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MG MGF Technical - The great Unsprung Weight debate

Hi All,

I remember standing around in the cold this time last year at North Weald weighing different types of wheel/tyre combo's. Did we ever see the results? I ask because I've been asked about the weight of my cup wheels but I can't remember that far back (and I didn't have them then at any rate, but Rob did so I'll use the weight of his instead.


Phil Brindley

I think that debate fizzled out for the 'F.
(It raged for a while on the Mini BBS. They have bigger tyres/wheels and run on run-flats too so it's a big thing for them.)

I do however remember seeing the weights - but cannot find them now. :-(

Gut feeling is that it will not make a huge difference to handling. Possibly braking.
Not sure if I argued that way last time tho. <grin>

Paul Nothard

Makes little diffrence on modern cars wich have very little unsprung weight due to IRS systems and lardy bodies. On the midget it is a real issue as it is live axle and no weight on the body (currently designing an IRS!)
Will Munns

IRS Will? Whatsat?
Paul Nothard

>> Gut feeling is that it will not make a huge difference to handling. <<

Unsprung mass is hugely important in terms of ride and handling: it is the difference between the tyre pattering over a bumpy road surface, making intermittent contact, and the tyre contact patch faithfully following the contour of the road.

But I think I know where you are coming from with that statement Paul: when it comes to wheels fitted to the MGF, there was surprisingly little difference between the wheel/tyre combinations we weighed (they have been on a thread, either here, or on the MGoT forum) - although the 11-spoke alloys used for the Trophy and TF 160 were significantly heavier than any of the others - be they 15" or 16"

Will, how's the IRS project coming along?
Rob Bell

IRS = Independent Rear Suspension ;o)
Rob Bell

IRS no not the tax man but independant rear suspension
Mike (Mersea)

Found it in the MGF Technical archive [Thread # 2005031115491523587]:

"The 'Unsprung weigh-in' @ North Weald"

15" 5-spoke VVC [GY F1 GS-D2 205/50 ZR15] 15.0kg
15" 5-spoke VVC [Avon ZV1 205/50 VR15] 15.0kg
15" 5-spoke VVC [Bridgestone RE720 205/50 ZR15] 17.0kg (!)
15" 6-spoke 1.8i [Falken 205/50 ?R15] 15.5kg

16" Multispoke (from 75LE) [GY F1 GS-D2 215/40 ZR16] 15.5kg
16" 6-spoke "Cup/Abingdon" [GY F1 GS-D3 215/40 ZR16] 16.5kg
16" TSW Blade [Maragoni 205/45 ZR16] 18kg
16" 6-square spoke [GY F1 GS-D3 215/40 ZR16] 18kg
16" 11-spoke "Trophy" [Bridgestone S-02 205/45 ZR16] 19.0kg
16" 11-spoke "Trophy" [GY F1 GS-D2 215/40 ZR16] 18.5kg
16" 11-spoke ULW [GY Eagle F1 215/40] 15.6kg

Ian Matheson

I have always known that the Trophy wheels are heavier than the multispokes but from the results posted above is someone being conned because it appears the ULW are the same weight as the multispokes.
The ULW's come in that funny grey colour but if I remember were/are about a 1500 more as an option from june2001 price list and thats in leiu of standard wheels from whatever model is chosen.
Joe one

Nice one guys, thanks. My question is answered.


Phil Brindley

>> I have always known that the Trophy wheels are heavier than the multispokes but from the results posted above is someone being conned because it appears the ULW are the same weight as the multispokes. <<

I agree if that were true Joe- but I don't recall weighing any ULW wheels at North Weald?!
Rob Bell

That's correct Rob, I provided the weight of the ULW ;o)

If Erik's scales are correct then multispoke =ULW.
I have a set of 16" Trophy and multispoke wheels,when you look at the back of the multispokes you will see that the wheel centre/hub has only the bare essential of metal its as if the weight of the wheel was desined to be light.
Joe one

Thanks for clearing that up Erik! I hope your scales have a similar calibration to the set we used on a chilly afternoon in Essex! LOL

>> If Erik's scales are correct then multispoke =ULW. <<

You're right Joe: there may not be as much difference as one might hope given the cost of the ULW wheels from MGR! Having said that, it is very important to note that a sizeable proportion of that mass is actually in the tyre. Even comparing apparently identical wheel/tyre combinations reveal sizeable differences in measured weights according to the extent of tyre wear, which made our attempts at comparisons very difficult to interpret.

In essence, if one is truely serious about unsprung weight, you need to look at the tyre you're fitting: it represents something in the order of 60% of the total weight measured above: for example, of the 16.5kg of 'Cup' alloy plus GY F1 GS-D3, only 6.5kg of that weight was the alloy wheel itself...
Rob Bell

>>> If Erik's scales are correct then multispoke =ULW. <<<
I wish I could have used my own scales, but unfortunatly I haven't got a set of ULW's, so I asked MG Rover Belgium.

Apart from unsprung weight, as rotational the weight difference is multiplyed.



Is it possible that MG Rover Belgium actually sent the work experience kid to measure them and he actually weighed a set of gunmetal multispokes?

Just a thought, would certianly explain the similarity.

Phil Brindley

I think that Marvin may have a set of ULWs sitting around somewhere - if he's agreeable, I'll ask him to weigh them for us to corroborate Erik's findings. :o)
Rob Bell

This thread was discussed between 11/03/2005 and 14/03/2005

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