13" wheels for sprints and hill climbs

Technical Area Motorsport & Trackday Preparation
2

Has anybody used 13" wheels on a mx5 for spints / hill climbs? im looking to gear it down for lots of acceleration, top speed not so important. fitting smaller wheels seemed possably the way to go as lots of choice in 13" tyres too. What does a Mk1 MX handle like on 13’s do they clear the calipers ok? which 13" are best to go for as there dont seem to be much choice about in 4x100 13". some of VW’s and Hondas use them, are they any good for an MX mk1?

Any guidence appreciated.

Dave

3

I know of a car that had some 13" steel wheels, I doubt you’d get an alloy to fit AND I doubt it would fit over 1.8 brakes…

It’s the second to third that hurts most on hill climbs / sprints so change your diff ratio to 4.655… then you don’t need to change your wheels… 

4

Yes, originally changing the diff was my though then i thought maybe changing the wheels was a easier option. looks like thats not the case. so back to looking at swapping the diff. Is the 4.655 diff a bolt on option from another mx5 model or is it a case of changing the crown wheel and pinion?

5

 We have 13inch alloys for sale currently on mx5 but very wide Minilite design with polished lip .May need wider arches to accomodate width.Email me if you want photo,s      robert.maguire@eircom.net

6

 All the diffs swap directly over complete cbtu you may need driveshaft and halfshafts depending on what diff you currently have ie 1.6 or 1.8 ???

7

Which class will you be running in?

Some classes restrict modifications to wheels that were fitted as standard. I suggest you check the MSA Blue Book

8

Im going to stick with 14" wheels now. ive bought some 185 55 14 A048r road legal slicks now. first hillclimb this weekend!

Going to go for a LSD this winter when i do some more upgrades. which is better the Torsen 1 or 2 ( to go on a 95 1.8)

9

Aren’t those tyres list 1B?

If so I take it you will be running in modified and the organising club has obtained dispensation to allow them.

I would have a quick check of the SRs

10

 Hi Colin S, Im in road going saloons under 2000cc . I checked the blue book under section S11 which is the section that the event SR’s say we have to conform to, and under the section on tires (s11.6.2 i think) it states that except for some historic classes tires from both lists 1a and 1B are permissible  the SR’s dont make any other reference to tires apart from ensuring compliance to S11 tech specs. based on your post i phoned one of the local scrutineers from the blue book and asked him. He wasn’t sure but after referring to the blue book he seemed to think there will not be a problem. so hopefully all will be well this weekend as it would be very disappointing not to be able to run.

 

 

 

 

 

 

 

 

11

Are you at Gurston this weekend then n630hjo?  I got round to getting my licence and will be there on Sunday to do my first ever hillclimb (Prescott at the national not included).  Dark grey 1.6 mk1.  

12

Just had another look in 2013 Blue Book

 

Page 190

Production Tyres

2.2.
For Production Saloon and Sports Car racing, only
standard road tyres in List IA are permitted, and only to
rim and tyre sizes as laid down for specific car models
on Production Car Specification Sheets.

Does your car have an approved ROPS? If so you may just get moved into modified.

The SRs should state if 1B are allowed as if they don't then they are not (page 194) as special dispensation has to be sought from the MSA to allow them

Please note I am not trying to be awkward here -but having quite a lot to do with organising sprints etc. beleive me, it is no fun at all having to tell someone they can't run because they have the wrong tyres on.

I am just trying to forestall any problems before you turn up with the car.

If you are wondering about the reasons, it is largely because Road Going do not have to have a ROPS and the extra grip obtained with 1Bs makes it a lot more likely that they will roll if something goes wrong -and they do sometimes, a Corsa went over big time at an airfield sprint not long ago

I hope you get it sorted and have a good days motor sport.
 
13

No that’s wrong - that’s the RACING regulations, a Hill Climb is a Speed Event and has it’s own set of regulations…

The Sprints, Hillclimbs and Drag Racing regulations are in Section S - Pages 321 to 443… Roadgoing Series Production Cars regulations are in Para 11

Paragragh 11.6.2 Except for Period Defined Vehicle (Non-Rally) A - H inclusive tyres are to List 1A AND List 1B…

There are no restrictions on the type of wheel either… Remember that means the tyres must be on the list and you can’t run anything else - (I’ve had this point clarified by the MSA)…

These rules apply but are subject to any Event Supplimentary Regulations… Some local club events and championships remove List 1B

 

14

You are correct n630hjo… 11.6.2… is the right answer… If the SR don’t make any mention then the Blue Book applies - 11.6.2…

Where are you doing your first event?

15

do Gurston allow 1B’s Tony? (for MSP)

Cheers, B

 

16

Well thanks for ll the replies everyone. Im just going to have to hope for the best as I’m at Gurston this sunday and I only have only one set of wheels and tyres and thats the A048R’s (list 1B) Noithing in the SR’s for the weekend that I can see to preclude them so fingers crossed for sunday!!

Dave

17

 Dave

The Blue book clearly states that 1A and 1B are allowed in road going, I would highlight it or turn the corner of the page over in case you need to show it to save time.

The South West  championship regs make reference to the Blue book , so certainly in that championship I cannot see why I cannot run 1B tyres?

I actually have Yokohamas from list 1A as I cannot budget for new tyres just yet!

Let us know how you get on  as I am considering changing to 1B in the future.

I see you are in Dorset, are you doing any South West championship rounds?  I am getting back into speed events and the cars first event will be Wiscombe in May.

Best of luck

Steve

18

Well, there was no problem with tyre types, both Dave & I had list 1B tyres and scrutineering was fine with that.

19

Looking about on the day I think pretty much everybody in the production cars class was running list 1B. mind you as Andrew kindly pointed out I had inadvertatly mixed my wheels up on the wrong axles so the rotation arrows for the tyres where all facing the wrong way! well spotted. a quick change round with not long before 1st practice got that sortedStick Tongue Out looking forward to round 2 in June.

 

 

20

 

Yes… :slight_smile: