Mike Barnby R500 Mag Wheel Size Confusion

[Nifty]

Having bought another set of MB mag wheels a month ago I eventually went to sort out tyres to put on them ... only to discover that the rear wheels are too wide for the stockpile of tyres I have in the garage.

 

When I bought my first set of MBs from Richard Ince back in 2002 they had come off his R500 and were fitted with 185/60/R13s on the front and 205/60/R13s on the back (Yoko 032Rs).

 

I thought the wheel widths were 6" (or 6.5") front and 7.5" back, however, two people in the last month have told me they have a set of standard CC R500 mags and both sets have 8.5" rear wheels.

 

Also, one of these sets has 215 tyres on the rear rims and the rim sticks out from the tyre to quite a degree, suggesting by sight that a 215 would be the minimum tyre width for this wheel.

 

I always thought that the general opinion was that the R500s ran best on 205s and anymore was overtyred. Obviously the racers ran 205 rears because that's where a lot of my stockpile comes from.

 

So .. can someone give me a categoric answer as to the original spec. of wheel and tyre for the original R500s please

 

Keep off the straight and narrow 😬

[Peter Carmichael]

6.5 8.5 were the original size for the big ACB10s which were standard fitment on the SLR.

 

[Edited because I was obviously wrong!]

 

Edited by - Peter Carmichael on 26 May 2008 21:53:17

[Nifty]

That makes some sense Peter

 

Can anyone verify this 🤔

 

Keep off the straight and narrow 😬

[BYKer Will]

Nifty My rears are 8.5 and originally had very wide acb10s.

 

If it helps though 205 60 R888's fit fine. I know Toyo state a max rim width less than 8.5 but the width hasn't caused any problems. My newest set even went on easily despite expectations.

 

I have also had 205 cr 500s on without a problem.

 

Won't the yoko's stretch a bit?

 

Will

 

PS good to meet you briefly last week. I would have been very interested in your wheels had I not ordered the cxr's recently and a garage full of broken bits.

[Mark Durrant]

Nifty

 

Why not keep the wheels and get a pair of new rear inner rims from Mike Barnby that are an inch smaller.

 

Mark D

Comp Sec

 

[Nifty]

That thought has crossed my mind Mark.

I'll give MB a ring tomorrow and discuss.

 

With the 8.5" wheels the outer rim is also deeper, so in effect I'd be increasing the track at the back.

Whilst this is possibly a benefit it could mean that the car behaves differently depending on which set of wheels I had on ....

 

 

 

Will,

 

Not sure I'd want the tyre to stretch a bit.

I like the way the car handles and like the idea of having a little rubber to scuff before grinding the rims. I rather fancy that stretching the tyre onto a wider rim reduces tyre wall flexing and increases risk of failure.

 

Keep off the straight and narrow 😬

[jason liddell]

My 2001 Superlight came to me (2nd owner) with MB R500 Mags fitted with CR500s - all as originally supplied/fitted by Caterham when the car was factory built. Wheels were 6.5" front, 8.5" rear.

 

The orig spec sheet described the option as: W&T-13" Magnesium Wheels-Avon CR500 Radials-SLR

 

 

 

^{(Mainly ) Scottish Motorsport/Trackday Pics Here.}

[Nifty]

Since these threads are used as a resource of information I'll add what Keith Jecks has just E-mailed to me:

 

FYI: 205/60/R13 Yokohama 032Rs and 48Rs are what I have always used with

those rims - they work just fine. They are the wheel/rim combo that many

Seveners use all the time.

I know what the Yoko charts say, but I prefer to go with experience!

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 26 May 2008 18:40:44

[Nifty]

Just done a quick measurement with a ruler on my old MB mags (from Richard's R500 racer) and I think that they are 6.5" front and rear ..... still more confusion

 

Might give George Polley ring tomorrow too and just ask him about his recommended wheel widths.

 

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 26 May 2008 19:25:53

[BYKer Will]

Nifty Looks like Richard sold you 4 fronts. I would ask for a discount 😬

 

If my memory serves me I think I asked Steve from simply tyres if 205 R888 's are OK on 8.5 inch and he said whilst not formally recomended it was fine.

 

Do let us know what polleys say as I have ordered my new cxrs in 8.5inch.

 

Will

[neilg]

Nifty, This new ( to me) blackbird car i'm getting has a set of Barmbies with ACB10's on and they're 245 at the back ( and they look ENORMOUS 😳)and 195 for the front. I'm no expert on MB or ACB10's but can confirm that Steve at Simply tyres said that 205 Toyo's are ok on these wide MB's . Seem ok on Will's car.

Cheers Neil

[Slipper man]

Nifty - although those rims didn't come with my car, they are definitely the same size as the original equipment wheels. I got my 32R's and 48R's from George Polley and I am pretty sure he said they were OK for those rims. Anyway, as I said above, many people use 205 tyres on those rims and I am not aware of anyone having had any issues. Dave Jackson has as much experience of these things as anyone I suspect, and the tyre sizes I use are the ones he uses too.

 

Why don't you try fitting a pair of rears and see how they feel to you before selling the wheels?

 

Edited by - Slipper man on 26 May 2008 22:34:03

[Nifty]

Thanks for all the posts.

 

Whilst I accept that many people are satisfactorily using 205s on 8.5" wheels, personally I (currently) feel I don't wish to do that.

 

Firstly, Polley's website states the optimum to be 7" and I can see logic in not going 8.5" because you are changing the profile of the tyre wall and are right on the limit of permitted width. Picturing it in my head I can see that it would be easier to push the tyre off the rim (particularly if on our potholed lanes).

 

Secondly, I don't wish to scratch the rims on the concrete every time I lay them down.

 

Thirdly, as stated these tyres came from Mr Ince who would have had a good reason for placing the 205s on the 6.5" rim .. no expense is spared when he's racing to win, so I'd imagine this was not a mistake since his budget would have easily extended to 8.5" rims if they were the preferred option.

 

Can I phrase my question in a different way 🤔

 

What is the advantage of running the same sized tyre on a wider rim or what is the disadvantage of running on the narrower rim 🤔

(Running the 6.5" or 7" rim will save on unsprung weight and rotational inertia )

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 27 May 2008 08:26:05

[Rob Walker]

I have run with 205 tyres on a variety of rim widths from 6" to 8.5" it has been my experiece that the 205 tyre stretched onto 8.5" gives the best performance by far. The sidewalls distort less so the carcase of the tyre and surface of the tyre is more stable therefore you can push the tyre harder and I even noticed reduced tyre wear. Only down side is it is difficult for the tyre fitter to initially inflate the tyre.

 

If you fit a 205 on a 6" rim and push it hard it feels as if its rolling off the rim by comparison plus you get higher wear.

[Nifty]

Polley's response today was that the tyre would be better on an 8" rather than an 8.5", but 8.5" is OK, and that they sit better on the wider rims than the 6.5" rims.

 

I was always under the impression that 7s were designed to run a higher aspect tyre with the consequential tyre wall flexing.

 

Tomorrow I'll try to speak to Richard or Tranzpower to find out why they fitted the 205s to 6.5" rims.

 

Keep off the straight and narrow 😬

[BYKer Will]

Nifty Just one more point regarding your concern that an 8.5 will stick out beyond the tyre and be damaged in use or storage. In short they don't with toyo's and from memory nor did they with the cr500s because the rim bulges the tyre wall out beyond the rim.

 

Will

 

 

[Nifty]

The 205/55 CR500 is actually 230mm section I learnt yesterday, which is why they are perfectly happy at home on an 8.5" rim.

 

I may well give the 032Rs a try on the 8.5 rim and see how they look.

The 215 Kumhos I have on another set of 8.5" rims certainly don't stick wider than the rim and a visual check of the bare rim against an 032R suggests these won't either.

 

Keep off the straight and narrow 😬

[Simon.Rogers1]

Why not put medium kumho's on the other set of rims.

 

They are great on road or track and you can keep the same set up!

[Nifty]

Because I have a stockpile of 032Rs to use up before buying any more tyres

 

(Sadly they won't fit the Esprit which needs new rear tyres)

 

Keep off the straight and narrow 😬

[rj]

Nifty,

 

 

You can just wrap the 032s up and ship them off to Denmark. I shall happily help you wearing them out.

 

(more seriously: I've got three set of MB wheels, all rears are 8.5")

[Julian Thompson]

Nifty

 

Richard DID use a lot of 8.5's because I have about 8 sets of his old wheels in my garage! Maybe he just fitted some to 6.5's for a bit more compliance on a wet day or something?

 

I run 6.5's on my LA car on the road as the sidewalls flex more and give me a better ride but switch to 8.5's when I go on track. Both with 205's (Ex Ince!) and both work fine.

 

[BYKer Will]

"8 sets" bit greedy 😬 If you ever making some room for spare blackbird engines give me a shout.

 

Best wishes

 

 

Will

[Nifty]

Julian,

 

I was going to ring you this afternoon to ask you exactly what you got from Richard ... thanks for that.

 

On further thought I wonder whether he gave me the 6.5" all round because at the time I was only running the 1400 SS engine

I was only borrowing them to start with but having "forgotten" to return them after a while I suggested I purchased them

 

Anyway, I stuck a 205 032R onto one of the 8.5" rims and they don't look as bad as I thought and the tyre wall does stick out slightly further than the edge of the rim, thus offering a small amount of protection to the rim.

 

I think I'll keep these and use them for the track and get the old set crack tested, powdercoated and then use them on the road as you suggest Julian ... I've also got those miniltes you sold me last year, they are also fitted with 205 048Rs on a 6.5" rim

 

Keep off the straight and narrow 😬

[Julian Thompson]

*thumbup*

 

Will let you two boys (Will + Nifty) have first refusal if I decide to reduce my wheel collection 😬

[k80rum]

As a cheeky aside , if anyone's got surplus inner/outer rims for MB wheels after jiggling around sizes, i'm after some here to build up some specific widths.

 

 

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54