Alloy Wheel Problem

Hello all

I have just spent a lot of my hard earned cash on a new set of nice bright shiney alloys and tyres. I have gone up from the standard 15" to a 7x18" with 215/35 rubber. The rims are BSA model 263.

However, althought the car now looks brilliant, the performance now is crap! I reckon I've lost about 25% of the power!! The overall circumference is exactly the same as the old wheels and tyres but the new ones are slightly heavier. Surely this will not make that much of a difference? Everything is free, no rubs or anything and the wheels turn freely when off the ground.

To get some perspective on this, a wee bit of road near my house, I can get up to 80mph from a standing start to a marked point with my old wheels. Now, with the new ones, I am stuggling to get 60! Pretty servere if you ask me!

Can anyone enlighten me on this matter cos its a real downer! Oh, the wheels might now be for sale if anyone is interested?? In chrome too!

Any help would be greatly recieved.

Thanks, Jonathan

[Maputosimon]

Well. the limited info I've been given by a wheel dealer and street racer in Tokyo is that a larger diameter wheel will give you a higher top speed but dramatically reduce your acceleration. (that's why minis have such great acceleration from a stop - REAL minis, not German pseudo-Golfs: tiny wheels.)

Being at 60 instead of 80 is down to your acceleration, but if you are able to compare your revs at a given speed, say 80 in 4th gear, with both sets of wheels, you should see that you have more of the rev band left to achieve a higher top speed with the larger wheels.

If you convert the /40 tyre depth of your new wheels into inches and double it (to allow for tyre top & bottom) you'll find, as I did with my 225/35/18s that the actual height, and by default of physics, circumference, is indeed larger, by over an inch, than 205/55/15s.

Hope this helps...if not, kept me awake for a bit longer anyway!

[G-Force]

The overall circumference is exactly the same as the old wheels

Weight is a factor obviously - however i doubt theyd make that much difference ! Have you tried swapping the wheels back and trying in the same weather conditions ect ?

Also Simon is right that a larger wheel will accelerate slower and give a higher top end but this will also effect your speedo - if they are the same size as you originally said this shouldnt be an issue.

Find a strech of dual carrige way and agree a speed with a frein say 60 to be safe - u sit at 60 get them to pull along side and get them to remember there speed - just to see if its your speedo thats out and also give u an indication that the wheels arent exactly the same size ?

I find it hard to believe that wheels would lead to such a loss....

Let us know how u get on with the above - ooh and a piccy of said wheels would be nice ?

Regards

G

[kenholland]

Just checked the "Tire Size Calculator" site (http://www.miata.net/garage/tirecalc.html) and those 215/35/18's are indeed the correct size and circumference to match standard Mazda 15" and 16" wheels.

So it ain't that then...

Hi Guys

Thank you for your replies. Today, I took the new wheels off the car and swopped back to the old ones. The problems goes away so that rules out and possible co-incidental engine problem.

I got the bathroom scales out and weighed the wheels, both with tyres on. The originals weigh 16kg (about 35lbs) and the new ones weigh 22kg (about 48lbs). Thats quite a weight difference when you start spinning it at whatever speed.

As for the size of the wheels, I got a piece of string and measured the circumferences of both wheels, on the outside of the tread that actually touches the road. There was about 1/4" bifference between the two, which when you take into account a brand new tyre and a part worn one, it's nothing.

I understand what you have been saying about large and small wheels and acceleration/top speed, but this does no seem to be the case. I reckon its down to the weight.

Pure bummer! I would put a picture of them on this but I dont seem to be able to for some reason, I can't find an attach button. But is you go to eBay and type in 2423995493 as an item search, or Alloys Wheels, !8" BSA 263's, Chrome & tyres and you'll see them there. You'll like them I promise! If you read the whole ad there is a picture of them on the car.

Any other comments about the prob would be greatly recieved.

Cheers, Jonathan

[Ian]

i've never seen alloys like these before, very different if not a bit bling bling.

[BeDlaM]

Hi mmeallbhan

I got to say i can't see how 13lbs on the each wheel make so much of a diff, so lets say all in you got 52lbs extra weight on the car which is just under 4stone about the weight off a small kid, now i will need some cinvicing that me carrying my niece in the car ahd she is a lot heavier than that, that i am gonna loose 1/4 or all the power from my car.

Tell you what mmeallbhan, PM me where you are in Scotalnd and if your not to far from me i will come over and put them on my car and see what diff it makes to mine, I'm in Glasgow.

Andy

[Norseman]

It's the extra weight that's doing it, I think.

I know of a guy with a Golf GTI of some kind, who went from
15" to 18", and lost almost a second on the 0-100 km/h.

22 kgs is kinda heavy...

The problem isn't the extra 30-40 kgs themselves, it's where you
place them. And giving the car more rotating mass on the wheels
is the worst possible place.

I've been drooling over the OZ Superleggeras in 16" - only 7.5 kg
I think. But they were impossible to get hold of here in Norway,
with delivery-dates months into the future. So I settled for some-
thing less hardcore; SMC Hs in 17". Haven't been on the bath-
room-weight with them, but I guess they are around 15 kgs.
Maybe more...

http://www.smcwheels.de/smc/index_e.html
("Program" in the upper left corner...)


/Jon.

[BeDlaM]

I take your point Norseman

But your friend didn't even loose a full second on his run, lets say his car had 200bhp to start with, now adding the 18" rims to the car and it's gonna make him loose 50bhp, which is what is happening to "mmeallbhan", still don't convince me that much can be lost, i know the 1/4 mile would be down a bit due to the large wheel, but overall the topend speed,would or should be greater.

Andy

[Mark 626GT]

I think it's not beyond the realms of impossibility and those wheels sound awfully heavy, just look what a few pounds off your flywheel can do for your 0 to 60s.

Try doing a run from say 60 to 80 (or 50 to 70 if you want to stay legal) with both sets of wheels on. If the times are closer by ratio than say 0 to 40 then that’s a pretty good indication of the rotating mass being the problem, as the problem should get less as speeds increase.
While you are there you might want to check out your braking distances, as stopping will be made harder too.

Just to make you feel bad I have the Supperleggs on mine and they are sweet, they are the 17" ones though but they are still lighter than stock so even Scoobies have a hard time embarrassing me (although it's not impossible for them to do so )

Hello

I think weight is the problem here, as you say, taking weight off a flywheel makes a big difference, so it would also work in reverse. 22kg is a heavy wheel.

Andy - Cheers for the offer. I would if I were closer but I'm in the NW Highlands, which is just a wee drive from you!!

As for braking, it seems to be better than the old wheels.

There is something that I noticed today that might make a difference. I feel like a complete idiot! I don't know if I fitted the right wheels to the right sides on the car, for tyre rotation. I know for sure that I fitted the front left one on, with the tread facing the wrong way! Doh!! It should have gone on the right side of the car. As for the rest of the wheels, I've no idea if they where right or wrong. Would this add to the problem d'you think?
It would make a difference in the wet as the tread wouldn't be pushing the water out of the way properly, but as for acceleration. . . .?

The only way to tell is to put all the rims back on again, the right way this time!, and go for a drive.

Cheers, Jonathan

[mx6-uk]

Both are true.

IE going for larger wheels does and always will reduce acceleration and any added weight will too.
Bigger and wider means more tramlining too.

All that said kepp the speed up through the corners and your winning.


Take a good read of this thread (LONG THREAD)

http://www.gtr.co.uk/forum/upload/sh...?threadid=8227

[Rusty]

Just a thought. As you have now increased your unsprung weight by a considerable amount, your dampers may be to soft to keep your wheels in effective contact with the road, you may notice this more at speed on poor road surfaces. Sorry to say this but you have taken a backward step by fitting those wheels. It's traditional to reduce the unsprung weight to improve your car' handling etc, not increase it!

Russ.