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Suspension Dropping unsprung weight in my MINI.... an invite to a discussion.
SuspensionSprings, struts, coilovers, sway-bars, camber plates, and all other modifications to suspension components for Cooper (R50), Cabrio (R52), and Cooper S (R53) MINIs.
Also, this is coming up with the 17” size. Just click the 16” option on the page. Even at that, the 17” size is only 14.6 lbs.
Originally Posted by Eddie07S
Also, in a 195-55x16 tire I found a 2 lb per tire weight difference between brands and models without looking really hard. A larger tire (e.g.: 205-50x16, etc.) will be even heavier.
Awesome find on the rims... good price and lightweight !
Not just for track... I've found that on the road... a nice light unsprung weight just feels better on the road in these cars.
in the Ecsta...
195/55/16 = 19 lbs
205/50/16 = 20 lbs
205/45/17 = 20 lbs
Last edited by mountainhorse; 12-12-2018 at 01:12 PM.
For factory 16's, the X-lites are going to be your best option. If you are willing to go to 15's 949racing makes wheels that are dedicated 4x100 and tip the scales at a whooping 10.9 pounds and they are reasonably priced. With these, even with tires, they will be nearly lighter than just the s-lites alone. Shedding more than nearly 15 pounds per corner. I think that Wilwood makes a BBK that will fit 15's. This could drop a few more pounds as well as the rotor will be smaller. https://949racing.com/15x7.5-6UL.aspx
I read somewhere on the internet, so you know it's true, that for every pound of unsprung weight you drop, it's like adding 10 hp. This might be marginally true to a certain point... but it couldn't be a linear correlation.
I know in my R50 when I go from my Panasports (17lbs) to my 8-spokes (15lbs) or the 7-holes (12lbs), there is a marked and very noticeable difference in how the car accelerates. The Panasports have the summer rubber. The 15s have AS and winter tires so cornering is not their best feature.
Great points this morning...I love this forum!
The 949.... Good looking wheel.
For me the 15".... a bit too much compromise in terms of looks and future BBK application to the car.
I understand that this size is the favorite of the track day people though... and also, I can understand the benefits in the diameter/weight equation.
The options out there in the 195 16's in terms of grip, weight, NVH, ride, performance, feel... seem to be a good fit and not too much compromise... for me and my stuff.
Nice to have lots of different options.
949 Racing Beryllium color... 15x6UL... +40ET, 10.7 lbs... but still a 15" $149 each https://949racing.com/15x6-6UL.aspx
Their 17's are light too.. but the narrowest is 8" (just not too good for the curbs around town)
Last edited by mountainhorse; 12-12-2018 at 01:08 PM.
So, a 10 lbs decrease in each tire/wheel weight is like adding 10 Hp to the engine and vice versa.
And, yes, it is very noticeable.
Also, there is a gain to be had by decreasing the radius at which the mass is located. That is, if the tire diameter is decreased by, say, 2 inches, the rotational mass decreases, even if the static mass stays the same. This will also show up in acceleration of the car.
Great points!! Acceleration is one thing that is a benefit for sure.... not just in terms of propulsion... but also acceleration of the parts in their up/down path of the suspension.
One thing that stands out is the cars with the heavy wheel/tire combos tend to mushroom the strut towers the most. This is a side effect of the wheels leaving the pavement for longer moments and inducing forces into the chassis that are not desirable.
Also you make an excellent point on the distance of the weight from the center in terms of gyroscopic/centripetal-forces.
Resistance to directional change in maneuvering as well as acceleration change greatly by moving the mass outward.
On our cars though... taking for granted a relatively light wheel... the rubber is still mostly the same diameter, outside, with the different rim/tire combos at approx 24".
Makes me wonder what the difference is in the change...and going to smaller diameter tire has some costs in terms of rolling over bumps and other things.... smaller OA-diameter will give more harshness in the ride.
All a balancing act... but in the end... a lighter wheel/tire combo will be very noticeable and those interested in lap times and expense to find the true 'tipping points' will know this from trial/error testing on the track... where so many other variables also make those fraction of second differences. I'm not discounting this at all, but...for me... a more pragmatic approach keeps me more sane !
There is so much more to look at from an more 'exacting' engineering approach... but this is a good 'broad stroke' discussion.
Thank you to all that are participating... great stuff!
Good point on the center of mass PNW... important as pointed out above.
The reason why axles are really not part of the equation for rotating mass discussions!
Originally Posted by DneprDave
Fill your tires with helium!
Originally Posted by pnwR53S
Just some interesting thought. Helium will not give you any measurable lightness. Fill with vacuum is lighter, if that is possible.
Additionally for argument shake, filled with helium will not improve acceleration as it is the rotational mass, not weight, and how far from the center the mass is located that matter. Even assume for a moment that the helium nullify all the weight of the tire and wheel, you gain nothing on the acceleration as the mass cannot be nullified by the gas.
Alternately, you can have 1000 lb wheel and the angular acceleration can be infinite if the mass is concentrated at the dead center, with a pin point area.
I run both 17” and 15” wheels on the track, depending on the track I go to. I use that Wilwood BBK that you posted above with both the 17” (Enkei Racing) and 15” (Kosei) wheels. The nice thing about that Wilwood BBK is that the only difference between the 11.75” rotor setup and the 12.2” rotor setup is a spacer in the mounting of the caliper, so I also switch between the 2 sizes of rotors to match the 2 sizes of wheels. For the road there is no lack of stopping power with the 11.75” rotor setup, so I would not limit the wheel size contingent upon BBK selection. The 11.75” rotor setup will fit al lot of different 15” wheels. For the track, the 11.75” rotor setup with the 15” wheels is fine for all but the most brake-demanding tracks (for example - Watkins Glen). There I have found that the limitation is not with the BBK but the closeness of the wheel to the caliper which limits the brake cooling. In that case the 11.75” rotor setup works well with the 17” wheels which allows for better brake cooling. Of course the 12.2” rotor setup works that much better.
As for ride, I run a 205-50x15 with an OD of 23” (RE71Rs). This is in comparison to the 17” wheels which I run 225-45 (R888s) or 215-45 (ZIIs) tires, which are about 25” and 24.8” OD respectively. Not a huge difference. But the ride seems to be more a function of the sidewall height and stiffness than the actual diameter. All of the tire/wheel combinations seem to ride about the same and have no more or less harshness over ridges or bumps.
For the street I run...are you ready for this?????
The OEM Continental 195-55x16 RFTs on stock wheels. Talk about heavy, but they have TPMS and I don’t have to worry about flats. When I changed/upgraded the shocks, the RFTs became tolerable.
These haven't occur to me until this thread. High rotational inertia like wheels, tires, and brakes negatively affects the car's dynamic performance in three ways. Call it triple jeopardy if you'd like.
1) Rotational inertia - resistance to angular acceleration, which contributes to car's linear +/- acceleration.
2) Gyroscopic force inertia - contributes to the car's resistance in changing direction.
3) Linear inertia - contributes to the car's linear +/- acceleration.
The degrees of significance vary, but they exist. So these applies to everything in the car that rotates and has a mass. For a motorcycle these effects are much more pronounce.
I will be able to give you an EXACT weight difference from a Wilwood 4pot complete brake system from the JCW R53 Brake and Rotor Kit. I recently got a Wilwood 12.2" kit for my 2006 Silver JCW MINI (aka 'Emma). The car currently has the Poor Mans (I wrote that article) JCW brake kit (R56 front brake conversion). I will remove the JCW kit and weight it for a total weight and I will weigh the Wilwood kit for a total weight. It will be interesting to see the difference.
The Cat (her name is Donut) will not be included in the weight of either kit!
Dang.... thats 8.5 lbs less per corner on the front...
Drop 10 lbs with a good wheel... and 8 lbs with the brakes... Makes for a HUGE 18lb drop, PER FRONT CORNER, in unsprung weight without going truly exotic.
NICE!!
.
Last edited by mountainhorse; 01-06-2019 at 10:20 PM.
72 lbs off the total car weight without really trying. And all of this includes a larger set of brakes.
But note that the brake mass will only have a small affect on the rotational inertia as weight decrease is mostly in the caliper (a non-rotating mass) and the hub of the rotor (which is close to the center of rotation). So, it will be the change in wheel weight that will have the most noticeable affect on the acceleration of the car.
True!
And going to a smaller diameter (the OD of my 15” tires is 2” less than my 17” tires) will also help.
But, with respect to tire weight and within a single tire size or one size up or down, the thing I have struggled with is finding tires that are more than a pound or two different in weight. In the type of tire I use they are almost identical in weight. It seems the manufacturers have pretty well locked that down and there is little to be gained there. However, if you are willing to make a radical change in size, there may be multiple pounds to be gained. I think my 205-55x15 tires are each 5 or 6 pounds lighter than my 225-45x17s.
To me, the factory mini R53 unsprung weight is grossly heavy.... and lightening it up is a good thing.... even lighter by 15 lbs per corner... the suspension/wheels/brakes are not featherweight by any measure... and I believe that there will be very little if any additional NVH in the ride... with a better handling and traction overall.
Thoughts??
.
Last edited by mountainhorse; 01-08-2019 at 04:19 PM.
I run the wilwood 11.75 setup with 15x8 949racing wheels (11.6 lb each) and I'm very happy with them.
Are you doing autocross or HPDE/track? Wilwood and a few others make some VERY light front rotors for circle track that you could use if you are not going to be doing trackdays
7 pounds for the ultralight rotors vs 9 for the GT36, they have a scalloped rotor that's 5.4 pounds!
To me, the factory mini R53 unsprung weight is grossly heavy.... and lightening it up is a good thing.... even lighter by 15 lbs per corner... the suspension/wheels/brakes are not featherweight by any measure... and I believe that there will be very little if any additional NVH in the ride... with a better handling and traction overall.
Thoughts??
.
The biggest factor relative to NVH from the suspension, as well as handling and traction, is the shocks. I have taken close to 80 lbs of unsprung weight out the car and I have replaced the shocks in both of our MINIs. I see little difference between my 15" Kosie wheels at 10# each with 21# tires and my 17" Enkie wheels at 18# each with tires that are 24# each in the way of traction or handling (before that I ran stock wheels at 25# each). How well the shocks control the movement of the unsprung weight has as much to do with the handling and traction as the weight itself. The MINI shocks don't do well at all at controlling the unsprung weight. As I found out and many others have reported, a better shock (and most out there are better than the MINI shocks) is much better all around for handling, traction, ride and NVH.
12-12-2018, 12:01 PM
(just not too good for the curbs around town
)
