Brakes Wheels 1st Gen Tires Wheel weight to feel difference...

Discussion in '1st Generation: 2002–06 R50, R53 & 2004–08 R52' started by ED955S, Nov 2, 2009.

  1. ED955S

    ED955S New Member

    Oct 9, 2009
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    How much wheel weight reduction / corner (stock 24 lbs S-lites) before feeling a significant handling and acceleration improvement? Your honest actual experiences and timed drag data will be appreciated.
     
  2. PGT

    PGT Wheel Whore

    May 4, 2009
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    I went from stock R84's and runflats to 10lb 15x7 BBS RG-F. Any difference I felt was offset by the utter lack of steering response from the gumball tires. Sure, it road great, but that's not why I bought the car. If I had it to do over again, I would have put a super sticky r-comp on instead of the lightest tire I could find (some things matter more than weight, like steering response).

    I think I dropped 50% of the weight off the wheel/tire combo - a HUGE difference. Some people will say that light wheels and tires make a difference...I'm not convinced on cars that have adequate power like a Cooper S. They made a huge difference on my CRX but with 108hp, that was to be expected.
     
  3. Deviant

    Deviant Banned

    Apr 23, 2009
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    On my old car with it's softer suspension and much less power the small drop in wheel weight was pretty noticeable. With the MINI I notice the small loss in sidewall and increase in grip, but not so much the mild drop in unsprung weight.
     
  4. danf

    danf New Member

    Aug 30, 2009
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    I used to have an R56 cooper that came with 16" bridgespokes and runflats. I replaced those with 16" Rota RBs and dunlop direzza's. The wheel weight difference was 5 lbs. less per wheel, not sure about the tire weight difference. There was a noticeable difference in acceleration and handling with the new setup though.

    I have since sold the cooper and picked up an R53. The R53 came with S-lites/runflats. I have replaced those with the same Rota/dunlop combo above. The difference wasn't as great as above but it sure did handle lots better.
     
  5. Dinan604

    Dinan604 New Member

    Oct 29, 2009
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    Hey Ed,

    It's hard to answer this question without eliminating a lot of factors that people are posting about. If you keep the same tire and just swap out the wheel for a light one, then you're not going to feel much of an acceleration improvement but it will be there, even if it's a 10th of a second. The biggest difference will be the fact that your dampers won't be working as hard keeping your heavier wheels in check. This is especially more noticeable on the bumpy streets versus on the track, where the tarmac is generally smooth. So your steering will be easier and smoother.

    Another thing to keep in mind of is rotational inertia and wheel sizing. It's much easier to improve handling and acceleration by decreasing the radius that the mass has to rotate on, basically going to a smaller wheel size...even if it's the exact same weight as your S-lites (which are heavy...25lbs IIRC).

    There is a thread that I've saved from the MINI2 forums. In it, a person used a G-Tech to test the theory of losing unsprung weight.

    In defense of 17"s - long - Page 3 - MINI2 - MINI Forum

    I've noticed much improved handling and acceleration on all my previous cars, from the low-powered A4 to my DSM and WRX, simply by using a 15" or 16" wheel that is lighter and smaller than stock, even if the tire at the time wasn't much of an improvement.

    On my R53, with my 17x7" GramLights (17.1lbs) with 215/45 Star Specs, the car rides a lot rougher and the stiffly sprung and damped CROSS coilovers are pretty harsh on streets. With my 16x6.5" x-lites, the car is much more comfortable and steering input is much easier and lighter. I can't compare acceleration from a dig as I'm on Pirelli Snowsports now for the winter, so outright grip has been compromised. However, I will say that from a roll, it accelerates much faster as less force is needed to spin the wheels/tires now.

    The ultimate reduction for me was using a set of 15x7 wheels (11lbs each) and running R888s at a reduced size of 225/45/15. The car hauls compared to the 17"s and the reduced gearing was a plus.

    Let's face it, I run 17" GramLights on the street only because they look great. There is no performance gain simply by going to a larger wheel. I'm already thinking of going to a 16" wheel for street use now simply for comfort...my spine will thank me.

    Remember, every 1lb of unsprung weight removed = 10lbs of sprung weight removed. Also, every 100lbs of vehicle weight removed = 0.100 of a second in the 1/4 mile. For example 5lbs of unsprung weight removed x 4 corners = 20 lbs of unsprung weight. Using the formula, that's 200lbs of vehicle weight reduced and 0.2 seconds quicker down the 1/4 mile.

    Here is another page with an Excel document to calculate the difference in your stock wheel to another wheel of your choice. You will need many factors including tire weight but it's easy to see the difference.

    http://se30.dyndns.org:8080/SVX/rot_inertia.html

    Cheers,
    Steve
     
  6. Dr Obnxs

    Dr Obnxs New Member

    Jun 11, 2009
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    Where's this come from?

    A decent approximation for most apps is that dropping 1 lb of weight from a tire wheel combo gives an effective mass reduction of about 2.6 lbs. (1 lb + 1.6 lbs reduction in moment)

    It's all interesting reading.

    Matt
     
  7. Dinan604

    Dinan604 New Member

    Oct 29, 2009
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    #7 Dinan604, Nov 5, 2009
    Last edited: Nov 5, 2009
    Sorry I used unsprung weight instead of rotational mass. What I meant was 1 lb of rotational mass reduced or lost = to roughly 10 lbs of vehicle weight removed. This can vary as the moment of inertia is different on tire/wheel combos. For example a 24lbs tire on a 17lb wheel will have a higher moment of inertia than a 21lb tire on a 20lb wheel. So while total weight removed from the wheel/tire combo is the same in both cases, the latter example will give you the most benefit.

    I've also heard of the approximation you've given. Both "formulas" I've heard about during my drag days with my DSM. I remember that if you dropped 100lbs of vehicle weight, the average drop in 1/4 mile time was 0.100 seconds barring driver error and many other factors, but the general result was just that. So people have tested with lighter wheels with the same tire and got roughly an average improvement once they dropped about 10lbs of rotational mass in wheels. It's not exact, but it's a good way to get a rough measure before choosing certain wheels or tires.

    It's a great read and unfortunately, I was only average at physics while in school...but it sure is fun to learn about.

    Steve
     
  8. Dr Obnxs

    Dr Obnxs New Member

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    But 1 lb dropped isn't 10 lbs of equivalent weight reduced.

    It's about 2.5, plus or minus. It's real for sure, but I think in your example above you double counted. 1 lb per corner comes out to about 10 lbs equivalent for the whole car. You went from 5 lbs a corner to 20 lbs for the car to 200 lbs equivalent weight. It's more like 50.... Persnikity details, I'm just keeping the numbers honest.

    What's more interesting is that improved suspension performance can increase contact patch effectiveness, raising the amount of traction available for both acceleration and braking. That's pretty cool.

    Matt
     
  9. ED955S

    ED955S New Member

    Oct 9, 2009
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    Steve,

    Thanks for the info. I am leaning to a package that will reduce about 8 lbs / corner from my S-lites & GY Runflats.
    My choice will be most likely the the Breyton GTS-R (16.2 lbs) in 205x45x17 Michelin PE2.

    From my understanding, the handling and feel are better benefits than few tenths of a second in 1/4 mile acceleration gain.

    Ed

    PS: anybody here using the Michellin PE2? How's the turn-in response? Spongy? THANKS.
     
  10. ED955S

    ED955S New Member

    Oct 9, 2009
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    Have not been in MA for awhile but just an update: Car felt slightly livelier and more tossable after installing Enkei PF01 and Hankook Ventus V12 (17x7). Weight reduction is about 12 lbs/corner coming from S-Lites and GY runflats.
     
  11. Jason Montague

    Jason Montague New Member
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    Jan 5, 2010
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    :cornut: I went to 14lb OZ Allegrettes and nonrun flat tires dropping 18lbs/corner or 72lbs total unsprung weight and the already tight 'Sport Suspension' felt like it had had a very expensive upgrade. The difference that I feel was well worth the cost.:Thumbsup:

    Jason
     
  12. Dwight

    Dwight Racing with the Gods
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    Jul 7, 2009
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    ANY reduction in un-sprung weight is a good thing! :Thumbsup:
     

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