop, ie another variable to to tuning grip and suspension. To eliminate that I'm just going to run 20mm front wheels. I don't think I will need to go any lower with my current setup, I actually might have to add ride height (hsv, pn lowdown springs, pn lowdown knuckles, removed spring pre-load plate). Good to know if I need more front grip and I've exhausted other tuning options.

Regarding drag brake (didn't know that's what it's called), that's good to know as well. I'm a technical guy so thanks for pointing that out.

This has been a good thorough thread on front wheel diameters. I think we've covered everything?

Thanks,

BlackBerry.

imxlr8ed
2012.02.03, 06:46 PM
Been noticing lately that all of my most controllable cars have extremely worn, taped on front tires. I think the sidewall is the biggest factor because when it gets low like that the contact patch doesn't morph into an outer edge intermittently on the turns. There is no edge now on those tires... really, but they are very consistent from corner entry to exit.

Makes me think back to when my cars had less, and I was big on running my tires down to near nothing... my cars handled much better then. I guess I got away from it because new tires can make a car really consistent as well, but I think I end up tuning for what tires are on the car and the second the tires start to go, I'm stuck with a poor handling car.

Seems to me that running lower tires on the front just calms the car a bit. It's almost like running a bigger camber on the front.

Been trying to figure out a setup that lasts for a while now though, can't seem to find one that has the tight turn-in I want with a planted rear that hold up for more than a weekend. New rear tires are pretty much becoming a necessity for me each time I run.

BlackBerry
2012.02.06, 01:13 PM
On a stock Kyosho tire, how much will my overall diameter be reduced by mounting on a 19mm wheel vs 20mm? I really don't want to start truing tires.

Front clearance really seems to be an issue with the HSV and a lowered chassis. I might need to switch to 19mm. Didn't noticed till I got home from the track that more than 50 percent steering caused front wheel rub, which explains the consistent spinning issues I had :).

BlackBerry

blt456
2012.02.06, 07:48 PM
If you use the exact same tire, the diameter will be 1mm smaller on the 19mm wheel compared to the 20mm wheel.

I tried PN15s un-trued on 19mm rims at my track. The tires had way too much front grip...I think a general rule of thumb is the more tire on the wheel, the more grip.

BlackBerry
2012.02.06, 07:54 PM
If you use the exact same tire, the diameter will be 1mm smaller on the 19mm wheel compared to the 20mm wheel.


But that doesn't factor in the increased sidewall from less tire stretch, unless its so small its not necessarily measurable?

BlackBerry

blt456
2012.02.06, 08:02 PM
You are not adding or taking away rubber. It doesn't make any sense because the only changing variable is the wheel diameter. (not including the tire on it, obviously)

BlackBerry
2012.02.06, 08:09 PM
You are not adding or taking away rubber. It doesn't make any sense because the only changing variable is the wheel diameter. (not including the tire on it, obviously)

Minor or not sidewall is definitely affected when changing wheel diameter as the tire would be stretched differently than when mounted on a 20mm wheel. Yes we would only be changing one variable but that change has an effect on other aspects.

color01
2012.02.06, 08:10 PM
But that doesn't factor in the increased sidewall from less tire stretch, unless its so small its not necessarily measurable?

BlackBerry
Almost unnoticeable. If you're running the tire at full untrued height, it might make a 0.1-0.2mm difference in the sidewall height, which is pretty unnoticeable. The sidewall stretching effect and the overall diameter is much more important.